Hemodynamic determinants of exercise-induced abnormal blood pressure response in hypertrophic cardiomyopathy

OBJECTIVES: We sought to assess the hemodynamics of exercise in patients with hypertrophic cardiomyopathy (HCM), with and without an exercise- induced abnormal blood pressure (BP) response, by ambulatory radionuclide monitoring of left ventricular (LV) function with the VEST device (Capintec Inc., Ramsey, New Jersey). BACKGROUND: Blood pressure fails to increase >20 mm Hg during exercise in about one-third of patients with HCM. This carries a high risk of sudden death. METHODS: Forty-three patients with HCM and 14 control subjects underwent maximal symptom- limited exercise on a treadmill during VEST. The VEST data were averaged for 1 min and analyzed at baseline, 3 min and peak exercise. The LV end- diastolic, end-systolic and stroke volumes, cardiac output and systemic vascular resistance were expressed as the percentage of baseline. RESULTS: Ejection fraction and stroke volume fell in patients with HCM, although they increased in control subjects (p < 0.001 and p = 0.002, respectively). Cardiac output increased significantly more in control subjects than in patients with HCM (p = 0.001). In 17 patients with HCM (39%) with an abnormal BP response, ejection fraction and stroke volume fell more (p = 0.032 and p = 0.009, respectively) and cardiac output increased less (p = 0.001) than they did in patients with HCM with a normal BP response. Systemic vascular resistance decreased similarly in patients with HCM, irrespective of the BP response. CONCLUSIONS: In patients with HCM with and without an abnormal BP response, abnormal hemodynamic adaptation to exercise was qualitatively similar but quantitatively different. An abnormal BP response was associated with exercise-induced LV systolic dysfunction. This causes hemodynamic instability, associated with a high risk of sudden cardiac death.