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(October 9, 2006). doi:10.1510/mmcts.2004.000539 Copyright © 2006 European Association for Cardio-thoracic Surgery Procedure Off-pump myocardial revascularizationGasthuisberg University Hospital, Katholieke Universiteit Leuven, Belgium * Corresponding author: * Cardiale Heelkunde, Gasthuisberg University Hospital, Katholieke Universiteit Leuven, Herestraat 49, B-3000, Leuven, Belgium Tel.: +32-16-344260; fax +32-16-344616. E-mail: paul.sergeant{at}uzleuven.be
Since 1998, a large body of literature regarding off-pump coronary bypass surgery has been published, although varying techniques and outcomes likely have led to its inconsistent application. One approach has been developed and standardized at KU Leuven. This approach is straightforward and can be replicated without need for conversion toward cardiopulmonary bypass. The patient is ‘conditioned’ before and during the procedure. Both mammary arteries are harvested through a standard sternotomy. The anterior surface of the heart is exposed with a horizontal line of left-sided pericardial stitches, just above the level of the heart. The anterior coronary vessels are anastomosed after routine shunting. The lateral and inferior aspects of the heart are exposed without deforming the atrio-ventricular axis. This is performed in a stepwise manner. The first step is anchoring a sling into the posterior pericardium under the roof of the left atrium. Second, this sling is gradually pulled upwards, supporting the heart as a cradle. Once the heart is exposed toward the zenith, an apical suction device stabilizes, reformats and exposes the ventricle. The lateral and inferior walls are then revascularized. As a strict no-touch technique is used, free grafts are anastomosed to in-situ arterial grafts.
Key Words: OPCAB • Off-pump coronary artery bypass • Beating heart surgery
In 1910, Carrel [1] first anastomosed a preserved carotid artery from the aorta to a coronary artery on the beating heart of a dog. The first description of a coronary bypass using the mammary artery to the left anterior descending (LAD) off-pump was by Kolesov in Leningrad, 1967 [2]. The widespread application of standard coronary artery bypass grafting (CABG) followed, made possible by cardiopulmonary bypass (CPB). This was used in a variety of approaches, with or without cardioplegic protection. The technique of off-pump coronary artery bypass (OPCAB) surgery did not become popular again until the late 1990s, when it attracted renewed interest. R.d.C. Lima's technique, using a series of pericardial retraction sutures, allowed access to the marginal arteries [3]. Improved exposure of the lateral wall, by placing a single stitch in the oblique sinus of the posterior pericardium, would later be described [4]. While these developments were occurring, Grundeman and Borst [5,6] advanced OPCAB surgery by applying suction technologies to expose and stabilize the coronary vessels. They studied spatial motion and the biological consequences of suction stabilization in the experimental laboratory and identified the superior stabilization of this technique. Since then conflicting and supporting evidence has been published, confused by the variability in technique, surgical discipline, and patient selection. Moreover, the literature is inconsistent with the use of statistical analysis. In 1999, Katholieke Universiteit Leuven formally adopted OPCAB for the coronary surgery service in a deliberate reengineering. Since that time, over 3000 consecutive off-pump cases have been performed, representing 99% of the coronary volume.
The OR setup The OR room should be kept warm until the patient is fully draped with the goal of keeping the patient's core temperature above 36 °C for the duration of the procedure. The most effective method for maintaining this ideal body temperature is to prevent cooling of the patient during the setup. A heated mattress is placed immediately beneath the patient; intravenous fluids and inhaled gases are also warmed. The table should be capable of raising the patient's legs independent of the thorax. A magnetic mat stabilizes the most important instruments and is positioned on top of the legs, allowing unobstructed movement of the table (Photo 1).
A suction tree is used, with separate controls for apical suction, stabilizer, and cell saver. The apical device is set no higher than 200 mmHg and the stabilizer is set no higher than 320 mmHg. The reason for such specific parameters is twofold. First, high rates of suction can cause hematomas and/or trauma to the myocardium. Second, the amount of force needed to expose the heart should be distributed between the suction device and the sling support to be described. The patient's legs are secured with a padded block secured to the right side of the table to allow rotation of the table to the right, important for unloading the heart from the sling. It is routine at KU Leuven to monitor the pulmonary artery pressures (PAP) via a Swan-Ganz catheter and have a transesophageal echo probe (TEE) in place. A less expensive alternative to the Swan-Ganz is direct measurement with a small catheter placed directly into the pulmonary artery.
