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THE CONSERVATORY OF MEDICAL ARTS AND SCIENCES
XVII
THE SEARCHLIGHT MESSENGER
THE SEARCHLIGHT MESSENGER
Blog
Arrhythmias in Adult Congenital Heart Disease
| Posted on July 13, 2014 at 10:22 PM |
Historically, many congenital
cardiac defects resulted in death in infancy or early childhood, with few
individuals living into young adulthood. Through advances in modern
cardiovascular care, there are now almost 1 million adults with congenital
heart disease (CHD) living in the United States and, interestingly, more adults
than children. As a consequence of these operative repairs and the added
longevity, arrhythmias are increasingly common. Mayo Clinic's campus in Rochester,
Minnesota, is home to one of the largest adult CHD centers in the world and
manages all types of CHD using a multidisciplinary team approach of
cardiologists, cardiac surgeons and electrophysiologists. Many key insights
into these complex disorders have developed out of research from this group,
and it is seen as a leader in disease-specific syndromes such as Ebstein's
anomaly and tetralogy of Fallot.
"Arrhythmias in this group are
a major cause of hospital admission and morbidity in patients with CHD and also
are the most common reason for late mortality," says Christopher J. McLeod, M.B., Ch.B., Ph.D., congenital
electrophysiologist at Mayo Clinic in Rochester. "Moreover, some of the
rhythm abnormalities such as the atrial arrhythmias, which are often benign in
the general population, are poorly tolerated and are associated with a
substantial increase in mortality in this group."
Background Some element of CHD is present in
about 1 percent of live births. Of these, about half have milder forms of
disease, such as atrial septal defects (ASDs) and ventricular septal defects
(VSDs), while the remainder have more complex physiology, the most common of
these being tetralogy of Fallot. Symptomatic bradyarrhythmias can
cause considerable morbidity and mortality. Pacemaker implantation is required
in about 3 to 4 percent of patients with Ebstein's anomaly or ASD closure, but
in more than 80 percent of patients who have complete transposition of the
great arteries who had a Mustard or Senning operation or patients with
congenitally corrected transposition of the great arteries.
Atrial tachyarrhythmias afflict at
least a quarter of all individuals with CHD during their lifetimes. About half
of patients with ASD repair after age 25 and nearly one-third of patients with
tetralogy of Fallot develop atrial tachyarrhythmias. Ventricular arrhythmia and
sudden cardiac death also are inextricably interwoven in this group of
patients, as they occur in about a quarter of patients. This incidence is 25 to
100 times higher than in an age-matched control population, and risk
stratification for implantable cardioverter-defibrillator (ICD) implantation
for primary prevention remains a major hurdle. The mechanism behind these
arrhythmias can be inherent to the congenital anomaly, such as abnormalities in
atrioventricular (AV) nodal function in the AV septal defects. However,
bradycardias are most commonly seen as a consequence of the operative repair,
either in the early postoperative period or later due to fibrosis developing in
the context of prior operative scars. Tachycardias most commonly have a
reentrant mechanism and typically propagate in areas affected by the presence
of patches, suture lines or late fibrosis.
 Tetralogy
of Fallot Ventricular tachycardia is the most
common cause of late mortality in this group of patients, and ICD implantation
plays a firm role in preventing sudden death. As tetralogy of Fallot is the
most common complex congenital heart syndrome, ICD therapy, electrophysiology
studies, and surgical and percutaneous ablative intervention have been
well-studied in this group of individuals. Atrial tachyarrhythmias are also a
frequent cause of morbidity and are seen in around a third of patients; this is
typically an intra-atrial reentrant tachycardia that is amenable to ablation
and less so to medications. Anti-arrhythmic medications are useful adjuncts in
addressing these rhythm abnormalities in symptomatic patients, but they are
limited by long-term toxicity and poor efficacy.
Ebstein's
anomaly  Ebstein's anomaly encompasses a wide
spectrum of maldevelopment of the tricuspid valve, massive right atrial
dilation and underdeveloped right ventricular function. Accessory pathways are
present in at least one-fifth of patients with Ebstein's anomaly, almost always
right-sided (or concordant with the side of Ebstein valve in case of
transposition) and not infrequently multiple. Catheter ablation is highly
effective in eliminating these accessory pathways and should be considered as
first-line therapy. Atrial arrhythmias are especially
common in this group and, importantly, can conduct rapidly to the ventricle via
the accessory pathway, resulting in hemodynamic deterioration, syncope and even
death. In the setting of atrioplasty, maze procedures and prosthetic valves,
these atrial rhythm abnormalities can be complex and frequently require
ablation or anti-arrhythmic drug therapy or both.
