EFFECTS OF DOBUTAMINE ON ISOVOLUMIC AND EJECTION PHASE INDEXES OF CARDIAC CONTRACTILITY IN CONSCIOUS HEALTHY DOGS

The aim of this study was to determine cardiac contractility using ind ices derived from cardiac catheterisation in conscious healthy dogs du ring dobutamine infusion. Eight dogs were studied. An ECG was recorded together with left ventricular pressure and volume which were measure d using a conductance catheter with an integrated microtip pressure se nsor. Eight indices of left ventricular systolic performance were deri ved from these records. Measurements were realised under basal conditi ons and during an incremental dobutamine challenge. The maximal rate o f rise in ventricular pressure (max dP/dt), max dP/dt divided by the d eveloped pressure and the mean systolic ejection rate were the most se nsitive indices to detect dobutamine induced changes in contractility with maximal percentage changes of 122+/-11 per cent, 130+/-7 per cent and 102+/-24 per cent respectively. Ejection fraction increased signi ficantly during dobutamine infusion (maximal percentage change of 43+/ -9 per cent) whereas the pre-ejection period (PEP) and the left ventri cular ejection time (LVET) decreased significantly (maximal percentage change of -41+/-2 per cent and -28+/-3 per cent respectively). All th ese six indices were significantly correlated with each other. Convers ely, the ratio PEP/LVET and the LVET corrected for heart rate dependen cy showed a maximal percentage change of only -10+/-1 per cent and -16 +/-7 per cent, respectively, during the dobutamine infusion and were n ot significantly correlated with the other contractility indices. This study demonstrated the feasibility of the conductance method to deter mine cardiac contractility in conscious healthy dogs submitted to a ph armacological stress testing and provides control values for eight ind ices of left ventricular contractility during dobutamine infusion at i ncreasing dosages.