Assessment of myocardial perfusion and viability with stress Tc-99m-MIBI SPECT before surgical revascularisation. Correlation with postoperative perfusion improvement.
BACKGROUND: The immediate result of successful revascularisation of the myocardium is the improvement of perfusion (and in patients with depressed ventricular function, functional recovery is expected as an effect of coronary flow improvement). The main goal of the work was to assess the value of myocardial stress-rest MIBI perfusion scintigraphy in predicting myocardial perfusion state measured early (< 5 months) after CABG. MATERIAL AND METHODS: Forty-three patients (39 males, mean age 52 +/- 9 years) with chronic coronary artery disease underwent prerevascularisation and postrevascularisation stress-rest Tc-99m-MIBI SPECT studies. Eighty-one percent of patients had a history of myocardial infarction, the number of stenosed main coronary arteries was 2.3 +/- 0.6 per patient, and the left ventricle ejection fraction was 18-70% (mean 46 +/- 14%). Preoperative perfusion defects were considered as small, medium or severe (depending upon stress uptake deficiency) and as transient or persistent (depending upon uptake improvement in rest). Changes in perfusion defects (improvement, lack of changes or deterioration) were evaluated very early after CABG (mean 31 +/- 12 days) in all patients and additionally about 3 months later (mean 119 +/- 17 days after CABG) in 36 patients. RESULTS: In transient perfusion defects, the probability of early postoperative perfusion improvement was 80% (in small defects: 89%, CI(0,95) = 80-94%) and was significantly higher than in small persistent defects (51%) and than in medium-and-severe persistent defects (21%). In medium-and-severe persistent defects, the lack of changes in perfusion was observed in 76% of defects (in severe defects: 81%, CI(0,95)= 69-91%) and was significantly higher than in small persistent defects (37%), than in medium-and-severe transient defects (17%), and than in small transient defects (4%). The probability of later postoperative perfusion improvement was 78% in transient perfusion defects (in small defects: 85%, CI(0,95)=74-92%) and was significantly higher than in small, medium, and severe persistent defects (28%). In medium-and-severe persistent defects, the lack of changes in perfusion was observed in 71% of defects (in severe defects: 81%, CI(0,95)=66-91%) and was significantly higher than in small persistent defects (40%), and than in severe, medium, and small transient defects (11%). CONCLUSIONS: 1. The result of preoperative stress-rest Tc-99m-MIBI SPECT myocardial perfusion study is an exact predictor of the state of perfusion measured early (< 5 months) after CABG; the postoperative regional perfusion improvement is most dependent upon reversibility and also upon severity of stress defect. 2. In small persistent defects, changes in perfusion are different than in other types of defects - so they should not be considered together with transient defects (as "viable") or with persistent defects (as "nonviable"). 3. Preoperative viability assessment on the basis of Tc-99m-MIBI study performed solely in rest is unjustified: at the similar perfusion defect at rest, the presence of even minimal inducible ischaemia is associated with increased probability of perfusion improvement after CABG.