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Ann Thorac Surg 2000;70:2013-2016
© 2000 The Society of Thoracic Surgeons

Original article: cardiovascular

Reduced incidence of atrial fibrillation with minimally invasive direct coronary artery bypass

Thomas A. d’Amato, MD, PhDa, Edward B. Savage, MDa, Robert J. Wiechmann, MDa, Tamara Sakert, CCPa, Daniel H. Benckart, MDa, James A. Magovern, MDa

a Department of Cardiothoracic Surgery, Allegheny General Hospital, Pittsburgh, Pennsylvania, USA

Accepted for publication May 8, 2000.

Address reprint requests to Dr Magovern, Department of Cardiothoracic Surgery, Allegheny General Hospital, 320 East North Ave, 14 S.T., Pittsburgh, PA 15212
e-mail: jmagover{at}wpahs.org


   Abstract
Top
 Abstract
Introduction
 Patients and methods
 Results
 Comment
 References
 
Background. Atrial fibrillation (AF) is a frequent complication after coronary artery bypass graft (CABG) surgery. The purpose of this study was to determine the incidence of postoperative AF after minimally invasive direct coronary artery bypass (MIDCAB) in comparison with CABG.

Methods. Between November 1995 and May 1997, 96 MIDCAB procedures were performed. During the same period, 42 patients underwent traditional single CABG using the left internal mammary artery graft (S-CABG). The incidence of in-hospital AF, defined as a sustained episode requiring treatment, was compared between the two groups.

Results. There was no difference in age, ejection fraction, or preoperative risk score between the groups. The use of ß-blockers before or after surgery was not different. The incidence of postoperative AF in the first 6 weeks after surgery was 4% (4 of 96) for MIDCAB and 28% (12 of 42) for S-CABG (p = 0.003). Patients with postoperative AF were older than those without AF (AF 75.5 ± 13.2, non-AF 64.4 ± 10.9, p = 0.005). MIDCAB patients had a shorter hospital stay (4.0 ± 1.2 versus 7.0 ± 5.1 days, p < 0.05). Increased hospital stay attributable to AF was 0.6 ± .5 days for MIDCAB and 0.9 ± .2 days for S-CABG patients. There were no hospital deaths in either group.

Conclusions. The incidence of postoperative AF after single vessel bypass surgery is reduced to a very low level after MIDCAB in comparison with CABG.


   Introduction
Top
 Abstract
 Introduction
Patients and methods
 Results
 Comment
 References
 
Atrial arrhythmias are common after cardiac surgery, with a reported incidence of 20% to 40% in most clinical series [1–4]. The exact cause for atrial fibrillation (AF) after heart operations is not known, but increasing patient age, prior AF, and valvular heart disease are preoperative variables that are associated with this problem [5]. Multiple operative and postoperative factors such as pericardial inflammation, electrolyte abnormalities, hemodynamic instability, and atrial ischemia are also associated with postoperative AF [6–8]. Aortic occlusion time and methods for myocardial preservation are not strongly associated with this problem [9–11].

Minimally invasive direct coronary artery bypass (MIDCAB) is a new method for surgical revascularization for patients with single vessel coronary disease. MIDCAB avoids sternotomy, atrial cannulation, cardiopulmonary bypass, and aortic cross-clamping and has resulted in lower rates of immediate postoperative complications [12, 13]. This study was undertaken to determine if the incidence of postoperative AF was different with MIDCAB than with CABG for patients having a single bypass to the left anterior descending coronary artery (LAD) utilizing the left internal mammary artery (LIMA).


   Patients and methods
Top
 Abstract
 Introduction
 Patients and methods
Results
 Comment
 References
 
Patients
This study is a retrospective review of all patients having a single vessel LIMA to LAD coronary bypass graft at Allegheny General Hospital, Pittsburgh, Pennsylvania, between November 1995 and May 1997. A total of 138 patients were analyzed, of whom 96 had MIDCAB and 42 had a single CABG (S-CABG). During the same period, 1,642 isolated coronary revascularizations were performed. Data were obtained on the patients from the cardiothoracic surgery database at Allegheny General Hospital, which collects extensive prospective data on all patients having cardiac surgery. A clinical risk score based entirely on preoperative data was assigned to each patient. The risk score is a composite score that reflects left ventricular function, comorbid diseases, urgency of operation and laboratory values [14]. The choice for traditional S-CABG or MIDCAB was made by individual surgeon and patient preferences, and no randomization process was used.

