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(October 9, 2006). doi:10.1510/mmcts.2004.000745 Copyright © 2006 European Association for Cardio-thoracic Surgery Procedure Blood cardioplegiaUniversity Hospital Freiburg, Department of Cardiovascular Surgery, Hugstetter Strasse 44, D-79106 Freiburg, Germany * Corresponding author: * Tel.: +49-761-270 2818; fax: +49-761-270 2550 E-mail: martin{at}ch11.ukl.uni-freiburg.de
We present the technical details of blood cardioplegia as the standard clinical practice in most centers today. In addition, the contribution refers to the advanced strategies using blood cardioplegia in specific situations, including warm cardioplegia induction, controlled reperfusion in acute myocardial infarction, and the application of leucocyte filtration.
Key Words: Myocardial protection • Blood cardioplegia • Controlled reperfusion
Currently, blood cardioplegia is the preferred cardioprotective strategy in the United States and in most West European countries. The technical details of blood cardioplegia have evolved as a consequence of experimental studies and clinical application, including multidose cold blood cardioplegia, warm blood cardioplegic reperfusion, warm induction, antegrade and retrograde delivery, continuous cold blood perfusion, and intermittent warm blood cardioplegia. The fact that blood cardioplegia has emerged as the preferred cardioprotective strategy is based on its versatility, because a blood vehicle for cardioplegic delivery blends onconicity, buffering, rheology, and antioxidant benefits with its capacity to augment oxygen delivery and ability to ‘resuscitate’ the heart, prevent ischemic injury, and limit reperfusion damage. In detail, the cardioprotective potential of blood cardioplegia is represented by the synergistic effect of its different components:
In this chapter we describe the so-called ‘standard blood cardioplegia’ that is based on the intensive experimental and clinical investigations of Gerald Buckberg's research group and has been proven in leading cardiac centers worldwide over the last 20 years. Blood cardioplegia is provided by a mixture of native blood and a commercially-available crystalloid solution (Köhler-Chemie, Alsbach-Hähnlein, Germany, www.koehler-chemie.de) at a ratio of 4:1.
Arterial and venous cannulation is performed according to the planned surgical procedure. The cannulas are connected to the heart-lung machine. Insertion of a combined antegrade cardioplegia-vent catheter [1], cannulation of the coronary sinus [2], and connection of the cardioplegia-catheters to a manifold cardioplegia delivery system and the pressure monitoring lines are performed thereafter. Cardiopulmonary bypass is commenced and the perfusionist initiates delivery of blood cardioplegia by mixing oxygenated blood with a crystalloid solution at a ratio of 4:1 using a double-headed roller pump (Schematic 1). The blood cardioplegic solution is guided through a special heat exchanger (i.e. Sidus – MMCTSLink 107) before it is applied to the patient's heart. Careful de-airing of the delivery system and of the aortic root is necessary to avoid coronary artery air embolism.
Cardiopulmonary bypass for routine cardiac surgery is instituted with linear flow at 2.6 l/min per m2, maintaining perfusion pressure of 60–80 mmHg and systemic blood temperature at 35 °C.
Application of standard blood cardioplegia
This method usually allows discontinuation of bypass within 5 min of releasing the aortic clamp.
Advanced strategies using blood cardioplegia in specific situations Normothermic blood cardioplegia (solution for warm induction, Table 1) is administered initially at 250–300 ml/min via the aortic root until cardioplegic arrest is achieved. Thereafter, cardioplegic flow is reduced to 150 ml/min (antegrade perfusion pressure 40–60 mmHg). Warm cardioplegic perfusion is applied ante- and retrogradely (1 min each). This is followed by cold cardioplegic standard blood cardioplegia.
Controlled reperfusion Controlled reperfusion is a strategy to reduce reperfusion injury after acute coronary occlusion. After completion of the final distal anastomosis and release of the aortic clamp, the controlled blood cardioplegic solution (Table 1) is given at a flow rate of up to 50 ml/min per graft with a perfusion pressure not exceeding 50 mmHg for 20 min into the grafts only. Cannulation of a side branch of the vein graft makes delivery of the reperfusate possible while the proximal anastomosis is being performed (Schematic 2) [4]. In a multicenter trial, the results of controlled reperfusion were evaluated in 156 consecutive patients with acute coronary occlusion and compared to 1203 patients who underwent PTCA as the primary therapy [5]. Controlled reperfusion reduced overall mortality from 8.7% to 3.9%.
Blood cardioplegia leucocyte filtration Myocardial ischemia and reperfusion are associated with activation of neutrophils and expression of adhesion molecules on the myocardial endothelium surface. In the case of long cross-clamp time, acute myocardial infarction, or in heart transplantation, activated leucocytes in blood cardioplegia or initial reperfusate may cause significant myocardial damage. Clinical studies have demonstrated the benefit of blood cardioplegia filtration in patients undergoing emergency coronary bypass surgery or prolonged crossclamping, in patients with depressed ejection fraction, and in heart transplantation [6,7,8]. Experimental studies have shown that at least 90% of leucocytes must be removed to attenuate reperfusion injury markedly. In addition, leucocyte depletion should be maintained for 5–10 min after the start of initial reperfusion prior to aortic clamp release. Commercially available blood cardioplegia filters remove more than 90% of the leucocytes up to a total volume of 1500 ml of blood cardioplegia (i.e. Pall BC1B – MMCTSLink 108).
