SYSTEM AND METHOD FOR UNIPHASIC AND BIPHASIC SHOCK INVERSION TIME DOMAIN SHIFTING FOR SHOCK ENERGY VECTORING IN TRANSVENOUS AND SUBCUTANEOUS DEFIBRILLATORS WITH TWO OR MORE SHOCK VECTORS

Abstract

Method for truncating and summating shock vector energy between at least two shock vectors in a defibrillator, including the procedures of applying at least two biphasic defibrillating shock vectors simultaneously via at least two electrode sets until a voltage inversion point, terminating at least a first one of the biphasic defibrillating shock vectors at the voltage inversion point, and directing a remaining energy of the first one of the biphasic defibrillating shock vectors to a second phase of at least a second one of the biphasic defibrillating shock vectors.

Claims

1. Method for truncating and summating shock vector energy between at least two shock vectors in a defibrillator, comprising the procedures of: applying at least two biphasic defibrillating shock vectors simultaneously via at least two electrode sets until a voltage inversion point; terminating at least a first one of said at least two biphasic defibrillating shock vectors at said voltage inversion point; and directing a remaining energy of said at least first one of said biphasic defibrillating shock vectors to a second phase of at least a second one of said biphasic defibrillating shock vectors.

2. The method according to claim 1, further comprising the procedure of modifying said voltage inversion point of said at least two biphasic defibrillating shock vectors.

3. The method according to claim 2, wherein said procedure of modifying comprises the sub-procedure of modifying said voltage inversion point according to at least one of patient characteristics and defibrillator characteristics.

4. The method according to claim 3, wherein said patient characteristics comprises an anatomy of a patient.

5. The method according to claim 3, wherein said defibrillator characteristics comprises an actual placement of a plurality of electrodes of said defibrillator in a patient.

6. The method according to claim 2, wherein said procedure of modifying comprises the sub-procedure of modifying said voltage inversion point to achieve energy symmetry between said at least two biphasic defibrillating shock vectors.

7. The method according to claim 1, wherein said at least first one of said at least two biphasic defibrillating shock vectors which is terminated at said voltage inversion point exhibits lower impedance compared to said at least second one of said at least two biphasic defibrillating shock vectors.

8. The method according to claim 1, wherein said defibrillator is selected from the list consisting of: an external defibrillator; an intravenous defibrillator; a transvenous defibrillator; and a subcutaneous defibrillator.

9. The method according to claim 1, wherein a defibrillating threshold for effective defibrillation of said defibrillator is as low as possible.

10. Subcutaneous defibrillator for truncating and summating at least two biphasic defibrillating shock vectors, comprising: a body; a plurality of electrodes, positioned on said body, for applying said at least two biphasic defibrillating shock vectors; and a plurality of sensors, positioned on said body, for detecting arrhythmias, said body comprising: at least one capacitor, for storing charge for providing said at least two biphasic defibrillating shock vectors; a processor, coupled with said at least one capacitor; and at least one battery, coupled with said at least one capacitor and said processor, for charging said at least one capacitor and for providing energy to operate said processor, wherein said plurality of electrodes applies at least a first one of said at least two biphasic defibrillating shock vectors and at least a second one of said at least two biphasic defibrillating shock vectors simultaneously until a voltage inversion point; wherein said processor terminates said at least first one of said at least two biphasic defibrillating shock vectors at said voltage inversion point; and wherein said processor directs a remaining energy of said at least first one of said at least two biphasic defibrillating shock vectors to a second phase of said at least second one of said at least two biphasic defibrillating shock vectors.

11. The subcutaneous defibrillator according to claim 10, further comprising a wireless transceiver, coupled with said processor, for programming said processor wirelessly.

12. The subcutaneous defibrillator according to claim 11, wherein said wireless transceiver is selected from the list consisting of: a Bluetooth transceiver; and an infrared transceiver.

13. The subcutaneous defibrillator according to claim 11, wherein said processor can toggle said truncating and summating of said at least two biphasic defibrillating shock vectors on and off via said wireless transceiver.

14. The subcutaneous defibrillator according to claim 13, wherein said subcutaneous defibrillator applies said at least two biphasic defibrillating shock vectors as at least two biphasic defibrillating shock vectors when said processor toggles said truncating and summating off.

