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(February 19, 2007). doi:10.1510/mmcts.2004.000943 Copyright © 2007 European Association for Cardio-thoracic Surgery Procedure Pump-assisted beating heart surgeryCNR Institute of Clinical Physiology ‘G. Pasquinucci’ Hospital, Via Aurelia Sud, 54100 Massa, Italy * Corresponding author: * Tel.: +39-0585 493 604; fax: +39-0585 493 614 E-mail: glauber{at}ifc.cnr.it
Presentation of the revascularization of ischemized myocardium: beating heart technique using pump-assisted extracorporeal circulation. Main technique of revascularization is presented with highlights of modern mini extracorporeal circulation and beating heart surgery devices. Clinical physiological aspects of the method are described and bibliographical data provided.
Key Words: Myocardial revascularization • Pump-assisted beating heart surgery
Revascularization of the ischemic myocardium remains the most frequent cardiac surgical procedure. Amazingly, with the exclusion of new techniques of myocardial protection, the technical aspects of the procedure have remained unmoved for years. The enduring nature of coronary artery bypass grafting (CABG) bespeaks of its proven history of safety and efficacy. Additionally, it has been a technique that can be performed by a wide variety of surgeons with varying degrees of technical skills and acumen with generally good results. However, conventional bypass grafting utilizing cardioplegic arrest continues to be associated with singular complications that may negate an otherwise successful procedure. Hence, the physiologic aspects of both conventional bypass surgery and beating heart surgery benefits are well investigated. There is still a discussion about a full range of benefits and complications from both surgical revascularization techniques. Cardiac surgery using standard cardiopulmonary bypass (CPB) initiates a systemic inflammatory response owing to patient blood contact with a foreign surface and to the activation of the complement [1]. CABG surgery without CPB has been introduced to avoid the deleterious systemic effects of standardized extracorporeal circulation; but it is well known that the limitations of off-pump CABG are related mainly to hemodynamic instability occurring as a consequence of cardiac displacement. This led to a search for a less aggressive technique to perform this procedure. The basic idea of a pump-assisted beating heart surgery (PABHS) is to ensure adequate perfusion by a closed, extremely minimized extracorporeal circuit, in combination with beating heart surgery technique. This system, based on a rotary blood pump and a high performance membrane oxygenator, can eliminate blood-air contact by avoiding a venous reservoir and by means of suction blood separation. It also aims to minimize hemodilution and mechanical blood trauma, at the same time allowing the same working capacities as during the conventional bypass procedure [2]. Up to 25% of coronary artery bypass operations are being performed without the use of a cardiopulmonary bypass. Concerns remain about the quality of the coronary anastomoses and the completeness of revascularization. Randomized trials have not revealed the significant reduction in morbidity or mortality that the early enthusiasts had hoped for. Yet a number of non-randomized studies have shown clinical benefit from the avoidance of an extracorporeal circulation, but these have been criticized for potential bias in patient selection and management. A majority of surgeons have not yet adopted this technique and are waiting for the accumulation of more evidence [3]. The technique of pump-assisted beating heart myocardial revascularization surgery allows combining the CPB safety and stability in management with effectiveness and less invasiveness of a beating heart surgery technique. The concept of pump-assisted beating heart surgery is based on considerations to revascularize an ischemic myocardium with less response of the heart and hemodynamics to surgical procedure and with maximal effect to the patient. Current cardioplegia techniques do not consistently avoid myocardial ischemic damage in high-risk patients undergoing coronary artery bypass grafting. Alternatively, revascularization without cardiopulmonary bypass is not always technically feasible [3, 4]. The development of CPB and the improvement in methods of myocardial protection allow the best technical conditions for cardiac surgery, although the systemic deleterious effects of CPB remain well known and may lead to the inflammatory response syndrome, adult respiratory distress syndrome, and multiorgan failure [5, 6, 7]. A minimized extracorporeal circulation system (MMCTSLink 136) has been developed to avoid morbidity related to conventional CPB and to permit technical surgical conditions more favorable than the off-pump technique for CABG (Schematic 1).
The system does not have cardiotomy suction. The intrapericardial blood is sucked in by a cell salvage device. The venous line is directly connected to the pump head, and the tubing length does not exceed 1.5 m (Photo 1).
Suppression of the open venous reservoir eliminates the blood-air surface and allows lower priming volumes (680 ml) and less (Schematics 2 and 3, and Photo 2). The main benefit of this minimized system is the reduction of the blood surface contact area due to a shorter circuit, and that it is a heparin-coated system, requiring only moderate systemic heparinization, compared with standard CPB. These technical characteristics should lead to a lower postoperative systemic inflammatory response, as is reported [5].
