Assessment of viable myocardium by nitrate augmented ^99mTc MIBI myocardial perfusion imaging

Objective: To determine the efficacy of ^99mTcMIBI with nitrate administration for the detection of viable myocardium in patients with MI. Methods: Thirty-five patients (31 men, 4 women; mean age 51.91 ± 8.86 years, median = 50) with previous history of myocardial infarction (with mean duration of 11.50 ± 11.4, median =4months after MI) were included in the study. All patients underwent baseline rest and Nitroglycerine ^99mTcMIBI myocardial perfusion imaging (2 day protocol). Fifteen out of 34 patients were also submitted for rest and redistribution TI-201 imaging (3 day protocol). The data were reconstructed in transaxial slices and then reoriented into short, vertical long and horizontal long axis slices. The images were divided into seven different segments for qualitative as well as semi quantitative analysis. The images were interpretated by two independent observers. The segments with tracer activity of more than 55% as compared to maximum, were considered as viable. Results: In the baseline study with ^99mTcMIBI, 168/245 (68.57%) were viable segments and these were increased to 197 (80.40%) in the Nitrate MIBI study (p=0.001 vs. baseline). Total 21 (60%) out of 35 patients demonstrated viable myocardium. The concordance for viable segments detection between Nitroglycerine MIBI and redistribution TI-201 imaging was found in 100 out of 105 segments (95.24%) for 15 patients, with significant kappa =0.746 ± 0.079 SE. Conclusion: The data suggest that use of nitrate augmented ^99mTcMIBI protocol in Cardiac SPECT imaging results in improved detection of viable but hypoperfused segments and achieves results similar to those from standard TI-201 rest and redistribution protocol.