15. The subcutaneous defibrillator according to claim 13, wherein said subcutaneous defibrillator applies said at least two biphasic defibrillating shock vectors as at least one truncated uniphasic defibrillating shock vector and at least one summated biphasic defibrillating shock vector when said processor toggles said truncating and summating on.

16. The subcutaneous defibrillator according to claim 11, wherein said processor can modify said voltage inversion point via said wireless transceiver.

17. The subcutaneous defibrillator according to claim 10, wherein said plurality of electrodes comprises at least three electrodes, wherein at least one of said at least three electrodes is disconnected at a given time during the application of said at least two biphasic defibrillating shock vectors.

18. The subcutaneous defibrillator according to claim 10, wherein said at least first one of said at least two biphasic defibrillating shock vectors has a lower impedance compared to said at least second one of said at least two biphasic defibrillating shock vectors having a higher impedance.

19. The subcutaneous defibrillator according to claim 18, wherein said processor truncates said at least first one of said at least two biphasic defibrillating shock vectors having said lower impedance at said voltage inversion point

20. The subcutaneous defibrillator according to claim 18, wherein said processor electronically switches said remaining energy from a first set of said plurality of electrodes applying said at least first one of said at least two biphasic defibrillating shock vectors having said lower impedance to a second set of said plurality of electrodes applying said at least second one of said at least two biphasic defibrillating shock vectors having said higher impedance.

21. Defibrillator for truncating and summating at least two biphasic defibrillating shock vectors, comprising: a can; and a plurality of leads, coupled with said can, for detecting arrhythmias; said can comprising: at least one capacitor, for storing charge for providing said at least two biphasic defibrillating shock vectors; a processor, coupled with said at least one capacitor; and at least one battery, coupled with said at least one capacitor and said processor, for charging said at least one capacitor and for providing energy to operate said processor, wherein said plurality of leads applies at least a first one of said at least two biphasic defibrillating shock vectors and at least a second one of said at least two biphasic defibrillating shock vectors simultaneously until a voltage inversion point; wherein said processor terminates said at least first one of said at least two biphasic defibrillating shock vectors at said voltage inversion point; and wherein said processor directs a remaining energy of said at least first one of said at least two biphasic defibrillating shock vectors to a second phase of said at least second one of said at least two biphasic defibrillating shock vectors.

22. The defibrillator according to claim 21, wherein said defibrillator is selected from the list consisting of: an external defibrillator; an intravenous defibrillator; and a transvenous defibrillator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The disclosed technique will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

[0023] FIG. 1A is a schematic illustration of a transvenous defibrillator showing two shock vectors, as is known in the prior art;

[0024] FIG. 1B is a schematic illustration of a subcutaneous defibrillator showing two shock vectors, as is known in the prior art;

[0025] FIG. 2A is a graph showing the waveform energy of a biphasic shock vector used in a defibrillator, as is known in the prior art;

[0026] FIG. 2B is a graph showing the waveform energy of a uniphasic shock vector used in a defibrillator, as is known in the prior art;

[0027] FIG. 3 is a graph showing current delivery and decay curves across different impedances in a defibrillator, constructed and operative in accordance with an embodiment of the disclosed technique;

[0028] FIG. 4 is a schematic illustration of a subcutaneous defibrillator showing two shock vectors, constructed and operative in accordance with another embodiment of the disclosed technique;

[0029] FIG. 5 is a set of graphs showing the truncation and summation of shock energy between two shock vectors, constructed and operative in accordance with a further embodiment of the disclosed technique;

[0030] FIG. 6 is a set of graphs showing different truncations and summations of shock energy between two shock vectors by displacement of an inversion point, constructed and operative in accordance with another embodiment of the disclosed technique;

[0031] FIG. 7 is a schematic illustration of defibrillators for truncating and summating shock energy between two shock vectors, constructed and operative in accordance with a further embodiment of the disclosed technique; and