Operative technique and management
Single CABG
All operations were done via median sternotomy with cardiopulmonary bypass and cold blood cardioplegia. Cannulation of the right atrium with a two-stage cannula for venous drainage and a coronary sinus catheter for retrograde cardioplegia were routine. The ascending aorta was cannulated for arterial inflow, delivery of antegrade cardioplegia, and aortic root venting. The cardiopulmonary bypass circuit used a membrane oxygenator and a centrifugal pump. Blood temperature was allowed to drift down during cardiopulmonary bypass, and rewarming to a bladder temperature of 35°C was done before discontinuing bypass. Anesthetic management consisted of induction with etomidate (0.2 mg/kg) and fentanyl (5 to 10 mcg/kg), and maintenance with isoflurane (0.5 to 1.0 MAC), fentanyl (10 to 20 mcg/kg), and midazolam (0.1 to 0.2 mg/kg). Patients also received neuromuscular blocking agents for muscle relaxation prior to intubation (curare 3 mg and succinylcholine 120 mg) and during surgery (pavulon 4 to 6 mg). The anticipated time for extubation was within 12 hours after surgery.

MIDCAB
All operations were done through a left anterior thoracotomy incision in the fourth intercostal space. A double lumen endotracheal tube was used to facilitate mobilization of the LIMA under direct vision. Cardiopulmonary bypass was not used. The anterior wall of the heart was immobilized with a mechanical stabilizing retractor (Cardio Thoracic Systems, Cupertino, CA) during construction of the anastomosis. A single chest tube was used to drain the left pleural cavity, and a flexible drain was used to drain the posterior pericardial space. Intercostal nerve blocks with 0.25% bupivacaine were performed in the second through the sixth intercostal spaces to reduce initial postoperative pain and facilitate immediate extubation. Anesthesia was similar to that for CABG except that smaller doses of fentanyl (5 to 10 mcg/kg) and midazolam (0.05 to 0.1 mg/kg) were used. Extubation in the operating room was the goal in all patients.

Postoperative care
Both groups stayed in the surgical intensive care unit overnight and were transferred the next day if stable. Magnesium and potassium supplements were given to both groups of patients during and after surgery to maintain levels greater than 2 mEq/L and 4.0 mEq/L, respectively. Selective ß-blocker therapy, using metoprolol 25 mg given orally twice per day, was initiated on the first postoperative day unless a contraindication was present, such as bradycardia, heart block, or a systolic blood pressure less than 100 mm Hg. Ambulation and cardiopulmonary rehabilitation were started on the first postoperative day.

A standard protocol for detection and treatment of atrial fibrillation was used for both groups of patients. All patients had EKG monitoring for 3 to 4 days after surgery. Patients with postoperative AF that was symptomatic or sustained for more than 15 minutes were treated. Rate control was achieved with intravenous diltiazem, using a 10-mg bolus followed by an infusion of 5 to 10 mg per hour. If sinus rhythm was not restored within 12 hours, then additional drugs such as procainamide, quinidine, or amiodarone were started. Brief episodes of AF that were not treated pharmacologically were not included in the analysis.

Complete follow-up information was obtained for all patients. Patients were seen by a cardiologist at 2 weeks and by a surgeon at 6 weeks after operation. Information was collected for each patient regarding hospital readmission and/or outpatient institution of antiarrhythmic drugs for treatment of AF.

Statistical analysis
Categorical variables were compared using {chi}2 analysis or Fisher’s exact test. Student’s t test was used for continuous variables. A p value of 0.05 or less was considered statistically significant.


   Results
Top
 Abstract
 Introduction
 Patients and methods
 Results
Comment
 References
 
Patient groups were well matched with respect to age, preoperative ejection fraction, and clinical risk score (Table 1). The percentage of female patients was slightly higher in the MIDCAB group but this was not statistically significant. A prior history of episodic AF and preoperative ß-blocker use were also similar. There was no difference in postoperative ß-blocker use. The incidence of in-hospital postoperative AF in the MIDCAB group (3%) was remarkably low and was significantly less than in the S-CABG group (28%). One MIDCAB patient was readmitted to the hospital because of AF, which occurred during the first week after initial discharge, but none of the S-CABG patients developed AF after hospital discharge. The 6-week incidence of postoperative AF was 4% (4 of 96) for MIDCAB and 28% (12 of 42) for S-CABG (Fig 1).


