Nursing Center - Journal Issue

Keywords: atrial fibrillation, maze, minimaze, pulmonary vein isolation

Abstract

The Cox Maze procedure, a cardiac intervention that was developed by James Cox, MD, was first performed in 1988 to surgically cure atrial fibrillation. Over the years, changes in techniques of the classic maze were made, culminating in the Cox Maze III procedure, the Gold Standard. Modifications in the original procedure included simplifying the procedure to a minimally invasive approach. As a result of some of these modifications, the initial maze-like series of surgical atrial incisions has been reduced with the use of alternate energy sources that create hyperthermic lesion lines of conduction block that isolate and interrupt the abnormal impulses. The minimaze, a minimally invasive thorascopic approach, can be performed off pump, thus avoiding a median sternotomy and cardiopulmonary bypass and cardioplegic arrest intraoperatively and ensuring a shorter, less painful recovery.

A TRIAL FIBRILLATION, the most common cardiac arrhythmia, affects more than 2.2 million Americans, with more than 350,000 new cases diagnosed each year.1 Literature review discloses that atrial fibrillation causes a significant increase in mortality due to thromboembolic events, tachycardia-induced cardiomyopathy, and hemodynamic compromise.1 Thus, several factors prevent the establishment of global recommendations for standardizing treatment in all patients experiencing atrial fibrillation.2 These factors include the pathogenesis of atrial fibrillation, patient symptoms, and variability in patient profiles.2,3 Presently, multiple therapeutic and surgical interventions based on the patient's symptoms are available for the treatment of atrial fibrillation. Treatment options include the use of pharmacological agents, known as traditional medical management, or surgical interventions, such as surgical ablation, Cox Maze, modified maze, or minimaze, known as advanced therapy or curative procedures.

Patients may undergo a surgical procedure for atrial fibrillation when a pharmacological intolerance exists; traditional medical management proves ineffective or does not correct atrial fibrillation; an intolerance to anticoagulants exists; atrial fibrillation exists in spite of medical management; embolic events occur; and patients undergo surgery for a coexisting heart condition.2,3

ATRIAL FIBRILLATION

Atrial fibrillation increases dramatically the risk and severity of stroke and is associated with increased morbidity and mortality. Benussi 4 reports that the prevalence of atrial fibrillation is 0.4% in the general population and about 5% in people older than 60. As stated by Bennusi,4 lone atrial fibrillation (LAF) accounts for about 30% of the cases. Bloom5 noted that the prevalence of atrial fibrillation is as high as 9% in patients 80 years or older. The projected incidence of atrial fibrillation by 2050 is expected to be more than 5.6 million patients (Fig 1).

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Figure 1. Heart in atrial fibrillation.

Common diseases that contribute to the etiology of atrial fibrillation include, but are not limited to, hypertension, coronary artery disease, valvular disease, chronic lung disease, heart failure, cardiomyopathy, congenital heart disease, pulmonary embolism, hyperthyroidism, pericarditis, and viral infection. Atrial fibrillation may also be related to alcohol consumption, excessive caffeine intake, stress, and electrolytic or metabolic imbalance. In 10% of the cases, there is no underlying heart disease.2-4

The 3 detrimental sequelae associated with atrial fibrillation are loss of atrial transport function, irregular rhythm, and risk of embolic events.3 Gage and associates6 state that the major morbidity of atrial fibrillation is attributable to left atrial thrombus formation and subsequent thromboembolic events, especially embolic stroke.

TREATMENT OPTIONS FOR ATRIAL FIBRILLATION

The optimal treatment for atrial fibrillation depends upon the proper understanding of the electrophysiological basis of its clinical manifestations as noted by Cox.7 The choice of intervention, pharmacological or nonpharmacological, is determined by whether atrial fibrillation is continuous or intermittent, depending on variable underlying electrophysiology.7

