| Philip J Podrid, MD |
Jan 4, 2000 |
Conduction from the atria to the ventricles normally occurs via the atrioventricular node (AV)-His-Purkinje system. Patients with a preexcitation syndrome have an additional or alternative pathway, known as an accessory pathway, which directly connects the atria and ventricles and bypasses the AV node. In the Wolff-Parkinson-White (WPW) syndrome, AV conduction is through an AV bypass tract (the bundle of Kent). This results in earlier activation (preexcitation) of the ventricles than if the impulse had traveled through the AV node.
Symptoms associated with the WPW syndrome are a result of arrhythmia with a rapid heart rate due, for example, to preexcited atrial fibrillation or atrial flutter with a rapid ventricular response. Symptoms range from mild palpitations to syncope and even sudden cardiac death due to ventricular fibrillation. Fortunately, the incidence of sudden death in patients with the WPW syndrome is quite low, ranging from 0 to 0.39 percent annually in several large case series, with the lowest risk seen in asymptomatic patients. (See "Tachyarrhythmias associated with the Wolff-Parkinson-White syndrome", section on Ventricular fibrillation and sudden death).
Patients with the WPW syndrome are treated because of symptomatic arrhythmia or the risk of a life-threatening arrhythmia. Asymptomatic patients with the WPW electrocardiographic pattern are not treated. In one review of 29 such patients underwent repeat electrophysiologic study at least three years after the initial study [1]. Only two patients developed a symptomatic arrhythmia (both supraventricular tachycardia) during follow-up and, in nine patients (31 percent), antegrade conduction via the accessory pathway spontaneously disappeared. (See "Electrocardiographic features and course of the Wolff-Parkinson-White pattern").
This card will review the nonpharmacologic therapies, including antitachycardia devices and surgical and catheter ablation, that are available. The latter can cure the underlying problem by ablating the accessory pathway that is responsible for preexcitation. Pharmacologic therapies are discussed separately. In some patients, a combinations of these therapies is necessary. (See "Pharmacologic therapy of arrhythmias associated with the Wolff-Parkinson-White syndrome").
ANTITACHYCARDIA THERAPY ！ Antitachycardia therapy includes the use of external DC cardioverters, temporary pacemakers, and permanently implanted antitachycardia pacemakers that can be manually or automatically activated. Cardioversion and temporary pacemakers are used for the acute termination of arrhythmias. In comparison, the role of permanent pacemakers is limited, especially since the advent of radiofrequency ablation.
Electric cardioversion ！ External DC cardioversion may be emergently necessary for any arrhythmia associated with the WPW syndrome (eg, atrioventricular reentrant tachycardia, atrial fibrillation, or atrial flutter) when the patient is hemodynamically unstable or initially prescribed therapy is either ineffective or leads to abrupt worsening of the patient's condition. (See "Cardioversion for specific arrhythmias").
Temporary pacemaker termination ！ Atrioventricular reentrant tachycardia (AVRT) can often be easily terminated with a pacemaker because the entire heart is involved in a reentrant circuit. (See "Electrophysiologic evaluation of arrhythmias associated with the Wolff-Parkinson-White syndrome"). Thus, temporary pacemaker stimulation of the right atrium or ventricle or transesophageal pacing are alternatives to electric cardioversion if an AVRT episode persists following initial attempts to terminate it with an intravenous antiarrhythmic drug [2]. This approach assumes that the patient's hemodynamic state permits time to insert a transvenous pacing catheter.
Once concern with temporary pacing is the risk of inadvertently inducing preexcited AF with a rapid ventricular response. This is most likely to occur if multiple atrial extrastimuli are delivered at close coupling intervals or if the atrium is paced at rates in excess of 250 beats/min [3,4]. The risk may be reduced by the prior administration of intravenous procainamide to slow the tachycardia rate and lengthen bypass tract refractoriness [5].
Type I atrial flutter that is conducted with preexcitation can also be pace-terminated after pretreatment with an antiarrhythmic drug to protect the ventricles from 1:1 AV conduction and to decrease the atrial flutter rate [2,6]. Pacemaker stimulation is not effective for termination of atrial fibrillation.
Permanent pacemaker therapy ！ Similar to the use of temporary pacemakers for acute termination of arrhythmia, a permanently implanted antitachycardia pacemaker may be of use in some patients with frequent episodes of AVRT (show table 1) [7]. There are, however, major concerns with this approach which, as noted above, has primarily been replaced by ablative therapy.
• Pacemaker therapy is contraindicated in patients with the WPW syndrome who have preexcitation due to accessory pathways with short antegrade refractory periods. In this setting, a rapid ventricular rate can occur if AF, a potential complication of antitachycardia pacing, were inadvertently precipitated during automatic antitachycardia pacing.