Blood cardioplegia in heart transplantation
In addition to the classic ‘standard technique’ of blood cardioplegia, several modifications have evolved and are used in different centers.
Continuous warm blood cardioplegia
Intermittent antegrade warm blood cardioplegia
Tepid blood cardioplegia
Since its initial description, blood cardioplegia has become the preferred tool to arrest the heart for open heart surgery. This shift from crystalloid-type to blood cardioplegia occurred because experimental and clinical studies demonstrated superior protection of the arrested myocardium by blood cardioplegia [12,13,14]. The efficacy of myocardial protection with a single aortic crossclamp and blood cardioplegia was evaluated in a clinical study including 819 consecutive patients (stratified for risk profile) and compared with antegrade crystalloid cardioplegia in 2582 patients [13]. The use of combined antegrade/retrograde blood cardioplegia resulted in lower postoperative morbidity by significantly reducing perioperative myocardial infarction, wound complications, and length of stay in patients having reoperations. However, there was no significant difference in one-year mortality between the two groups. Kirklin compared the results of primary isolated coronary bypass operations in the 1977–1981 era (crystalloid cardioplegic solution) with those from 1986–1988. During the latter era cold blood cardioplegic perfusions and warm reinfusions were used in patients with longer clamping times [14] (Graph 1). There was a significant drop in 30-day mortality after introduction of blood cardioplegia, i.e. after 180 min cross-clamping from 7.3% to 1.7%. These clinical results confirm the experimental findings and demonstrate that warm, controlled reperfusion provides a powerful tool to limit reperfusion damage and minimize the adverse effects of prolonged aortic clamping.
In a multicenter trial patients were randomized to receive either continuous warm blood cardioplegia or intermittent cold blood cardioplegia [15]. The investigators found similar myocardial preservation (mortality, postoperative incidence of myocardial infarction, need for intraaortic balloon counterpulsation). Another randomized study in 1001 patients compared continuous warm blood cardioplegia with intermittent cold crystalloid cardioplegia [16]. The data showed no difference in the postoperative rates of myocardial infarction, death or need for intraaortic balloon counterpulsation. Of substantial concern was an unexpected increased rate of perioperative stroke and overall neurologic events in the warm cardioplegic group. Systemic body temperature was actively maintained >35 °C in the warm blood cardioplegia group. The ‘CABG patch trial’ enrolled a high-risk group of 885 coronary artery disease patients with an ejection fraction of <36% [17]. The patients were randomized with respect to the use of blood and crystalloid cardioplegia. Patients receiving crystalloid cardioplegia versus those receiving blood cardioplegia were found to have significantly more operative deaths (2% vs. 0.3%), postoperative myocardial infarctions (10% vs. 2%), shock (13% vs. 7%), and postoperative conduction defects (21.6% vs. 12.4%). Despite this, there was no significant difference in early or late survival. Cardiogenic shock is the leading cause of death after acute myocardial infarction. Modern myocardial preservation strategies using blood cardioplegia have been used with promising results for surgical revascularization in acute myocardial infarction [18]. Recent analyses of the New York State Cardiac Surgery Registry revealed that there is a significant correlation between hospital mortality and time interval from acute myocardial infarction to time of operation. Coronary bypass operation within the first 24 h was associated with an in-hospital mortality of 14% in transmural infarction. In contrast, mortality had decreased to 3% after a time interval of more than 7 days [19]. Despite of these good results logistic and economic constraints relegate surgical revascularization to a third option behind thrombolysis and PTCA for the primary treatment of acute myocardial infarction. The SHOCK (should we emergently revascularize occluded coronaries for cardiogenic shock) trial found clear survival benefits for early revascularization by PTCA or CABG over initial medical stabilization by thrombolytic therapy [20]. Excellent recovery of myocardial contractility after intermittent warm blood cardioplegia could be demonstrated in elective coronary artery bypass patients. The analysis of pressure-volume-loops after cardiopulmonary bypass revealed no change in end-systolic elastance while the diastolic chamber stiffness was significantly increased indicating impaired diastolic function [21].
The versatility of blood cardioplegia provides the cardiac surgeon with a tool to actively treat the jeopardized myocardium as well as to prevent ischemic damage. The known benefits of using blood as the vehicle for delivering oxygenated cardioplegia include oxygen carrying capacity, active resuscitation of myocardium, avoidance of reperfusion damage, limitation of hemodilution, provision of onconicity, buffering, rheologic effects, and endogenous oxygen free radical scavengers. The major prerequisite to provide these benefits to the patient is ensuring adequate delivery of the cardioplegic solutions. Current standard of myocardial protection using blood cardioplegia has evolved as a consequence of experimental studies and their subsequent clinical application over the last decades. It combines different principles, such as cold blood cardioplegia, warm blood cardioplegic reperfusion, warm induction, and alternating and simultaneous ante- and retrograde delivery to compensate for the individual shortcomings of each procedure and permit optimum myocardial preservation. It is essential to understand and use the various techniques to obtain the desired protective effect. Some surgeons who are not familiar with blood cardioplegia criticize it as cumbersome and overly complicated compared to the simpler administration of crystalloid cardioplegia. However, in this case, simplicity and safety are not synonymous [22]. Cardiac damage from inadequate myocardial protection leading to low-output syndrome can prolong hospital stay and cost, and may result in delayed myocardial fibrosis.
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Summary
Introduction
