Source: http://www.google.com/patents/US6889077?dq=7,172,682
Timestamp: 2014-12-20 19:58:00
Document Index: 168591369

Matched Legal Cases: ['art.\n5', 'art.\n6', 'art.\n7', 'art.\n14', 'art.\n15', 'art.\n16', 'art.\n25', 'art.\n26', 'art.\n27', 'art.\n34', 'art.\n35', 'art.\n36', 'art.\n45', 'art.\n47', 'art.\n54', 'art.\n55', 'art.\n56', 'art 12', 'art 12', 'art 130', 'art 150']

Patent US6889077 - Implantable cardiac stimulation device that defibrillates the atria while ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsAn implantable cardiac stimulation device applies defibrillating electrical energy to the atria of a heart at a time which avoids inducing ventricular fibrillation of the heart. The device includes an atrial fibrillation detector that detects atrial fibrillation of the heart, a pacing pulse generator...http://www.google.com/patents/US6889077?utm_source=gb-gplus-sharePatent US6889077 - Implantable cardiac stimulation device that defibrillates the atria while avoiding the ventricular vulnerable period and methodAdvanced Patent SearchPublication numberUS6889077 B2Publication typeGrantApplication numberUS 10/086,580Publication dateMay 3, 2005Filing dateFeb 28, 2002Priority dateFeb 28, 2002Fee statusPaidAlso published asUS20030163165Publication number086580, 10086580, US 6889077 B2, US 6889077B2, US-B2-6889077, US6889077 B2, US6889077B2InventorsGene A. Bornzin, Paul A. LevineOriginal AssigneePacesetter, Inc.Export CitationBiBTeX, EndNote, RefManPatent Citations (23), Referenced by (4), Classifications (6), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetImplantable cardiac stimulation device that defibrillates the atria while avoiding the ventricular vulnerable period and methodUS 6889077 B2Abstract An implantable cardiac stimulation device applies defibrillating electrical energy to the atria of a heart at a time which avoids inducing ventricular fibrillation of the heart. The device includes an atrial fibrillation detector that detects atrial fibrillation of the heart, a pacing pulse generator that applies a ventricular pacing pulse to the heart responsive to detection of atrial fibrillation, a timer that times a time period through an evoked response and a T-wave caused by the pacing pulse, and a defibrillation pulse generator that applies defibrillating electrical energy to the atria of the heart after the timer completes the timing of the time period.
1. An implantable cardiac stimulation device that applies defibrillating electrical energy to at least one atrium of a heart at a time which avoids inducing ventricular fibrillation of the heart, the device comprising:
an atrial fibrillation detector that detects atrial fibrillation of the heart; a pacing pulse generator that applies a pacing pulse to at least one of the ventricles responsive to the atrial fibrillation detector detecting atrial fibrillation of the heart; a timer that times a time period through an evoked response end a T-wave caused by the pacing pulse, the time period completing a predetermined time period after the T-wave ends; and a defibrillation pulse generator that applies the defibrillating eletrical energy to the at least one atrium of the heart responsive to the timer completing the timing of the time period. 2. The device of claim 1 wherein the timer commences timing of the time period beginning with the application of the pacing pulse.
3. The device of claim 2 wherein the time period is between about 350 milliseconds and 450 milliseconds.
4. The device of claim 1 wherein the pacing pulse generator applies the pacing pulse to the right ventricle of the heart.
5. The device of claim 1 wherein the pacing pulse generator applies the pacing pulse to the left ventricle of the heart.
6. The device of claim 1 wherein the pacing pulse generator applies the pacing pulse to both the right ventricle and the left ventricle of the heart.
7. The device of claim 1 further comprising a cardiac interval timer that times cardiac intervals of the heart responsive to the atrial fibrillation detector detecting atriel fibrillation of the heart and wherein the pacing pulse generator applies the pacing pulse after the interval timer times a cardiac interval longer than a minimum cardiac interval.
8. The device of claim 1 further comprising an evoked response detector that detects the evoked response and wherein the defibrillation pulse generator inhibits the application of the defibrillating energy responsive to the evoked response detector failing to detect the evoked response.
9. The device of claim 1 wherein the pacing pulse generator applies a plurality of pacing pulses to at least one of the ventricles responsive to the atrial fibrillation detector detecting atrial fibrillation of the heart, and wherein the timer times the time period following a last one of the plurality of pacing pulses through the evoked response and T-wave caused by the last one of the plurality of pacing pulses.
10. The device of claim 9 wherein the pacing pulse generator applies the plurality of pacing pulses on demand and wherein the timer times the time period after the pacing pulse generator applies the plurality of pacing pulses during consecutive cardiac cycles.
11. The device of claim 9 wherein the timer commences timing of the time period beginning with the application of the last one of the pacing pulses.
