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ORIGINAL CONTRIBUTION |
Department of Cardiac Surgery Mayo Hospital Lahore, Pakistan
For reprint information contact: Shahzad G Raja, MRCS Tel: 44 151 252 5635 Fax: 44 151 252 5643 Email: drrajashahzad{at}hotmail.com Department of Paediatric Cardiac Surgery, Alder Hey Hospital, Eaton Road, Liverpool L12 2AP, UK
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONPATIENTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONPATIENTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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PATIENTS AND METHODS |
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TOPABSTRACTINTRODUCTIONPATIENTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Preoperative cardiac and antihypertensive medications were suspended on the day of surgery. Medication was resumed on the 1st postoperative day with beta-blockers, angiotensin-converting enzyme inhibitors, and/or antihypertensive agents. Daily aspirin administration was also started 6 hours postoperatively, provided that there was minimal chest tube drainage.
Intraoperative left-sided pressures and cardiac output were monitored by pulmonary catheterization. Patients were placed on a water-filled warming mat and covered with a warming trouser suit to maintain their core temperature between 35°C and 37°C during the operation. Anesthesia was induced with a combined infusion of propofol (3 mg•kg–1•h–1) and sufentanil (1 µg•kg–1•h–1). When we began performing OPCAB, 150 IU•kg–1 heparin was used to maintain the activated clotting time above 250 seconds. Since January 2001, the dosage has been raised to 300 IU•kg–1 to achieve an activated clotting time of at least 350 seconds. At the same time, heparin reversal with protamine at the completion of anastomosis was halved from 1 mg for every 100 IU heparin to 0.5 mg. Aprotinin infusion (500,000 kallikrein inactivator units•h–1) was used in patients undergoing redo coronary surgery. Patients requiring grafting on the posterior wall were monitored intraoperatively by transesophageal echocardiography (TEE).
Surgery was performed through a median sternotomy. Blood was cleared from the operative field with a sterile humidified carbon dioxide blower. An Octopus 2 suction stabilizer (Medtronic, Inc., Minneapolis, MN, USA) was used during grafting in the first 2 years of performing OPCAB. Subsequently, we switched to Octopus 3 and Octopus 4, which provide much more flexibility and improved exposure and stabilization. The target vessel was exposed and snared at the proximal anastomotic site with 4/0 monofilament suture. Ischemic preconditioning, intracoronary shunts, and pharmacological stabilization were used whenever required. A right vertical pericardiotomy was made down to the phrenic nerve during grafting of posterolateral wall vessels. Hypotension that accompanied cardiac manipulation was counteracted by placing the patient in the steep Trendelenburg position combined with infusion of 1 to 1.5 L normal saline. If bradycardia occurred, atrial pacing was established.
When multiple grafts were indicated, a sequence of grafting to reduce the magnitude of systemic effects resulting from local ischemia during coronary occlusion was predetermined. In general, the LAD was bypassed first with the left internal mammary artery (LIMA) to secure revascularization to the anterior wall and the interventricular septum. Subsequently, the collateralized vessel that was occluded or was highly stenotic was bypassed before the collateralizing vessel. Exposure of the LAD and the circumflex artery was improved with deeply placed traction sutures in the left pericardium that caused the heart to rotate forward. Distal anastomoses with vein grafts and internal mammary arteries (IMAs) were made with 7/0 and 8/0 polypropylene sutures, respectively. Proximal anastomoses were made with 6/0 polypropylene sutures under partial occlusion clamping. A cell saver was used in patients requiring more than 1 distal anastomosis.
Pressure control ventilation was established after the operation. The patient was extubated when hemodynamic stability, normothermia, and an absence of bleeding were achieved. Fluid replacement with lactated Ringers was given at 100 to 150 mL•h–1, while red blood cell replacement was instigated if the hemoglobin level fell below 8.5 mg•dL–1. The first 86 patients (50 single-vessel and 36 multivessel) had coronary angiography at 6 weeks postoperatively. Subsequently, angiography was performed only when there was clinical suspicion of recurrent angina.
