Successful restoration of function of frozen and thawed isolated rat hearts.

Objective: Long-term organ preservation for transplantation may allow optimal donor-recipient matching with potential reduction in the incidence and severity of rejection. Complete cessation of metabolism may be obtained by freezing. Previous attempts to freeze intact mammalian hearts were limited to -3.6 degrees C, restricting tissue ice content to 34%. We hypothesized that our method will allow recovery of function of the intact rat heart after freezing to -8 degrees C, a temperature at which most of the tissue water is frozen. Methods: Isolated rat hearts were attached to a Langendorff apparatus. After normothermic perfusion, cold cardioplegia was induced followed by perfusion with a cryo-protecting agent. Hearts were than frozen to -8 degrees C (45 +/- 8 minutes), thawed, and reperfused (60 minutes). Results: All frozen and thawed hearts regained normal electric activity. At -8 degrees C, ice content was 64.36% +/- 13%. The use of 10% ethylene glycol for cryoprotection (n = 13) resulted in recovery (mean +/- standard deviation) of 49.7% +/- 21.8% of +dP/dt, 48.0% +/- 23.5% of -dP/dt, 65.2% +/- 30.8% of coronary flow, and 50.4% +/- 23.9% of left ventricular developed pressure. Hearts in this group (n = 4) maintained 81.3% +/- 10% viability compared with 69.3% +/- 14% (not significant) in control hearts kept at 0 degrees C for the same duration. Energy stores, represented by adenosine triphosphate and phosphocreatine, were depleted to 12.2 +/- 6.1 mu mol/g dry weight and 22.5 +/- 6.4 mu mol/g dry weight, respectively, compared with 19.0 +/- 2.5 mu mol/g dry weight and 36.6 +/- 3.0 mu mol/g dry weight, respectively (P < .05) in the control hearts. The integrity of muscle fibers and intracellular organelles after thawing and reperfusion was demonstrated by electron microscopy. Conclusion: We demonstrate for the first time the feasibility of functional recovery after freezing and thawing of the isolated rat heart while maintaining structural integrity and viability.