Providing blood pool direction vectors based on measured impedance

Abstract

The present disclosure provides a method comprising monitoring an impedance of a plurality of functional electrodes relative to a reference electrode when manipulating a catheter within a lumen of an organ, the catheter comprising: (i) a shaft having a distal end; and (ii) an expandable distal end assembly coupled to the distal end of the shaft and including a plurality of functional electrodes. A direction vector is estimated from the monitored impedance, along which the catheter is freely advanceable within the lumen of the organ without being obstructed by the tissue walls. And displaying the direction vector to the user.

Description

Technical Field

[0001] The present disclosure generally relates to anatomical mapping and, more particularly, to improvements in cardiac electroanatomical (EA) mapping. Background Art

[0002] There are techniques in the patent literature to assist in guiding an EA mapping catheter within a cardiac chamber to obtain clinically relevant data for constructing an EA map of the cardiac chamber. Such techniques may be accompanied by medical imaging (such as fluoroscopy) to assist the physician in navigating the catheter to the region of interest within the heart. Generally, it is desirable to minimize the use of fluoroscopy to avoid exposing the patient as well as medical personnel to harmful radiation. Although highly beneficial in cardiac treatment planning as well as the treatment itself, manipulating a catheter within a cardiac chamber to reach the region of interest requires a high degree of expertise from the physician performing the procedure.

[0003] The present disclosure will be more fully understood from the following detailed description of embodiments of the disclosure in conjunction with the accompanying drawings, in which: Brief Description of the Drawings

[0004] Figure 1 is a schematic illustration of a catheter-based electroanatomical (EA) mapping and ablation system according to an example of the present disclosure;

[0005] Figure 2 is a schematic illustration of a basket assembly according to an example of the present disclosure, the basket assembly being configured to obtain electrical measurements to determine the blood pool direction of the assembly relative to the wall of the cardiac chamber;

[0006] Figure 3 is a schematic illustration of a tissue wall proximity-based guidance scheme for a basket assembly of a catheter within the left atrium of a patient according to an example of the present disclosure; and

[0007] Figure 4 is a flow chart schematically showing a method and algorithm for estimating and presenting a blood pool direction vector based on impedance measurements of functional electrodes according to an example of the present disclosure. Detailed Description

[0008] Overview

[0009] The wall tissue of a cardiac chamber can be electroanatomically (EA) mapped using a catheter having a plurality of functional electrodes disposed at an expandable distal end assembly of the catheter. During a mapping procedure within the cardiac chamber, a physician can manipulate the expanded distal end assembly to bring the electrodes into contact with the chamber wall, thereby acquiring and / or applying electrical signals. The resulting EA map can include a number of anatomical details that are important for facilitating treatment planning, such as with respect to the left atrium, the four pulmonary vein (PV) ostia, and the left inferior appendage.

[0010] However, at an early stage of the mapping procedure, the physician typically has no information on where to direct the catheter to achieve effective mapping. Only after some portions of the endocardial surface have been mapped can the physician make the mapping more effective by informatively accessing clinically relevant but less accessible locations in the heart chamber, such as the ostia, appendages, and valves. Even in the later stages, it is often difficult to understand how to maneuver within the three-dimensional structure of the chamber. These difficult challenges during the start-up phase of EA mapping can prolong the mapping procedure and make it medically more complex for the patient. In some examples, the physician may want to reach the treatment area with a minimal mapping performed during a treatment procedure using a therapeutic catheter.

[0011] Examples of the present disclosure described herein provide a technique that accelerates the early stage of EA mapping by addressing or bypassing the above difficulties of efficiently mapping an unknown surface using a catheter.

[0012] In one example of the technique, the physician maneuvers an extended distal end assembly of a catheter within a heart chamber. The catheter includes a distal end assembly having a plurality of functional electrodes, such as a basket assembly or a balloon assembly having a plurality of electrodes thereon. When the catheter is being maneuvered, a processor monitors the impedance of the plurality of functional electrodes relative to a reference electrode. Using the monitored impedance, the processor estimates a blood pool direction vector along which the catheter can freely advance within the heart chamber. The processor displays the direction vector to the user as a corresponding blood direction arrow.

