Die Wirkung moderater Hypothermie auf Kontraktilität und calciuminduzierte Inotropie von humanem atrialen Myokard

In this study we examined the influence of induced moderate hypothermia on human atrial and rabbit ventricular myocardium. We measured contraction force, time relationship and its reaction to different positive inotropic agents such as calcium, isoproterenol and the phosphodiesterase inhibitor milrinone. Temperatures ranged between 37° C and 31°C. Human atrial muscle stripes were obtained from patients in sinus rhythm undergoing elective open heart surgery after receiving informed consent.Embedded in 2ml bath solution, the tissue stripes were stimulated at 20% above threshold at a temperature of 37°C. After reaching a steady state the temperature was reduced degree by degree until the target temperature was reached. Following the different setups, the muscles were then exposed to the different inotropic agents at a chosen temperature. Dose ot effect- relations were established. Maximum force of contraction (F), time to peak tension (TPT), time to 50% of contraction (Tsys50) and time to 50% relaxation (Tdia50) were continuously measured during this time. In atrial tissue the exerted hypothermia leads to a negative inotropic effect, adversely to the observed positive inotropic effect in ventricular tissue. Both tissue types showed a prolongation in contraction times as well as in relaxation process. Raising the extracellular calcium content, known for a strong positive inotropic effect under normothermia, only exerted a minimal inotropic change under hypothermia in both tissue types. The observed negative inotropic effect of hypothermia on human atrial myocardium differs from results found in previous studies on atrial tissue from other species. Different mechanisms in calcium-handling could provide an explanation, though a multifactorial cause seems to be more realistic