Data are expressed as mean ± standard deviation. The preoperative characteristics of the patients are shown in Table 1
. The predicted operative mortality, taking into account preoperative risk factors, was calculated using the full logistic version of the European system for cardiac operative risk evaluation (EuroSCORE).3
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RESULTS |
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TOPABSTRACTINTRODUCTIONPATIENTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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. A total of 1,117 distal anastomoses were made with a mean of 2.2 ± 1.0 bypass grafts per patient. A total of 400 patients (76.9%) had multivessel bypass. Arterial grafts were exclusively used for multiple bypass in 96 patients (18.5%). The LAD was bypassed in 498 patients (95.8%), while LIMA grafts were used in 504 patients (96.9%). A concentration of cases with a particular risk profile in any year was not evident. The total number and the proportion of OPCAB cases grew steadily throughout the years, and the mean number of grafts increased during the study period. The mortality predicted by EuroSCORE was 4.2% ± 4.8%; the observed mortality was 2.5% (13 patients). Six patients died from multiorgan failure secondary to sepsis: 3 of them had poorly controlled diabetes, 2 were on long-term dialysis for chronic renal failure, and 1 was on steroids for rheumatoid arthritis. Another patient died from massive pulmonary embolism 6 days after surgery. Three patients who had sustained preoperative myocardial infarction and underwent emergency surgery died of heart failure. Two patients died of perioperative myocardial infarction and heart failure. A patient who underwent redo bypass surgery had sustained malignant ventricular arrhythmia unresponsive to therapy and died while being converted to CPB. Conversion to CPB was necessary in 12 cases (2.3%). Ten patients (1.9%) were re-operated for bleeding or graft failure. The postoperative data are listed in Table 3.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONPATIENTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Generally, grafting of target vessels on the anterior and lateral aspects of the heart is not accompanied by significant hemodynamic changes. However, access to the marginal arteries is hampered by space limitation, which may compromise the quality of the anastomoses and often causes hemodynamic instability following cardiac manipulation. Dislocation of the heart leads to biventricular dysfunction due to kinking of the low-pressure right atrium and ventricle, impairing blood flow in the pulmonary circulation. The resulting low left ventricular (LV) preload leads to systemic circulatory failure.7 In our experience, a median sternotomy is the most practical incision for multiple grafting as it provides access to all sides of the heart. It also facilitates harvesting of intrathoracic arterial grafts and conversion to CPB, if needed. Our strategy during surgery is always to first graft the anterior wall vessels and the RCA as accessing these areas does not necessitate excessive tilting of the heart, in contrast to accessing the posterior wall. The sequence of grafting also depends on the extent of occlusion in the native vessel. A fully occluded artery is grafted first to allow collateral perfusion to the next artery to be operated under intracoronary shunting.
To reach the anterior wall vessels (LAD and diagonal arteries), we place 2 to 3 moistened gauze pads measuring 10 x 10 cm behind the left ventricle to elevate and rotate it into midline. However, this causes compression of the right heart, which is squeezed between the thick, bulky left ventricle and the right pericardium, usually resulting in a drop in right ventricular output, which is reflected in decreased mean pulmonary artery pressure, mean systemic arterial pressure, and cardiac output. Increasing right heart filling by fluid loading or fluid redistribution through the Trendelenburg maneuver counteracts any hemodynamic instability. Exposure of the diagonal arteries causes additional compression, suction, and rotation of the left ventricle to the right with further right heart compression. This results in significant reduction in the stroke volume. A right vertical pericardiotomy down to the phrenic nerve and opening of the right pleura along with infusion of an alpha-adrenergic agonist, or occasionally low doses of an inotropic drug, are the measures adopted by us to prevent hemodynamic compromise. After completing anterior wall anastomoses, the gauze pads are removed before moving to the right or the posterior wall.
To allow a good surgical view of the RCA and its distal branches, the operating table is placed in the head-down position and both suction arms are moved ventrally in order to elevate the target area by 3 to 5 cm. This results in a tremendous expansion of the surgical view, but it also causes some obstruction of the tricuspid orifice. TEE and right atrial pressure monitoring are helpful in identifying the limit of elevation in order to prevent tricuspid valve blockage or insufficiency.
The most challenging site to graft on the beating heart is the posterior wall. In order to view this area and inspect the obtuse marginal arteries through the sternotomy, the heart must be tilted out of the pericardial cradle. This again leads to compression of the heart, and the ensuing premature ventricular beats cause hemodynamic deterioration. The mechanism of this hemodynamic disturbance is the same as in the anterior area but is more pronounced. This unstable period persists in most instances for less than 30 seconds.8 Unlike in LAD and RCA grafting, coronary circulation is only impaired in the obtuse marginal area, since the other areas have already been bypassed. In order to normalize flow through these grafts after tilting the heart, we increase the coronary perfusion pressure using an alpha agonist or low doses of an inotrope. Normalization of the mean systemic arterial pressure restores residual myocardial blood flow, as well as the flow through the grafts on the anterior and inferior walls, leading to the resolution of acute low cardiac output syndrome in almost all cases. It is very important to avoid overshooting with inotropes, especially beta-adrenergic agonists, as the increased oxygen demand may compromise local cardiac wall stability, the accuracy of anastomosis, and cardiac performance.
Over the last 5 years of our experience with OPCAB, we have come to acknowledge the fact that, although there are hemodynamic alterations in the different locations of grafting, multivessel OPCAB is well tolerated in most patients provided meticulous attention is directed towards correction and normalization of hemodynamics before grafting. We firmly believe that the quality of anastomosis should not be compromised by rushing an operation because of hemodynamic instability. During placement of the stabilizer, especially on the tilted heart, it is crucial to correct hemodynamics appropriately without overshooting. If hemodynamic instability persists for too long, circulation will not normalize and grafting will be impossible, necessitating conversion to CPB, which in turn increases morbidity and mortality. During this brief period, communication between the surgeon and the anesthesiologist is vital in guiding the stabilization process and correcting the circulation.