• Antitachycardia pacemakers do not prevent AVRT and frequently have relatively poor long-term efficacy [8].
• Permanent antitachycardia pacing is uncomfortable for patients who experience severe symptoms during their tachycardia episodes, especially if the episodes occur frequently and/or require multiple pacing attempts before termination finally occurs.
ABLATIVE THERAPY ！ Ablative therapy, either surgical or with a catheter using radiofrequency energy, offers a cure for patients with symptomatic WPW by ablating the accessory pathway responsible for the arrhythmias. Although both techniques are highly effective, radiofrequency ablation has largely replaced the surgical approach.
Surgical ablation ！ Prior to the advent of radiofrequency energy catheter-mediated ablation, surgical ablation of AV bypass tracts was the standard technique in patients suffering from drug-refractory WPW syndrome. The long-term success rate for WPW surgery is now almost 100 percent with an operative mortality rate of less than 1 percent [9,10,11].
Radiofrequency ablation ！ The success rate with radiofrequency energy catheter-mediated ablation rivals that of surgery, with a comparable or lower mortality and a lower acute morbidity. Several series have reported success rates of 90 to 95 percent, depending upon the location of the accessory pathway and the precision of accessory pathway localization as determined by catheter mapping techniques (show figure 1 and show figure 2A-2B) [12,13,14,15,16,17,18,19].
A new nonfluoroscopic catheter-based electroanatomic mapping system, CARTO,
has a magnetic field emitter and sensor and can create a replica of the
anatomy of the cardiac chamber in which the tachycardia focus is located,
permitting more precise localization of the arrhythmia focus (show
figure 3) [20,21].
Electroanatomic mapping images also allow identification of areas of interest
around an arrhythmia focus. (See
"Pathophysiology and mapping of accessory pathways in the preexcitation
syndrome").
In one report of 250 patients, 88 percent had all accessory pathways ablated
during the initial procedure and 94 percent had all accessory pathways ablated
and were free of tachycardia at a mean 10 month follow-up [17].
In a second study of 519 patients, pathway conduction was abolished in 92
percent of patients, although in 5.6 percent one or two additional attempts
were required [22].
Among the successfully treated patients, 85 percent were asymptomatic after a
mean follow-up of 22 months; however, 17 percent required antiarrhythmic
drugs, primarily a beta blocker or sotalol,
because of symptoms suggesting an arrhythmia.
Ablation of multiple pathways, which may be found in as many as 13 percent of
patients with WPW, requires a longer procedure time and greater amount of
radiation exposure compared to single pathway ablation [17,23,24].
However, the success rate is identical in both groups.
Ablation is a preferred treatment for permanent or incessant junctional
reciprocating tachycardia since this arrhythmia is often drug refractory [25,26].
As an example, one study of 36 patients found that eight had a recurrence
after a mean of 1.2 months and required one to three additional ablation
procedures; however after a mean follow-up of 21 months, 94 percent remained
asymptomatic [25].
A tachycardia-mediated cardiomyopathy was present in seven patients (mean left
ventricular ejection fraction 28 percent); all these patients had an
improvement in left ventricular ejection fraction after ablation (mean of 51
percent).
A compelling argument has been made for the cost-effectiveness of
radiofrequency ablation compared with prolonged periods of unsuccessful
therapy with multiple antiarrhythmic drugs. This is especially true in
patients with a history of a cardiac arrest or those with symptomatic AVRT or
atrial fibrillation [14,27].
Complications ！ The nonfatal
complication rate from radiofrequency ablation is about 4 percent [17].
The use of transseptal catheterization for ablating left sided accessory
pathways can acutely cause an intraatrial shunt in up to 50 percent of
patients; however, there are usually no adverse sequelae [28]
and in one transesophageal echocardiographic study no interatrial shunts
persisted after three weeks [29].
Serious complications, such as cardiac tamponade due to myocardial perforation
or coronary artery spasm with or without myocardial infarction, are rare.
There are case reports of complete heart block as a result of ablation of a
left posteroseptal accessory pathway [30,31].
The mortality rate is well under 1 percent.
