Marked bradycardia in a young woman with weight loss.

A 21-year-old woman with a history of disabling irritable bowel syndrome (IBS) was admitted to the internal medicine ward with abdominal pain. During the last few weeks she had experienced a 15% weight loss due to malnourishment secondary to the abdominal complaints and light-headedness upon standing, but no syncope. Because of a regular heart rate of 35 beats/min an electrocardiogram was taken (figure 1) after which she was transferred to the cardiology department for further examination and observation. All laboratory analyses including serum sodium, potassium, magnesium, calcium, phosphate and thyroid-stimulating hormone were in the normal range. The medication used by our patient was not known to influence cardiac conduction or cause arrhythmias.