[Diastolic behavior during postischemic hypercontraction phase in rabbit stunned myocardium]

The objective was to determine whether "hypercontraction" (HC) that occurs at the beginning of reperfusion (R) in stunned myocardium is accompanied by diastolic alterations and determine if the R with low Ca2+. Ringer's solution modifies these alterations. Isolated isovolumic rabbit hearts were divided into 2 groups. Group 1 (G1, n = 11) was perfused with Ringer's solution ([Ca2+] = 2 mM) and subjected to 15 min of global ischemia and 30 min of R. Group 2 (G2, n = 10) was R during the first 10 min with ([Ca2+] = 1 mM), which was increased to 1.5 mM and 2 mM in the perfusate at 30 min of R. The left ventricular +dP/dtmax, left ventricular end diastolic pressure (LVEDP) (stiffness index), and relaxation rate (t 1/2 and +P/-P ratio) were measured, from the beginning of R every 10 sec for 2 min, and then at 5 and 30min. At 60 sec of R the +dP/dtmax in G1 was increased (76.88 +/- 5.37% vs preischemic value) and was attenuated in G2 (48.22 +/- 3.40%; P < 0.05 vs G1). The LVEDP in G1 was increased early in the R, although it was negatively correlated with HC degree (r = .0.7477; p = 0.008). This increase was attenuated in G2 (P < 0.05 vs G1) at 60 sec R. There was a dealy in the relaxation at 60 secR in both group (G1 vs G2, NS).

HC is accompanied by diastolic alterations. The improvement of HC is inversely related with LVEDP. During R the stiffness during the relaxation rate was normal. The R with low Ca2+ attenuated the HC and the diastolic stiffness.