POSITRON EMISSION TOMOGRAPHIC MEASUREMENTS OF ABSOLUTE REGIONAL MYOCARDIAL BLOOD-FLOW PERMITS IDENTIFICATION OF NONVIABLE MYOCARDIUM IN PATIENTS WITH CHRONIC MYOCARDIAL-INFARCTION

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 kineti cs. Background. Under steady state basal conditions there is a minimal level of blood flow required to sustain myocardial viability. Therefo re, the hypothesis predicts that regions with flow below a certain thr eshold are likely to be composed primarily of scar. Methods. Studies w ere conducted in 26 patients with chronic myocardial infarction. Posit ron emission tomographic measurements of basal regional myocardial blo od flow (N-13 ammonia) and fluorine 18 (F-18) fluorodeoxyglucose uptak e were made and correlated with information about coronary anatomy and regional wall motion to assess myocardial viability. Results. In pati ents 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). Goo d correlation was noted between relative F-18 fluorodeoxyglucose uptak e and relative regional myocardial blood flow in all zones (r = 0.63, p < 0.001). Mismatch between blood flow and F-18 fluorodeoxyglucose up take, with a single exception, was not observed in any segment with bl ood how <0.25 ml/min per g. All dyskinetic segments (n = 5) also had b lood flow <0.25 ml/min per g. In contrast, 43 of 45 myocardial segment s (23 patients) with normal contraction or only mild hypokinesia had f low greater than or equal to 0.39 ml/min per g (average flow 0.78 +/- 0.35 ml/min per g). Conclusions. in patients with chronic myocardial i nfarction, myocardial viability is unlikely when basal regional myocar dial blood flow is <0.25 ml/min per g. Average basal how in segments w ith normal or nearly normal wall motion is 0.78 +/- 0.35 ml/min per g. Thus, positron emission tomographic measurement of regional myocardia l blood flow is helpful in identifying nonviable myocardium in these p atients.