Asian Cardiovasc Thorac Ann 2002;10:201-205
© 2002 Asia Publishing EXchange Pte Ltd
Surgical Steps Toward Complete Revascularization in Off-Pump Coronary Bypass
Kit V Arom, MD,
Robert W Emery, MD,
Thomas F Flavin, MD,
Vibhu R Kshettry, MD,
Patricia Janey, RN
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The John Nasseff Heart Hospital and Minneapolis Heart Institute Minneapolis, Minnesota, USA
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For reprint information contact: Kit V Arom, MD Tel: 1 612 863 3982 Fax: 1 612 863 3739 email: karom{at}csa-heart.com Cardiac Surgical Associates, P.A., 920 East 28th Street, Suite 420, Minneapolis MN 55407, USA.
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ABSTRACT
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Surgical techniques aimed at complete myocardial revascularization without the use of cardiopulmonary bypass are described. Between January 1998 and June 2000, coronary artery bypass was performed in 3,003 patients; an off-pump technique was used in 676 and cardiopulmonary bypass was employed in 2,327. Patient characteristics, demography, and preoperative risk factors of the two groups were compared retrospectively, and differences in operative variables and postoperative outcomes were analyzed. Using a commercially available suction stabilization device and the surgical and anesthetic techniques described herein, off-pump coronary revascularization was accomplished with results comparable to the on-pump approach.
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INTRODUCTION
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Two significant advancements altered the thinking on surgical treatment of coronary artery disease in the 1990s. The first was documentation that complete revasculariza-tion further improved patient survival, increased the symptom-free interval, and decreased the incidence of reoperation.1 The second was the development of minimally invasive cardiac surgery that offers the alternative approaches of selective minimally invasive direct coronary artery bypass or off-pump coronary artery bypass. Evidence is accumulating that coronary artery bypass grafting (CABG) without the use of cardio-pulmonary bypass (CPB) is safe and effective.2,3 Complete revascularization can be successfully performed without CPB in many, if not all, patients via a sternotomy. Mack and colleagues4 demonstrated 97% patency of arterial anastomoses with the left anterior descending artery (LAD) performed via a left thoracotomy without the use of CPB. Such good results have not been achieved with grafts elsewhere on the heart; access to the posterior, postero-lateral, and inferior surfaces of the strongly beating heart may be inadequate with existing stabilizing equipment. This clinical report describes surgical techniques using recently available devices aimed at complete revascularization.
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PATIENTS AND METHODS
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The Cardiac Surgical Associates database was searched to obtain details of all CABG procedures performed at our institutions between January 1, 1998, and June 30, 2000. These dates were selected to exclude the time considered to be the learning period. Patients included were those who had a full sternotomy with or without CPB, thus minimally invasive direct coronary artery bypass procedures were excluded from this study. There were 3,003 patients; 676 underwent off-pump CABG and the other 2,327 were operated upon under CPB. Males comprised 72% of off-pump CABG patients and 75% of the on-pump group; mean ages were 66.7 and 65.1 years, respectively. Patient characteristics, demography, pre-operative risk factors, operative variables, and post-operative outcomes of the two groups were analyzed. The selection of patients was largely influenced by the surgeon’s preference.
SURGICAL TECHNIQUES
Off-pump and on-pump CABG are performed through a median sternotomy incision, with or without taking down the left internal mammary artery, as described elsewhere.5 Anesthesia is induced with intermediate-acting agents, muscle relaxants, and avoidance of high-dose narcotics to facilitate early extubation. Pulmonary artery catheters are used routinely to continuously monitor end-organ tissue perfusion and cardiac output during the procedure. Transesophageal echocardiography is used occasionally to detect subtle, but significant, hemodynamic and ischemic changes. During cardiac manipulation, parti-cularly exposure and grafting of the right coronary artery (RCA) branches and the circumflex artery, mixed venous oxygen saturations and cardiac output may decline by as much as 40%, but restoration to baseline levels typically occurs within 1 to 2 minutes. Systemic anticoagulation with intravenous heparin is established using one-third of the CPB-loading dose, and periodically supplemented to maintain an activated clotting time between 200 and 300 seconds throughout. Heparin reversal with protamine is necessary in most patients. Temperature homeostasis is achieved using high room temperature, forced-air-warming blankets, warm infusion solutions, and low-flow anesthetic gas and oxygen delivery systems. Ischemic prophylaxis is accomplished by intravenous nitroglycerin infusion and short-acting alpha blockers, such as esmolol, to control heart rate and minimize myocardial oxygen consumption. Although stroke volume may be com-promised during cardiac manipulation, cardiac output may become increasingly rate-dependent. Mean arterial blood pressure and, therefore, tissue perfusion pressure can be maintained using alpha agonists such as phenyl-ephrine, as infusions and timely intravenous boluses during periods of induced hypotension. Volume loading, keeping the filling pressure above 20 mm Hg by infusion of colloids, and placing the patient in the Trendelenburg position optimize cardiac output and maintain hemo-dynamic stability during cardiac manipulation. Lidocaine boluses are infrequently necessary as prophylaxis for ventricular tachycardia or fibrillation during manipulation or coronary occlusion.