The system exhibits a lower activation of the coagulative response and platelet aggregation. PABHS may be performed on the beating heart without need of a cross-clamp and at various temperatures. The use of composite arterial grafting can minimize aortic manipulation in pump-assisted surgery as well as eliminate it completely in the off-pump situation [9]. The tendency to incomplete revascularization and technical difficulties in constructing coronary anastomoses on the beating heart remain the principal limitations to the off-pump CABG, where the PABHS allows the same possibilities as CABG with a conventional CPB system. The quality of anastomoses performed during PABHS remains a debatable question. The quality of anastomoses is more dependent of surgical skills during off-pump surgery, whereas there is not much influence on anastomotic technique during PABHS. Performing a coronary anastomosis using the beating heart technique without circulatory and heart-lung bypass remains a technical and psychological challenge for the surgeon. PABHS can be implemented with a possibility of performing a complete revascularization without deleterious effect on heart geometry and systemic hemodynamics [3]. Randomized studies indicate that there is no difference between off-pump and on-pump CABG in completeness of revascularization and cardiac outcome after 1 month. Mortality, stroke, myocardial infarction, and renal failure are not reduced in off-pump coronary artery bypass surgery [10]. There are no reports of selected high-risk patients, but evidence from the American College of Cardiology (ACC)/American Heart Association (AHA) 2004 Guideline update for coronary artery bypass graft surgery for mixed risk (high and low) surgical patients shows level A evidence (data derived from multiple randomized clinical trials or meta-analyses) of similar risk of mortality and level B evidence (data derived from a single randomized trial or non-randomized studies) of reduced risk of mortality at 30 days post-surgery for off-pump surgery. At 1–3 years of follow-up, mortality is similar between groups (evidence levels A and B) [3, 11]. Left ventricular function: patients with low/poor left ventricle function can be selected for this type of surgery. The goal to achieve is performing a surgery with less hemodynamic deterioration of the heart during cardiac surgical procedure. Major changes in ventricular geometry, valvular competence and heart retraction, can be decreased with PABHS approach in establishing the necessary flow and pressure. Heart stabilization and positioning: heart displacement by positioning and stabilizing causes significant hemodynamic changes, where the application of pump-assisted circulation is the most acceptable technique [12]. Coronary bypass grafting of posterior circumflex branches requires full displacement of the heart (apex pointing ventrally), which, in the beating heart, results in an arterial pressure drop [12, 13]. Cerebral injury risk: cognitive impairment seems to be strongly associated to CPB and the occurrence of microemboli. The off-pump technique appears to be promising in order to eliminate the source of these neuropsychological impairments following CABG operation [14]. Neurological injury mainly can be caused by ischemia and embolization. In selected high-risk patients, on-pump, beating-heart coronary artery bypass grafting may be an acceptable trade-off between conventional cardioplegia and off-pump operations. It is still associated with the potentially detrimental effects of cardiopulmonary bypass but eliminates intraoperative global myocardial ischemia [4].
Procedure The operation is performed through median sternotomy. All types of conduits are used as for a traditional CABG procedure. Preparation of the aorta and right atrium for cannulation is performed as for the traditional CPB. Small size aortic cannula and small size two stage venous cannulas are used. Two medium-sized concentric purse-string sutures are placed in the ascending aorta. Aortic and venous cannulas are inserted. The heart is properly cannulated for cardiopulmonary bypass (Video 1).
Prior to initiating bypass it is obligatory to attempt to localize the target vessels and prepare for positioning the heart. Cardiopulmonary bypass is initiated.
Positioning the patient The coronary arteries are exposed and the heart is manipulated with the use of deep pericardial traction sutures or apical suction devices [18]. Appropriate tension on these sutures helps us to rotate and expose the anterior, lateral, posterolateral, and inferior arteries of the heart. Utilization of dedicated positioning and stabilizing devices is strongly recommended. The proximal anastomosis can be performed first or according to the personal choice of the surgeon. The aorta is prepared, side-clamped and punched. The particles are washed out as during a traditional CABG procedure (Video 2).
Previously harvested conduits are prepared and measured to target vessels. The graft should be sized to the location where the anastomosis will rest with the heart in anatomic position, and not where the anastomosis is performed. During our procedure, first proximal anastomosis is performed using a saphenous vein graft (Video 3).
