Method and system for determining baseline electrode impedance for tissue contact detection

Abstract

To provide a method for evaluating the quality of a specific baseline value of each electrode on a catheter.SOLUTION: A method of determining a baseline impedance value of a first electrode in a plurality of electrodes disposed on a medical device for tissue contact detection includes measuring an impedance value of the first electrode generated in response to a drive signal to the first electrode. The method further includes assigning a baseline impedance value to the first electrode based on each impedance value measured in the predetermined time interval and determining a confidence value associated with the baseline impedance value. The method further includes utilizing the baseline impedance value in determining the contact state of the first electrode when the confidence value is greater than or equal to a predetermined threshold.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates generally to catheters and methods and systems for detecting tissue contact based on electrode impedance. [Background technology]

[0002] Catheters are utilized in many procedures within the human body. In many of these applications, whether collecting data from surrounding tissue or administering therapy, it is important to determine the proximity of the catheter, particularly the electrodes collecting data or administering therapy, to adjacent tissue. Many methods are used to make this determination, including monitoring electrocardiogram signals (e.g., the voltage measured between the electrodes) and / or electrode impedance. For example, impedance is generally understood to increase in response to contact with tissue. However, many other factors can also result in impedance variations, including the location of the electrode within the body (i.e., different ventricles exposed to different amounts of blood flow may exhibit different impedance values) and movement of surrounding tissue, for example, as a result of the heart beating. Summary of the Invention [Problem to be solved by the invention]

[0003] To assess whether an electrode is in contact with tissue, the measured impedance can be compared to a baseline value, which by definition represents the magnitude of impedance when the electrode is not in close proximity to tissue. However, baseline values ​​are highly variable from patient to patient, from procedure to procedure, and must be determined for each electrode at least once during the procedure. Furthermore, it is difficult to determine the time at which an electrode leaves tissue. It would be beneficial to develop a method and system for assessing the quality of the specific baseline value for each electrode on a catheter. [Means for solving the problem]

[0004] According to one aspect, a method for determining a baseline impedance value for a first electrode in a plurality of electrodes disposed on a medical device for tissue contact detection includes measuring impedance values ​​of the first electrode generated in response to a drive signal to the first electrode. The method further includes assigning a baseline impedance value to the first electrode based on each impedance value measured over a predetermined time interval and determining a confidence value associated with the baseline impedance value. The method further includes utilizing the baseline impedance value in determining a contact state of the first electrode when the confidence value is equal to or greater than a predetermined threshold.

[0005] According to another aspect, a method for assessing the reliability of a baseline impedance value for a first electrode in a plurality of electrodes includes applying a drive signal between a first electrode and a second electrode of a pair of electrodes in the plurality of electrodes. A bipolar electrode complex impedance (BECI) value for the first electrode produced in response to the drive signal is measured, and a baseline BECI value for the first electrode is determined, the baseline BECI value being a first smallest BECI value measured during a first predetermined time interval that is greater than a predetermined lower threshold and less than a predetermined upper threshold. The method further includes determining tissue contact based on the BECI value measured during a second time interval being greater than the baseline BECI value by a predetermined amount, and assigning a confidence state for the baseline BECI value based at least in part on the measured BECI value for the first electrode.

[0006] A method for determining a baseline impedance value for a first electrode of a plurality of electrodes disposed on a medical device for tissue contact detection includes measuring an impedance value for the first electrode generated in response to a drive signal to the first electrode and measuring impedance values ​​for each of the other electrodes of the plurality of electrodes generated in response to the drive signal to each of the other electrodes. The baseline impedance value is assigned to the first electrode based on a minimum impedance value measured over a predetermined time interval, and a confidence value associated with the baseline impedance value is determined based on the BECI value measured for the first electrode and the BECI values ​​measured for one or more of the other electrodes of the plurality of electrodes. When the confidence value is equal to or greater than a predetermined threshold, the baseline impedance value is utilized in determining a contact status of the first electrode. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic diagram of a system including a medical device for insertion into a patient, the system being configured to utilize impedance between electrodes to determine contact status of one or more electrodes disposed at a distal end of the medical device, according to some embodiments.

[0008] [Figure 2] 1 is a schematic diagram of a distal end of a medical device having multiple splines and multiple electrodes disposed on each spline positioned adjacent to cardiac tissue, according to some embodiments.

[0009] [Figure 3] 1 is a schematic diagram of a distal end of a medical device having multiple splines, each spline containing multiple electrodes organized in a grid-like array, according to some embodiments.

[0010] [Figure 4] 1 is a schematic diagram of a distal end of a medical device having multiple splines, each spline containing multiple electrodes organized in a basket-like array, according to some embodiments.

[0011] [Figure 5] 1 is a schematic diagram of components utilized to measure impedance between two electrodes placed on a medical device, according to some embodiments.

[0012] [Figure 6] 1 is a flowchart illustrating steps utilized to determine a baseline impedance value for a first electrode in a plurality of electrodes, according to some embodiments.

[0013] [Figure 7] A state machine for determining a confidence state associated with a baseline impedance value for a first electrode, according to some embodiments.

[0014] [Figure 8] 10 is a plot illustrating an exemplary impedance magnitude signal and corresponding baseline impedance values ​​and confidence states, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0015] According to some embodiments, the claimed invention facilitates quantifying the quality of baseline impedance values ​​for each electrode of a plurality of electrodes of a medical device. Baseline impedance is defined as the magnitude of impedance when the electrode is not near tissue. The baseline impedance value may be utilized in a tissue contact algorithm for determining the tissue contact status of the electrode, and therefore, a quality baseline value for impedance is central to accurately determining the tissue contact status. If the baseline impedance is set too low, the electrode may be too sensitive to the proximity of tissue, which may result in false contact. If the baseline impedance is set too high, it may not even be an indication that the electrode is in firm contact with the tissue. The method disclosed herein allows for appropriate resetting of the baseline impedance when appropriate. The method specifically includes repeating baseline measurements that include intervals that include evidence of tissue contact.

