Measurements of the effects of percutaneous nitroglycerin on left ventricular performance in patients with coronary artery disease with a cardiac probe

Tl-201 myocardial perfusion SPECT: role of nitrate-augmented redistribution

PURPOSE

TI-201 myocardial perfusion SPECT is commonly used to assess myocardial perfusion and viability. Nitrate-augmented redistribution with repeated injection facilitates the detection of reversible segments compared with standard redistribution. In this study, we investigated the potential of nitrate augmentation to improve myocardial perfusion and viability assessment without repeated injection and we also compared nitrate-augmented redistribution with delayed redistribution.

METHODS

Eighteen patients underwent a stress-redistribution TI-201 SPECT study. Immediately after redistribution SPECT, each patient was administered 0.6 mg glyceryl trinitrate and nitrate-augmented redistribution SPECT acquired 30 minutes later. Each patient then returned the next day and was injected with a booster dose of TI-201 30 minutes before the delayed redistribution SPECT acquisition. For each SPECT study, the myocardium was divided into 11 segments, and 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.

RESULTS

Reduced stress perfusion was identified in 150 segments: 23 (15.3%) had improved perfusion after redistribution; 60 (40%) segments had improved perfusion after nitrate-augmented redistribution; 52 (34.7%) segments with reduced stress perfusion had improved perfusion after delayed redistribution. The cardiac perfusion score after stress was 15.9+/-5.5 (means+/-SD). The score increased to 17.4+/-5.4 after redistribution. The perfusion score improved to 19.7+/-5.8 (P < 0.05 versus redistribution) after nitrate augmentation. The cardiac perfusion score, 19.2+/-6.4, did not improve further after delayed redistribution.

CONCLUSIONS

TI-201 SPECT with nitrate-augmented redistribution is as good or better than delayed redistribution with repeated injection for myocardial perfusion and viability assessment. TI-201 SPECT with nitrate-augmented redistribution has significant logistical and economic advantages over traditional delayed redistribution with TI-201 repeated injection.

Nitrate-augmented myocardial imaging for assessment of myocardial viability

201Tl myocardial perfusion imaging is presently done by several possible strategies. Stress/delayed redistribution, stress/redistribution/reinjection, and rest/redistribution imaging can be useful in the clinical assessment of myocardial viability. Unfortunately, the extent of myocardial viability may still be underestimated even by 201Tl reinjection imaging, compared with 18F-fluorodeoxyglucose positron emission tomography. 99mTc-labeled sestamibi imaging provides results similar to those of 201Tl imaging in the detection of coronary artery disease, but several previous studies suggest that stress/rest 99mTc-labeled sestamibi imaging significantly underestimates myocardial viability. Recently it has been reported that the administration of nitrates, before 201Tl reinjection, improves detection of defect reversibility. Several studies also suggested that administration of nitrates before the injection of 99mTc-labeled sestamibi significantly improved detection of reversibility with this agent, whereas additional studies showed further that this combination improves the predictive accuracy for recovery of left ventricular function and perfusion after coronary revascularization, compared with a standard rest 99mTc-labeled sestamibi study. Nitrate administration before the injection of 201Tl and 99mTc-labeled sestamibi may thus be a potentially attractive alternative for the evaluation of myocardial viability. Although the available results are encouraging, further studies are needed to evaluate the clinical value of 201Tl and 99mTc-labeled sestamibi imaging, in combination with nitrates, for predicting recovery of left ventricular dysfunction.