Influence of temperature on the positive inotropic effect of levosimendan, dobutamine and milrinone

BACKGROUND AND OBJECTIVE: Patients in cardiac surgery and critically ill patients often demonstrate either hypothermia or fever. In addition, owing to heart failure, they frequently require inotropic support. The relative effectiveness of modern inotropic agents at various temperatures has not yet been evaluated. Therefore, we investigated the influence of levosimendan, dobutamine and milrinone on the contractile response of myocardial trabeculae at various temperatures. METHODS: A total of 120 guinea pig ventricular trabeculae were placed in oxygenated 4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid (HEPES) buffer, stimulated at a frequency of 1.3 Hz and randomly assigned to a temperature of 31 degrees C, 34 degrees C, 37 degrees C or 40 degrees C. Concentrations of all substances were increased stepwise from 10(-9) to 10(-5) mol l(-1) (milrinone up to 10(-4) mol l(-1)). Maximum developed force, time to peak tension, Tsystolic(50%) and Tdiastolic(50%) were continuously recorded. RESULTS: All agents showed a dose-dependent positive inotropic effect (P < 0.0001 for all). Levosimendan acted at every temperature as a positive inotrope (P = 0.0643). Dobutamine-related inotropy showed a clear trend towards temperature dependence, although statistical evaluation did not prove this (P = 0.0624). Milrinone-related inotropy was abolished at 31 degrees C and 34 degrees C, and temperature dependence was significant (P < 0.0001). Hypothermia induced a positive inotropic effect. CONCLUSION: Our results suggest no modulation of levosimendan-induced inotropy under the experimental temperatures tested. This observation is possibly due to its Ca2+-sensitizing mechanism, which might not be influenced by temperature-related changes in intracellular Ca2+ levels. In contrast, the inotropic effect of cyclic AMP-coupled dobutamine and milrinone is suppressed under hypothermia-related interaction with intracellular Ca2+ homeostasis. Hence, levosimendan might prove to be the preferred inotropic drug in hypothermic patients.