PROSPECTIVE IDENTIFICATION OF MYOCARDIAL STUNNING USING TC-99M SESTAMIBI-BASED MEASUREMENTS OF INFARCT SIZE

Objectives. We sought to prospectively identify patients with stunning and hyperkinesia at hospital discharge on the basis of mismatches bet ween left ventricular (LV) function and infarct size as assessed by te chnetium-99m (Tc-99m) sestamibi perfusion tomographic imaging. Backgro und. Mechanical indexes of LV function may not accurately reflect myoc ardial damage after acute myocardial infarction (MI) because of myocar dial stunning and compensatory hyperkinesia in noninfarct-related terr itories. Myocardial perfusion techniques are unaffected by these varia bles. Methods. Eighty-four patients with acute MI underwent hospital a dmission and discharge Tc-99m-sestamibi tomographic imaging. Global LV ejection fraction (LVEF) was measured at hospital discharge and 6 wee ks later. The perfusion defect size was quantified and expressed as a percentage of the LV. The discharge perfusion defect, which is a measu re of infarct size, was used to predict the 6-week LVEF for each patie nt based on a previously reported regression equation. Patients were c lassified into one of three groups depending on whether their LVEF at hospital discharge fell within, above or below one standard error (6.8 LVEF points) of the predicted 6 week LVEF. Results. There were 48 pat ients classified as having a ''match'' between function and infarct si ze; these patients demonstrated no significant change in LVEF at 6 wee ks. There were 21 patients (25%) classified as ''mismatch stunned'' wh o had discharge LVEFs lower than those predicted by infarct size. Thes e patients demonstrated a significant improvement in mean LVEF at 6 we eks (mean [+/-SD] discharge LVEF 0.41 +/- 0.08, 6-week LVEF 0.47 +/- 0 .10; p = 0.003). Fifteen patients (18%) were classified as ''mismatch- hyperkinetic.'' The mean LVEF for these patients significantly decline d at 6 weeks (discharge LVEF 0.64 +/- 0.06, 6-week LVEF 0.58 +/- 0.09; p = 0.002). There was a marked increase in LVEF within the infarct zo ne (8 +/- 15 LVEF points; p = 0.03) for patients predicted to have stu nning and a marked decline in LVEF outside the infarct zone (9 +/- 15 LVEF points; p 0.06) in patients predicted to have hyperkinesia. Both discharge LVEF (p < 0.0001) and group classification (p = 0.005) were independent predictors of LVEF 6 weeks later. Conclusions. Perfusion i maging with Tc-99m-sestamibi can identify post-MI patients at hospital discharge in whom LV function is discordant with the measured infarct size. Patients with stunning have late increases in LVEF; patients wi th hyperkinesia have late decreases. This methodology, performed at di s charge, is predictive of late changes in LV function. (C) 1997 by th e American College of Cardiology.