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OBJECTIVES: To evaluate the possible pain reduction of the plateau waveform in atrial fibrillation (AF) patients. BACKGROUND: Previous studies have indicated that reduced amplitude waveforms would be less painful than a conventional (65/65% tilt) biphasic waveform. Computer modeling suggested that a moderately long (10-12 msec) plateau (flat topped) shock waveform would deliver equivalent effectiveness with the lowest possible peak amplitude. METHODS: We enrolled 27 patients at two sites with persistent AF with a total of 220 shocks delivered during internal atrial cardioversion using an interleaved crossover design. Patient response was scored in three ways: (1) a verbally reported discomfort score, (2) visual analog scale (VAS), and (3) a blinded observer reporting a contraction score. RESULTS: All scores were significantly reduced (P < 0.0001) by the plateau waveform with impressive statistics: Verbal discomfort (3.51 +/- 0.13 to 2.89 +/- 0.12), VAS (7.00 +/- 0.56 to 5.91 +/- 0.36), and contraction scores (1.94 +/- 0.12 to 1.62 +/- 0.12). The average pain threshold shift (TS) for the Verbal score was 2.34, while that for the VAS score was 2.30. (This means that the patient typically could tolerate 2.34 times as much energy with the plateau waveform for the same level of verbally reported discomfort.) The contraction TS was less at 1.57. Response scores were also corrected for the shock sequence number to control for the sensitization effect from multiple shocks. This increased the TS for the Verbal score to 3.58, but the shock number was not significant for the VAS. A pulmonary artery electrode return was associated with lower pain compared with a coronary sinus position. CONCLUSION: A plateau shaped biphasic waveform resulted in significantly increased shock energy pain tolerances. Controlling for session sensitization, patients tolerated over three times as much energy for the same verbally reported discomfort score.

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BACKGROUND: Even with biphasic waveforms, patients with high defibrillation thresholds (DFTs) still are seen; thus, improved defibrillation waveforms may be of clinical utility. The stepped waveform has three parts: the first portion is positive with two capacitors in parallel, the second is positive with the capacitors in series, and the last portion is negative, also with the capacitors in series. OBJECTIVES: The purpose of this study was to assess the clinical utility of improved defibrillation waveforms. METHODS: We measured the delivered energy DFT in 20 patients in a dual-site study using the stepped waveform and a 50/50% tilt biphasic truncated exponential as the control. All shocks were delivered using an arbitrary waveform defibrillator, which was programmed to mimic two 220-microF capacitors (110 microF in series and 440 microF in parallel). RESULTS: The peak voltage at DFT was reduced in 19 of the 20 patients. The median peak voltage was reduced by 32.0%, from 472 V to 321 V (P <.001). The median energy DFT was reduced by 33%, from 11.7 J to 7.8 J (P = .008). The mean voltage and energy were reduced by 25.3% and 20.2%, respectively. On average, the stepped waveform was able to defibrillate as well as the 50/50% tilt biphasic, with 33% more energy. The benefit was more pronounced in patients with either a lower ejection fraction or a superior vena cava coil. The benefit of the stepped waveform had an inverse quadratic correlation with the resistance (r(2) = 0.47), suggesting that the capacitance values chosen for the stepped waveform were close to optimal for a 35-Omega resistance. CONCLUSION: The stepped waveform reduced the DFT compared to the 50/50% tilt waveform in this preliminary study.

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BACKGROUND: Shock pain has limited the acceptance of the implantable atrial cardioverter and is a complication of ventricular implantable cardioverter-defibrillator therapy. Rounding off of the peak of a shock waveform reduces pain. Whether the pain reduction results from reduction in the peak voltage or from the rounding has not been established. In other words, does reducing the extreme dV/dt (voltage derivative) of the conventional truncated exponential capacitive discharge waveform reduce pain? OBJECTIVES: The purpose of this study was to compare the relative contributions of peak voltage and waveform shape to pain. METHODS: We compared rounded and conventional waveforms with equal peak voltages. Eighty-five shocks of 50 to 500 V were delivered to 10 patients requiring atrial cardioversion for persistent atrial fibrillation. The patient touched an analog pain scale (0-15 cm) and orally reported a pain score on a scale from 0 to 5. An observer scored thoracic contractions on a scale from 0 to 5. RESULTS: No differences between the rounded and conventional waveform on any scale were noted for either univariate or multivariate analyses. However, all three response scales were strongly predicted by voltage with r(2) = 0.77 (oral), r(2) = 0.86 (analog), and r(2) = 0.85 (contraction) after correcting for patient variability and including a log voltage term. CONCLUSIONS: Patient pain perception was determined primarily by waveform peak voltage and not by the rounding, per se.

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