A Woman in Her Late 50s With Palpitations and Light-headedness.

A white woman in her late 50s presented with palpitations, breathlessness, chest pain, and episodes of light-headedness. Her risk profile included a family history of sudden cardiac death: her cousin died unexpectedly in his mid-40s while playing football. A physical examination showed no remarkable findings. Her systolic blood pressure was 125 mm Hg, diastolic blood pressure was 70 mm Hg, and resting heart rate was 52 beats/min. Portions of her electrocardiogram (Figure 1A) and 24-hour Holter monitoring trace (Figure 1B) are shown. Echocardiographic findings included mildly impaired systolic function (left ventricular ejection fraction, 45%-50%) but were otherwise normal. Coronary angiography was performed and revealed normal coronary arteries.