Abnormal bradycardia is a slow cardiac rate that results chronically or episodically in inadequate cardiac output or life-threatening ventricular arrhythmias.

During the early 1700s, peripheral pulsations of the circulation began to be timed, and in 1717, Gerbezius recognized bradycardia as a deviation from the usual pulse rate. Morgagni is believed to have surmised the relationship between bradycardia and syncope in 1761, but he attributed both to melancholy. In 1827, Adams accurately described what became known as Adams-Stokes syndrome and proposed that it had a cardiac origin. This idea was not well accepted until Stokes, in 1846, collected reports of seven patients with the condition and agreed with Adams’ concepts. The phrase maladie de Adams-Stokes was originated in 1899 by Huchard.

Understanding the morphologic basis of Adams-Stokes syndrome began after Harvey described the cardiac cycle. Purkinje first described cardiac conduction tissues in 1845, which he mistook as cartilage tissue. The atrioventricular (AV) conduction bundle was described by His in 1893, and in 1896, Aschoff and Tawara described the AV node and its connection to the His bundle. Then in 1907, Keith and Flack described the sinoatrial (SA) or sinus node. Its function was demonstrated in 1906 by Einthoven.

It has long been known that the heart responds to external electrical stimulation. As long ago as 1804, Aldini successfully stimulated systole in the hearts of decapitated criminals. Apparently, it was known during the late 1800s that direct heart puncture with or without injecting drugs would occasionally produce effective cardiac contractions. Mond reported that in 1929, Lidwill in Australia successfully paced the heart of a stillborn infant for a time by direct ventricular puncture. In 1932, Hyman atrially paced several patients with what he termed an artificial pacemaker , and Bigelow and colleagues in Toronto paced canine hearts by esophageal and precordial electrodes in 1950. ^,

In 1952 in Boston, Zoll reported successfully pacing of hearts in patients with complete heart block with external cutaneous electrodes and a large and relatively nonmobile pulse generator. This method was the only one available when intracardiac surgery came into existence during the mid-1950s, and although stimulation of each heartbeat was accompanied by skeletal muscle contractions and excoriation of the skin under the electrodes, this method kept some cardiac surgical patients alive until sinus rhythm returned. However, for patients whose sinus rhythm did not return, the agony of skeletal muscle contractions and skin excoriations increased as the days passed. Sheer terror developed with approach of the surgeon who would each day provoke an Adams-Stokes episode by turning off the pacer to see whether an adequate idioventricular rhythm, let alone sinus rhythm, would replace the electrocardiographic (ECG) image of P waves without any QRS complex.

Change began when Lillehei, in Minneapolis, enlisted the help of Earl Bakken, a television engineer and later founder of Medtronic Corporation, in developing a small portable pacemaker. More importantly, he devised the technique of leaving a wire attached to the ventricular epicardium at operation and bringing it out externally. The external electrode was used to pace the heart with minimal patient discomfort. Later, Thevenet, Hodges, and Lillehei devised a method of inserting the wire into the ventricle through a needle passed through the skin over the precordium without an operation. These systems used a portable pacemaker system devised by Bakken.

In 1959, Elmquist and Senning in Stockholm reported placing the first totally implantable pacemaker system using epicardial electrodes. This advance was made possible by invention of transistors during the 1950s. In 1960, Chardack, Gage, and Greatbatch described a self-contained, implantable pulse generator driven by a mercury cell battery for use with implanted epicardial leads.

During the previous year, Furman and Robinson had reported the use of endocardial electrodes introduced transvenously rather than epicardially. Their data supported the idea that endocardial and epicardial electrodes perform similarly. This led to widespread availability by 1961 of both endocardial electrodes inserted transvenously and epicardial electrodes inserted by thoracotomy. These early pacemakers paced at a set rate and did not sense spontaneous cardiac activity. They were crude by present standards but allowed 85% of patients having Adams-Stokes episodes to survive for at least 1 year, in contrast to less than 50% before their introduction.

Rapid developments followed, and pulse generators that sensed the QRS and fired only when no spontaneous QRS occurred within a specified time became available during the mid-1960s. Much work led by Greatbatch during the late 1960s and early 1970s to improve the cells (batteries) resulted in commercial availability of lithium cell–powered pulse generators during the early 1970s. The lithium cells were much more reliable, and, with hydrogen gas no longer being liberated in the pulse generator, hermetic sealing of the entire device became possible. More complicated electronic circuits were developed to permit programming of rate and stimulus duration as well as better QRS sensing as transistorized circuits with a few components evolved into hybrid circuits with more components, into integrated circuits, and finally into implantable pulse generators containing microprocessors.

Further improvements permitted atrial sensing and pacing as well as ventricular sensing and pacing (universal pacing) and ventricular pacing synchronized with the patient’s atrial contractions, as well as sequential AV pacing. Currently available pacemakers provide sensing of either body motion or increase in respirations and use the information to alter pacing rate appropriate for patient activity. Finally, the combination of multiprogrammability with diagnostic radio and telephonic transmission has permitted accurate evaluation of pacemaker function and noninvasive adjustment of pacemaker variables for optimal treatment of the patient.

Improvements in pacing electrodes have been made through the years in the form of better wire alloys, antifracture characteristics, electrode pacing threshold properties, and lead insulation. These improvements have diminished the occurrence of high pacing thresholds and lead fracture. In the past few years, a new generation of leadless pacing electrodes has evolved from bench experimentation into clinical use. The clinical studies and experience with leadless pacing technology demonstrated generally good safety and few complications. The now-extensive clinical follow-up confirms longer-term safety and efficacy that was demonstrated in initial clinical trials. The leadless pacemaker offers some advantages over the traditional pacing systems in terms of infections and the impact on the venous system, and it will probably result in fewer tricuspid valve-related complications. These new systems require constant surveillance to assess their long-term function and safety. The success of these single-chamber leadless pacemakers will lead to the development and implementation of multichambered pacing systems in the future.

