Selective Heart Rate Reduction Improves Metabolic Syndrome-related Left Ventricular Diastolic Dysfunction.

Background: Enhanced heart rate observed in metabolic syndrome ( MS) contributes to the deterioration of left ventricular ( LV) function via impaired LV filling and relaxation, increased myocardial O-2 consumption, and reduced coronary perfusion. However, whether heart rate reduction (HRR) opposes LV dysfunction observed in MS is unknown. Methods: We assessed in Zucker fa/fa rats, a rat model of MS, the cardiovascular effects of HRR induced by the If current inhibitor S38844 ( 3 mg center dot kg21 center dot d(-1)). Results: Delayed short-term ( 4 days) and long-term ( 90 days) HRR induced by S38844 reduced LV end-diastolic pressure and LV enddiastolic pressure-volume relation, increased myocardial tissue perfusion, decreased myocardial oxidized glutathione levels, and preserved cardiac output, without modifying LV end-systolic pressure and LV end-systolic pressure-volume relation, although only long-term S38844 opposed LV collagen accumulation. Long-term S38844 improved flow-induced endothelium-dependent dilatation of mesenteric arteries, while metabolic parameters, such as plasma glucose levels, and Hb1c, were never modified. Conclusions: In rats with MS, HRR induced by the If inhibitor S38844 improved LV diastolic function and endothelium- dependent vascular dilatation, independent from modifications in metabolic status. Moreover, this improvement in cardiac function involves not only immediate effects such as improved myocardial perfusion and reduced oxidative stress but also long- term effects such as modifications in the myocardial structure.