ECG Challenge: What Caused This Man's Atrial Arrhythmia?

Philip J. Podrid, MD

Disclosures

September 27, 2021

The correct diagnosis is atrial fibrillation with PVC and Ashman phenomenon (Figure 2).

Figure 2.

Discussion

The rhythm is irregularly irregular without any organized atrial activity. Most of the QRS complexes are narrow, with normal morphology and a physiologic left axis between 0 and -30 degrees (positive QRS complex in leads I and II, and negative in lead aVF). Only three supraventricular rhythms are irregularly irregular:

  • Sinus arrhythmia (a normal respirophasic arrhythmia) in which there is 1 P wave morphology and stable PR interval.

  • Multifocal atrial rhythm/wandering atrial pacemaker with a rate < 100 beats/min or multifocal atrial tachycardia with a rate > 100 beats/min in which there are three or more different P wave morphologies, none of which is dominant. PR intervals are variable.

  • Atrial fibrillation in which there are no organized P waves but there are fibrillatory waves.

The arrhythmia is atrial fibrillation. There are two premature ventricular contractions (PVCs) (*) — complexes 2 and 6 — with the same morphology; ie, they are unifocal PVCs. The first two complexes in leads V-V3 (+) are wide and show a right bundle branch block (RBBB) morphology with an RSR' morphology in lead V1 (←). These two complexes are preceded by a long (↔) short (⨆) cycle.

Although this may be considered rate related RBBB, there are other RR intervals that are shorter (∏) and are not associated with a RBBB, indicating an Ashman phenomenon.

Rate-related bundles are caused by underlying disease of the His-Purkinje system, affecting the ability to conduct at a faster rate, whereas the Ashman phenomenon is caused by normal rate-related changes in His-Purkinje refractoriness that are unrelated to any abnormality of the system itself.

The same change accounts for rate-related changes in the QT interval. When heart rate is slow, His-Purkinje refractoriness lengthens (hence, a longer QT interval). When heart rate accelerates, His-Purkinje refractoriness shortens (and thus a shorter QT interval). With an abrupt increase in heart rate, His-Purkinje refractoriness does not adapt quickly and is still long due to the slow rate. Therefore, one or several complexes may not be conducted and will be blocked in the part of the conduction system that is still refractory, manifesting the aberration. This often presents as a RBBB, possibly because the right bundle has a longer refractoriness compared with the left bundle. The Ashman phenomenon is seen commonly with atrial fibrillation in which there are frequent changes in heart rate.

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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