Abnormal bradycardia may be the result of complete heart block, a condition in which P waves (atrial depolarization) occur at a constant interval but are unrelated to the less frequently occurring or absent and often broad QRS complexes (ventricular depolarization).

Bradycardia from both spontaneous heart block and spontaneous sinus node dysfunction tends to occur in elderly patients. The mean age of patients at the time of diagnosis of spontaneously occurring heart block is 70 years. ^,

Development of techniques and devices for cardiac pacing has involved surgeons, physicians, interventional cardiologists, and industry, and advances continue to be made. Methods of insertion and the devices implanted are constantly being improved. Whereas in the 1960s pacemakers were usually inserted by cardiothoracic surgeons, currently, in many parts of the world, they are inserted, managed, and followed by cardiologists, and often by cardiologists with specialized knowledge of cardiac electrophysiology. Because of these developments, it is no longer practical to include detailed descriptions in a textbook of cardiac surgery. Instead, only general information regarding cardiac pacemaking and basic device insertion procedures are discussed.

Usual care for cardiac surgical patients is given early postoperatively (see Chapter 4 ). In addition, a chest radiograph is obtained to ascertain position of the leads. Pacing threshold is usually not determined by noninvasive testing prior to hospital discharge because thresholds obtained at this time are always higher than those obtained 6 weeks to 3 months later. Reprogramming of the pulse generator at an appropriate voltage is best done later, leaving the relatively higher and safer pacing voltage until that time.

The electrodes are considered to have become stable by about 6 months after implantation. Around that time they are rechecked, and the pulse generator is set at the lowest output considered to be safe.

The most common indication for permanent cardiac pacing is symptomatic bradycardia. It may be intermittent or permanent due to complete heart block, second-degree AV block, or sinus node dysfunction. Symptoms must be directly attributable to the bradycardia and may include syncope, dizziness, exercise intolerance, and heart failure. When ambulatory ECG monitoring is negative for abnormal bradycardia, electrophysiologic study is indicated in patients with unexplained transient neurologic symptoms. The finding of prolongation of the HV interval (time from onset of activation of the bundle of His to the earliest onset of ventricular depolarization) of at least 70 milliseconds supports a diagnosis of paroxysmal AV block as the cause of the symptoms and justifies elective pacemaker implantation. In the absence of neurologic symptoms, however, the finding of such HV prolongation rarely, if ever, warrants prophylactic pacemaker implantation.

Another indication is surgically induced complete heart block because of the risk of an Adams-Stokes episode. Patients in sinus rhythm after repair of congenital malformations, but in whom complete heart block follows repair and persists for a number of days before reversion to sinus rhythm, are at increased risk for developing late symptomatic heart block. These patients should be considered for prophylactic pacemaker implantation before hospital discharge, particularly when subsidiary escape pacemakers have been absent or unreliable.

In some situations, permanent pacing may be indicated in asymptomatic patients because of risk of an Adams-Stokes episode. These situations include profound bradycardia (ventricular rate <40 beats · min ⁻¹ ) , second-degree AV block at the infra-His level, advanced second-degree AV or complete heart block after myocardial infarction, and congenital heart block with a wide QRS escape rhythm. Other rhythms may be an indication for pacing in asymptomatic patients. These include new bundle-branch block with transient second-degree AV block postmyocardial infarction, bifascicular bundle-branch block with intermittent type II second-degree AV block, sinus node dysfunction, and transient postsurgical AV block that reverts to bifascicular block in children. ^, In sinus node dysfunction, for example, when symptoms are relatively infrequent, the decision to advise permanent pacing may rest on the demonstration of asymptomatic sinus pauses, SA exit block, or both.

A special situation is extensive intraatrial operations such as the Senning or Mustard operation (see “ Senning Technique ” and “ Mustard Technique ” under Technique of Operation in Chapter 44 ) or the Fontan operation (see Chapter 52 ). Junctional rhythm often develops late postoperatively with the potential of tachybradycardia and sudden death. This situation is an indication for atrial pacing (AAI).

In response to publication of studies advancing the knowledge of the natural history of cardiac arrhythmia optimally treated by cardiac pacing and important advances in pacing device technology, the American College of Cardiology (ACC), the American Heart Association (AHA), the North American Society for Pacing and Electrophysiology (NASPE), and the Heart Rhythm Society (HRS) appointed a committee of physicians to develop guidelines for implanting cardiac pacemakers and arrhythmia devices. The most recent version of the guidelines appeared in 2008. This comprehensive document is the definitive statement on indications for cardiac pacing. A summary of these indications for commonly occurring conditions is shown in Boxes 15.1 through 15.3 . As new information accumulates, other indications for cardiac pacing are being identified ( Box 15.4 ). ^,

Abnormal tachycardia is a rapid heartbeat out of proportion to metabolic demands on the circulation.

Surgical procedures that successfully controlled many abnormal tachycardias resistant to drug treatment were developed during the 1970s and 1980s. Electrophysiologic studies accomplished by cardiac catheterization were necessary for precise diagnosis of many abnormal tachyarrhythmias, and cardiac electrophysiology rapidly became a field of special interest and competence among cardiologists. With the advent of interventional cardiology, methods for highly selective catheter ablation of areas identified by electrophysiologic studies have become successful and have replaced more invasive intraoperative mapping techniques of intraoperative ablation that were performed in the past utilizing basic surgical techniques and cryoablation.

