Effects of diltiazem on left ventricular systolic and diastolic function in hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HC) is characterized by impaired diastolic function, and left ventricular (LV) outflow tract obstruction in about one-fourth of patients. Verapamil improves diastolic properties, but may have dangerous adverse effects. This study investigates the effects of diltiazem on hemodynamics and LV function in 16 patients with HC who were studied with cardiac catheterization and simultaneous radionuclide angiography. Studies were performed during atrial pacing (15 beats above spontaneous rhythm) at baseline and during intravenous diltiazem administration (0.25 mg x kg(-1) over 2 minutes, and 0.014 mg x kg(-1) x min(-1). Diltiazem induced a systemic vasodilation (cardiac index: 3.4 +/- 1.0 to 4.0 +/- 1.0 L x min(-1) x m(-2), p = 0.003; aortic systolic pressure: 116 +/- 16 to 107 +/- 19 mm Hg, p = 0.007; systemic resistance index: 676 +/- 235 to 532 +/- 193 dynes x s x cm(-5) x m(-2), p = 0.006), not associated with changes in the LV outflow tract gradient. The end-systolic pressure/volume ratio decreased (30 +/- 42 to 21 +/- 29 mm Hg x ml(-1) x m(-2); p = 0.044). Pulmonary artery wedge pressure (11 +/- 5 to 15 +/- 6 mm Hg, p = 0.006), and peak filling rate increased (4.1 +/- 1.3 to 6.0 +/- 2.4 stroke counts x s(-1), p = 0.004). The time constant of isovolumetric relaxation tau decreased (74 +/- 40 to 59 +/- 38 ms, p = 0.045). The constant of LV chamber stiffness did not change. Thus, active diastolic function is improved by the acute administration of diltiazem by both direct action and changes in hemodynamics and loading conditions. LV outflow tract gradient does not increase despite systemic vasodilation. In some patients, however, a marked increase in obstruction and a potentially harmful elevation in pulmonary artery wedge pressure do occur. Passive diastolic function is not affected.