Effects of nitroglycerin-induced hypotension on myocardial blood flow in a two vessel occlusion-stenosis anesthetized canine model

The effects of acute occlusion of the left anterior descending coronary artery on regional blood flow (microspheres) to the remote bed supplied by either an unstenosed or a stenosed circumflex coronary artery were assessed during the infusion of intravenous nitroglycerin in 11 open chest barbiturate-anesthetized mongrel dogs. Left anterior descending coronary artery occlusion in the presence of an unstenosed left circumflex artery during nitroglycerin infusion caused systolic aortic and distal circumflex pressure to decrease significantly from 98 ± 4 to 91 ± 3 and from 99 ± 4 to 92 ± 3 mm Hg, respectively. Remote circumflex bed flow was unchanged. The infusion of intravenous nitroglycerin in the presence of a left circumflex stenosis (gradient 31 ± 3 mm Hg) reduced systolic aortic and distal circumflex pressure to 98 ± 2 (p = 0.001) and 71 ± 4 mm Hg (p = 0.001), respectively, and lowered remote circumflex bed endocardial flow from 1.00 ± 0.08 to 0.79 ± 0.07 ml/min per g (p = 0.001). When the left anterior descending coronary artery was occluded under these conditions, systolic aortic and distal left circumflex pressure decreased to 89 ± 3 (p = 0.005) and 62 ± 4 mm Hg (p = 0.08), respectively. Remote circumflex artery bed endocardial and transmural flow were significantly reduced to 0.58 ± 0.07 (p = 0.01) and 0.65 ± 0.07 ml/min per g (p = 0.03), respectively. The decrease in circumflex artery bed endocardial flow after left anterior descending coronary artery occlusion was related directly to the change in distal circumflex artery pressure and inversely to the change in circumflex stenosis resistance (regression analysis). These results suggest that modest hypotension resulting from the infusion of nitroglycerin at the time of acute coronary occlusion may have adverse effects on flow to remote myocardium supplied by a stenosed vessel.