Rounded Biphasic Waveform Reduces Energy Requirements for Transvenous Catheter Cardioversion of Atrial Fibrillation and Flutter

Abstract

We postulated that reducing peak leading edge shock voltage and its rate of rise (waveform rounding) would reduce energy requirements for cardioversion of AF and AFl, and may therefore reduce patient discomfort. Transvenous defibrillating catheters (In-Control Inc.) were placed in the RAA (active fixation) and the CS of six anesthetized sheep. AF or AFl was induced by electrical stimulation (100 Hz, 2 V; Grass stimulator). A standard trapezoidal biphasic (S) waveform (3-ms duration each phase) was compared with a similar waveform that had the first phase rounded (R). Cardioversion was attempted after 30 seconds of arrhythmia, using a Ventritex HVS-O2 defibrillator modified to allow waveform rounding. Each waveform was randomly tested several times at 100-, 150-, and 200-V leading edges, and percentage cardioversion success calculated. Shock energy was calculated from delivered current and voltage using Flukeview (Fluke, Inc.) software. At 100-V leading edge R (64% success) and S (59%), shocks were similarly efficacious (P = 0.37). However, R delivered less current, voltage, and energy than the comparable S shock (means 1.30 A, 65.0 V, 0.33 J R vs 1.92 A, 94.2 V, 0.47 J S; P = 0.0001). Both waveforms were equally successful at 150 V (88% vs 100%; P = NS) and 200 V (100% vs 100%), but again R delivered less current, voltage, and energy (2.05 A, 102.5 V, 0.82 J R vs 2.78 A, 142.3 V, 1.11 J S at 150 V; 2.76 A, 141.2 V, 1.58 J R vs 3.77 A, 189.4 V, 2.03 J S at 200 V; both P = 0.0001). No arrhythmic or other complications occurred in the 174 shocks delivered. Waveform rounding reduces delivered peak voltage, current, and energy without reducing defibrillation efficacy. To determine if these changes are associated with a reduction in discomfort, patients with AF are currently being cardioverted with these waveforms during electrophysiological studies.

Transoesophageal low-energy cardioversion of atrial fibrillation. Results with the oesophageal–right atrial lead configuration

“…However, several recent improvements in the energy delivery mode have increased patients' tolerance for low energy internal cardioversion. In particular, the use of a single effective shock [10] , of biphasic waveforms [11] , of reduced peak voltages [12] , of rounded peak voltages [13] and of sequential shocks delivered through dual-current pathways [14] , together with mild sedation, have all contributed to a significant reduction in the discomfort while maintaining a high success rate.…”

Novel Passive Implantable Atrial Defibrillator Using Transcutaneous Radiofrequency Energy Transmission Successfully Cardioverts Atrial Fibrillation

“…Waveform rounding has been shown to significantly reduce the delivered mean peak voltage and current compared with the standard while maintaining efficacy 9 : the authors postulated that patients therefore would better tolerate an efficacious shock. This clearly is important for the functioning of an implantable atrial defibrillator.…”

“…The latter had been reported to produce lower defibrillation energy thresholds than the standard truncated exponential waveform. 9 Probes connected to the interface device captured the delivered voltage and current ( Figure 3). These were then plotted as voltagetime and current-time curves on a digital oscilloscope (TDS 420A, Tektronix Inc) and stored for further analysis of the delivered energy and impedance.…”

“…The transthoracic method is efficacious 1,2 but requires high energies and anesthesia and may be detrimental to the heart. [3][4][5][6] In both animal [7][8][9] and clinical 10 -13 studies, the transvenous route for cardioversion has proved to be safe and efficacious at significantly lower energy levels while requiring minimal or no sedation. 11,14 This led to the development of the automatic implantable atrial defibrillator.…”

Comparing the Efficacy and Safety of a Novel Monophasic Waveform Delivered by the Passive Implantable Atrial Defibrillator With Biphasic Waveforms in Cardioversion of Atrial Fibrillation

“…Reduction in waveform tilt has improved efficacy. 3 Harbinson and coworkers 4 showed that rounding of the first phase of a STB waveform reduced the peak delivered voltage, current, and energy while maintaining efficacy. A similar result was observed with rounding of both phases.…”