Aims Classic heat stroke is associated with high in-hospital mortality and morbidity. The relation between the ECG findings in heat stroke and the clinical outcomes of these patients has not been studied. The aim of this study was to describe the electrocardiographic features in patients with classic heat stroke and to determine if there is any correlation of ECG findings with in-hospital outcomes.

Methods We performed a retrospective study on 50 patients with classic heat stroke during summer months of 2016–2018. All 12-lead electrocardiographic recordings obtained from these patients were subjected to in-depth analysis. Statistical analysis was done to determine the correlation of electrocardiographic findings with in-hospital outcomes.

Results 37 patients were in sinus rhythm, while supraventricular arrhythmias including atrial fibrillation (n=6), ectopic atrial tachycardia (n=4) and atrial flutter (n=2) were observed in the rest. There was a high prevalence of QTc prolongation, low voltage P waves, conduction defects like incomplete right bundle branch block and repolarisation abnormalities. The ratio of QRS voltage in the limb leads to that in precordial leads was ≤0.5 in nearly three-fourths of the patients. Among the observed electrocardiographic features, low P-wave voltage (<0.01 mV) in lead II was found to have statistically significant correlation with adverse in-hospital outcome (OR 8.93, p=0.04), after adjustment for clinical covariates.

Conclusion There was high incidence of atrial arrhythmias in patients with classic heat stroke. A low P-wave voltage (<0.01 mV) in lead II was predictive of adverse in-hospital outcome in this cohort of patients.