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Ann Thorac Surg 2002;74:115-118
© 2002 The Society of Thoracic Surgeons

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Original article: cardiovascular

Off-pump coronary artery bypass grafting decreases morbidity and mortality in a selected group of high-risk patients

^a Division of Cardiothoracic Surgery, University of Minnesota, Minneapolis, Minnesota, USA
^b Albert Starr Academic Center, Providence St. Vincent Heart Institute and Medical Center, Portland, Oregon, USA

Accepted for publication March 28, 2002.

* Address reprint requests to Dr Bittner, University of Minnesota, Division of Cardiothoracic Surgery, Department of Surgery, Box 207, 420 Delaware St, Minneapolis, MN 55455, USA
e-mail: bittn006{at}tc.umn.edu

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. The ideal indication for off-pump coronary artery bypass grafting (OPCABG) has yet to be defined. High-risk surgical patients may benefit the most when cardiopulmonary bypass (CPB), aortic cross clamping, and cardioplegic arrest are avoided. The aim of this study was to determine whether off-pump coronary artery bypass grafting might decrease the operative morbidity and mortality in a select group of high-risk patients with multivessel coronary artery disease.

Methods. Utilizing a Parsonnet risk stratification model we analyzed prospectively collected data on a cohort of high-risk coronary artery disease patients, which were operated on with beating-heart technology by the same group of surgeons in a tertiary care university medical center. High-risk patients were defined as those with a Parsonnet score of 15 or greater.

Results. Fifty-seven multivessel disease OPCABG patients (over a period of 2 years) had markedly increased Parsonnet scores (24.3 ± 10.6). The average ejection fraction of the patients was 42% (±12.3) and their age ranged from 52 to 85 years (mean 70.6 ± 10.4, 26% women). Unstable angina was present in 42 patients (74%) and 10 patients underwent OPCABG within 24 hours of the occurrence of acute myocardial infarction. In addition to severe coronary artery disease 32% of the patients presented with congestive heart failure, insulin-dependent diabetes (18%), renal failure (22%), peripheral vascular disease (31%), pulmonary disease (18%), and neurologic disorders (14%). An average of 2.6 ± 0.9 grafts/patient were performed and the posterior descending artery or marginal branches of the circumflex artery or both were grafted in 90%. The 30-day mortality rate was 3.5% (n = 2).

Conclusions. OPCABG can be performed with a reasonable low morbidity and mortality in this select group of high-risk patients. OPCABG is a reasonable, and might even be preferable, operative strategy in this high-risk group of patients.

	Introduction

Top Abstract Introduction Material and methods Results Comment References

 
In an effort to avoid the adverse effects of cardiopulmonary bypass, myocardial revascularization without cardiopulmonary bypass or off-pump coronary artery bypass grafting has been rediscovered. It has assumed an increasing role in many surgical practices. Over the last 3 years several groups reported its safety, effectiveness, and excellent short-term results in selected patients [1–3]. The most critical issues in beating heart coronary artery bypass grafting are that of patient selection and benefit, long-term graft patency, and safety of beating heart coronary revascularization for multivessel coronary artery disease. The purpose of this study is to report the outcome and indication of coronary revascularization without cardiopulmonary bypass in a select population of high-risk surgical patients with coronary artery disease.

	Material and methods

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Over a 2-year period the surgical procedures and outcomes of 57 prospectively selected patients were reviewed. These patients underwent coronary revascularization without cardiopulmonary bypass (off-pump [OPCABG]). The age of the patients ranged from 52 to 85 years in a predominantly male population (Table 1). The majority (67%) of patients underwent surgical revascularization within 24 hours of their hospital presentation. Ten patients were transferred directly from the heart catheterization laboratory to the operating room for emergency surgical coronary artery revascularization because of failed percutaneous interventions, acute myocardial infarctions, or pathoanatomic complexity of the coronary artery lesions. Left ventricular function was assessed by ejection fraction (EF) on contrast ventriculograms or by transesophageal echocardiogram (4 patients). The EF ranged from 10% to 60% (mean 42% ± 12.3%). The risk of the patients was assessed using a univariate model of risk stratification [4] and high-risk patients were defined as those with a Parsonnet score of 15 or greater. Operative mortality was defined as any death occurring within 30 days of surgery. The intention was to perform complete coronary revascularization with or without cardiopulmonary bypass as an urgent treatment option for single- or multivessel coronary artery disease. No consideration was given to perform minimally invasive coronary revascularization in order to select patients for earlier discharge, less blood product administration, or reducing hospital charges.

