Techniques of Exposure and Stabilization in Off-Pump Coronary Artery Bypass Graft

392

NEW TECHNOLOGY IN CARDIAC SURGERY

Techniques of Exposure and Stabilization in Off-Pump Coronary Artery Bypass Graft Paulo Soltoski, M.D., Jacob Bergsland, M.D., Tomas A. Salerno, M.D., Hratch L. Karamanoukian, M.D., Giuseppe D'Ancona, M.D., Marco Ricci, M.D., Ph.D., and Anthony L. Panos, M.D.

Division of Cardiothoracic Surgery, Kaleida Health and VA Medical Center, State Uni- versity of New York at Buffalo, Buffalo, New York

ABSTRACT Recent advances in techniques of coronary artery exposure and myocardial stabilization in off-pump myocardial revascularization have provided cardiac surgeons with a wide variety of new devices and techniques. Until recently, the main obstacle t o performing complete myocardial revascularization without using cardiopulmonary bypass (CPB) has been the technical difficulties of exposing and stabilizing coronary targets, especially those located on the lateral and inferior wall of the heart. The extraordinary cardiac tolerance t o nonconstrictive anterior elevation and lateral displacement, however, has allowed the development of new strategies of coronary exposure. These advances, in combination with the development of new techniques of mechanical myocardial stabilization, have impacted on the feasibility and safety with which coronary anastomoses on the beating heart can be constructed. The aim of this article is t o describe the technical aspects involved in off-pump coronary revascularization, focusing primarily on the most recent strategies of cardiac elevation and coronary exposure, the various techniques of myocardial stabilization, and some of the technical details of constructing distal anastomoses on the beating heart. (J Card Surg 7 999; 14:392-400)

Myocardial revascularization on the beating heart was introduced in the late 194Os, when Dr. Vineberg first reported on the implantation of the left internal mammary artery directly on the myocardium in an attempt to improve its perfusion.l,* The importance of coronary artery occlusion as a key element in the pathogenesis of ischemic heart disease, however, was recog-

Address for correspondence: Tomas A. Salerno, M.D., De- partment of Cardiothoracic Surgery, Kaleida Health-Buf- falo General Hospital Site, 100 High Street, Buffalo, NY 14203. Fax: (71 6) 859-4697; e-mail [email protected] Dr. Sclerno is a consultant for CTS, Cupertino, California.

nized and investigated in experimental studies only in the early 1950s by Murray and coworkers.3 A few years later, Bailey et al. reported on a successful case of coronary endarterectomy performed in the setting of coronary artery occlusive d i~ease .~ It was not until the early 1960s, however, that many of the most significant contribu- tions to coronary artery surgery were made, primarily as a result of the revolutionary approach to cardiac surgery determined by the introduction of the cardiopulmonary bypass circuit by Dr. Gibbon in Philadelphia.5,6 Using such innovative techniques, Dr. Sabiston at Johns Hopkins pioneered the initial development of coronary surgery, and