AV nodal reentrant tachycardia is the most common cause of paroxysmal tachycardia. One of its characteristics is the electrophysiologic phenomenon of dual AV nodal pathways. The fast pathway (with a normal AV conduction rate) is believed to be located within or near the AV node, and the slow one adjacent to and usually inferior to the node, lying closer to the coronary sinus.

A successful surgical approach to this problem, using cryosurgical ablation, was developed and used by Sealy, Cox, Holman, and colleagues. Results of this type of surgical therapy have been good, with no deaths among 23 patients (CL 0%–8%) who underwent surgical correction without the production of heart block. Currently, however, catheter ablation techniques are used for this purpose, and they are directed at selective ablation of the slow or fast pathway, usually the slow one, to eliminate the reentry circuit (and thus the tachycardia) while avoiding the need for implanting a permanent pacemaker. ^, This can be successful in up to 90% of patients. Rarely, open cryosurgical ablation is performed in symptomatic patients who require open cardiac surgery for other indications.

Ectopic foci of activation in either right or left atrium can provoke paroxysms of atrial tachycardia. When localized by electrophysiologic studies, they can be treated successfully by catheter ablation. However, most ectopic atrial tachycardias, particularly those originating in the right atrium, have multiple sites of origin and are best treated pharmacologically.

Development of modern devices for cardiac pacemaking and for implantable cardioverter-defibrillators (ICDs) has made sophisticated understanding of cardiac electrophysiology and electrical engineering necessary for proper care of patients with these conditions. Currently, these requirements are met by few cardiac surgeons. Furthermore, most interventional therapies for these abnormal atrial tachycardias can now be performed using catheter-based percutaneous techniques.

Wolff-Parkinson-White (WPW) syndrome, as originally described, is a condition in which episodes of rapid heart rate (paroxysmal tachycardia) occur in otherwise healthy young people in combination with an ECG demonstrating delta waves and a broad QRS complex (bundle branch block with short PR interval) . WPW is one of the preexcitation syndromes , a term that implies activation of a cardiac chamber partially or wholly by an impulse arising in another chamber and arriving earlier than would be expected if the impulse had proceeded over the normal conduction system pathway.

WPW syndrome characteristically allows PAT by atrioventricular reentry . In some patients, however, the accessory pathways conduct only in a retrograde manner (concealed AV accessory pathways) and do not produce the typical WPW ECG.

Although Cohn and Fraser in 1913 and Wilson in 1915 described what apparently was WPW, and Mines in 1914 described “circulating excitations” in the turtle heart, the specific ECG pattern of WPW syndrome was not reported until 1930 by Wolff, Parkinson, and White. In 1967, Durrer and Roos demonstrated by epicardial mapping that in patients with WPW, AV conduction occurs over an accessory AV conduction pathway, or bypass tract, a concept first proposed in 1932 by Holtzmann and Scherf. This was confirmed in the same year by Burchell and colleagues, who also showed that ventricular preexcitation could be temporarily abolished by injecting procaine into the AV groove at the site of earliest ventricular activation.

In 1893, Kent described muscular bridges connecting right atrium to right ventricle in several mammalian species, and Wood and colleagues supported those observations in 1943. ^, Truex and colleagues in 1958 and 1960 demonstrated the presence of muscular accessory pathways in human hearts, and Lev and colleagues added further information on accessory pathway morphology in the early 1960s. Further proof of the morphologic basis of WPW syndrome came in 1968, when Cobb, Sealy, and colleagues reported dividing the accessory pathway; PR interval and QRS complex became normal, the delta wave disappeared, and ventricular preexcitation and recurrent supraventricular tachycardia were eliminated. In that operation, an epicardial approach was used, and a transmural ventricular incision made below the AV groove. Iwa and colleagues published a confirmatory report in 1970 and introduced the endocardial approach. Sealy and colleagues then also adopted an endocardial approach from within the atria, which consisted of separating atrium from anulus after dissecting away the AV fat pad. Sealy, Gallagher, and their colleagues also pioneered a successful surgical approach for patients whose accessory pathways were in the septal area and introduced cryosurgical ablation. ^, This method was combined with the epicardial approach using CPB by Guiraudon and colleagues.

These surgical developments provided much of the information that made catheter ablation of the accessory pathways possible beginning in the early 1980s. ^{, ,} Early experiences in patients used direct current (DC) as the energy source, but limitations were imposed by this method. Catheter ablation became reproducible and safe when radiofrequency (RF) energy was introduced. Different effects can be achieved by varying the RF output mode, frequency, waveform, and power output. Currently, catheter ablation techniques have replaced surgical techniques for interventional therapy of supraventricular tachycardia of all types and at all ages, except for occasional patients being operated on for other cardiac conditions or when the accessory pathway is impossible to ablate via catheter-based approach.

Accessory AV conduction pathways (Kent bundles) mediating WPW syndrome may occur at any point around the anulus of either AV valve except along the junction of the mitral anulus and aortic valve. However, they are most commonly located:

• •

  Along the strong, well-formed mitral anulus, adjacent to the free wall of the left ventricle laterally or posteriorly (WPW type A)

• •

  At the less well-developed tricuspid valve anulus anterosuperiorly, adjacent to the right ventricular free wall (WPW type B)

• •

  Along the tricuspid anulus, adjacent to the anterior aspect of the ventricular septum

• •

  Along the tricuspid or mitral anulus, adjacent to the posterior aspect of the ventricular septum, near the crux cordis

Accessory pathways adjacent to the posterior aspect of the ventricular septum lie in the potential space overlying the inlet portion of the septum and may be on either its right or left ventricular aspects.

