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Ann Thorac Surg 2001;72:2182
© 2001 The Society of Thoracic Surgeons
a Center for Less Invasive Cardiac Surgery and Robotic Heart Surgery, Buffalo General Hospital, Kaleida Health and The Department of Cardiothoracic Surgery, University of Buffalo, 100 High Street, Buffalo, NY 14203, USA
e-mail: lisbon5{at}yahoo.com
To the Editor
We read with great interest the case report by Grubitzsch and colleagues [1] about stunned myocardium and off-pump coronary artery bypass (OPCAB). In this timely article, the authors postulate that myocardial stunning can result from temporary snaring of coronary arteries during beating heart coronary revascularization. Despite these convincing case reports, off-pump coronary artery revascularization has been demonstrated to reduce surgical morbidity and mortality in patients with myocardial ischemic dysfunction [2]. Furthermore, in patients with hibernating myocardium, OPCAB resulted in significant improvement of cardiac function without affecting myocardial metabolism [3]. In our experience, standard protocols are exercised to ensure reproducible success with OPCAB. For every constructed graft with OPCAB, we use (1) ischemic preconditioning and (2) coronary shunting. Furthermore, we document graft patency before constructing additional grafts to avoid myocardial ischemia resulting from a newly constructed but occluded graft. Ischemic preconditioning should be performed by direct coronary occlusion with pledgetted suture. A 3-minute period of ischemic preconditioning must be accompanied not only by strict electrocardiographic monitoring, but also by continuous cardiac output monitoring to prevent any sudden hemodynamic impairment, which can result in unexpected and hurried conversion to cardiopulmonary bypass. The importance of preconditioning is more critical when noncritical lesions of the coronary arteries are present. The preconditioning must be followed by a reperfusion period before performing the arteriotomy. During this phase, close monitoring of the electrocardiogram and hemodynamic parameters are also recommended.
The use of shunts remains controversial. Despite case reports showing coronary endothelial injury temporally related to OPCAB, and presumably resulting from intracoronary shunting, this cause and effect relationship is plausible but not consistent. Adequate and agile shunt positioning may be difficult to achieve rapidly, especially if this maneuver is not performed routinely. We suggest shunt placement immediately after coronary arteriotomy; the shunt should be placed before suturing, and well before hemodynamic impairment occurs from myocardial ischemia. Limiting coronary shunting to those cases in which coronary occlusion exceeds 15 minutes [1] may cause catastrophic ischemia, ventricular failure, and forced conversion to cardiopulmonary bypass. Emergent placement of shunts is more likely to cause injury to the endothelium that controlled shunting. Shunting not only prevents myocardial ischemia, but also can make construction of the anastomosis easier by "temporarily stenting" the vessel open, artificially creating a shunt-endothelium interface by color differences, minimizing excessive bleeding, and thus maximizing conditions for technical perfection. Finally, intraoperative graft patency verification should be mandatory whenever OPCAB is performed. Flow testing assesses the quality of the anastomosis and potential graft flow dysfunction during different phases of the operation. Elevation and rotation of the heart may cause hypotension or traction on newly constructed grafts, which can cause sudden reduction of flow; kinking of venous grafts is more likely with manipulation of the heart than kinking from arterial grafts. Vigilance is required to prevent such technical problems.
Interestingly, in a recent retrospective review, we found that these technical problems are not accompanied by electrocardiogram or hemodynamic changes in more than 33% of patients, but if prolonged they may result in myocardial ischemia, cardiovascular collapse, and conversion to cardiopulmonary bypass.
Close intraoperative monitoring of graft flow may soon follow with noninvasive technologies [4] because graft pulsation by manual palpation is certainly not a good indicator of graft flow [1]. Postoperative angiography is usually performed too late, unless the operating theater is set up for hybrid technology. Patients are not rushed to the angiography suite when hemodynamic deterioration occurs and when they are performed, the low-flow phenomena are already resolved. We have documented via Transit Time Flow Measurement many cases of temporary low-flow status that can be properly addressed and resolved only if immediately diagnosed [4].
In our opinion, every surgeon wishing to perform OPCAB should first become familiar with the techniques of ischemic preconditioning, intracoronary shunting, and intraoperative graft patency verification.
We again congratulate Dr Grubitzsch for his timely article on stunned myocardium during OPCAB.
References
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