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SOLTOSKI. ET AL. 393 EXPOSURE AND STABILIZATION IN OFF-PUMP CABG

in 1962 performed the first human coronary artery bypass grafting using the extracorporeal circulation, which consisted of a saphenous vein graft from the aorta to the right coronary artery.' The following two decades were characterized by the most important advances in the field of extracorporeal circulation, which significantly con- tributed to the popularization of coronary artery revascularization. Not surprisingly, the attractive- ness of a bloodless and perfectly motionless operative field largely overshadowed the risks associated with the use of CPB, until initial reports on the adverse neurological events resulting from the use of extracorporeal circulation were published by Rosenblum and coworkers.8 Despite the growing enthusiasm for the new techniques of extracorporeal circulation and its widespread popularization in cardiac surgery, attempts were made a t performing coronary surgery without CPB. This innovative approach was pioneered by Kolessov in 1967,9 who reported on a patient in whom the left internal mammary artery (LIMA) was anastomosed to the left anterior descending coronary artery (LAD) through a left thoracotomy, without using CPB. The technique of coronary revascularization without CPB was subsequently adopted and refined by DeBakeylO and Favalorol in the late 1960s and early 1970s. During the years following, as a consequence of the technical difficulties related to the initial experience with off-pump myocardial revascularization and the refinements of techniques of extracorporeal circulation and myocardial preservation, the off- pump approach was largely abandoned in favor of CPB. Nevertheless, in the 1980s two indepen- dent groups of investigators lead by Benetti in Ar- gentina12-14 and Buffolo in Brazill5,l6 relentlessly continued their work on off-pump coronary revascularization and reported favorable outcomes from their large series of patients. Not surprisingly, those reports determined a remarkable resurgence of interest for techniques of off-pump CABG in an attempt to eliminate the untoward systemic effects of CPB. Despite the growing enthusiasm, however, this technique was initially adopted predominantly, and perhaps almost exclusively, for revascularization of the LAD territory for the technical difficulties of exposing coronary arteries located on the lateral and inferior wall of the heart. Only during the last decade have the innovative techniques of myocardial elevation, coronary exposure, and mechanical stabilization

lead to the widespread use of this approach and, more importantly, have allowed the development of complete revascularization of all coronary territories, including those on the "topographically difficult" areas. As such, this new approach to minimally invasive CABG without CPB has been recently proposed as a new alternative to conventional myocardial revascularization.

In this perspective, the aim of this article is to describe some of the technical details of off-pump coronary revascularization, focusing predominantly, but not exclusively, on recent advances in coronary artery exposure and mechanical myocardial stabilization. In addition, pitfalls and strategies commonly adopted are described.

TECHNICAL ASPECTS OF OFF-PUMP REVASCULARIZATION

As previously described,17 the feasibility of myocardial revascularization without CPB is largely dependent on the ability to expose all target vessels, minimize their motion during construction of distal anastomoses, and preserve visualization by maintaining a bloodless operative field.

Surgical approaches in off-pump CABG

A variety of different approaches may be used in the setting of myocardial revascularization without CPB. These include median sternotomy, partial sternotomy, left anterior small thoracotomy (LAST),I8 left posterolateral thoracotomy, sub xyphoid access, and "hybrid approaches" (such as the LAST procedure in combination with the sub xyphoid access). While some of these may be use- ful, especially during redo operations, complete myocardial revascularization in the setting of primary operation is most commonly performed through a median sternotomy. In our experience, however, complete revascularization also can be accomplished through a partial sternotomy (only the distal two thirds of the sternum are divided), although the operative time may be slightly prolonged. This a p proach still allows complete access to the great vessels in a few patients in whom cardiopulmonary bypass is required, and it may decrease the risk of wound complications in the postoperative period. More importantly, it may be particularly advantageous in patients with severe emphysema, COPD, and impaired respiratory mechanics in whom the improved stability of the chest wall and the reduc-

394 SOLTOSKI, ET AL. EXPOSURE AND STABILIZATION IN OFF-PUMP CABG

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tion in postoperative pain may beneficially affect ventilation and respiratory function.

Exposure of the coronary targets

Adequate exposure of the coronary arteries identified as potential targets on preoperative coronary angiography cannot be obtained without a combination of variable degrees of elevation and lateral displacement of the heart. Obviously, the degree of cardiac elevation and displacement necessary to obtain adequate visualization are primarily determined by the location of the target coronary artery on the surface of the heart, although other factors such as size of the cardiac chambers and morphology of the chest wall may play a role. In this regard, the principles of vessel exposure do not differ significantly from those used in conventional coronary operations on the electromechanically arrested heart. However, in "off-pump" revascularization this has to be accomplished while the heart is beating, thereby maintaining cardiac function and preserving hemodynamics.

