Association between preexisting electrocardiographic abnormalities and shockable initial rhythm in out-of-hospital...

The initial rhythm in out-of-hospital cardiac arrest (OHCA) strongly predicts survival. However, the association between electrocardiographic (ECG) abnormalities preceding OHCA and the initial rhythm remains unclear.

Individuals experiencing a first OHCA between 2016 and 2021 were identified from the Danish Cardiac Arrest Registry and linked to the most recent hospital-recorded ECG obtained 30-365 days prior to arrest, when available. The outcome was a shockable initial rhythm. Adjusted odds ratios (ORs) were estimated using logistic regression, with normal ECGs as reference. Analyses were stratified by witness status.

Among 22,516 individuals experiencing a first OHCA, 11,167 (49.6%) were bystander-witnessed. Of these, 4,321 (38.7%) had a preceding ECG. Among bystander-witnessed arrests, shockable rhythms occurred in 21.8% of individuals with normal ECGs, compared with 29.9% (OR 1.44, 95% CI 1.10-1.90) in those with ≥1 abnormality and 37.0% (OR 1.65, 95% CI 1.28-2.16) in those without a prior ECG. Among specific abnormalities, higher odds of a shockable rhythm were observed for pathological Q-waves (31.5%, OR 1.40, 95% CI 1.16-1.69), left ventricular hypertrophy (27.0%, OR 1.47, 95% CI 1.14-1.89), atrial fibrillation (33.9%, OR 1.70, 95% CI 1.38-2.10), intraventricular conduction delay (42.8%, OR 1.85, 95% CI 1.38-2.46) and left bundle branch block (39.7%, OR 2.03, 95% CI 1.49-2.77). Among unwitnessed arrests, the prevalence of a shockable initial rhythm was lower and associations were less consistent.

Among bystander-witnessed arrests, pathological Q-waves, left ventricular hypertrophy, atrial fibrillation, intraventricular conduction delay and left bundle branch block on the most recent hospital-recorded ECG within 30-365 days before OHCA were associated with higher odds of a shockable initial rhythm compared with individuals with normal ECGs.