The following revascularization strategy was practiced. The culprit lesion was revascularized first. The distal anastomosis was completed before the proximal anastomosis. Sequential grafting was not performed. Single aortic side clamping was performed to minimize risk of aortic trauma in the case of multiple proximal anastomoses. Lesions of the left anterior descending artery (LAD) were bypassed with a left internal thoracic artery (LITA) pedicle graft. Routine intracoronary shunting of the target artery was not performed. An initial dose of heparin 10,000 U was given intravenously and the activated clotted time (ACT) measured. Additional doses of Heparin were administered to maintain ACTs greater than 250 seconds. Protamin reversal was performed at the end of the operations for ACTs greater than 300 seconds.

Target artery immobilization and regional myocardial motion control were achieved through a commercially available mechanical stabilization system (Cohn Stabilizer; Genzyme Surgical Products, Fall River, MA) mounted on a special retractor (Genzyme Surgical Products), which in combination with silastic bands allowed gentle and controlled vessel occlusion. A CO₂-blower/NaCl mister device was used in situations where a bloodless field was not achieved with proximal target vessel occlusion. CO₂-flow was set at 2 to 3 L/min with the saline solution pressurized at 150 mm Hg. The tip of the device was held at least 5 cm from the target area. Coronary stabilizer changeovers and reconfiguration of the stabilizer were required during multivessel surgery. Three deep 2-0 monofilament pericardial retraction sutures were placed in order to rotate the heart in the pericardial well. The first suture was placed 1 cm anterior to the left superior pulmonary vein. The second suture was placed close to the left inferior pulmonary vein. The third suture was placed in the pit of the pericardial sac between the second suture and the inferior vena cava, which also fixes the end of a gauze sling over a tourniquet [5]. A second gauze sling was passed through the transverse sinus of the heart. Traction on sutures 1 and 2 brought the LAD and diagonal branches into midline. Traction on retractor suture 3 in combination with slight traction on the gauze slings rotated the apex of the heart toward the right pericardium and elevated it leading to exposure of the posterior-lateral coronary circulation (circumflex artery marginal branches, posterior descending artery [PDA]). This rotation and exposure can be facilitated with a right-sided pericardial incision, especially if bypass grafting is performed on dilated and enlarged hearts. The surgical table, rotated rightwards and set in Trendelenburg position, assisted in exposing the posterior coronary territory and maintaining right ventricular preload. If a right-sided pleuropericardial split and incision were made suture closure was done at the end of the operation.

Quality control of the anastomosis
Just before the completion of the distal anastomosis a fine vascular microdilator (sizes 1.0 and 1.5 mm) was used and the patency of the anastomosis probed. After antegrade flow was established (completion of the proximal anastomosis) or positioning of the LITA pedicle, flow was assessed qualitatively with an Ultrasonic Doppler Flow Detector (model 812; Parks Medical Electronics).

	Results

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OPCABG was performed in high-risk patients with an average Parsonnet score of 24.3 ± 10.6. The intraoperative and perioperative mortality was 0%. Two patients died during their hospitalization (30-day mortality rate of 3.5%). One patient (an 85-year-old women with critical left main coronary artery disease) died 3 weeks after surgery in respiratory failure after atrial fibrillation-induced cerebrovascular accident (CVA) and aspiration pneumonia. A second female patient died 3 weeks postoperatively. This patient had a failing kidney transplant, acute oliguric renal insufficiency, recurrent CVA, and a non-Q-wave myocardial infarction with a troponin value of 14 ng/mL on postoperative day 14 and heart failure. The morbidity in the OPCABG group included 1 myocardial infarction, 1 CVA, and 1 take-back for anterior wall ischemia and revision of the LITA to LAD anastomosis. The conversion rate to on-pump CABG was 9% (n = 5) and primarily related to arrhythmias (n = 3) while attempting to bypass proximal lesions of the right coronary artery. One patient had severe pericardial adhesions and constriction due to pericarditis, which obscured the epicardial coronary vasculature. One patient had a contained left ventricular rupture, failed PTCA and stenting of the proximal circumflex artery after acute infarction. These patients successfully underwent on-pump beating heart coronary revascularization.

Arrhythmias occurred most frequently during OPCABG right coronary artery revascularization leading to urgent intraluminal shunt insertion in 4 cases. All distal anastomoses were evaluated by means of inserting a fine vascular dilator and confirmed with an ultrasound Doppler probe in the OPCABG patients. Routine cardiac enzyme analysis and ECG evaluations after the operations were negative for myocardial infarction. Follow-up coronary angiography was performed in 10 OPCABG patients 2 to 4 weeks postoperatively, which revealed graft patency in all cases. One patient had a 50% proximal anastomotic vein graft stenosis. All patients where free of angina or reintervention at their follow-up clinic visit (4 to 6 weeks postoperatively).

	Comment

Top Abstract Introduction Material and methods Results Comment References

 
The refinements in off-pump technology and new mechanical stabilizers have led to the widespread application of coronary revascularization without CPB. Recent studies describe the success of complete revascularization in beating heart surgery [6–9]. However, the precise role of beating heart technology and the indications for OPCABG remain to be defined. Until the results of prospective randomized trials are released it is still too early to state that off-pump coronary surgery is more cost effective, is associated with less morbidity, accelerates postoperative recovery, and shortens the time to return to work compared with the conventional approach.

