[Posture-dependent left ventricular outflow tract obstruction in a case of Lewy body dementia that presented with transient loss of consciousness].

An 80-year-old woman with a history of hypertrophic obstructive cardiomyopathy and Lewy body dementia was admitted to our hospital with a first episode of syncope while walking. The pressure gradient of left ventricular outflow tract (LVOT) had been stable at nearly 10 mmHg for 3 years before the admission. We evaluated the cause of syncope. Echocardiography showed that the pressure gradient of LVOT was unchanged, even in the supine position ergometer exercise test. Although the head-up tilt test revealed a drop in blood pressure of 44 mmHg systolic and 23 mmHg diastolic, she was asymptomatic during the test. The orthostatic hypotension was considered to be a manifestation of autonomic failure due to Lewy body dementia; however, it was insufficient to explain the syncope on exertion. Echocardiography in a sitting-up position showed that the pressure gradient of LVOT was exacerbated to 41 mmHg, which might be the cause of syncope while walking. Orthostatic hypotension, especially in patients with Lewy body dementia, is a common cause of syncope in the elderly. However, we should keep in mind that the exacerbation of LVOT obstruction due to posture-dependent fluid shift can be a cause of syncope in patients with hypertrophic cardiomyopathy or sigmoid-shaped interventricular septum. In such patients, echocardiography in a sitting-up position can be an effective tool to diagnose the cause of syncope.