Myocardial blood supply through a direct left ventricle–coronary artery shunt is not aided by augmented coronary capacitance

Myocardial blood supply by left ventricle-to-coronary artery channel: an old idea revisited

Coronary artery disease is one of the most important causes of death in Western society. Attempts to revascularize the coronary artery by myocardial retroperfusion, direct revascularization from the left ventricle, and bypass surgery have finally led to percutaneous transluminal coronary angioplasty (PTCA) and coronary artery bypass grafting (CABG) as standard treatment for coronary artery disease. Direct revascularization from the left ventricle has already been studied in the late 1960s, but the idea was rejected because of a decrease in flow in combination with a failure of myocardial function. Recently, a left ventricle-to-coronary artery (LV-CA) stent has renewed interest as an alternative procedure when PTCA and CABG are no option. Animal studies showed a change in flow pattern from diastolic coronary inflow at baseline to systolic coronary inflow followed by diastolic regurgitive flow during direct ventricular sourcing, resulting in a coronary flow of 50-75% of baseline flow. Global myocardial function decreased in the same extent as the coronary flow suggesting perfusion-contraction matching. In a recent pilot study in the anaesthetized pig, direct revascularization after acute proximal coronary ligation resulted in sufficient blood supply to the outer layers of the myocardium, however, in the inner layers a metabolic disbalance occurred. Incorporation of a valve-like mechanism to minimize the diastolic regurgitive flow may be necessary to improve the performance of the LV-CA stent. In addition, further research should be done in chronic ischemic animal models in which the effect of the collateral circulation on myocardial perfusion and performance is an important issue.

Transmural Differences in Myocardial Function and Metabolism During Direct Left Ventricular to Coronary Artery Sourcing

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.