ECG Challenge: In the ED With Palpitations and Shortness of Breath

Philip J. Podrid, MD


November 30, 2021

The correct diagnosis is atrial fibrillation with complete heart block and an escape junctional rhythm (Figure 2).

Figure 2.


The QRS complexes are narrow and have a normal morphology. The axis is physiologically leftward with a positive QRS complex in lead I and II, and negative in lead aVF. The QRS complex voltage is low in each limb lead (ie, < 5 mm in amplitude). The voltage is low in the precordial leads, although not truly low (defined as < 10 mm in amplitude).

The QRS complexes occur at a regular interval of 40 beats/min. Prominent atrial waves are present in lead V1 (^), but the atrial waveforms are not organized and are irregular in morphology, amplitude, and interval. This irregular pattern is also apparent in leads II, III, and aVF.

Hence this is coarse atrial fibrillation (AF) and not atrial flutter. With atrial flutter, caused by a single reentrant circuit, the atrial waveforms are uniform in morphology, amplitude, and interval, showing a "sawtooth"-like morphology. Occasionally the rhythm seen here is termed "fib-flutter," but this is not a true arrhythmia.

Although atrial flutter may convert to AF, the two arrhythmias do not exist at the same time under normal situations. The coarse atrial fibrillatory waveforms generally indicate a recent-onset arrhythmia, and over time (months to years) the waveforms become finer. Additionally, the coarser the fibrillatory waves are, the higher the success rate of cardioversion and the lower the energy needed.

With AF, the RR intervals are irregularly irregular. The regularity of the QRS complexes (regularization of AF) indicates a complete heart block. Because the QRS complexes are narrow and normal, the escape rhythm is junctional; hence, the heart block is at the level of the atrioventricular (AV) node. This could be due to the beta-blocker, high vagal tone, or intrinsic AV nodal disease.

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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