Left Atrial Reduction. A New Concept in Surgery for Chronic Atrial Fibrillation

INTRODUCTION

Chronic atrial fibrillation (AF) is frequently associated with mitral valve disease, especially when the left atrium (LA) is enlarged. Mitral surgery per se does not suffice to eliminate AF in the majority of cases. Although various techniques have been described for the elimination of chronic AF,^1-6 most of them are laborious and require prolonged surgery. Sankar et al⁷ have described left atrial reduction as a surgical treatment for chronic AF. This technique consists of isolation of the pulmonary veins (PV) and the excision of a circumferential band of tissue of the LA, including the base of the left appendage (LAp). The result obtained is the isolation of probable macroreentrant circuits of AF in the LA, as well as an important reduction in atrial size. Nevertheless, it should be noted that the fundamental part of this surgical technique is the isolation of the PV. We have used this technique in 23 cases with excellent results, achieving a complete remission of chronic AF in all the patients.

PATIENTS AND METHOD

Between August 1998 and June 2001, 23 patients, 18 women and 5 men, underwent surgery. The mean age of patients was 44.9±15.2 years (standard deviation) at the time of surgery. A total of 18 patients (78%) had double mitral lesion and 5 (22%) had mitral insufficiency. The etiology was rheumatic in 18 cases (78%), degenerative in 4 patients (17%), and congenital in one (5%). A total of 18 patients (78%) were functional class II of the New York Heart Association (NYHA) and 5 (22%) were functional class III. All the patients had an AF of more than 3 months of evolution. The duration of AF was 3.9±2.9 years (range, 1-14 years). The echocardiographic data obtained in each patient were the superoinferior and cross-sectional diameters in the 4-chamber apical axis view, and the anteroposterior diameter in the parasternal axis view. The echocardiographic studies were made in each patient preoperatively, transoperatively, and at 1 month and 6 months after surgery. The LA transport function was studied by transmitral flow echo-Doppler in which the reappearance of the «a» wave of atrial contraction was measured. In all the patients, the atrial «a» wave was absent in the Doppler transmitral flow study in before surgery. All the patients were taking one or more antiarrhythmic drugs (1.7±0.9; range, 1-4). Pharmacological antiarrhythmia treatment was maintained until the third postoperative month. All patients received anticoagulant treatment before surgery. Oral anticoagulant treatment was used for 6 weeks after surgery; then it was discontinued in the patients who had undergone mitral plasty or implantation of a biological mitral prosthesis and exhibited sinus rhythm and an «a» wave in the echo-Doppler study of transmitral flow. Mitral valve surgery and left atrial reduction were performed in all patients.

Statistical analysis

Values are expressed as percentages and the mean and standard deviation. Pre and postoperative LA values were compared with the Student t test for quantitative variables. A difference was considered statistically significant if P<.01.

Surgical technique

Surgery was performed using medial sternotomy. The ascending aorta and vena cava were cannulated as usual. An angled cannula was placed in the superior vena cava (SVC), near its union with the vena anonymae and the right brachycephalic venous trunk, and cardiopulmonary bypass was begun. Once the aortic root was clamped, continuous retrograde cardioplegia was maintained with warm, high-potassium solution infused through the coronary sinus. The SVC was completely sectioned about 3 cm above its opening on the right atrium to expose the roof of the LA. Two incisions were made in the LA. The first was made conventionally, parallel to the interatrial sulcus, and extended around the PV. The LA was sectioned completely (Figure 1). The second incision was made 1 to 3 cm inward, toward the mitral valve, and surrounded the LA (Figure 2). A circumferential band of LA tissue with the base of the LAp was obtained. Mitral valvuloplasty was performed in 11 cases (47.8%) and mitral valve replacement in 12 (52.2%). An anastomosis was made between the LA and SVC with continuous sutures of polypropylene 3-0 and 5-0, respectively (Figure 3). The cardiopulmonary bypass and aortic clamping times were 156.6±24.4 min and 98.6±13.2 min, respectively.

Fig. 1. This schematic illustration shows the first incision in the LA, which totally surrounds the cap of the PV.

Fig. 2. In this figure the arrow indicates the line of dashes that represents the second incision in the LA.

Fig. 3. Once both surgical incisions are made, a circumferential band of left atrial tissue is obtained with the LAp included (which is indicated by the arrow). The final step in this surgical technique is reanastomosis of the LA.

