Increased myocardial voltage is achieved by configuring a shocking circuit
of an ICD to generate a defibrillation pulse waveform having a positive
phase with three distinct voltage peaks. The shocking circuit employs
three capacitors along with switching circuitry for selectively
discharging the capacitors so as to generate the defibrillation pulse
waveform. More specifically, the switching circuitry generates a first
step of the pulse waveform by discharging the capacitors while connected
in parallel, then generates a second step of the pulse waveform by
discharging the capacitors while the two of the three capacitors are
connected in parallel and the third is connected in series, and finally
generates a third step of the pulse waveform by discharging the capacitors
while connected in series. By employing a three capacitor shocking circuit
configured as described herein, the amount of energy required to reach a
myocardial defibrillation threshold is less than for one-capacitor or
two-capacitor systems, regardless of the total capacitance of the system.
Hence, battery power can be saved and device longevity improved, while
still providing effective defibrillation. Moreover, the total amount of
time required to reach the defibrillation threshold is less than with
one-capacitor or two-capacitor systems, permitting the patient to be
defibrillated more quickly. Additionally, the three-capacitor system is
generally less influenced by variations in underlying parameters and
operating conditions.