The treatment goals for atrial fibrillation are conversion to sinus rhythm, controlling the heart rate, reducing the risk of stroke, and reducing or preventing embolic events. This can be accomplished by pharmacologic intervention, rhythm or rhythm-control drugs, rate-control medications, or a combination of warfarin with either a rate-control medication or a rhythm-control medication. Rhythm-control drugs restore the sinus rhythm, eliminating the risk of atrial fibrillation, and include drugs such as procainamide, sotalol, or amiodarone. Rate-control medications include digoxin, beta blockers, and calcium channel blockers. These drugs are administered to control the ventricular rate, minimize symptoms, and reduce the likelihood of complications. Another option recommended is either electrical or chemical cardioversion. A patient undergoing an electrical cardioversion experiences an electrical shock synchronized with the intrinsic activity of the heart, whereas in a chemical cardioversion, medications are administered either intravenously or orally in an attempt to convert the heart rhythm to sinus rhythm.

Device therapy is another intervention used for treating atrial fibrillation. Patients may have an implantable atrial defibrillator inserted to treat the symptoms. The defibrillator can be preprogrammed to identify an episode of atrial fibrillation. It may also be manually controlled by the patient to turn the device on when symptoms occur to treat atrial fibrillation. A permanent pacemaker may be implanted to mange the arrhythmia and improve the heart function.

Another treatment option for atrial fibrillation is catheter ablation. Catheter ablation began as an experimental attempt to recreate the Cox Maze III procedure. The goal of ablation therapy in atrial fibrillation is either to improve symptoms or to decrease atrial thrombus formation and subsequent embolic events (Fig 2).

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Figure 2. Catheter ablation procedure.

However, since 1994, the catheter ablation procedure has undergone procedural changes and techniques because of recent advances in understanding of the pathophysiology of atrial fibrillation and the contributions of the pulmonary veins to the initiation and maintenance of atrial fibrillation.8 As a result, 3 pulmonary vein ablation techniques-termed segmental pulmonary vein isolation, circumferential pulmonary vein ablation, and circumferential pulmonary vein isolation9-are utilized for catheter ablation of atrial fibrillation. Interventional procedures are required for patients with atrial fibrillation and for patients with a rapid ventricular response that cannot be controlled with drugs. Radiofrequency catheter ablation of the atrioventricular junction with pacemaker implantation is an effective therapeutic approach that relieves cardiac symptoms associated with a rapid and irregular rhythm. This approach can also improve left ventricular function in patients with tachycardia-induced cardiomyopathy.10 Jordaens11 states that the constraints of the atrioventricular junctional ablation with pacemaker implantation include the inevitable need for anticoagulation therapy, loss of atrioventricular synchrony, and lifelong pacemaker dependency. Possible complications of catheter ablation for atrial fibrillation include systemic thromboembolism, pulmonary vein stenosis, pericardial effusion, cardiac tamponade, and phrenic nerve paralysis.11

Surgical treatment for atrial fibrillation includes the Cox Maze, the modified maze, and "keyhole" and minimally invasive approaches. Surgical treatment is considered when traditional medical management proves ineffective, medication or anticoagulation tolerance exists, embolic events occur, or coexisting heart conditions exist.

Patients undergoing the Cox Maze procedure, also known as the "cut and sew" maze, experience a traditional surgical incision, where the sternum is opened, and are placed on the cardiopulmonary bypass machine. During the procedure, a series of precise incisions are made in the right and left atria to create lines of conduction block to stop electrical impulses from forming. In more than 90% of the patients, the classic Cox Maze cures atrial fibrillation 7; however, the procedure takes 1 hour to complete. Since 1996, technological and procedural modifications of the Cox Maze procedure resulted in other surgical approaches for the treatment of atrial fibrillation. These approaches reduce the number of incisions that comprise the Cox Maze procedure and create a more limited lesion set around the pulmonary vein orifices with various alternate energy sources that prevent the need to cut and sew the atrial wall. For patients who have atrial fibrillation and are undergoing open heart surgery for valvular or bypass grafting surgery, many surgeons prefer to use a modified maze (Fig 3).

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Figure 3. (a) Medial sternotomy for open heart. (b) Modified maze procedure. (c) One type of isolator used in modified maze.

