Efficacy and Pain Perception of Two Biphasic Waveforms.
Introduction: We evaluated the influence of the peak voltage of waveforms used for internal cardioversion of atrial fibrillation on defibrillation efficacy and pain perception. A low peak voltage biphasic waveform generated by a 500-microF capacitor with 40% tilt was compared to a standard biphasic waveform generated by a 60-microF capacitor with 80% tilt.
Methods and results: In 19 patients with paroxysmal atrial fibrillation (79% male, age 55 +/- 11 years, 21% with heart disease), the atrial defibrillation threshold (ADFT) was determined during deep sedation with midazolam for both waveforms in a randomized fashion using a step-up protocol. Internal cardioversion with a single lead (shock vector: coronary sinus to right atrium) was successful in 18 (95%) of 19 patients. ADFT energy and peak voltage were significantly lower for the low-voltage waveform (2.1 +/- 2.4 J vs 3.5 +/- 3.9 J, P < 0.01; 100 +/- 53 V vs 290 +/- 149 V, P < 0.01). Sedation then was reversed with flumazenil after ADFT testing. Two shocks at the ADFT (or a 3-J shock if ADFT >3 J) were administered to the patient using each waveform in random order. Pain perception was assessed using both a visual scale and a numerical score. ADFTs were above the pain threshold in 17 (94%) of 18 patients, even though the ADFT with the 500-microF waveform was <100 V in 63% of the patients. Pain perception was comparable for both waveforms (numerical score: 6.5 +/- 2.4 vs 6.3 +/- 2.6; visual scale: 5.4 +/- 2.6 vs 5.2 +/- 3.1; P = NS, 500-microF vs 60-microF). The second shock was perceived as more painful in 88% of the patients, independent of the waveform used.
Conclusion: Despite a 66% lower peak voltage and a 40% lower energy, the 40% tilt, 500-microF capacitor biphasic waveform did not change the pain perceived by the patient during delivery of internal cardioversion shocks. Pain perception for internal cardioversion probably is not influenced by peak voltage alone and increases with the number of applied shocks.