LONG-TERM ORAL NITRATE THERAPY PREVENTS CHRONIC VENTRICULAR REMODELING IN THE DOG

Objectives. The purpose of this experiment was to assess the long-term effects of oral nitrate therapy on ventricular remodeling in a canine model of discrete myocardial damage. Background. A progressive increase in left ventricular mass and volume has been documented after experimental and clinical myocardial infarction. This ventricular remodeling has been associated with the development of congestive heart failure. Nitrate therapy, especially when combined with hydralazine, is effective in the management of clinical heart failure. Moreover, nitrates inhibit infarct expansion, one of the earliest manifestations of ventricular remodeling. Whether nitrates can attenuate chronic left ventricular remodeling is unknown. Methods. Dogs with discrete myocardial necrosis produced 24 h earlier by transmyocardial direct current shock were randomized to receive isosorbide mononitrate, 30 mg twice daily (n = 10), or no treatment (n = 4); the latter group was augmented by 13 control dogs from a prior study in which an identical protocol was used. Ventricular structure was assessed with nuclear magnetic resonance imaging at baseline and at 1 and 16 weeks after myocardial damage. Results. Left ventricular mass increased at 1 week in the control group (mean +/- SD 68.1 +/- 10.7 g to 80.1 +/- 12.1 g, p = 0.0001) but not in the nitrate-treated group (70.2 +/- 7.7 g to 69.6 +/- 7.3 g, p = NS). No change in left ventricular volume was observed in either group during the 1st week after myocardial damage. After 16 weeks of follow-up left ventricular mass had increased by 12.7 +/- 7.1 g (p = 0.001) in the control group and had decreased by 1.2 +/- 7.7 g in the nitrate group. Left ventricular volume was increased at 16 weeks by 14.2 +/- 10.3 ml in the control group but was decreased by 3.7 +/- 7.5 nd in the nitrate group. Isosorbide mononitrate produced transient hemodynamic effects with a return of most measured variables toward baseline within 2 h after administration of the drug. At 1 week there was no intergroup difference in rest hemodynamic variables assessed 12 h after drug administration. At 16 weeks, pulmonary capillary wedge pressure (15 +/- 4 vs. 8 +/- 3 mm Hg, p = 0.0001), pulmonary artery pressure (24 +/- 5 vs. 16 +/- 3 mm Hg, p = 0.0001) and right atrial pressure (10 +/- 3 vs. 6 +/- 3 mm Hg, p = 0.008) were all higher in the control group. Conclusions. Long-term oral nitrate therapy attenuates the early and late manifestations of ventricular remodeling after myocardial damage in the dog. Hemodynamic observations suggest the possibility that drug-induced preload or afterload reduction does not completely explain this effect.