The modified maze is also called surgical pulmonary vein isolation. Under direct observation, an alternate energy probe of choice, such as cryoablation, laser, microwave, or radiofrequency, is used to create the lesion lines of conduction block and promote the normal conduction of impulses through the proper pathway. During this procedure, the left atrial appendage is excised and the tissue is closed with a stapler. The average surgical time is 15 to 20 minutes and it restores normal sinus rhythm in 75% to 85% of patients.12-15

Thermal techniques, such as ultrasound, laser, microwave, and radiofrequency, for atrial ablation have been dominant in the resurgence of surgical procedures for the treatment of atrial fibrillation. These alternate energy sources create lines of conduction block without the standard cut-and-sew techniques. Given this surgical technique, the procedure can be performed more rapidly and by an increasing number of surgeons.

As a result of positive outcomes from the Cox Maze procedure, surgical ablation plays a significant role in curing atrial fibrillation in patients undergoing concomitant cardiac surgical procedures. This has been attributed to the simplification of the surgical intervention, which has resulted in a reduction of operating time and complications. Gait and associates 14 state that although various techniques have been proposed, it is noteworthy that the posterior part of the atrium and the osteo of the pulmonary veins are involved in all approaches despite variations in energy sources (ie, radiofrequency or cryoenergy) and intended lesion designs.

However, this procedure is not without complications such as atrioesophagus fistula and coronary damage.14 It is recommended that surgical ablation be more routinely performed in patients with permanent or intermittent atrial fibrillation undergoing cardiac surgery. However, procedural and technological modifications have enabled minimally invasive surgical ablation in patients with LAF.

SURGICAL PROCEDURE: DIFFERENCE BETWEEN MAZE AND MINIMAZE

The original Cox Maze procedure underwent significant modifications that included a more extensive use of cryosurgery and avoidance of excision of the left atrial appendage.13 As described by Ad and Cox,12 the original Cox Maze III procedure included a 30- to 40-cm median sternotomy and approximately 12 incisions in the two atria, including excision of the left and right atria appendages and the pulmonary veins surgically isolated. The surgical procedure is based on the principle of the development of a maze. Appropriately placed atrial incisions interrupt the conduction routes of the most common reentrant circuits and direct the electrical impulses to the atrioventricular node.7 Modifications to the original Cox Maze III procedure resulted in a new minimally invasive, cryosurgical approach with a smaller chest wall incision, a 7-cm right minithoracotomy, lesser and smaller atriotomies, left atrial appendage not excised, and the remainder of the procedure performed with specifically designed cryoprobes.7,12,13

The development of minimally invasive surgery has led to epicardial ablation of atrial fibrillation and even removal of the left atrial appendage without entering the heart.8,16 In this thorascopic approach, the surgeon views the epicardial surface of the heart using an endoscope. Specialized instruments are used to isolate the pulmonary veins and create lines of conduction block. The benefit of this procedure is that the patient is not placed on cardiopulmonary bypass12,13 (Fig 4).

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Figure 4. Thorascopic approach for minimally invasive minimaze.

Ronald K. Wolf, a cardiothoracic surgeon, developed the minimaze, a minimally invasive surgical procedure for the treatment of atrial fibrillation.17 The minimaze is a video-assisted bilateral pulmonary vein isolation and left atrial appendage exclusion for atrial fibrillation. The minimaze procedure combines an ablation method and the Cox Maze procedure without performing open heart surgery. Three small incisions are made on each side of the chest wall. Wolf uses an Isolator clamp, a bipolar radiofrequency clamp, to ablate and electrically isolate the pulmonary veins bilaterally, where the triggers that initiate atrial fibrillation are located. With the Isolator clamp, the average time an ablation can be performed is 8 seconds. The ablation part of the procedure is the endoscopic exclusion of the left atrial appendage. The left atrial appendage is a suspected major source of cardioembolic stroke in patients with atrial fibrillation (Figs 5 and 6).

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Figure 5. An example of a radiofrequency clamp used in minimaze.

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Figure 6. Minimally invasive minimaze bilateral scars.

