Differentiation between Clinical and Academic Myocardial Viability. Complementary Myocardial Perfusion SPECT and Low Dose Dobutamine Echocardiography Role vs. Histopathological Study

Background: Rest-Redistribution thallium(R-RD Tl) imaging has high negative predictive value (NPV) but low positive predictive value (ppv) for the prediction of recovery of regional myocardial dysfunction after revascularization (Rev). Combining myocardial perfusion (MP) and functional data with nitrate-enhanced gated SPECT MIBI (GSM) at rest appears to be a promising approach for viability detection. Aim of the Study: Differentiate between clinical and academic viability. Methods: Total of 66 patients with CAD underwent R-RD Tl,2 sets of resting GSM using 2 MIBI injections, and echocardiography at rest andafter low dose dobutamine (LDD). One hour before GSM2, trimetazidine (TMZ) andnitrate, had been given. All pts had their echo repeated after (Rev) as a golden standard for clinical viability one year later. Myocardial biopsy was taken for mitochondrial assessment as a golden standard for academic viability. Results: 389/1122 segments were found to have abnormal resting wall motion (RWM) on echo. 165/217 hypokinetic, 48/102 akinetic and 6/66 dyskinetic showed contractile response for LDD echo. The MP images showed normal uptake, complete, partial reversibility and poor uptake in Tl, GSM1 and GSM2 images as following:(58,31,47), (36,22,35), (198,119,190) and (32,148,50) of segments respectively. Sensitivity and specificity of Tl, GSM1 and GSM2 and LDD echo for clinical viability had been found respectively to be (94.9%,74.1%), (59.9%,93.6%), (93.5%, 90%) and (78.5%,100%). Mitochondrial degeneration had been found to be more in the segments with partial reversibility and those with poor uptake with sensitivity and specificity of (90,85.6%), (57.2%,94.2%), (89.4%,98%) and (75%, 88.2%) respectively. From this data we can grade viability into 4 grades. Conclusion: Clinical definition of viability is better looked for in GSM2. Viability could be assessed into 4 grades.