We do not consider the off-pump technology in competition with CPB because both have their place in the strategy of myocardial revascularization. For us, coronary artery surgery without CPB seems to be a promising new alternative in patients where the adverse effects of extracorporal circulation and cardioplegic arrest may aggravate preexisting complications and disorders. CPB and cardioplegic arrest can cause myocardial dysfunction, negative central nervous system effects, neuropsychiatric phenomena, severe systemic inflammatory response, and coagulopathy associated with end-organ injury [10–13]. A number of studies have demonstrated that advanced age, urgent operation, impaired left ventricular function, cerebrovascular disease, female sex, New York Heart Association class III or IV status, and left main coronary artery stenosis were independent predictors of operative risk [4, 14] leading to high scores in risk stratification and assessment programs for cardiac surgery. Patients with these described comorbid conditions are the subject of this report. The cumulative risk score reached an average of 24 points using Parsonnet’s operative predicted risk stratification method. The results of this study demonstrated that complete coronary revascularization was achieved in all patients with a reasonable operative morbidity and mortality in this cohort of high-risk patients. The morbidity and mortality observed in the OPCABG group of patients is significantly better than that predicted by the Parsonnet risk stratification model, which would predict a 10% to 15% mortality in this subset of patients [4].

The results of this report are comparable with the findings of a high-risk group of 15 patients with an average Parsonnet acuity score of 22 operated on by Rizzo and associates [15] using the off-pump MIDCABG technique. The mortality rate was 0%. However these patients presented primarily with LAD disease and the number of grafts per patient was only 1.6. Moshkovitz and colleagues [16] and Mohr and associates [17] used the off-pump technique in patients with acute myocardial infarction and in patients with impaired left ventricular function. The mean number of grafts was 1.8 and only 23% of the patients received a graft to marginal branch of the left circumflex artery. The mortality rate was 3.8% and a perioperative myocardial infarction rate 2.7% and improved compared with an equivalent patient population operated on with CPB [16, 17].

The youngest patient of the series presented with a large acute anterior wall myocardial infarction and had a devastating CVA on the first postoperative day after successful off-pump LAD and PDA bypass grafting. Presumably the stroke was caused by embolization from a postmyocardial infarction left ventricular cavity thrombus. Even though the predicted rate of adverse neurologic outcomes was high in 10 OPCABG patients with a history of previous stroke or severely occluded bilateral internal carotid arteries [18], no new neurologic events were observed. With beating heart surgery, avoidance of the embolic potential associated with aortic cannulation and decannulation and of the generation of microgaseous and microparticulate emboli from the pump circuit would be expected to decrease cerebral embolic load and improve outcomes. It has been demonstrated that there is a correlation between aortic atherosclerotic load and the amount of cerebral embolization as a result of the "jet" of perfusate through the aortic cannula scouring the atherosclerotic aortic lumen. Maintaining more normal aortic flow patterns during beating heart surgery would be expected to decrease the incidence of cerebral and systemic atheroemboli [19]. That alone provides a sound rationale for investigating alternative surgical approaches and identifying the optimal off-pump technology as well as the ideal patient.

The OPCABG patients who present with either acute myocardial infarction or severely impaired left ventricular function tolerated proximal target artery occlusion, heart manipulation, and adverse anatomical position very well. In these patients the LIMA was mobilized with a very long pedicle. The LAD was grafted first before branches of the left circumflex or posterior descending artery were bypassed. These patients made a rapid recovery tolerated the weaning of the preoperatively inserted intraaortic balloon pumps and the discontinuation of inotropic support. There was no evidence for new myocardial infarction or myocardial ischemia.

Efficiency with smooth flow of the operation and adequate target stabilization remained primary challenges and goals for successful beating heart surgery, particularly for multiple-graft operations. Our rapid progression to off-pump multivessel revascularization in high-risk patients was inspired from the refinement of cardiac stabilizers permitting unhindered surgical access to all coronary territories, the improvement of a surgical off-pump technique enabling hemodynamically stable heart manipulations and circumflex exposure, and the encouraging initial angiographies revealing excellent graft patency. The use of deep pericardial sutures in particular is of significant value. The pericardial-based sling is a simple and gentle traction and rotation tool in order to expose and stabilize the posterior-lateral coronary branches.

In conclusion our results indicate that complete coronary artery revascularization is feasible on the beating heart in very high risk patients with low morbidity and mortality and excellent early results. The ideal patient selected for OPCABG is actually the one who is elderly with other comorbid conditions such as severe cardiac dysfunction and low ejection fraction, evolving myocardial ischemia, pulmonary or renal failure, severe peripheral vascular disease, and prior stroke.

	References

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