ECG Challenge: A 70-year-old man with a history of coronary artery disease and an ischemic cardiomyopathy with a left ventricular ejection fraction of 38% presents to the emergency room with complaints of lightheadedness. His medications include a β-blocker, an angiotensin-converting enzyme inhibitor, and Imdur. His pulse is noted to be slow, and a 12-lead ECG is obtained.
The rhythm is regular at a rate of 30 bpm. The QRS complexes are wide (0.14 second), and there is a left bundle-branch block morphology with a QS in lead V1 (←) and a broad R wave in leads I, V5, and V6 (→). The axis is normal between 0° and +90° (positive QRS complex in leads I and aVF). The QT/QTc intervals are prolonged (680/480 milliseconds) but are normal when corrected for the prolonged QRS complex duration (640/450 milliseconds). There is a P wave before each QRS complex (+), and the PR interval (^) is stable (0.28 second). Between each QRS complex, there are 2 nonconducted P waves (*). The PP intervals are constant (└┘) with a rate of 90 bpm. The P waves are positive in leads I, II, aVF, and V4 through V6; that is, this is a normal sinus rhythm. Thus, this is a second-degree atrioventricular block (ie, an occasional nonconducted on-time P wave). With Mobitz type I, there is only 1 nonconducted P wave, whereas with Mobitz type II, there may be ≥2 nonconducted P waves. Hence, this is Mobitz type II, which has been called high-degree atrioventricular block as a result of the 2 nonconducted P waves. Because the PR interval of the conducted P waves is prolonged (0.28 second), there is also a first-degree atrioventricular block or first-degree atrioventricular conduction delay.
Please go to the journal’s blog, OpenHeart, for more ECG Challenges: http://goo.gl/tQPNFp. Challenges are posted on Tuesdays and Responses on Wednesdays.
- © 2016 American Heart Association, Inc.