12. The device of claim 11 wherein the time period is between about 350 milliseconds and 450 milliseconds.
13. The device of claim 9 wherein the pacing pulse generator applies the pacing pulses to the right ventricle of the heart.
14. The device of claim 9 wherein the pacing pulse generator applies the pacing pulses to the left ventricle of the heart.
15. The device of claim 9 wherein the pacing pulse generator applies the pacing pulses to both the right ventricle and the left ventricle of the heart.
16. The device of claim 9 further comprising an evoked response detector that detects the evoked response and wherein the defibrillation pulse generator inhibits the application of the defibrillating energy responsive to the evoked response detector failing to detect the evoked response.
17. The device of claim 9 further comprising an atrial pacing pulse generator that applies an atrial pacing pulse to at least one of the atria after the timer completes the timing of the time period and before the defibrillation pulse generator applies the defibrillating electrical energy to the atria.
18. The device of claim 9 further comprising an atrial sensing circuit that senses P-waves of the heart and wherein the defibrillation pulse generator applies the defibrillating electrical energy to the atria in timed relation to a sensed P-wave.
19. An implantable cardiac stimulation device that applies defibrillating electrical energy to at least one atrium of a heart at a time which avoids inducing ventricular fibrillation of the heart, the device comprising:
an atrial fibrillation detector that detects atrial fibrillation of the heart; a pacing pulse generator that applies a pacing pulse to at least one of the ventricles responsive to the atrial fibrillation detector detecting atrial fibrillation of the heart; a timer that times a time period through an evoked response and a T-wave caused by the pacing pulse, the time period completing after the T-wave; a defibrillation pulse generator that applies the defibrillating electrical energy to the at least one atrium of the heart responsive to the timer completing the timing of the time period; and an atrial pacing pulse generator that applies an atrial pacing pulse to at least one of the atria after the timer completes the timing of the time period and before the defibrillation pulse generator applies the defibrillating electrical energy to the atria. 20. An implantable cardiac stimulation device that applies defibrillating electrical energy to at least one atrium of a heart at a time which avoids inducing ventricular fibrillation of the heart, the device comprising:
an atrial fibrillation detector that detects atrial fibrillation of the heart; a pacing pulse generator that applies a pacing pulse to at least one of the ventricles responsive to the atrial fibrillation detector detecting atrial fibrillation of the heart; a timer that times a time period through an evoked resoonse and a T-wave caused by the pacing pulse, the time period completing after the T-wave; a defibrillation pulse generator that applies the defibrillating electrical energy to the at least one atrium of the heart responsive to the timer completing the timing of the time period; and an atrial sensing circuit that senses P-waves of the heart and wherein the defibrillation pulse generator applies the defibrillating electrical energy to the atria in timed relation to a sensed P-wave. 21. An implantable cardiac stimulation device for applying defibrillating electrical energy to at least one atrium of a heart at a time which avoids inducing ventricular fibrillation of the heart, the device comprising:
atrial fibrillation detecting means for detecting atrial fibrillation of the heart; ventricular pacing pulse generating means for applying a pacing pulse to at least one of the ventricles responsive to the detection of atrial fibrillation; timing means for timing a time period through an evoked response and T-wave caused by the ventricular pacing pulse and ending a predetermined time period after the T-wave ends; and defibrillation pulse generating means for applying defibrillating electrical energy to the atria after the timing means times the time period. 22. The device of claim 21 wherein the timing means commences timing of the time period beginning with the application of the pacing pulse.
23. The device of claim 22 wherein the time period is between about 350 milliseconds and 450 milliseconds.
24. The device of claim 21 wherein the pacing pulse generating means applies the pacing pulse to the right ventricle of the heart.
25. The device of claim 21 wherein the pacing pulse generating means applies the pacing pulse to the left ventricle of the heart.
26. The device of claim 21 wherein the pacing pulse generating means applies the pacing pulse to both the right ventricle and the left ventricle of the heart.
27. The device of claim 21 further comprising cardiac interval timing means for timing cardiac intervals of the heart responsive to the atrial fibrillation detector means detecting atrial fibrillation of the heart and wherein the pacing pulse generating means applies the pacing pulse after the interval timing means times a cardiac interval longer than a minimum cardiac interval.
28. The device of claim 21 further comprising evoked response detecting means for detecting the evoked response and wherein the defibrlliation pulse generating means wtthholds the application of the defibrillating energy responsive to the evoked response detecting means failing to detect the evoked response.
29. The device of claim 21 wherein the ventricular pacing pulse generating means applies a plurality of pacing pulses to at least one of the ventricles responsive to the detection of atrial fibrillation, and wherein the timing means times the time period following a last one of the plurality of pacing pulses through the evoked response and T-wave caused by the last one of the plurality of pacing pulses.
30. The device of claim 29 wherein the ventricular pacing pulse generating means applies the plurality of pacing pulses on demand and wherein the timing means times the time period after the ventricular pacing pulse generating means applies the plurality of pacing pulses during consecutive cardiac cycles.
