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Optimal flow rates for integrated cardioplegia
1Division of Cardiovascular Surgery, Toronto Hospital, Ontario, Canada.
Insights
Integrated cardioplegia with high flow (200 ml/min) effectively clears lactate and hydrogen ions, improving ventricular function after coronary bypass surgery compared to low flow rates.
Area of Science:
- Cardiovascular Surgery
- Myocardial Protection
Background:
- Antegrade cardioplegia can be limited by coronary occlusions.
- Retrograde cardioplegia may lead to inhomogeneous perfusion and metabolite buildup.
- Integrated cardioplegia aims to improve metabolite washout.
Purpose of the Study:
- To compare high (200 ml/min) versus low (100 ml/min) flow rates for integrated cardioplegia.
- To determine optimal flow rates for metabolite washout during coronary bypass surgery.
Main Methods:
- Prospective randomized trial of 20 patients undergoing isolated coronary bypass surgery.
- Comparison of two flow rates for tepid blood cardioplegia delivery.
- Measurement of myocardial metabolism via arterial and coronary sinus blood sampling.
Main Results:
- Higher flow rates (200 ml/min) significantly increased washout of lactate and hydrogen ions.
- Improved ventricular function was observed in the high flow group post-reperfusion.
Conclusions:
- Tepid retrograde cardioplegia alone can cause toxic metabolite accumulation.
- Integrated cardioplegia with antegrade vein graft infusions enhances metabolite washout.
- A flow rate of 200 ml/min optimizes washout and improves ventricular function, potentially enhancing coronary bypass surgery outcomes.
Background:
Antegrade cardioplegic delivery may be impaired by coronary occlusions, whereas retrograde delivery of cardioplegic solution may be inhomogeneous, leading to an accumulation of lactate and hydrogen ions, the products of anaerobic metabolism. Integrated cardioplegia using continuous retrograde cardioplegia and antegrade infusions into completed vein grafts washes out metabolites accumulated in regions inadequately perfused by retrograde cardioplegia alone. To determine the flow rates required to achieve the greatest washout, we compared a high flow rate (200 ml/min) to a low flow rate (100 ml/min).
Methods:
Twenty patients scheduled for isolated coronary bypass surgery were prospectively randomized to compare two flow rates for integrated cardioplegic protection using tepid (29 degrees C) blood cardioplegia. Arterial and coronary sinus blood samples were collected to evaluate myocardial metabolism. After antegrade arrest, cardioplegic solution was delivered by coronary sinus perfusion and simultaneous infusions into each completed vein graft at either high or low flow.
Results:
Increasing from low to high flow increased the washout of lactate and hydrogen ions during the aortic crossclamp period. Two hours after crossclamp removal, ventricular function was better in the high flow groups.
Conclusions:
Tepid retrograde cardioplegia resulted in an accumulation of toxic metabolites. The addition of antegrade vein graft infusions at a flow rate of 100 ml/min resulted in a washout of these metabolites. A flow rate of 200 ml/min further improved this washout and resulted in improved ventricular function. An integrated approach to myocardial protection using a flow rate of 200 ml/min may improve the results of coronary bypass surgery.
