Myocardial Oxygenation and Recovery after Topical Cooling of the Ischaemic Heart and after Hypothermic Coronary Perfusion:A Clinical Study of Aortic Valve Replacement Patients

Abstract

Myocardial oxygenation and recovery during aortic valve replacement were studied at different stages of operations, in which either topical cooling of the ischaemic heart (TCI) or hypothermic coronary perfusion (HCP) was used for myocardial protection. During HCP the utilization of available oxygen by the myocardium decreased by 65%. During rewarming significant lactate washout and production by the myocardium was found in the TCI-group with no significant signs of defective oxygen utilization. Already 10 min after initiation of reperfusion a greater oxygen extraction by the heart was seen in the TCI-group than in the HCP-group. This tendency persisted until the end of operation. There was some lactate production in the HCP-group during rewarming. The CI relative to PCWP showed a marked increase over prebypass values after bypass during lonotropic load in both patient groups, but the increase was more marked in the HCP-group, probably indicating a greater reserve of mechanical performance capacity. The increase in CI was associated with an increase in heart rate, but because of simultaneous decrease of systemic arterial pressure the pulse-pressure product, an indicator of myocardial oxygen consumption, did not increase. There were no intergroup differences in the cardiac performance after the immediate post-bypass period. The total activity of creatine kinase (CK) in blood increased nearly twice as much in the HCP-group as in the TCI-group. On the basis of the metabolic findings, it is concluded that there is no significant postischaemic reperfusion injury after TCI, that there is probably a transitory diminution in the reserve of mechanical performance capacity of the heart after TCI and that the greater increase in the total CK-activity after HCP is related either to a greater degree of skeletal muscle injury because of longer bypass time or to a greater degree of myocardial injury.