[0013] As described above, the disclosed technique can overcome the difficulties of effectively mapping an initially unknown tissue surface using a catheter. For example, as Figure 3 shown, when the blood pool direction is aligned with the axis of the catheter (e.g., by indicating that the direction arrow is aligned with the longitudinal axis icon of the virtual representation of the distal end assembly), the disclosed technique indicates the best way to reach landmarks such as the ostia of the PVs, the left atrial appendage (LAA).

[0014] When the method is applied to a heart chamber, it can be applied to another chamber of the organ by measuring the chamber volume and wall impedance.

[0015] To estimate the blood pool direction vector, in some examples, the processor first identifies the maximum and minimum impedances for the patient and normalizes the impedance range between the maximum and minimum values. In addition to the variability between patients, the detected maximum and minimum values for each functional electrode depend on the distance between the functional electrode and the reference electrode. These differences can be considered, and a normalized range, such as 0 to 1, can be defined for each electrode based on the identified maximum and minimum impedances.

[0016] In some examples, to estimate the blood pool direction vector, the processor relies on the known geometry of the extended distal end component. In some examples, the center point of the content volume is calculated and vectors extending from the center point to each electrode are defined. In some example implementations, the deformation of the distal end component is tracked and the center point of the content volume is dynamically defined based on the tracked deformation.

[0017] The magnitude of each vector is defined as a scaled value of the impedance sensed at the electrode. Generally, the impedance increases as the electrode approaches the tissue. Since it is desired to indicate the direction away from the tissue and the impedance decreases according to the distance from the tissue, the magnitude of each vector in the vector can be defined as the maximum impedance level minus the instantaneous impedance level. For example, for an impedance value range normalized between 0 and 1, the magnitude of each vector can be one minus the normalized impedance value.

[0018] The processor converts the impedance of each functional electrode into a weighted vector. For example, the magnitude of the vector is the weight of the vector in the direction from the common origin to the functional electrode, and the weighted vectors on all functional electrodes are summed. In the blood pool, such vectors are fixed (e.g., close to zero for a fully symmetric arrangement of functional electrodes) and can be assumed to be only properties of the component. Only when a portion of the functional electrodes of the component approaches the tissue wall does the sum of the impedance weighted vectors result in a different blood pool direction vector.

[0019] System Description

[0020] Figure 1 is a schematic illustration of a catheter-based electroanatomical (EA) mapping and ablation system 10 according to an example of the present disclosure. The system 10 is configured to determine, for example, whether a given functional electrode 26 among the plurality of functional electrodes 26 of the basket catheter 14 is in sufficient proximity to the tissue or is immersed in the blood pool 33 of the heart chamber before performing a diagnosis and / or ablation.

[0021] System 10 includes one or more catheters that are inserted by physician 24 through a patient's vasculature via the skin into a chamber or vascular structure of the heart 12. Typically, a delivery sheath catheter is inserted into the left atrium or right atrium near a desired location within the heart 12. Then, one or more catheters can be sequentially inserted into the delivery sheath catheter to reach the desired location. The one or more catheters can include a catheter dedicated to sensing intracardiac electrogram (IEGM) signals, a catheter dedicated to ablation, and / or a catheter dedicated to both sensing and ablation. An exemplary basket catheter 14 configured for sensing IEGM is shown herein. As shown in inset 45, physician 24 brings the basket-type expandable distal end assembly 28 (hereinafter also referred to as "expandable distal end assembly 28") mounted on the shaft 44 of catheter 14 into proximity with the heart wall to sense a target site within the heart 12. For ablation, physician 24 similarly brings the distal end of the ablation catheter to the target site for ablation.

