Eur J Cardiothorac Surg 1998;14:S3-S6
© 1998 Elsevier Science NL
The expanded role of minimally invasive coronary grafting
James D Fonger*,
John R Doty
Washington Adventist Hospital, 7610 Carroll Avenue, Suite 410, Takoma Park, MD 20912, USA
* Corresponding author. Tel.: +1 301 8915313; fax: +1 301 8915097.
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Abstract
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The evolution of minimally invasive direct coronary artery bypass (MIDCAB) grafting has extended the role of this approach for limited coronary revascularization. MIDCAB techniques can now be used to address isolated stenoses in the inferior and lateral coronary distributions. MIDCAB techniques are increasingly being used in the reoperative setting, and multiple vessels can be bypassed during a single operation. This article reviews the expanded role of MIDCAB grafting in the treatment of coronary artery disease.
Key Words: Minimally invasive direct coronary artery bypass • Gastroepiploic • Radial • Thoracotomy • Coronary • Reoperative
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1. Introduction
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The grafting of the human coronary artery on the anterior surface of the heart using an arterial conduit through a small directed thoracotomy incision is an approach which has become increasingly popularized over the past 3 years. Two very different philosophies for the creation of the anastomotic environment have evolved in parallel. The port access approach adheres to the tenet that only full cardioplegic arrest will allow sufficient accuracy for the suturing and flexibility of choice of operative targets in the hands of all surgeons. To accomplish this, the patient is supported on cardiopulmonary bypass as in conventional surgery, usually through femoral vessel access. Grafting is done through a small incision but the risks of cardiopulmonary bypass and arterial cannulation remain [1–5].
The alternate philosophy is based on the notion that the isolated epicardial site which needs to be exposed and stabilized for grafting can be controlled with local mechanical measures without resorting to cardiopulmonary bypass support and cardioplegic arrest. This so-called `beating heart' approach is most often termed minimally invasive direct coronary artery bypass (MIDCAB). The pedicled or skeletonized arterial conduit may or may not be harvested under direct vision. However, the actual conduit to coronary artery anastomosis is by definition done under direct vision on a beating heart with local mechanical stabilization and control of bleeding. The world-wide combined experience for anterior coronary grafting using the internal mammary artery now exceeds 2000 cases. Results from experienced centers have demonstrated equal patency to conventional single vessel bypass grafting of roughly 95% at one year after the requisite learning curve [6–10]. The fundamental question that remains about this approach is how much more broadly applicable this may be for other coronary locations or unusual clinical situations. Three specific questions remain to be addressed. Firstly, can the MIDCAB technique be used for multiple vessel grafting? Secondly, can `beating heart' coronary grafting be done in other locations around the heart? And finally, are these techniques as readily applicable in the reoperative setting as they are with primary coronary grafting?
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2. Inferior (subxyphoid) approach
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The right coronary system is often the only native coronary artery involved in patients presenting with limited coronary disease. This usually involves the proximal or mid portion of the vessel, making these patients poor candidates for minimally invasive right internal mammary artery to mid right coronary artery grafting. Often the proximal vessel has been heavily instrumented with multiple previous catheter-based interventions, and the patient presents as a therapy failure. The most appropriate site for grafting is usually either the distal right coronary or the proximal posterior descending branch in areas which are distal to the acute margin of the heart. Minimally invasive dissection of the right internal mammary artery does not yield a long enough conduit to wrap around the acute margin of the heart and anastomose to these targets without undue tension. Therefore, the only other pedicled arterial conduit in that proximity is the right gastroepiploic artery, which has been used clinically for over 10 years in conventional bypass grafting [11–14].
Placing this conduit to the undersurface of the beating heart through a limited incision is often referred to as the inferior or subxyphoid MIDCAB approach.
Exposure for this operation is gained through a 15 cm vertical epigastric incision beginning over the xyphisternum and extending halfway down to the umbilicus. After division of the abdominal fascia, the plane between the diaphragm and the undersurface of the heart is developed by releasing the attachments of the diaphragm under each costal margin. Further diaphragmatic tendon releasing incisions can also be placed on the right and left side to allow additional diaphragmatic retraction without actually dividing the diaphragmatic muscle. The distal right coronary and posterior descending branch of this vessel are easily identified and an adequate native coronary target is confirmed.
