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Ann Thorac Surg 1999;68:797-798
© 1999 The Society of Thoracic Surgeons
a Department of Anesthesia and Critical Care, The University of Chicago, Chicago, Illinois, USA
Address reprint requests to Dr Aronson, Department of Anesthesia and Critical Care, The University of Chicago, 5841 S Maryland Ave, Chicago, IL 60637
The infusion of potassium-rich cardioplegia solution has been instrumental in reducing the morbidity and mortality associated with open heart surgery. Optimal myocardial protection during cardiopulmonary bypass (CPB) is predicated on adequate homogenous distribution of cardioplegia solution to all myocardial segments. Traditionally, the efficacy of cardioplegia perfusion has been assessed by quiescence of electrical activity on the electrocardiogram (ECG), a decrease in myocardial temperature, and direct visualization. Recently, contrast ultrasonography has been used to indicate the adequacy of cardioplegia distribution within the myocardium during cardiac surgery [1–11].
Monitoring cardioplegia delivery with contrast ultrasound is a direct, real-time, intraoperative technique that enables the surgeon and anesthesiologist to assess the adequacy of cardioplegia distribution to all myocardial
See also page 955.
segments. Zaroff and associates [3] retrospectively investigated the relationship between immediate outcome after cardiac surgery, preoperative left ventricular ejection fraction, and homogeneous delivery of cardioplegia with intraoperative contrast echocardiography in 21 patients undergoing coronary artery bypass grafting (CABG) surgery. They found that low ejection fraction alone did not predict low output syndrome after CPB, while the combination of inadequate intraoperative myocardial protection (as indicated by nonhomogeneous delivery of cardioplegia to myocardial regions at risk) and low ejection fraction always predicted the need for exogenous support to separate from CPB.
Although critical, coronary artery stenosis may impair antegrade delivery of cardioplegia solutions through the aortic root and thereby contribute to perioperative ischemia and infarction. It has been shown with intraoperative contrast ultrasonography that retrograde infusion of cardioplegia provides myocardial distribution to areas subserved by the left anterior descending and left circumflex coronary arteries even in the presence of complete stenosis of these vessels [4]. Furthermore, retrograde perfusion of cardioplegia in humans has been reported to provide information regarding transmural distribution of cardioplegia with the ratio of endocardial to epicardial flow 1.46 ± 0.27 and 1.39 ± 0.33 in the left ventricular free wall and interventricular septum, respectively [4].
In general, retrograde delivery of cardioplegia for myocardial protection is an approach fostered by coronary venous and arterial anatomy. Its efficacy is highly predicated on individual coronary venous drainage patterns that vary greatly. Winkelman and associates [6] have shown that retrograde-delivered cardioplegia through a balloon tip coronary sinus catheter is not distributed equally to the right ventricle and interventricular septum. They used intraoperative contrast echocardiography and online videodensitometric analysis to demonstrate that right ventricular free wall opacification was significantly less (peak pixel intensity 48 ± 9) compared with the posterior septum (peak pixel intensity 89 ± 12) or anterior septum (peak pixel intensity 107 ± 10), after retrograde-delivered cardioplegia.
In a related study by Allen and associates [7], it was confirmed that retrograde cardioplegia provided poor ventricular myocardial perfusion when assessed by contrast echocardiography and coronary ostial drainage. The poor perfusion was unable to meet the myocardial demands of the right ventricle as assessed by oxygen extraction during retrograde perfusion. Villanueva and associates [8], in an experimental protocol, used radiolabeled isotopes and myocardial contrast echocardiography to evaluate microvascular flow and nutrient delivery during retrograde and antegrade delivery of cardioplegia. They concluded that microvascular and nutrient flow rates were lower during retrograde delivery due to microvascular differences between coronary arterial and venous systems. Myocardial cooling was, however, equally efficient with either delivery technique, suggesting that the clinical benefit of retrograde delivery was primarily cooling, and substrate replenishment was better achieved (at similar flow rates and temperatures) with antegrade delivery. Their data, however, presumed normal coronary artery anatomy and did not consider the influence of collateralization. In patients with ischemic heart disease, predicting the distribution of cardioplegia and understanding its contribution to myocardial protection in each individual patient is difficult without direct assessment during delivery.
Quintilio and associates [9] used intraoperative myocardial contrast echocardiography to determine the myocardial distribution of cardioplegia during combined antegrade and retrograde delivery. They showed that overall myocardial opacification was greater after retrograde delivery in patients with three-vessel disease undergoing elective CABG surgery. However, collateral circulation was the most important determinant for adequacy of myocardial cardioplegia delivery. If adequate collaterals were present, than retrograde delivery offered no advantage for distribution of cardioplegia to regions at risk. On the other hand, they did show that aortic root delivery may not provide adequate myocardial protection in the subset of patients without evidence of significant collateral circulation. In a related study, we employed intraoperative myocardial contrast echocardiography (MCE) during CABG surgery to determine the contribution of collateral blood flow for regional myocardial cardioplegia distribution when delivered antegrade and retrograde [10]. The role of the preoperative electrocardiogram and coronary angiogram for determining the distribution of cardioplegia in 15 patients (all with total occlusion of their right coronary artery) was also evaluated and compared with direct assessment with intraoperative MCE. In that study, coronary angiograms were evaluated for native epicardial anatomy and evidence of collateral coronary circulation supplying the right ventricle, left ventricular apex, and interventricular septum. Evaluation of the preoperative ECGs was also performed, and prediction of regional distribution of cardioplegia was compared with delivery of cardioplegia determined with myocardial contrast echocardiography using Albunex. Eighty-seven out of 90 (97%) segments were analyzed for cardioplegia distribution at the time of CPB during delivery of cardioplegia. It was demonstrated that the preoperative angiogram and ECG poorly predicted regions at risk for incomplete cardioplegia distribution. Antegrade delivery of cardioplegia was distributed to the right ventricle in 31% of patients despite 100% occlusion of the right coronary artery, whereas retrograde delivery of cardioplegia to the right ventricle occurred only 20% of the time. It was concluded that in the presence of 100% occlusion of the right coronary artery, retrograde cardioplegia delivery is not often observed and antegrade delivery of cardioplegia to the right ventricle is not expected unless coronary collateral circulation is well developed. Furthermore, compared with intraoperative contrast echocardiography, the preoperative angiogram and ECG were not predictive of coronary collateral circulation and therefore not predictive of cardioplegia distribution to the right ventricle.
The story of cardioplegia delivery and the potential influence of collateral circulation appears to be advanced further by the recently published work of Borger and associates [11]. They support previous observations and offer additional evidence that intraoperative MCE may be an effective method to determine the adequacy of coronary revascularization by demonstration of improved antegrade delivery after CPB. MCE appears to be the only reliable method to determine the adequacy of coronary collateral circulation during surgery at the time of cardioplegia delivery.
References
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