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Ann Thorac Surg 1999;68:931-933
© 1999 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Is atrial fibrillation caused by extracorporeal circulation?

^a Department of Cardiac Surgery, Feiring Heart Clinic, Feiring, Norway

Address reprint requests to Dr Saatvedt, Feiring Heart Clinic, 2093 Feiring, Norway
e-mail: saatvedt{at}online.no

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. Atrial fibrillation is the most common rhythm disturbance encountered after open heart operations, with a reported incidence up to 40%. Despite its high incidence and clinical relevance its etiology remains obscure. It has been hypothesized that atrial fibrillation might be related to extracorporeal circulation. We performed a retrospective study (January 1, 1997 to December 31, 1997) comparing the incidence of atrial fibrillation in 3 groups of patients revascularized with and without extracorporeal circulation.

Methods. The first group comprised patients with coronary artery disease operated on with standard revascularization technique with cardiopulmonary bypass (n = 685). The second group included patients who had minimally invasive coronary artery bypass grafting without the use of extracorporeal circulation (n = 19). Patients in the third group had off-pump transmyocardial laser revascularization (n = 19).

Results. There was no significant difference in the incidence of atrial fibrillation in the group that had conventional coronary artery bypass and the group that had minimally invasive coronary artery bypass without cardiopulmonary bypass. The incidence of atrial fibrillation was significantly lower in the transmyocardial laser group compared with the other two groups.

Conclusions. The present study found that postoperative atrial fibrillation is not caused solely by extracorporeal circulation, but patients who had transmyocardial laser revascularization had a significantly lower incidence of atrial fibrillation.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Atrial fibrillation (AF) after conventional coronary artery bypass grafting (CABG) is a frequent clinical problem, and in large series incidences of 20% to 40% have been reported [1–4]. A common suggestion has been that AF after cardiac operations is related to the extracorporeal circulation (ECC), and it has been suggested that changes in cannulation technique, the performance of ECC, or the substitutes of the cardioplegia might affect the incidence of AF after cardiac operations [4–6]. In the present study we compared the incidence of AF in patients who had conventional CABG with a group that had minimally invasive coronary artery bypass grafting (MICABG) without ECC and with a group that had transmyocardial laser revascularization (TMLR) also without ECC.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
This retrospective study was based on the hospital’s database and included detailed preoperative, intraoperative, and postoperative data from patients operated on between January 1997 and December 1997. Physicians prospectively collected clinical data on cardiac history and comorbidity. Intraoperative and postoperative data, including complications and adverse effects, were assessed. Table 1 shows clinical characteristics of the patients in the three groups.

Anesthesia
Patients in all 3 groups were premedicated with intramuscular injection of morphine chloride and scopolamine bromide. Anesthesia was then achieved with fentanyl and fluothane. In the TMLR group isoflurane was used instead of fluothane.

Operative procedure
For CABG, a median sternotomy and standard cardiopulmonary bypass technique were used. The cardiopulmonary bypass circuit consisted of roller pumps (Jostra HLM 15, Hirrlingen, Germany ) or occasionally a centrifugal pump (Medtronic, Minneapolis, MN). During cardiopulmonary bypass moderate hypothermia was induced to maintain the nasopharyngeal temperature between 30° and 32°C. Myocardial preservation during aortic cross-clamping was achieved by St. Thomas’ cardioplegic solution infused into the aortic root before CABG was done. After cardiopulmonary bypass, protamine chloride was administered to neutralize the effect of heparin. The sternotomy was closed in the standard manner.

For MICABG, a standard median sternotomy was used. The left internal mammary artery was harvested from the first rib down to its bifurcation or at the level of the seventh or eight rib space. Heparin was administered at a dose of 1 mg/kg. The left anterior descending artery was stabilized proximally by a looping suture and paraincisionally by a stabilizer (CardioThoracic Systems, Cupertino, CA). In 6 patients a distal occluding suture was applied. The left internal mammary artery to coronary artery anastomosis was done with a running 7-0 or 8-0 polypropylene suture. After the anastomosis was complete, the looping suture and the stabilizer were removed. If a vein graft was used to bypass a stenosis of the diagonal, circumflex, or right coronary artery vessels, an identical technique was used. Protamine chloride was administered to neutralize the effect of heparin. Standard technique was used to close the incision.

