Lyle W. Larson, PhD, PA-C, is clinical faculty in the Department of Medicine, Division of Cardiology, Cardiac Electrophysiology, at the University of Washington, Seattle.
ANSWER
The correct interpretation is atrial fibrillation with aberrantly conducted complexes. The lead I rhythm strip at the bottom of the ECG shows the irregularly irregular rate. There are narrow complexes (see beats 3-7 and 16-18), indicating normal conduction through the atrioventricular node and His-Purkinje system. The remainder of the complexes are wide and aberrantly conducted and are in the same vector as the normally conducted (narrow) complexes.
An important take-away from this case: The computer reading includes a PR interval as well as a QRS duration of 88 ms. There is no PR interval in atrial fibrillation—highlighting the importance of reading the ECG and not relying on the computer’s interpretation. The QRS duration is measured in the normally conducted beats only; it does not include the aberrantly conducted beats.
