Efficacy of tuned waveforms based on different membrane time constants on defibrillation thresholds: primary results from the POWER trial.
BACKGROUND
The efficacy of tuned defibrillation waveforms versus the nominal fixed-tilt waveform has been previously studied. However, the optimal membrane time constant for tuning was not known. The POWER (Pulsewidth Optimized Waveform Evaluation tRial) trial was designed to determine the optimal membrane time constant for programming "tuned" biphasic waveforms.


METHODS
This acute, multicenter study included 121 implantable cardioverter-defibrillator/cardiac resynchronization therapy defibrillator patients who were randomized at implant to any two of the three membrane time constant waveforms (2.5, 3.5, and 4.5 ms). Fixed pulse widths were programmed using the measured high voltage shock impedance. The defibrillation threshold (DFT) estimates were obtained using a hybrid protocol starting with an upper limit of vulnerability estimate followed by a step-up/step-down ventricular fibrillation induction process.


RESULTS
DFT voltage was significantly lower using 3.5- and 4.5-ms waveforms as compared to the 2.5-ms waveform (P = 0.004 and 0.035, respectively). DFT voltage with both 3.5- and 4.5-ms waveforms was ≤ that obtained with the 2.5-ms waveform in 78.5% of the cases. The mean difference in DFT voltage using the 3.5-ms waveform and the 4.5-ms waveform was not significant (P = 0.4). However, the 3.5-ms waveform gave a lower DFT than the 4.5-ms waveform in 19 patients although the reverse was true in only nine (P = 0.02 not significant for multiple comparisons).


CONCLUSIONS
The use of a 3.5- or 4.5-ms time constant-based waveforms had lower DFTs when compared to the 2.5-ms waveform. This study suggests that the first defibrillation attempt at implantation should be with 3.5- or 4.5-ms time constant-based waveforms. The 3.5-ms-based waveform trended toward the best choice.
Saint John's Health Center, Santa Monica, California, USA.
Shephal K
SK
Doshi
Michael D
MD
Pittaro
Russell
R
Reeves
Ker
K
Boyce
John P
JP
Payne
Mark W
MW
Kroll
Robert J
RJ
Graumann
Ashish L
AL
Oza
Jesus E
JE
Val-Mejias
D000368:Aged; D000369:Aged, 80 and over; D058409:Cardiac Resynchronization Therapy Devices; D017147:Defibrillators, Implantable; D004554:Electric Countershock; D004867:Equipment Design; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016896:Treatment Outcome; D014693:Ventricular Fibrillation / Q000628:therapy; D058067:Wavelet Analysis