This procedure and technology are designed to treat patients who have long-standing or chronic intermittent atrial fibrillation and are nonresponsive or experience intolerance to pharmacologic treatment. The Wolf minimaze is specifically focused on treating atrial fibrillation as a stand-alone condition, that is, LAF/atrial flutter with no other heart problems. Some advantages of the minimaze are avoidance of a sternotomy, cardiopulmonary bypass, and cardioplegic arrest intraoperatively, a shorter and less painful recovery, and decrease in medication reactions.12,18

PATIENT SELECTION FOR SURGICAL TREATMENT

Fuster and associates 2 state that the initial clinical evaluation of a patient with suspected or proved atrial fibrillation includes characterizing the pattern of the arrhythmia as paroxysmal or persistent, determining the etiology, and defining the associated cardiac and extracardiac factors. This is accomplished by a thorough history and physical examination, review of current problems, pulmonary function, electrocardiogram, echocardiogram, Holter Monitor Test, chest x-ray, and other diagnostic testing as required.

As noted by Nitta,15 indications for surgery include patients with atrial fibrillation associated with structural heart disease who undergo cardiac surgical procedures; high-risk patients susceptible to systemic thromboembolic complications related to left atrial thrombi; patients with failure or recurrence following one or more catheter ablation procedures; and patients with intolerable symptoms or an impaired quality of life due to atrial fibrillation.

Candidates considered for the Cox Maze are patients with isolated atrial fibrillation especially after failed percutaneous ablation, continual atrial fibrillation and/or enlarged atria, and/or coexisting valvular or coronary artery disease. For the minimally invasive surgical ablation, that is, "keyhole" and thorascopic approach or the Cox Maze procedure, patients need to have a history of either isolated or intermittent atrial fibrillation. In both the "keyhole" and thorascopic approaches, the surgical technique includes isolation of the pulmonary veins and left atrial excision.13

For patients undergoing a Wolf minimaze procedure, patient selection criteria can include the following: man or woman aged between 18 and 80; have a drug refractory atrial fibrillation; experience an intolerance of antiarrhythmic drugs or Coumadin; have left ventricular ejection fraction of 30% to 35%, which is determined by echocardiography performed within 60 days; a transesophageal electrocardiogram confirms lack of thrombus in the left atrial appendage; a left atrial size less than or equal to 6 cm; life expectancy of at least 2 years; compliance with returning for follow-up visits; tolerance to single lung ventilation; and body mass index less than or equal to 28 to 32.

POSTOPERATIVE AND FOLLOW-UP CARE

Postprocedure for the Cox Maze, modified minimaze, and/or minimaze, the patient is transferred to the critical care unit for close cardiac monitoring for 24 to 48 hours. Upon admission to the unit, the patient's endotracheal tube is connected to the ventilator, but usually the patient is able to be extubated 5 to 6 hours postoperatively. Depending upon the surgeon's postoperative orders, the patient may be required to lie in supine position for 4 to 6 hours.

Chest tubes, which are inserted in stab wounds distant from the primary surgical incision to reduce the risk of infection, are monitored by the nurse. Thoracic cavity management consists of assessing and evaluating the chest drainage system for the type and amount of drainage from the chest tubes. The nurse performs respiratory assessments and observes for complications such as tension pneumothorax, redness around the insertion site, or hemorrhagic shock.

In providing wound management, initially, a surgically sutured wound is not disturbed unless there is drainage present. However, the nurse must assess the appearance of the incision and observe for inflammation, drainage, and/or swelling and notify the surgeon if any of these signs are present. When the primary dressing is removed, the wound is kept cleaned and assessed each shift for any complications.

While in the unit, the patient is monitored for excessive pain, fluid retention, hemodynamic changes, blood loss, arrhythmias, signs of pericarditis, infection, elevated temperature, and changes in neurological status. Any changes in the clinical parameters are reported to the cardiac surgeon immediately. When hemodynamically stable, the patient is transferred to a telemetry unit for further observation.