[0016] Quantifying the quality of an electrode's baseline impedance value can include incrementally increasing the electrode's confidence state based on impedance data collected for that electrode. In some embodiments, the confidence state is further increased based on impedance data collected for other electrodes in the medical device. Multiple electrodes in a medical device can be arranged in pairs. Each electrode can have its own baseline impedance value, and each pair can have a "paired baseline" (pairedBL) value that is the average of the baseline impedance values ​​of each of the two electrodes in the pair. The goal is to obtain the lowest stable impedance value for each electrode to use as the baseline impedance value; the more data collected, the greater the confidence in the quality of the baseline value. The confidence state or confidence level can be used to determine whether to use the baseline impedance in determining tissue contact status.

[0017] 1 is a schematic diagram of a system 100 including a medical device 102 and a local system 103. In some embodiments, the local system includes a switch 108, a digital-to-analog (D to A) converter 110, a filter 112, an analog-to-digital (A to D) converter 114, a filter 116, a display 130, and an electronic control unit (ECU) 118. The electronic control unit 118 may include a signal source 120, a synchronization demodulation circuit 122, a contact assessment module 124, a memory 126, and a processor 128. In some embodiments, one or more surface patch electrodes 105 may be adhered to the patient's skin.

[0018] In some embodiments, the medical device 102 is an elongated medical device, such as a diagnostic and / or therapeutic catheter, introducer, sheath, or other similar type of device. The medical device 102 includes a distal end 104, a proximal end (not shown) including a handle that is manipulated by a technician, and an interface for interfacing the medical device 102 to a local system 103. The distal end 104 may include various sensors and / or components for locating / navigating the distal end 104 within a patient, mapping physiological parameters within the patient, and delivering therapy. In particular, the distal end 104 of the medical device includes multiple electrodes that may be utilized for one or more of these purposes.

[0019] In some embodiments, the contact status of one or more electrodes located at the distal end 104 of the medical device 102 is determined based on one or more electrical properties measured at the electrodes. For example, in some embodiments, the measured electrical property is bipolar electrode complex impedance (BECI) generated by driving an excitation signal between two electrodes forming a bipolar pair. The resulting voltage at each electrode is measured and utilized to derive a complex impedance signal. In some embodiments, the contact assessment module 124 utilizes the BECI measurements, alone or in combination with other measured electrical properties, to determine the contact status of each electrode. In some embodiments, the term "contact status" is a binary determination of whether an electrode is "in contact" or "not in contact" with tissue. In other embodiments, the term "contact status" may include additional contact statuses, such as "intermittent contact." In still other embodiments, the term "contact status" may refer to the proximity of an electrode to adjacent tissue.

[0020] In the embodiment shown in FIG. 1 , a signal source 120 is utilized to generate excitation signals. In some embodiments, the signal source 120 generates one or more excitation or drive signals, each with a unique frequency. More specifically, the signal source 120 may generate multiple excitation or drive signals with unique frequencies, in one embodiment, within a range of approximately 1 kHz to greater than 500 kHz, more typically within a range of approximately 2 kHz to 200 kHz, and even more typically within a range of approximately 10 kHz to approximately 20 kHz. Each drive signal may have a constant current, in one embodiment, typically within a range of 1-200 μA, more typically approximately 5 μA. The signal generator 120 may also generate signals involved in determining the position of electrodes within the patient's body, which may be utilized, for example, for mapping, navigation, and / or therapy delivery. The digital signals generated by the signal source 120 are converted to analog signals by a digital-to-analog converter 110 and supplied to selected bipolar electrodes via a filter 112 and a switch 108. In response to an analog signal applied across a selected bipolar electrode, the resulting voltage is measured at the electrode pair by switch 108, filter 116, ADC 114, and synchronous demodulation circuitry 122. In some embodiments, switch 108 selects the electrode to monitor in response to the applied excitation or drive signal. Filter 116 and ADC 114 convert the analog signal to a digital signal that can be manipulated by ECU 118. Synchronous demodulation circuitry 122 separates the signals from one another based on the frequency of the excitation or drive signals, allowing multiple bipolar electrode pairs to be analyzed substantially simultaneously based on the multiple excitation or drive signals applied to the electrode pairs.

[0021] In some embodiments, the memory 126 may be configured to store respective data for the medical device 102, the patient, and / or other data (e.g., calibration data). Such data may be known before a medical procedure (e.g., medical device-specific data, number of catheter electrodes, etc.) or may be determined and stored during the procedure. The memory 126 may also be configured to store instructions that, when executed by the processor 128 and / or the contact assessment module 124, cause the ECU 118 to perform one or more methods, steps, functions, or algorithms described herein. For example, without limitation, the memory 126 may include data and instructions for determining the impedance of each of one or more electrodes in the medical device 102 and utilizing the impedance measurements to determine the contact status of the one or more electrodes. Additionally, the memory 126 may include data and instructions for determining and quantifying the quality of baseline impedance values. In some embodiments, the contact assessment module 124 utilizes a processor, application-specific integrated circuit (ASIC), or other type of processor to execute instructions stored in the memory 126. The ECU may be connected to a display 130, which may display an output of the sensed tissue (e.g., heart), the medical device (not shown), and / or the determined contact state of one or more electrodes of the medical device 102.

[0022] FIG. 2 is a schematic diagram of a distal end 104 of a medical device 102 having multiple splines positioned adjacent to cardiac tissue and multiple electrodes 204a, 204b disposed on each spline, according to some embodiments. In the embodiment shown in FIG. 2, the electrodes 204a and 204b form a bipolar electrode pair. In some embodiments, impedance measurements are generated by applying an excitation signal to the electrodes 204a and 204b, resulting in a current flow between the electrodes 204a and 204b, as indicated by the dashed arrows 208a, 208b. At least a portion of the current 208a, 208b passes through the patient tissue 206 at the electrode-tissue interface, thereby affecting the inductive, capacitive, and / or resistive effects of the electrode response to the drive signal(s). That is, tissue contact affects the impedance measurements of the electrodes 204a, 204b. Generally, when electrodes 204a, 204b are not in contact with tissue 206, a circuit is formed within the patient's blood pool, resulting in a decrease in impedance measurement due to the conductive path formed within the blood pool. When the circuit path includes tissue 206, as shown in FIG. 2, the impedance measurement increases, reflecting the higher impedance of tissue 206 compared to measurements within the blood pool. The impedance measurement is used to determine the tissue contact status of the electrodes. In some embodiments, the contact status may include a determination of contact or no contact. In other embodiments, the contact status may include other contact conditions, such as intermittent contact or a range of contact conditions. In some embodiments, the measured impedance is a bipolar complex impedance (BECI) value.

