Assessment of myocardial viability using I-123-labeled iodophenylpentadecanoic acid at sustained low flow or after acute infarction and reperfusion

(123)l-labeled iodophenylpentadecanoic acid (IPPA) is a synthetic fatty aci d that may be useful for determination of myocardial viability. We investig ated the uptake and clearance kinetics of this tracer in canine models of i schemia and infarction. Methods: In protocol 1, 185 MBq (5 mCi) (123)l-IPPA were injected intravenously in 19 dogs with 50% left anterior descending a rtery (LAD) flow reduction. In 9 dogs, (TI)-T-201 was coinjected. In protoc ol 2, 5 dogs underwent LAD occlusion for 3 h, and (123)l-IPPA was injected 60 min after reperfusion. All dogs had flow measured by microspheres, regio nal systolic thickening by ultrasonic crystals and measurements of postmort em risk area and infarct size. Tracer activities were quantified by gamma w ell counting and by serial imaging. Results: In protocol 1 dogs with sustai ned low flow (50% +/- 4 %) and absence of systolic thickening (-3.2% +/- 1% ), (123)l-IPPA defect magnitude (LAD/left circumflex artery [LCX] count rat ios) decreased from 0.65 +/- 0.02 to 0.74 +/- 0.02 at 30 min and to 0.84 +/ - 0.03 at 2 h (P < 0.01), indicative of rest redistribution. Final transmur al (123)l-IPPA LAD/LCX activity ratio (0.99 +/- 0.05) was significantly gre ater than the flow ratio (0.53 +/- 0.04) at injection, confirming complete rest redistribution. The final (123)l-IPPA activity ratio was significantly greater than the (TI)-T-201 ratio over the 2-h period (P < 0.01). In proto col 2 dogs that underwent 3 h of total LAD occlusion and reflow (infarct si ze = 51% +/- 13% of risk area), viability was overestimated with (123)l-IPP A, because uptake averaged 64% of normal in the central necrotic region, wh ere flow averaged <10% of normal. Conclusion: These findings suggest that s erial 123l-IPPA imaging may be useful for assessing myocardial viability un der conditions of sustained low flow and myocardial asynergy, such as appea rs to exist in patients with chronic coronary artery disease and depressed left ventricular function. In contrast, (123)l-IPPA given early after reper fusion following prolonged coronary occlusion overestimates the degree of v iability and therefore may not provide useful information pertaining to the degree of myocardial salvage after reflow in the setting of acute myocardi al infarction.