Routine Stress-Rest Tc-99m MIBI Myocardial Perfusion Scintigraphy Underestimates Ischemia and Viability

Objective: The study included patients with known or suspected coronary artery disease. It aimed to demonstrate the incremental value of the routine nitrate augmentation in stress-rest technetium-99m methoxyisobutylisonitrile (Tc-99m MIBI) myocardial perfusion scintigraphy (MPS). Material and Methods: Standard stress and rest MPS was performed, followed by a second rest study with isosorbide dinitrate intervention within 5 days. The redistribution of Tc-99m MIBI was compared between stress and rest images, and interpretation of the study done as normal, scarred, and ischemia ± mixed lesion groups. The rest studies were compared with the rest nitrate studies. Summed rest score (SRS) and summed rest nitrate score (SRNS) were calculated. The summed difference score (SDS) of SRS and SRNS was calculated for each group. Results: A total of 50 patients were included in the study. Based on the routine MPS, patients were divided into the scar (n = 20), ischemia (n = 18), and normal (n = 12) groups. After the administration of nitrate, a significant fall in the blood pressure (P < .001) and an increase in the heart rate (P < .001) were noted. SDS was not significant in the normal MPS group (0.17 ± 0.57, P = .19). In comparison, substantial SDS was found in the ischemia ± mixed lesion (4.33 ± 3.43) and scarred (3.5 ± 3.15), respectively (both P < .001). Percentage improvement in the SRS from SRNS was found less than 2% for normal MPS while 18% and 29% for scarred and mixed groups, respectively. Conclusion: Routine MPS (stress followed by rest) underestimate ischemia and viability, which can be significantly reduced by utilizing nitrate augmentation in all patients with abnormal stress MPS. This could lead to a significant change in the extent and severity of ischemia and viability.