31. The device of claim 29 wherein the timing means commences timing of the time period beginning with the application of the last one of the pacing pulses.
32. The device of claim 31 wherein the time period is between about 350 milliseconds and 450 milliseconds.
33. The device of claim 29 wherein the pacing pulse generating means applies the pacing pulses to the right ventricle of the heart.
34. The device of claim 29 wherein the pacing pulse generating means applies the pacing pulses to the left ventricle of the heart.
35. The device of claim 29 wherein the pacing pulse generating means applies the pacing pulses to both the right ventricle and the left ventricle of the heart.
36. The device of claim 29 further comprising evoked response detecting means for detecting the evoked response and wherein the defibrillation pulse generating means withholds the application of the defibriliating energy responsive to the evoked response detecting means failing to detect the evoked response.
37. The device of claim 29 further comprising atrial pacing pulse generating means for applying an atrial pacing pulse to at least one of the atrial after the timing means times the time period and before the defibrillation pulse generating means applies the defibrillating electrical energy to the atria.
38. The device of claim 29 further comprising atrial sensing means for sensing P-waves of the heart and wherein the defibrillation pulse generating means applies the defibrillating electrical energy to the atria in timed relation to a sensed P-wave.
39. An implantable cardiac stimulation device for applying defibrillating electrical energy to at least one atrium of a heart at a time which avoids inducing ventricular fibrillation of the heart, the device comprising:
atrial fibrillation detecting means for detecting atrial fibrillation of the heart; ventricular pacing pulse generating means for applying a first pacing pulse to at least one of the ventricles responsive to the detection of atrial fibrillation; timing means for timing a time period through an evoked response and T-wave caused by the ventricular pacing pulse; defibrillation pulse generating means for applying defibrillating electrical energy to the atria after the timing means times the time period; and atrial pacing pulse generating means for applying an atrial pacing pulse to at least one of the atria after the timing means times the time period and before the defibrillation pulse generating means applies the defibrillating eletrical energy to the atria. 40. An implantable cardiac stimulation device for applying defibriliating electrical energy to at least one atrium of a heart at a time which avoids inducing ventricular fibrillation of the heart, the device comprising:
atrial fibrillation detecting means for detecting atrial fibrillation of the heart; ventricular pacing pulse generating means for applying a first pacing pulse to at least one of the ventricles responsive to the detection of atrial fibrillation; timing means for timing a time period through an evoked response and T-wave caused by the ventricular pacing pulse; defibrillation pulse generating means for applying defibrillating electrical energy to the atria after the timing means times the time period; and atrial sensing means for sensing P-waves of the heart and wherein the defibrillation pulse generating means applies the defibrillating electrical energy to the atria in timed relation to a sensed P-wave. 41. In an implantable cardiac stimulation device, a method of applying defibrillating electrical energy to at least one atrium of a heart, the method comprising:
stimulating at least one of the ventricles with a ventricular pacing pulse to cause an evoked response and T-wave; waiting until the T-wave ends; and applying defibrillating electrical energy to the at least one atrium a predetermined period after the T-wave ends. 42. The method of claim 41 wherein waiting comprises commencing timing of a predetermined time period beginning with the application of the pacing pulse.
43. The method of claim 42 wherein the time period is between about 350 milliseconds and 450 milliseconds.
44. The method of claim 41 wherein stimulating comprises applying the pacing pulse to the right ventricle of the heart.
45. The device of claim 41 further comprising detecting the evoked response including the T-wave and wherein applying is performed after the detected T-wave ends.
46. The method of claim 41 wherein stimulating comprises applying the pacing pulse to both the right ventricle and the left ventricle of the heart.
47. The method of claim 41 further comprising timing cardiac intervals of the heart responsive to detecting atrial fibrillation of the heart and wherein stimulating is performed after the timing of a cardiac interval longer than a minimum cardiac interval.
48. The method of claim 41 further comprising detecting the evoked response and wherein applying is performed only when the evoked response is detected.
49. The method of claim 41 wherein stimulating comprises applying a plurality of pacing pulses to at least one of the ventricles responsive to the detection of atrial fibrillation, and wherein timing comprises timing the time period following a last one of the plurality of pacing pulses through the evoked response end T-wave caused by the last one of the plurality of pacing pulses.
50. The method of claim 49 wherein stimulating comprises applying the plurality of pacing pulses on demand and wherein timing is commenced after the plurality of pacing pulses are applied during consecutive cardiac cycles.
51. The method of claim 49 wherein timing comprises commencing the timing of the time period beginning with the application of the last one of the pacing pulses.
52. The method of claim 51 wherein the time period is between about 350 milliseconds and 450 milliseconds.
53. The method of claim 49 wherein stimulating comprises applying the pacing pulse to the right ventricle of the heart.
54. The device of claim 49 wherein stimulating comprises applying the pacing pulses to the left ventricle of the heart.
55. The method of claim 49 wherein stimulating comprises applying the pacing pulses to both the right ventricle and the left ventricle of the heart.
