Rise in defibrillation threshold after postoperative cardiac remodeling in a patient with severe Ebstein’s anomaly

Introduction Implantable cardioverter-defibrillators (ICDs) are considered standard of care for patients with life-threatening cardiac arrhythmias. In small children and patients with venous anatomy that prohibits placement of traditional transvenous leads, nontransvenous coil positions have been used and can be characterized as epicardial, pleural, subcutaneous, or a hybrid of any of the 3 positions. Based on the critical mass hypothesis, the defibrillation threshold is attained when a sufficient mass of excitable cells are simultaneously depolarized, which interrupts activation wavefronts. Defibrillation is thus dependent on reaching a threshold current density in the myocardium. In transthoracic defibrillation, the magnitude of myocardial current density is dependent on the transcardiac current fraction (Fc), which is the ratio of the transcardiac threshold current (IC) to the transthoracic threshold current (IT). Over 95% of the transthoracic current is shunted by the thoracic cage and the lungs, with approximately 4% of the current traversing the heart. Rise in defibrillation threshold may be due to use of certain medications, electrolyte abnormalities, underlying cardiac disease, ischemia, or increase in tranthoracic threshold current. We report a case of rise in defibrillation threshold associated with cardiac remodeling after surgical repair in a patient with Ebstein’s anomaly.