Method for determining a position of a catheter tip

Abstract

The invention relates to a method for determining a position of a catheter tip in the interior of a body, including the following steps: detecting an intravascular ECG lead between the catheter tip and a surface electrode by measurement, wherein the surface electrode is arranged at a defined surface position of the body; calculating a virtual intravascular ECG lead between a virtual catheter tip and a virtual surface electrode with computer assistance, wherein the calculation is implemented using a numerical simulation model that models physical properties of the body, the surface position of the surface electrode, an electrical cardiac activity and an electric field resulting from the electrical cardiac activity, wherein a modeled electrical cardiac activity that forms the basis of the numerical simulation model is modeled and / or corrected in a manner dependent on the ECG lead detected by measurement, wherein the modeled electrical cardiac activity is matched to the actual electrical cardiac activity that is the cause of the ECG lead detected by measurement, and wherein the calculation is carried out for a plurality of different virtual positions of the virtual catheter tip; comparing the ECG lead detected by measurement with the calculated virtual ECG lead, wherein the comparison is implemented for the plurality of virtual positions of the virtual catheter tip; determining the position of the catheter tip in a manner dependent on the comparison.

Description

[0001] Method for determining the position of a catheter tip

[0002] The invention relates to a method for determining the position of a catheter tip inside a body. The invention also relates to a medical system configured to carry out such a method.

[0003] Catheters are well known in medicine. When a catheter is inserted, its tip is inserted into a body-side access port and advanced to the desired location. The insertion of the catheter is also referred to as catheter placement.

[0004] Central venous catheters are typically inserted into the venous system via a vein in the upper half of the body. The catheter tip is typically advanced into the right atrium. Misdirected advancement and insufficiently precise positioning of the catheter tip can lead to problems. To counteract such problems, monitoring the position of the catheter tip is necessary. Ideally, this determination is performed in real time, i.e., during catheter insertion. Various procedures are known for this in clinical practice.

[0005] In one known procedure, the position of the catheter tip is recorded x-rayed after or during catheter insertion. The associated radiation exposure poses health risks and therefore precludes widespread use. Furthermore, x-ray procedures require complex equipment and are comparatively time- and cost-intensive.

[0006] Another known procedure involves electrocardiographic position control (e.g., W. Schummer et al.: "Optimized Positioning of Central Venous Catheters Through a Modified Application of Intravascular Electrocardiography," Anesthesiologist 54 (2005), pp. 983-990). An ECG signal is recorded between a surface electrode attached to the patient's body surface and a catheter guidewire. This ECG signal can also be referred to as an intravascular ECG recording. This known procedure takes advantage of the fact that the P wave of the intravascular ECG recording changes depending on the advancement of the catheter tip. When the catheter tip enters the atrium, a characteristic change in the P wave occurs. Position control is performed by observing this change.The current electrocardiographic procedure only allows confirmation of correct positioning in front of the right atrium. It is not possible to determine the position of the catheter tip in areas far from the atrium.

[0007] In addition, there is a medical system known as the “Sherlock 3CG™ Tip Confirmation System,” which uses magnetic field sensors to determine the position of the catheter tip.

[0008] The object of the invention is to provide a method and a medical system of the type mentioned above which offer advantages over the prior art.

[0009] To achieve this object, the invention provides a method having the features of claim 1 and a medical system having the features of claim 4. Advantageous embodiments are specified in the dependent claims. The wording of all claims is incorporated into the description by reference.

[0010] The method according to the invention comprises: measuring an intravascular ECG lead between the catheter tip and a surface electrode, wherein the surface electrode is arranged at a defined surface position of the body; computer-assisted calculation of a virtual intravascular ECG lead between a virtual catheter tip and a virtual surface electrode, wherein the calculation is carried out using a numerical simulation model that models physical properties of the body, the surface position of the surface electrode, electrical cardiac activity, and an electric field resulting from the electrical cardiac activity, wherein a modeled electrical cardiac activity underlying the numerical simulation model is modeled and / or corrected depending on the measured ECG lead,The modeled electrical cardiac activity is adjusted to the actual electrical cardiac activity causative of the measured ECG lead, and the calculation is performed for several different virtual positions of the virtual catheter tip; comparing the measured ECG lead with the calculated virtual ECG lead, the comparison being performed for the several virtual positions of the virtual catheter tip; determining the position of the catheter tip based on the comparison. The solution according to the invention eliminates the use of X-rays or electromagnetic radiation to determine the position of the catheter tip. This avoids radiation exposure of the patient. Furthermore, the cost of equipment can be reduced. In contrast to methods known from the prior art, the position can also be determined with sufficient accuracy away from the atrium.particularly in the area of ​​the extremities. The invention is based on the finding that the electric field resulting from electrical cardiac activity is increasingly distorted inside and on the surface of the body in the area of ​​the extremities. Due to this distortion, sufficiently accurate position determination using methods known from the prior art is not readily possible. The inventive solution takes said field distortion into account in the computer-aided calculation, i.e., using the aforementioned numerical simulation model.