[0023] In other embodiments, the distal end 104 of the medical device 102 may incorporate a number of different shapes and / or designs. The embodiment shown in FIG. 2 includes a number of splines arranged in a basket shape, with each spline including a number of electrodes. The embodiment shown in FIG. 4 similarly includes a number of splines, with each spline including only a single electrode. In other embodiments, the distal end of the medical device 202 is a grid-like array of electrodes, as shown in more detail in FIG. 3. In other embodiments, the distal end of the medical device may be curved or looped with a number of electrodes spaced along the distal end. Similarly, a variety of different types, shapes, and sizes of electrodes may be utilized at the distal end of the medical device.

[0024] 3 is a top view of a grid array catheter 300. In some embodiments, the grid array catheter 300 includes a shaft 302, shaft electrodes 304a and 304b, a proximal end 306, a plurality of splines 308a, 308b, 308c, and 308d, a distal end 310, and a plurality of spline electrodes 312. In some embodiments, bipolar electrode complex impedance measurements may be taken between any pair of adjacent electrodes. For example, impedance measurements may be taken between shaft electrodes 304a and 304b. In other embodiments, impedance measurements may be taken between any pair of spline electrodes 312. As mentioned above, in some embodiments, the impedance measurements are BECI measurements.

[0025] 4 is an isometric view of a basket catheter 400. In some embodiments, the basket catheter 400 includes a shaft 402, a proximal end 404, a distal end 406, and a plurality of splines 410a-410f extending between the proximal end 404 and the distal end 406. Each of the plurality of splines 410a-410f includes a corresponding electrode 412a-412f. In some embodiments, BECI measurements may be taken between a pair of adjacent electrodes, such as between electrodes 412a and 412b or between electrodes 412c and 412d.

[0026] FIG. 5 is a circuit diagram illustrating circuit elements utilized to excite a bipolar pair of electrodes and measure the resulting complex impedance, according to some embodiments. Specifically, the circuit diagram includes a signal source 120 (shown in FIG. 1), one pair of electrodes 204a, 204b (shown in FIG. 2), first and second operational amplifiers 502a, 502b, and an ECU 118 (also shown in FIG. 1). In some embodiments, the signal source 120 generates an excitation signal that is supplied to the first and second electrodes 204a, 204b. The first operational amplifier 502a includes a first terminal (e.g., a positive terminal) connected to the first electrode 204a and a second terminal (e.g., a negative terminal) connected to the reference electrode 105 (e.g., a surface electrode). The output of the operational amplifier 502a reflects the voltage difference between the first electrode 204a and the reference electrode 105. The second operational amplifier 502b includes a first terminal (e.g., a positive terminal) connected to the second electrode 204b and a second terminal (e.g., a negative terminal) connected to the reference electrode 105 (e.g., a surface electrode). The output of the operational amplifier 502b reflects the difference in voltage between the second electrode 204b and the reference electrode 105. The outputs of the first operational amplifier 502a and the second operational amplifier 502b are provided to the ECU 118, which uses the respective measurements to determine a bipolar electrode complex impedance (BECI).

[0027] FIG. 6 is a flowchart illustrating steps of a method 600 utilized to determine a baseline impedance value and a confidence level associated with the baseline impedance for a first electrode of a plurality of electrodes, according to some embodiments. In some embodiments, an algorithm is applied separately to each of the plurality of electrodes. However, as described in more detail below, in some embodiments, the determination of the confidence level associated with the determined baseline impedance is based, in part, on the baseline impedance and / or the determined confidence levels of other electrodes of the plurality of electrodes. The plurality of electrodes may be disposed on a catheter, for example, such as any of the catheters shown in FIGS. 2, 3, and 4. In step 602, a drive signal is applied to a first electrode, as described above. More specifically, the drive signal may be applied between a first electrode and a second electrode, the first electrode and the second electrode forming a first pair. In step 604, an impedance value of the first electrode is measured over a time interval in response to the drive signal. According to some embodiments, the measured impedance is a bipolar electrode complex impedance (BECI). Impedance measurements can be collected while the catheter is actively moved around the heart chamber to collect impedance measurements not only when the electrodes are in the blood pool, but also when the electrodes are in contact with tissue.

[0028] In step 606, a baseline impedance is assigned to the first electrode. In some embodiments, the baseline impedance is the minimum impedance detected or measured over the time interval. In some embodiments, the baseline impedance is not simply the minimum impedance detected within the time interval. For example, in some embodiments, the baseline impedance is determined as the average of selected minimum impedances measured within the time interval (e.g., the average of the 10 lowest measured impedances selected from the time interval). In some embodiments, the baseline impedance may be selected based on a percentile of the measured impedances (e.g., the impedance at the 10th percentile of the monitored impedances is selected as the baseline impedance). In some embodiments, selecting a baseline value other than the minimum, even initially, can prevent an obviously erroneous impedance value from being selected to represent the baseline. This may include a situation where electrodes are touching each other and exhibit an extremely low impedance value that does not represent a baseline (e.g., in the blood pool) value. In some embodiments, rather than utilizing an average or percentile, one or more constraints are included in step 606 to ensure that the minimum detected impedance is a reasonable indicator that the electrodes are not near tissue (i.e., in the blood pool) and therefore a good candidate for the baseline value. For example, such constraints may include that the range of measured impedance (i.e., maximum impedance value minus minimum impedance value) is less than a first predetermined value (i.e., small variability), that this minimum value is greater than a second predetermined value (i.e., the selected baseline value must be greater than this predetermined value), and / or that this minimum value is less than a third predetermined value (i.e., the baseline value cannot be greater than this predetermined value). In some embodiments, these constraints ensure that the baseline values ​​are reasonable.It is recognized that other parameters or constraints can be used to ensure that the minimum impedance value is likely to be collected in the blood pool. If these constraints are met, the minimum measured impedance can be used as the baseline impedance for the first electrode. If these constraints are not met, additional measurements can be taken for the first electrode until the minimum measured impedance can be assigned to the first electrode.

