Shock-induced termination of reentrant cardiac arrhythmias: Comparing monophasic and biphasic shock protocols

Abstract

In this article, we compare quantitatively the efficiency of three different protocols commonly used in commercial defibrillators. These are based on monophasic and both symmetric and asymmetric biphasic shocks. A numerical one-dimensional model of cardiac tissue using the bidomain formulation is used in order to test the different protocols. In particular, we performed a total of 4.8 Â 10 6 simulations by varying shock waveform, shock energy, initial conditions, and heterogeneity in internal electrical conductivity. Whenever the shock successfully removed the reentrant dynamics in the tissue, we classified the mechanism. The analysis of the numerical data shows that biphasic shocks are significantly more efficient (by about 25%) than the corresponding monophasic ones. We determine that the increase in efficiency of the biphasic shocks can be explained by the higher proportion of newly excited tissue through the mechanism of direct activation. In the present paper, we show how numerical simulations can be used to understand the efficiency of different defibrillation protocols. Fibrillation is a rapid, irregular electrical activity of the heart. This fatal medical condition is usually treated by the application of an external electric shock to the patient chest through external paddle electrodes. The shape of the electric waveforms that are usually applied are either monophasic or biphasic. This means that in the latter the polarity is switched at some point in the course of the application of the shock. Empirical observations suggest that biphasic shocks are more efficient than monophasic shocks in terminating fibrillation. In this paper, by using a simplified mathematical model of cardiac tissue, which, however, includes a realistic response of the cells to large electric fields, we confirm and explain this experimental observation. The model developed here could be used in subsequent studies in order to design and test more complex waveforms, which could be done systematically because the model is simple and not very computationally costly. The next goal is to find the optimal waveform that reduces the energy needed for defibrillatory shocks. This would be of great benefit for patients undergoing defibrillation by limiting the damage to the heart tissue caused by such a strong electric shock.

Control of electrical turbulence by periodic excitation of cardiac tissue

“…4. This is in line with earlier findings 39 . On the other hand, the defibrillation success is almost unaffected by the boundary conditions.…”

“…We fixed the total pulse duration to 10 ms and optimized the ratio of forward to backward duration. For fixed parameters, we found that 7 ms (forward) and 3 ms (backward) leads to best defibrillation results, in agreement with 38,39 , where the best efficiency is obtained when the first phase is about twice as long as the second phase. Our low-energy antifibrillation pacing (LEAP) protocol contains n identical biphasic pulses, where the interval T between two pulses is constant and defined between the onsets of neighboring pulses.…”

Advantage of four-electrode over two-electrode defibrillators

“…This simplification was exploited in a seminal work by Glass and Josephson [13] in the 1990s, in which a one dimensional geometry was used to study the annihilation and the resetting of reentrant waves. This original study was further broadened by the inclusion of conductivity heterogeneities and multiple stimuli [12,[14][15][16][17][18].…”

“…In this study [12], it was shown that the threshold E 50 , the applied electric field corresponding to a 50% of probability of success for defibrillation shocks, is achieved mainly by front to front interactions or interactions of the front with the refractory tissue, while the threshold E 90 needed for a 90% of probability of success is mainly obtained through a different mechanism, consisting of a direct activation of the whole cardiac tissue. Examining the mechanisms for defibrillation at low energy (i.e.…”

“…The present study is motivated by the analysis of results obtained with the standard two-electrode system in a simple model of a one-dimensional ring of cardiac tissue [12] recently developed by the authors. In this study [12], it was shown that the threshold E 50 , the applied electric field corresponding to a 50% of probability of success for defibrillation shocks, is achieved mainly by front to front interactions or interactions of the front with the refractory tissue, while the threshold E 90 needed for a 90% of probability of success is mainly obtained through a different mechanism, consisting of a direct activation of the whole cardiac tissue.…”