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Ann Thorac Surg 2005;80:161-162
© 2005 The Society of Thoracic Surgeons
Division of Cardiothoracic Surgery, Jackson Memorial Hospital, University of Miami, 1611 NW 12th Ave, East Tower 3072 (R-114), Miami, FL 33136
(Email: tsalerno{at}med.miami.edu).
de Zeeuw and colleagues [1] have developed an elegant and technically challenging model to evaluate myocardial perfusion after creation of a left ventricular-to-coronary artery shunt (LV-CA). This animal model specifically assesses transmyocardial blood flow and coronary physiology in a normal porcine heart without collateral circulation. This is a physiologic state that is uncommon in patients with chronic arterial occlusive disease. However, it may represent a plausible intervention in the treatment of patients with coronary artery disease.
A valveless LV-CA bypass has a significant impact on regional myocardial perfusion. The conduit used in this study reverses mid-left anterior descending coronary artery (LAD) blood flow from diastole to systole. The regurgitant flow during diastole negates the increased systolic blood flow thereby culminating in a 64% decrease in mid-LAD flow. The authors created a "steal phenomenon" that led to significant aberrations in transmyocardial perfusion, thus leading to cellular anoxia. Subendocardial myocardial metabolism is affected during baseline experiments and is further evident in the augmentation of lactate production and glucose depletion during left ventricular (LV) loading. As expected, the diminished myocardial perfusion produces impairment in myocardial function. Anaerobic metabolism in the subepicardial regions is evident only after 30 minutes of LV sourcing and higher doses of dobutamine infusion. This study does question the utility of LV sourcing because the data clearly demonstrate subendocardial ischemia and myocardial dysfunction. One must ask, therefore, how does this potentially help the ischemic heart? As practicing cardiac surgeons, do we see this technique as part of our armamentarium?
The answer is evident in a recent article by Vicol and colleagues [2] in which an LV-CA stent was used in human subjects. The purpose of that study was to prove feasibility and elucidate early results. However, one can appreciate this innovation and its future applications in our clinical practice. Most interesting is that their pre-clinical studies showed a net increase in coronary flow distal to a >70% stenosed artery and LV-CA stent with negligible regurgitant flow. The authors of this article may consider using a valved conduit in the LV sourcing model and repeating these experiments in a diseased heart that is either hypertrophied or with coronary artery disease. Further-more, why does the coronary artery need to have a degree of native flow to influence net forward flow with the LV-CA stent? Can we use these stents to maintain concomitant bypass grafts patent? These are a few interesting questions the authors may want to ponder.
Overall, the author’s work is to be applauded for their methodology and ardent task to demonstrate myocardial perfusion in different aberrant conditions. The idea of connecting the left ventricle to the coronary artery is not new. However, with minor modifications, the LV-CA stent may become an alternative treatment for patients with end-stage coronary artery disease. As with transmyocardial revascularization, this may initially have a role in patients with refractory angina either as an adjunct to coronary artery bypass surgery or as a stand-alone procedure. Most importantly, pre-clinical animal experiments should be repeated with the hope of underscoring the augmentation in myocardial perfusion and metabolism with LV sourcing.
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