Two QRS Complexes for a Single P Wave: What is the Mechanism?

Abstract

Case PresentationA 49-year-old man with hypertension was found to have an irregular heart rhythm during preoperative evaluation for kidney stone. The patient also noted fatigue, neck throbbing, and dyspnea on exertion for 6-8 months. Echocardiogram showed mild left ventricular dysfunction with ejection fraction of 40%. Coronary angiogram revealed nonobstructive coronary artery disease. An initial trial of dronedarone was discontinued due to gastrointestinal side effects. He was subsequently referred to our center for second opinion. The initial electrocardiogram (ECG) is shown in Figure 1. During the electrophysiology study, the baseline intracardiac electrogram demonstrated a single atrial activity following by 2 Hisian activities (Fig. 2). What is the mechanism of arrhythmia in this case? CommentaryAt a glance, the baseline ECG in this case (Fig. 1) showed a pattern of grouped beating. There was an absence of nonconducted P wave and the P waves of the first and third beats in each group were marching through with the cycle length of approximately 1,000 milliseconds. These findings suggested that the patient was in normal sinus rhythm with an additional QRS complex representing the second beat in each group. The similarity of the QRS morphology between ectopic beat and sinus beat excluded ventricular or fascicular ectopy and was consistent with supraventricular origin. Given these findings on the baseline ECG, there were 3 possible mechanisms of the ectopic beats: premature atrial complex, 1:2 Atrioventricular (AV) node physiology, and AV nodal or Hisian ectopy. The 1:2 AV node physiology refers to an antegrade conduction of sinus rhythm through both the fast and slow AV nodal pathways. Of note, the PR interval of