Electrocardiogram Abnormalities and the Risk of Out-of-Hospital Cardiac Arrest: A Nationwide Cohort Study.

BACKGROUND: Electrocardiograms (ECGs) potentially represent strong risk predictors, but their role in risk stratification for out-of-hospital cardiac arrest (OHCA) is unclear. OBJECTIVE: This study aimed to assess 5-year OHCA risk for different ECG abnormalities. METHODS: Data on patients and their respective first-recorded ECG, from hospital or ambulance setting, were retrieved from Danish Nationwide Electrocardiogram Cohort and Danish Cardiac Arrest Registry. Patients were followed from ECG recording until OHCA, death from other causes, emigration, or end-of-study. Cox proportional hazards models were used to estimate rates of OHCA and death from other causes, adjusted for comorbidities and medication use, and then utilized to estimate 5-year OHCA risk. RESULTS: This study included 2,155,155 patients. Five-year OHCA risk for patients with normal ECGs was 0.50% [95% CI: 0.49-0.51%]. Following ECG abnormalities were associated with significantly higher 5-year OHCA risk: atrial fibrillation (0.61% [95% CI: 0.58-0.64%]), left bundle branch block (0.73% [95% CI: 0.68-0.78%]), intraventricular conduction delay (0.68 [95% CI: 0.63-0.73]), left posterior fascicular block (0.87% [95% CI: 0.67-1.06%]), Q-wave (0.59% [95% CI: 0.57-0.61%]), ST-depression (0.67% [95% CI: 0.64-0.71%], left ventricular hypertrophy (0.74% [95% CI: 0.71-0.77%]) and QTc prolongation (0.84% [95% CI: 0.81-0.86%]). Corresponding results were observed regarding relative risk. CONCLUSIONS: This nationwide study of over two million patients, spanning almost 20 years, showed that several ECG abnormalities were associated with increased 5-year risk of OHCA.