Superficial or anterior pericardial traction sutures are placed in the usual fashion. Three deep pericardial sutures are placed in the left side of the pericardial gutter to facilitate pericardial retraction for cardiac elevation and exposure. The 1st suture is placed between the superior and inferior pulmonary veins, the 2nd beyond the inferior pulmonary vein, and the 3rd toward the diaphragmatic surface near the inferior vena cava. Tension is applied to these sutures, and they are fixed to the left lateral chest wall. Varying amounts of traction on the first two sutures will lift the cardiac apex up to the sternotomy level for LAD and diagonal artery exposure. Further vertical tilting can be achieved by pulling on the 3rd deep traction stitch and rolling the heart toward the surgeon to expose the circumflex and the posterolateral branches of the RCA. Trendelenburg positioning further elevates the apex, and right-sided rotation of the table increases exposure of the inferolateral aspect of the heart. Care is taken to ensure that the deep suture adjacent to the left superior pulmonary vein does not ensnare or lacerate the left atrial appendage. Rubber snares are used on the sutures to prevent injury to the epicardium. After these maneuvers, the heart usually stands upright, allowing easy access to all arteries, with good hemodynamic stability, direct visualization, and an ergonomic surgical setup. Opening the right pleural cavity by incising the right pleura and freeing the right anterior abdominal wall muscle from the diaphragm allows the heart to drop further into the pleural cavity, thus minimizing sternal retraction and postoperative chest wall pain. The LAD and diagonal arteries are accessed with the operating table in the usual position. For the circumflex artery and RCA branches, the table is put in the Trendelenburg position and rotated sideways toward the surgeon to facilitate exposure of the inferolateral aspect and the base of the heart.
Stabilization of the target arteries in the early phase of this study was accomplished using a CTS tissue stabilizer (Cardiothoracic Systems, Inc., Cupertino, CA, USA), and more recently, with the Octopus II and III stabilizers (Medtronic, Inc., Minneapolis, MN, USA). With the additional suction capabilities of the Octopus device, presentation and stabilization of remote target arteries on the inferolateral aspect of the heart are more feasible. The Octopus stabilizer is usually best pointed superiorly from the inferiorly placed retractor bar on the surgeon’s side. The Octopus’ stabilizer pods (footplates) are placed straddling and parallel to the target vessel. The blades of the footplate may be swiveled in any direction. For the LAD and diagonal arteries, the tips of the footplate are usually pointed cephalad and positioned parallel to the course of the artery. For the obtuse marginal and posterolateral branches, the tips of the footplate can be pointed away from the surgeon and are usually positioned to the right of the retractor. The Octopus may be moved up or down the side arm of the retractor so that the footplate can rest in the most convenient location. If there is any hemodynamic compromise after suction is applied, pulling up the arm of the Octopus will minimize compression and regain hemodynamic stability. This maneuver cannot be performed with other compression stabilizing devices. For the RCA, the segment distal to the crux is exposed and the stabilizer is applied with the tip pointing away from the surgeon and the footplate parallel to the course of the artery. Occlusion of a dominant RCA can cause hemodynamic instability. For RCA branches, the tips of the footplate are pointed caudally with the Octopus attachment moved slightly toward the patient’s head but remaining on the surgeon’s side. This maneuver works well for posterior descending and posterolateral branches.