[0011] The measurement of the intravascular ECG lead is carried out in a manner known to those skilled in the art. The intravascular ECG lead can also be referred to as a catheter lead. The catheter lead can be wired or wireless. For example, the catheter lead can be made via a distal end of a guidewire or other wire. Alternatively, the catheter tip can be provided with a catheter electrode. Further alternatively, the catheter lead can be made via a catheter lumen filled with electrically conductive fluid, in particular saline solution. The surface electrode can also be referred to as a skin electrode and is arranged at a defined position on the body surface (surface position). The catheter lead is recorded for at least one cycle of the patient's cardiac activity, i.e. for at least one heartbeat and / or one complete revolution of the so-called ECG vector.

[0012] The computer-aided calculation of the virtual intravascular ECG lead is performed using the numerical simulation model. The virtual intravascular ECG lead is also referred to below as the virtual and / or simulated catheter lead. The numerical simulation model used to calculate the virtual catheter lead models the metrological recording of the (real / actual) catheter lead. The numerical simulation model is preferably based on fundamentally known nonlinear differential equations and a discretization method suitable for solving such equations, for example, a finite element or finite difference method. The numerical simulation model models the relevant problem area, in this case the patient's body and its relevant physical properties.The surface position of the (actual) surface electrode, the electrical activity of the heart (electrical cardiac activity), and the electrical field inside the body and on the body surface resulting from the cardiac activity are also modeled. The electrical field is (approximated) calculated. On this basis, the virtual catheter lead can finally be calculated. The virtual catheter lead is determined for at least one cycle of the electrical cardiac activity, i.e. for at least one heartbeat and / or one complete revolution of the so-called ECG vector. The virtual catheter lead is calculated for different virtual positions of the virtual catheter tip. Consequently, the position of the virtual catheter tip is changed, in particular step by step, during the computer-assisted calculation, for example along a plausible advance path within the body.The computer-assisted calculation therefore provides a corresponding virtual catheter lead for each virtual position of the catheter tip. The modeled electrical cardiac activity underlying the simulation model is modeled and / or corrected depending on the measured ECG lead, whereby the modeled electrical cardiac activity is adjusted to the actual electrical cardiac activity that caused the measured ECG lead. In other words, a correction and / or adjustment takes place between the measured catheter lead and the calculated catheter lead. Such a correction and / or adjustment can fundamentally be performed in different ways. In this embodiment of the invention, however, the correction and / or adjustment is particularly advantageously performed based on the measured ECG vector, because this represents the patient's actual electrical cardiac activity.If the modeled electrical cardiac activity underlying the numerical simulation model is based on actual cardiac activity, discrepancies between the measured data and the computer-aided calculation can be avoided, and improved accuracy can be achieved. When cardiac activity is simulated, the electric field must be "corrected" by the actual cardiac activity. In one embodiment, the electric field is calculated and subsequently corrected using the measured ECG signal, in particular by the measured ECG vector(s). In another embodiment, the electric field is calculated for the actually measured, real ECG signal.

[0013] Comparing involves comparing the measured catheter lead with the calculated catheter lead for the different positions of the virtual catheter tip. For this purpose, the measured catheter lead can be subtracted from each of the calculated catheter leads, or vice versa. Based on such a subtraction, a difference value can be determined, for example, that represents the deviation between the calculated and measured catheter lead. Furthermore, a mean square error (MSE) can be calculated, representing the deviation between the calculated and measured catheter lead.

[0014] The position is determined based on the comparison. If a difference value or a mean square deviation is determined, the position of the actual catheter tip is approximately in the range of the virtual position of the virtual catheter tip at which the determined value reaches an extreme value, in particular, becomes minimal.

[0015] The method according to the invention is particularly advantageous for determining the position of central venous catheters, PICCs (peripherally inserted central venous catheters), and so-called midlines. However, the solution according to the invention is not limited to such catheters, but is also advantageously suitable for pulmonary catheters, dialysis catheters, and / or arterial catheters, for example.

