ECG Review

Bradycardia with a Cause

Figure: 12-lead ECG obtained from an 81-year old man with bradycardia.

By Ken Grauer, MD, Professor, Department of Community Health and Family Medicine, University of Florida. Dr. Grauer is the sole proprietor of KG-EKG Press, and publisher of an ECG pocket brain book.

Clinical Scenario:

There is a cause for the slow ventricular rate that is seen in this 12-lead ECG, obtained from an 81-year-old man. What is the cause likely to be?

Interpretation/Answer:

The rhythm appears to be sinus bradycardia at a rate of just over 50 beats/minute. Clearly, an upright sinus P wave with a fixed and normal PR interval is seen to precede each QRS complex in the Lead II rhythm strip at the bottom of the tracing. However, this is not the cause of the slowed ventricular rate. Instead, close inspection of selected leads on this 12-lead ECG suggest the presence of additional atrial activity. This is perhaps best seen in lead V1 (dots in this lead). Despite the artifactual baseline wander seen in this lead, a regularly occurring negative P wave at a rate of 100/minute is seen. That there is an underlying, regular atrial rate at 100/minute is further suggested by the presence of a subtle but real 'extra shoulder' (See arrow) on the terminal portion of the T wave in each of the inferior leads, as well as a slight peak to the T wave in lead V3. Confirmation that the rhythm is 2° AV block with 2:1 AV conduction was forthcoming on subsequent tracings, when further slowing of the atrial rate resulted in clearly discernable separation of the extra P wave from the end of preceding T wave. Otherwise, there is IRBBB (incomplete right bundle branch block), and minimal non-specific ST segment flattening on the ECG, but no acute changes.

An important point to emphasize is that at times, definitive diagnosis of the rhythm is simply not possible from a single tracing. As was the case here, subsequent tracings may be needed for clarification. Our suspicion that additional P waves were 'hiding' in the terminal part of the T wave could only be confirmed by additional tracings after the heart rate had slowed.