Preoperative prediction of the outcome of coronary revascularization using positron emission tomography

Previous assessments of myocardial viability using positron emission tomography (PET) relied on demonstration of glucose metabolism in hypoperfused asynergic segments using the glucose analogue [18F]2-fluoro-2-deoxyglucose (FDG). Recently, it was shown that myocardial viability could be assessed by calculating the water-perfusable tissue index (PTI) for the asynergic region. PTI represents the proportion of the myocardium that is capable of rapid transsarcolemmal exchange of water and thus perfusable by water. The aim of the present study was to assess myocardial viability by PET using PTI in patients undergoing coronary revascularization.

Twelve patients with chronic coronary artery disease and previous myocardial infarction were studied. Analysis of transmission (tissue density) and 15O-labeled carbon monoxide (blood pool), and 15O-labeled water (myocardial blood flow [MBF]) emission PET data enabled the simultaneous quantification of MBF (ml.min-1.g perfusable tissue-1) and PTI (gram of perfusable tissue per gram of total anatomic tissue). In addition, PET imaging with FDG after 75-g oral glucose load was performed in eight patients. Preoperative echocardiography identified 33 hypocontractile and 26 control segments. Follow-up echocardiography performed 3 to 5 months later demonstrated 26 of 33 segments with improved wall motion (recovery) and seven of 33 segments without improvement (nonrecovery). MBF in the control segments (0.97 +/- 0.22 ml.min-1.g perfusable tissue-1) was significantly higher (p < 0.001) than in both the recovery (0.73 +/- 0.18 ml.min-1.g perfusable tissue-1) and the nonrecovery (0.45 +/- 0.11 ml.min-1.g perfusable tissue-1) segments. PTI in the recovery regions (0.99 +/- 0.15) was > or = 0.7 in all cases and slightly less than in control regions (1.10 +/- 0.15, p < 0.02). FDG uptake in these regions was 92 +/- 17% (n = 13) of the uptake in control segments with normal wall motion. In the nonrecovery group, PTI was 0.62 +/- 0.06 (p < 0.02 versus control and recovery) and always < 0.7. In the one patient in whom a comparison with metabolic imaging was made, FDG uptake was 46% of the uptake in a reference region with normal wall motion.

These data showed that contractile recovery occurred only in segments where PTI was > or = 0.7, suggesting that > or = 70% of myocardial tissue in a given asynergic segment should be perfusable by water to enable contractile recovery. There was good agreement between the PTI and FDG methods for predicting improvements in regional wall motion after revascularization. Although further studies should be performed in a larger patient group, the preliminary results are promising and suggest that PTI may be a good predictor of contractile recovery after coronary revascularization.