[0022] As shown in inset 65, catheter 14 is an exemplary catheter that includes one and preferably a plurality of functional electrodes 26 that are optionally distributed on a plurality of splines 22 at the expandable distal end assembly 28 and are configured to sense IEGM signals. Catheter 14 additionally includes a proximal position sensor 29 (e.g., a three-axis sensor (TAS) 29 including three EMCs) embedded in the distal end 46 of the shaft 44 near the expandable distal end assembly 28 to track the position of the distal end of the expandable distal end assembly 28. Optionally and preferably, the position sensor 29 is a magnetic-based position sensor that includes magnetic coils for sensing three-dimensional (3D) position. The distal end 46 of the shaft 44 can include an amplifier circuit that is configured to amplify the output of the three EMCs from the sensor 29.

[0023] The magnetic position sensor 29 operates in conjunction with an external position pad 25 that includes a plurality of magnetic coils 32 configured to generate a magnetic field within a predefined workspace. Using an operation with the external position pad 25 (each EMC using a different frequency), the processor can determine the position of each EMC 29 on the coordinate system of the position tracking system.

[0024] Details of magnetic-based position sensing techniques are described in U.S. Pat. Nos. 5,539,199, 5,443,489, 5,558,091, 6,172,499, 6,239,724, 6,332,089, 6,484,118, 6,618,612, 6,690,963, 6,788,967, and 6,892,091.

[0025] System 10 includes one or more electrode patches 38 positioned in contact with the skin of patient 23 to establish a position reference for impedance-based tracking of position pad 25 and functional electrodes 26. For impedance-based tracking, current is directed toward electrodes 26 and sensed at electrode skin patches 38 such that the position of each electrode can be triangulated via electrode patches 38. The real-time orientation of the expandable distal end assembly 28 of catheter 14 can be calculated based on the tracked positions of electrodes 26. This relative orientation is represented by the angle formed between distal end 46 and the longitudinal axis 42 of expandable assembly 28 (to the distal edge 16 of the assembly).

[0026] Details of impedance-based position tracking techniques are described in U.S. Pat. Nos. 7,536,218, 7,756,576, 7,848,787, 7,869,865, and 8,456,182.

[0027] Catheter 14 is configured to acquire electrical signals indicative of the proximity of any given functional electrode 26 to the tissue wall of heart 12. To this end, signal generator 35 is configured to generate an AC signal between reference toroidal electrode 17 and each of functional electrodes 26. The processor measures the corresponding impedance between each functional electrode 26 and reference toroidal electrode 17, which is located on the base 37 of expandable distal end assembly 28, outside the content volume 77 defined by the splines of assembly 28. The circuit paths between each functional electrode 26 and the circuit path between reference toroidal electrode 17 and assembly 28 improve the sensitivity of the measurement to tissue proximity. Reference toroidal electrode 17 is positioned at a location on the base of assembly 28 that prevents contact with the tissue wall when distal end assembly 28 is in the expanded state, as Figure 2 further described in.

[0028] Recorder 11 displays electrocardiogram 21 captured using body surface ECG electrodes 18 and intracardiac electrogram (IEGM) captured using functional electrodes 26 of catheter 14. Recorder 11 may include pacing capabilities for pacing the heart rhythm and / or may be electrically connected to an independent pacemaker.

[0029] System 10 may include an ablation energy generator 50 adapted to conduct ablation energy to a subset of the plurality of electrodes 26 at the distal assembly 28 of catheter 14 configured for ablation. The energy generated by ablation energy generator 50 may include, but is not limited to, radiofrequency (RF) energy or pulsed field ablation (PFA) energy (including monopolar or bipolar high voltage DC pulses that can be used to effect irreversible electroporation (IRE)), or combinations thereof.