[0032] FIG. 8 is a method for truncating and summating shock energy between two shock vectors, operative in accordance with another embodiment of the disclosed technique.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The disclosed technique overcomes the disadvantages of the prior art by providing a novel method and system for optimizing the energy delivered in defibrillators with two or more shock vectors. By optimizing the energy provided to each shock vector, problems relating to energy shunting in multi-vectorial defibrillation pulses can be minimized and lower DFTs can be achieved in external, transvenous and subcutaneous defibrillators. According to the disclosed technique, in defibrillators employing two or more biphasic shock vectors, the shock vector with the lower impedance is truncated at its inversion point such that it is made into a unipolar shock vector having only one phase (similar to a uniphasic shock vector) and terminated at its inversion point. The energy of the second phase of the shock vector with lower impedance is transferred and added to the shock vector with higher impedance. Thus, the remaining energy of the second phase of the shock vector with lower impedance is electronically switched from one set of electrodes and directed to another set of electrodes which deliver the shock vector of higher impedance. The biphasic shock vector of higher impedance now includes additional current and voltage from the other biphasic shock vector (now uniphasic) and thus provides an increase in deliverable energy via the shock vector with higher impedance. According to the disclosed technique, some of the energy being provided to an area of lower impedance in and around the heart is therefore shifted to an area of higher impedance in and around the heart, thus achieving an increase in symmetry in the total energy delivered to the heart by shock vectors having difference impedances.

[0034] Also according to the disclosed technique, further symmetry between the shock vectors can be achieved by moving the inversion point of the shock vector with lower impedance. In this manner, substantially full symmetry and balance of energy delivery between the shock vectors can be achieved. By moving the inversion point sooner in time, more energy can be transferred to the shock vector with higher impedance, whereas extending the inversion point in time will provide less energy transfer to the shock vector with higher impedance. According to the disclosed technique, a physician or clinician can optimize the delivery of energy to the two or more shock vectors of a defibrillator of a patient such that the DFT of the particular patient for achieving effective defibrillation is as low as possible. Lower overall DFTs (which by definition provide effective defibrillation) are better for patient comfort and can increase the battery life of an implanted defibrillator, whether implanted transvenously or subcutaneously. As compared with the prior art, the disclosed technique enables the energy delivery in defibrillators to be dynamically shifted and optimized between two or more shock vectors.

[0035] Reference is now made to FIG. 3, which is a graph showing current delivery and decay curves across different impedances in a defibrillator, generally referenced 150, constructed and operative in accordance with an embodiment of the disclosed technique. Graph 150 includes an x-axis 152 showing time in milliseconds and a y-axis 154 showing current in amperes (or for short, amps). Graph 150 shows the distribution of current over time for three different waveforms of shock vectors used in a defibrillator (not shown), each one representing a different amount of impedance as per a legend 162. A first waveform 156 shows the amount of current provided by the defibrillator where the shock vector experiences the least amount of impedance. A second waveform 158 shows a reduced amount of current provided by the defibrillator with an increase in impedance whereas a third waveform 160 shows a further reduced amount of current provided by the defibrillator with a further increase in impedance. First waveform 156 provides the most amount of energy in a shock vector to fibrillating myocardium whereas third waveform 160 provides the least amount of energy in a shock vector to fibrillating myocardium. As explained above, the particular placement of electrodes of an implantable defibrillator as well as the unique anatomy of a patient usually results in multi-vectorial pulses (i.e., defibrillators with two or more shock vectors) encountering different amounts of impedance as they cross the heart of a patient. Therefore typically, a patient being defibrillated by two or more shock vectors can experience a first shock vector similar to first waveform 156, which may defibrillate a first part of the heart (such as the right ventricle) effectively, whereas a second shock vector may be similar to third waveform 160, which will not defibrillate a second part of the heart (such as the left ventricle) effectively. According to the disclosed technique, the energy between two or more shock vectors can be distributed differently such that both shock vectors defibrillate effectively even if the path travelled by each shock vector has a different impedance as shown in graph 150.