56. The method of claim 49 further comprising detecting the evoked response and wherein applying is performed only when the evoked response is detected.
57. The method of claim 49 further comprising pacing at least one of the atria after the timing of the time period and before the applying of the defibrillating electrical energy to the atria.
58. The method of claim 49 further comprising sensing P-waves of the heart and wherein applying comprises applying the defibrillating electrical energy to the atria in timed relation to a sensed P-wave.
59. In an implantable cardiac stimulation device, a method of applying defibrillating electrical energy to at least one atrium of a heart, the method comprising:
stimulating at least one of the ventricles with a ventricular pacing pulse to cause an evoked response and T-wave; waiting until the T-wave ends; applying defibrillating electrical energy to the at least one atrium after the T-wave ends; and pacing at least one of the atria after the timing of the time period and before the applying of the defibrillating electrical energy to the atria. 60. In an implantable cardiac stimulation device, a method of applying defibrillating electrical energy to at least one atrium of a heart, the method comprising:
stimulating at least one of the ventricles with a ventricular pacing pulse to cause an evoked response and T-wave; waiting until the T-wave ends; applying defibrillating electrical energy to the at least one atrium after the T-wave ends; and sensing P-waves of the heart and wherein applying comprises applying the defibrillating electrical energy to the atria in timed relation to a sensed P-wave. 61. An implantable cardiac stimulation device comprising:
a lead assembly that is in electrical communication with a heart to sense physiologic activity of the heart and generate corresponding signals, and to deliver stimulation energy to the heart; a pulse generator connected to the lead assembly and that generates stimulation pulses to be delivered to the heart via the lead assembly; and control circuitry connected to the lead assembly and pulse generator, the control circuitry being operative to process the signals from the lead assembly to determine whether atrial fibrillation exists, the control circuitry being operative in response to detection of atrial fibrillation to control the pulse generator to generate at least one pacing pulse for delivery to at least one ventricle to cause an evoked response and T-wave in the at least one ventricle, the control circuitry further being operative to control the pulse generator to generate a defibrillation pulse for delivery to at least one atrium a predetermined period after the T-wave ends.
FIELD OF THE INVENTION The present invention generally relates to an implantable cardiac stimulation device. The invention more particularly relates to such device and method for defibrillating the atria of a heart while avoiding the ventricular vulnerable period of the heart.
BACKGROUND OF THE INVENTION Atrial fibrillation is a common cardiac arrhythmia. Although it is not life threatening, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. Symptoms of atrial fibrillation may include heart palpitations, dizziness, and even loss of consciousness.
Atrial fibrillation can occur suddenly. It is caused by chaotic activity of the atria of the heart. The chaotic atrial activity in turn causes the ventricular activity to be disassociated from the atrial activity. The ventricular activity becomes rapid and variable.
To terminate atrial fibrillation, it is often necessary to defibrillate the atria. This entails the delivery to the heart of a brief electrical shock. The shock may be applied externally through two electrodes placed on the chest or directly by an implantable device through implanted electrodes.
When atrial fibrillation is terminated by an electrical shock, it is most desirable to deliver the shock at a time which avoids the vulnerable period of the ventricles. The vulnerable period is that time within a cardiac cycle wherein myocardial tissue is prone to develop tachycardia or fibrillation when stimulated, even with a low magnitude electrical pulse. The vulnerable period of the ventricle is approximately represented on an electrocardiogram by the top of the T-wave. The T-wave represents the time in which the ventricular myocardium repolarizes following a ventricular depolarization (R-wave). To be safe, it is generally considered prudent to not deliver any shock to the heart during a T-wave.
The key then to defibrillating the atria is to avoid the T-wave of the ventricles. However, avoidance of the T-wave requires that the time of the T-wave be accurately known. This is difficult in the atrial fibrillation environment where the ventricular activity is erratic. During atrial fibrillation, the ventricular rate is generally elevated and irregular. Hence, predicting with any certainty as to when a T-wave will begin or end in an effort to safely terminate atrial fibrillation with a defibrillating shock would be clinically impossible.
SUMMARY OF THE INVENTION The present invention provides an implantable cardiac stimulation device that applies defibrillating electrical energy to the atria of a heart and at a time which avoids the ventricular vulnerable period. More particularly, the device, after detecting atrial fibrillation, applies a ventricular pacing pulse to the heart to cause a ventricular evoked response. This results in a following T-wave. Since the evoked response results from a pacing pulse, the occurrence and duration of the resulting T-wave may be predicted to permit an atrial defibrillating pulse to be applied after the T-wave to defibrillate the heart during a time which is known not to be a ventricular vulnerable period.
