Surgical treatment of atrial fibrillation : Clinical, hormonal and electrophysiological aspects of the Maze operation

Abstract: Background: Atrial fibrillation (AF) is the most common arrhythmia, associated with significant mortality and morbidity, due to hemodynamic impairment and the increased risk of stroke. Traditional pharmacological treatment may be insufficient or cause intolerable side-effects. The Maze operation is an open-heart procedure, developed to cure AF by restoring permanent sinus rhythm, atrio-ventricular synchrony and atrial contraction. Associated concerns have been efficacy in combined cases, excessive postoperative fluid retention and damage to the cardiac conduction system. The aims of this thesis were to: 1) Evaluate the reproducibility, safety and local clinical results of the Maze operation for treatment of symptomatic and medically refractory AF during a 4-year period. 2) Evaluate the benefits and risks of the combined operation of mitral valve (MV) surgery and the Maze operation, in comparison with mitral valve surgery alone. 3) Examine perioperative plasma levels of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), antidiuretic hormone (ADH), aldosterone and angiotensin II, in patients undergoing the isolated Maze operation, and to assess hormonal changes in relation to postoperative fluid retention. 4) Examine the plasma levels of ANP, BNP, ADH, aldosterone and angiotensin 11 preoperatively and long-term postoperatively in patients undergoing the isolated Maze operation. 5) Evaluate by standardized electrophysiological methods (EPS), the pre- and postoperative function of the sinus node and other parts of the cardiac conduction system, in patients undergoing the Maze operation. Patients, methods and results: 1) Twenty-six patients with medically refractory AF, mean age off 55 (33-75) years, underwent the isolated Maze operation (65%) or combined procedures (35%). Follow-up was 3-55 (median 18) months. No mortality or neurological complications occurred. Twenty-four patients (92%) were free of AF and in sinus or atrially paced rhythm, of whom 23 were in NYHA class I or If. No further antiarrhythmic or anticoagulant therapy was needed in 90% of the patients after surgery. 2) Forty-seven patients with MV disease and long-standing AF, underwent combined Maze and MV repair or bioprosthetic valve replacement. They were matched with 47 patients undergoing MV surgery alone, for age, gender, NYHA class, left ventricular function and type of MV surgery. There were no differences in perioperative morbidity and mortality, despite increased procedure complexity in the Maze group. Although no difference in survival, follow-up showed increased return of sinus rhythm (75 vs 36%, p=0.0004), lower incidence of thromboembolic events (p=0.03) and reduced needs for antiarrhythmic and anticoagulant medication (p=0.005) in the Maze group. 3) Sixteen Maze patients were assessed perioperatively for levels of neurohormones in relation to hemodynamic variables. Ten patients undergoing coronary bypass surgery served as controls. The Maze group required more of diuretic therapy (p<0.05), and levels of ADH and aldosterone were significantly elevated (p<0.001) as compared to controls. ANP levels were similar and in parallell to atrial pressures in both patient groups. 4) Fifteen Maze patients were assessed before and 6 months after surgery for neurohormones in relation to hemodynamic variables. All patients were free of AF. Cardiac output was higher (p<0.001) and plasma levels of BNP, ANP and angiotensin If were reduced (p=0.03) after surgery, as possible hormonal indicators of improved ventricular function after restoring sinus rhythm. The ANP response to hemodynamic challenge by ventricular pacing was reduced postoperatively (p<0.001), possibly due to atrial scarring. 5) Thirty-seven Maze patients underwent EPS before, and 6 and 15 months after surgery. The Maze operation did not cause permanent dysfunction of the sinus node, the AV-node or of other parts of the conduction system. No postoperative pacemaker demands were caused by the surgical effects per se on sinus node function. Follow-up (mean 45, range 16-93 months) showed sinus or paced rhythm in 86%, and recurrence of AF necessitating alternative therapy in 14% of patients. Induction of sustained atrial arrhythmias during EPS after surgery was possible in 5 patients, of whom 4 eventually had permanent recurrences off AF. Conclusions: The Maze operation as surgical treatment for medically refractory AF, is reproducible and has very good clinical results with acceptable risks, performed either isolated or as a combined procedure. The operation may prevent thromboembolic events and reduce the need for AF-associated medication. Excessive postoperative fluid retention may be caused by elevations in water-retaining neurohormones. Reductions in natriuretic hormones after restoring sinus rhythm may indicate improved ventricular function. Based on EPS, the Maze operation does not permanently damage the cardiac conduction system. EPS-findings in Maze patients may prognosticate the need for postoperative pacemaker and convey further therapeutic guidance.