ECG Quiz Answer: An Irregular Pulse in a Skydiver

John D. Cantwell, MD

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Diagnosis

The resting ECG shows 5:4 Wenckebach second-degree atrioventricular (AV) block (figure 2). The loudness of the first heart sound is inversely related to the length of the PR interval on the resting ECG. A longer PR interval allows the AV valves more time to drift closer to the closed position, resulting in a softer sound. The exercise ECG is normal (figure 3); the PR intervals usually become regular as the athlete exercises.

Discussion

In 1906, the noted Dutch physician Karel Frederik Wenckebach first reported periodic prolongation of the PR interval with dropped ventricular beats (1). Wenckebach had previously discovered that extrasystoles were seen in healthy individuals as well as in those with cardiac disease.

Wenckebach AV block (also referred to as Mobitz type I AV block) can be normal in a highly-trained athletic person such as this patient. It is probably related to an increase in resting vagal tone and subsides during the stress of exercise when blood catecholamine levels rise.

We advised the company that the young man was healthy and recommended that he be hired. We added that his maximum oxygen uptake was 54.7 mL/kg/min, placing him in the high fitness category for men his age.

Reference

1. Fye WB: Karel Frederik Wenckebach, 1864-1940. Clin Cardiol 1990;13(2):146-148

Dr Cantwell is director of preventive medicine and cardiac rehabilitation at Georgia Baptist Medical Center and clinical professor of medicine at Morehouse School of Medicine in Atlanta. He is a member of the editorial board of The Physician and Sportsmedicine and chief medical officer of the 1996 Centennial Olympic Games. Address correspondence to John D. Cantwell, MD, 340 Boulevard NE, Suite 200, Box 413, Atlanta, GA 30312.

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