eMedicine Specialties > Cardiology > Arrhythmias

Wolff-Parkinson-White Syndrome: Differential Diagnoses & Workup

Author: Vibhuti N Singh, MD, MPH, FACC, FSCAI, Director, Suncoast Cardiovascular Center; Chair, Cardiology Division and Cath Labs, Department of Medicine, Bayfront Medical Center; Clinical Assistant Professor, Division of Cardiology, University of South Florida College of Medicine
Coauthor(s): Rakesh K Sharma, MD, FACC, Adjunct Associate Professor of Medicine and Cardiology; University of Arkansas for Medical Sciences, Medical Center of South Arkansas
Contributor Information and Disclosures

Updated: Aug 24, 2009

Differential Diagnoses

Atrioventricular Nodal Reentry Tachycardia (AVNRT)
Ebstein Anomaly
Lown-Ganong-Levine Syndrome
Syncope

Other Problems to Be Considered

In Lown-Ganong-Levine (LGL) syndrome, patients have a short PR interval and SVT, but no delta wave.

Mahaim fibers connect the atria to the right bundle or the AV node to the ventricle. Such bypass tracts are called atriofascicular. If atriofascicular fibers are present, the ECG findings are a normal or short PR interval and the QRS complex is abnormally wide with a left-bundle appearance. These fibers have decremental conduction properties and can perpetuate clinically significant tachycardias or act as innocent bystanders for other types of tachycardias (eg, AVNRT).

Sometimes, the fibers arise in the His bundle or bundle branches and insert into the ventricular myocardium. These are called fasciculoventricular tracts and, generally, are not involved in tachycardias.

Differential diagnosis of accessory pathway syndromes using EP studies

In patients with LGL syndrome who have an atriohisian tract, the QRS complex remains normal and the short atriohisian interval remains fixed during atrial pacing at rapid rates.

Patients with fasciculoventricular connections show a short His-ventricle (HV) interval and no change in the QRS complex during rapid atrial pacing.

Atriofascicular tract pathways usually represent a duplication of the AV node and the distal conducting system. They occupy the right ventricular free wall. Their proximal end resides adjacent to the lateral tricuspid annulus and exhibits slow conduction, with AV nodelike characteristics. The distal end, which conducts rapidly, inserts into the distal right bundle branch or the apical region of the right ventricle. Preexcitation may not be apparent during sinus rhythm but can be demonstrated with premature right atrial stimulation. Because retrograde conduction is absent, only an antidromic AV reentry tachycardia (ie, preexcited tachycardia) can develop.

Furthermore, concerning atriofascicular tracts, preexcited tachycardia has a left bundle-branch block pattern, long AV interval (due to the long conduction time over the accessory pathway), and short VA interval. If RBBB develops, it can become, by increasing the length of the tachycardia circuit (ie, VA interval prolongs owing to delay in retrograde activation of the His bundle), proarrhythmic and the tachycardia can become perpetual and persistent.

Patients with PSVT usually have narrow QRS complexes. The QRS may become wider owing to aberrant conduction, coexisting bundle-branch block, or involvement of an accessory pathway.

Other forms of tachycardia in patients with WPW syndrome

Patients with WPW syndrome can have other tachycardias where the accessory pathway is just a bystander, such as AVNRT or an atrial tachycardia that conducts to the ventricle over the bypass tract.

Atrial flutter or fibrillation may also occur in the atrium, unrelated to the bypass tract.

Patients with WPW syndrome who have atrial fibrillation frequently have inducible reciprocating tachycardias. Interruption of the accessory pathway with ablation may or may not prevent recurrence of the atrial fibrillation.

Atrial fibrillation presents a potentially serious risk. At rapid rates, the refractory period of the accessory pathway can shorten, allowing an exceedingly rapid ventricular response. However, such a phenomenon is uncommon, occurring at an estimated frequency of less than 0.1%.

Patients who have intermittent preexcitation or those who lose ECG evidence of preexcitation with exercise or when injected intravenously with procainamide generally have a long refractory period of the bypass tract. These patients are thought to have a low risk of developing a rapid ventricular rate should atrial flutter or fibrillation develop.

Workup

Laboratory Studies

Routine blood studies may be needed to help rule out noncardiac conditions triggering tachycardia. These may include the following:

• Complete blood cell count
• Chemistry panel
  • Blood urea nitrogen and creatinine to assess renal status
  • Liver function tests (eg, bilirubin and transaminase levels)
• Thyroid panel
• Blood levels of antiarrhythmic medications during therapy and monitoring

Imaging Studies

Echocardiogram is needed to evaluate left ventricular function and wall motion abnormalities and to help rule out valvular disease, Ebstein anomaly, hypertrophic cardiomyopathy (in which the incidence of accessory pathways is increased), or other congenital cardiac defects.

