Nakatani M, Yokota Y, Yokoyama M. Kobe University School of Medicine, Japan. Clin Cardiol 1996 May;19(5):385-92. BACKGROUND AND HYPOTHESIS: Supraventricular tachycardia and ventricular tachycardia are often observed in patients with hypertrophic cardiomyopathy (HCM) and they often alter the clinical features of HCM. We examine the influence of supraventricular tachycardia on cardiac function and assess the clinical characteristics of patients with HCM. METHODS: We studied 32 patients with HCM and 8 normal volunteers using echocardiography under transesophageal rapid atrial pacing. RESULTS: Presyncope-associated hypotension was observed during rapid atrial pacing in 8 HCM patients, but in none of the normal controls. During rapid atrial pacing (144 +/- 8 beats/min in HCM, 146 +/- 5 beats/min in controls), systolic blood pressure (SBP), the product of left ventricular filling volume (FV) and heart rate, and fractional shortening (%FS) in the HCM patients decreased significantly compared with the basal values (138 +/- 19 mmHg vs. 99 +/- 24 mmHg, 5.0 +/- 1.2 l/min vs. 2.9 +/- 0.9 l/min, 41.7 +/- 6.2% vs. 35.2 +/- 6.0%, respectively), but these decreases were not observed in normal controls. The decrement of SBP during rapid atrial pacing in HCM patients with a history of syncope was more marked than that in those without such history. The decrement correlated positively with the indices of left ventricular hypertrophy (maximal wall thickness and wall thickness index) and with %FS, and correlated negatively with the endsystolic left ventricular diameter at rest. CONCLUSIONS: In some patients with HCM, supraventricular tachycardia causes marked hemodynamic deterioration that may be related to a history of syncope, marked hypertrophy, hyperkinesis, small cavity size, and small filling volume of the left ventricle.