Hence, the present invention provides an implantable cardiac stimulation device that applies defibrillating electrical energy to atria of a heart at a time which avoids inducing ventricular fibrillation of the heart. The device includes an atrial fibrillation detector that detects atrial fibrillation of the heart, a pacing pulse generator that applies a pacing pulse to at least one of the ventricles responsive to the atrial fibrillation detector detecting atrial fibrillation of the heart, a timer that times a time period through an evoked response, and a T-wave caused by the pacing pulse, the time period completing after the T-wave and before an immediately following R-wave, and a defibrillation pulse generator that applies the defibrillating electrical energy to the atria of the heart responsive to the timer completing the timing of the time period.
The present invention further provides an implantable cardiac stimulation device for applying defibrillating electrical energy to atria of a heart at a time which avoids inducing ventricular fibrillation of the heart. The device includes atrial fibrillation detecting means for detecting atrial fibrillation of the heart and ventricular pacing pulse generating means for applying a pacing pulse to at least one of the ventricles responsive to the detection of atrial fibrillation. The device further includes timing means for timing a time period through an evoked response and T-wave caused by the ventricular pacing pulse and the fibrillation pulse generating means for applying defibrillating electrical energy to the atria after the timing means times the time period.
The present invention still further provides a method of applying defibrillating electrical energy to atria of a heart at a time which avoids inducing ventricular fibrillation of the heart in an implantable cardiac stimulation device. The method includes the steps of detecting for atrial fibrillation of the heart, stimulating at least one of the ventricles with a ventricular pacing pulse responsive to the detection of atrial fibrillation, timing a time period through an evoked response and T-wave caused by the ventricular pacing pulse, and applying defibrillating electrical energy to the atria after timing the time period.
Before applying the atrial defibrillation shock, the pacing pulse generator may apply a plurality of pacing pulses to at least one of the ventricles responsive to the atrial fibrillation detector detecting atrial fibrillation of the heart. The timer may time the time period following a last one of the plurality of pacing pulses through the evoked response and T-wave caused by the last one of the plurality of pacing pulses. The pacing pulse generator preferably applies the plurality of pacing pulses on demand and the timer times the time period after the pacing pulse generator applies the plurality of pacing pulses during consecutive cardiac cycles.
FIG. 1 is a simplified diagram illustrating an implantable cardiac stimulation device embodying the present invention in electrical communication with at least three leads implanted in a patient's heart and which is capable of delivering multi-chamber stimulation and shock therapy including atrial defibrillation therapy in accordance with the present invention;
FIG. 2 is a functional block diagram of the multi-chamber implantable stimulation device of FIG. 1 illustrating the basic elements of a stimulation device which can provide cardioversion, defibrillation and pacing stimulation in four chambers of the heart;
FIG. 3 is a ventricular electrocardiogram illustrating a ventricular evoked response and T-wave to lend better understanding of the preferred embodiment of the present invention;
FIG. 4 is a flow chart describing an overview of the operation of one embodiment of the present invention; and
FIG. 5 is a flow chart describing an overview of the operation of another embodiment of the present invention.
As will be described subsequently, the coil electrodes 28 and 38 may be employed for defibrillating the atria. This electrode configuration is most advantageous for atrial defibrillation because it directs the electrical energy primarily through atrial myocardium.
The microcontroller 60 further includes timing control circuitry 79 which is used to control the timing of such stimulation pulses (e.g., pacing rate, atrio-ventricular (AV) delay, atrial interconduction (A�A) delay, or ventricular interconduction (V�V) delay, etc.) as well as to keep track of the timing of cardiac intervals, refractory periods, blanking intervals, noise detection windows, evoked response windows, alert intervals, marker channel timing, etc., which is well known in the art.
For arrhythmia detection, including atrial fibrillation detection, the device 10 includes an arrhythmia detector 62 which utilizes the atrial and ventricular sensing circuits, 82 and 84, to sense cardiac signals to determine whether a rhythm is physiologic or pathologic. As used herein �sensing� is reserved for the noting of an electrical signal, and �detection� is the processing of these sensed signals and noting the presence of an arrhythmia. The timing intervals between sensed events (e.g., P-waves, R-waves, and depolarization signals associated with fibrillation which are sometimes referred to as �F-waves� or �Fib-waves�) are then classified by the microcontroller 60 by comparing them to a predefined rate zone limit (i.e., bradycardia, normal, low rate VT, high rate VT, and fibrillation rate zones) and various other characteristics (e.g., sudden onset, stability, physiologic sensors, and morphology, etc.) in order to determine the type of remedial therapy that is needed (e.g., bradycardia pacing, anti-tachycardia pacing, cardioversion shocks or defibrillation shocks, collectively referred to as �tiered therapy�).
