EFFECT OF INOTROPIC STIMULATION ON THE SYNCHRONY OF LEFT-VENTRICULAR WALL-MOTION IN A DOG-MODEL OF MYOCARDIAL STUNNING

Background: Reperfusion after short coronary occlusion induces regiona l myocardial dysfunction (''stunning''), including asynchrony of left ventricular (LV) wall motion. Contractile function of stunned myocardi um can be increased by inotropic stimulation, but whether this has an influence on wall motion asynchrony is unknown. Methods: In six anaest hetized dogs, the effect of inotropic stimulation on regional myocardi al function, and LV asynchrony was tested after the induction of regio nal stunning (by 15 min of left circumflex artery side branch occlusio n). Regional myocardial function was assessed as mean systolic wall th ickening velocity (v(swt)) by sonomicrometry in the stunned (posteroba sal wall) and normal myocardium (anteroapical wall), and LV asynchrony by the phase difference (phi) of the first Fourier transform of the w all thickness signals. Results: In the stunned myocardium, v(swt) dece ased from 8.6+/-1.0 to 1.7+/-1.4 mm s(-1) (mean+/-SEM), P<0.01, and si multaneously phi increased from 10.8+/-3.6 to 85.7+/-14.3 degrees, P<0 .01. Intra-coronary noradrenaline (NADR, 0.25 mu g) improved v(swt) th e stunned region and (8.3+/-1.4 mm s(-1), P<0.01) in changed phi to -3 8.1+18.0 degrees, P<0.05. Systemic NADR (5 mu g) also increased v(swt) of the stunned region (to 3.8+/-2.1 mm s(-1), P<0.05), but left phi u nchanged (82.9+/-19.8 degrees). Conclusion: Regional function of stunn ed myocardium can be augmented by inotropic stimulation with noradrena line, but this does not result in an improvement of LV wall motion asy nchrony during systemic inotropic stimulation.