Comparison of Biphasic Truncated Exponential and Pulsed Waveforms for Cardioversion of Atrial Fibrillation-High Energy Escalation Strategy and Introduction to Manual Pressure Application

Background Commercially available defibrillators generate direct current (DC) shock with various waveforms using distinct technologies. These waveforms are suggested to have different efficacy and safety. Although the superiority of biphasic over monophasic waveforms is well established, the relative efficacy and safety of the available biphasic waveforms is not clear.

Various BTE waveforms apply different potential gradients on the thorax that might produce various defibrillation effects. Apart from efficacy, the most important aspect is the patient safety, considering that larger potential gradients in the myocardium lasting longer could potentially induce an electroporation and then a fibrillation. A frequently observed effect of electroporation are the post-shock ST-segment deviations in the surface ECG, representing the potential difference between the normal tissue and sustained depolarized critical mass of myocardium closest to the associated origin of the electrical current. Although ST-segment changes are an easily ignored phenomenon, occurring acutely and resolving during the first few minutes post-shock, their presence in a short-term basis can identify electroporation by dangerously high potential gradients, while the sustained ST-changes in a long-term basis can identify cases with myocardial injury. The most reliable marker of shock-induced myocardial injuries is the high sensitive cardiac Troponin I (hsTnI).

In a previous study Trendafilova et al. were compared fixed-high energy protocols (200J-200J-200J) delivered by two different defibrillation waveforms: Pulsed (BTE-PE) and High-energy BTE (BTE-HE). This study concluded on non-inferiority between devices. Cumulative energy, efficiency of the waveforms and safety (measured by High-sensitive Troponin) were not reaching significant difference for both waveforms. Delivered energy of the first efficient shock was significantly lower for BTE-PE and although BTE-PE delivered almost 28J lower energy after the whole procedure, significance could not be reached due to wide variance.

In a Danish study Schmidt et al. compared two cardioversion protocols - one is fixed-high energy (360J-360J-360J), the other is low energy escalating (125J-150J-200J). The overall efficacy of fixed-energy protocol was better than escalating. Safety is non significantly different. Schmidt et al. raised the question of the usefulness of escalating energy protocols compared to fixed high-energy protocols.

There is an ethical consideration to apply maximal energy shocks to all patients without considering patient individuality. Ramirez et al. remind that failed shocks might depend on other factors like transthoracic impedance. Lavignasse et al. found that cumulative energy setting differs with patient characteristics, having significant association with: AF duration, gender, BSA, LV TDD, valvular disease and chronic respiratory disease. Indeed, some authors (Voskoboinik et al. and Ramirez et al.) showed that decreasing impedance by manual pressure application (MPA) had a positive impact on cardioversion outcome.