[0036] Reference is now made to FIG. 4, which is a schematic illustration of a subcutaneous defibrillator showing two shock vectors, generally referenced 180, constructed and operative in accordance with another embodiment of the disclosed technique. As shown, subcutaneous defibrillator 180 is placed around a heart 182 of a patient (not labeled). Subcutaneous defibrillator 180 includes a body 184, a plurality of electrodes 194A-194D and a plurality of sensors 196A and 196B. High energy shocks can be provided by subcutaneous defibrillator 180 between any two of plurality of electrodes 194A-194D. A portion of body 184 of subcutaneous defibrillator 180 is placed anteriorly whereas another portion of body 184 is placed posteriorly in the back 192 of the patient. As shown, a dotted line 188 demarcates the anterior and posterior locations of subcutaneous defibrillator 180, where a portion 186A of body 184 is placed anterior to heart 182 and a portion 186B of body 184 is placed posterior to heart 182. Subcutaneous defibrillator 180 is placed around heart 182 such that a significant portion of it is placed in the abdominal region 190 of the patient. The positioning and functioning of an embodiment of subcutaneous defibrillator 180 is explained in more detail in PCT international publication number WO 2016/038599 A1.

[0037] An example of two shock vectors being provided to heart 182 is shown in FIG. 4. A first shock vector 198A is provided from electrode 194B to electrode 194A and a second shock vector 198B is provided from electrode 194B to electrode 194D. Other shock vector configurations are possible between different electrodes, including the possibility of more than two shock vectors, for example between electrode 194C and electrode 194A, between electrode 194D and electrode 194B and between electrode 194A and 194D. Both first shock vector 198A and second shock vector 198B are provided simultaneously to heart 182. In addition, first shock vector 198A and second shock vector 198B are biphasic shock vectors, meaning that during a first phase of both shock vectors, electrical current is passed from electrode 1948 to electrodes 194A and 194D respectively. During a second phase of both shock vectors, when the polarity of the voltage is inverted, electrical current is passed from electrodes 194A and 194D to electrode 194B respectively, in the opposite direction. Due to the placement of plurality of electrodes 194A-194D and the anatomy of the patient, first shock vector 198A will experience less impedance as compared with second shock vector 198B. Thus the right ventricle (not labeled) of heart 182 will most probably receive enough energy to effectively defibrillate whereas the left ventricle (not labeled) of heart 182 will most probably not receive enough energy to effectively defibrillate. This is due to the increased distance and cavities second shock vector 198B has to travel between electrodes as compared with first shock vector 198A.

[0038] The imbalance in energy delivery between the two shock vectors in FIG. 4 can be balanced according to the disclosed technique as shown below and explained in FIGS. 5 and 6. Reference is now made to FIG. 5, which is a set of graphs showing the truncation and summation of shock energy between two shock vectors, generally referenced 220, constructed and operative in accordance with a further embodiment of the disclosed technique. A first graph 222A shows a waveform energy curve 228 of a first biphasic shock vector. First graph 222A includes an x-axis 224A showing time in microseconds and a y-axis 226A showing voltage in volts. As shown, the first biphasic shock vector includes two phases, a first phase 230A wherein the waveform energy is applied using a positive voltage and a second phase 230B wherein the waveform energy is applied using a negative voltage. The inversion point in time where the voltage of the applied waveform energy changes from positive to negative is shown via a line 232. As mentioned above, the area under waveform energy curve 228 represents the amount of energy delivered by the first biphasic shock vector. An area 234A in first phase 230A shows the energy delivered by the first phase of the biphasic shock vector whereas an area 234B in second phase 230B shows the energy delivered by the second phase of the biphasic shock vector.

[0039] A second graph 222B shows a waveform energy curve 236 of a second biphasic shock vector. Second graph 222B includes an x-axis 224B showing time in microseconds and a y-axis 226B showing voltage in volts. As shown, the second biphasic shock vector includes two phases, a first phase 238A wherein the waveform energy is applied using a positive voltage and a second phase 238B wherein the waveform energy is applied using a negative voltage. Like in waveform energy curve 228, an inversion point in time for waveform energy curve 236, shown via an arrow 233, is where the voltage of the applied waveform energy changes from positive to negative. As mentioned above, the area under waveform energy curve 236 represents the amount of energy delivered by the second biphasic shock vector. An area 240A in first phase 238A shows the energy delivered by the first phase of the biphasic shock vector whereas an area 240B in second phase 238B shows the energy delivered by the second phase of the biphasic shock vector.