Kent bundles are said to have an average width of 1.8 mm. Multiple functioning bundles are present in 10% to 20% of cases.

From the standpoint of cardiac surgeons and electrophysiologists, location of accessory AV pathways is important, as are the normal location of the AV node and bundle of His (see “ Conduction System ” in Chapter 1 ) and details of the structures and spaces around the AV valve anulae and fibrous skeleton of the heart. The central fibrous body , where mitral, tricuspid, and aortic valves meet, is the most prominent part of the fibrous skeleton. The area of fibrous continuity between aortic and mitral valves, the aortic-mitral anulus , contributes to the fibrous skeleton. The leftward extension of this anulus is the left fibrous trigone . The right fibrous trigone is at the right-sided extremity of the mitral-aortic anulus and is part of the central fibrous body. It lies adjacent to the AV portion of the membranous septum at the point where tricuspid, mitral, and aortic anulae come together. Atrial muscle is not in juxtaposition with ventricular muscle in the area between left and right fibrous trigones (along the aortic-mitral anulus), and thus accessory AV connections are not found in this area. As the surgeon views the mitral valve through the opened left atrium, the right fibrous trigone is just anterior to the medial commissure, and the left fibrous trigone is just lateral to the lateral commissure. As the surgeon views the tricuspid valve, the central fibrous body is in the region of the muscular portion of the AV septum (see “ Cardiac Valves ” in Chapter 1 ).

Normal anatomy in the region of the crux cordis and contiguous posterior septal area is of critical importance in therapy to ablate accessory AV conduction pathways in the region of the posterior aspect of the ventricular septum. Sealy and Gallagher described this anatomy as a “toppled pyramid enclosing a fat-filled space.” The apex of the pyramid is the right fibrous trigone, and its base is the epicardium over the crux. In adults, a distance of about 30 mm separates base from apex ( Fig. 15.4 ). ^, The two sides of the pyramid are right and left atria, which fuse in the region of the right fibrous trigone to become the atrial septum. It is important to note that the mitral valve anulus lies a somewhat variable distance superior to the tricuspid anulus, which accounts for there being an AV septum (see “ Atrioventricular Septum ” under Ventricular Septum in Chapter 1 ). Also, the interatrial groove, marking the posterior aspect of the atrial septum, lies somewhat to the left of the posterior aspect of the interventricular groove, and here, the right atrium somewhat overlies or wraps around the interatrial groove. The third side of the pyramid is the wall of the posterior superior process of the left ventricle and the muscular ventricular septum posteriorly. This pyramidal space contains fat, branches of the coronary artery, and the undersurface of the coronary sinus with its branches from right and left ventricles.

Schematic representation of normal anatomy in region of the crux cordis. Distance from crux cordis to right fibrous trigone is 30 mm, which is essentially alongside the atrioventricular portion of the membranous septum (AMS) , which lies just on the atrial side of the tricuspid valve anulus. Distance from the most posterior aspect of the mitral valve to right fibrous trigone is 28 mm, and that from the most posterior aspect of tricuspid valve to the trigone is 35 mm. The latter is the area of Sealy’s “toppled pyramid.” Note the aorta (Ao) is wedged into position between mitral (MV) and tricuspid valves (TV) .

(From Sealy WC, Mikat EM. Anatomical problems with identification and interruption of posterior septal Kent bundles. Ann Thorac Surg . 1983;36:584.)

The heart is usually otherwise normal in patients with WPW syndrome. However, in some, accessory muscle bundles coexist with Ebstein anomaly, fossa ovalis–type atrial septal defect, AV discordant connection, and other anomalies.

ECG diagnosis of preexcitation WPW syndrome is made in about 0.25% of healthy young people, with documented tachyarrhythmias occurring in about 2% of those with preexcitation. However, in other patient subsets of WPW, prevalence of tachyarrhythmias is as high as 80%. Half the infants and children with supraventricular tachycardia difficult to control medically have WPW or concealed accessory muscle bundles (see Section IV later in this chapter).

Patients with WPW may present at any age, including the early months of life. The syndrome is more common in males. ^, Most adults with WPW have otherwise normal hearts, although it may complicate a variety of acquired and congenital cardiac defects, including Ebstein anomaly. Patients with Ebstein anomaly often have multiple right-sided accessory pathways, and preexcitation is said to be limited to the atrialized portion of the ventricle. ^, Rossi and Thiene have shown in patients having arrhythmogenic death that a few of them have accessory conduction pathways combined with very mild downward displacement of the tricuspid septal leaflet.

Among patients with WPW and tachyarrhythmias, 80% have paroxysmal supraventricular tachycardias of a reciprocating type, 15% have atrial fibrillation, and 5% have atrial flutter. Sinus node dysfunction is said to be more common in patients with WPW than in those without it.

Patients with WPW, otherwise normal hearts, and no tachycardia have normal cardiac function and life expectancy. Morbidity is considerable in those with recurrent tachycardia, and sudden death occurs in a small proportion. These sudden deaths are most likely the result of combined paroxysmal atrial fibrillation and fast antegrade conduction across the accessory AV pathways. ^, Some children and young adults with WPW and recurrent tachycardia lose the tendency toward developing tachyarrhythmias as they grow older. Also, preexcitation may be intermittent with loss of the delta wave, a situation suggesting a benign prognosis.

