ECG Challenge: A Routine Check-up Reveals Cardiac Abnormalities

Philip J. Podrid, MD

Disclosures

March 01, 2021

The correct diagnosis is AV dissociation with an accelerated junctional rhythm (Figure 2).

Figure 2. Courtesy of Dr Podrid.

Discussion

There is a regular rhythm, although the fourth and ninth QRS complexes (*) are slightly early — ie, a shorter RR interval. The QRS complexes are narrow and have a normal morphology and axis. The rate of the QRS complexes is 75 beats/min. P waves occur (+) at a regular rate (↔) of 58 beats/min. There is no relationship between the P waves and the QRS complexes — ie, the PR intervals are variable. This is AV dissociation.

There are two etiologies for AV dissociation. One is complete heart block, in which the atrial rate is faster than the rate of the QRS complexes, which represent an escape rhythm and may be junctional or ventricular on the basis of the QRS complex morphology and not the rate of the escape rhythm. Another etiology is accelerated lower pacemaker, which may be junctional or ventricular (atrial rate slower than rate of the QRS complexes).

Because the rate of the QRS complexes is faster than the atrial rate, this is sinus bradycardia with an accelerated junctional rhythm. The fourth and ninth QRS complexes that are slightly early are preceded by P waves and the same PR interval. Hence, these are captured complexes.

Philip Podrid, MD, is an electrophysiologist, a professor of medicine and pharmacology at Boston University School of Medicine, and a lecturer in medicine at Harvard Medical School. Although retired from clinical practice, he continues to teach clinical cardiology and especially ECGs to medical students, house staff, and cardiology fellows at many major teaching hospitals in Massachusetts. In his limited free time he enjoys photography, music, and reading.

You can follow Dr Podrid on Twitter @PPodrid

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