The microcontroller further includes a capture detector 64. Advantageously, the data acquisition system 90 may be coupled to the microcontroller to support detection of evoked responses from the heart 12 in response to applied stimuli. Capture occurs when an electrical stimulus applied to the heart depolarizes the cardiac tissue, thereby causing the heart muscle to contract. The capture detector 64 of the microcontroller 60 may detect a depolarization signal during a window following a stimulation pulse, the presence of which indicates that capture has occurred. The microcontroller 60 enables capture detection by triggering the ventricular pulse generator 72 to generate a stimulation pulse, starting a capture detection window using the timing control circuitry 79 within the microcontroller 60, and enabling the data acquisition system 90 via control signal 92 to sample the cardiac signal that falls in the capture detection window. Based on the amplitude of the signal within the capture detection window, the capture detector 64 determines if capture has occurred. As will be seen subsequently, evoked response detection may be used as a prerequisite to atrial defibrillation.
In the case where the stimulation device 10 is intended to operate as an implantable cardioverter/defibrillator (ICD) device, it must detect the occurrence of an arrhythmia, and automatically apply an appropriate electrical shock therapy to the heart aimed at terminating the detected arrhythmia. To this end, the microcontroller 60 further controls a shocking circuit 116 by way of a control signal 118. The shocking circuit 116 generates shocking pulses of low (up to 0.5 Joules), moderate (0.5-10 Joules), or high energy (11 to 40 Joules), as controlled by the microcontroller 60. Such shocking pulses are applied to the patient's heart 12 through at least two shocking electrodes, and as shown in this embodiment, selected from the left atrial coil electrode 28, the RV coil electrode 36, and/or the SVC coil electrode 38. As noted above, the housing 40 may act as an active electrode in combination with the RV electrode 36, or as part of a split electrical vector using the SVC coil electrode 38 or the left atrial coil electrode 28 (i.e., using the RV electrode as a common electrode). As further noted above, the electrode configuration of the coil electrodes 38 and 28 is particularly advantageous for defibrillating the atria of the heart.
Cardioversion shocks are generally considered to be of low to moderate energy level (so as to minimize pain felt by the patient), and/or synchronized with an R-wave and/or pertaining to the treatment of tachycardia. Defibrillation shocks are generally of moderate to high energy level (i.e., corresponding to thresholds in the range of 5-40 Joules). For ventricular defibrillation, the shocks may be delivered asynchronously (since R-waves may be too disorganized). For atrial defibrillation, shock delivery is preferably timed in accordance with the present invention as described, for example, in connection with the preferred embodiment herein.
The microcontroller 60 further includes another timer 66. Timer 66 may be employed in accordance with the present invention to time a time period which extends through a ventricular evoked response and resulting T-wave. The timer 66 may extend the timing by X milliseconds, for example, 100 milliseconds.
The purpose of the timer 66 will now be generally described with reference to the electrocardiogram of FIG. 3. After the arrhythmia detector 62 detects atrial fibrillation, the atria are defibrillated. The timing of the atrial fibrillation is controlled by the timer 66.
More specifically, once atrial fibrillation is detected, a pacing pulse is applied to either one or both of the ventricles at time T1. This causes the timer 66 to commence timing. The timer 66 times through the resulting evoked response 120 and the resulting T-wave 122. The T-wave completes (the ventricular myocardium is fully repolarized) at time T2 after a time period of STIM-T. This begins a time window beyond the ventricular vulnerable period where the atria may be defibrillated safely without inducing ventricular fibrillation. In accordance with this embodiment, the timer 66 continues to time for an additional X milliseconds to time T3 where X may be, for example, 100 milliseconds. The additional time of X milliseconds may be provided to assure that the ventricular vulnerable period has passed. The atria may now, after time T3, be defibrillated with the application of electrical energy by the shocking circuit 116 across the coil electrodes 28 and 33. The atrial cardioversion/defibrillation window remains open until the next intrinsic ventricular activation (R-wave) is sensed.
As a condition for atrial defibrillation, the capture detector 64 may be required to actually detect the evoked response. This confirmation will confirm the presence of the T-wave 122 and assure proper timing of the electrical shock relative to the T-wave 122. If the capture detector 64 fails to detect the evoked response 120, the delivery of the atrial defibrillation/cardioversion shock may be aborted.
In FIG. 4, a flow chart is shown describing an overview of the operation and particular novel features implemented in one embodiment of the device 10. In this flow chart, and the flow chart of FIG. 5 to be described subsequently, the various algorithmic steps are summarized in individual �blocks�. Such blocks describe specific actions or decisions that must be made or carried out as the algorithm proceeds. Where a microcontroller (or equivalent) is employed, the flow chart provided herein provides the basis for a �control program� that may be used by such a microcontroller (or equivalent) to effectuate the desired control of the stimulation device. Those skilled in the art may readily write such a control program based on the flow chart and other descriptions presented herein.