A dry operative field can be achieved before or after positioning the footplate, using double loops of 4/0 polypropylene or silastic single-loop suture. It is of the utmost importance to use gentle traction on these stay sutures for occlusion of flow only, and never for presentation of the artery. The vessel is opened without ischemic preconditioning. Intravascular control with a Flo-Rester occluder (Biovascular, MC, Redondo Beach, CA, USA) or a Flo-Coil shunt (Cardiothoracic Systems, Inc., Cupertino, CA, USA) is seldom needed. However, a shunt occluder may be of benefit when grafting the main RCA or when cardiac perfusion is predominantly maintained by a single artery. A carbon dioxide blower with a saline aerosol (Clear View blower/mister; Medtronic Inc., Minneapolis, MN, USA) is very useful to clear the anastomosis site.
The LAD and diagonal arteries are generally grafted first because of ease and minimal manipulation of the heart. The order of subsequent vessels depends on their size, importance, and the ease in maintaining hemodynamic stability while achieving vertical displacement of the heart; usually, those with the easiest exposure and least anticipated technical complexity have priority. However, the next distal anastomoses may be sequential with arterial or venous conduits, starting at the distal right beyond the crux or posterior descending artery to the posterolateral branches, and subsequently, to the proximal obtuse marginal branches. The intermediate artery can be anastomosed sequentially with the obtuse marginal branches or bypassed separately. All distal anastomoses are usually completed first. In a few instances, proximal anastomosis may be carried out before completing all distal anastomoses, to permit revascularization of an important artery. In general, no more than 2 proximal anastomoses are undertaken as sequential bypasses are liberally performed. Both interrupted and running techniques are used for distal anastomosis. The surgeon should be prepared to work in considerably less space than that achieved with an arrested and emptied heart on CPB. The interrupted suture technique works well in limited space; for a running technique, the needle may have to be passed separately through the conduit and the coronary vessel. Proximal anastomosis is always performed with a single partial occlusion clamp; blood pressure is lowered pharmacologically to 90 to 100 mm Hg before applying the clamp. Proximal anastomoses are completed one at a time, rather than cutting all holes together, as the clamp can slip due to the pulsatile pressure. If there are any concerns about the ascending aorta in terms of lesions or application of the clamp, bolus adenosine is given to stop the heart for 12 to 15 seconds and the clamp is applied after the aorta has become flaccid. Clearing the aorta of pericardium, particularly on the pulmonary artery side, permits more stable clamping.
Most patients undergoing off-pump CABG can be extubated in the operating room or within 3 hours of returning to the critical care unit. These patients are more awake at this time than those undergoing CPB. Attention to pain management during this period is considered an important priority in order to obtain a rapid recovery.
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RESULTS
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The majority of variables tested in this study showed no difference between the two groups of patients, and most of the preoperative variables with significant p values (< 0.05) had no influence on the ability to attempt complete revascularization (Table 1
). There were differences in the number of diseased vessels, with more triple-vessel disease in the on-pump group. The predicted mortality and ejection fractions were better in the on-pump group. Resource consumption (ventilation, intensive care and hospital stay, and intraaortic balloon pump support), postoperative enzyme levels, 30-day mortality, and the readmission rate were more favorable in the off-pump group. The rate of conversion to on-pump CABG was less than 5%. Regarding the number of distal anastomosis, there were more single and double grafts in the off-pump group, 3 to 8 grafts were placed in the on-pump patients (Table 2). The mean number of grafts per patient was 2.9 for off-pump CABG, and 3 for on-pump CABG (p < 0.05).
It has been our custom to document the diameter of the native vessel at the site of anastomosis, using a probe. This measurement may not be absolutely scientific, but the data allow rough comparisons of arterial size. It is interesting to note that the estimated sizes of the arteries at each site at the time of surgery were similar in both groups (Figure 1). When the distribution of graft sites was analyzed, it was found that the LAD was the most commonly grafted vessel, followed by the first obtuse marginal and the posterior descending artery (Figure 2). It can be seen that the main RCA and intermediate arteries were bypassed less often in off-pump CABG. This might be related to more frequent hemodynamic instability during stabilization and occlusion of these vessels during off-pump CABG.
