Atrial tachyarrhythmias in adults with congenital heart disease

Macroreentrant atrial tachycardia

For macroreentrant atrial tachycardias (MRATs) in adults with repaired CHD, three RA circuits are generally identified: (1) lateral wall circuits with reentry around or related to the lateral atriotomy scar; (2) septal circuits with reentry around an atrial septal patch; and (3) peritricuspid reentry circuits (typical atrial flutter [AFL]) using the cavotricuspid isthmus (CTI). Typical clockwise or counterclockwise AFL is the most common single mechanism and usually coexists with other forms. Atrial macroreentry in the RA free wall is the most common form of non-CTI-dependent RA macroreentry. Left atrium (LA) macroreentrant circuits are infrequent in this patient population.

The complexity of the MRAT circuits depends on the underlying congenital anomaly and the complexity of the surgical repair. Very complex or multiple reentry circuits can be seen after placement of an intra-atrial baffle (Mustard or Senning correction for transposition of the great vessels), in an extremely dilated RA, after a Fontan procedure, and in patients with a univentricular heart.

Anatomical factors promoting macroreentry in patients with CHD include abnormalities of the underlying cardiac anatomy, surgically created anastomoses, and atriotomy scars, resulting in barriers to impulse propagation and protected isthmuses with adjacent anatomical structures. Conduction abnormalities can be further aggravated by atrial remodeling (dilatation, hypertrophy, and scarring) secondary to persisting pressure or volume overload after cardiac surgery or because of residual septal defects, valvular abnormalities, or ventricular dysfunction. At greatest risk are patients with single ventricular physiology and Fontan circulation, atrial baffles created by Mustard and Senning procedures for treatment of d-transposition of the great arteries, and repaired tetralogy of Fallot, but even patients with simple atrial septal defect repair can be vulnerable years after surgical repair. Of note, epicardial mapping studies revealed that atrial conduction abnormalities (primarily at the RA and Bachmann’s bundle) are already present early after birth in pediatric patients with CHD without history of atrial tachyarrhythmias. It remains to be investigated whether the observed conduction abnormalities are related to structural remodeling induced by short-lasting volume or pressure overload or genetic factors.

The best characterization of MRAT caused by atriotomy is activation around an incision scar in the lateral RA wall, with a main superoinferior axis ( Fig. 15.1 ). This is a common problem in patients who have undergone surgery for congenital or valvular heart disease. The length, location, and orientation of the atriotomy incisions, as well as potential electrical conduction gaps across the atriotomy, are important determinants of arrhythmogenicity. Not only does the central obstacle include the scar, but also functional block can magnify this obstacle to include the superior vena cava (SVC). The anterior RA wall is commonly activated superoinferiorly (descending activation pattern), as in counterclockwise typical AFL. However, the septal wall frequently lacks a clear-cut inferosuperior (ascending) activation pattern. A line of double potentials can be recorded in the lateral RA, extending superoinferiorly. Double potential separation can be more marked and demonstrate a voltage lower than in typical AFL. Narrow passages (isthmuses) in the circuit can be found between the SVC and the superior end of the atriotomy scar, between the inferior vena cava (IVC) and the inferior end of the atriotomy, between the atriotomy scar and the tricuspid annulus, between the atriotomy and the crista terminalis, or even within the scar itself ( Fig. 15.1 ).

Typical AFL is also often associated with RA atriotomy. In fact, the single most common form of AT among patients with CHD appears to be CTI-dependent AFL, accounting for more than 70% of all MRATs, particularly in patients with simpler anatomical lesions (e.g., tetralogy of Fallot, atrial and ventricular septal defects) ( Fig. 15.2 ). The atriotomy scar in the lateral or posterolateral RA forms a fixed posterior barrier to conduction in the superoinferior direction between the vena cavae, a lateral boundary necessary for the development of a peritricuspid reentry (typical AFL) by preventing short-circuiting of the tricuspid annulus via the posterior atrium. Other RA MRATs involving free wall atriotomy become progressively more common with more extensive atrial incisions.

