Method and apparatus for anti-tachycardia pacing and defibrillation

• US 20050222629A1
• Filed: 04/02/2004
• Published: 10/06/2005
• Est. Priority Date: 04/02/2004
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Bloomfield, Rebecca, Perschbacher, David L., Roof, Karin K.
• Granted Patent: US 7,277,750 B2
• Time in Patent Office: Days
• US Class Current: 607/4
• CPC Class Codes: A61N 1/3621 for treating or preventing abnormally high heart rate
• CPC Class Codes: A61N 1/39622 Pacing therapy
• CPC Class Codes: A61N 1/3987 characterised by the timing or triggering of the shock

Abstract

An implantable cardioverter/defibrillator (ICD) includes an Anti-Tachycardia Pacing Before Charge (ATP-BC) mode according to which one or more high-voltage capacitors for storing defibrillation energy are charged in preparation of delivering a defibrillation shock only if a ventricular tachycardia (VT) sustains after an ATP delivery. Fast ATP delivery and effect verification methods are applied to avoid significant delay in delivering the defibrillation shock when found necessary to terminate the VT. A switch is provided such that a user decides whether to activate the ATP-BC mode or to deliver the defibrillation shock without delivering the ATP.

Claims

1. A cardiac rhythm management system comprising:

a sensing circuit to sense a cardiac signal;

a pacing circuit to deliver an anti-tachycardia pacing (ATP);

a defibrillation circuit to deliver a shock, the defibrillation circuit including;

a defibrillation capacitor to store an electrical energy for the shock; and

a capacitor charging circuit to charge the defibrillation capacitor in response to a charging signal;

a ventricular tachycardia (VT) detector to detect a VT based on at least the cardiac signal;

a VT verification module adapted to receive a first VT verification command and a second VT verification command and perform a VT verification test to determine whether the VT sustains based on at least the cardiac signal after one of the first and second VT verification commands is received; and

a controller coupled to the pacing circuit, the defibrillation circuit, the VT detector, and the VT verification module, the controller including;

an ATP activator to receive an ATP activation command and produce an ATP activation signal in response to a receipt of the ATP activation command;

a first VT verification controller to issue the first VT verification command after the VT is detected and produce a first VT verification signal if the VT sustains after being detected;

an ATP controller to detect a presence of the ATP activation signal and, if the ATP activation signal is present, to receive the first VT verification signal and control an ATP delivery after the first VT verification signal is received;

a second VT verification controller to issue the second VT verification command after the ATP delivery and produce a second VT verification signal if the VT sustains after the ATP delivery;

a charging controller to detect the presence of the ATP activation signal and, if the ATP activation signal is present, receive the second VT verification signal and produce the charging signal after the second VT verification signal is received, and if the ATP activation signal is not present, receive the first VT verification signal and produce the charging signal after the first VT verification signal is received; and

a defibrillation controller to control a delivery of the shock after the charging of the defibrillation capacitor is completed.

2. The system of claim 1, wherein the ATP activator includes a command input to receive the ATP activation command and a heart rate input to receive a heart rate, the ATP activator adapted to produce the ATP activation signal in response to the receipt of the ATP activation command if the heart rate is below a predetermined threshold rate.

3. The system of claim 1, wherein the VT verification module receives a third VT verification command and performs the VT verification test to determine whether the VT sustains after one of the first, second, and third VT verification commands is received, the controller further comprises a third VT verification controller to issue the third VT verification command while the defibrillation capacitor is being charged and produce a third VT verification signal if the VT sustains while the defibrillation capacitor is being charged, and the charging controller receives the third VT verification signal and issues a signal to stop the charging of the defibrillation capacitor after the third VT verification signal is received.

4. The system of claim 3, wherein the VT verification module receives a fourth VT verification command and performs the VT verification test to determine whether the VT sustains after one of the first, second, third, and fourth VT verification commands are received, the controller further comprises a fourth VT verification controller to issue the fourth VT verification command after the charging of the defibrillation capacitor is completed and produce a fourth VT verification signal if the VT sustains after the charging of the defibrillation capacitor is completed, and the defibrillation controller receives the fourth VT verification signal and controls the delivery of the shock after the fourth VT verification signal is received.

5. The system of claim 1, wherein the VT detector comprises:

a heart rate detector to detect a heart rate; and

a comparator to compare the heart rate to one or more predetermined threshold rates.