[0040] First and second biphasic shock vectors, with their waveform energy curves as shown in graphs 222A and 222B, are applied simultaneously. According to the disclosed technique, the waveform of the first biphasic shock vector, as shown in graph 222A, is terminated at the inversion point shown by line 232 such that waveform energy curve 228 is effectively only a unipolar shock vector. The energy of second phase 230B, represented by area 234B and shown by the letter A is directed, shown by an arrow 242, to the second biphasic shock vector, as shown in graph 222B as an addition area 240C to second phase 238B. Since both the first and second biphasic shock vectors are applied simultaneously, terminating the first biphasic shock vector at the end of its first phase and directing the remaining energy to the second biphasic shock vector effectively increases the amount of energy delivered by the second biphasic shock vector. The first biphasic shock vector is thus converted into a uniphasic shock vector whereas the second biphasic shock vector remains biphasic with an increase in energy in its second phase.

[0041] Referring back to the example shown in FIG. 4, using the disclosed technique, first shock vector 198A (FIG. 4) is thus unipolar and substantially uniphasic whereas second shock vector 1988 (FIG. 4) has increased energy in its second phase. Since the path travelled by first shock vector 198A has less impedance, less energy is required to effectively defibrillate. Since the path travelled by second shock vector 198B has more impedance, more energy is required to effectively defibrillate. According to the disclosed technique, more energy can be provided to second shock vector 198B to compensate for the increase in impedance in the path travelled by that shock vector without increasing the actual amount of energy delivered by subcutaneous defibrillator 180 (FIG. 4). This is achieved by terminating first shock vector 198A at its inversion point and transferring the remaining energy of first shock vector 198A to the electrodes delivering second shock vector 1988.

[0042] Reference is now made to FIG. 6, which is a set of graphs showing different truncations and summations of shock energy between two shock vectors by displacement of an inversion point, generally referenced 260, constructed and operative in accordance with another embodiment of the disclosed technique. FIG. 6 shows three different graphs 262A, 262B, 262C of waveform energy curves for shock vectors used in accordance with the disclosed technique. Each graph includes an x-axis showing times in milliseconds, respectively an x-axis 264A, an x-axis 264B and an x-axis 264C and a y-axis showing voltage in volts, respectively a y-axis 266A, a y-axis 266B and a y-axis 266C. For reference as well, each graph shows a waveform energy curve wherein the inversion point has not been displaced, respectively waveform energy curves 268A, 268B and 268C. As mentioned above in FIG. 5, more energy can be delivered to a shock vector traversing a path of higher impedance by terminating a first shock vector at its inversion point and transferring the remaining energy of the first shock vector to a second shock vector, which is the shock vector traversing the path of higher impedance, thereby increasing the energy of the second phase of the second shock vector. Since the first and second shock vectors are delivered simultaneously in a defibrillator, further distribution between the energy delivered by each shock vector can be achieved by displacing the inversion point wherein the first shock vector is terminated and its remaining energy is transferred to the second shock vector. Terminating the first phase of the first shock vector earlier in time results in greater energy being transferred to the second shock vector whereas terminating the first phase of the first shock vector later in time results in less energy being transferred to the second shock vector.

[0043] Graph 262A shows a waveform energy curve 272A truncated at an early inversion point 270A. An area 274A represents the energy of the first phase of waveform energy curve 272A whereas an area 276A represents the energy of the second phase of waveform energy curve 272A. Area 274A is designated with the letters A and B showing that the energy in area 274A is delivered by both a first shock vector (zone A) and a second shock vector (zone B). In accordance with the disclosed technique, the first shock vector is terminated and truncated at inversion point 270A and the remaining energy of the first shock vector, area 276A, is added, or summated, to the energy of the second shock vector. Area 276A is thus shown as zone B to indicate that this energy from the first shock vector is added to the energy of the second shock vector.

[0044] Graph 2626 shows a waveform energy curve 2726 truncated at a later inversion point 2706 as compared with inversion point 270A. An area 2746 represents the energy of the first phase of waveform energy curve 2726 whereas an area 2766 represents the energy of the second phase of waveform energy curve 2726. Area 2746 is designated with the letters A and B showing that the energy in area 2746 is delivered by both a first shock vector (zone A) and a second shock vector (zone B). In accordance with the disclosed technique, the first shock vector is terminated and truncated at inversion point 2706 and the remaining energy of the first shock vector, area 2766, is added, or summated, to the energy of the second shock vector. Area 2766 is thus shown as zone B to indicate that this energy from the first shock vector is added to the energy of the second shock vector.

