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J Thorac Cardiovasc Surg 1998;115:226-230
© 1998 Mosby, Inc.

CARDIOPULMONARY SUPPORT AND PHYSIOLOGY

Optimal flow rates for integrated cardioplegia

From the Division of Cardiovascular Surgery and the Department ofClinical Biochemistry; The Toronto Hospital and the University of Toronto.Toronto, Ontario, Canada.

Presented in part at the Sixty-ninty Scientific Sessions of theAmerican Heart Association, New Orleans, La., Nov. 9–13, 1996

Received for publication Nov. 29, 1996; revisions requested March7, 1997; revisions received August 27, 1997; accepted for publication Sept.16, 1997 Address for reprints: Richard D. Weisel, MD, EN 14–215, TheToronto Hospital, Toronto, Ontario, Canada M5G 2C4.

Abstract

Background: Antegrade cardioplegicdelivery may be impaired by coronary occlusions, whereas retrograde deliveryof cardioplegic solution may be inhomogeneous, leading to an accumulationof lactate and hydrogen ions, the products of anaerobic metabolism. Integratedcardioplegia using continuous retrograde cardioplegia and antegrade infusionsinto completed vein grafts washes out metabolites accumulated in regions inadequatelyperfused by retrograde cardioplegia alone. To determine the flow rates requiredto achieve the greatest washout, we compared a high flow rate (200 ml/min) to a lowflow rate (100 ml/min).
Methods: Twenty patientsscheduled for isolated coronary bypass surgery were prospectively randomizedto compare two flow rates for integrated cardioplegic protection using tepid(29° C) blood cardioplegia. Arterial and coronary sinus blood sampleswere collected to evaluate myocardial metabolism. After antegrade arrest,cardioplegic solution was delivered by coronary sinus perfusion and simultaneousinfusions into each completed vein graft at either high or low flow.
Results: Increasing from low to high flow increased the washout of lactate and hydrogenions during the aortic crossclamp period. Two hours after crossclamp removal,ventricular function was better in the highflow group.
Conclusions: Tepid retrogradecardioplegia resulted in an accumulation of toxic metabolites. The additionof antegrade vein graft infusions at a flow rate of 100 ml/min resulted ina washout of these metabolites. A flow rate of 200 ml/min further improvedthis washout and resulted in improved ventricular function. An integratedapproach to myocardial protection using a flow rate of 200 ml/min may improvethe results of coronary bypass surgery.

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