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  		Table 1. Characteristics of Patients Receiving MIDCAB or Single CABG

 


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  		Fig 1. The cumulative 6-week incidence of postoperative atrial fibrillation in the traditional single coronary artery bypass group (S-CABG) and in the minimally invasive direct coronary artery bypass group (MIDCAB). *Indicates a statistically significant difference with p = 0.003.

 
There was no operative mortality in either group. Postoperative patient characteristics are shown in Table 2. Patients with S-CABG had statistically longer length of stay compared with those receiving MIDCAB. However, the increased length of stay attributable to AF was not statistically significant. The duration of postoperative ventilation was longer in the S-CABG group. Patients with postoperative AF were older than those without AF (AF 75.5 ± 13.2, non-AF 64.4 ± 10.9, p = 0.005). MIDCAB patients who developed AF were older by approximately a decade than S-CABG who developed AF.


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  		Table 2. Postoperative Data for MIDCAB and S-CABG Patients

 

   Comment
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
References
 
The incidence of postoperative AF was significantly lower for MIDCAB than for traditional S-CABG. The most notable differences between MIDCAB and CABG groups are the use of cardiopulmonary bypass for circulatory support and cardioplegia for cardiac arrest. The etiology, risk factors, and recommendations for the prevention and treatment of AF were recently reviewed [5]. The most important factors contributing to this problem after coronary bypass are older age, a history of prior AF, surgical stress, electrolyte abnormalities, and atrial ischemia/irritability. It is not obvious why MIDCAB patients have a reduced incidence of postoperative AF but the elimination of atrial trauma from cannulation and atrial ischemia from cardiac arrest are the most likely factors. A reduced stress-response to surgery due to the avoidance of a sternotomy and cardiopulmonary bypass is another possibility. The difference cannot be attributed to differences in patient age or the use of ß-blockers, as these two factors were equivalent between the two groups. Both groups were treated with prophylactic ß-blockers, and approximately 70% of patients in each group received the drugs, while roughly 30% did not, owing to a variety of circumstances. The evidence that ß-blockers reduce postoperative AF is mixed [15,16]. The 28% incidence of postoperative AF in the S-CABG group is consistent with the published literature, even when prophylactic drugs are given [17, 18].

The number of bypass grafts does not influence the incidence of AF, which means that S-CABG patients are just as likely to develop postoperative AF as patients having multiple grafts. There have been two recent publications that report early results in large numbers of MIDCAB patients. Calafiore and associates [12] reported a series of 434 MIDCAB procedures with an 8% incidence of postoperative AF, and Subramanian and colleagues [13] reported 185 patients with a 7.5% incidence of postoperative AF. Our incidence of 4% is less than those two series, but all three reports show a remarkably low rate of postoperative AF after MIDCAB, which is significantly less than the expected incidence of 20% to 40%. In contrast, Cohn and associates [19] reported an age-matched incidence of AF for MIDCAB of 26% and for S-CABG of 20%. However, they defined AF as any episode of AF regardless of treatment or duration and did not control for ß-blocker use. MIDCAB patients were less likely to be discharged from the hospital on antiarrythmics, suggesting that several patients in this group had a brief episode of AF that did not require therapy but nevertheless included them in an AF group.

One aspect of postoperative AF that is often overlooked is the association with increasing patient age. This problem is uncommon in patients younger than 50 and very common in the elderly, especially those older than 70 [1–3]. The two patient groups in this study had the same mean age but patients in each group who developed AF were older than those who did not.

Postoperative AF is well tolerated by most patients but it often results in increased costs due to additional medications, nursing care, and hospitalization [20]. MIDCAB has been shown to be associated with less morbidity than traditional CABG [12, 13, 16]. The reduction in postoperative AF is one aspect of this reduced morbidity that contributes to improved outcome in high-risk and elderly patients.