Reentry circuits can also occur in the sinus node region, possibly as a result of injury related to the superior atrial cannulation site for the bypass pump. These circuits can be quite small, often manifesting as focal tachycardia in the sinus node region, and they frequently can be ablated in a single location without establishing a particular line of block.

More recently, ATs arising from the morphologic LA (i.e., the pulmonary venous atrium) have been described after surgical repair of CHD. The incidence of those ATs is higher in patients with univentricular hearts and those with prior ipsilateral atrial surgery. The mechanism of those ATs is more heterogeneous than that arising from the morphologic RA (i.e., the systemic venous atrium). Macroreentry is a less predominant mechanism, accounting for less than 50% of cases.

Focal atrial tachycardia

Focal mechanisms underlying postoperative AT have been rarely reported in this patient population. Nonautomatic focal ATs are predominantly found in adults, with most foci in the RA, and often arise from surgical scar borders. The mechanism underlying focal AT is unknown. Both triggered and microreentrant mechanisms have been suggested. Viable myocardial fibers embedded within areas of scar tissue, which play a pivotal role in the initiation and perpetuation of macroreentrant tachycardias, can also be the site of origin of a focal AT and thus play an important role in the pathogenesis of these ATs. Importantly, recent studies using ultra-high-resolution electroanatomical mapping have found that a significant proportion of “focal” ATs that occurred at areas of scarred myocardium were in fact caused by localized reentrant mechanisms.

Atrial fibrillation

During long-term follow-up, AF develops in more than one-third of patients with CHD. Compared with MRAT patients, those with AF tend to be older and the arrhythmia develops later after surgery. AF is frequently associated with markers of left-sided heart disease (i.e., left ventricular systolic dysfunction and LA dilation) and is most commonly seen in patients with congenital aortic stenosis, mitral valve disease, palliated single ventricles, unrepaired heart defects, or end-stage heart disease. Compared to patients without congenital heart defects or with simple congenital heart defects, AF develops at a younger age in patients with complex congenital heart defects. Coexistence of episodes of AF and regular AT has been reported in a considerable number of patients (33%). Regular AT preceded development of AF in approximately two-thirds of patients. Approximately 30% of patients who have previously undergone successful catheter ablation for MRAT develop AF during long-term follow-up.

Early postoperative atrial tachycardia

Arrhythmias are also frequently observed in the early postoperative period after corrective surgery in children, occurring in 14% to 48% in the first few days following surgery. The most common arrhythmia in this period is junctional tachycardia, occurring in 5% to 10% of the operated children and is usually self-limiting. Other supraventricular arrhythmias are also seen in 4%. The occurrence of early postoperative arrhythmias seems to be related to procedural factors of cardiac surgery, which are, in turn, related to the complexity of the congenital malformation. Local inflammation, metabolic and hemodynamic stress, as well as inotropic drug therapy can potentially promote automatic and triggered activity-related focal atrial and junctional tachycardias. Early postoperative arrhythmias influence the long-term outcome of patients with CHD and have been found to be a predictor of late complications, such as ventricular dysfunction, late arrhythmias, and late mortality. However, whether preventing these arrhythmias will influence the long-term survival of patients with CHD is unknown.

Atrial septal defect

Atrial septal defects are among the most common congenital heart lesions in adults. In the absence of surgical repair, the prevalence of supraventricular arrhythmias increases with age, with typical AFL being the most common. In the presence of atriotomy incisions, sutures, or patches, non-CTI-dependent MRATs can occur or coexist with typical AFL. Common substrates include macroreentry along the lateral RA wall and double-loop or figure-of-eight circuits. The septal patch itself is rarely a critical conduction obstacle.