In our experience, exposure is best accomplished by placing several stitches in the posterior pericardium and connecting them to a "vaginal tape," which can them be manipulated and pulled in various directions, thus lifting the heart and exposing the areas where the targets are located. This technique, originally described by Ricardo Lima from Brazil and never published, initially consisted of placing four stitches at the level of the aorto-pericardial reflection, right superior and inferior pulmonary veins, and half-way between the left inferior pulmonary vein and the inferior vena cava. Alternatively, in an attempt to simplify this approach, we have described and currently use a modification to this technique that essentially consists of placing a single suture in the oblique sinus of the posterior pericardium ("single suture" technique) (Fig. l ) .19

After the sternum is divided and the heart is ex- posed, the surgeon, standing on the right side of the patient, uses his left hand to rapidly elevate the heart and expose the posterior pericardium. Then the "single suture," usually a O-silk, is placed on the oblique sinus of the pericardium, situated between the right and left, superior and inferior pulmonary veins. Care must be taken to place the stitch only through the pericardial layers, because the esophagus and descending thoracic aorta are

commonly located in close proximity. As soon as the suture is placed, the heart is rapidly relocated within the pericardial cradle and the silk suture is secured to a "vaginal tape," which is pushed down with a snare to the posterior pericardium. This is commonly performed because the vaginal tape, in contrast to the silk suture, does not trau- matize the heart ("sewing effect") once it is used to obtain cardiac elevation. Only a few seconds of cardiac lifting usually are necessary to place the suture in the posterior pericardium. As a result, any drop in blood pressure is usually transient and of no clinical relevance. Once the "single suture" is placed, manipulation and traction on the vaginal tape allow cardiac elevation and lateral displacement, which allows proper visualization of all coronary targets, including those located on the lateral and inferior wall of the heart, which are the most difficult to expose. The vaginal tape is gently secured under tension to the left blade of the sternal retractor, only slightly lifting the heart upward and toward the right, if the LAD system has to be ex- posed. Alternatively, just by opening the vaginal tape in two arms, the apex of the heart can be el- evated toward the ceiling and laterally displaced toward the left shoulder, thereby exposing the posterior descending coronary artery or the posterolateral branches of the right coronary artery. In addition, exposure of the circumflex system can be obtained by brining the two arms of the vaginal tape to the left of the heart and securing them to the right blade of the sternal retractor. Although adequate exposure of the circumflex system may be the most difficult to obtain, opening the right pleuropericardial space may considerably facilitate exposure by allowing the heart to herniate into the right chest.

Hemodynamic consequences of cardiac elevation and displacement

Concerns have been raised regarding the possibility of deterioration of the hemodynamic parameters during cardiac elevation and manipulation, which may be more pronounced in the case of exposure of the circumflex territory. A significant decrease in systolic, and particularly diastolic arterial pressure would invariably determine a significant reduction in coronary perfusion pressure, particularly detrimental in patients affected with underly- ing coronary artery disease. Furthermore, suboptimal myocardiac perfusion during cardiac

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SOLTOSKI, ET AL. 395 EXPOSURE AND STABILIZATION IN OFF-PUMP CABG

elevation and manipulation, in theory, may further decrease left ventricular performance, thereby further aggravating hemodynamics. However, in our experience20,21 as well as those reported by others,22 alteration of left ventricular geometry with deterioration of hemodynamic parameters even during maximal cardiac elevation is usually an uncommon event if some principles are followed. In this regard, we have observed that cardiac elevation should be accomplished progres- sively, occasionally over several minutes, to obtain adequate exposure, allowing the heart to hemodynamically adjust to the new position. Moreover, suboptimal exposure for limited cardiac elevation or lateral displacement may be compensated for by changing the position of the operating table (Trendelenburg position, inclina- tion toward one side or the other). Not surprisingly, positioning of the patient in the Trendelen- burg position considerably facilitates exposure of the inferior wall of the heart. Similarly, rotation of the table toward the right side of the patient (surgeon's side) improves exposure of the circumflex territory. Moreover, as reported by other^,^^,^^ the Trendelenburg position may significantly improve systemic venous return and preload to the right- sided heart chambers, thus maintaining adequate cardiac output.