[0029] In step 608, a confidence value for the assigned baseline impedance may be determined. Initially, the confidence value is low (e.g., state zero). The confidence value increases as impedance data for the first electrode is collected, which confirms that the selected impedance value is appropriate. In some embodiments, the confidence value is also based on impedances and confidence values ​​associated with additional electrodes of the plurality of electrodes. In some embodiments, the confidence value is incremented (or possibly decremented) according to a state machine model, such as that shown in FIG. 7 and described below. Transition from one state to the next is contingent on the satisfaction of one or more conditions, with each state representing a quantified confidence (i.e., each state indicates a quantified reliability associated with the selected baseline value). Just as the confidence value may increase in step 608 as additional data is collected, the confidence value may also decrease, and method 600 may include resetting the baseline impedance under certain conditions.

[0030] According to some embodiments, the confidence state or confidence level can be displayed to the technician via a display. The display can include a numerical confidence state and / or confidence level associated with each electrode. Alternatively or in addition to numerical values, the display can use color coding or other graphical elements, such as a graphical representation of the confidence level associated with each electrode (e.g., color-coded to quickly indicate to the user the confidence value associated with the determined contact condition), to visually represent whether the confidence threshold has been met for each electrode in the medical device.

[0031] In step 610, the contact status of the first electrode is determined based on the baseline impedance value and the current (i.e., most recent) impedance value. A high-quality baseline impedance is necessary for optimal results of the algorithm used to determine tissue contact. The tissue contact algorithm compares the measured impedance value against the baseline impedance value. If the assigned baseline impedance is too low, the first electrode may be overly sensitive to tissue proximity, and the algorithm may indicate a false positive for tissue contact. On the other hand, if the baseline impedance is too high, tissue contact may not be confirmed. Thus, a high-quality baseline impedance is important for effectively determining contact. In some embodiments, the confidence value assigned in step 608 is utilized to determine whether tissue contact can be determined. For example, in some embodiments, tissue contact is determined only if the confidence value associated with the baseline impedance is equal to or greater than a selected threshold. In other embodiments, tissue contact is determined regardless of the confidence value determined in step 608, but the confidence value is displayed along with the tissue contact status to provide the user with an indication of the confidence associated with the determined tissue contact status. If the confidence level of the assigned baseline impedance is too low, it may not be advisable to employ the baseline impedance in the tissue contact algorithm.

[0032] According to some embodiments, the method 600 may include setting a confidence threshold that must be met before utilizing the baseline impedance value in determining the contact status 610. The confidence threshold may be based on a percentage. In addition to or as an alternative to a percentage value, the confidence threshold may correspond to a state number within a state machine.

[0033] 7 is a state machine diagram 700 illustrating the conditions and criteria utilized to quantify a confidence value for a first electrode according to some embodiments. Each state represents increasing confidence (quantified confidence) associated with a determined baseline impedance value. In some embodiments, the selected baseline impedance remains unchanged, but the confidence value associated with the selected baseline impedance value increases as the electrode progresses through the state machine (i.e., progressing from state 704 to state 706 results in an increase in the confidence value associated with the determined baseline impedance).

[0034] Many variations of state machine 700, including additional or alternative logic, are within the scope of the present invention. The states are briefly described below, followed by further details for each state. While state machine 700 is described with reference to a first electrode, it is recognized that the state machine can be used for each electrode of multiple electrodes in a medical device. Zero state 702 is the starting state or "undefined" (each electrode starts in state 702). Zero state 702 represents a zero confidence or initial state. An electrode progresses from zero state 702 to first state 704 in response to a first condition being met. For example, in one embodiment, the first condition is the detection of a "low and quiet" interval in the measured impedance magnitude indicating the electrode is located in the blood pool. In first state 704, a baseline impedance value is selected, but the confidence value associated with the baseline impedance is set to a value indicative of state 704 (i.e., relatively low). The first electrode progresses from the first state 704 to a second state 706 in response to a detected increase or sufficiently high impedance value indicating tissue contact. A detected increase in impedance compared to the baseline impedance established in the first state 704 confirms that the baseline impedance is likely a baseline or low impedance value, thereby increasing the confidence in the baseline impedance value. The first electrode progresses from the second state 706 to a third state 708 when there is another low, quiet interval in which the baseline impedance is confirmed. In the third state 708, the confirmation of the baseline impedance (established in the first state 704) further increases the confidence value associated with the baseline impedance value.

[0035] In some embodiments, additional states may be utilized to further increase the confidence value associated with the baseline impedance value. In some embodiments, an electrode progresses from the third state 708 to the fourth state 710 in response to its paired electrode (second electrode) also progressing to state 708. That is, if the confidence value of each electrode in an electrode pair reaches a threshold value (e.g., the third state 708), the confidence value associated with both electrodes further increases from the third state 708 to the fourth state 710. In some embodiments, a first electrode may be paired with two or more electrodes, and the confidence value of the baseline impedance associated with the first electrode may continue to increase (from the fourth state 710 to the fifth state 712, the sixth state 714, and the seventh state 716) based on a comparison with each additional pair of electrodes in the medical device. In the example shown in FIG. 7, there are eight electrodes on the medical device or catheter. There are three additional pairs of electrodes (in addition to the first pair defined as the first and second electrodes), resulting in the fifth, sixth, and seventh states 712, 714, and 716, respectively. The higher the state, the more confident the first electrode has detected a valid baseline value. In some embodiments, each state provides a quantified confidence value. For example, in an embodiment having eight states, each state may be assigned a confidence value, with the zeroth state being assigned a value of "0" and the seventh state being assigned a value of "1." Intermediate states are assigned decimal values ​​that increase linearly from "0" to "1," although other embodiments are within the scope of the invention.

