DIMINISHED MYOCARDIAL-FUNCTION PRECEDES TISSUE ACIDOSIS DURING CORONARY HYPOPERFUSION

The current study sought to elucidate the relationship between myocard ial pH and function during a significant but not absolute reduction in coronary flow, In a canine model, a partial coronary arterial stenosi s was created, with the left anterior descending coronary artery (LAD) flow reduced by 50% compared to prestenosis levels, and maintained at that level for the duration of the study. During the experiment, inte rstitial myocardial pH and regional myocardial function, as assessed b y the regional preload recruitable work area (PRWA), were measured. PR WA was depressed to 60% of baseline values, on average, for the entire period of reduced LAD flow. In contrast to the pattern observed with myocardial blood flow and systolic function, metabolic evidence of myo cardial ischemia, that is, reduced myocardial pH did not become signif icantly different from baseline levels until after LAD flow had been r educed for 15 min. Thus, measurable changes in myocardial pH appeared slowly over time despite the fact that regional myocardial blood flow was decreased immediately. Therefore, myocardial pH cannot be used to anticipate alterations in myocardial contractile function.