In patients with unoperated atrial septal defects, the prevalence of atrial arrhythmias ranges between 10% and 20% depending on age. Surgical and transcatheter closure of the atrial septal defect decreases the prevalence of atrial arrhythmias by one-third. The timing of surgical closure of the atrial septal defect appears to affect the incidence of atrial arrhythmias. Approximately 60% of patients who have undergone surgical closure at adult age (older than 40 years) continue to have atrial tachyarrhythmias (AT and AF) during long-term follow-up. In contrast, surgical closure performed during childhood provides a substantially lower incidence of arrhythmias. The impact of transcatheter closure of atrial septal defects on atrial arrhythmias is less clear. In one series, all patients with persistent arrhythmias remained in AF or AFL after closure. ^,

Tetralogy of fallot

Tetralogy of Fallot is the most common cyanotic congenital heart condition, and it accounts for approximately 10% of the adult CHD patient group. ATs occur commonly (12%–34%) during extended follow-up after tetralogy of Fallot repair. The observed prevalence of atrial arrhythmias is modestly higher than that of ventricular arrhythmias (15%). The most common atrial circuit is typical AFL. Other circuits often involve the lateral RA wall and may be multiple, often with a double-loop type of reentry. Nonautomatic focal ATs are infrequent and most commonly arise adjacent to suture points, with radial spread of activation. The prevalence of AF increases with advancing age. In the first few decades of life, AF is far less common than MRAT, but it becomes more common (more than 30%) than MRAT after 55 years of age. ^,

D-transposition of the great arteries

Dextro-transposition of the great arteries accounts for 5% to 7% of congenital heart defects. The Mustard and Senning procedures utilize an intra-atrial baffle constructed from prosthetic material or pericardium (Mustard) or from the atrial septum and RA free wall (Senning) to redirect the venous blood from the SVC and IVC to the left ventricle via the mitral valve and the pulmonary venous blood to the right ventricle via the tricuspid valve (“atrial switch procedure”). The “new RA” is called the systemic venous atrium and the “new LA” becomes the pulmonary venous atrium ( Fig. 15.3 ). Both procedures were performed from the early 1960s until approximately 1985 as the major long-term surgical palliation procedures for young children having d-transposition of the great arteries. Hence, there is a population of patients in their early 30s to late 50s who have undergone these operations and who are at an increased risk (15%–48%) of having supraventricular arrhythmias, with similar rates in patients with Mustard and Senning baffles. Since the mid-1980s, with the development of coronary artery reimplantation techniques, arterial switch surgery has supplanted atrial redirection as the procedure of choice for d-transposition of the great arteries, and it has been associated with a significantly lower risk of arrhythmias, and a reported arrhythmia-free survival rate of 97% after 25 years of follow-up.

The most common arrhythmia in patients after Mustard or Senning operations for transposition is atrial macroreentry, occurring in up to 30% of these patients ( Fig. 15.4 ). Typical AFL accounts for up to 75% of all MRATs, but non-CTI-dependent MRATs with critical zones of slow conduction between a suture line and the SVC orifice, mitral valve annulus, and pulmonary vein orifice have all been described. Focal ATs adjacent to suture lines are not uncommon. Importantly, the tricuspid valve is on the pulmonary venous side, while the IVC is on the systemic venous side of the circulation; as a consequence, the CTI is necessarily divided between the two sides. Therefore, access to the pulmonary venous atrium is almost always necessary for ablation of MRAT and typical AFL, which can be accomplished via a retrograde aortic approach through the tricuspid valve or by transbaffle puncture. ^{, ,}

Univentricular hearts with fontan palliation

Among patients with CHD, the incidence of MRAT is highest in older patients (up to 50% within a decade of surgery) who have had older-style palliative surgeries for univentricular hearts, typically varieties of the Fontan procedure ( Fig. 15.5 ). In the older-style Fontan operations (atriopulmonary [RA appendage-to-pulmonary artery] anastomosis), extensive suture lines and long-term hemodynamic stress result in marked RA dilation, hypertrophy, and fibrosis. Overall, the most common arrhythmia in these patients is typical AFL, but other MRATs as well as focal ATs are also observed ( Fig. 15.6 ). MRAT circuits in Fontan patients can be complex and multiple, and they represent the most challenging arrhythmias for mapping and ablation. Pericaval circuits have been identified specifically in Fontan patients. In all CTI-dependent circuits, successful ablation requires access to the pulmonary venous atrium (via a fenestration in the intracardiac baffle or a transbaffle puncture) to create the line between the tricuspid annulus and IVC. ^,