Instruments
Anesthesia The patient's temperature is maintained above 36 °C, most importantly by avoiding any heat loss during induction and draping. The thermostat in the room is set at 24 °C, and a heating mattress, warm fluids and gasses are used. The room temperature is normalized after draping if no temperature loss is observed. Selective, long acting beta blockers are used to reduce heart rates above 80 bpm and atrial pacing to increase rates below 55 bpm. Atrial and ventricular wires are placed in case of any conduction disturbance. Ventricular wires are inserted in the presence of chronic atrial fibrillation to allow anesthesia to over-pace a blocked ventricular response. All pacing wires are placed and tested before the start of the ‘anastomotic interval’. The patient's potassium is kept between 4 and 5 MeQ/dl and is checked every 15–20 min, to avoid any atrial ectopy. The pulmonary artery diastolic pressure is used to monitor ventricular filling and as an early marker for ischemia. This is monitored using a Swan-Ganz or a catheter directly in the PA. The PAD is corrected and maintained between 10–15 mmHg. Raising and lowering the patient's legs is the first line of adjustment for this parameter, followed by fluid delivery and finally, if needed, selective alpha-1 agonists are used. When the core temperature exceeds 37 °C additional vasoconstriction is often required. Ionotropes are avoided by all means, since increased oxygen consumption may tip the patient into a zone of instability, leading to unnecessary and risky conversions. Long acting beta blockers and an increased depth of anesthesia are used to reduce high PA pressures.
General exposure
Anterior wall revascularization
The suction stabilizer is then attached to the sternal retractor in the right lower position. With the stabilizer clamped in the right lower position its arms will be pointing in the opposite direction of flow in the LAD. This approach allows an unobstructed approach of the graft towards the anastomotic target. The malleable arms of the device are shaped to allow optimal stabilization of the LAD while requiring less suction and placing less pressure on the cardiac surface. The stabilizer is transformed by enlarging the space between the arms, rotating or bending the arms. The holes can be occluded with bone wax to avoid suction on top of side branches. The coronary vessel is then dissected and explored. The use of everting traction sutures exposes and further stabilizes the target vessel (Video 2).
The anastomotic region is surveyed in the usual fashion and an estimation of the internal diameter is made so that a proper size shunt is chosen. Strict attention is paid to proximal disease and side branches. This information will determine which direction the long end of the shunt will point, so as to avoid obstructing a side branch or creating selective perfusion. If necessary, the longest section is directed toward a tortuous vessel to straighten it and ensure flow. A 4.0 prolene suture on a 180° needle with a soft tourniquet is placed around the coronary vessel proximal to the grafting site. If the coronary artery has an intramural or intraseptal pathway, the risk of injuring the vessel is increased and this suture is then omitted. The vessel is incised normally using a full set of arteriotomy scissors covering all possible angulations. The tourniquet is then gently tightened to allow a clear field while placing the shunt. The longest section of the shunt is inserted first then the short end is inserted in a ‘goose-neck’ fashion. Once the proximal portion of the shunt is in place, the tourniquet is released and removed. The distal coronary perfusion area is then inspected for color and contractility (Video 3).
A shunt is no guarantee of sufficient perfusion. As such, anesthesia will closely monitor the markers of ischemia and correct by increasing volume, administering selective vasoconstrictors or giving vasodilating agents. If ischemic changes occur, the surgeon is obligated to re-inspect the size and the pathway of the selected shunt. The anastomosis is created by first placing a mattress stitch in the heel of the graft and then approximating it immediately to the vessel. The anastomosis is completed with the graft down on the target vessel. As a rule, the graft is not parachuted since it would later become difficult when grafting an obtuse marginal (OM) where there is little room to maneuver. For the sake of training, routine and speed, all anastomoses are created in an identical fashion (Video 4).
Enucleation Exposing the lateral and inferior walls of the heart, while maintaining stable hemodynamics, is the goal of every multi-vessel off-pump coronary. The preparation for enucleating the heart requires constant communication with anesthesia. This process is divided into three major steps: the deep stitch, the sling and the enucleation. For the deep stitch: the surgeon needs three tools: a high-powered stiff suction, a folded dry gauze and a 100 cm #1 prolene, loaded and ready. The conditioning of the patient is reviewed by the surgeon and, if needed, optimized before continuing the procedure. Anesthesia is notified that the deep stitch is about to be placed and, when ready, gives permission to the surgeon to lift the heart (Video 5 and Schematic 1).
