Objectives: This study tested the hypothesis that nonviable myocardium can be identified by quantitative measurements of regional myocardial blood flow obtained using positron emission tomography in conjunction with a mathematical model of nitrogen-13 (N-13) ammonia tracer kinetics.
Background: Under steady state basal conditions there is a minimal level of blood flow required to sustain myocardial viability. Therefore, the hypothesis predicts that regions with flow below a certain threshold are likely to be composed primarily of scar.
Methods: Studies were conducted in 26 patients with chronic myocardial infarction. Positron emission tomographic measurements of basal regional myocardial blood flow (N-13 ammonia) and fluorine-18 (F-18) fluorodeoxyglucose uptake were made and correlated with information about coronary anatomy and regional wall motion to assess myocardial viability.
Results: In patients with chronic myocardial infarction, normal zone blood flow (0.81 +/- 0.32 ml/min per g [mean +/- SD]) was greater (p < 0.02) than that of border zones (0.59 +/- 0.29 ml/min per g), which in turn exceeded (p < 0.001) that of infarct zone flow (0.27 +/- 0.17 ml/min per g). Good correlation was noted between relative F-18 fluorodeoxyglucose uptake and relative regional myocardial blood flow in all zones (r = 0.63, p < 0.001). Mismatch between blood flow and F-18 fluorodeoxyglucose uptake, with a single exception, was not observed in any segment with blood flow < 0.25 ml/min per g. All dyskinetic segments (n = 5) also had blood flow < 0.25 ml/min per g. In contrast, 43 of 45 myocardial segments (23 patients) with normal contraction or only mild hypokinesia had flow > or = 0.39 ml/min per g (average flow 0.78 +/- 0.35 ml/min per g).
Conclusions: In patients with chronic myocardial infarction, myocardial viability is unlikely when basal regional myocardial blood flow is < 0.25 ml/min per g. Average basal flow in segments with normal or nearly normal wall motion is 0.78 +/- 0.35 ml/min per g. Thus, positron emission tomographic measurement of regional myocardial blood flow is helpful in identifying nonviable myocardium in these patients.