To assess the myocardial perfusion state after myocardial infarction, Tl-201 SPECT (Thallium-201 Single Photon Emission Computed Tomography) with a repeated "booster" injection before the acquisition of delayed redistribution image is more sensitive and more effective than conventional 4 hour redistribution image. However, this protocol has several disadvantages such as patient inconvenience, additional Tl-201 dose and compromised quantitative analysis. In this study, we compared 4 hour nitrate-augmented redistribution protocol with standard 24 hour delayed redistribution protocol with reinjection to evaluate the usefulness of sublingual nitrate to augment myocardial perfusion and the effectiveness of myocardial assessment for each protocol.

In 20 myocardial infarction patients, stress-redistribution Tl-201 SPECT was performed. Immediately after resting redistribution image was taken, each patient was administered 0.6 mg of nitroglycerin sublingually without additional Tl-201 and nitrate-augmented SPECT was taken after 30 minutes. Each patient then returned the next day and was injected with a booster dose of Tl-201 30 minutes before the delayed redistribution SPECT acquisition. For the analysis of SPECT study, the myocardium was divided into 22 segments, and the perfusion to each segment was scored on a four-point scale by consensus. An overall cardiac perfusion score was derived by summing the perfusion score for each segment.

Reduced stress perfusion was identified in 258 segment among total 440 segments: 61 (23.6%) had improved perfusion after rest redistribution; 145 (56.2%) had improved perfusion after nitrate-augmented redistribution; 140 (54.2%) had improved perfusion after 24 hour delayed redistribution after Tl-201 reinjection. The cardiac perfusion score after stress was 38.2±13.1. The score increased to 41.5±13.1 after rest redistribution. The perfusion score were improved to 46.3±10.4 (p≤0.05 vs. rest redistribution) after nitrate augmentation. The cardiac perfusion score, 46.2±10.8, did not improve further after delayed redistribution.

Tl-201 SPECT with sublingual nitrate-augmented redistribution is as same or better than 24-hour delayed redistribution with reinjection to detect viable myocardium. Therefore, Tl-201 SPECT with sublingual nitrate-augmented redistribution has economic and time sparing advantage over traditional 24 hour delayed redistribution with reinjection.