Typical medications include antiarrhythmic drugs, anticoagulant therapy, diuretics, steroids, and pain medication. Postoperatively, the patient may experience short episodes of atrial fibrillation or skipped heartbeats. This is common due to the inflammation of the atrial tissue and is treated with antiarrhythmic medication. In some cases, the treating surgeon and/or cardiologist may recommend cardioversion to control the persistent atrial fibrillation if the patient does not respond to pharmacological intervention, prior to discharge. However, after the incisions on the heart have healed, the atrial fibrillation should subside. Approximately 6% of patients may require a pacemaker because of an underlying rhythm such as sinus sick syndrome or heart block.13

Depending upon the surgeon's preferences and the patient's response to therapy, the patient may be discharged within 2 to 3 days postprocedure for the minimaze and 5 to 7 days depending on the surgical approach, such as a Cox Maze with open heart surgery, and the patient's response to treatment.

Major complications for LAF operations or as a concomitant procedure include renal failure, reoperation for bleeding, mediastinitis, stroke, and balloon pump insertion. The Cox Maze III has equivalent operative risks and long-term efficacy for patients undergoing both LAF operations and concomitant procedures.19 However, the Cox Maze procedure remains the standard against which alternative procedures for atrial fibrillation must be judged.13 Postoperatively, an early complication of the Cox Maze is fluid retention, which is treated by fluid management and diuretics. Other complications are bleeding, wound infection, stoke, and pneumonia.

Throughout the hospitalization, the patient is initially followed by the cardiac surgeon. Upon discharge, patient instructions include, but are not limited to, notifying the referring physician or cardiologist immediately if symptomatic from atrial fibrillation; a temperature of more than 100 degrees Fahrenheit; and redness, swelling, or drainage at the incision site.

Posthospitalization, the patient is followed up by the cardiac surgeon and the patient's referring physician or cardiologist. The patient is seen by the cardiac surgeon in 1 to 3 weeks, postdischarge, to inspect the incision sites. The referring physician or cardiologist follows the patient to monitor his/her heart rhythm. By 3 months, the patient is weaned off antiarrhythmic and anticoagulant medications depending on the efficacy of treatment. It is recommended that an electrocardiogram be performed at 3, 6, and 12 months after surgery and then annually. At 3- and 12-month periods, posthospitalization, Szaley and colleagues 20 state that additional diagnostic studies and evaluations may be requested, such as a stress electrocardiogram and a 24-hour electrocardiogram to detect bradycardic episodes and to assess the effect of exercise on the patient's heart rate and a electrophysiological evaluation to measure sinus node recovery and to provoke atrial fibrillation or atrial flutter. As noted by Szaley and associates,20 echocardiography and magnetic resonance imaging may be ordered to classify atrial transport function and determine whether anticoagulation could be discontinued.

Successful results of the maze procedure are long-term cure from atrial fibrillation; decreased symptoms such as fatigue and dyspnea; decreased incidence of embolic events; decreased atrial size in patients with an enlarged atria preoperatively, particularly those who undergo the maze with a mitral valve replacement; improved cardiac ejection fraction; and the discontinuation of Coumadin. In reviewing the long-term effectiveness of the Cox Maze III procedure for lone versus concomitant procedures for atrial fibrillation, a study performed by Prasad and associates 1 noted the following: only 4 (4.1%) of 98 patients in the lone group were in atrial fibrillation at follow-up and 2 (2.5%) of 79 patients were in atrial fibrillation in the concomitant group. Szaley and colleagues20 stated that the following preoperative predicators for failure of a concomitant minimaze operation for symptomatic chronic atrial fibrillation were longer duration of preoperative atrial fibrillation; increased left atrial diameter; increased right atrial diameter; reduced left ventricular function; increased left ventricular end-diastolic diameter; and the presence of preoperative mitral valve stenosis.

CONCLUSION

There are many treatment options for atrial fibrillation, but when traditional medical management fails, surgical interventions, such as the Cox Maze and Wolf minimaze, provide alternatives for these patients that previously did not exist.12 The underlying etiology that promotes and sustains atrial fibrillation is an important factor in selection of the appropriate arrhythmic intervention. The understanding of the pathophysiology of atrial fibrillation has led to continual improvements in the treatment of this arrhythmia.7 Given the technological improvements and procedural modifications to the original Cox Maze procedure, patients are experiencing faster, simpler, and minimally invasive approaches.18,19 As these procedural and technological changes continue to be developed, these new approaches will be assessed and evaluated on their ability to continue to reduce morbidity and mortality and effectively treat atrial fibrillation.