ECG Challenge: On-Again, Off-Again Lightheadedness

Medscape

20-06-2025

A 72-year-old man with a history of coronary artery disease treated medically presents to his primary care provider with complaints of palpitations and occasional episodes of lightheadedness. He has had episodic lightheadedness with presyncope, but no syncope, over the past 2 months. The episodes have become more frequent over the past 2 weeks. While an ECG is obtained, he complaints of lightheadedness.
Figure 1. Courtesy of Philip J. Podrid, MD.
The correct diagnosis is tachycardia-bradycardia (sick sinus syndrome; Figure 2).
Figure 2. Courtesy of Philip J. Podrid, MD.
Discussion
The initial four RR intervals are irregularly irregular. No organized P waves are seen, but there are irregular undulations of the baseline (^). The QRS complexes have a normal duration (0.08 sec) and morphology. Therefore, the initial rhythm is atrial fibrillation.
The atrial fibrillation abruptly terminates after the first four QRS complexes, followed by a QRS complex (*) that has the same duration and morphology as the first four. However, no P wave occurs before this QRS complex. Therefore, this is a junctional escape complex.
This is followed by three additional junctional QRS complexes (v). The RR intervals are shortening (rate faster) because the junctional complexes are from an ectopic focus which manifests a change in its rate. The last two QRS complexes have the same duration and morphology. However, they are preceded by a P wave (+) with a stable PR interval (0.16 sec). Thus, these are sinus complexes. The QT/QTc intervals are normal (320/390 msec). After the termination of the atrial fibrillation there is a delay of 8 seconds before sinus rhythm is restored. This represents a tachycardia-bradycardia (tachy-brady) syndrome, which is a common manifestation of sick sinus syndrome.
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.