This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Ott, P. Search for Related Content PubMed PubMed Citation Articles by Ott, P. Related Collections Electrocardiology Arrhythmias, clinical electrophysiology, drugs Chronic ischemic heart disease

(Circulation. 2001;103:617.)
© 2001 American Heart Association, Inc.

Images in Cardiovascular Medicine

Unusual ECG

Peter Ott, MD

From the University of Arizona Health Sciences Center, Department of Medicine, Sarver Heart Center, Tucson.

Correspondence to Peter Ott, MD, University of Arizona Health Sciences Center, Department of Medicine, Sarver Heart Center, 1501 N Campbell Ave, Tucson AZ 85724. E-mail: ottp@u.arizona.edu

A 72-year-old woman was admitted because of a near-syncopal episode. Her ECG showed a normal sinus rhythm at a rate of 65 bpm, and her PR interval was prolonged (240 ms). The ECG also showed a pattern of right bundle branch block and left posterior hemiblock. The morphology of the QRS complex was identical to that of QRS complexes 3 and 5 on the ECG. Her heart rhythm became irregular, and an ECG was recorded (Figure).

View larger version (47K): [in this window] [in a new window]   Figure 1. A 12-lead ECG and lead II rhythm strip. Note that because of the slow heart rate, not all leads show each QRS complex. In addition, lead V6 did not record.

The rhythm was sinus (rate, 65 bpm) with 2:1 and Wenckebach-type atrioventricular conduction. Of interest is the changing QRS morphology. QRS complexes 1, 2, 4, and 6 are conducted with a right bundle branch block/left anterior hemiblock pattern; thus, ventricular activation occurs via the left posterior fascicle. However, this QRS pattern occurs only after a long R-R interval, which is due to atrioventricular block. Thus, block in the left anterior fascicle is bradycardia-dependent. When the QRS is conducted with a short R-R interval, the left anterior fascicle conducts before (ahead of) the left posterior fascicle, thus resulting in a left posterior hemiblock pattern. Slow, rather than blocked, conduction in the left posterior fascicle explains its ability to conduct during bradycardia-dependent left anterior hemiblock, thus resulting in a wider QRS complex. This is best seen when comparing QRS complexes 4 and 5 in lead . . . [Full Text of this Article]