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 regional myocardial dysfunction ("stunning"), including asynchrony of left ventricular (LV) wall motion. Contractile function of stunned myocardium can be increased by inotropic stimulation, but whether this has an influence on wall motion asynchrony is unknown. METHODS: In six anaesthetized dogs, the effect of inotropic stimulation on regional myocardial function, and LV asynchrony was tested after the induction of regional stunning (by 15 min of left circumflex artery side branch occlusion). Regional myocardial function was assessed as mean systolic wall thickening velocity (Vswt) by sonomicrometry in the stunned (posterobasal wall) and normal myocardium (anteroapical wall), and LV asynchrony by the phase difference (phi) of the first Fourier transform of the wall thickness signals. RESULTS: In the stunned myocardium, Vswt decreased from 8.6 +/- 1.0 to 1.7 +/- 1.4 mm s-1 (mean +/- SEM), P < 0.01, and simultaneously phi increased from 10.8 +/- 3.6 to 85.7 +/- 14.3 degrees, P < 0.01. Intracoronary noradrenaline (NADR, 0.25 microgram) improved Vswt (8.3 +/- 1.4 mm s-1, P < 0.01) in the stunned region and changed phi to -38.1 +/- 18.0 degrees, P < 0.05. Systemic NADR (5 micrograms) also increased Vswt of the stunned region (to 3.8 +/- 2.1 mm s-1, P < 0.05), but left phi unchanged (82.9 +/- 19.8 degrees). CONCLUSION: Regional function of stunned myocardium can be augmented by inotropic stimulation with noradrenaline, but this does not result in an improvement of LV wall motion asynchrony during systemic inotropic stimulation.