[0045] Graph 262C shows a waveform energy curve 272C truncated at an even later inversion point 270C as compared with inversion points 270A and 270B. An area 274C represents the energy of the first phase of waveform energy curve 272C whereas an area 276C represents the energy of the second phase of waveform energy curve 272C. Area 274C is designated with the letters A and B showing that the energy in area 274C is delivered by both a first shock vector (zone A) and a second shock vector (zone B). In accordance with the disclosed technique, the first shock vector is terminated and truncated at inversion point 270C and the remaining energy of the first shock vector, area 276C, is added, or summated, to the energy of the second shock vector. Area 276C is thus shown as zone B to indicate that this energy from the first shock vector is added to the energy of the second shock vector.

[0046] As shown in graphs 262A, 262B and 262C, the inversion point of the waveform energy curve can be shifted in the time domain to change when the first shock vector is truncated and its remaining energy is summated to the energy of the second shock vector. Graph 262A shows an early inversion point and thus a significant amount of energy transfer to the second shock vector whereas graph 262C shows a later inversion point and closer to the energy transfer shown above in FIG. 5. In all the examples shown in FIG. 6, the first shock vector is unipolar, as shown by letters A and B in areas 274A, 274B and 274C, with the remainder of the energy of the first shock vector being transferred to the second shock vector which remains a biphasic shock vector. Even though the energy provided by the first shock vector to zone A is also provided by the second shock vector to zone B during the first phase of both shock vectors, which may deliver more energy to a lower impedance path through the heart of a patient, the second phase of both shock vectors is only provided to zone B, to the second shock vector, thus increasing the total amount of energy transferred to the second shock vector which traverses a path of higher impedance. By moving the timing of the inversion point, more energy can be shunted to the shock vector which has to traverse a path of higher impedance (i.e., zone B), thus balancing the total energy delivered between zones A and B. As described below, the particular inversion point for a given patient is to be determined by the clinician based on the patient's anatomy and the actual placement of the electrodes of the defibrillator in the patient.

[0047] Reference is now made to FIG. 7, which is a schematic illustration of defibrillators for truncating and summating shock energy between two shock vectors, generally referenced 300, constructed and operative in accordance with a further embodiment of the disclosed technique. FIG. 7 shows a transvenous (or intravenous) defibrillator 302 as well as a subcutaneous defibrillator 320. Transvenous defibrillator 302 includes a can 304 and a plurality of leads 306, similar to transvenous defibrillator 12 (FIG. 1A). Can 304 includes a capacitor 308, a processor 310 and a battery 312. Processor 310 is coupled with capacitor 308 and battery 312 and capacitor 308 is also coupled directly with battery 312. Battery 312 is used to power processor 310 and to charge capacitor 308 with electrical charge. Plurality of leads 306 may include sensors (not shown) for detecting arrhythmias as well as electrodes (not shown) for applying electrical shocks to the heart of a patient. Processor 310 may include circuitry (not shown) for determining when an arrhythmia is occurring and for discharging electrical charge on capacitor 308 via plurality of leads 306. Given that transvenous defibrillator 302 includes a plurality of leads, transvenous defibrillator 302 can provide at least two or more shock vectors simultaneously to the heart of the patient. Processor 310 directs capacitor 308 to discharge equal amounts of charge as two separate shock vectors on different sets of electrodes (not shown) on the leads. Processor 310 can be programmed to apply a first shock vector as a unipolar or uniphasic shock vector and a second shock vector as a bipolar or biphasic shock vector. At the inversion point when processor 310 directs capacitor 308 to reverse the polarity of the discharged electricity to both shock vectors, the energy discharged to the electrodes delivering the first shock vector is truncated and shunted towards the electrodes delivering the second shock vector. It is noted that this function of the processor diverting the energy of the second phase of the first shock vector to the second shock vector may be made a programmable feature of processor 310 such that a clinician can decide to either have transvenous defibrillator 302 transmit two biphasic shock vectors, as in prior art defibrillators, or to transmit a truncated uniphasic shock vector and summated biphasic shock vector, as described above in FIG. 5.

