Successful Defibrillation After Conversion From Fixed‐Tilt to Tuned‐Duration Waveform

Figures

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  FIGURE 1. Intracardiac electrograms during unsuccessful defibrillation attempts. (A) Sustained monomorphic VT persisted despite multiple antitachycardia pacing (ATP) attempts and a 25‐J shock. (B) Additional 36‐J and 40‐J shocks also failed to terminate the arrhythmia, despite maximum ICD output.

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  FIGURE 2. Estimation of membrane time constant and selection of tuned‐duration waveform. (A) Ventricular evoked response during pacing (120 bpm, eight beats) showed a peak‐to‐peak interval of 74 ms. (B) Based on the membrane time‐constant block and measured impedance (74 Ω), optimal durations were calculated as 5.0 ms (Phase 1) and 3.0 ms (Phase 2). (Table used with permission from Abbott.)

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  FIGURE 3. Successful defibrillation using a tuned‐duration waveform. During DFT testing with individualized phase durations (5.0/3.0 ms), a 22‐J shock successfully terminated ventricular fibrillation, restoring an adequate safety margin.

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  FIGURE 4. Defibrillation waveforms and membrane response curves. (A) Appropriately timed Phase‐1 and Phase‐2 pulses produce effective depolarization and charge neutralization (“charge‐burping”), suppressing post‐shock activation. (B) Excessive Phase‐2 prolongation, as seen under high‐impedance conditions, causes reverse membrane charging and increases the likelihood of refibrillation.