   References
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 References
 

  1. Leitch J.W., Thomson D., Baird D.K., Harris P.J. The importance of age as a predictor of atrial fibrillation and flutter after coronary artery bypass grafting. J Thorac Cardiovasc Surg 1990;100:338-342.[Abstract]
  2. Creswell L.L., Schuessler R.B., Rosenbloom M., Cox J.L. Hazards of postoperative arrhythmias. Ann Thorac Surg 1993;56:539-549.[Abstract]
  3. Hashimoto K., Ilstrup D.M., Schaff H.V. Influence of clinical and hemodynamic variables on risk of supraventricular tachycardia after coronary artery bypass. J Thorac Cardiovasc Surg 1991;101:56-65.[Abstract]
  4. Cox J.L. A perspective of postoperative atrial fibrillation in cardiac operations. Ann Thorac Surg 1993;56:405-409.[Medline]
  5. Ommen S.R., Odell J.A., Stanton M.S. Atrial arrhythmias after cardiothoracic surgery. N Engl J Med 1997;336:1429-1434.[Free Full Text]
  6. Chidambaram M., Akhtar M.J., al-Nozha M., al-Saddique A. Relationship of atrial fibrillation to significant pericardial effusion in valve-replacement patients. Thorac Cardiovasc Surg 1992;40:70-73.[Medline]
  7. Smith P.K., Buhrman W.C., Levett J.M., Ferguson T.B., Jr, Holman W.L., Cox J.L. Supraventribular conduction abnormalities following cardiac operations: a complication of inadequate atrial preservation. J Thorac Cardiovasc Surg 1983;85:105-115.[Medline]
  8. Mullen J.C., Khan N., Weisel R.D., et al. Atrial activity during cardioplegia and postoperative arrhythmias. J Thorac Cardiovasc Surg 1987;94:558-565.[Abstract]
  9. Warm Heart Investigators. Randomized trial of normothermic versus hypothermic coronary bypass surgery. Lancet 1994;343:559-563.[Medline]
  10. Fontan F., Madonna F., Naftel D.C., Kirklin J.W., Blackstone E.H., Digerness S. Modifying myocardial management in cardiac surgery: a randomization trial. Eur J Cardiothorac Surg 1992;6:127-136.[Abstract]
  11. Butler J., Chong J.L., Rocker G.M., Pillai R., Westaby S. Atrial fibrillation after coronary artery bypass grafting: a comparison of cardioplegia versus intermittent aortic cross-clamping. Eur J Cardiothorac Surg 1993;7:23-25.[Abstract]
  12. Calafiore A.M., DiGiammarco G., Teodori G., et al. Midterm results after minimally invasive coronary surgery (last operation). J Thorac Cardiovasc Surg 1998;115:763-771.[Abstract/Free Full Text]
  13. Subramanian V.A., McCabe J.C., Geller C.M. Minimally invasive direct coronary artery bypass grafting: two year clinical experience. Ann Thorac Surg 1997;64:1648-1655.[Abstract/Free Full Text]
  14. Magovern J.A., Sakert T., Magovern G.J., Jr, et al. A model that predicts morbidity and mortality after coronary artery bypass surgery. J Am Coll Cardiol 1996;28:1147-1153.[Abstract]
  15. White H.D., Antman E.M., Glynn M.A., et al. Efficacy and safety of timolol for prevention of supraventricular tachyarrhythmias after coronary artery bypass surgery. Circulation 1984;70:479-484.[Abstract/Free Full Text]
  16. Ivey M.F., Ivey T.D., Bailey W.W., Williams D.B., Hessel E.A., II, Miller D.W., Jr Influence of propranolol on supraventricular tachycardia early after coronary artery revascularization: a randomized trial. J Thorac Cardiovasc Surg 1983;85:214-218.[Abstract]
  17. Daoud E.G., Strickberger S.A., Man K.C., et al. Preoperative amiodarone as prophylaxis against atrial fibrillation after heart surgery. N Engl J Med 1997;337:1785-1791.[Abstract/Free Full Text]
  18. Martinussen H.J., Lolk A., Szczepanski C., Alstrup P. Supraventricular tachyarrhythmias after coronary bypass surgery—a double-blind randomized trial of prophylactic low dose propranolol. Thorac Cardiovasc Surg 1988;36:206-207.[Medline]
  19. Cohn W.E., Sirois C.A., Johnson R.G. Atrial fibrillation after minimally invasive coronary artery bypass grafting: a retrospective, matched study. J Thorac Cardiovasc Surg 1999;117:298-301.[Abstract/Free Full Text]
  20. Aranki S.F., Shaw D.P., Adams D.H. Predictors of atrial fibrillation after coronary artery surgery. Current trends and impact on hospital resources. Circulation 1996;94:390-397.[Abstract/Free Full Text]



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