An inappropriate sinus tachycardia may be present in some patients after
ablation of a posteroseptal accessory pathway, suggesting disruption of the
parasympathetic and/or sympathetic inputs into the sinus and AV nodes [32,33,34]
Conduction block over an anatomical structure may occur as a result of
catheter manipulation, ie, catheter-induced trauma. This complication, which
has been observed with radiofrequency ablation of the atrioventricular node
and bundle branches, also occurs with ablation of accessory pathways. One
study of 381 patients observed that this complication occurred in 9.7 percent
of patients undergoing radiofrequency ablation of an accessory pathway; the
incidence of trauma was especially high for ablation of either a right
anteroseptal (38.5 percent) or right atriofascicular pathway (33.3 percent),
possibly because of the superficial subendocardial location of these pathways
[35].
Persistent trauma-induced conduction block resulting in discontinuation of the
procedure occurred in 24 percent of patients; immediate application of
radiofrequency energy (< one minute after occurrence) was associated with
long-term success in 78 percent while the success was only 25 percent when
pulses were delivered 30 minutes after the development of block. (See
"Catheter ablation of cardiac arrhythmias: Overview and technical
aspects", section on complications).
As a cautionary counterpoint, appropriate concerns have been raised about the
mutagenic and carcinogenic risks to patients and personnel resulting from the
often lengthy fluoroscopic exposure times required for successful completion
of the procedure [36].
In addition, the long-term risk of future arrhythmias resulting from lesions
created during radiofrequency ablation of AV bypass tracts is unknown. Animal
studies and the accumulated clinical experience suggest that this risk is low.
Arrhythmia recurrence ！
Recurrence, as manifested by return of delta waves on the electrocardiogram or
spontaneous paroxysmal supraventricular tachycardia, has been reported in 6 to
12 percent of patients [12,13,24,37].
The recurrence rate is higher with ablation of multiple pathways or right or
left free wall or septal accessory pathways [19,24,37].
Approximately one-half of recurrences occur in the first twelve hours after
the procedure [37].
Intravenous adenosine,
administered immediately after the ablation procedure, unmasks residual
accessory pathways by creating transient AV nodal blockade; it may therefore
identify patients who are likely to experience arrhythmia recurrence [38].
Repeat ablation usually leads to permanent cure in patients who recur [37].
RECOMMENDATION ！ We use the following
approach in patients with symptomatic arrhythmias due to the WPW syndrome:
• Therapy is indicated for all patients who
experience symptomatic arrhythmias, regardless of the etiology. Therapy is
particularly important for patients with rapid conduction over the accessory
pathway during atrial fibrillation or atrial flutter.
The treatment of choice for these patients is radiofrequency catheter ablation
of the accessory pathway. Although surgical ablation is only infrequently
performed, it may be indicated in good surgical risk patients suffering from
highly symptomatic and hemodynamically unstable, drug-refractory arrhythmias
in whom radiofrequency energy catheter ablation has failed at centers with a
proven track record of success in performing the procedure [39].
Patients with symptomatic arrhythmia who undergo cardiac surgery for other
indications may be candidates for having concomitant bypass tract resection
performed if the added surgical trauma and cardiopulmonary bypass time is not
likely to substantially increase the operative mortality risk [40,41].
• Patients who experience only infrequent and
minimally symptomatic OAVRT may consider "cocktail" pharmacologic
treatment: large single-dose pharmacologic therapy, taken when needed for an
arrhythmic event, along with properly taught self-performed vagomimetic
maneuvers to assist in terminating arrhythmia episodes. Drugs that can be
administered in this fashion include quinidine
(600 mg), disopyramide
(300 mg), procainamide
(1500 mg), and propafenone
(450 mg). However, these patients should first undergo an electrophysiologic
study to assure that the antegrade conduction properties of the accessory
pathway are not potentially malignant; performing atrial pacing using a
transesophageal electrode might offer a less invasive method for performing
this assessment.
• Patients whose life expectancy is severely
limited by other diseases and/or who are elderly are probably best treated
with chronic pharmacologic therapy, particularly amiodarone,
guided by electrophysiologic testing. However, relatively healthy elderly
patients should not be denied radiofrequency energy catheter ablation therapy
because of their age alone if they experience highly symptomatic arrhythmia
that responds poorly to medical treatment.
• Asymptomatic patients are likely to remain
asymptomatic and conduction via the accessory pathway may disappear
spontaneously in a substantial proportion of patients [1].
(See
"Electrocardiographic features and course of the Wolff-Parkinson-White
pattern", section on Prevalence and course). A cost-effectiveness
analysis of radiofrequency ablation supported the practice of observing
asymptomatic patients [27].
Nevertheless, electrophysiologic evaluation and radiofrequency ablation is
advisable for certain patients who have an accessory pathway with a very short
refractory period because of the potential for rapid ventricular rates during
atrial fibrillation or atrial flutter. Included in this group are patients in
high-risk professions, professions involving risk to others, athletes, and
those with a family history of sudden death [42].