OBJECTIVE:To assess the influence of the postischemia/reperfusion stunned myocardium (PIRSM) on the inotropic and lusitropic effects of heart rate (HR). METHODS: Nine preparations of isolated dog hearts in isovolumic contraction and nourished by the arterial blood of another dog underwent heart rate elevation from 60 bpm to 200 bpm, in 20-bpm stages. The following variables were assessed before (B) and after (A) ischemia (15 min) and reperfusion (30 min): the pressure developed during contraction (PD), its first positive (+dP/dt) and negative (-dP/dt) derivative, the time of maximum pressure (TMP), the pressure at rest (Pr), and the time necessary for the developed pressure to decrease by 90% of its maximum value (time for relaxation - TR90%). RESULTS: The stimulating effects of HR elevation on inotropism and relaxation were similar before and after ischemia/reperfusion as follows: +dP/dt values increased, TMP decreased, -dP/dt values were intensified, and TR90% decreased. The values of PD did not change, and Pr increased. CONCLUSION: The results confirmed the positive inotropic effect of HR elevation (Bowditch effect) and the depressive action of ischemia/reperfusion. They also evidenced that PIRSM does not alter the stimulating action of the Bowditch effect, in accordance with the current concept that PIRSM does not impair calcium myocardial kinetics, favoring the prevalent hypothesis that the decrease in the contractile capacity after ischemia/reperfusion depends on the reduction of the myofilament responsiveness to calcium.
postischemia/reperfusion stunned myocardium; Bowditch effect; heart rate; systolic function; diastolic function