[0036] In some embodiments, the state machine 700 defines the operation of a baseline impedance algorithm that can be separate from the tissue contact algorithm described above for determining tissue contact. In some embodiments, a baseline impedance algorithm can be used for each electrode, W MA moving window W of sample length (nominally 0.5 seconds, and such future values ​​are also nominal and unconstrained) can be kept track of its state (corresponding to a quantified confidence value), its current baseline value, its "candidate" baseline value (described below), and its impedance magnitude. The moving window W is defined by a length of time and predetermined minimum and maximum impedance magnitude values. If at any time the impedance signal is determined to be saturated or otherwise "invalid," the algorithm variables can be reset to default values ​​(window empty, state set to zero, ohms value set to high).

[0037] For clarity, the description will again use the first electrode, but it will be appreciated that each electrode begins in a zero state 702. In some embodiments, the baseline impedance algorithm transitions the first electrode from the zero state 702 to the first state 704 when one or more of the following conditions of low variability are met: the window W of the first electrode is greater than or equal to the full W MThe first state 704 is determined by the following criteria: the electrode has a sample whose range (maximum impedance magnitude minus minimum impedance magnitude of the sample) is less than a first predetermined value (nominally 12 ohms); its minimum value is greater than a second predetermined value (e.g., a minimum ohm value such as 40 ohms) and less than a third predetermined value (e.g., a maximum ohm value such as 86 ohms); and its minimum value is less than the current baseline (if a current baseline exists), and the state is equal to or less than 1. In some embodiments, if these conditions are met, the criteria for "blood pool detected" are met, indicating that at least some of the impedance measurements collected during the window correspond to impedance measurements made while the electrode was in the blood pool (i.e., correspond to the desired baseline impedance). Thus, a baseline impedance value can be set based on one or more of the collected impedance values, and the electrode changes to the first state 704. In some embodiments, the selected baseline value is selected as the minimum impedance value (meeting the criteria) measured during the window, while in other embodiments, the selected baseline value may represent an average or percentile selected from the measured impedance values. In other embodiments, one or more of the criteria utilized above may be utilized alone or in combination with each other to transition from the zero state 702 to the first state 704. As discussed above, the transition from the zero state 702 to the first state 704 increases the confidence value associated with the baseline value.

[0038] In some embodiments, in the first state 704, the baseline impedance algorithm clears window W, sets an impedance baseline, and sets / updates a “paired baseline” or “pairedBL” for the first pair (first electrode and second electrode) to be the average of the current baseline of the first electrode and the current baseline of the second electrode. As described in more detail below, the “paired baseline” is utilized to transition to a higher state (i.e., a greater confidence value) as a result of matching baseline impedances for the electrode pair. In some embodiments, window W is cleared and new impedance values ​​are collected to determine whether to transition from first state 704 to second state 706. However, in other embodiments, window W continues to move as new impedance values ​​are collected, and clearing window W is not required.

[0039] In some embodiments, the first electrode transitions from the first state 704 to the second state 706 when an increased magnitude of impedance is observed, indicating tissue contact of the first electrode. Specifically, if the measured impedance exceeds the current baseline impedance by more than a fourth predetermined value (e.g., 10 ohms, or alternatively, a predefined percentage or factor), the algorithm determines that the electrode has contacted tissue. The higher the detected impedance value indicating tissue contact, the greater the confidence that the baseline value established in the first state 704 represents the impedance value measured in the blood pool. In this manner, the transition to the second state 706 increases the confidence value associated with the baseline value established in the first state 704. The baseline value itself does not change in the transition from the first state 704 to the second state 706, only the confidence value associated with the transition from the first state 704 to the second state 706.

[0040] In some embodiments, the electrode transitions from the second state 706 to the third state 708 when the baseline impedance algorithm detects a measured impedance near the current baseline impedance, confirming movement out of the tissue and back into the blood pool. This confirmation indicates that the baseline impedance value established in the first state 704 is likely accurate, thus further increasing confidence in the baseline impedance value. In some embodiments, the first electrode transitions from the second state 706 to the third state 708 in response to the minimum impedance value detected within the window W being less than some predetermined factor of the current baseline impedance (i.e., within some threshold of the current baseline value, indicating that the baseline impedance value is a good estimate of the electrode impedance when in the blood pool). For example, the factor may be equal to 1.0 plus a predetermined window tolerance (“WindowTolerance”), such as 0.03. In some embodiments, additional constraints similar to those provided in the first state 704 may be imposed to determine whether the minimum value detected within the window W represents a baseline impedance value. For example, in some embodiments, the one or more additional constraints include that the range of impedance within window W is less than a first predetermined value, that the minimum impedance detected within window W is greater than a second predetermined value, and that the minimum impedance detected within window W is less than a third predetermined value. In some embodiments, if the minimum impedance value detected within window W is less than a predetermined factor of the current baseline impedance (and if the one or more additional constraints are met), the electrode transitions to the fourth state 710. The confidence value associated with the baseline impedance value established for the first electrode in first state 704 is increased, but the baseline impedance value itself remains unchanged. If these conditions are met, the current baseline impedance is confirmed and does not change.

[0041] However, if the minimum impedance detected within window W in second state 706 is not near the baseline impedance value, this indicates that the baseline impedance value established in first state 704 may not be representative of the baseline impedance in the blood pool. In some embodiments, the electrode transitions from second state 706 back to zero state 702, indicating a lack of confidence in the baseline value originally established in first state 704. In particular, if the minimum impedance value measured within window W while in second state 706 is greater than a predetermined factor of the current baseline and / or if the minimum impedance is outside a predetermined tolerance of the current baseline, the electrode transitions from second state 706 to zero state 702 and the process begins again to select a baseline impedance value and build confidence in the selected value.