[0016] In one embodiment of the invention, the metrological recording and the computer-assisted calculation are carried out for different surface positions of the surface electrode and / or for several differently positioned surface electrodes, and the comparison of the metrologically recorded ECG leads and the calculated virtual ECG leads is carried out for the different surface positions of the surface electrode and / or for the several differently positioned surface electrodes. Consequently, in this embodiment of the invention, not only the (virtual) position of the virtual catheter tip is changed during the computer-assisted calculation. Rather, the position of the surface electrode is also changed and / or several differently positioned surface electrodes are used. This occurs both during the metrological recording and the computer-assisted calculation.This allows for even greater accuracy. Preferably, at least three differently positioned surface electrodes are used to measure the catheter lead and for its computer-assisted calculation.

[0017] In a further embodiment of the invention, the physical properties of the body underlying the numerical simulation model comprise at least one body measurement, a body mass, and / or a body fat percentage. In this embodiment of the invention, the numerical simulation model is adapted to real-life conditions in an improved manner by taking relevant physical properties of the body into account during modeling. For example, the at least one body measurement, such as body length, body mass (weight), and / or body fat percentage. The aforementioned properties influence the field variables resulting from the electrical cardiac activity and thus the accuracy of the calculated virtual catheter leads.

[0018] The medical system according to the invention is configured to carry out a method according to the preceding description. The medical system according to the invention comprises a measuring device and a calculation device. The measuring device is configured to metrologically acquire an intravascular ECG lead between a catheter tip and a surface electrode, wherein the surface electrode is intended to be arranged at a defined surface position of the body. The calculation device is configured for computer-assisted calculation of a virtual intravascular ECG lead, for comparing the metrologically acquired ECG lead with the calculated virtual ECG lead, and for determining the position of the catheter tip depending on the comparison. This is in each case in accordance with the preceding description of the method according to the invention.To avoid repetition, express reference is made to the description of the method according to the invention and its embodiments. What is stated therein also applies, mutatis mutandis, to the medical system according to the invention. Embodiments of the medical system emerge directly and unambiguously from the disclosure of the embodiments of the method according to the invention.

[0019] Further advantages and features of the invention emerge from the claims and from the following description of a preferred embodiment of the invention, which is illustrated with reference to the drawings.

[0020] Fig. 1 shows a schematically simplified representation of an embodiment of a medical system according to the invention,

[0021] Fig. 2, 3 an exemplary usage situation of the medical system according to Fig. 1 and

[0022] Fig. 4 shows a schematic block diagram of an embodiment of a method according to the invention using the medical system according to Fig. 1.

[0023] According to Figs. 1 to 3, a medical system 1 is provided for determining a position P of a catheter tip 5. In this case, the position determination or localization takes place inside a body K. The body K can be a human or animal body. The catheter tip 5 to be located is in this case part of a central venous catheter 4. However, the medical system 1 is not limited to use with central venous catheters. Instead of a central venous catheter 4, for example, a PICC catheter or a so-called midline can be located. The medical system 1 has a measuring device 2 and a computing device 3.

[0024] In the embodiment shown here, the medical system 1 also comprises the central venous catheter 4 to be localized. In an embodiment not shown in the figures, however, the catheter to be localized is not part of the medical system.

[0025] The measuring device 2 is used to measure an intravascular ECG lead E between the catheter tip 5 and at least one surface electrode 7. The surface electrode 7 is attached to a defined surface position Q of the body K during use of the medical system 1. The attachment takes place in a manner known to those skilled in the art. In the usage situation shown in Fig. 2, the catheter tip 5 is located inside the body K. The catheter can be inserted in a manner known to those skilled in the art, for example, using the Seldinger technique. The intravascular ECG lead E can also be referred to as a catheter lead, with both terms being used interchangeably below.

[0026] In the embodiment shown, the central venous catheter 4 is provided with a catheter electrode 6 in the region of its distal catheter tip 5. The catheter electrode 6 is connected to the measuring device 2 via a signal line 61. The surface electrode 7 is connected to the measuring device 2 via a signal line 71.

[0027] The measured catheter lead E results from a potential difference between the catheter electrode 6 and the surface electrode 7. The potential difference arises in a known manner as a result of the electric field F resulting from the electrical cardiac activity HA of the heart H inside the body K and on its surface. Fig. 2 shows exemplary and schematically highly simplified field lines L of the electric field F for an imaginary point in time of the electrical cardiac activity HA. It is understood that the field lines L change during one cycle of cardiac activity HA, i.e., one heartbeat of the heart H.

