Quantitative Assessment of the Effects of Therapeutic Hypothermia on Early Repolarization in Idiopathic Ventricular Fibrillation Survivors

Abstract

Background— The early repolarization (ER) pattern on ECG is associated with an increased risk of idiopathic ventricular fibrillation (ID-VF). Hypothermia is known to result in similar electrocardiographic changes. In this retrospective cohort study, we examine the impact of therapeutic hypothermia on ER in survivors of cardiac arrest attributed to ID-VF and draw comparisons with a control group who experienced coronary artery disease–related VF (CAD-VF). Methods and Results— All patients who had cardiac arrest and were treated with therapeutic hypothermia over a 7-year period were considered for inclusion in the study. Forty-three patients were identified with ID-VF or CAD-VF arrest. ECGs were obtained during cooling and again after rewarming. ECGs were digitized and assessed for the presence of ER by 2 independent observers. Cooling significantly increased the prevalence (74% during cooling versus 51% at baseline temperature; P =0.044) and mean amplitude (0.78±0.10 mV during cooling versus 0.56±0.09 mV at baseline temperature; P =0.038) of ER in the overall cohort. During cooling, ER was more common among survivors of ID-VF than of CAD-VF (100% versus 67%; P =0.043). ER magnitude was significantly greater among ID-VF survivors than CAD-VF survivors both during cooling (1.16±0.18 versus 0.70±0.11 mV; P =0.044) and at baseline temperature (1.02±0.21 versus 0.42±0.09 mV; P =0.005). Conclusions— Hypothermia increases both the prevalence and magnitude of ER in cardiac arrest survivors. Despite the association of ER with ID-VF, therapeutic hypothermia only increases ER amplitude in CAD-VF survivors.