Effect of coronary hyperperfusion on regional myocardial function and oxygen consumption of stunned myocardium in pigs

Summary

The “Gregg phenomenon” implies that myocardial function and oxygen consumption ($M\dot VO_2$) increase when coronary perfusion is enhanced within or above the autoregulatory range. We have recently demonstrated that the “Gregg phenomenon” has no significance for regional myocardial function and$M\dot VO_2$ in anesthetized swine in situ. There is, however, some evidence that the “Gregg phenomenon” may exist within stunned myocardium. To test whether coronary hyperperfusion increases regional myocardial function and$M\dot VO_2$ in stunned myocardium, in six anesthetized swine the left anterior descending coronary artery (LAD) was cannulated and perfused at constant pressure (CAP) using an extracorporal circuit. The coronary vein which parallels the LAD was cannulated to allow measurement of regional$M\dot VO_2$ and regional systolic wall thickening (WT%) of the anterior myocardium was assessed using sonomicrometry. Blood flow (CBF) to the LAD was increased by increasing CAP within the extracorporal circuit or by intracoronary adenosine infusion (150 μg/min). In normal myocardium, increasing CBF from 71.4 ± 19.7 (SD) to 156.7 ± 48.8 ml/min/100 g by increasing CAP from 100 ± 10 to 190 ± 10 mm Hg or increasing CBF from 75.1 ± 29.1 to 189.2 ± 45.8 ml/min/100 g by intracoronary adenosine infusion did not increase WT% (34.3 ± 12.2 % vs 32.1 ± 10.6 % and 32.3 ± 10.7 % vs 30.1 ± 13.2 %, respectively).$M\dot VO_2$ was not changed during enhanced CAP (6.94 ± 1.05 vs 8.10 ± 1.08 ml/min/100 g) and during intracoronary adenosine infusion (6.67 ± 1.45 vs 7.30 ± 2.23 ml/min/100 g). Twenty min of hypoperfusion followed by 30 min of reperfusion depressed WT% by 47 % (p < 0.05). However,$M\dot VO_2$ was only decreased by 23 % (NS). In the stunned myocardium, increasing CBF from 62.1 ± 36.4 to 157.1 ± 60.0 ml/min by increasing CAP was not associated with an increase in WT%.$M\dot VO_2$, however, increased from 5.14 ± 1.07 to 8.88 ± 1.83 ml/min/100 g (p < 0.05). Comparable results were achieved when CBF was increased from 60.3 ± 28.7 to 176.9 ± 48.5 ml/min by intracoronary adenosine infusion. WT% was unaffected, while$M\dot VO_2$ increased from 4.69 ± 0.92 to 9.46 ± 3.39 ml/min/100 g (p < 0.05). Thus, increasing coronary perfusion within or above the autoregulatory range increases$M\dot VO_2$ in stunned myocardium, but without a simultaneous increase in regional myocardial function.