Interatrial Block Detected by a Series of ECGs Before and During Acute Coronary Syndrome Predicts Atrial Fibrillation, Atrial Flutter, and Ischemic Stroke.

Background: Interatrial block (IAB) in an ECG, manifesting atrial pathology, is a possible risk factor for atrial arrhythmias and ischemic stroke. IAB is often transiently expressed, posing a major challenge for risk estimation when only a limited number of ECGs are available.

Methods: This is a retrospective study of 9674 consecutive patients diagnosed with acute coronary syndrome (ACS) between 2007 and 2018. All standard ECGs registered between January 2007 and March 2023 (n=206 668) were digitally stored and analyzed using the General Electric Marquette 12SL algorithm for the presence of an IAB, atrial fibrillation, and atrial flutter. The population was stratified by the extent of the IAB, and patients without an IAB served as controls. Clinical phenotype data and end point data for ischemic stroke were collected by a full disclosure review of hospital records and death certificate data including written accounts of deaths.

Results: The prevalence of an advanced IAB was 8.5% if all previous ECGs, including those recorded during ACS, were screened, whereas it was only 2.4% during ACS. The risk of atrial fibrillation/atrial flutter after ACS increased with the severity of the IAB, and the highest risk was attributable to advanced IAB (age- and sex-adjusted hazard ratio [HR], 2.87 [95% CI, 2.48-3.32]; P<0.00001; and fully risk-factor adjusted [including left ventricular ejection fraction] HR, 2.22 [95% CI, 1.89-2.62]; P<0.00001). Advanced IAB was also associated with an almost 2-fold risk of ischemic stroke if adjusted for the CHA₂DS₂-VASc score (HR, 1.95 [95% CI, 1.47-2.58]; P<0.00001).

Conclusions: Automatic detection of an IAB from serial ECGs reveals a strong association between atrial pathology and the risk of atrial fibrillation, atrial flutter, and ischemic stroke in patients with ACS.