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Assessment of Myocardial Viability Using ¹²³I-Labeled Iodophenylpentadecanoic Acid at Sustained Low Flow or After Acute Infarction and Reperfusion

Experimental Cardiology Laboratory, Cardiovascular Division, Department of Medicine, University of Virginia Health Sciences Center, Charlottesville, Virginia

Correspondence: For correspondence or reprints contact: David K. Glover, ME, Cardiovascular Division, Department of Medicine, Box 500, University of Virginia Health Sciences Center, Charlottesville, VA 22908.

ABSTRACT

¹²³I-labeled iodophenylpentadecanoic acid (IPPA) is a synthetic fatty acid that may be useful for determination of myocardial viability. We investigated the uptake and clearance kinetics of this tracer in canine models of ischemia and infarction. Methods: In protocol 1, 185 MBq (5 mCi) ¹²³I-IPPA were injected intravenously in 19 dogs with 50% left anterior descending artery (LAD) flow reduction. In 9 dogs, ²⁰¹Tl was coinjected. In protocol 2, 5 dogs underwent LAD occlusion for 3 h, and ¹²³I-IPPA was injected 60 min after reperfusion. All dogs had flow measured by microspheres, regional systolic thickening by ultrasonic crystals and measurements of postmortem risk area and infarct size. Tracer activities were quantified by gamma well counting and by serial imaging. Results: In protocol 1 dogs with sustained low flow (50% ± 4 %) and absence of systolic thickening (-3.2% ± 1%), ¹²³I-IPPA defect magnitude (LAD/left circumflex artery [LCX] count ratios) 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 transmural ¹²³I-IPPA LAD/LCX activity ratio (0.99 ± 0.05) was significantly greater than the flow ratio (0.53 ± 0.04) at injection, confirming complete rest redistribution. The final ¹²³I-IPPA activity ratio was significantly greater than the ²⁰¹Tl ratio over the 2-h period (P < 0.01). In protocol 2 dogs that underwent 3 h of total LAD occlusion and reflow (infarct size = 51% ± 13% of risk area), viability was overestimated with ¹²³I-IPPA, because uptake averaged 64% of normal in the central necrotic region, where flow averaged < 10% of normal. Conclusion: These findings suggest that serial ¹²³I-IPPA imaging may be useful for assessing myocardial viability under conditions of sustained low flow and myocardial asynergy, such as appears to exist in patients with chronic coronary artery disease and depressed left ventricular function. In contrast, ¹²³I-IPPA given early after reperfusion following prolonged coronary occlusion overestimates the degree of viability and therefore may not provide useful information pertaining to the degree of myocardial salvage after reflow in the setting of acute myocardial infarction.

Key Words: myocardial viability • radionuclide imaging • fatty acids • ²⁰¹Tl • myocardial ischemia • myocardial infarction

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				C. Q. Shi, L. H. Young, E. Daher, E. V.R. DiBella, Y.-H. Liu, E. N. Heller, S. Zoghbi, F. J.Th. Wackers, R. Soufer, and A. J. Sinusas Correlation of Myocardial p-123I-Iodophenylpentadecanoic Acid Retention with 18F-FDG Accumulation During Experimental Low-Flow Ischemia J. Nucl. Med., March 1, 2002; 43(3): 421 - 431. [Abstract] [Full Text] [PDF]