Transmural contractile reserve after reperfused myocardial infarction in dogs

OBJECTIVES The goal of this study was to characterize detailed transmural l eft ventricular (LV) function at rest and during dobutamine stimulation in subendocardial and transmural experimental infarcts. BACKGROUND The relation between segmental LV function and the transmural ex tent of myocardial necrosis is complex. However, its detailed understanding is crucial for the diagnosis of myocardial viability as assessed by inotro pic stimulation. METHODS Short-axis tagged magnetic resonance images were acquired at five t o seven levels encompassing the LV from base to apex in seven dogs 2 days a fter a 90-min closed-chest left anterior descending coronary occlusion, fol lowed by reflow. Myocardial strains were measured transmurally in the entir e LV by harmonic phase imaging at rest and 5 ig.kg(-1).min(-1) dobutamine. Risk regions were assessed by radioactive microspheres, and the transmural extent of the infarct was assessed by 2,3,5 triphenyltetrazolium chloride s taining. RESULTS Circumferential shortening (Ecc), radial thickening (Err) and maxim al shortening at rest were greater in segments with subendocardial versus t ransmural infarcts, both in subepicardium (-1.1 +/- 1.0 vs. 2.5 +/- 0.6% fo r Ecc, -0.5 +/- 1.9 vs. -1.8 +/- 1.0% for Err, p < 0.05) and subendocardium (-2.0 +/- 1.4 vs. 2.8 +/- 0.8%, 2.4 +/- 1.7 vs. 0.0 +/- 0.9%, respectively , p < 0.05). Under inotropic stimulation, risk regions retained maximal con tractile reserve. Recruitable deformation was found in outer layers of sube ndocardial infarcts (p < 0.01 for Ecc and Err) but also in inner layers (p < 0.01). Conversely, no contractile reserve was observed in segments with t ransmural infarcts. CONCLUSIONS Under dobutamine challenge, recruitment of myofiber shortening and thickening was observed in inner layers of segments with subendocardial infarcts. These results may have important clinical implications for the d etection of myocardial viability. (C) 2000 by the American College of Cardi ology.