The object of catheter ablation (or operation) is electrical isolation of the ventricles from the atria, except for the normal AV nodal pathway. Patients are brought to a cardiac electrophysiology laboratory. The study is performed under sedation, and accessory pathways are mapped and localized. A catheter-based ablation is usually performed utilizing RF, but in some cases, cryoablation is being used. Repeat ablations at subsequent procedures are required in a few patients.

Surgical procedures for termination of WPW syndrome were successful in 80% to 90% of patients. ^, Interruption of the accessory pathways prevents both reentrant AV arrhythmias and those due to atrial tachycardia, flutter, or fibrillation associated with rapid antegrade conduction across the accessory pathways.

RF catheter ablation is highly successful. ^, Accessory pathway conduction was eliminated in 164 (99%) of 166 patients in one study, without mortality. Preexcitation or AV reentrant tachycardia recurred in only 15 (9%; CL 7%–12%), all of whom underwent a second successful catheter ablation.

Symptomatic tachyarrhythmias associated with one or more accessory AV pathways are an indication for catheter ablation.

When cardiac operation is indicated for a different pathology in an asymptomatic patient with WPW, accessory pathways should probably be interrupted by catheter ablation techniques before operation because serious postoperative tachycardias and life-threatening atrial fibrillation can result from their presence. When catheter ablation is not available, a surgical procedure is indicated for interruption of the accessory pathways by either the endocardial or epicardial approach at the time of the concomitant cardiac surgical procedure. ^, The well-tested endocardial approach was described in the first edition of this textbook and has been clearly illustrated by others. ^,

Atrial fibrillation is an arrhythmia characterized by rapid (350–500/min), irregular, disorganized atrial impulses, and ineffective atrial contractions. P waves are absent from the ECG, and the bipolar electrogram reveals beat-to-beat polarity, morphology, amplitude, and cycle length that vary. The QRS complex is irregularly irregular. Atrial flutter is a disorder of cardiac rhythm characterized by rapid (250–350/min) regular atrial impulses. QRS complexes are uniform in morphology, and P waves may have saw-toothed configuration (F waves). Atrial flutter can be typical when it is right atrial isthmus dependent and atypical when it is left atrial mitral valve isthmus dependent.

The first clear description of atrial fibrillation is attributed to Herring in 1903 (pulsus irregularis perpetuus), although this was before the era of electrocardiography. Withering, in his studies on digitalis, was probably also aware of atrial fibrillation because he noted that digitalis was a “moderator and regulator of rhythm.” The beneficial effect of digitalis in atrial fibrillation was clearly noted in 1836 by Bouillaud in his classic textbook, quoted by Meijler. By 1914, Mackenzie and Sir Thomas Lewis had framed the controversy on the mechanism of action of digitalis, presaging continuing discussions as to the etiology of atrial fibrillation and electrophysiologic state of the atria during atrial fibrillation.

Pharmacologic interventions, notably digitalis (to slow the rate) and quinidine (to convert the rhythm), were the mainstays of treatment. There are obvious advantages of sinus rhythm, and in 1962, Lown and colleagues and in 1963, Oram and colleagues published their landmark studies of electrical cardioversion as treatment for atrial fibrillation. Perhaps only 15% of patients with persistent or longstanding persistent atrial fibrillation respond to these interventions. Therefore, there has been a continuing interest in finding an interventional solution to the problem of atrial fibrillation.

Catheter-induced His bundle ablation introduced by Scheinman and colleagues and Gallager and colleagues in 1982 controlled the tachycardia of established atrial fibrillation but required implanting a pacemaker. In 1990, Guiraudon and colleagues reported seven of nine patients were free of atrial fibrillation after an operation designed to isolate a corridor of right atrial tissue connecting the sinus and AV nodes. Creating a maze by multiple atrial incisions was developed by Cox and colleagues and was first performed on a patient in September 1987.

Cox and colleagues have reviewed the development of the Maze procedure and its preceding operations. The left atrial isolation procedure was described in 1980. This operation confined atrial fibrillation to the left atrium and obviated the need for a permanent pacemaker while restoring cardiac hemodynamics, especially in patients with normal ventricular diastolic function. Vulnerability to systemic thromboembolism remained unchanged. In 1982, Scheinman and colleagues, as noted previously, described catheter ablation of the His bundle with insertion of a permanent pacemaker to restore regular rhythm as a means of controlling ventricular rate. Risk of thromboembolism was unaffected. Guiraudon and colleagues described the corridor procedure in 1985. This procedure isolated a strip of atrial septum (the “corridor”) containing both the SA node and the AV node so that the SA node could once again pace the ventricles, even though the atria continued to fibrillate. AV synchrony was not restored, and risk of thromboembolism persisted. Understanding the electrophysiology of atrial fibrillation based on work of Boineau and colleagues and Alessie and colleagues led to development of the atrial transection procedure. ^, Initial success in a patient was followed by recurrence of atrial fibrillation. Further advances in the understanding of atrial fibrillation using more sophisticated means of atrial mapping led to the concept that interruption of the multiple macro-reentrant circuits responsible for the arrhythmia would be possible. The surgical procedure was based on the concept of a maze and was named the Maze procedure . ^,

