ECG Challenge: Heart Racing and Short of Breath

Philip J. Podrid, MD


April 20, 2020

The correct diagnosis is atrial fibrillation, bibundle branch block, trifascicular disease (Figure 2).

Figure 2. Courtesy of Philip J. Podrid, MD


The rhythm is irregularly irregular (ie no consistency to the RR intervals). There are three supraventricular rhythms that are irregularly irregular:

  1. Sinus arrhythmia, in which there is one P wave morphology and one PR interval.

  2. Wandering atrial pacemaker (when the rate is < 100 beats/min) or multifocal atrial tachycardia (when the rate is ≥ 100 beats/min). In this situation, there are three or more different P wave morphologies and often different PR intervals and none of the P wave morphologies is dominant.

  3. Atrial fibrillation, in which there are no organized P waves but rapid and irregular fibrillatory waves.

In this ECG, there are no organized P waves, but irregular undulations of the baseline are especially obvious in lead V1 (^). The undulations are irregular in amplitude, morphology, and interval. Therefore, the rhythm is atrial fibrillation (not atrial flutter).

There are three different QRS complex morphologies. Complexes 1, 3, 6-11, and 13-15 are wide (0.16 sec) and they have a left bundle branch block morphology with a broad R wave in lead I and V6 (v) and a deep QS wave in lead V1 (↓). Complexes 5, 6, and 12 are also wide (0.16 sec), and they have a morphology of a right bundle branch block with an RSR' in lead V1 (→) and a broad terminal S wave in lead V5 (←).

The presence of both right and left bundle branch block is termed "bibundle branch block," and this is a manifestation of trifascicular disease. The alternating bundle branch block is not related to rate and appears to be intermittent. The QT/QTc intervals are normal: 360/440 msec and 300/370 msec when the prolonged QRS complex duration is considered. The second QRS complex (*) resembles neither of the other two complexes and is therefore a premature ventricular complex.

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.

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