Attention is then focused below the diaphragm where the right gastroepiploic artery is dissected off the greater curvature of the stomach as a pedicled arterial graft. Care is taken to extend the proximal dissection of this conduit down into the abdomen to free up any lateral fascial attachments and allow maximum length of the proximal conduit. This allows the tapered distal portion to be discarded, leaving an adequate caliber conduit for the actual bypass grafting. After 10 000 units of intravenous heparin, the pedicle is transected and papaverine and verapamil are instilled into the lumen to optimize the dilation of the conduit. The pedicled conduit is directed anterior to the stomach and left lobe of the liver and over the upper edge of the diaphragm for grafting antegrade to the distal right coronary artery. If the proximal posterior descending coronary branch is selected as the grafting site, the pedicle is brought over the left lobe of the liver and then through a surgically created foramen in the right lobe of the diaphragm. With temporary silastic coronary occlusion and mechanical stabilization of the arteriotomy, a standard end-to-side anastomosis is fashioned and the pedicle secured to the epicardium. Transit time ultrasound is used to confirm adequate flow through the pedicled conduit and a suction drain is placed across the abdomen into the lower pericardium. The wound is closed in a routine fashion and the performance of the conduit can be followed with transmitted doppler velocities in the postoperative period.
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3. Lateral approach
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Another alternate approach for isolated coronary grafting is the limited posterior thoracotomy for revascularization of a singular circumflex target on the side of the heart. Our initial experience began with a full thoracotomy placing a saphenous vein graft onto the beating heart and directing this down to the descending aorta below the hilum of the left lung. As our clinical experience progressed, we realized that only the posterior aspect of this thoracotomy incision was actually necessary to accomplish the operation. We have now reduced the approach to a 15 cm posterior thoracotomy through the 6th intercostal space. The original grafting strategy of placing a saphenous vein graft retrograde onto the native coronary artery or the hood of an old vein graft has given way to almost exclusive use of a free radial artery conduit placed in an antegrade fashion onto the distal native coronary artery The radial artery graft is then brought in an `S' shape configuration down below the hilum of the left lung and anastomosed with a side-biting clamp to the descending aorta. A very important part of this procedure is the placement of a radiopaque marker around the proximal anastomosis in case there is the need to do catheterization of the graft at a later date. Exposure of the native coronary artery is obtained through a small pericardial window placed posterior to the left phrenic nerve. To achieve an adequate opening through this short thoracotomy, the ribs above and below the intercostal incision are released posteriorly. A bupivacaine intercostal nerve block and standard chest tube are placed and the lung is re-inflated at the end of the procedure. Prior to closure, transit time ultrasound is done to confirm adequate flow through the conduit. These patients cannot be followed postoperatively with transmitted doppler velocities because of the acoustical artifact introduced by the underlying lung. Our experience to date involves 45 cases, 19 of which have been reported previously.
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4. Multiple grafting
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The development of these approaches to allow MIDCAB grafting of all surfaces of the heart raises the possibility of multiple coronary grafting at the same operation. Most commonly, when the angle and configuration of the diagonal coronary is suitable, a sequential internal mammary artery conduit can be placed across the diagonal to the left anterior descending as is done with conventional bypass grafting. This is accomplished through the same 4th intercostal incision generally used for anterior MIDCAB grafting. When a high ramus branch or circumflex coronary also needs to be grafted, one approach for better exposure is to move higher and more lateral on the chest wall through the 3rd intercostal space just anterior to the scapula as popularized by Subramanian [15]. This allows for multiple grafting of the left anterior descending and further lateral targets either with sequential grafting or `T' grafts off the proximal internal mammary artery conduit.