[0030] The Patient Interface Unit (PIU) 30 is configured to establish electrical communication between the catheter, the electrophysiology equipment, the power supply, and the workstation 55 for controlling the operation of the system 10. The electrophysiology equipment of the system 10 may include, for example, a plurality of catheters, the position pad 25, the body surface ECG electrodes 18, the electrode patches 38, the ablation energy generator 50, and the recorder 11. Optionally and preferably, the PIU 30 further includes processing capabilities for performing real-time calculations of catheter positions and for performing ECG calculations.

[0031] The workstation 55 includes a memory 57, a processor unit 56 with a memory or storage device loaded with appropriate operating software, and user interface capabilities. The workstation 55 may provide a plurality of functions, optionally including: (i) performing three-dimensional (3D) modeling of the endocardial anatomy and rendering the model or the anatomical map 20 for display on the display device 27; (ii) on the display device 27, displaying the activation sequence (or other data) compiled from the recorded electrograms 21 as representative visual markers or images superimposed on the rendered anatomical map 20; (iii) displaying the real-time positions and orientations of a plurality of catheters within the heart chambers; and (iv) displaying the sites of interest, such as where ablation energy is applied, on the display device 27. A commercial product embodying the elements of the system 10 may be the CARTO TM 3System, which is purchased from Biosense Webster, Inc., 31A Technology Drive, Irvine, CA 92618.

[0032] Although Figure 1 a basket assembly is described, the disclosed techniques may be applied, with necessary modifications, to expandable balloon assemblies with expandable membranes on which functional electrodes are disposed.

[0033] Estimation of the Blood Pool Direction of Expandable Components

[0034] Figure 2 is a schematic illustration of a basket assembly 281 according to an example of the present disclosure, the basket assembly being configured to obtain electrical measurements to determine the approach vector 215 of the assembly 281 to the wall of the heart chamber tissue.

[0035] The basket assembly 281 can be used to implement the above Figure 1 described basket assembly 28. As shown, the assembly 281 is part of a catheter 214, which also includes a shaft 244 having a distal end 246. The distal end assembly 228 includes a proximal base 227, which is configured to couple the assembly to the distal end 246 of the shaft 244. The distal axis 278 of the assembly is defined by the longitudinal axis of the distal end 246 of the shaft 244.

[0036] The basket-shaped assembly 281 is implemented as an expandable frame including a plurality of splines 222, with functional electrodes 226 coupled to the splines. Each of the splines 22 is electrically insulated from the environment over most of its area by an insulating layer 262.

[0037] When expanded, as Figure 3 shown, the expandable distal end assembly 281 defines a content volume 277. At the base of the assembly within the volume 277, a far-field electrode 223 is used to remove far-field signals from the IEGM signals acquired by the electrodes 226.

[0038] A plurality of functional electrodes 226 are at least partially outside the content volume and are configured to be placed in contact with the wall tissue of the heart chamber. A reference toroidal electrode 217 (such as Figure 1 the toroidal electrode 17) is located on the proximal base 227 of the expandable distal end assembly 281 and is outside the content volume 277. The toroidal electrode 217 on the base 227 is positioned to avoid tissue wall contact when the distal end assembly 281 is in the expanded state.

[0039] In Figure 2 the example of, the reference toroidal electrode 217 is a ring fitted on the outer periphery of the proximal base section 227. The reference toroidal electrode 217 can be disposed on an insulating layer (not shown), for example when the base section 227 is conductive (e.g., made of nitinol).

[0040] The proximal base section 227 further includes a mechanical guard ring 231 that projects outward from the proximal base, i.e., further outward than the reference electrode 227, to prevent the reference electrode 227 from contacting the tissue wall. Further improvement in measurement accuracy can be achieved by applying an internal electrical insulation coating 241 to the electrodes 226 to minimize the electrode portion in the blood when in contact with the tissue. The coating 241 can be a type of polymer or an additional dielectric layer (e.g., silicon nitride).

[0041] The processor 56 receives impedance signals between each of the electrodes 226 and the reference electrode 217. When the catheter is moving in the blood pool and is also in contact with the tissue, the processor obtains an impedance range that has a magnitude range between a minimum value R B from the electrodes 226 in the blood pool and a maximum value R T from the electrodes 226 that are close enough to or in contact with the tissue.

