Myocardial preservation

Heart transplantation-associated perioperative ischemic myocardial injury. Morphological features and clinical significance

BACKGROUND

The frequency and clinical significance of perioperative ischemic myocardial injury (PIMI) after heart transplantation and the diagnostic features distinguishing PIMI from rejection are not well defined.

METHODS AND RESULTS

We evaluated PIMI in the first four weekly endomyocardial biopsies and/or autopsy myocardium from 140 consecutive orthotopic heart transplantation recipients (1984 to 1991) by grading the severity of coagulative myocyte necrosis (CMN) as absent, 0; mild-focal, 1; moderate-multifocal, 2; or severe-confluent, 3, and determining the evolution of morphological features of its healing. CMN (often with contraction bands) was noted in 124 patients (89%); 24 patients (17%) had grade 3 CMN, of which 4 died within 30 days of transplantation. Nevertheless, at 1 year after surgery, survival was similar in patients with and without severe injury. Increased cold ischemic time but neither donor age nor intensity of inotropic support correlated with more severe early ischemic injury. PIMI inflammation was characterized by a predominantly polymorphonuclear/histiocytic infiltrate that contained lymphocytes and plasma cells, expanding the interstitium but not encroaching upon and separable from adjacent viable myocytes. Histological features of PIMI developed and resolved more slowly than those of typical myocardial infarct necrosis in nonimmunosuppressed patients; at 4 weeks, CMN persisted in 20% of patients and residual healing in nearly half. Diagnostic rejection was observed concurrently with PIMI in 54 of 533 biopsies (10%).

CONCLUSIONS

Diagnosed by conventional histological criteria, PIMI is prevalent early after heart transplantation and has a protracted healing phase that can mimic or coexist with rejection. Extensive PIMI has deleterious impact on short-term survival, but the long-term impact of PIMI remains to be established.

Pulmonary mechanics after cardio-pulmonary transplantation, an experimental study

An experimental model was developed in pigs (weight: 25 +/- 2 kg), to evaluate pulmonary mechanics during the first 2 h of reperfusion following heart-lung transplantation. We studied two groups with three transplantations each: group A (45 min of preservation) and group B (6 h of preservation). After rinsing out the heart-lung mass by the injection of a cold intracellular solution (K+ = 115 mEq/l) into the aorta and the pulmonary artery, the organs were removed and conserved in a cold environment (0.5 degrees C). The orthotopic heart-lung transplantation was carried out using extra-corporeal circulation. Pulmonary mechanics were evaluated before and after transplantation by measuring the pulmonary compliance (C), and the aero-dynamic resistance (R) with an interrupted air flow technique. [table: see text] The duration of ischaemia appeared to be a pernicious factor in cardiopulmonary function. In all cases, the protection protocol of the heart-lung block had allowed a cutting-off of the cardiorespiratory assistance. However, there were major pulmonary mechanical perturbations, associated with a reduction in the pulmonary compliance and a very important increase in the aerodynamic resistance.

Oxygen-derived free radical damage in canine heart transplantation

To study the role of free radical-induced myocardial injury during heart transplantation, five groups of dog hearts were orthotopically transplanted. Control group I and experimental groups II, III, and IV (each n = 8) were reperfused for 1 hr after 49 min of operational ischemia. Control group V (n = 4) remained ischemic for 90 min. In the three experimental groups, the free radical scavengers superoxide dismutase (10 mg/kg; group II), catalase (10 mg/kg; group III), or both (10 mg/kg each; group IV) were administered just before reperfusion and during reperfusion for 1 hr. The generation of free radicals, remained at low levels in all groups during ischemia, but significantly increased when groups I-IV were reperfused. This increase was also associated with an increase in creatinine kinase MB isoenzyme. In the experimental groups, free radical scavengers significantly inhibited the appearance of thiobarbituric acid reactive substances and the release of creatinine kinase MB isoenzyme during reperfusion (P less than 0.05). Regarding cardiac functions, 60 min after the termination of the cardiopulmonary bypass, a significant improvement was demonstrated in the treated groups (P less than 0.05). These results indicate that (1) the generation of oxygen free radicals occurs primarily during reperfusion, (2) both superoxide dismutase and catalase reduce production of free radicals during this time, and (3) combined administration did not provide a greater improvement in cardiac metabolic recovery. This study confirms the efficacy of free radical scavengers during heart transplantation.