ECG Challenge: 'I'm Having Trouble Breathing'

Philip J. Podrid, MD


January 04, 2021

The correct diagnosis is accelerated idioventricular rhythm, or slow ventricular tachycardia (Figure 2).

Figure 2. Courtesy of Dr Podrid.


There is a regular wide complex rhythm at a rate of 95 beats/min. Occasional P waves occur (+) before some but not all of the QRS complexes, indicating atrioventricular (AV) dissociation. Consistent with AV dissociation is the presence of a fusion complex (QRS complex 2 -*) — which is preceded by a P wave (+) and has a different morphology compared with the other QRS complexes (**) — and normal or captured QRS complexes (o), also termed Dressler beats. They result from an atrial impulse that occasionally passes through the AV node to partially or completely fuse with the ventricular complex generated within the ventricular myocardium.

A P wave (+) occurs before the fused complex (*-complex 2) and a P wave (v) occurs before the captured complexes (o); the PR intervals (▲) associated with these two captured complexes are the same. The QRS complexes are wide and do not have a morphology reminiscent of a typical right or left bundle branch block. In addition, the axis is indeterminate (negative QRS complex in leads I and aVF). An indeterminant axis with a wide QRS complex indicates direct myocardial activation, as seen with a biventricular paced complex, Wolff-Parkinson-White syndrome, or a ventricular complex.

The presence of AV dissociation and an indeterminate axis is consistent with a ventricular rhythm. Because the rate is less than 100 beats/min, this is an accelerated idioventricular rhythm (AIVR) or slow ventricular tachycardia. Irregularities in ST-T waves (^) are consistent with a ventricular rhythm and may be superimposed dissociated P waves. The ventricular rate may be slow as a result of amiodarone.

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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