Viability After Myocardial Infarction: Can It Be Assessed Within Five Minutes by Low-Dose Dynamic Iodine-123-Iodophenylpentadecanoic Acid Imaging with a Multicrystal Gamma Camera?

Abstract

Although positron emission tomography (PET) assesses myocardial viability (V) accu rately, a rapid, inexpensive substitute is needed. Therefore, the authors developed a low- dose (1 mCi) Iodine-123-Iodophenylpentadecanoic Acid (IPPA) myocardial viability scan requiring analysis of only the first three minutes of data acquired at rest with a standard multicrystal gamma camera. Twenty-one patients > 2 weeks after myocardial infarction (MI) (24 MIs, 10 anterior, 14 inferoposterior, 21 akinetic or dyskinetic) had cardiac catheterization and resting IPPA imaging. V was determined by either transmural myocar dial biopsy during coronary bypass surgery (12 patients, 14 MIs) or reinjection tomo graphic thallium scan (9 patients, 10 MIs), and 50% of MIs were viable. The IPPA variables analyzed were: time to initial left ventricular (LV) uptake in the region of interest (ROI), the ratio of three-minute uptake in the ROI to three-minute LV uptake, three-minute clearing (counts/pixel) in the ROI (decrease in IPPA after initial uptake), and three-minute accumulation (increase in IPPA after initial uptake) in the ROI. Rules for detecting V were generated and applied to 10 healthy volunteers to determine normalcy. While three-minute uptake in nonviable MIs was only 67% of volunteers (P < 0.0001) and 75% of viable MIs, uptake alone identified only 50% of viable MIs and 75% of nonviable MIs. IPPA clearing, however, was ≥ 13.5 counts/pixel in 10/12 (83%) of viable MIs, and IPPA accumulation ≥ 6.75 counts/pixel identified one more viable MI, for a sensitivity for V of 11/12 (92%), with a specificity of 11/12 (92%), and a 100% normalcy rate. The authors conclude low-dose IPPA (five-minute acquisition with analysis of the first three minutes of data) has potential for providing rapid, inexpensive V data after MI. Since newer multicrystal cameras are mobile, IPPA scans can be done in emergency rooms or coronary care units, generating information that might be useful in decisions regarding thrombolysis, angioplasty, or bypass surgery.