RESULTS

There was no operative mortality. Three patients (3/23; 13%) presented a recurrence of AF in the first hours after surgery, which was converted with medicational therapy between the sixth and eighth postoperative days. No patient was reintervened for bleeding. No problems in atrioventricular conduction were observed in any case. All patients were extubated in the first 12 h after surgery. The stay in the postoperative intensive care unit was 1.7±0.5 days, and the postoperative intrahospital stay was 6.8±0.8 days. An intraoperative echocardiographic study was made one and six months after surgery to evaluate the size of the LA, as well as the recovery of the atrial «a» wave. An important reduction was observed in the superoinferior diameter of the LA by echocardiography after surgery (4.8±0.77 versus 8.1±1.47 cm; P<.01). Also the reappearance of the atrial «a» wave was demonstrated in the echo-Doppler transmitral flow study in 20 of the 23 patients operated (87%) (Table 1). In a follow-up of 3 to 36 months (13.9±11 months) after surgery, 22 patients (96%) were functional class I of the NYHA, and one (4%) was class II; in addition, all the patients maintained sinus rhythm. In all the patients antiarrhythmic treatment was eliminated after the third postoperative month. In the 23 patients who underwent surgery, oral anticoagulant treatment was discontinued suppressed in all cases in which mitral valvuloplasty was performed or a biological mitral prosthesis was implanted (14/23; 61%).

DISCUSSION

Chronic AF usually accompanies mitral valve disease at the time of surgery, especially when the LA is enlarged, which is the main determinant factor in the appearance and maintenance of chronic AF.^8,9 LA size in excess of 45 mm is one of the independent predictive factors for the appearance and recurrence of AF. AF is rare in LA with a diameter of less than 40 mm.¹⁰ The ability of LA to fibrillate is determined by the relation between the effective refractory period of the atrial myocardium and the atrial area available for the development of a macroreentrant circuit.¹¹ That is to say that a critical mass or critical area of atrial muscle is needed for the appearance of AF. It thus seems logical that a strategic part of surgery to eliminate AF must include the reduction in size of the LA.¹²

Several procedures have been described to eliminate chronic AF, from those designed to control ventricular response with digitalis,¹³ ablation of the His bundle followed by implantation of a ventricular pacemaker surgically¹⁴ or by transvenous catheter,¹⁵ LA isolation,⁵ the surgical corridoring procedure,⁴ and the Cox maze procedure with its modifications.^1,2,6,16-18

The procedure described by Cox¹ has achieved successful results. Although a success rate of 98% has been reported with this procedure, it involves many surgical incisions in both atria, particularly in the posterior plane of the LA, and is technically demanding and has a high risk of lethal bleeding complications. At the same time, this technique involves the use of the cryoablation of two points of the coronary sinus, which restricts its use to hospital centers equipped with this technology. Hioki et al⁶ have modified the Cox maze procedure in an attempt to simplify it with an incision between the right and left PV, instead of around them. Nevertheless, the percentage of recurrences of AF could be very high because complete isolation of the PV from the rest of the LA is not achieved, thus allowing the development of macroreentrant circuits from the PV. The deliberate use of cryolesion to eliminate surgical incisions¹⁶ has not been shown to be sufficiently effective, since 51.8% of patients required antiarrhythmic drugs for recurrent AF after surgery. The corridoring procedure¹⁹ has the drawback of only controlling the frequency of the atrioventricular electrical impulse, but the rest of the atrial tissue continues to fibrillate, thus losing the atrial transport function. In addition, the risk of thromboembolism is not eliminated and the use of permanent oral anticoagulation is required.⁴ Sankar et al⁷ have performed 6 left atrial reduction procedures to eliminate chronic AF concomitant with mitral valve surgery, with a success rate of 100%.