[0028] In the embodiment shown, the intravascular ECG lead E is recorded for at least one cycle of cardiac activity HA.

[0029] Calculation device 3 is used to calculate a virtual intravascular ECG lead. The calculation is performed in a manner described in more detail below, using computer support and based on a simulation model M. Position P is determined based on the measured ECG lead E and the computer-supported calculation.

[0030] The computer-assisted calculation takes place, as illustrated in Fig. 3, between a virtual catheter tip 5' and at least one virtual surface electrode 7'. The calculation is carried out on the basis of the numerical simulation model M. In the embodiment shown, the numerical simulation model M is executed on a processor unit 31 of the calculation device 3. The numerical simulation model M forms physical properties A1, A2 to A nof the body K, the surface position Q of the at least one surface electrode 7, the said electrical cardiac activity HA, and the electrical field F resulting from the electrical cardiac activity HA. These modeled quantities / properties are each provided with an apostrophe in Fig. 3 using the same reference numerals and letters. Thus, one can also speak of a virtual electrical field F', a virtual electrical cardiac activity HA', a virtual body K', and virtual field lines L'. "Virtual" means modeled and / or calculated.

[0031] The calculation is performed not just for a single, but for several virtual positions PT to P6' of the virtual catheter tip 5'. The virtual position of the virtual catheter tip 5' is changed during the calculation, particularly stepwise and / or iteratively. Figure 3 schematically illustrates only six virtual positions. It is understood that significantly more than the six positions shown here can be used as a basis for the calculation.

[0032] Using the numerical simulation model M, a catheter lead ET to E6' is calculated for each of the multiple virtual positions PT to P6'. For example, the virtual position PT is assigned to the catheter lead ET and vice versa. For the remaining virtual positions P2' to P6', a corresponding assignment to the remaining calculated catheter leads E2' to E6' applies. As further illustrated in Fig. 3, the measured catheter lead E is compared with each of the calculated catheter leads ET to E6'. This comparison is carried out in a separate determination unit 32 of the calculation device 3. However, the determination device 32 can also be formed by the aforementioned processor unit 31 or be assigned to it. Comparing the measured catheter lead E with the calculated catheter leads ET to E6' preferably comprises calculating a comparison value.This comparison value can be a difference value, which is formed, for example, by a subtraction between the measured catheter lead E and the calculated catheter leads ET to E6'.

[0033] The position P is determined based on the comparison (see Fig. 3). The virtual position PT to P6' for which the difference value is minimal approximately represents the actual position P of the catheter tip 5.

[0034] Furthermore, it is intended that the virtual / modeled cardiac activity HA' is adjusted to the actual, real cardiac activity HA. For this purpose, the measured catheter lead E serves as an input variable for the numerical simulation model M. This adjustment or correction can be carried out specifically as explained below: For each time point of the (time-discrete) measured ECG vector, a phase of the measured ECG vector is calculated. For each of these calculated phases, the amplitude of the simulated ECG signal for a specific position of the surface electrode and the intravascular electrode is looked up in a table (or is calculated). This amplitude is corrected by the amplitude of the measured ECG vector at exactly this time point. This process is repeated for all time-discrete measured positions of the ECG vector.From the results, the virtual ECG signal is generated at the intravascular position determined above, depending on the measured ECG signal and the skin electrode position.

[0035] Furthermore, the already mentioned physical properties A1, A2 to A n are fed to the numerical simulation model M as input variables. The physical properties in this case are a body measurement A1 , for example the body length, a body mass K, ie the body weight, and a body fat percentage A n . The aforementioned physical properties of the body K influence the properties of the electric field F resulting from the electrical cardiac activity HA. By taking these properties into account, the calculation of the virtual catheter lead or catheter leads ET to E6' can be carried out with improved accuracy.

[0036] Furthermore, it is provided here that the metrological recording and the computer-aided calculation are not carried out solely using the aforementioned surface electrode 7 and its position Q. Rather, a further surface electrode 8 and its position R are also taken into account in both the measurement and the calculation. The further surface electrode 8 is connected to the measuring device 2 via a further signal line 81. The surface electrodes 7, 8 can also be referred to as the first surface electrode 7 and the second surface electrode 8. This can also achieve improved accuracy. It is understood that more than the two surface electrodes shown here can be used, for example three, four, five, six or even more than six surface electrodes.It may be useful to place at least one or more of the surface electrodes along an (expected) advancement path of the catheter tip.