[0042] The processor defines a weight f j for the electrode direction unit vector v j of the electrode having an impedance R as f j =(R T -R) / (R T -R B)。As can be seen, the weight f j is the magnitude of the unit vector v j and is equal to the impedance value after normalization within a range, such as a value between zero and one. For simplicity, it is assumed that all vectors v j have the same unit magnitude (i.e., it is assumed that the spherical expandable distal end assembly is normalized to a unit sphere). The weight f j can have any value between 0 and 1.

[0043] The electrode immersed in blood has f j = 1, while the electrode in sufficient proximity to tissue has f j = 0. By way of example, some impedance weighted vectors f j v j , 236, originating from the assembly center 280 are shown.

[0044] The blood direction vector B represented by the arrow 350 in Figure 3 is given by the weighted sum of all vectors v j :

[0045]

[0046] Although Figure 2 a basket assembly is described, the disclosed techniques can be applied, with necessary modifications, to an expandable balloon assembly having an expandable membrane on which functional electrodes are disposed.

[0047] Providing a Blood Pool Direction Vector Based on Measured Impedance

[0048] Figure 3 is a schematic illustration of a proximity-based guidance scheme for a basket catheter 214 inside the left atrium of a patient according to an example of the present disclosure. The figure shows the output of the scheme in a window 300 presented to a physician 24 on a display 27, for example. Window 300 presents in real time an early stage of EA mapping at which a small portion of the left atrial wall has been EA mapped. Window 300 shows the tissue wall portion 331 of the EA mapping, the icon 341 of the distal end assembly 281, and an arrow 350 indicating the direction of the blood pool (as found by B), where the arrow 350 indicates to the physician 24 the direction in which the distal end assembly 281 can be advanced without engaging the tissue wall.

[0049] By way of example, the probing phase of the distal end assembly is represented in three windows 300 (i.e., (a), (b), and (c)). Each of the windows (a), (b), and (c) provides real-time advice to the physician regarding the blood pool direction 350 to move the catheter, thus allowing the physician to progress more quickly during the probing phase of the EA mapping procedure, for example, to expand the rendering 331 into a clinically more meaningful portion of the EA mapping.

[0050] As indicated by the arrows, window (c) can represent an advanced stage of detection compared to what is seen in window (b). Similarly, window (b) can represent an advanced stage of detection compared to what is seen in window (a). Figure 3 (c) indicates to the user that optimal access to the ostium of the PV is achieved when the blood pool direction 350 is aligned with the axis of the catheter (e.g., by indicating when the direction arrow 350 is aligned with the longitudinal axis icon 450 (e.g., virtual representation 341) of the distal end assembly icon 341 within a predetermined tolerance).

[0051] Once EA mapping has been collected on a sufficient number of anatomical landmarks (e.g., ostia of the pulmonary veins), the physician's job of performing EA mapping of the cardiac chamber becomes easier.

[0052] Method for Providing a Blood Pool Direction Vector Based on Measured Impedance

[0053] Figure 4 is a flowchart schematically showing a method and algorithm for estimating and presenting a blood pool direction arrow 350 based on impedance measurements of functional electrodes according to an example of the present disclosure. The algorithm according to this embodiment performs a process that begins at a basket movement step 402 by moving an extended basket assembly 281 into a cardiac chamber of the heart 12.

[0054] As the basket is moved, at a baseline impedance monitoring step 404, the system 10 monitors the impedance between each of the functional electrodes 226 and the reference toroidal electrode 217.

[0055] At an impedance range identification step 406, when the basket occasionally contacts the wall of the cardiac chamber tissue, the processor identifies touch and non-touch impedance ranges for the monitored cumulative impedance values. A dedicated range is defined for each of the electrodes, as the range is a function of the distance between the functional electrode and the reference electrode. However, by compensating for the different distances between each of the functional electrodes 226 and the reference electrode, the ranges for the individual electrodes can be inferred based on the aggregated output from all of the functional electrodes 226.

