Regional differences in left ventricular wall motion in the anesthetized dog

Data regarding left ventricular function suggest that the extent of shortening may differ between regions. This study was undertaken to determine the effects of negative inotropic drugs used during anesthesia on different areas of the left ventricle. Forty mongrel dogs were anesthetized and instrumented for measurement of global and regional function. Regional function in the short axis of the basal and apical territories of the left ventricle was assessed by subendocardial sonomicrometry. Three different interventions were performed: In the first group 67% N2O, replacing 67% N2, was added to opiate anesthesia; in the second group halothane was given by stepwise increases in inspired concentration to 2%; in the third group verapamil (60 micrograms.kg-1.h-1) was infused during isoflurane anesthesia. Apical and basal segmental shortening were compared. During baseline conditions and with agents in concentrations that caused minimal myocardial depression (67% N2O or 1.0% as opposed to 0.5% halothane) differences in systolic shortening between regions were statistically significant. Further myocardial depression affected the apex significantly more than the base: when substantial myocardial depression was induced by halothane (1.5 or 2%) or verapamil, differences in regional function were abolished. Thus, the apical region of the left ventricle is more dynamic and more sensitive to negative inotropic interventions than the basal region. This should be borne in mind when segmental myocardial function is evaluated.