All varieties of conduits used in conventional bypass grafting can likewise be used in pump-assisted beating heart surgery. Extension of pericardial incision can be performed laterally for better exposure of the lateral vessels and can be exaggerated along the right diaphragmatic reflection to make room for positioning the right ventricle. Also, the right pleura can be incised to create enough space when dealing with hypertrophied hearts. By creating a vacuum-type seal to the epicardial surface apical suction devices and heart positioners allow us to distract and move the heart as needed. These devices extend from reticulating arms attached to the sternal retractor allowing the heart to be positioned for optimal vessel exposure. Stabilization of the vessel for the anastomosis can be performed by a suction stabilizer (Video 4) – MMCTSLink 137.
The anterior descending, diagonal, and obtuse marginal vessels are presented by applying suction and moving the apex of the heart towards the right sternum. Suction applied to the acute margin of the heart with retraction towards the left shoulder exposes the distal right coronary artery and its branch vessels. In combination with pump-assisted technique these devices maintain the hemodynamic stability of the heart and lower the right ventricle compression outcomes, when working on difficult arteries, especially in patients with reduced ejection fractions.
Grafting technique
The left anterior descending artery (LAD) is typically the first anastomosis performed using the internal mammary artery and is the easiest to expose and access. In our procedure the sequential anastomoses to the diagonal branch (side-to-side) (Video 6) and left anterior descending artery (end-to-side) are performed.
A stabilizing base is placed for the target area and the vessel exposed. The dissection is not initiated until the stabilizing foot is in place. A carbon dioxide blower is in use to clear blood from the field and open the arteriotomy during the anastomosis. Dissection then proceeds proximally until a segment of artery is identified. The use of intracoronary shunts is recommended, especially for LAD and RCA (Video 7). These are very useful when hemodynamically significant ischemia develops. After intracoronary shunt insertion the anastomosis is performed (Video 8).
Prior to the completion of the LAD anastomosis, we can see the intracoronary shunt removal, the normal coronary artery lumen flow restoration, and the final stitches to anastomosis. Then a suture is placed to fix the pedicle to the epicardium to reduce torsion on the anastomosis. Grafting is then continued by performing next anastomoses in a standard manner by placing the silastic suture for inflow occlusion and stabilizing the target site. Here we can observe the posterior wall exposure, with a placement of the apical suction device and stabilizer (Videos 9 and 10).
Finally, the distal anastomosis to PDA with a vein graft completes the main part of the procedure (Video 11).
Upon finishing the grafts, anastomoses are evaluated (Video 12), possible bleeding is checked. Hemodynamic stability, electrocardiogram (ECG), and ventricular function assessment of the patient is performed. Small drainage tubes are placed to facilitate immediate extubation. Pacing wires are placed according to the surgeon's discretion. The sternotomy is closed in standard fashion, and cell saver blood is returned to the patient.
Analyzing the difference of off-pump and PABHS technique from revascularization with traditional CPB and cardioplegia [4], we can observe more or less identical data in mortality and morbidity. Modern cardioplegia techniques not always allow to avoid myocardial injury in high risk patients undergoing CABG [3, 4]. Reduced aortic manipulation demonstrates real benefits in off-pump technique [9]. In some groups the completeness of revascularization differs in on-pump and off-pump groups, with reduced completeness in off-pump group, where there are data showing no difference in either techniques. Stroke rate, mortality and renal complications are not reduced in off-pump CABG. Mortality of low and high risk patients undergoing CABG is similar [3, 9, 10]. Neurocognitive complications are reduced in off-pump versus on-pump, where main ranges of problems are associated with CPB [14]. Considering the main advantages of PABHS, we have used this technique in 49 patients. Patients were selected on the basis of poor left ventricular function, taking into account all possible problems associated with this kind of procedure, like neurocognitive injury and embolization. There was no mortality in patients undegoing this kind of procedure. Other complications are presented by some aspects of the operation, like the use of cardiopulmonary bypass machine, quality of anastomoses performed, completeness of revascularization, myocardial protection, preoperational condition of the patient, surgical skills, postoperative management, etc. Thus, still there is no evident conception around this issue, as that part of the discussion differs from team to team, and requires further study and development by all the supporters of this technique.
Hemodynamically unstable patients due to an acute myocardial infarction, acute coronary artery closure or dissection, or other catheterization misadventures represent a difficult population for beating heart surgery. In these situations, the risk of total myocardial ischemia overshadows the use of extracorporeal circulation. One approach is to initiate cardiopulmonary bypass with standard aortic and venous cannulas, and perform the grafts with the heart beating but supported. Performed in similar fashion to off-pump beating heart surgery, the technique of pump-assisted beating heart surgery not only supplies hemodynamic stability, but also avoids ischemic cardioplegia arrest. Summing up, in our opinion this technique of PABHS should be taken into consideration in patients with severe vascular disorders, severe left ventricular dysfunction, and high risk patients.
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