[0056] At a blood pool direction vector calculation step 408, using the monitored impedance and its identified ranges, the processor calculates a blood pool direction vector B 350.

[0057] Finally, at a direction arrow display step 410, the processor displays a corresponding blood pool direction arrow 350 associated with the rendering of the distal end assembly, such as arrow 350 on window 300.

[0058] Figure 4The example flowcharts shown are chosen solely for clarity of concept. This embodiment also includes additional steps of the algorithm, such as obtaining an intracardiac electrocardiogram, which have been intentionally omitted from the present disclosure to provide a simplified flowchart.

[0059] Examples

[0060] Example 1

[0061] A method comprising: monitoring an impedance of a plurality of functional electrodes (26) relative to a reference electrode (17) while manipulating a catheter (14) within a lumen of an organ (12), the catheter comprising: (i) a shaft (44) having a distal end (46); and (ii) an expandable distal end assembly (28) coupled to the distal end (46) of the shaft (44) and including the plurality of functional electrodes. Estimating a direction vector based on the monitored impedance, the catheter being free to advance within the lumen of the organ along the direction vector without being obstructed by the tissue wall of the lumen. Displaying (300) the direction vector to a user.

[0062] Example 2

[0063] The method according to embodiment 1, wherein estimating the direction vector includes estimating a blood pool direction (350) based on the monitored impedance.

[0064] Example 3

[0065] The method according to any one of embodiments 1 and 2, wherein estimating the blood pool direction vector includes: based on a known geometry of the distal end assembly (28), converting each impedance of the functional electrodes (26) into a weighted vector in the direction of the functional electrode, and summing the weighted vectors over all of the functional electrodes (26).

[0066] Example 4

[0067] The method according to any one of embodiments 1 to 3, wherein converting each impedance of the functional electrodes (26) into a weighted vector in the direction of the functional electrodes (26) includes: (i) identifying an impedance range for the accumulated impedance values; and (ii) normalizing each impedance within the range to a weight of a corresponding weighted vector according to the range.

[0068] Example 5

[0069] The method according to any one of Embodiments 1 to 4, wherein converting each impedance of the functional electrodes (26) into a weighted vector includes: calculating a weight by normalizing the impedance to a value between zero and one with respect to the range.

[0070] Example 6

[0071] The method according to any one of Embodiments 1 to 5, wherein displaying (300) the direction vector includes: presenting a direction arrow (350) on a virtual representation of the distal end assembly (341) shown on an EA mapping diagram generated using electroanatomical (EA) signals from the functional electrodes.

[0072] Example 7

[0073] The method according to any one of Embodiments 1 to 6, wherein displaying the direction vector includes: indicating that the direction arrow (350) is aligned with a longitudinal axis icon (450) of the virtual representation (341) of the distal end assembly (28).

[0074] Example 8

[0075] The method according to any one of Embodiments 1 to 7, wherein the distal end assembly is one of a basket assembly (281) and a balloon assembly.

[0076] Example 9

[0077] A system, the system includes: an interface (30) and a processor (56). The interface (30) is configured to monitor the impedance of a plurality of functional electrodes (26) relative to a reference electrode (17) when manipulating a catheter within a lumen of an organ (12), the catheter including: (i) a shaft (44) having a distal end (46); and (ii) an expandable distal end assembly (28) coupled to the distal end of the shaft and including a plurality of functional electrodes (26). The processor (56) is configured to: (i) estimate a direction vector based on the monitored impedance, along which the catheter can freely advance within the lumen of the organ without being obstructed by tissue walls; and (ii) display (300) the direction vector to a user.

[0078] Although the embodiments described herein are mainly directed to cardiac diagnostic applications, the methods and systems described herein can also be used in other medical applications.

