Purkinje fibers after myocardial ischemia-reperfusion.

The purpose of this study was to evaluate the effects of ischemia-reperfusion on Purkinje fibers, comparing them with the adjacent cardiomyocytes. In a model of heterotopic heart transplantation in pigs, the donor heart was subjected to 2 hours of ischemia (n=9), preserved in cold saline, and subjected to 24 hours of ischemia with preservation in Wisconsin solution, alone (n=6), or with an additive consisting of calcium (n=4), Nicorandil (n=6) or Trolox (n=7). After 2 hours of reperfusion, we evaluated the recovery of cardiac electrical activity and took samples of ventricular myocardium for morphological study. The prolonged ischemia significantly affected atrial automaticity and A-V conduction in all the groups subjected to 24 hours of ischemia, as compared to 2 hours. There were no significant differences among the groups that underwent prolonged ischemia. Changes in the electrical activity did not correlate with the morphological changes. In the Purkinje fibers, ischemia-reperfusion produced a marked decrease in the glycogen content in all the groups. In the gap junctions the immunolabeling of connexin-43 decreased significantly, adopting a dispersed distribution, and staining the sarcolemma adjacent to the connective tissue. These changes were less marked in the group preserved exclusively with Wisconsin solution, despite the prolonged ischemia. The addition of other substances did not improve the altered morphology. In all the groups, the injury appeared to be more prominent in the Purkinje fibers than in the neighboring cardiomyocytes, indicating the greater susceptibility of the former to ischemia-reperfusion injury.

Vitamin E action on oxidative state, endothelial function and morphology in long-term myocardial preservation.

This study assesses the effects of a vitamin E analogue, Trolox, on the oxidative state, endothelial function and morphology in experimental heart transplantation. Heterotopic heart transplantation was carried out in pigs: untreated after 2 and 24 hours of ischemia and treated with Trolox after 24 hours of ischemia. Prolonged preservation of donor hearts was achieved with continuous perfusion and University of Wisconsin solution, in which acid-base balance and enzymes were determined during the procedure. In recipients, hemodynamic and biochemical parameters were determined at baseline and during reperfusion. Trolox diminished the pH of the preservation solution (p<0.01), the left ventricle of the transplanted heart recovered a systolic pressure equaling that of the 2h group and higher than that of the untreated 24h group (p<0.01), the antioxidant levels were not decreased and the glutathione reductase level was maintained throughout the first part of reperfusion. In this group also there was a direct correlation between the concentration of this enzyme and the antioxidant levels (p<0.001). Although the endothelin concentrations increased, the change was less marked in the Trolox group than in the untreated 24h group (p<0.01). Morphologically, mitochondria and myocardial vessels presented a normal structure in the Trolox group, and interstitial edema, inflammatory infiltrate and contraction bands were less prominent than in the untreated group. All these effects indicate that Trolox protected the transplanted heart, at least partially, against ischemia-reperfusion injury.

Calcium-supplemented University of Wisconsin solution in long-term myocardial preservation.

The purpose of this study was to assess the effects of the addition of calcium to University of Wisconsin solution in long-term myocardial perfusion. In a heterotopic heart transplantation model, performed in pigs, the donor heart was preserved for 24 hours by means of continuous perfusion in this solution, without (24hUW group) or with calcium, 2.4 mmol/L (24hUW+Ca). During this period, the oxygenation and pH of the solution were measured, as were the calcium and lactate concentrations and enzyme release. After two hours of reperfusion, samples were collected from both ventricles for the morphological study. In the control group, there were no signs that reperfusion had triggered the calcium paradox. The addition of this cation to the preservation solution improved the intercellular junction integrity but, at the same time, favored intracellular calcium overload. This is manifested by increased enzyme release during preservation (LDH: 242+/-95 vs 140+/-25; CK: 668+/-371 vs 299+/-83 (U/L). p<0.01 in both cases) and signs of ventricular contracture: hardness and stiffness were significantly more prominent than in the group without calcium supplementation. Moreover, in comparison with the control group, the structural morphology of 24hUW+Ca is characterized by the more prominent and extensive presence of contraction bands and disorganized actin structure. Thus, under the experimental conditions employed in this study, we consider the addition of calcium to Wisconsin solution to be unadvisable.