atrial arrhythmia atrial premature beat 2026-05-04T14:15:01Z atrial extrasystole APC atrial ectopics MP:0031730 AEB MPheno.ontology AES PAC atrial premature complex APB atrial ectopic beat premature atrial contraction an extra heart beat originating from an ectopic focus within the atria, rather than the sinoatrial node, and characterized on ECG by an abnormal (non-sinus) P wave, usually followed by a normal QRS complex