System and method of generating a low-pain multi-step defibrillation waveform for use in an implantable cardioverter/defibrillator (ICD)

• US 6,772,007 B1
• Filed: 09/28/2001
• Issued: 08/03/2004
• Est. Priority Date: 05/14/1997
• Status: Expired due to Fees

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Kroll, Mark W.
• Primary Examiner(s): Schaetzle, Kennedy
• Application Number:
  US09/967,652
• Time in Patent Office: 1,040 Days
• Field of Search: 607/5, 607/63, 607/7, 607/46, 607/72
• US Class Current: 607/7
• CPC Class Codes: A61N 1/3906 characterised by the form of the shockwave
• CPC Class Codes: A61N 1/3912 Output circuitry therefor, e.g. switches
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion

Abstract

A shocking circuit is provided for use in an ICD for generating rounded multi-step defibrillation shocking pulse waveforms having reduced voltage peaks to minimize pain within a patient receiving the shocking pulse. The shocking circuit includes a set of capacitors, a resistive-capacitive (RC) filter, and low pain waveform control unit for selectively discharging the capacitors through the RC filer to generate the rounded pulse waveform. In one example, a pair capacitors are provided for generating a two-step pulse. The low pain waveform control unit initially discharges the capacitors in parallel to generate a first step of the pulse waveform while periodically shunting a portion of charge through the RC filter to reduce peak voltage. The low pain waveform control unit then discharges the capacitors in series to generate a second step of the pulse waveform while also periodically shunting a portion of charge through the RC filter to reduce peak voltage. With this circuit arrangement, a rounded, multi-step waveform can be readily generated for use within an ICD without requiring a high voltages or large capacitors. The shocking pulse itself is generated so as to approximate an input rounded waveform having an initial portion that increases monotonically to a final rounded peak, then decreases sharply.

Claims

1. In a defibrillator, a shocking circuit comprising:

a set of capacitors;

a resistive-capacitive (RC) filter; and

low pain switching circuitry connected to the capacitors and operative to selectively discharge the capacitors through the RC filter to generate a first phase of a defibrillation pulse waveform wherein the first phase includes multiple steps each having rounded initial voltage peaks.

2. The shocking circuit of claim 1 wherein the set of capacitors comprises first and second capacitors.

3. The shocking circuit of claim 2, wherein the low pain switching circuitry is operative to:

generate a first step of the pulse waveform by discharging the first and second capacitors in parallel while periodically shunting a portion of charge through the RC filter to reduce a peak voltage of the first step of the pulse waveform; and

generate a second step of the pulse waveform by periodically discharging the first and second capacitors in series while periodically shunting a portion of the charge through the RC filter to reduce a peak voltage of the second step of the pulse waveform.

4. The shocking circuit of claim 3, wherein the low pain switching circuitry is operative to periodically shunt the charge through the RC filter so as to approximate an input rounded waveform.

5. The shocking circuit of claim 4, wherein the input rounded waveform is selected so as to achieve reduced pain within the patient receiving the shock as compared with a patient receiving a shock having a non-rounded waveform while achieving the same final myocardial voltage.

6. The shocking circuit of claim 4, wherein the input waveform being approximated includes an Initial portion that increases sharply from zero voltage to a initial voltage (V_initial), a central portion that increases exponentially from the initial voltage to a peak voltage (V_peak), and a tall portion that decreases sharply back to zero voltage.

7. The shocking circuit of claim 6, wherein the central portion of the predetermined rounded waveform being approximated has an exponential shape represented by:

8. The shocking circuit of claim 7, wherein V_initial is in the range of 20-30 Volts, V_peak is in the range to 350-350 Volts, and T is within the range of 5-7 milliseconds.

9. The shocking circuit of claim 6, wherein the low pain switching circuitry is operative to periodically shunt charge through the RC filter during the central portion of the waveform with a switching period in the range of 8-12 microseconds so as to approximate the predetermined rounded waveform.

10. The shocking circuit of claim 2 wherein the low pain switching circuitry includes:

an output circuit connected to the RC filter;

a chopping switch coupled between the first and second capacitors and the RC filter;

a low pain waveform control unit for alternately coupling the capacitors to the chopping switch either in parallel or in series and for controlling the chopping switch to periodically shunt current from the capacitors through the RC filter to the output circuit.

11. The shocking circuit of claim 10 wherein the output circuit is an H-bridge.

12. The shocking circuit of claim 10:

wherein the low pain switching circuitry includes an input waveform storage unit for storing an input waveform shape; and

wherein the low pain waveform control unit is operative to control the storage capacitors and the chopping switch to feed current from the capacitors through the RC filter so as to generate an output pulse waveform approximating the input waveform.

13. In a defibrillator, a method for generating a shocking waveform comprising the steps of:

generating a first step of a first phase of a shocking waveform wherein the first step has a rounded initial voltage peak;

generating a second step of the first phase of the shocking waveform wherein the second step also has a rounded initial voltage peak; and

applying the shocking waveform to heart tissue of the patient.

14. The method of claim 13, wherein the steps of generating the first and second steps of the first phase of the shocking waveform. is performed so as to approximate a single waveform shape having a voltage magnitude increasing monotonically up to a voltage peak then decreasing sharply to zero.

15. The method of claim 14, wherein the single waveform shape being approximated includes an initial portion that increases sharply from zero voltage to a initial voltage (V_initial), a central portion that increases exponentially from the initial voltage to a peak voltage (V_peak), and a tail portion that decreases sharply back to zero voltage.

16. The method of claim 15, wherein the central portion of the waveform being approximated has an exponential shape represented by:

17. The method of claim 16, wherein V_initial is in the range of 20-30 Volts, V_peak is in the range to 350-350 Volts, and T is within the range of 5-7 milliseconds.

18. The method of claim 13 for use in a defibrillator having a shocking circuit with first and second capacitors, a resistive-capacitive (RC) filter;

and a low pain waveform control unit connected to the capacitors and operative to selectively discharge the capacitors through the RC filter to generate a rounded, multi-step defibrillation pulse waveform and

wherein the first step of a multi-step shocking waveform is generated by discharging the first and second capacitors in parallel while periodically shunting a portion of charge through the RC filter to reduce a peak voltage of the first step of the pulse waveform; and

wherein the second step of the multi-step shocking waveform is generated by periodically discharging the first and second capacitors in series while periodically shunting a portion of the charge through the RC filter to reduce a peak voltage of the second step of the pulse waveform.

19. In a defibrillator, a shocking circuit comprising:

means for inputting a waveform shape having first and second steps each with rounded initial voltage peaks;

means for generating a first step of a first phase of a shocking waveform by approximating the first step of the input waveform;

means for generating a second step of the first phase of a shocking waveform by approximating the second step of the input waveform;

means for applying the shocking waveform to heart tissue of the patient.

20. The shocking circuit of claim 19, wherein the means for inputting a waveform shape inputs a waveform shape having first and second steps that form a single continuous waveform having a magnitude Increasing monotonically up to a voltage peak then decreasing sharply to zero.