Effect of coronary vasodilators and pacing upon regional oxygen balance of the ischaemic myocardium.

In anaesthetized open-chest dogs, regional contractile force, epicardial tissue blood flow, and local NADH redox levels were recorded during graded ventricular pacing in the range 150-285 bpm. These parameters were measured before, and 30 min following LAD coronary artery occlusion. It was found that during pacing, blood supply to the untreated ischaemic region was reduced by 65.4 +/- 11% of control values at a rate of 150 bpm, and fell to -105 +/- 40.2% at a rate of 225 bpm. Hypopneic respiration prevented this pacing induced flow reduction. Pacing in the presence of nitroglycerin resulted in a marked increase in regional flow. Similarly, the vasodilator treatments prevented the marked elevation in NADH levels (77.5 +/- 15.6%) produced by pacing in the untreated ischaemic myocardium. The reduction in regional contractile force in the ischaemic region produced following pacing (-30.5%) was reversed during both vasodilator treatments (+47.2% during nitroglycerin and +23.4% during hypopnea). It was concluded that vasodilation improves regional ischaemic myocardial oxygen balance, thus expanding the functional reserve of the ischaemic muscle. Nitroglycerin is more active.