Prognostic value of 99mTc-Sestamibi stress Myocardial Perfusion Single Photon Emission Computed Tomography (SPECT) in ischemic heart disease

Abstract

Aim: To study prognostic value of 99mTc-Sestamibi stress Myocardial Perfusion Single Photon Emission Computed Tomography (SPECT) in suspected or diagnosed ischemic heart disease, in an urban Indian population.

Methods: Eight hundred and eighty one patients with clinically suspected or diagnosed ischemic heart disease who underwent 99mTc-MIBI stress-rest Myocardial Perfusion SPECT (MPS) between 1st February 2001 to October 2002 were followed up for 14 +/- 2 months after the scan by questionnaire and telephonic interview with queries about cardiac death, myocardial infarct (hard events) and admission for unstable angina, CABG and PTCA (soft events). Patients were classified into pre-test: low, intermediate or high risk subsets based on clinical risk factors and ECG criteria. They were then reclassified based on MPS scan into post-test: high, intermediate and low risk subsets. Subsequent cardiac event rate was compared in the three subsets. A 12-lead ECG was an integral component of the stress MPS evaluation.

Results: MPS changed (1) the pre-test low risk category in 114 out of 613 patients to intermediate and 102 to high risk; (2) pre-test intermediate risk in 110 patients out of 163 to low risk and 19 patients to high risk (3) pre-test high risk category in 56 patients out of 105 to low risk and 28 to intermediate risk (total change 429 out of 881 patients). The hard cardiac event rate at one year was less than 0.5% in low risk, 2.3% in intermediate risk and 4.2% in high risk group.

Conclusions: 99mTc-Sestamibi stress SPECT MPS thus provided incremental information for prognostic evaluation of patients with suspected or diagnosed coronary artery disease by assessing the effect of ischemic burden on LV function. This incremental information is crucial since coronary arteriography alone is not enough for prognosis and management decisions. Patients with a normal or low risk MPS have generally a benign prognosis with a low annual hard cardiac event rate of 0.5%. Future challenge is to identify high risk subsets within this group, with CT coronary calcium score > or = 100 and inflammation markers such as high hsCRP so that more aggressive secondary preventive measures can be instituted to prevent future hard cardiac events.