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Figure 1. Mean diameters of the grafted vessels, measured with a probe during surgery. D1 = 1st diagonal artery, D2 = 2nd diagonal artery, IM = intermediate artery, LAD = left anterior descending artery, LVB = left ventricular branch, OM1 = 1st obtuse marginal artery, OM3 = 3rd obtuse marginal artery, PDA = posterior descending artery, RCA = right coronary artery.
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Figure 2. Percentage of grafted vessels (diameter at least 1.5 mm) at each site. D1 = 1st diagonal artery, D2 = 2nd diagonal artery, IM = intermediate artery, LAD = left anterior descending artery, LVB = left ventricular branch, OM1 = 1st obtuse marginal artery, OM3 = 3rd obtuse marginal artery, PDA = posterior descending artery, RCA = right coronary artery.
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DISCUSSION
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Obviously, the main challenge in off-pump CABG is access to the circumflex and posterolateral branches of the RCA. Benetti and colleagues6 have probably the most extensive experience with this procedure. They described a technique in which large silk pericardial stay sutures are placed deeply to help rotate the apex while an assistant gently retracts the apex by pulling the heart up and down slowly with every stitch, to preserve hemodynamics. We believe the factors crucial to achieving optimal exposure and outcomes include perfect placement of the 3 deep pericardial traction stitches to allow vertical displacement of the heart, raising the filling pressures of both sides of the heart to 20 mm Hg or greater before and during Trendelenburg positioning, and allowing near normaliza-tion of hemodynamic parameters after application of the stabilizers prior to arteriotomy and anastomosis. The other maneuvers described may facilitate exposure and minimize postoperative pain.
This study revealed that fewer RCA grafts were performed off-pump, supporting the idea that the greatest risk of intraoperative cardiac arrest might arise from vascular isolation of the RCA. Grafting of the posterior descending artery or posterior ventricular branch is preferable to grafting the RCA itself. When grafting of the RCA directly is necessary, an occluder that simultaneously maintains perfusion may be most beneficial. If CPB becomes necessary, cardioplegic arrest may still be avoided, affording substantial benefit to the patient. Fewer intermediate grafts were performed off-pump, perhaps because the stabilizer might compress the right ventricular outflow tract during apical elevation, leading to hemodynamic instability.
The immediate results showed no significant difference in operative mortality between the 2 groups, and a ratio of observed/expected mortality of less than one. The readmission rate was similar in both groups and mainly related to minor problems such as pleural effusion and phlebitis. This study documented more resource utilization in the on-pump CABG group, including longer operating room times, more blood loss, and longer periods of ventilation and intensive care. However, the length of hospital stay was not reduced by avoidance of CPB.
Certain patients may be suboptimal candidates for complete revascularization, including those whose preoperative angiograms demonstrate small, intramyo-cardial, or heavily calcified vessels that may require endarterectomy. Very hypertrophied but not dilated hearts are particularly difficult to position for off-pump grafting, and usually contraindicate this procedure. Hemo-dynamically unstable patients are clearly not candidates for off-pump CABG.
Active participation by the anesthesiologist using anticipatory as well as reactive strategies is essential to achieve a safe and successful outcome. There is no question that complete off-pump revascularization is technically far more demanding for both the anesthesiologist and surgeon than working on an arrested heart or off-pump CABG of the anterior arteries only. Off-pump complete revascularization cannot be carried out efficiently without the expertise of the surgeon and anesthesiologist working in harmony.
The excellent results and minimal complications with off-pump multivessel CABG in this study were comparable to those with the on-pump procedure. The number of grafts per patient and the number of grafts at each anastomosis site were nearly identical in each group. This experience indicates that despite the technical demands, complete revascularization can be achieved in many cases without the need for CPB.
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REFERENCES
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- Bell MR, Gersh BJ, Schaff HV, Holmes DR Jr, Fisher LD, Alderman EL, et al. Effect of completeness of revascularization on long-term outcome of patients with three-vessel disease undergoing coronary artery bypass surgery. A report from the Coronary Artery Surgery Study (CASS) Registry. Circulation
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ABSTRACT
INTRODUCTION