[0037] Fig. 4 schematically illustrates the method already explained with reference to Figs. 1 to 3. Thus, the method 1000 basically provides for measurement-based acquisition 1100, computer-assisted calculation 1200, comparison 1300, and determination 1400.

[0038] During the measurement-technical acquisition 1100, the said intravascular ECG lead E is measured between the catheter tip 5, in this case the catheter electrode 6, and at least the first surface electrode 7. For this purpose, the measuring device 2 is present.

[0039] The computer-aided calculation 1200 is carried out on the basis of the previously explained numerical simulation model M and using the calculation device 3. The comparison 1300 and the determination 1400 are also carried out using the calculation device 3, which is also set up for this purpose.

Claims

Patent claims 1. A method (1000) for determining a position (P) of a catheter tip (5) inside a body (K), comprising the steps of: measuring (1100) an intravascular ECG lead (E) between the catheter tip (5) and a surface electrode (7, 8), wherein the surface electrode (7, 8) is arranged at a defined surface position (Q, R) of the body (K); computer-assisted calculation (1200) of a virtual intravascular ECG lead (ET to E6') between a virtual catheter tip (5') and a virtual surface electrode (7', 8'), wherein the calculation (1200) is carried out using a numerical simulation model (M) which has physical properties (A1, A2 to A n) of the body (K), the surface position (Q, R) of the surface electrode (7, 8), an electrical cardiac activity (HA) and an electrical field (F) resulting from the electrical cardiac activity (HA), wherein a modeled electrical cardiac activity (HA') underlying the numerical simulation model (M) is modeled and / or corrected as a function of the metrologically recorded ECG lead (E), wherein the modeled electrical cardiac activity (HA') is adjusted to the actual electrical cardiac activity (HA) causing the metrologically recorded ECG lead (E), and wherein the calculation (1200) is carried out for several different virtual positions (PT to P6') of the virtual catheter tip (5'); Comparing (1300) the measured ECG lead (E) with the calculated virtual ECG lead (ET to E6'), wherein the comparison is carried out for the plurality of virtual positions (PT to P6') of the virtual catheter tip (5'); Determining (1400) the position (P) of the catheter tip (5) depending on the comparison (1300).

2. Method (1000) according to claim 1, characterized in that the metrological detection (1100) and the computer-assisted calculation (1200) are carried out for different surface positions of a single surface electrode and / or for a plurality of differently positioned surface electrodes (7, 8), and in that the comparison (1300) of the metrologically detected ECG lead (E) and the calculated virtual ECG lead (ET to E6') is carried out for the different surface positions of the surface electrode and / or for the plurality of differently positioned surface electrodes (7, 8).

3. Method (1000) according to one of the preceding claims, characterized in that the physical properties (A1, A2 to A n ) of the body (K) at least one body measurement (A1), a mass (A2) of the body (K) and / or a body fat percentage (A n ) include.

4. A medical system (1) for determining a position (P) of a catheter tip (5) inside a body (K), comprising a measuring device (2) configured for the metrological detection (1100) of an intravascular ECG lead (E) between the catheter tip (5) and a surface electrode (7, 8), wherein the surface electrode (7, 8) is configured for arrangement at a defined surface position (Q, R) of the body (K), and a calculation device (3) configured for the computer-assisted calculation (1200) of a virtual intravascular ECG lead (ET to E6') between a virtual catheter tip (5') and a virtual surface electrode (7', 8'), wherein the calculation (1200) is carried out using a numerical simulation model (M) which comprises physical properties (A1, A2 to A n) of the body (K), the surface position (Q, R) of the surface electrode (7, 8), an electrical cardiac activity (HA) and an electrical field (F) resulting from the electrical cardiac activity (HA), wherein a modeled electrical cardiac activity (HA') underlying the numerical simulation model (M) is modeled and / or corrected as a function of the metrologically recorded ECG lead (E), wherein the modeled electrical cardiac activity (HA') is adjusted to the actual electrical cardiac activity (HA) causing the metrologically recorded ECG lead (E), and wherein the calculation (1200) is provided for several different virtual positions (PT to P6') of the virtual catheter tip (5'), and for comparing (1300) the metrologically recorded ECG lead (E) with the calculated virtual ECG lead (ET to E6'),wherein the comparison is provided for the plurality of virtual positions (PT to P6') of the virtual catheter tip (5'), and for determining (1400) the position (P) of the catheter tip (5) as a function of the comparison (1300).,

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