[0042] In some embodiments, the third state 706 may represent the highest confidence state. In this embodiment, the first electrode reaches the third state 706 based entirely on the impedance measurements received from the first electrode. In some embodiments, progression to additional states 710, 712, 714, and / or 716 may depend on the measured baseline values ​​of one or more paired electrodes. In some embodiments, the first electrode changes to the fourth state 710 if its paired electrode (the second electrode) is also in the third state 708 (or a higher state). In some embodiments, the first electrode changes to the fourth state 710 if the first and second electrodes have impedance values ​​sufficiently close to each other. In this case, if the second electrode is also in the third state 708 and the first electrode changes to the fourth state 710, the second electrode will also change to the fourth state 710. In some embodiments, when the first electrode and the second electrode transition to the fourth state 710, a "paired baseline" (pairedBL) value is determined that can be used to quantify the confidence state of other electrodes in the medical device. In some embodiments, the "paired baseline" value is the average of the baseline impedances associated with the first electrode and the second electrode. In other embodiments, the "paired baseline" value may be the minimum of the baseline impedances associated with the first electrode and the second electrode.

[0043] In some embodiments, the transition of the first electrode to the fifth state 712, sixth state 714, and seventh state 716 is based on a comparison of the paired baseline values ​​associated with the first and second electrodes to other electrode pairs. For each additional pair of electrodes having a "Paired BL" value that is within a predetermined tolerance of the baseline impedance value of the first electrode pair, the electrode transitions to the next state, and the confidence value associated with the baseline impedance associated with the first electrode correspondingly increases in value. For an exemplary catheter with eight electrodes, there are three other pairs of electrodes, so the maximum confidence state is 7; if the other three pairs all meet the above criteria, the confidence state can increase from 4 to 7.

[0044] In some embodiments, if a lower baseline value is detected, the baseline impedance can be reset. The specific details for resetting the baseline impedance depend on the state the first electrode is in when the lower baseline value is detected. For example, with respect to the second state 706, if the minimum impedance value measured within the window W while in the second state 706 is greater than a predetermined factor of the current baseline and / or if that minimum impedance is outside a predetermined tolerance of the current baseline, the baseline impedance can be reset (and the electrode returned to the first state 704). Similarly, in some embodiments, if the first electrode transitions to the third state 708 or higher and a lower baseline is detected relative to the current baseline (e.g., less than a factor of 1.0-WindowTolerance), the baseline is not automatically reset to the new lower baseline. Rather, the new lower baseline can be retained as a candidate baseline ("candidate BL") until the conditions associated with the conditions of the second state 706 are again met for the first electrode and another low fluctuation window is detected to confirm the candidate baseline. The low variability window or tolerance is defined as the minimum impedance that is less than or equal to (1.0 + WindowTolerance) multiplied by the candidate baseline ("candidateBL"). When these conditions are met, the candidate baseline becomes the new baseline impedance value.

[0045] For any of the eight electrodes in the exemplary catheter used in state machine 700, if the electrode is in state 3 and its paired electrode (or companion) is in state 3 or higher, the algorithm sets its state to 4 and updates the pairedBL for that pair. The paired electrode can also be updated immediately. The baseline impedance algorithm then examines each of the other three pairs of electrodes, and for each other pair in state 4 whose pairedBL is within a relative factor of the paired tolerance ("PairedTolerance," nominally 0.36), the algorithm can increase its state value by 1. (Note that some electrode pairs may be in the maximum state 7 while others are not.) Monitoring the pairedBL of other electrode pairs can progress the electrodes through states 5 and 6 to state 7 (the highest quality state).

[0046] The highest quality state depends on the total number of electrodes in the catheter. State machine 700 in Figure 7 is based on a catheter with eight electrodes. It is recognized that catheters with more than eight electrodes will have a higher maximum state, and catheters with fewer than eight electrodes will have a lower maximum state. For impedance measurements such as BECI measurements that rely on electrode pairs, the total number of electrodes for the state machine is always an even number.

[0047] In some embodiments, each state in the state machine represents a confidence value associated with the established baseline impedance for a given electrode, which can be expressed as a confidence percentage ranging from 0 to 100. Zero percent confidence represents a starting or undefined state (state zero) where there is no confidence that the current baseline value is correct because no data has yet been collected. In contrast, 100 percent confidence represents the highest quality state, where there is a high degree of confidence that the baseline impedance value is correct. The progression from zero percent to 100 percent can be done in discrete steps corresponding to the number of states in the state machine. Again, the number of states is based on the number of electrodes in the catheter or medical device. The number of non-zero states is equal to 3 + (n / 2), where n is the number of electrodes. Using the same 8-electrode catheter as in the example, the number of states is equal to 3 + (8 / 2), or 7. At Confidence State 2, the confidence is equal to 2 divided by 7, or 29%. At Confidence State 3, the confidence is equal to 3 divided by 7, or 43%. Table 1 below shows the decimal values ​​of the corresponding states, which can be converted to percentages. Table 1 summarizes the various states in the eight electrode catheter state machine. [Table 1]

[0048] To explain how state machines work, an eight-electrode catheter will be used as an example. It will be recognized that the state machine concept can be applied to any even number of electrodes. For a catheter with n electrodes, there will be n simultaneously executing state machines. As another example, for a six-electrode catheter, the number of non-zero states will equal 3 + (6 / 2), or a total of six states. As yet another example, for a ten-electrode catheter, the number of non-zero states will equal 3 + (10 / 2), or a total of eight states.

[0049] Figure 8 is a plot showing an exemplary impedance magnitude signal for an electrode and the baseline impedance established by the baseline impedance algorithm described above. Figure 8 also shows on the x-axis the time at which each confidence state of the electrode is achieved.

[0050] As shown in Figure 8, a baseline value is set at Confidence State 1. At Confidence State 2, a noticeable increase in impedance magnitude (approximately 10 ohms) is observed. At Confidence State 3, the detected minimum impedance is nearly identical to the baseline impedance value, confirming repeated detection within the blood pool. A lower baseline is observed between States 4 and 5. Because the Confidence State was greater than 3 when the lower minimum impedance was detected, the Confidence State can continue to increase rather than returning to States 0 and 1. However, the new lower minimum impedance is not immediately accepted (rather, the algorithm designates it as a candidate baseline) until another peak indicating tissue contact is observed.

[0051] While the present invention has been described with reference to exemplary embodiment(s), those skilled in the art will recognize that various modifications may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but rather to include all embodiments falling within the scope of the appended claims.