[0048] In addition, processor 310 may be programmed with an option for changing or shifting the inversion point of the applied shock vectors. As explained above in FIG. 6, shifting the inversion point according to the disclosed technique can alter the energy distribution applied by each of two or more shock vectors applied to a patient's heart. Dynamically changing the inversion point in the time domain utilizing the disclosed technique will result in changes in the relative energy delivered between the two shock vectors. Processor 310 may include Bluetooth and/or infrared technology (not shown) for enabling a clinician to communicate with processor 310 via software and to either modify the inversion point or to turn the truncating/summating option of the two shock vectors on or off.

[0049] Subcutaneous defibrillator 320 includes a body 322 and a plurality of electrodes 324A and 324B, similar to subcutaneous defibrillator 52 (FIG. 1B). Body 322 includes a capacitor 326, a processor 328 and a battery 330. Processor 328 is coupled with capacitor 326 and battery 330 and capacitor 326 is also coupled directly with battery 330. As described above regarding transvenous defibrillator 302, battery 330 is used to power processor 328 and to charge capacitor 326 with electrical charge. Plurality of electrodes 324A and 324B can apply electrical shocks to the heart of a patient and may also include sensors (not shown) for detecting arrhythmias. Processor 328 may include circuitry (not shown) for determining when an arrhythmia is occurring and for discharging electrical charge on capacitor 326 via plurality of electrodes 324A and 324B. Given that subcutaneous defibrillator 320 includes a plurality of electrodes, subcutaneous defibrillator 320 can provide at least two or more shock vectors simultaneously to the heart of the patient. Processor 328 directs capacitor 326 to discharge equal amounts of charge as two separate shock vectors (not shown) on different sets of electrodes. Processor 328 can be programmed to apply a first shock vector as a unipolar or uniphasic shock vector and a second shock vector as a bipolar or biphasic shock vector. At the inversion point when processor 328 directs capacitor 326 to reverse the polarity of the discharged electricity to both shock vectors, the energy discharged to the electrodes delivering the first shock vector is truncated and shunted towards the electrodes delivering the second shock vector. It is noted that this function of the processor diverting the energy of the second phase of the first shock vector to the second shock vector may be made a programmable feature of processor 328 such that a clinician can decide to either have subcutaneous defibrillator 320 transmit two biphasic shock vectors, as in prior art defibrillators, or to transmit a truncated uniphasic shock vector and summated biphasic shock vector, as described above in FIG. 5. Using the disclosed technique in the case of a subcutaneous defibrillator, the summated biphasic shock vector can be shifted from the anterior part of a patient's body (which usually has a lower impedance) to the posterior part of the patient's body (which usually has a higher impedance) thus achieving a more ideal defibrillation shock vector for a particular patient based on their heart shape, their thorax and lung shape and the particular placement of the subcutaneous defibrillator.

[0050] In one embodiment of the disclosed technique, for example with a subcutaneous defibrillator including a plurality of electrodes such as three or more electrodes (not shown), at least one of the electrodes can be disconnected at any given time during the delivery of a shock vector. By disconnecting at least one of the electrodes the energy distribution of the shock vectors to the heart can be directed as desired. Such an embodiment is possible when there are more than two electrodes.

[0051] By changing the inversion point timing sequence, the relative amount of energy delivered to each respective shock vector can be dynamically adjusted with the total amount of energy applied by the defibrillator remaining the same yet with its energy distribution being different for each shock vector. Using a numerical example, in a subcutaneous defibrillator which can apply electrical shocks of around 70 joules (i.e., the capacitor can hold sufficient energy to apply 70 joules in a given therapy session of applying electrical shocks), time domain shifting of the inversion point can allow 10 joules to go to one shock vector and 60 joules to the other shock vector, or 35 joules to each shock vector. The energy delivery balance between the two shock vectors can be adjusted such that the DFT is as low as possible while still remaining effective.

[0052] As mentioned above, processor 328 may be programmable with options for changing or shifting the inversion point of the applied shock vectors and turning the truncating/summating option of the two shock vectors on or off. Body 322 may include Bluetooth and/or infrared technology (not shown) for enabling a clinician to communicate with processor 328 via software. The software may be a computer application, smartphone application and the like. The decision regarding whether the truncating/summating option of the two shock vectors should be used and to what degree the inversion point should be shifted in time is patient specific and can be determined by the clinician. A number of visits by the patient to the clinician as well as follow-up sessions by the patient after implantation of his/her defibrillator can aid the clinician in determining if the truncating/summating option reduces the DFT and if time domain shifts of the inversion point reduce the number of arrhythmias experienced by the patient.

