Quantitative Assessment of the Effects of Therapeutic Hypothermia on Early Repolarization in Idiopathic Ventricular Fibrillation Survivors: A Seven Year Cohort Study

Background—The early repolarization (ER) pattern on the electrocardiogram (ECG) is associated with an increased risk of idiopathic ventricular fibrillation (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 idiopathic VF (ID-VF) and draw comparisons with a control group who experienced coronary artery disease related VF (CAD-VF).

Methods and Results—All patients who suffered cardiac arrest and were treated with therapeutic hypothermia over a 7 year period were considered for inclusion in the study. 43 patients were identified with ID-VF or CAD-VF arrest. ECGs were obtained during cooling and again after re-warming. ECGs were digitized and assessed for the presence of ER by two independent observers. Cooling significantly increased the prevalence (74 % during cooling vs. 51 % at baseline temperature, P=0.044) and mean amplitude (0.78±0.10 mV during cooling vs. 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 idiopathic VF than of CAD-VF (100 % vs. 67 %, P=0.043). ER magnitude was significantly greater among idiopathic VF survivors than CAD-VF survivors both during cooling (1.16±0.18 mV vs. 0.70±0.11 mV, P=0.044) and at baseline temperature (1.02±0.21 mV vs. 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 idiopathic VF, therapeutic hypothermia only increases ER amplitude in CAD-VF survivors.