NITROGEN-13-AMMONIA AND OXYGEN-15-WATER ESTIMATES OF ABSOLUTE MYOCARDIAL PERFUSION IN LEFT-VENTRICULAR ISCHEMIC DYSFUNCTION

Measurements of resting myocardial blood flow (MBF) in patients with c hronic left ventricular ischemic dysfunction by O-15-water with N-13-a mmonia and PET have yielded conflicting results. The aim of this study was to perform a head-to-head comparison of both tracers in the same patient population and to answer the question of whether distinctive t racer properties account for differences in estimates of MBF in chroni cally dysfunctional myocardium by both tracers. Methods: A total of 30 patients with chronic dysfunction of the anterior myocardial wall due to significant left anterior descending coronary artery disease under went PET measurements of absolute MBF in the anterior wall by use of O -15-water and N-13- ammonia before coronary revascularization by eithe r coronary artery bypass graft (n = 24) or percutaneous transluminal c oronary angioplasty (n = 6), Improvement of regional contractile funct ion was assessed by two-dimensional echocardiography at a mean of 7.5 +/- 2.1 mo after revascularization. As judged from the changes in ante rior myocardial wail motion after revascularization, patients were con sidered to have either reversibly (n = 16) or persistently (n = 14) dy sfunctional myocardium. Estimates of MBF by O-15-water and N-13-ammoni a, obtained in every patient before revascularization, were compared a mong the two patient groups by use of previously validated methods. Re sults: With N-13-ammonia, resting regional MBF was significantly highe r in reversibly as opposed to persistently dysfunctional segments [84 +/- 8 versus 48 +/- 6 ml (min.100 g)(-1), mean +/- s.e.m., p < 0.01]. By contrast, no such difference was found when using O-15-water to mea sure MBF [74 +/- 6 versus 86 +/- 9 ml (min.100 g)(-1), p = ns]. This w as mainly due to the fact that the perfusable tissue fraction (PTF), a fitted parameter of the O-15-water model, was significantly higher in reversibly as opposed to persistently dysfunctional segments (0.63 +/ - 0.03 versus 0.50 +/- 0.03, p < 0.05). As a consequence, the O-15-wat er perfusable tissue index (PTI), which is the ratio of the PTF to the anatomical tissue fraction, was greater in reversibly dysfunctional a s opposed to persistently dysfunctional segments (1.07 +/- 0.07 versus 0.79 +/- 0.05, p < 0.01). Conclusion: This study demonstrates signifi cant differences in MBF estimates between O-15-water and N-13-ammonia in chronically dysfunctional ischemic myocardium. Our results indicate that the O-15-water method yields higher absolute MBF values than the N-13-ammonia approach. Our results also support the use of PTI as a m arker of myocardial tissue viability.