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Urgent message: Identifying the most likely cause of a 73-year-old male’s sensation that his heart is “missing beats” — while being mindful of the most potentially serious sources—will guide decisions on the right course of action. The ECG you order will offer invaluable clues as to the appropriate steps to take.

By John F. O’Brien, MD

The patient is a 73-year-old male who presents with a primary complaint that it occasionally feels as if his heart is “missing beats.” He wonders aloud whether his pacemaker is working properly.
An ECG is administered immediately. Review it and consider the following questions (which will be discussed below):

1. What does this ECG suggest?

2. Does this patient need emergent referral and treatment?


1. This ECG is more easily interpreted if one looks at a lead where the P waves are easily distinguished from the T waves, like V1 (as they look alike in many other leads). Here we see atrioventricular dissociation—although there may be AV capture of the second-to-last ventricular beat.

The atrial rate is slightly less than 100 beats per minute, with the ventricular rate around 50 beats per minute. Every ventricular beat is preceded by a pacing spike, with the QRS complex showing an appropriate left bundle branch block pattern.

2. There is no need for emergent referral or immediate treatment of the findings on this ECG.

However, there is failure of appropriate atrial tracking. This implies a problem with atrial depolarization sensing by the pulse generator of the pacemaker.

The patient requires non-urgent referral to his cardiologist for further evaluation of his pacemaker.

Dr. O’Brien is the associate residency director of the Department of Emergency Medicine at Orlando Regional Medical Center in Orlando, FL. He is also an associate professor at the University of Central Florida School of Medicine and Florida State University School of Medicine. Dr. O’Brien has received numerous teaching awards on the local and national levels.

ECG Challenge: A 73-year-old Male with Concerns About His Pacemaker
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