[0079] It should be understood that the above embodiments are cited by way of example, and the present disclosure is not limited to what is specifically shown and described above. On the contrary, the scope of the present disclosure includes combinations and sub - combinations of the various features described above, as well as their variations and modifications, which will occur to those skilled in the art upon reading the above description and which are not disclosed in the prior art.

Claims

1. A method, comprising: monitoring impedance of a plurality of functional electrodes relative to a reference electrode while maneuvering a catheter within a lumen of an organ, the catheter comprising: (i) a shaft having a distal end; and (ii) an expandable distal tip assembly coupled to the distal end of the shaft and comprising the plurality of functional electrodes; estimating a direction vector based on the monitored impedance, along which the catheter can freely advance within the lumen of the organ without being hindered by a tissue wall of the lumen; and The direction vector is displayed to a user.

2. The method according to claim 1, wherein: Estimating the direction vector includes estimating the blood pool direction based on the monitored impedance.

3. The method according to claim 2, wherein: Estimating the blood pool direction vector includes: converting each impedance of the functional electrode into a weighted vector in the direction of the functional electrode based on the known geometry of the distal tip assembly, and summing the weighted vectors on all the functional electrodes.

4. The method according to claim 3, wherein: Converting each impedance of a functional electrode into a weighted vector in the direction of the functional electrode comprises: identifying an impedance range for the accumulated impedance values; and Each impedance within the range is normalized to a weight of a corresponding weighting vector according to the range.

5. The method according to claim 4, wherein: Converting each impedance of the functional electrode into a weighted vector includes calculating a weight by normalizing the impedance with respect to the range to a value between zero and one.

6. The method according to claim 1, wherein: Displaying the direction vector includes presenting a direction arrow on a virtual representation of the distal tip assembly shown on an electroanatomical (EA) map generated using EA signals from the functional electrodes.

7. The method according to claim 6, wherein: Displaying the direction vector includes indicating that the direction arrow is aligned with a longitudinal axis icon of the virtual representation of the distal tip assembly.

8. The method according to claim 1, wherein: The distal end assembly is one of a basket assembly and a balloon assembly.

9. A system, comprising: An interface configured to monitor impedance of a plurality of functional electrodes relative to a reference electrode when maneuvering a catheter within a lumen of an organ, the catheter comprising: (i) a shaft having a distal end; and (ii) an expandable distal end assembly coupled to the distal end of the shaft and comprising the plurality of functional electrodes; and A processor, the processor being configured to: estimating a direction vector based on the monitored impedance, along which the catheter can freely advance within the lumen of the organ without being hindered by a tissue wall of the lumen; and The direction vector is displayed to a user.

10. The system according to claim 9, wherein: The processor is configured to estimate the direction vector by estimating the blood pool direction based on the monitored impedance.

11. The system according to claim 10, wherein: The processor is configured to estimate the blood pool direction by converting each impedance of a functional electrode into a weighted vector in the direction of the functional electrode based on a known geometry of the distal tip assembly, and summing the weighted vectors over all of the functional electrodes.

12. The system according to claim 11, wherein: The processor is configured to convert each impedance of a functional electrode into a weighted vector in the direction of the functional electrode by: identifying an impedance range for the accumulated impedance values; and Each impedance within the range is normalized to a weight of a corresponding weighting vector according to the range.

13. The system according to claim 12, wherein: The processor is configured to convert each impedance of the functional electrode into a weighted vector by calculating a weight calculated by normalizing the impedance with respect to the range to a value between zero and one.

14. The system according to claim 9, wherein: The processor is configured to display the direction vector by presenting a direction arrow on a virtual representation of the distal tip assembly shown on an EA map generated using the EA signals from the functional electrodes.

15. The system of claim 14, wherein: The processor is configured to display the direction vector by indicating that the direction arrow is aligned with a longitudinal axis icon of the virtual representation of the distal tip assembly.

16. The system of claim 9, wherein: The distal end assembly is one of a basket assembly and a balloon assembly.

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