It has been observed that temporary occlusion of the target vessel to obtain a bloodless field during anastomosis may cause regional myocardial dysfunction.9 To circumvent this problem, we use an intracoronary shunt and a proximal suture snare for occlusion. Shunting not only allows unhurried anastomosis in a bloodless field but offers the additional benefit of maintaining distal perfusion.
Another important modification in our practice over the last 2 years is increasing the dosage of heparin for anticoagulation with partial reversal at the completion of surgery. This change was prompted by the death of a patient from massive pulmonary embolism and increasing reports in the literature that patients undergoing OPCAB have a procoagulant activity that is strongly evident 24 hours postoperatively.10 This change in strategy has not increased postoperative bleeding or the need for transfusion. On the other hand, we think that partial neutralization of heparin results in controlled iatrogenic impairment of hemostasis, which prevents graft thrombosis and may presumably last until a full postoperative regimen of antiplatelet therapy is established. In addition, using a cell saver enables us to reduce intra and postoperative transfusion, thereby decreasing exposure to the hazards of transfusion as well as lowering the cost of surgery. Furthermore, the use of aprotinin in all redo bypass operations significantly reduces blood loss.11
The 48 redo cases in our series had a predicted EuroSCORE of 9.2% but an observed mortality of only 2.1% (1 patient). The outcome in these high-risk patients lends support to the observation from other studies that high-risk patients can benefit most from avoiding CPB.12–14
An important finding of our series is the extremely low incidence of postoperative stroke. We attribute this to a relatively young patient population as well as to a variety of strategies that we have adopted to minimize the occurrence of this potentially fatal complication of coronary surgery. We have been using routine intraoperative TEE in all cardiac operations in the last 5 years to evaluate and grade each patient for the presence of atheroma in the ascending, transverse, and descending aorta.15 The results are used to stratify patients in terms of neurologic risk and to guide operative management.16 TEE also provides a more reliable assessment of aortic disease than intraoperative manual palpation of the aorta. In addition, following TEE, we use an epiaortic probe to select sites for proximal anastomoses, as this method is superior to TEE for this purpose.17 Moreover, in high-risk patients, total arterial revascularization is performed using in situ skeletonized IMAs and the radial artery anastomosed proximally to an IMA graft as a Y graft.
With effective vessel stabilization and efficient visualization systems, the reported early and midterm patency of OPCAB is encouraging18 and comparable to that of ONCAB.19 The results of our series are comparable to those of other OPCAB studies.18,19 We attribute our encouraging results to a gradual adoption of OPCAB. Careful patient selection has helped us maintain acceptable results throughout the early period, when patients with LV dysfunction, left main disease, and triple-vessel disease were excluded from OPCAB. Furthermore, prior to starting OPCAB, all surgeons underwent training at teaching centers that provided considerable exposure to off-pump techniques. As our experience with specialized techniques and devices grew, more complex and higher-risk cases were successfully operated off-pump. Since 2001, OPCAB has been applied in a broad spectrum of clinical settings, including advanced age, multivessel disease, depressed LV function, left main disease, and complete arterial revascularization. Currently, all patients scheduled for isolated coronary bypass are considered candidates for OPCAB, except those with intramyocardial coronary arteries, small and calcified target vessels, cardiomegaly, and acute myocardial infarction, as well as those requiring coronary endarterectomy. An additional indicator of our growing experience with this technique is the reduction in operative time from a mean of 210 minutes for an average of 3 grafts to 160 minutes over the 5 years.
The outcome of any operation depends on patient selection, the surgeon’s skill and expertise, the surgical technique, as well as intra and postoperative patient management. All these factors have gradually been refined over the years in our application of OPCAB. It is important to note that the technical solutions that we apply have been extensively described and are part of the knowledge of all cardiac surgeons; however, we concentrate our effort on the careful evaluation of each case and on the systematic individualization of the surgical approach to the clinical and anatomic conditions of every single patient. Consequently, some patients at high risk have been treated by integrating OPCAB with angiographic interventions.
OPCAB techniques are continuously being refined, and many areas of potential benefit are being vigorously explored. A growing number of surgeons are expanding their OPCAB practice and offering many more patients this option. OPCAB is establishing itself alongside ONCAB as a complementary method of surgical revascularization. With encouraging early to midterm results, the prospect is good. However, there are still many unanswered questions and concerns that need to be explored. The findings of our study are limited by their retrospective nature and by the lack of comparison with ONCAB. We eagerly await the results of ongoing prospective randomized controlled trials as well as studies on reintervention with OPCAB and the evaluation of long-term patency and complications. Further research into various aspects of this surgical approach is needed before its benefits can be firmly established.
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TOPABSTRACTINTRODUCTIONPATIENTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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This article has been cited by other articles:
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  S. G Raja and G. D Dreyfus Current Status of Off-pump Coronary Artery Bypass Surgery Asian Cardiovasc Thorac Ann, April 1, 2008; 16(2): 164 - 178. [Abstract] [Full Text] [PDF]
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