[0052] Consideration of possible embodiments. The following is a non-exclusive description of possible embodiments of the present invention.

[0053] According to some embodiments, a method for determining a baseline impedance value for a first electrode in a plurality of electrodes disposed on a medical device for tissue contact detection includes measuring impedance values ​​of the first electrode generated in response to a drive signal to the first electrode and assigning the baseline impedance value to the first electrode based on each impedance value measured over a predetermined time interval. The method may further include determining a confidence value associated with the baseline impedance value and utilizing the baseline impedance value in determining a contact state of the first electrode when the confidence value is equal to or greater than a predetermined threshold.

[0054] The method of the preceding paragraph may optionally additionally and / or alternatively include one or more of the following features, steps, configurations, and / or additional components.

[0055] For example, the step of assigning a baseline impedance value to the first electrode may include selecting the minimum impedance value measured in a predetermined time interval.

[0056] In some embodiments, if the minimum impedance value is greater than a predetermined impedance threshold and less than a predetermined impedance limit, the minimum impedance value becomes the assigned baseline impedance value.

[0057] In some embodiments, the impedance value is a bipolar electrode complex impedance (BECI) value resulting from applying a drive signal between a first electrode and a second electrode in a plurality of electrodes.

[0058] In some embodiments, determining a confidence value associated with the baseline impedance value may include gradually increasing the confidence value based on measured impedance values ​​that exceed the assigned baseline impedance value by more than a predetermined amount.

[0059] In some embodiments, determining a confidence value associated with the baseline impedance value includes incrementally increasing the confidence value for the first electrode based on measured impedance values ​​that are within a predetermined tolerance range of the assigned baseline impedance value.

[0060] In some embodiments, determining a confidence value associated with the baseline impedance value comprises decreasing the confidence value if the measured impedance value is outside a predetermined tolerance range of the assigned baseline impedance value.

[0061] In some embodiments, determining a confidence value associated with the baseline impedance value further includes gradually increasing the confidence value based on impedance data collected for a second electrode of the plurality of electrodes that is paired with the first electrode.

[0062] In some embodiments, determining a confidence value associated with the baseline impedance value further comprises gradually increasing the confidence value based on impedance data collected for additional electrode pairs in the plurality of electrodes.

[0063] According to another aspect, a method for assessing the reliability of a baseline impedance value for a first electrode in a plurality of electrodes includes applying a drive signal between a first electrode and a second electrode of a pair of the plurality of electrodes and measuring a bipolar electrode complex impedance (BECI) value for the first electrode generated in response to the drive signal. The method may further include determining a baseline BECI value for the first electrode, the baseline BECI value being a first smallest BECI value measured during a first predetermined time interval that is greater than a predetermined lower threshold and less than a predetermined upper threshold, and determining tissue contact based on the BECI value measured during a second time interval being greater than the baseline BECI value by a predetermined amount. The method may further include assigning a confidence state for the baseline BECI value based at least in part on the measured BECI value for the first electrode.

[0064] The method of the preceding paragraph may optionally additionally and / or alternatively include one or more of the following features, steps, configurations, and / or additional components.

[0065] For example, the step of assigning a confidence state for the baseline BECI value may further include increasing the confidence state when a second minimum BECI value is measured during a second predetermined time interval and the second minimum BECI value is greater than a predetermined lower threshold, less than a predetermined upper threshold, and within a predetermined tolerance range of the first minimum BECI value, and decreasing the confidence state and setting a new baseline BECI value when the second minimum BECI value is outside the predetermined tolerance range of the first minimum BECI value.

[0066] In some embodiments, decreasing the confidence state and setting a new baseline BECI value includes utilizing the second minimum BECI value as the new baseline value, and the method further includes repeating the steps of determining tissue contact and assigning a confidence state.

[0067] In some embodiments, assigning the confidence state for the baseline BECI value is further based on a BECI value measured for a second electrode.

[0068] In some embodiments, assigning the confidence state for the baseline BECI value further includes increasing the confidence state when the second electrode has a minimum BECI value that is within a predetermined tolerance range of the first minimum BECI value or the second minimum BECI value of the first electrode.

[0069] In some embodiments, assigning a confidence state for the baseline BECI value is further based on BECI values ​​measured for additional electrode pairs in the plurality of electrodes.

[0070] In some embodiments, assigning a confidence state for the baseline BECI value further includes increasing the confidence state for each additional electrode pair having an average baseline BECI value that is within a predetermined tolerance range of the first minimum BECI value or the second minimum BECI value of the first electrode.

[0071] According to another aspect, a system for use with a medical device having a plurality of electrodes and configured for insertion into a patient includes a signal generator, a measurement circuit, and a contact assessment module. In some embodiments, the signal generator is configured to apply a plurality of drive signals across each electrode of the plurality of electrodes, and the measurement circuit is configured to measure responses of the plurality of electrodes to the drive signals and generate an impedance value for each electrode of the plurality of electrodes. In some embodiments, the contact assessment module is configured to determine a baseline impedance value for each electrode and to determine a confidence state for the baseline impedance value for each electrode based at least in part on the impedance value measured for the particular electrode.

[0072] The systems of the preceding paragraphs may optionally additionally and / or alternatively include one or more of the following features, steps, configurations, and / or additional components.

[0073] For example, the determined confidence state for each electrode may be based on the impedance value measured for the particular electrode and the impedance values ​​measured for other electrodes in the plurality of electrodes.

[0074] In some embodiments, the contact assessment module may utilize a baseline impedance value for an electrode to determine the contact status of that electrode when the confidence state is above a predetermined threshold.

[0075] According to another aspect, a method for determining an electrode baseline impedance value for a first of a plurality of electrodes disposed on a medical device for tissue contact detection includes measuring an impedance value for the first electrode generated in response to a drive signal to the first electrode and measuring impedance values ​​for each of the other electrodes of the plurality of electrodes generated in response to the drive signal to each of the other electrodes. The method may further include assigning the baseline impedance value to the first electrode based on a minimum impedance value measured over a predetermined time interval, and determining a confidence value associated with the baseline impedance value based on the BECI value measured for the first electrode and the BECI values ​​measured for one or more of the other electrodes of the plurality of electrodes. The method may further include utilizing the baseline impedance value in determining a contact status of the first electrode when the confidence value is equal to or greater than a predetermined threshold.