As cited by Cox and colleagues following dialogues between Mackenzie and Lewis, three theories have evolved regarding the electrophysiologic mechanism of atrial fibrillation. Rothberger believed there was a single automatic atrial focus, the inference being that its resection or isolation might cure atrial fibrillation. Engleman suggested the presence of multiple small automatic foci. Garrey experimentally disproved both hypotheses by isolating smaller and smaller segments of fibrillating atrial tissue. His observations suggested that (1) some critical atrial mass was necessary to sustain atrial fibrillation and (2) the underlying mechanism was reentry, not automaticity. Based on experiments using programmed electrical stimulation, Moe hypothesized the existence of multiple wavelets with different refractory periods within the atrial mass. Inhomogeneous tissue refractoriness lends itself to reentry, not automatic mechanisms. Moe’s theories were later confirmed by Allessie’s group using multiplexed computerized recordings in rabbit atria. Boineau and colleagues mapped circus motion around the superior vena cava orifice in a dog with naturally occurring atrial flutter. They concluded that in addition to functional factors (nonuniform repolarization), anatomic factors also contribute to atrial dysrhythmias. Cox and colleagues then created atrial fibrillation in experimental animals following the induction of severe mitral insufficiency and mapped the electrophysiologic events. In their 1991 publication, they concluded, “The presence of macro-reentrant circuits and the absence of either micro-reentrant circuits or evidence of atrial automaticity suggests that atrial fibrillation should be amenable to surgical ablation.” They subsequently demonstrated the ability to terminate atrial fibrillation in humans by performing the classic Maze I procedure that was quickly modified twice to the Maze III procedure. In 1994, Haissaguerre and colleagues reported successful ablation procedures for atrial fibrillation using a catheter-based technique. Since the publication of these two landmark studies, many modifications of the initial ablation techniques to terminate atrial fibrillation have been introduced.

Theories of the mechanism of atrial fibrillation involve two processes : (1) focal triggers of enhanced automaticity and (2) multiple wavelets of macro-reentry activation migrating across the atria. Rapidly firing foci, located mostly in pulmonary veins and also but less frequently in the right atrium, superior vena cava, or coronary sinus, can initiate atrial fibrillation in susceptible patients. Fractionation of multiple wavefronts, as they spread across the atria, results in self-perpetuating “daughter wavelets” that cause a complete absence of coordinated atrial systole. The reentry circuits follow different pathways each time after initiation and have been thought in the past to be random.

Recent evidence suggests that there may be more organization than previously thought. Allessi and colleagues have identified three patterns of atrial fibrillation:

• •

  Single wavefronts

• •

  One or two wavefronts

• •

  Multiple activation wavefronts propagating in different directions across the atria

Focal triggers as the only mechanism of atrial fibrillation probably apply to patients with normal atria. Triggers plus macroreentry (substrate) mechanisms apply to enlarged or diseased atria.

Risk factors for developing atrial fibrillation include older age, inflammation, oxidative stress, and atrial morphology. In addition, genetic susceptibility factors related to several ion channels have been implicated in its pathogenesis. Missense mutations of the gap junction protein connexin-40 (encoded by the GJA5 gene), which plays a critical role in electrical intercellular coupling, has been implicated in a small number of cases of atrial fibrillation. Lu and colleagues have found that microRNA-328 contributes to adverse atrial electrical remodeling in atrial fibrillation by targeting L-type calcium channel genes. Goudarzi and colleagues identified specific aspects of mitochondrial dysfunction in patients with AF.

Atrial fibrillation is not a benign arrhythmia and presents a difficult clinical challenge. It is the most common cardiac arrhythmia, accounting for about one-third of arrhythmia diagnoses. It is estimated that 2.2 million people in the United States and more than 5 million people worldwide have atrial fibrillation. ^, It is present in approximately 1% of the general population and 6% of those older than age 65 years. There are about 360,000 new patients diagnosed annually in the United States. ^, It is well established that the associated comorbidities and vascular risk factors directly impact the rate of ischemic strokes associated with AF. Among the risk factors are congestive heart failure, diabetes, hypertension, peripheral artery disease, gender, and age, as defined by the CHA2DS2-VASc score.

Atrial fibrillation is more prevalent with increased age, and the risk of ischemic strokes is also increased with age. In general, it is estimated that up to 30% of diagnosed ischemic strokes are directly related to AF. In one study based on Canadian and Swiss data between the years 2003 to 2019, 32% of ischemic strokes were associated with AF. Accurate data on the actual prevalence of AF outside Europe and the United States are lacking. Therefore, it is fair to estimate that the number of patients affected by AF worldwide is higher. According to the Centers for Medicare and Medicaid Services, atrial fibrillation resulted annually (up until 1990) in 227,000 hospitalizations (50% as emergencies) at a cost of $6.6 billion.

Thromboembolism associated with atrial fibrillation results from slow and stagnant blood flow in the atria, and risk of stroke associated with atrial fibrillation is 5% to 12% per year. ^, Factors that increase the risk of stroke in patients with atrial fibrillation include older age, diabetes, heart failure, previous myocardial infarction, and previous embolism. Chronic atrial fibrillation is associated with cellular changes that progress to atrial myocardial fibrosis. The progressive nature of the condition leads to enlargement of the atria and eventual loss of function of the atrial myocardium. Tachycardia-induced cardiomyopathy is an end-stage complication of atrial fibrillation.

In general, two treatment strategies are used to manage patients with atrial fibrillation: (1) rate control combined with oral anticoagulation when indicated and (2) interventions aimed at rhythm control, restoration, and maintenance of sinus rhythm.

Interruption of macro-reentrant circuits

A series of operative techniques based on contemporary electrophysiologic understanding has led to effective methods of operative or catheter-based intervention for treating atrial fibrillation.

Cox-Maze III procedure.