The incidence of atrial tachyarrhythmias appears to be reduced by 50% to 70% in patients with total cavopulmonary connections in comparison with classical atriopulmonary connections. Newer Fontan designs (total cavopulmonary connections) bypass the RA to a large extent, using either a lateral tunnel or an extracardiac conduit, thereby avoiding RA dilation and resulting in significant reduction in MRAT incidence to 2% to 7%. In the latter group, however, the macroreentry circuits are typically located on the pulmonary venous side of the tunnel or conduit, requiring complex techniques for accessing the arrhythmia substrate (tunnel/conduit puncture). In patients who have already developed arrhythmias and then undergo lateral caval tunnel conversion to decompress the RA, arrhythmias often subside after this procedure (during which various forms of maze surgery can also be performed), but in many cases, atrial arrhythmias remain problematic. ^,

Ebstein’s anomaly of the tricuspid valve

Ebstein’s anomaly of the tricuspid valve is a relatively rare form of CHD. The central anatomic abnormality involves a malformation of the tricuspid valve with adherence of the septal and posterior leaflets to the underlying RV myocardium due to embryologic failure of delamination. The anterior leaflet is usually malformed, excessively large, and abnormally attached or adherent to the RV free wall. As a result, the functional tricuspid valve orifice becomes distorted and displaced down into the apical portion of the RV. The true tricuspid annulus, on the other hand, is not anatomically displaced but can be poorly developed, with extensive discontinuities of the fibrous architecture. Consequently, a portion of the RV is “atrialized” in that it is located on the atrial side of the tricuspid valve, and the remaining functional RV is small ( Fig. 15.7 ). The atrialized portion of the RV is morphologically and electrically ventricular but hemodynamically atrial. Ebstein anomaly can be associated with other cardiac anomalies, including a patent foramen ovale, atrial and ventricular septal defects, and RV outflow tract obstruction. Variable degrees of tricuspid regurgitation and stenosis result in RA enlargement with expansion of the true right AV groove and dilation of the atrialized portion of the RV.

Ebstein’s patients exhibit a dramatic predisposition toward tachyarrhythmias, most of which can be attributed to atrioventricular (AV) bypass tracts. The bypass tracts bridge the true anatomical tricuspid annulus, regardless of where the valve is located, and they tend to cluster along the septal and posterior aspects of the true AV ring where the leaflet tissue is most abnormal. Right-sided bypass tracts have been reported in 10% to 30% of patients with Ebstein anomaly, and they are multiple in up to 50% of patients.

In addition to bypass tract–related supraventricular tachycardias, a variety of atrial tachyarrhythmias can develop in response to abnormal hemodynamics and degenerative remodeling. Atrial macroreentry is the most common of these and can involve typical CTI-dependent AFL circuits around the tricuspid ring or circuits around atriotomy incisions or septal patches in postoperative patients. AF can develop in patients with long-standing cyanosis and right-to-left-shunting, which cause significant LA enlargement. Focal AT has also been encountered.

It is important to recognize that Koch’s triangle can be distorted by atrial distention and the compact atrioventricular nodal (AVN) displaced inferiorly toward the coronary sinus (CS) os. Additionally, a prominent ridge at the inferior aspect of the true annulus is a common feature in Ebstein’s anomaly. This ridge often presents a potential obstacle to catheter manipulation and delivery of ablation energy in the region of CTI. Catheter ablation at the CTI should be considered carefully given the risk of damage to the tricuspid valve leaflet tissue that can potentially complicate surgical delamination and repair.