[0053] It is noted that the examples given above of the disclosed technique relate to defibrillators providing two shock vectors, however the disclosed technique can be applied to defibrillators providing three or more shock vectors. According to the disclosed technique, in a defibrillator applying more than two biphasic shock vectors, at least one or more of the biphasic shock vectors can be made uniphasic and terminated at its inversion point, with the remainder of its energy diverted and summated to the other biphasic shock vectors being applied. Furthermore, the inversion point in time of the shock vectors can be shifted for balancing the energy distribution between shock vectors traversing paths of different impedance.

[0054] Reference is now made to FIG. 8, which is a method for truncating and summating shock energy between two shock vectors, operative in accordance with another embodiment of the disclosed technique. In a procedure 350, at least two biphasic defibrillating shock vectors are applied via at least two electrode sets until a voltage inversion point. The biphasic shock vectors are applied simultaneously such that each electrode set applies a shock vector. As shown above, a biphasic shock vector includes two phases, a first phase wherein energy is applied via a positive voltage and a second phase wherein energy is applied via a negative voltage. The first phase is separated from the second phase via its voltage inversion point. In this procedure, at least two biphasic shock vectors are applied between a respective at least two sets of electrodes during the first phase of the shock vectors. In a procedure 352, one of the biphasic defibrillating shock vectors is terminated at the voltage inversion point. Thus instead of being a biphasic shock vector, the terminated shock vector is effectively a unipolar shock vector. The termination of the shock vector however does not mean that the energy of the shock vector is lost. That energy is just not applied across the first electrode set. In a procedure 354, the remaining energy of the first biphasic defibrillating shock vector is directed to a second biphasic defibrillating shock vector applied via its second electrode set. The second phase of the second shock vector is thus summated with the energy remaining form the truncated first shock vector, resulting in the second phase of the second shock vector applying an increased amount of energy. As explained above in FIG. 5, since both the first and second biphasic shock vectors are applied simultaneously, terminating the first biphasic shock vector at the end of its first phase and directing the remaining energy to the second biphasic shock vector effectively increases the amount of energy delivered by the second biphasic shock vector. The first biphasic shock vector is thus converted into a uniphasic shock vector whereas the second biphasic shock vector remains biphasic with an increase in energy in its second phase.

[0055] In a procedure 356, the voltage inversion point of the biphasic defibrillating shock vectors is modified according to patient and defibrillator characteristics. Depending on the anatomy of the patient and the specific placement of the electrodes of the defibrillator (whether external, intravenously or subcutaneously), the truncating and summating of the energy of the first shock vector to the second shock vector may not be sufficient to balance the energy distribution between the shock vectors to lower the DFT and effectively defibrillate various parts of the heart. In this procedure, the voltage inversion point is shifted in the time domain, either forwards or backwards in time, to transfer either less or more energy from the truncated part of the second phase of the first shock vector to the second phase of the second shock vector. The amount of shifting of the inversion point is dependent on the patient's anatomy and the placement of the electrodes of the defibrillator in or around the patient's heart which can change the impedance of the path the shock vectors take between given sets of electrodes. Modifying the inversion point enables more energy to be delivered to the shock vector having to cross a path of higher impedance. After procedure 356, the method returns to procedure 350.

[0056] Procedure 356 can be applied many times until an ideal balance of energy between the two shock vectors is obtained and the DFT for effective defibrillation of a given patient is attained. As mentioned above, even though FIG. 8 and the procedures described therein have been described with reference to two defibrillating shock vectors, the method of the disclosed technique described in FIG. 8 can be used in any type of defibrillator applying at least two shock vectors, for example external, intravenous/transvenous and subcutaneous defibrillators, applying two, three, four or more shock vectors simultaneously.

[0057] It will be appreciated by persons skilled in the art that the disclosed technique is not limited to what has been particularly shown and described hereinabove. Rather the scope of the disclosed technique is defined only by the claims, which follow.