The Cox Maze procedure is an anatomic surgical concept in which multiple incisions are made bi-atrially that interrupt reentrant circuits associated with AF while allowing sinus node impulse to the AV node along a specified route. The entire atrial myocardium (except for the atrial appendages and the pulmonary veins) is electrically activated by providing multiple blind alleys about 2 to 3 cm wide off the main conduction route between the SA node and the AV node, thus preserving atrial transport function. A modification of the technique as described by Cox and colleagues, called the Maze III procedure with minor changes, is described here. ^,

Bicaval cannulation is required in most cases, although utilizing the multiple purse-strings approach would permit a two-or three-staged cannula in the right atrium as a single venous drainage ( Fig. 15.7 ) (see “ Preparation for Cardiopulmonary Bypass ” in Section III of Chapter 2 ). A cannula is inserted directly into the superior vena cava, and the inferior vena cava is cannulated through the right atrium as close as possible to the diaphragm. The inferior vena cava cannula is positioned slightly more medially than usual to allow the appropriate completion of the ablation line into the os of the inferior vena cava (IVC). Small venous cannulae (24 Fr) may be used if active venous uptake is provided by vacuum suction applied to the reservoir of the oxygenator (see “ Vacuum-Assisted Venous Return ” in Section II of Chapter 2 ). Perfusion is normothermic to maintain the heartbeat during initial phases of the operation on the right atrium.

Maze III procedure. (A) Operation is performed via median sternotomy. Cannulae for venous uptake are placed in superior vena cava and through the low right atrium into inferior vena cava. Small venous cannulae (24Fr) and vacuum-assisted venous return are employed. CPB is established, and tourniquets are tightened around venae cavae. First incision divides right atrial appendage and extends obliquely to midpoint of right atrial free wall. Medially, incision extends to atrioventricular groove. Longitudinal incision is made from superior to inferior vena cava along crista terminalis. Lower 2 cm of incision is closed with a continuous suture of 4-0 polypropylene to prevent tearing during retraction. Vertical incision is made from point of closure to atrioventricular groove. (B) Vertical incision is extended to tricuspid valve anulus in area of posterior leaflet (2-o’clock position, surgeon’s view), working on endocardial surface of atrium cutting through the entire atrial wall. Residual myocardial fibers are ablated by applying a 3-mm cryolesion (−70°C for 2 minutes) at tricuspid anulus. This portion of incision is closed with 4-0 polypropylene suture. (C) Incision of medial aspect of right atrial appendage is continued into atrial groove to tricuspid valve anulus (10-o’clock position, surgeon’s view) by dissecting on endocardial surface. A cryolesion is placed at anulus of tricuspid valve to ablate residual myocardial fibers. This portion of incision is closed with 4-0 polypropylene suture. (D) Aorta is occluded. Coronary sinus is cannulated, and cold cardioplegic solution is administered to achieve total electromechanical arrest. Left atrium is opened on right side behind interatrial groove and in front of pulmonary veins. Incision is extended superiorly and inferiorly. Atrial septum is divided at level of right superior pulmonary vein. This incision is curved inferiorly to divide the membrane of fossa ovalis. (E) Atrial septum is retracted anteriorly. Pulmonary vein encircling incision is developed, working within left atrium by extending incision across back wall of atrium above and below left pulmonary veins. (F) Heart is retracted inferiorly and to the right to expose left atrial appendage on external surface of heart. Two orientation sutures of 3-0 polypropylene are placed through left pulmonary vein encircling incision at level of left superior and left inferior pulmonary veins. Encircling incision is completed between orientation sutures (dashed line). Left atrial appendage is excised at its base. Atrial wall between atrial appendage and encircling incision is divided (dashed line). (G) Orientation sutures are tied, then used to close left atrium between them. Separate suture of 3-0 polypropylene is used to close bridge to and base of left atrial appendage. (H) Exposure returns to interior of left atrium. Orientation sutures are passed inside left atrium and used to close encircling incision superiorly to midpoint and inferiorly for about 2 cm of posterior wall of left atrium. Vertical incision is developed between encircling incision and mitral valve anulus. Incision is through entire left atrial wall into epicardial fat in atrioventricular groove, exposing coronary sinus. A cryolesion is made on exterior surface of coronary sinus, using a 15-mm cryoprobe applied for 3 minutes. After 1 minute, a 3-mm cryoprobe is placed on mitral valve anulus and a 2-minute cryolesion is made. Vertical incision is closed with 4-0 polypropylene. Mitral valve repair or replacement is performed at this point of operation if indicated. (I) Pulmonary vein encircling incision is closed to pulmonary veins on right side. Retraction is switched to right atrium, allowing all but final centimeter of encircling incision to be closed. Left ventricular venting catheter is placed through separate incision in right superior pulmonary vein. (J) Atrial septum is closed with 4-0 polypropylene suture. Separate sutures are used for left and right atrial surfaces of thick portion of atrial septum. Remainder of encircling incision is closed. (K) Right atrial incisions are closed. Longitudinal incision is closed, then vertical incision, and finally oblique incision, using 4-0 polypropylene suture.

