Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 42-year-old woman is evaluated for episodes of palpitations that last several seconds in duration. They occur once or twice a month and are accompanied by lightheadedness and mild dyspnea. She has not experienced loss of consciousness. The episodes are not precipitated by any particular activity, including exercise. She takes no medications.

On physical examination, the patient is afebrile, blood pressure is 110/68 mm Hg, pulse rate is 72/min, and respiration rate is 16/min. BMI is 29. Cardiac examination reveals physiologic splitting of S₂, regular rate and rhythm, and no gallop. Estimated central venous pressure is normal. She has no edema. Serum thyroid-stimulating hormone level is normal.

A 12-lead electrocardiogram shows normal sinus rhythm.

Which of the following is the most appropriate diagnostic testing option?

A: 30-Day wearable loop recorder
B: Echocardiogram
C: Exercise treadmill stress test
D: 48-Hour ambulatory electrocardiographic monitor
E: Implantable loop recorder

MKSAP Answer and Critique

The correct answer is A: 30-Day wearable loop recorder.

This patient’s symptomatic episodes are intermittent and short-lived; therefore, a 30-day wearable recorder with looping memory is the best diagnostic strategy to uncover the nature of her palpitations. These recorders are worn continuously and record a continuous “loop” of heart rhythm. When the patient experiences symptoms, she can depress a button and the device captures the rhythm before, during, and after the symptoms. Loop recorders are useful for recording episodes accompanied by syncope or presyncope and for episodes that are too short to be captured by a patient-triggered event recorder.

A patient-triggered event recorder (without looping memory) is useful for recording infrequent episodes that last long enough (1-2 minutes) for the patient to hold the device to the chest and trigger it to capture the heart rhythm. A self-applied event recorder is not useful for brief episodes because the time taken to apply the monitor may be longer than the symptomatic episode.

If a patient has an abnormal cardiovascular examination or is demonstrated to have an arrhythmia, echocardiography should be performed to evaluate for the presence of structural heart disease. In this patient, however, the cardiac examination is normal, and there is no documentation of an arrhythmia at this point. Many patients with symptoms suggestive of arrhythmia are found to have causes for their symptoms that are not related to heart rhythm.

An exercise treadmill stress test would be reasonable if the episodes were precipitated by exertion or exercise, but this patient’s episodes are not associated with exertion.

Given the infrequency of this patient’s symptoms, 48-hour ambulatory electrocardiographic monitoring is not likely to capture the symptomatic episodes.

In patients with very infrequent or rare episodes (>30 days between episodes), an implanted loop recorder may be appropriate. These devices, which are approximately the size of a pen cap and are implanted under the skin of the chest next to the sternum, have several years of battery life. Although they are invasive, these devices have a higher diagnostic yield than other forms of outpatient heart rhythm monitoring.

Key Point

• A looping event recorder is useful for recording episodes of palpitations that are accompanied by syncope or presyncope and for episodes that are too short to be captured by a patient-triggered event recorder.

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