In the very few patients in whom cardiac elevation and adequate exposure cannot be accomplished avoiding hemodynamic instability, in spite of additional administration of volume and inotropic support, conversion to cardiopulmonary bypass is promptly undertaken and generally does not adversely affect perioperative outcomes.21

Preserving hemodynamics during cardiac elevation

In recent years, the advances made in the field of mechanical stabilization have lead to the popularization of strategies of coronary grafting without CPB. Similarly, the introduction and development of mechanical stabilizers of the new generation have rendered pharmacological techniques of stabilization virtually obsolete, so that the use of beta- blockers, calcium channel blockers, and adenosine, previously used by some investigators to reduce

-- ,motion by reducing inotropism and chronotropisrn, is no longer required. In this perspective, because a motionless field can be obtained effectively by using the new stabilizers, pharmacological manipula-

tion of the cardiovascular system using drugs that may adversely affect cardiac performance is avoided. Conversely, various strategies are frequently used to improve contractility and chronotropism in an attempt to maintain hemodynamics during maximal cardiac elevation. These primarily include the use of temporary pacing wires, volume administration, and thoughtful inotropic support. Not surprisingly, their use may be particularly important when exposing the coronary arteries located on the inferior and lateral wall of the heart because this commonly results in deformation of the right-sided cardiac chambers and impaired right ventricular diastolic filling. As a result, temporary epicardial pacing wires may be used advanta- geously in the patients in whom bradycardia is thought to adversely affect cardiac performance. Placement of temporary epicardial atrial and ventricular pacing wires is also recommended when revascularizing the right coronary artery, particularly in its proximal portion. In this setting, transient ischemia due to right coronary manipulation may result in hypoperfusion of the AV node, which may lead to transient complete AV block. Similarly, in the vast majority of patients, fluctuations of the systemic arterial pressure often can be managed by increasing preload administering volume. lnotropic support (dopamine or neosynephrine) may be required in a minority of patients who display refrac- tory hypotension despite fluid administration.

Mechanical stabilizers

Optimal target stabilization remains the most important technical aspect of off-pump coronary revascularization. Mechanical stabilization, in con- tradistinction to the pharmacological stabilization no longer used, can be accomplished by direct pressure or suction. The pressure-type stabilizers originally introduced were hand-held by an assis- tant. Newer types of pressure stabilizers can be connected to one of the arms of the sternal retractor. In both cases, mechanical stabilization is effectively accomplished by the pressure on the epicardium surrounding the coronary target by adjusting a U-shaped footplate (Figs 2 and 3). We currently use the CTS Access Ultima System (CTS, Cupertino, CA, USA), which is the latest version of the CTS stabilizers. This device com- bines a sternal spreader-type retractor that can be connected to an adjustable arm and horseshoe-


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shaped stabilizing platform. This platform can be articulated in a tridimensional fashion (along the x, y, and zaxes) to reach any target vessel. Optimal stabilization is accomplished securing the arm and footplate into position.

The most popular suction-type mechanical stabilizer available is the Medtronic Octopus 2 (Medtronic Inc., Minneapolis, MN, USA), which was originally introduced and then developed by Borst and Grundeman from the Netherlands (Figs. 4-7). This device consists of two paddles with 4 or 5 small (6 mm) suction cups on each paddle.*5 The paddles are connected to two different arms that can be held in position by securing them to the operating table rail or, the arms of the sternal retractor. A negative pressure of ap- proximately 400 mmHG within the cups can then

Figure 3. Exposure of the posterolateral vessels of the heart with a pressure stabilizer.

Figure 1. The posterior pericardial stitches combined with proper positioning of the patient provide adequate exposure of all cardiac vessels.

