POWER (Pulse Width Optimized Waveform Evaluation Trial)

Sudden cardiac death (SCD) continues to be a significant cause of cardiac mortality with
annual deaths ranging from 250,000 to 400,000 in the United States. Accordingly, implantable
cardioverter-defibrillators (ICD's) have proven to be an important therapeutic option for
patients susceptible to SCD. Successful therapy and generator longevity are greatly dependent
on proper defibrillation threshold (DFT) determination.

All modern ICD's utilize a biphasic waveform for defibrillation. It has been clearly shown
that biphasic waveforms reduce the energy required for internal defibrillation of the heart.
However, there is no consensus on which pulse widths are best for defibrillation.

St. Jude Medical ICD's (implantable cardioverter defibrillators) have programmable pulse
widths, which allow the physician multiple options in dealing with ICD patients. By
implanting ICD's with programmable pulse widths, this study utilizes the Tissue RC
Resistance/Capacitance) model to try to identify the optimal pulse widths.

To determine the efficacy of an optimal membrane time constant estimate for the "tuned"
waveform, defibrillation testing must be performed. Upper limit of vulnerability (ULV) has
been proposed as an alternative means of predicting the DFT and it has been shown that ULV
guided DFT testing can achieve a defibrillation success rate of 95%.

Inclusion Criteria:

- Patient is a candidate for ICD/CRT-D implantation.

- Patient has a compatible transvenous defibrillation lead system.

- Patient has had an echocardiogram, MUGA, or cath procedure within 6 months of
ICD/CRT-D implant.

- Patient is able to tolerate ULV guided DFT testing.

Exclusion Criteria:

- Patient has a mechanical valve in the tricuspid position.

- Patient has epicardial defibrillation electrodes.

- Patient is pregnant.

- Patient is less than 18 years old.