For TMLR, the heart was approached through the fourth intercostal space. If a prior heart operation had been done, the adhesions between the pericardium and the heart were sharply divided. Transmyocardial laser revascularization was done with the carbon dioxide Heart Laser (PLC Medical System Inc, Franklin, MA), which has a peak output of 850 W. The laser was set to operate at a pulse energy of 35 J and a pulse duration of 44 milliseconds. The delivery of each laser pulse was synchronized with the electrocardiographic R wave. Transmyocardial laser penetration was confirmed by transesophageal echocardiography by observation of intraventricular bubbles that were created when laser energy was converted into steam when striking blood. Homeostasis was achieved by external compression. A chest tube was placed for drainage and the incision was closed in the usual manner. We limited the TMLR treatment to the ischemic regions as indicated by thallium scintigraphy. In patients who had TMLR, it was the sole treatment.

Statistical analysis
StatView (version 4.0; Abacus Concepts Inc, Berkeley, CA) computer program was used to analyze data. Data are presented as mean ± one standard deviation in tables. Continuous variables were tested with the Mann-Whitney test for unpaired data, and categoric data were tested with Fisher’s exact test. A p value less than 0.05 indicated statistical significance.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
There were no significant differences between the groups with respect to age and gender. Reoperations were more frequent in the group that had TMLR than in the other groups (p < 0.01) (Table 1). Patients in the CABG group received a mean of 3.6 peripheral and 1.9 central anastomoses, with a mean aortic cross-clamp time and perfusion time of 29 and 52 minutes, respectively. In the MICABG group the numbers were 1.9 and 0.8, respectively. A mean of 47 laser holes were made with the high-energy carbon dioxide laser.

The incidence of atrial fibrillation was 36% (248 of 685) in the group that had CABG, 37% (7 of 19) in the MICABG group, and only 5% (1 of 19) in the patients who had TMLR treatment. The frequency of AF was significantly less in the TMLR group (p < 0.01).

	Comment

Top Abstract Introduction Patients and methods Results Comment References

 
The pathophysiologic mechanisms responsible for the high incidence of AF after cardiac operations are unknown, but AF far exceeds the prevalence in the general surgical population. The occurrence of AF might therefore be related to the procedure. Studies have focused on the contribution of ECC to postoperative AF. The present study showed that cardiac operation irrespective of the use of ECC could precipitate AF.

Many studies have attempted to determine possible etiologic factors in the pathogenesis of AF after CABG [7]. The present study found a significantly lower incidence of AF in patients treated with TMLR compared with patients who had conventional coronary revascularization. Most patients who had TMLR had a prior CABG operation. When these patients underwent the TMLR procedure a small left anterior thoracotomy was performed and only a part of the heart was visualized. The adhesions protect the atria from being exposed directly. The local inflammatory response might therefore be limited to the exposed areas of the heart and hence not affect the atria. In a study of 236 patients who had pneumonectomy, an increased incidence of postoperative AF was observed after intrapericardial dissection [8]. Another study found a relationship between AF and pericardial effusion in patients who had valve replace-ment [9], indicating that local pericardial inflammation might contribute to postoperative AF. Another factor might be that the TMLR procedure per se protects against arrhythmias [Dr O. Tjomsland, personal communication, May, 1999].

It is known that the systemic inflammatory response induced by ECC contributes to increased postoperative morbidity observed in cardiac surgical patients [10–12]. The patients who had open heart operations without ECC had a lower intensity of this reaction [13]. However, the local inflammatory response was similar. It seems that this local response is important in the occurrence of postoperative AF.

Studies have indicated that a hyperadrenergic postoperative state might contribute to the development of postoperative AF, and results from many trials suggest a benefit of continuing preoperative beta-blocking agents to prevent postoperative AF [14, 15]. Our policy is to continue beta-blocker therapy postoperatively. This policy was the same in all 3 groups.

Advances in continuous monitoring technology have led to more frequent diagnosis of AF, which remains the most common cause of morbidity after CABG [16]. Our results confirm the high incidence of AF in patients who had CABG. There was no reduction in the frequency of AF when minimally invasive cardiac operations without ECC were done. However, the incidence of AF after TMLR was significantly less compared with the groups that had coronary artery bypass operations. The limitations of this study were the small number of patients in the MICABG and TMLR groups and the fact that in this retrospective study the groups were not matched according to known predictors of postoperative AF. Even when those factors are considered, the incidence of AF in the non-ECC group is surprisingly high. The present study found that postoperative AF in cardiac operations may be caused by factors other than ECC. Future studies should focus more on factors not directly related to the procedure of cannulation and ECC.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

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