Figure 4. Medtronic Octopus 2, suction-type stabilizer.

Figure 2. CTS Access Ultima System pressure-type stabilizer. the Octopus 2.

Figure 5. Equipment required for stabilization using

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required, is frequently accomplished after all other distal anastomosis have been completed, in off- pump CABG revascularization we generally con- struct the distal anastomosis of the LIMA-to-LAD graft first. There are several reasons for this strategy. First, exposure of the LAD territory requires only minimal cardiac elevation and displacement, so that hemodynamics are usually well preserved while the distal LAD anastomosis is constructed. Second, this strategy allows expeditious revascularization of the anterior wall of the left ventricle. Accordingly, this may confer additional ischemic protection to the anterior wall of the left ventricle when more drastic cardiac elevation to expose other territories is used. Furthermore, early revascularization of the left ventricle may theoretically improve cardiac performance during maximal elevation. Last, we have noted that constructing the LIMA-to-LAD graft first does not adversely affect

place the heart provided that care is taken not to damage the LIMA-LAD graft during cardiac ma- nipulations. After revas,cularization of the LAD is accomplished, the circumflex and right coronary territories can be revascularized if needed.

Figure 6. of the Same using a sue- the ability to manipulate, elevate, or laterally dis- tion stabilizer.

The use of the coronary "snare"

After a target coronary has been identified and adequate exposure along with mechanical stabilization have been accomplished, we routinely place a 4-0 Prolene suture around the coronary

Figure 7. Exposure of the posterolateral vessels of the heart with a suction-type device.

be created to accomplish effective immobiliza- tion. No significant complications have been observed at the suction cup sites. Visualization and exposure of various coronary territories can be accomplished by adjusting and optimizing the position of the flexible arms.

In our experience, both devices described can accomplish epicardial stabilization efficiently, and the decision as to whether one or the other should be used is based on surgeons preference.

Sequence of coronary grafting

In contrast to conventional coronary surgery, during which revascularization of the LAD, when

Figure 8. Photograph illustrating proximal and distal snares used for hemostasis and ischemic preconditioning. In this case, adequate exposure is obtained using a pressure stabilizer in combination with a 6-0 Pro- lene suture to retract the perivascular tissues.


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artery, proximally to the area where the distal anastomosis will be constructed (Fig. 8). To avoid injury to the coronary artery, care is taken to place the stitch deep into the myocardium surrounding the vessel. In addition, the technical detail of placing a deep bite into the myocardium could also eliminate, or at least reduce, the likelihood of in- juring the artery when this Prolene "loop" is snared, because a greater portion of myocardium would be interposed between the suture and the artery. In our experience, the advantages of using such a technique (the "snare") overshadow the theoretical disadvantages. The Prolene suture can be easily snared down so that the coronary target can be gently occluded, thereby gaining proximal control and improving visualization as the coronary artery is entered. This strategy also permits a brief period (3-5 minutes) of ischemic preconditioning,2"28 which may improve myocardial tolerance to ischemia and may allow detection of ischemic electrocardiographic changes or ventricular dysfunction as the coronary artery is occluded, thus allowing modification of the strategy of revascularization. Intermittent occlusion of the native coronary may be particularly advantageous during graft flow assessment of Doppler- based techniques (Transit Time Flow Measure- ment [TTFMI), as described later in this article.

