The correct diagnosis is sinus node reentry (Figure 2).
Figure 2. Courtesy of Philip J. Podrid, MD.
Discussion
The initial part of the ECG shows a rate of 150 beats/min, with an abrupt termination of the rhythm (↓) to a regular rhythm at a rate of 100 beats/min. The QRS complexes during the tachycardia are the same as the QRS complexes during the slower rate.
A P wave occurs before each QRS complex during the tachycardia (+) and also before each QRS complex with the slower rate (▼). The P wave morphology and PR intervals associated with the tachycardia are the same as those seen with the slower rate.
Although the initial rhythm appears to be a sinus tachycardia, there is an abrupt slowing of the rate to a normal sinus rhythm. Sinus tachycardia gradually slows. The abrupt slowing of the rate is consistent with a diagnosis of sinus node reentry which is established by the presence of an abrupt onset and abrupt offset of what appears to be a sinus tachycardia.
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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Cite this: ECG Challenge: Mid-Sternal Pain With Exercise - Medscape - Apr 24, 2023.
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