6. The system of claim 1, wherein the VT detector comprises:

a heart rate detector to detect a heart rate for each heart beat of a predetermined number of consecutive heart beats;

a VT rate comparator to compare the heart rate for each beat to one or more predetermined VT threshold rates forming a detection window;

a VT beat counter to count a number of fast beats each being a heart beat having a heart rate falling within the detection window; and

a VT declaration module to declare that the VT is detected based on the number of fast beats and the predetermined number of consecutive heart beats.

7. The system of claim 6, wherein the VT declaration module comprises a VT detection comparator to compare the number of fast beats to a predetermined threshold number and declare that the VT is detected if the number of fast beats exceeds the predetermined threshold number.

8. The system of claim 6, wherein the VT declaration module comprises:

a VT beat ratio calculator to calculate a VT beat ratio of the number of fast beats to the predetermined number of consecutive heart beats; and

a VT detection comparator to compare the VT beat ratio to a predetermined threshold ratio and declare that the VT is detected if the VT beat ratio exceeds the predetermined threshold ratio.

9. The system of claim 1, wherein the VT verification module comprises:

a heart rate detector to detect a heart rate for each heart beat of a predetermined number of consecutive heart beats;

a VT rate comparator to compare the heart rate for each beat to one or more predetermined VT threshold rates forming a detection window;

a VT beat counter to count a number of fast beats each being a heart beat having a heart rate falling within the detection window; and

a VT declaration module to declare that the VT sustains based on the number of fast beats and the predetermined number of consecutive heart beats.

10. The system of claim 9, wherein the VT declaration module comprises a VT detection comparator to compare the number of fast beats to a predetermined threshold number and declare that the VT sustains if the number of fast beats exceeds the predetermined threshold number.

11. The system of claim 9, wherein the VT declaration module comprises

a VT beat ratio calculator to calculate a VT beat ratio of the number of fast beats to the predetermined number of consecutive heart beats;

and

a VT detection comparator to compare the VT beat ratio to a predetermined threshold ratio and declare that the VT sustains if the VT beat ratio exceeds the predetermined threshold ratio.

12. The system of claim 1, wherein the controller further comprises a precharging controller to produce the charging signal after the VT is detected and before the ATP delivery.

13. The system of claim 1, further comprising a user input including an ATP activation switch to receive a user command and produce the ATP activation command based on the user command.

14. The system of claim 13, further comprising an implantable metal can housing the sensing circuit, the pacing circuit, the defibrillation circuit, the VT detector, the VT verification module, and the controller.

15. The system of claim 14, further comprising an external programmer including the user input.

16. The system of claim 15, wherein the user input further comprises a detection window selector to receive selections relating detection windows each corresponding to at least one of the one or more predetermined threshold rates.

17. A method for operating an implantable cardioverter/defibrillator (ICD), comprising;

receiving an anti-tachycardia pacing (ATP) activation command activating a feature including delivering an ATP;

detecting a ventricular tachycardia (VT);

determining whether the VT sustains after being detected;

delivering the ATP if the ATP activation command is received and the VT sustains after being detected;

charging a capacitor if the ATP activation command is not received and the VT sustains after being detected;

determining whether the VT sustains after the delivering the ATP;

charging the capacitor if the VT sustains after the ATP is delivered; and

delivering a defibrillation shock after the capacitor is charged.

18. The method of claim 17, further including detecting a heart rate, and wherein delivering the ATP comprises delivering the ATP if the ATP activation command is received, the VT sustains after being detected, and the heart rate is below a predetermined threshold rate.

19. The method of claim 18, wherein delivering the ATP comprises delivering the ATP if the ATP activation command is received, the VT sustains after being detected, and the heart rate is below about 250 beats per minute.

20. The method of claim 17, further comprising detecting a ventricular fibrillation (VF).

21. The method of claim 17, wherein detecting the VT comprises:

detecting a heart rate for each heart beat of a predetermined number of consecutive heart beats;

comparing the heart rate for each of the consecutive heart beats to one or more threshold rates forming a detection window; and

declaring that the VT is detected if the heart rate falls within the detection window for at least a predetermined number of fast beats.

22. The method of claim 21, wherein detecting the VT comprises:

detecting a predetermined number of consecutive fast heart beats each having a heart rate falling within the detection window;

detecting the heart rate for each heart beat of the predetermined number of consecutive heart beats after the predetermined number of consecutive fast heart beats are detected;

comparing the heart rate for each of the consecutive heart beats to one or more threshold rates forming the detection window; and

declaring that the VT is detected if the heart rate falls within the detection window for at least the predetermined number of fast beats.