The theoretical disadvantages of inadvertent injury to the target coronary artery during placement of the stitch can be easily avoided, and the possibility of dislodgment of atherosclerotic material within the coronary artery once the Prolene suture is snared may also be prevented by properly choos- ing the site where the "snare" is applied. Accord- ingly, this technique should not be used in the presence of heavily calcified coronary arteries because it may fail to completely occlude the lumen of the heavily calcified vessel and may increase the risk of distal embolization. In addition, placement of the snare may not provide any advantage in the presence of a totally occluded native coronary artery. In this case it may be advantageous to place the Pro- lene suture distal to the site of construction of the anastomosis, particularly if there is angiographic ev- idence that the target coronary artery is perfused by collaterals in a retrograde fashion.

lntracoronary shunts

The use of intracoronary shunts (FloCoil, CTS) (Fig. 9) inserted within the target coronary arteries

Figure 9. Assortment of intraluminal shunts. Different models are commercially available. The major benefit is usually obtained using shunts of 2-mm diameter or larger.

during construction of distal anastomoses has been introduced as a method for improving distal perfusion while the vessel is grafted. As a result, this approach could prevent ischemia and preserve regional contractility of the territory supplied by the coronary artery, although its importance would invariably diminish in the face of total occlusion of the native coronary. In addition, the use of intracoronary shunts may also improve visualization as the distal anastomosis is constructed, thereby improving accuracy during suturing and reducing the possibility of technical errors.

Improving visualization: The CO, blower/saline aerosolizer

The CO, blower/saline aerosolizer has been introduced in an attempt to improve visualization during construction of distal an as tor nose^.^^ In our experience, this device along with the intracoronary shunt contributes remarkably to maintaining a bloodless field. It should be noted, that such a device is not entirely harmless, because it may result in inadvertent injury to the target coronary artery and intimal dissection if used too close to the area where the anastomosis is being constructed.

Coronary graft hemodynamic assessment by Transit Time Flow Measurement (TTFM)

Doppler-based techniques of coronary graft flow measurement recently have been intro-

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duced and popularized as a method to intraoper- atively assess graft patency during coronary revascularization. This technical aspect may be particularly important in the setting of myocardial revascularization without CPB, because it was originally believed that the technical challenge of performing distal anastomoses on the beating heart may increase the risk of technical failure. Al- though advances in techniques of mechanical stabilization and target visualization have considerably circumvented this problem and facilitated construction of distal anastomoses on the beating heart, we believe that flow measurement of the coronary grafts may play an important role in decreasing the risk of early graft occlusion due to technical error. Although there has been evi- dence that even Doppler-based techniques of flow measurement, more reliable than electro- magnetic-based techniques, may fail to detect mild or moderate graft stenosis of up to 75% of the cross-sectional area.30,31 The correct interpre- tation of graft hemodynamics allows early intra- operative detection and immediate correction of graft dysfunction in all patients with severe graft stenosis or occlusion without considerably delay- ing the operation or increasing costs. As previously described,32 a patent coronary graft usually presents a predominantly diastolic flow pattern in combination with a pulsatility index (PI) of < 5. In contrast, a systolic flow pattern along with PI fig- ures > 5 are often associated with severe graft dysfunction or occlusion. In this regard, the ap- propriate use of the snare during graft flow mea- surements may allow further investigation exclu- sion of distal runoff obstruction, and evaluation of the proportion of competitive flow in the native coronary artery.28

CONCLUSION

Historically, one of the main obstacles to complete myocardial revascularization without CPB has been represented by the inability to ade- quately expose the coronary targets and minimize their motion, preserving cardiac function and hemodynamic stability. However, the introduction of the stabilizers of the new generation in combination with the refinements in techniques of coronary revascularization on the beating heart have improved the feasibility and relia- bility with which distal anastomosis to all coronary arteries can now be constructed. In this

perspective, we believe that the only absolute contraindication to off-pump coronary grafting is represented by the inability to preserve hemodynamics while obtaining exposure and stabilization of the target vessels. Accordingly, although a variety of other factors such as left main disease, acute myocardial infarction, or the presence of an intramyocardial LAD have been con- sidered as contraindications to off-pump CABG, we believe that they do not represent absolute contraindications, although their presence may require modification of the operative strategies used and may be associated with a higher rate of conversion to CPB.

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Techniques of Exposure and Stabilization in Off-Pump Coronary Artery Bypass Graft

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