We have taken the model from Sankar et al⁷ for the elimination of the associated chronic AF to mitral valve disease in 23 patients, with a success rate of 100%. We have found this technique to be extremely satisfactory because it manages several circumstances simultaneously: a) reduction of LA size as a crucial part of the procedure, eliminating mass that is critical for AF; b) the isolation of the PV along with amputation of the LAp, thus eliminating 3 of the 6 main macroreentrant circuits for the origin of AF (two in the PV and one in the base of the LAp; c) amputation of LAp suppresses the most important source of LA embolisms, since it has been demonstrated that 57% of rheumatic patients with AF have thrombi in the LAp that extend to the LA, and 9% of the cases of non-rheumatic AF present an isolated thrombus or a thrombus originating in the LAp.²⁰ In addition, since the LAp has a narrow base, defined and with a hollow body located peripherally to the main blood flow in the LA, it is logical to think that the excision of this appendage reduces the subsequent threat intracavitary thrombus formation in the LA; nonetheless, if the fact that in patients treated with warfarin approximately 50% of embolic events occur in individuals that had an inadvertent therapeutic lapse or required the partial or permanent discontinuation of therapy with oral anticoagulants is considered, and that most of these thrombi originated in the LAp,²¹ it is imperative to amputate this anatomical structure during this type of procedures, and d) the excellent exposure of the mitral valve, which is essential when one of the goals is to reconstruction the valve, associated with the cure of AF.

Isolation of the PV is a fundamental part of surgery for the elimination of AF. Hasegüerre et al have demonstrated that the most frequent origin of ectopic electrical impulses that originate macroreentrant circuits of AF are the PV in up to 96% of cases,^22-25 above all in superior PV.²³ In fact, there is a direct relation between enlargement of the superior PV and the appearance of AF, as well as with muscular rings derived from the LA myocardium that penetrates to a variable degree the ostium and the most proximal portion of the superior PV. Structural changes in these portions of the atrial myocardium that invade the PV, perhaps due to its distention, can originate the chaotic rhythm that triggers AF.²⁶ This can also be due to the fact that the duration of the refractory period inside these PV is very short and can as high-frequency sites of activation due to reentrant activation with small waves.²⁷ This has motivated ablation strategies by applying radiofrequency directly to the ectopic foci in the PV, with a success rate of up to 69% in a follow-up of 8±4 months.^26,28 Nevertheless, these techniques have the drawback of high rates of recurrence of AF due to the subsequent appearance of new arrhythmogenic foci in the same PV. Therapy must include linear incisions by application of radiofrequency or surgery to reduce atrial tissue and prevent the reentrant waves in the required number.^29,30

Another important aspect is the depth and uniformity of tissue ablation by radiofrequency , since small residual isthmuses of atrial tissue could remain uninjured by the radiofrequency, allowing the conduction of chaotic electrical impulses from the PV to inside the LA, with the reappearance of AF. This has been observed in tissue isthmuses of 0.8 mm or more.³¹ The discontinuity in the ablation lines used in radiofrequency can be a proarrhythmic factor. It is obvious that isolation of the PV by complete continuous surgical incisions offers the maximum guarantees for completely isolating the PV.

We have used the last premise to surgically isolate the chamber containing the 4 PV, with only 3 cases (13%) of recurrence of AF that responded to pharmacological therapy in the first 8 postoperative days. The rest of the patients recovered normal sinus rhythm from the moment in which the aorta was unclamped. Currently, All of the 23 patients have sinus rhythm without antiarrhythmic medications.

The echocardiographic study made in this series of patients demonstrated an important reduction in LA size in the superoinferior diameter of the LA, since this diameter is more directly affected by this type of surgical technique, in comparison with the anteroposterior and transversal diameters. In addition, the reappearance of the atrial «a» wave was observed in most of the cases (20/23), indicating the restoration of LA transport function.

Likewise, we found that this technique can be easily applied when the superoinferior diameter of the LA (by echocardiography) is more than 7 cm, given the distance between the plane of the PV and the coronary sinus, which is the guideline to follow to obtain the size of the LA reduction.¹²

CONCLUSIONS

The technique of left atrial reduction proposed here is a safe surgical technique that is easily performed, can be implemented in every patient meeting the following conditions: a) to have undergone mitral valve surgery; b) have a LA superoinferior diameter of more than 7 cm (by echocardiography), and c) AF for more than 3 months before surgery.^32,33

Moreover, if the associated mitral procedure of choice is valvuloplasty or the implantation of a mitral biological prosthesis, it will be possible to achieve the endpoint: to maintain the patient free of anticoagulant use.^34,35

ACKNOWLEDGEMENTS

We thank Mrs. María del Carmen Colomer for her expert help in writing this document.

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Correspondence: Dr. O.A. García-Villarreal.
Vista Florida 460, Col. Linda Vista, 67130; Guadalupe,
Nuevo León, México.
E-mail: [e-mail]