13th International Congress
THE "NEW FRONTIERS"
OF ARRHYTHMIAS 1998

January 24-31, 1998
Marilleva, Trento, Italy

RT-203

Optimizing the second phase duration of biphasic shocks. Preliminary results of a prospective clinical study

Béla Merkely, Andrzej Lubinski*, Tibor Gyöngy, E. Lewicka-Nowak*, Ferenc Horkay, G. Swiatecka*, Orsolya Kiss, László Gelléer, Elek Bodor, Jürgen Pilz**, Max Schaldach**.
Dept. of Cardiovascular Surgery, Semmelweis Medical University, Budapest, Hungary; *Dept. of Cardiology, Medical University of Gdansk, Poland, **Institute for Biomedical Engineering, Friedrich-Alexander University of Erlangen-Nürnberg, Germany

Introduction

To defibrillate with a low amount of energy, the potential field generated by the defibrillating shock must be optimized. The defibrillation threshold (DFT) is known to depend on lead configuration, electrode quality and pulse morphology¹. The biphasic pulse form is known to influence defibrillation efficacy^2,3. The primary hypothesis is that the 1st phase leaves a residual charge on the membranes of the myocites, which can reinitiate fibrillation. The 2nd phase diminishes this charge, reducing the potential for refibrillation. Using a quantitative cellular model the optimal 2nd phase duration appears to be about 2.5 msec⁴. Shorter biphasic waveforms are reported to provide much more efficient defibrillation than other biphasic pulses⁵.

Our experimental results suggest that applying biphasic shocks with shorter 2nd phases results in lower DFTs in dogs⁶. However, the optimal 2nd phase duration for biphasic defibrillation in humans using smaller output capacitors has not yet been defined. The present clinical study was designed to evaluate the efficacy of shortening the 2nd phase of the biphasic pulse form.