Transmural differences in myocardial function and metabolism during direct left ventricular to coronary artery...

We investigated the hypothesis that in the absence of collateral circulation, a left ventricle-coronary artery (LV-CA) bypass will maintain normal LV wall function and metabolism transmurally, both at rest and during stress, when the left anterior descending coronary artery (LAD) is acutely occluded proximally.

In 18 anesthetized pigs (74 +/- 7 kg, mean +/- standard deviation), a covered stent was placed transmurally in the lateral wall of the beating LV and connected to the proximal LAD via an arterial graft. Subepicardial and subendocardial segmental shortening as well as interstitial lactate and glucose concentrations were measured regionally by sonomicrometry and microdialysis, respectively.

When the LAD was occluded proximally, direct left ventricular sourcing decreased the net LAD flow to 64 +/- 25% of the native flow (n = 18, all animals). In the subepicardium, systolic shortening (SS) decreased to 87 +/- 18% of baseline (p = 0.124), with the appearance of minor postsystolic shortening (PSS), and minor changes in interstitial lactate and glucose levels. In the subendocardium, in contrast, SS decreased to 54 +/- 20% (p = 0.001). Marked PSS concurred with a sixfold increase in lactate (p = 0.008), and a 65 +/- 31% decrease in glucose (p = 0.003), indicating subendocardial anaerobic metabolism. Stress induced by infusion of dobutamine increased lactate and decreased glucose concentration in the subepicardium to subendocardial levels, indicating transmural anaerobic metabolism.

In the anesthetized pig, direct sourcing by a LV-CA bypass distal to an acute coronary occlusion resulted in a 36% decrease in net forward coronary flow, subendocardial anaerobic metabolism, and loss of subendocardial contractile function at rest. These adverse effects extended into the subepicardium when the heart was stressed.