Atrial
septal defects ASD is one of the most common
congenital cardiac anomalies and is associated with a high incidence of atrial
arrhythmias that increase in frequency as the patient ages. The later in life
the ASD is repaired, the more likely atrial arrhythmias are to develop. Closure
does not mitigate the development of arrhythmias, and with the advent of
percutaneous ASD closure devices, can in fact complicate management. In
addition, significant thromboembolic complications have been observed in
patients who had ASD closure performed in the third decade or older, affecting
up to a quarter of these patients.  Therefore, anticoagulation should be
mandatory if atrial arrhythmias develop and should be actively sought using
ambulatory monitoring. Intra-atrial reentrant tachycardia circuits around a
patch or suture line frequently underlie the abnormality, and ablative therapy
is often first-line treatment.
Prior
maze procedure Modified Cox-maze operations are a
common, safe and highly effective surgical method of restoring sinus rhythm in
patients with CHD and atrial fibrillation or flutter. These interventions are
most commonly performed at the time of CHD operations and can be unilateral or
bilateral depending on the underlying congenital lesion. Unfortunately,
patients with prior maze procedures can develop breakthrough atrial
tachyarrhythmias at points of incomplete atrial block. This development is
substantially less common with traditional cut-and-sew maze procedures than
with open surgical radiofrequency or cryotherapy approaches. The maze procedure is not free of
complications; the extensive transmural lesions not only potentially interfere
with sinus and intra-atrial conduction but also likely disrupt atrial
innervation. Sinus node dysfunction, atrial bradyarrhythmias and
tachyarrhythmias, and chronotropic incompetence are not uncommon sequelae, and
pacemaker implantation is frequently necessary. New postmaze atrial tachyarrhythmias
can develop around and through the incomplete maze lesions, and ablation of
intra-atrial reentrant tachycardia in this setting is frequently undertaken.
Anti-arrhythmic drug therapy is also relied on in this context, and atrial
anti-tachycardia pacemakers can be of added utility in this particular type of
atrial arrhythmia.
Management It is critical for clinicians to
recognize that patients with congenital defects (and repairs) have not been
included in any of the large atrial fibrillation trials such as the Atrial
Fibrillation Follow-Up Investigation of Rhythm Management (AFFIRM) and How to
Treat Chronic Atrial Fibrillation (HOT CAFE) rate-versus-rhythm studies, any of
the anticoagulation trials evaluating risk stratification schemes such as
CHADS2, or efficacy trials involving novel anticoagulation agents. Each patient
therefore needs to be carefully evaluated and treated on an individual basis at
a center specialized in adult CHD. "Importantly, for any atrial
tachyarrhythmia that is associated with hemodynamic instability, synchronized
direct current cardioversion should be utilized without delay," says Dr.
McLeod. Anti-arrhythmic drugs remain a
cornerstone in the management of atrial arrhythmias in CHD patients; however,
most anti-arrhythmic drugs should not be routinely used in this patient group
because of the risks of proarrhythmia. Important differences in management are
highlighted as follows:
Ablation Radiofrequency catheter ablation is
now utilized early in the course of many adult patients with atrial
tachyarrhythmias, particularly for atrial arrhythmias. Radiofrequency catheter
ablation in these patients can be challenging and should be referred to
experienced centers. Although early success rates are excellent even in the
most complex defects, long-term recurrence rates remain suboptimal, especially
when multiple circuits coexist and atrial scars are abundant. The reentrant
circuit can often be modified sufficiently to reduce symptomatic recurrence and
improve anti-arrhythmic drug therapy or pacing efficacy.
Device
therapy Similar to acquired heart disease,
symptomatic bradyarrhythmias require permanent pacing, but knowledge of
intracardiac and vena caval anatomy is critical. To avoid thromboembolic
complications, epicardial pacemaker placement is mandatory if a residual
intracardiac shunt exists. Coronary sinus lead placement can also be utilized
in selective cases where the tricuspid valve cannot be crossed, and atrial
anti-tachycardia devices are typically reserved for patients who also present
with bradycardia. ICD implantation is frequently appropriate, and the newer
subcutaneous ICD systems provide a useful alternative in selected groups.
Anticoagulation
therapy Anticoagulation therapy should be
considered in CHD patients as soon as an atrial rhythm disturbance is
identified. Patients with Fontan circulations or reduced ventricular function
have low flow states in the heart and are at high risk of thrombus formation
within the atria. Patients with repaired ASD also appear to be at considerable
risk of thromboembolic complications in the setting of atrial arrhythmias,
accounting for about one-fifth of late deaths in one series.
"The use of conventional
thromboembolic risk-assessment scores, such as CHADS2, has not been evaluated
in these patient groups and likely is inappropriate," says Dr. McLeod. The
newer oral anticoagulant agents such as dabigatran, rivaroxaban, and apixaban
also have not been specifically studied in CHD patients.
Summary Atrial and ventricular arrhythmias
are a major cause of late morbidity and mortality in this group of patients and
should be managed at a specialized center. The Center for Congenital Heart
Disease and the Heart Rhythm Clinic at Mayo Clinic in Rochester continue to be
at the forefront in the multidisciplinary management of these complex patients
who typically require multimodality strategies involving anti-arrhythmic drugs,
detailed electrophysiological studies, radiofrequency catheter ablation and
device therapy.  |
Categories: Clinical Update
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