ECG Challenge: A Cardiac Patient With Slow Heartbeat and Fatigue

Philip J. Podrid, MD

Disclosures

May 24, 2022

The correct diagnosis is sinus bradycardia, AV dissociation, and accelerated junctional rhythm and occasional capture (Figure 2).

Figure 2.

Discussion

The rhythm is irregular, resulting from two premature QRS complexes (↓). Therefore, the rhythm is regularly irregular.

The other QRS complexes occur at a regular interval and a rate of 42 beats/min. These regular QRS complexes are normal in width (0.08 sec) and morphology and have an axis between 0 ° and +90 ° (positive QRS complex in leads I and aVF).

A tall R wave is present in lead V2 (v), which is consistent with early transition or counterclockwise rotation of the electrical axis in the horizontal plane. This is determined by picturing a view of the heart from under the diaphragm. With counterclockwise rotation, left ventricular forces develop early, resulting in the tall R wave in lead V2.

The QT/QTc intervals are normal (440 msec/370 msec). No P waves occur before any of these QRS complexes. However, P waves are present after each QRS complex (+,*) and have an inconsistent relationship with the QRS complex; ie, the RP interval is variable with progressive lengthening.

Although the P wave may be considered retrograde — resulting from the junctional complex, with retrograde ventriculoatrial Wenckebach accounting for the progressive lengthening of the RP interval — the P wave is positive in leads I, II, aVF, and V5. This is a sinus P wave, and a stable PP interval (⊔) occurs at a rate of 32 beats/min. Therefore, there is AV dissociation.

There are two etiologies for AV dissociation: a complete heart block (with an atrial rate faster than the rate of the QRS complexes) or an accelerated lower pacemaker (atrial rate slower than the rates of the QRS complexes).

Because the atrial rate is slower than the rate of the QRS complexes, this is an accelerated junctional rhythm with an underlying sinus bradycardia (rate of 38 beats/min). The two premature QRS complexes are preceded by an on-time P wave (*), and the PR interval is the same (^). The two complexes are captured or conducted. These captured complexes have a right bundle branch block with an RSR' morphology in lead V1 (←) and a broad S wave in leads I and V5 (→). The right bundle branch block is likely rate related, resulting from the shorter RR interval.

Philip J. 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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