TEMPOThe Effect of Metoprolol on Myocardial Function, Perfusion, Hemodynamics and Heart Failure Symptoms in Patients With Hypertrophic Obstructive Cardiomyopathy.

Background Hypertrophic cardiomyopathy (HCM) is characterized by an increase in left-ventricular wall thickness, typically localized at the interventricular septum. The hypertrophy can increase to an extend that causes a dynamic obstruction of the left ventricular outflow tract (LVOTO); these patients have hypertrophic obstructive cardiomyopathy (HOCM). Due to the obstruction, patients develop high interventricular pressure gradients, which may overtime become detrimental to the left ventricular function. HOCM patients often develop disabling symptoms of heart failure. Current treatment strategies are predicated on the empirical use of long-standing drugs, such as beta-adrenergics, although with little evidence supporting their clinical benefit in this disease. Metoprolol is currently the most widely used beta-blocker in symptomatic HOCM patients, but a randomized, placebo-controlled trial, that looks at the effect in HOCM patients has never been conducted. No studies of HOCM combine invasive pressure measurement with exercise and echocardiography. All previous studies, both invasive and echocardiographic, have been conducted during rest, and not during exercise. Symptoms of HOCM patients are function-related, and exercise testing is essential to assess the condition and the effect of drugs. Objective The investigators wants to quantify the effects of metoprolol on myocardial function and perfusion, hemodynamics and heart failure symptoms in patients with HOCM. Hypotheses Primary • Metoprolol treatment reduces ∆ pulmonary capillary wedge pressure (PCWP) (rest-exercise) Secondary * Metoprolol treatment reduces PCWP at rest * Metoprolol treatment increases maximal oxygen consumption (VO2-max) . * Metoprolol treatment reduces LVOT gradient during exercise * Metoprolol treatment increases the coronary flow reserve * Metoprolol treatment decrease External Work * Metoprolol treatment reduces heart failure symptoms, estimated by the Kansas City Cardiomyopathy Questionnaire Design and methods A randomized, double-blinded, placebo-controlled, crossover study, anticipated to examine 32 patients with HOCM both during treatment with metoprolol and placebo. Patients will be examined in a set-up of simultaneous 1) right heart catheterization 2) cardiopulmonary exercise test and 3) transthoracic echocardiography. The set-up allows the investigators to evaluate the hemodynamic values during rest and maximum exercise.