Claims

1. 1. A method for determining a baseline impedance value for a first electrode in a plurality of electrodes disposed on a medical device for tissue contact detection, comprising: measuring an impedance value of the first electrode generated in response to a drive signal to the first electrode; assigning a baseline impedance value to the first electrode based on each impedance value measured over a predetermined time interval; determining a confidence value associated with the baseline impedance value; and utilizing the baseline impedance value in determining a contact status of the first electrode when the confidence value is greater than or equal to a predetermined threshold.

2. 10. The method of claim 1, wherein assigning a baseline impedance value to the first electrode comprises selecting a minimum impedance value measured in the predetermined time interval.

3. The method of claim 2 , wherein if the minimum impedance value is greater than a predetermined impedance threshold and less than a predetermined impedance limit, the minimum impedance value becomes the assigned baseline impedance value.

4. 2. The method of claim 1, wherein the impedance value is a bipolar electrode complex impedance (BECI) value resulting from applying the drive signal between the first and second electrodes of the plurality of electrodes.

5. 2. The method of claim 1, wherein determining the confidence value associated with the baseline impedance value comprises incrementally increasing the confidence value based on measured impedance values ​​that exceed the assigned baseline impedance value by more than a predetermined amount.

6. 6. The method of claim 5, wherein determining the confidence value associated with the baseline impedance value comprises incrementally increasing the confidence value for the first electrode based on measured impedance values ​​that are within a predetermined tolerance range of the assigned baseline impedance value.

7. 7. The method of claim 6, wherein determining the confidence value associated with the baseline impedance value comprises decreasing the confidence value if the measured impedance value is outside the predetermined tolerance range of the assigned baseline impedance value.

8. 7. The method of claim 6, wherein determining the confidence value associated with the baseline impedance value comprises gradually increasing the confidence value based on impedance data collected for a second electrode of the plurality of electrodes that is paired with the first electrode.

9. 9. The method of claim 8, wherein determining the confidence value associated with the baseline impedance value comprises gradually increasing the confidence value based on impedance data collected for additional electrode pairs in the plurality of electrodes.

10. 1. A method for assessing reliability of a baseline impedance value for a first electrode in a plurality of electrodes, comprising: applying a drive signal between the first electrode and the second electrode that form a pair among the plurality of electrodes; measuring a bipolar electrode complex impedance (BECI) value for the first electrode generated in response to the drive signal; determining a baseline BECI value for the first electrode, the baseline BECI value being a first smallest BECI value measured during a first predetermined time interval that is greater than a predetermined lower threshold and less than a predetermined upper threshold; determining tissue contact based on the BECI value measured during a second time interval being greater than the baseline BECI value by a predetermined amount; and assigning a confidence state for the baseline BECI value based at least in part on the measured BECI value for the first electrode.

11. assigning the confidence state for the baseline BECI value comprises: measuring a second minimum BECI value during a second predetermined time interval, and increasing the confidence state when the second minimum BECI value is greater than the predetermined lower threshold, less than the predetermined upper threshold, and within a predetermined tolerance range of the first minimum BECI value; and 11. The method of claim 10, comprising decreasing the confidence state and setting a new baseline BECI value when the second minimum BECI value is outside the predetermined tolerance range of the first minimum BECI value.

12. reducing the confidence state and establishing a new baseline BECI value includes utilizing the second minimum BECI value as a new baseline value; The method of claim 11 , further comprising repeating the steps of determining tissue contact and assigning the confidence state.

13. The method of claim 10 , wherein assigning the confidence state for the baseline BECI value is further based on a BECI value measured for the second electrode.

14. 14. The method of claim 13, wherein assigning the confidence state for the baseline BECI value comprises increasing the confidence state when the second electrode has a minimum BECI value that is within a predetermined tolerance range of the first minimum BECI value or a second minimum BECI value of the first electrode.

15. The method of claim 10 , wherein assigning the confidence state for the baseline BECI value is further based on BECI values ​​measured for additional electrode pairs in the plurality of electrodes.

16. 16. The method of claim 15, wherein assigning the confidence state for the baseline BECI value comprises increasing the confidence state for each additional electrode pair having an average baseline BECI value that is within a predetermined tolerance range of the first minimum BECI value or a second minimum BECI value of the first electrode.

17. 1. A system for use with a medical device having a plurality of electrodes and configured for insertion into a patient, comprising: a signal generator configured to apply a plurality of drive signals across each electrode of the plurality of electrodes; a measurement circuit configured to measure a response of the plurality of electrodes to the drive signal and generate an impedance value for each electrode of the plurality of electrodes; and a contact assessment module configured to determine a baseline impedance value for each electrode and to determine a confidence state of the baseline impedance value for each electrode based at least in part on the impedance value measured for the particular electrode.

18. 20. The system of claim 17, wherein the confidence state for each electrode is based on an impedance value measured for the particular electrode and impedance values ​​measured for other electrodes in the plurality of electrodes.

19. 20. The system of claim 17, wherein the contact assessment module utilizes the baseline impedance value for the electrode to determine the contact state of the electrode when the confidence state is above a predetermined threshold.

20. 1. A method for determining a baseline impedance value for a first electrode of a plurality of electrodes disposed on a medical device for tissue contact detection, the method comprising: measuring an impedance value of the first electrode generated in response to a drive signal to the first electrode; measuring an impedance value for each other electrode of the plurality of electrodes, the impedance value being generated in response to a drive signal to each other electrode; assigning a baseline impedance value to the first electrode based on the minimum impedance value measured over a predetermined time interval; determining a confidence value associated with the baseline impedance value based on a BECI value measured for the first electrode and a BECI value measured for one or more of the other electrodes of the plurality of electrodes; and utilizing the baseline impedance value in determining a contact status of the first electrode when the confidence value is greater than or equal to a predetermined threshold.

Images