Rapid cooling contracture with cold cardioplegia

Background. Cold cardioplegia can induce rapid cooling contracture. The relations of cardioplegia-induced cooling contracture to myocardial temperature or myocyte calcium are unknown. Methods. Twelve crystalloid-perfused isovolumic rat hearts received three 2-minute cardioplegic infusions (1 mmol/L calcium) at 4°, 20°, and 37°C in random order, each followed by 10 minutes of beating at 37°C. Finally, warm induction of arrest by a 1-minute cardioplegic infusion at 37°C was followed by a 1-minute infusion at 4°C. Indo-1 was used to measure the intracellular Ca2+ concentration in 6 of these hearts. Additional hearts received hypoxic, glucose-free cardioplegia at 4° or 37°C. Results. After 1 minute of cardioplegia at 4°, 20°, and 37°C, left ventricular developed pressure rose rapidly to 54% ± 3%, 43% ± 3%, and 18% ± 1% of its prearrest value, whereas the intracellular Ca2+ concentration reached 166% ± 23%, 94% ± 4%, and 37% ± 10% of its prearrest transient. Coronary flow was 5.7 ± 0.2, 8.7 ± 0.3, and 12.6 ± 0.6 mL/min, respectively. Warm cardioplegia induction at 37°C reduced left ventricular developed pressure and [Ca2+]i during subsequent 4°C cardioplegia by 16% (p = 0.001) and 34% (p = 0.03), respectively. Adenosine triphosphate and phosphocreatine contents were lower after 4°C than after 37°C hypoxic, glucose-free cardioplegia. Conclusions. Rapid cooling during cardioplegia increases left ventricular pressure, [Ca2+]i, and coronary resistance, and is energy consuming. The absence of rapid cooling contracture may be a benefit of warm heart operations and warm induction of cardioplegic arrest.