The method illustrated in the flow chart 130 of FIG. 4 initiates at an activity block 132. In activity block 132 atrial fibrillation is detected. The atrial fibrillation episode may be detected as previously described herein or in accordance with other methods well known in the art. Once atrial fibrillation is detected in accordance with activity block 132, the process advances to activity block 134 wherein the timing control 79 times a cardiac interval having a length greater than a minimum interval. The minimum interval may be, for example, 500 milliseconds or greater. Detection of such a minimum interval prior to the application of the atrial therapy may be desirable to assure that the cardiac rate is acceptable for accurate vulnerable period timing.
Once the minimum cardiac interval has been timed, the process advances to activity block 136 wherein either one or both of the ventricles is paced. Here, the ventricular pulse generator 72 applies a pacing pulse to one of the right and left ventricles, or to both the right ventricle and left ventricle simultaneously. Upon the pacing of the ventricles in accordance with activity block 136, the process then advances to activity block 138 wherein the timer 66 begins timing the STIM-T+X time period as previously described with reference to FIG. 3. Again, as previously mentioned, the additional timing period of X milliseconds may be, for example, 100 milliseconds.
After the STIM-T+X time period has been timed, the atrial defibrillating/cardioverting electrical shock may be applied across the electrodes 28 and 38 in accordance with activity block 140. The electrical energy used to cardiovert/defibrillate the atria may have a magnitude of, for example, 5 joules and a biphasic waveform of the type well known in the art. Of course, those skilled in the art will appreciate that the magnitude of the electrical energy may vary from patient to patient and atrial defibrillation/cardioversion electrode configurations. Once the atria have been defibrillated in accordance with activity block 140, the process returns for the detection of the next atrial fibrillation episode.
The atrial therapy described with reference to FIG. 4 may include additional process steps if desired. For example, the delivery of the atrial defibrillating/cardioverting shock may be made dependent upon the detection of the evoked response 122 (FIG. 3) as previously described with reference to FIG. 3. Additionally, the electrical energy delivered to the atrial may be further timed off of atrial activity, such as a P-wave. To that end, the atrial sensing circuit 82 may be utilized for sensing a P-wave during the atrial cardioversion/defibrillation window commencing after time T3 from which the atrial defibrillating electrical energy may be timed. The atria may be defibrillated/cardioverted at any time during this period up to the sensing of the next intrinsic ventricular activation (R-wave).
As a further additional method step to the method described with reference to FIG. 4, the atrial defibrillating/cardioverting electrical energy may be applied after an atrial pacing pulse is applied to the atria. Here, once the timer 66 has timed the STIM-T+X time period, the atrial pulse generator 70 may issue a pacing pulse to either one or both of the atria. The delivery of the atrial defibrillating/cardioverting electrical energy may then be timed off from the atrial pacing pulse until the sensing of the next R-wave. The initial pacing of the atria prior to the application of the atrial defibrillating/cardioverting energy may be desirable because it may assist in synchronizing more of the atrial tissue and potentially allow atrial cardioversion/defibrillation at relatively low electrical energies.
The present invention provides a method of defibrillating/cardioverting the atria which has a number of advantages. First, the method in accordance with the present invention requires only one ventricular paced event to trigger atrial cardioversion/defibrillation. Further, the pacing of the ventricles provides an opportunity to detect the evoked response to confirm the presence of the T-wave and accuracy in the timing through the evoked response and T-wave to avoid the ventricular vulnerable period. Another advantage is that the method of the present invention provides more freedom in timing the atrial cardioversion. Once the timer 66 has timed through the T-wave, the atria may be cardioverted/defibrillated at any time up to the next sensed R-wave. Still further, the elective pacing of the atria prior to atrial cardioversion may reduce the energy required in cardioverting/defibrillating the atria. Alternatively, the atrial cardioverting/defibrillating electrical energy may be delivered at a time synchronized to a spontaneous atrial depolarization. As a result, the atrial defibrillation/cardioversion therapy contemplated by the present invention allows for the delivery of the defibrillating/cardioverting electrical energy to the atria at a time which is assured to be safe against the induction of ventricular fibrillation.
In FIG. 5, a flow chart is shown describing an overview of the operation and particular novel features implemented in a second embodiment of the device 10. In accordance with this embodiment, a series of ventricular pacing pulses is delivered at a programmable rate (e.g. 90 bpm). This will have the beneficial effect of stabilizing the ventricular rate by a phenomenon known as retrograde concealed conduction thus effectively eliminating potential long-short cycle sequences that may predispose to the adverse induction of ventricular tachyarrhythmias in response to a shock delivered to convert atrial fibrillation. The method illustrated in the flow chart 150 of FIG. 5 initiates at an activity block 152. In activity block 152 atrial fibrillation is detected. The atrial fibrillation episode may be detected as previously described herein or in accordance with other methods well known in the art. Once atrial fibrillation is detected in accordance with activity block 152, the process advances to activity block 154 wherein ventricular pacing is initiated at a programmable rate (e.g. 90 bpm) for a preset number of N cycles. Here, the ventricular pulse generator 72 applies pacing pulses to one of the right and left ventricles, or to both the right ventricle and left ventricle simultaneously. Preferably the pacing is performed on demand. With the Nth ventricular pacing pulse, the process advances to decision block 156. Here it is determined if the rhythm is stable. If the rhythm is stable, then the algorithm proceeds to block 158. If the rhythm is not stable as exemplified by multiple native ventricular beats interspersed within the ventricular paced rhythm, the process returns to block 154 and reinstates ventricular pacing while withholding shock therapy.
