Background- Donor hearts for transplant are stored in extreme hypothermic conditions to reduce ischemic damage. However, hypothermia-dependent cellular, biochemical, structural injuries are of concern. We hypothesized that hearts stored at sub-normothermia in a novel preservation solution ‘Somah' are less prone to hypothermic damage, efficiently meet ex vivo metabolic demands, and readily revivable on reperfusion.

Methods- Porcine donor hearts stored in Somah at 4, 13 or 21°C were weighed prior to and after 5-hrs with biopsies taken for histology and tissue high energy phosphates (HEP). Great vessels were cannulated and at end of 5-hrs, hearts perfused initially with Somah via aorta and then Somah-blood mixture. System temperature was raised to 37°C over 30-mins. Electroconversion and/or epinephrine used if required. Inflow (aortic) and outflow (caval) samples were taken at start and after 30-mins of perfusion for creatine kinase (CK), lactate and myocardial O₂ consumption (MVO₂). Epicardial 2D Echo was done using trans-esophageal echo probe at peak performance.

Results- Irrespective of storage temperature, after 5-hrs, heart weights were unaltered with normal histology; HEP levels were 55.7±5.1, 68.4±11.0 and 81.5 ± 19.8 nM/mg tissue and, upon reperfusion, outflow CK levels were 250.1±140.6, 45.7±18.9 and 36.6±11.3 U/L in 4, 13 and 21°C groups respectively. After 30-mins, lactate levels and MVO₂ were unaltered in 4°C group but significantly decreased (p<0.01) and increased (p<0.01) respectively in both 13 and 21°C groups. Stimulatory interventions were inversely related to ex vivo storage temperature. Hearts in 13 and 21°C groups showed significantly high % fractional area change (%FAC; 39.2±8.6, 42.9±13.1) and ejection fraction (p<0.001) compared to 4°C group (%FAC=16.33±2.6). Peak cardiac output was 1.23±0.05, 1.93±0.36 and 2.1±0.3 L/min in 4, 13 and 21°C groups respectively.

Conclusion- This study demonstrated for first time that hearts can be stored in functionally viable state at sub-normothermic temperature in Somah. A rapid switch from anaerobic to aerobic metabolism, lesser creatine kinase release and fewer stimulatory interventions upon reperfusion of hearts stored at 13 and 21°C, suggest that sub-normothermic stored hearts are less prone to ischemia-reperfusion injury and more readily revivable than those stored at extreme hypothermia.

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