The right atrial appendage is excised, removing all trabeculations attached to the appendage. Alternatively and preferably, an incision (see Fig. 15.7 A) is made through the tip of the right atrial appendage, extending to the base of the appendage medially and laterally to reduce the surgical trauma in that area of the overall sinus node complex. This incision is extended toward the midpoint of the right atrium. A longitudinal incision is made in the lateral wall of the right atrium along the crista terminalis. This incision extends onto the superior and inferior vena cava. The lower end of the incision is immediately closed to a point about 2 cm cephalad to the inferior vena cava cannula by a continuous suture of 4-0 polypropylene to prevent tearing during retraction. At this point, a vertical incision is made, extending anteriorly. The inside of the right atrium is exposed ( Fig. 15.7 B) so that the intraatrial incision may be extended to the tricuspid valve anulus at about the midpoint of the posterior leaflet. A 3-mm cryolesion is placed at approximately the 2-o’clock position on the tricuspid anulus for 2 minutes at −70°C. All muscle fibers of the right atrial wall are divided, exposing the fat of the AV groove and occasionally the right coronary artery. The atrial incision is closed from the anulus of the tricuspid valve to the free wall of the right atrium by a continuous 4-0 polypropylene suture. An incision is made on the medial aspect of the remnant of the appendage ( Fig. 15.7 C). This incision extends to the tricuspid valve anulus at the midpoint of the anterior leaflet or approximately at the 10 o’clock position. Alternatively, the medial ablation line from the cut edge of the appendage to the tricuspid valve anulus can be made with a cryoprobe. This minimizes risk of injury to the branch of the right coronary artery supplying the SA node. Another 3-mm cryolesion is placed at the tricuspid anulus for 2 minutes at −70°C. In some cases, it is preferable to perform the right atrial part of the Maze procedure following the left side, which will allow the removal of the cross-clamp and completion while the patient’s heart is reperfused and rewarmed.

Systemic cooling is then initiated. The aorta is occluded preparatory to the left atrial portions of the operation. Cold blood cardioplegic solution is administered ( Fig. 15.7 D) (see “ Methods of Myocardial Management during Cardiac Surgery ” in Chapter 3 ), and the left atrium is opened by incision just posterior to the interatrial groove near the orifices of the right pulmonary veins. The incision is extended superiorly and inferiorly onto the left atrium around the right pulmonary veins. The atrial septum is incised above the fossa ovalis. The incision is curved across the limbus of the fossa ovalis and the membrane of the fossa to the inferior margin of the fossa near, but not into, the tendon of Todaro ( Fig. 15.7 E). The left atrial incision is continued across the left atrium toward the left pulmonary veins to isolate and encircle them. The heart is retracted to the right to expose the left atrial appendage ( Fig. 15.7 F), which is excised at its base. It is incised in a cephalad direction near the AV groove across its base and back into the left atrium. The incision in the left atrial appendage is joined to the pulmonary vein encircling incision at a point near the left superior pulmonary vein. The incision in the base of the left atrial appendage is closed back to the encircling incision, and the portion of the encircling incision below the left atrial appendage is closed with continuous sutures of 3-0 polypropylene. It may be helpful to use a blue marker across the incisions mentioned to facilitate precise closure of the incisions ( Fig. 15.7 G). These sutures are passed from the outside into the left atrium and retrieved from within the atrium ( Fig. 15.7 H). The encircling incision closure is continued cephalad and around the superior aspect to the midpoint of the encircling incision. The encircling incision is closed inferiorly to the midpoint.

An incision is made across the floor of the left atrium to the midpoint of the anulus of the posterior leaflet of the mitral valve. This incision is carefully opened by sharp dissection.

The coronary sinus is exposed by incision into the fat of the AV groove. The circumflex coronary artery may also be visualized in the incision. A 15-mm cryoprobe is placed posteriorly on the coronary sinus, and a cryolesion is created at −60°C to −70°C for 3 minutes. After 1 minute, a 3-mm cryoprobe is placed at the mitral valve anulus at−60°C to −70°C for 2 minutes. Timing of freezing with the two probes is coordinated so thawing can occur simultaneously. Mitral valve repair or replacement is performed at this point if required. The incision in the floor of the left atrium is closed by a continuous suture of 4-0 polypropylene, beginning at the mitral anulus and continuing to the encircling incision ( Fig. 15.7 I). The sutures are joined and continued to close the encircling incision over to the right pulmonary veins.

The atrial septum is a thin membrane within the fossa ovalis. The limbus is muscular and thicker. There are discrete layers of the right and left atria that represent the infolding of the atria at the interatrial groove rather than true septum. These layers should be closed separately ( Fig. 15.7 J). The septal closure begins at the inferior border of the fossa ovalis using continuous sutures of 4-0 polypropylene. Suturing continues across the limbus and along the left atrial fold to the free margin. A second layer of closure is started at the limbus and continued along the right atrial fold to the junction, with the longitudinal incision in the right atrium. The remainder of the pulmonary vein encircling incision is closed and joined to the left atrial septal closure (see Fig. 15.7 J).

A venting catheter is inserted via the left superior pulmonary vein through a separate purse-string suture. Air is evacuated from the left cardiac chambers and aorta, and the aortic occlusion clamp is removed (see “ Completing Cardiopulmonary Bypass ” in Section III of Chapter 2 ). The heart is reperfused and defibrillated if necessary. The longitudinal incision in the right atrium is closed, beginning at the superior vena cava and working inferiorly ( Fig. 15.7 K). The suture is joined to the right atrial septal closure and then continued to the vertical right atrial incision. The vertical incision is closed. Operation is completed by closing the right atrial appendage opening, beginning at the midpoint of the right atrium and continuing through the appendage incision.

The Maze procedure has been performed experimentally and clinically as a closed heart procedure. ^, Radial incisions in the atria have been proposed as a modification of the Maze III procedure by Nitta and colleagues. Atrial incisions radiate from the SA node toward the AV anular margins to allow a more physiologic atrial activation sequence that may improve atrial transport function. These operations have not substantially reduced the time or complexity required to complete the standard Maze III operation.

Modified maze procedure and surgical ablation procedures.

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