Pseudo–Heart Block and Pseudo-Brugada Morphology From Signal-Averaging Artifact During Exercise Stress Testing

A 57-year-old woman with atypical chest pain presented for exercise stress testing with myocardial single-photon emission computed tomography perfusion imaging. The patient had a history of hypertension and hypothyroidism but no other history of coronary disease or risk factors. The patient's baseline ECG is shown in Figure 1, interpreted as incomplete right bundle-branch morphology. During exercise stress testing, apparent 2:1 A:V conduction occurred, as shown in Figure 2A. Physicians reading the exercise stress test also interpreted ST elevation most prominent in lead V1 as consistent with the type 1 Brugada ECG pattern.1 Intermittent 2:1 A:V block appeared to resolve at high heart rates in Figure 2B. The test was terminated, and the patient appeared to return to normal sinus rhythm conduction with resolution of the ST deviation, as in Figure 2C. She was referred to the electrophysiology service for consideration of pacemaker implantation.Figure 1. ECG tracing of the patient before stress testing. A magnified section of V1 is shown in the window . Although interpreted as incomplete right bundle-branch block by referring physicians, the QRS duration of <100 ms does not meet formal criteria for this diagnosis. The …