23. The method of claim 21, wherein detecting the VT comprises:

detecting the heart rate for each heart beat of about 10 consecutive heart beats;

comparing the heart rate for each of the about 10 consecutive heart beats to the one or more threshold rates forming the detection window; and

declaring that the VT is detected if the heart rate falls within the detection window for at least about 8 out of the about 10 consecutive heart beats.

24. The method of claim 23, wherein detecting the VT comprises:

detecting 3 consecutive fast beats each having a heart rate falls within the detection window;

detecting the heart rate for each heart beat of the about 10 consecutive heart beats after the 3 consecutive fast beats are detected;

comparing the heart rate for each of the about 10 consecutive heart beats to the one or more threshold rates forming the detection window; and

declaring that the VT is detected if the heart rate falls within the detection window for at least about 8 out of the about 10 consecutive heart beats.

25. The method of claim 21, wherein declaring that the VT is detected comprises declaring that the VT is detected if the heart rate falls within the detection window for at least a predetermined fraction of the predetermined number of consecutive heart beats.

26. The method of claim 21, wherein the one or more threshold rates comprises a lower threshold rate, and further comprising programming the lower threshold rate to about 180 beats per minute.

27. The method of claim 26, wherein the one or more threshold rates comprises an upper threshold rate, and further comprising programming the upper threshold rate to about 250 beats per minute.

28. The method of claim 17, wherein the determining whether the VT sustains after being detected and determining whether the VT sustains after the delivering the ATP each comprise performing a fast VT verification test.

29. The method of claim 28, wherein performing the fast VT verification test comprises:

detecting a heart rate for each of a predetermined number of consecutive heart beats;

comparing the heart rate for each of the consecutive heart beats to one or more predetermined threshold rates forming a detection window; and

declaring that the VT sustains if the heart rate falls within the detection window for at least a predetermined number of fast beats.

30. The method of claim 29, further comprising determining whether the episode of VT sustains while the capacitor is being charged, and stopping charging the capacitor if the VT is determined as sustained.

31. The method of claim 30, further comprising determining whether the episode of VT sustains after the capacitor is charged, and wherein delivering the shock after the capacitor is charged comprises delivering the shock if the VT sustains after the capacitor is charged.

32. The method of claim 30, wherein the determining whether the VT sustains after being detected, determining whether the VT sustains after the delivering the ATP, determining whether the episode of VT sustains while the capacitor is being charged and determining whether the episode of VT sustains after the capacitor is charged each comprise performing a fast VT verification test.

33. The method of claim 29, wherein performing the fast VT verification test comprises:

detecting the heart rate for each of about 10 consecutive heart beats;

comparing the heart rate each of the 10 consecutive heart beats to the one or more threshold rates forming the detection window; and

declaring that the VT sustains if the heart rate falls within the detection window for at least about 6 out of the about 10 consecutive heart beats.

34. The method of claim 29, wherein declaring that the VT sustains comprises declaring that the VT sustains if the heart rate exceeds the first threshold rate for at least a predetermined fraction of the predetermined number of consecutive heart beats.

35. The method of claim 34, wherein declaring that the VT sustains comprises declaring that the VT sustains if the heart rate exceeds the first threshold rate for at least about two third of the predetermined number of consecutive heart beats.

36. The method of claim 29, wherein the one or more threshold rates comprises a lower threshold rate, and further comprising programming the lower threshold rate to about 180 beats per minute.

37. The method of claim 36, wherein the one or more threshold rates comprises an upper threshold rate, and further comprising programming the upper threshold rate to about 250 beats per minute.

38. The method of claim 17, further comprising charging the capacitor while determining whether the VT sustains after being detected.

39. The method of claim 17, wherein delivering the ATP comprises delivering a first burst of about 8 pacing pulses at a first pacing interval upon an expiration of a coupling interval starting from the last sensed depolarization.

40. The method of claim 39, further comprising programming the coupled interval to an interval within a range of about 120 ms to 750 ms.

41. The method of claim 39, further comprising programming the first pacing interval to an interval calculated as a predetermined percentage of the coupling interval or a minimum pacing interval, whichever is longer.

42. The method of claim 41, further comprising programming the first pacing interval to an interval calculated as about 88% of the coupling interval or about 200 milliseconds, whichever is longer.

43. The method of claim 41, wherein delivering the ATP further comprises delivering a second burst of about 8 pacing pulses.