Sadek MM, et al. - Researchers evaluate the relevance of transthoracic impedance (TTI) to electrical cardioversion (ECV) success for atrial tachyarrhythmias when using biphasic waveform defibrillators. They assess de-identified data stored in biphasic defibrillator memory cards from ECV attempts for atrial fibrillation (AF) or atrial flutter (AFL) over a 2-year period at their centre. Presuming that TTI is predictive of ECV success with contemporary defibrillators. Nonetheless, the designing of contemporary defibrillators is done to compensate for TTI, the association of this variable with ECV failure in patients with AF continues. Procedural success could be improved with the strategies to lower TTI during ECV for AF.