Effects of three bradycardiac drugs on regional myocardial blood flow and function in areas distal to a total or partial coronary occlusion in dogs.

The effectiveness of three bradycardiac drugs for increasing distal coronary perfusion pressure and decreasing stenosis resistance (SR) in partially occluded vessels, and thereby for increasing collateral blood flow and segmental function (%SS) in an occluded area dependent on the stenotic vessel, was studied in anesthetized dogs. Initially, the distal portion of the left anterior descending (LAD) coronary artery was occluded followed by subsequent stenosis of the left circumflex (LC) coronary artery that supplies collateral flow to the ischemic LAD area. A decrease in LC flow (35 +/- 3 to 24 +/- 3 ml/min) and distal coronary pressure (109 +/- 4 to 47 +/- 4 mm Hg) resulted in an increase in SR (0.03 +/- 0.02 to 2.97 +/- 0.53 U), and decreases in LC %SS (9.3 +/- 1.1% to 1.9 +/- 2.0%), subendocardial blood flow (1.11 +/- 0.06 to 0.43 +/- 0.05 ml/min/g), and LAD collateral flow (0.36 +/- 0.11 to 0.22 +/- 0.05 ml/min/g). Upon intravenous administration on the beta-receptor-blocking drug sotalol (0.3 mg/kg) or metoprolol (0.1 mg/kg) and the non-beta-blocking bradycardiac drug N-dimethyl-propranolol (5.0 mg/kg) in doses that produced similar decreases in heart rate (30 to 40 beats/min), distal coronary pressure, subendocardial blood flow, and %SS in the LC area were markedly improved. SR was significantly reduced (2.97 +/- 0.53 to 1.66 +/- 0.37 U). The improvement in %SS of the LC area was highly correlated (r = .93, p less than .001) with the increase in subendocardial blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)