Technetium-99m isonitrile myocardial uptake at rest. II. Relation to clinical markers of potential viability

To determine the utility of rest-injected technetium-99m methoxybutyl isonitrile (Tc-99m isonitrile) uptake as a marker of myocardial viability, the regional uptake of this agent was compared with regional wall motion by equilibrium gated blood pool scan in 26 patients with previous myocardial infarction and with postrevascularization uptake in 8 patients after coronary bypass surgery. Rest left ventricular Tc-99m isonitrile uptake was assessed qualitatively in three coronary vascular territories as grade 0 (markedly reduced) to grade 2 (normal), and quantitatively by circumferential profile analysis. Wall motion was scored qualitatively in corresponding vascular territories as normal, hypokinetic or akinetic/dyskinetic. There was an overall relation between qualitative Tc-99m isonitrile uptake and wall motion. Abnormal wall motion occurred in 74% of vascular territories with perfusion grade 0, in 61% of those with grade 1 and in 30% of those with grade 2; however, 26% of territories with grade 0 uptake had normal wall motion. In the territories visually assigned perfusion grade 0, quantitative isonitrile uptake (mean value ± SD) was higher when corresponding wall motion was normal or hypokinetic (62 ± 15%) than when akinesia was detected by gated blood pool scan (39 ± 16%, p < 0.02). Qualitative Tc-99m isonitrile uptake improved after coronary bypass surgery in 12 of 13 territories with reduced uptake preoperatively; this included all 5 territories with a preoperative Tc-99m isonitrile score of 0. Quantitative uptake in these regions increased from 55 ± 18% to 73 ± 21% (p < 0.01). It is concluded that regions with a severe reduction in Tc-99m isonitrile uptake at rest may contain viable myocardium; such reduced perfusion should not necessarily be considered evidence of myocardial scar. Inferences about myocardial viability based on rest-injected Tc-99m isonitrile (as evidenced by intact wall motion) are better made using quantitative rather than qualitative image analysis.