Bilateral grafting of the left anterior descending and mid right coronary can be accomplished through mirror image MIDCAB incisions on either side of the sternum. This is done in patients who have occupational or personal reasons for avoiding a standard sternotomy incision. Otherwise, bilateral `off pump' grafting through a standard sternal incision works very well as long as the right coronary target is relatively proximal. Multiple grafting of the anterior and inferior circulation can be accomplished through separate 4th intercostal and epigastric incisions and is well tolerated in appropriate cases. The lateral limited posterior thoracotomy incision is generally not done in conjunction with other directed incisions, although sequential grafts can be accomplished on the lateral wall of the heart as described previously for the lateral MIDCAB. Sequential grafting of the gastroepiploic pedicle is generally not done because of the small caliber of the conduit and the difficulties in exposing the deep postero-lateral branch of the right coronary system through this approach. Therefore, either with sequential grafting, side arm `T' grafts, or multiple directed incisions, MIDCAB grafting does offer several reasonable approaches for multiple coronary grafts. In general, however if the patient needs three or four vessel bypass grafting, sternotomy is the preferred approach, usually with cardiopulmonary bypass. The sternotomy itself does not appear to be the limiting factor in decreasing the time to patient discharge, although it does prolong the return to full unrestricted activity.
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5. Reoperation
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The final question with respect to the expanded role of minimally invasive coronary grafting is the application of these techniques in the reoperative coronary grafting situation. The population of patients having undergone primary coronary grafting continues to increase, yielding a parallel increase in the number of patients facing reoperative coronary surgery, usually because of failed previous grafts. The most common presentation is that of a focal problem with a single graft to one coronary distribution while the remaining grafts are patent. The patient typically has failed medical management and the graft is refractory to further catheter based interventions. The morbidity and mortality associated with conventional reoperative coronary grafting is known to be related to the risks of resternotomy, cardiopulmonary bypass support, and manipulation of the ascending aorta. More specifically, disturbing stenotic but patent old saphenous vein grafts can release intraluminal debris into the distal coronary bed. The MIDCAB approach for reoperative coronary grafting affords the opportunity to use a directed incision and expose only the focal area of specific interest. This is usually the native coronary just distal to the prior anastomosis, but occasionally is the hood of an old graft or involves removal of an arterial conduit with revision and recycling of the distal end. All of these reoperative MIDCAB variations obviate sternotomy, cardiopulmonary bypass, and manipulation of the ascending aorta. Exposure and manipulation of the old saphenous vein grafts subtending the region of interest is kept to a minimum, as only the distal end is dissected to temporarily occlude the inflow to the arteriotomy.
Experience over the last 3 years has revealed that the reoperative MIDCAB approach represents as much as one third of the MIDCAB grafting done at established minimally invasive coronary centers. The distribution of this experience across the various MIDCAB approaches, however, varies considerably. The percentage of cases which are reoperative through the anterior approach is roughly 15%, but increased to approximately 50% through the inferior subxiphoid approach and through the lateral. Despite the decrease in risk required for the cardiac procedure, morbidity and mortality in the reoperative MIDCAB patient population remains significantly higher than primary MIDCAB surgery. These morbidities and mortalities are generally related to co-morbidities which can cause significant problems during the post-operative recovery. Nevertheless, the reoperative MIDCAB approach is usually justified, as conventional reoperative approach exposes the patient to the increased risks of conventional cardiac re-dissection without eliminating the same co-morbidities. Minimally invasive grafting itself is generally well tolerated, partly because a robust collateral circulation has often developed since the first surgery, and because the previous adhesions help stabilize the area of the arteriotomy. As experience increases with reoperative MIDCAB, a number of patients who have been previously managed on medical therapy because the risks of reoperative surgery have been too high can now consider a surgical approach to their problem.
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6. Summary
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In summary, the initiative to develop primary minimally invasive coronary grafting to the anterior circulation of the heart has led us to realize that there is an expanded role for the technique. Investigators continue to develop these new applications for limited coronary revascularization which include combining MIDCAB grafting with complimentary therapies such as catheter based interventions and transmyocardial laser revascularization. The ability to address limited coronary revascularization problems with new surgical approaches has not only expanded the role of MIDCAB grafting, but has also expanded the potential patient population that can be considered for surgical coronary revascularization in general. In particular there has been a shift towards MIDCAB grafting in patients who have traditionally been considered high risk for catheter based interventions, patients of advanced age, and patients with significant comorbidities. Current application of these new approaches along with careful evaluation of the actual outcomes will guide clinicians and help determine the ultimate role for expanded MIDCAB grafting.
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Abstract
1. Introduction