Once a stable paced cardiac interval has been determined in decision block 156, the process advances to activity block 158 wherein the timer 66 times the STIM-T+X time period as previously described with reference to FIG. 3. Preferably, the timer 66 is started with the delivery of the Nth pacing pulse. N may be, for example, eight or more pacing pulses and again, as previously mentioned, the additional timing period of X milliseconds may be, for example, 100 milliseconds.
After the STIM-T+X time period has been timed, the atrial defibrillating/cardioverting electrical shock may be applied across the electrodes 28 and 38 in accordance with activity block 160. The electrical energy used to cardiovert/defibrillate the atria may have a magnitude of, for example, 5 joules and a biphasic waveform of the type well known in the art. Of course, those skilled in the art will appreciate that the magnitude of the electrical energy may vary from patient to patient and atrial defibrillation/cardioversion electrode configurations. Once the atria have been defibrillated in accordance with activity block 140, the process returns for the detection of the next atrial fibrillation episode.
The atrial therapy described with reference to FIG. 5 may include additional process steps if desired. For example, following detecting of atrial fibrillation, the timing control 79 may time a cardiac interval having a length greater than a minimum interval of, for example, 500 milliseconds or greater. This may be desirable to assure accurate vulnerable period timing and success in being able to establish a stable rhythm through the ventricular pacing. Further, the delivery of the atrial defibrillating/cardioverting shock may be made dependent upon the detection of the ventricular evoked response 122 (FIG. 3) as previously described with reference to FIG. 3. Additionally, the electrical energy delivered to the atria may be further timed off of atrial activity, such as a Fibrillatory-wave. To that end, the atrial sensing circuit 82 may be utilized for sensing a Fibrillation-wave during the atrial cardioversion/defibrillation window commencing after time T3 (FIG. 3) from which the atrial defibrillating electrical energy may be timed. The atrial may be defibrillated/cardioverted at any time during this period up to the sensing of the next intrinsic ventricular activation (R-wave).
As a further additional method step to the method described with reference to FIG. 5, the atrial defibrillating/cardioverting electrical energy may be applied after an atrial pacing pulse is applied to the atria. Here, once the timer 66 has timed the STIM-T+X time period, the atrial pulse generator 70 may issue a pacing pulse to either one or both of the atria. The delivery of the atrial defibrillating/cardioverting electrical energy may then be timed off from the atrial pacing pulse until the sensing of the next R-wave. The initial pacing of the atria prior to the application of the atrial defibrillating/cardioverting energy may be desirable because it may assist in synchronizing more of the atrial tissue and potentially allow atrial cardioversion/defibrillation at relatively low electrical energies.
The present invention provides a method of defibrillating/cardioverting the atria which has a number of advantages. First, the method in accordance with the present invention requires only one ventricular paced event to trigger atrial cardioversion/defibrillation. Further, the pacing of the ventricles provides an opportunity to detect the evoked response to confirm the presence of the T-wave and accuracy in the timing through the evoked response and T-wave to avoid the ventricular vulnerable period. Another advantage is that the method of the present invention provides more freedom in timing the atrial cardioversion. In the second embodiment, a period of ventricular pacing is provided to stabilize the ventricular rhythm and eliminate long-short cycle sequences further improving the safety of the shock by reducing the chance of inducing ventricular fibrillation. Once the timer 66 has timed through the T-wave, the atria may be cardioverted/defibrillated at any time up to the next sensed R-wave. Still further, the elective pacing of the atria prior to atrial cardioversion may reduce the energy required in cardioverting/defibrillating the atria. Alternatively, the atrial cardioverting/defibrillating electrical energy may be delivered at a time synchronized to a spontaneous atrial depolarization. As a result, the atrial defibrillation/cardioversion therapy contemplated by the present invention allows for the delivery of the defibrillating/cardioverting electrical energy to the atria at a time which is assured to be safe against the induction of ventricular fibrillation.
While the invention has been described by means of specific embodiments and applications thereof, it is understood that numerous modifications and variations could be made thereto by those skilled in the art without departing from the spirit and scope of the invention. For instance, the disclosed features, either singularly or in groups, could be used with other leads to advantageous results. It is therefore to be understood that within the scope of the claims, the invention may be practiced otherwise than as specifically described herein.
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