The ECG may simply show sinus rhythm or sinus bradycardia. This is different than a first-degree atrioventricular, or AV, block, which shows a prolonged PR interval. Second-degree sinoatrial exit ...

In fact, up to 60% of athletes demonstrate ECG changes (in isolation or in combination) such as sinus bradycardia, sinus arrhythmia, first-degree atrioventricular (AV) block, early repolarisation, ...

including sinus pause, heart block, and cardiac arrest have occurred with the use of Toprol-XL. Increased risk for bradycardia in patients with first-degree AV block, sinus node dysfunction ...