For the sling: the surgeon needs three tools: a 28-cm thick silastic tube (see instruments), an extra-long 30 cm tourniquet guide and a moist 4x8 sponge. The conditioning of the patient is reviewed by the surgeon again and, if needed, optimized before continuation of the surgery. Anesthesia is notified that the sling is ready to be placed and, when ready, again gives permission to proceed (Video 6).
For enucleation: the surgeon gradually enucleates the heart by grasping both ends of the sling, rigorously avoiding any ectopic beat or cardiac dysfunction. The process is completed under strict anesthetic supervision. If this maneuver is performed correctly, the left atrium will mobilize in synchrony with the left ventricle without distortion of the mitral valve plateau (Video 7).
Once the apex is pointing upwards, the leg block is checked to ensure that the patient's legs do not fall to the side. The table is rotated 30° to the right, further exposing the lateral wall of the heart and unloading it from the sling. The apical suction device is clamped to the retractor in the upper right position. The optimal placement of the suction is on the antero-lateral side of the apex, avoiding the inferior wall and the LAD. Stay away the inferior surface so as to maintain suction despite the contour changes during reformatting. Once the apical suction device has been placed, the affect on the patient's hemodynamics must be checked. NOTE: if the heart's only functioning area is the anterior/apical region, the apical suction likely will not be tolerated. A deterioration of heart function when the device is applied indicates that the surgeon should cease its use and proceed without the apical suction. The use of the device accomplishes three tasks (Video 8), in order:
Lateral wall revascularization The same principles of stabilization of the anterior vessels apply here. The target is exposed and the graft is prepared. Length is carefully measured from the planned proximal site on the mammary artery to the lateral wall. If a target is planned for the inferior wall, a similar measurement is taken distally. The opening in the graft is made and the anastomosis is completed, occluding both ends of the conduit before the completion (Videos 9 and 10).
Ordinarily the next step is to complete revascularization of the inferior wall. However, in the event of ongoing ischemia or tight left main disease, the proximal anastomosis to the mammary artery should be completed first, to allow new blood flow to the suffering myocardium.
Inferior wall revascularization
Proximal anastomoses In an effort to reduce the perioperative stroke rate, this technique eliminates the use of proximal anastomoses to the aorta. The free right internal mammary (RIMA), or, alternatively, the saphenous vein graft (SVG), is connected to the proximal LIMA. This anastomosis may be shunted if there is ongoing ischemia or tight left main disease. The proximal and distal LIMA are occluded temporarily to facilitate the anastomosis. Air is removed from the vessels by retrograde filling.
The application of OBCAB should be broad if results are to influence mortality, morbidity and resource consumption in the CABG cohort. The distribution of vessel disease should not preclude the number and location of bypasses performed, since technology now allows for proper exposure [7,8]. Furthermore, with increased experience, performing cases on recent infarcts, re-operations and intra-myocardial vessels becomes a reality. At KU Leuven, virtually all (99%) of CABGs are performed using the OPCAB approach. Only those patients undergoing CPR, those who are electrically unstable (VT/VF), those who are in pulmonary edema (saturation below 90%) or those who are in severe cardiogenic shock (CI below 1L/M2) are excluded.
The term conversion is used liberally in the literature and in day to day practice. Some have reported that conversion carries a higher risk than performing the procedure on pump initially [9]. However, the term must be qualified for its meaning; a crash conversion and a confidence conversion are different. The surgeon must also consider whether it was conversion or the initial pathology that led to the increased mortality. The commitment of the entire coronary team is necessary if the intention is to master OPCAB and treat the full spectrum of coronary disease. Having strict standard operating procedures (SOP) in place prior to undertaking an OPCAB procedure will reduce the tendency to convert unnecessarily. ‘Conversion’ is defined at our unit as a switch towards CPB after the start of the first anastomosis and for whatever reason. Outcomes at KU Leuven after more than 3000 cases reveal a <0.4% conversion rate and not a single conversion in the last 1000 cases. Only one patient died of the 11 converted cases.
Critical analysis of the literature
Mortality
Morbidity
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