We induced ischaemia in the left anterior descending artery of 16 dogs while the heart was beating, followed by cardiopulmonary bypass (CPB), aortic cross clamping and blood cardioplegia. Half of the dogs received integrated blood cardioplegia and sudden uncontrolled reperfusion (group A) while the others received the same cardioplegia followed by pressure-controlled tepid initial reperfusion (group B). The effects on myocardial cell metabolism, oxidative stress and ultrastructure were recorded. The recovery period was significantly longer and cardiac output levels after CPB significantly lower in group A compared with group B. Group A showed a failure to uptake and utilize oxygen during the recovery period and significant lipid peroxidation. Marked tissue oedema was seen in group A but mitochondrial and organelle integrity was almost normal in both groups. We conclude that integrated cardioplegia could partially resuscitate the myocardium in this model, and pressure controlled reperfusion during the first 2 min is needed as an adjunct procedure.

We investigated the effects of pressure, temperature and additives on aortic root reperfusion success. Cardiopulmonary bypass and heart arrest were initiated in mongrel dogs and sudden uncontrolled normothermic (group 1), pressure controlled substrate enriched normothermic (group 2a), pressure controlled unmodified normothermic (group 2b) and pressure controlled unmodified tepid (group 3) reperfusion compared. In group 1, the first cardiac rhythm was ventricular fibrillation, but dogs in the other groups showed spontaneous sinus rhythm. Recovery times were significantly longer and cardiac output levels significantly decreased in group 1 compared with the other groups. Prolonged lactate production and oxygen uptake failure were observed in group 1 compared with the other groups; oxidative stress markers and microscopic studies confirmed significant tissue injury in group 1. All parameters were similar between groups 2a, 2b and 3, indicating that low reperfusion pressure in the first 2 min is the most effective component of reperfusion.

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