Other Tests

• The diagnosis and management of any cardiac arrhythmia can be accomplished by using findings from ECG and rhythm strip analysis and their relationship to the clinical setting. Recognizing arrhythmias on ECG findings requires a detailed knowledge of atrial and ventricular activation patterns and deductions related to the mechanisms of AV conduction.
• The standard 12-lead ECG and cardiac rhythm strips form a direct resource for analyzing abnormalities of the cardiac rhythm. For many simple arrhythmias, mere recognition of P-wave and QRS morphologies, with their relative timing and their vectors, may be sufficient to confirm a diagnosis.
• The location of the accessory pathway using ECG can often be determined by a thorough analysis of the spatial direction of the delta wave in the 12-lead ECG findings by reviewing the maximally preexcited QRS complexes.
  
  

  

  A 12-lead ECG showing short PR interval and delta waves consistent with the presence of an accessory pathway.

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  A 12-lead ECG showing short PR interval and delta waves consistent with the presence of an accessory pathway.

• Special ECG leads
  • When the standard ECG fails to provide adequate information to support a diagnosis, often because of a failure to recognize P waves, certain additional special lead systems can be used to help establish the diagnosis.
  • A bipolar esophageal lead is used to record left atrial activity, while an intra-atrial electrode during catheterization can be used to record atrial activity from within the right atrium.
• Continuous ECG recordings (ie, telemetry, 24-hour Holter monitor, event monitor, implantable loop recorder)
  • Continuous monitoring of cardiac rhythm can be performed on hospitalized patients in the coronary or the progressive care units with telemetry.
  • In the outpatient setting, a number of portable recording devices (eg, Holter monitors, event monitors) can be used.
  • Portable recording systems provide simultaneous 2-lead recording that improves the diagnostic yield tremendously. The 2 most commonly used leads for monitoring are lead II and MCL-I, the latter being similar to V₁. These devices have long-term storage capabilities that permit off-line analysis of complex arrhythmias, even if the physician is not available at the time the rhythm disturbance occurs.
  • For infrequently occurring arrhythmias, a number of event recorders are available. They allow the patient to activate the device by pressing a button when an event occurs, providing internal storage and transmission by telephone or wireless communication to a central station for later review.
  • Transtelephonic transmitters can be used in real time for somewhat more persistent or frequent events.
  • A small loop recorder can be implanted similar to a pacemaker and can be removed later for analysis. This can be used in patients with arrhythmias that are difficult to capture.
• ECG recognition of reentry over a retrograde (concealed) accessory pathway
  • A bypass tract that conducts unidirectionally only from the ventricle to the atrium is not detectable on the regular surface ECG findings because the ventricle is not preexcited; thus, the ECG manifestations of WPW syndrome are absent.
  • Such a bypass tract is described as concealed.
  • Tachycardia due to the concealed tract should be considered when the QRS complex is normal and the retrograde P wave occurs well after completion of the QRS complex, out in the ST segment or even in the T wave.
• Diagnosis of accessory pathways
  • During ventricular pacing, premature ventricular stimulation activates the atria before retrograde depolarization of the His bundle. This indicates that the impulse reached the atria before it depolarized the His bundle and must have traveled a different pathway (bypass tract).
  • If the ventricles can be stimulated prematurely during tachycardia at a time when the His bundle is refractory and the impulse still conducts to the atrium, this indicates that retrograde propagation traveled to the atrium over a pathway other than the bundle of His.
  • If the premature ventricular complex depolarizes the atria without lengthening of the VA interval and with the same retrograde atrial activation sequence, the stimulation site (ie, ventricle) may be assumed to be within the reentrant circuit without intervening His-Purkinje or AV nodal tissue that might increase the VA interval and therefore the AA interval.
  • In addition, if a premature ventricular complex delivered at a time when the His bundle is refractory terminates the tachycardia without retrograde activation of the atria, it most likely invaded, and blocked in, an accessory pathway.
  • The VA interval (a measurement of conduction over the accessory pathway) is generally constant over a wide range of ventricular paced rates and coupling intervals of premature ventricular complexes and during the tachycardia in the absence of aberration. Similar short VA intervals can be observed in some patients during AV nodal reentry, but if the VA conduction time or R-P interval is the same during tachycardia and ventricular pacing at comparable rates, an accessory pathway is almost certainly present. The VA interval is usually less than 50% of the R-R interval.
  • Tachycardia can be initiated easily following premature ventricular stimulation that conducts in retrograde fashion in the accessory pathway but blocks in the AV node or His bundle. Atria and ventricles are required components of the macroreentrant circuit; therefore, continuation of the tachycardia in the presence of AV or VA block excludes an accessory AV pathway as part of the reentrant circuit.
• Stress testing
  • This is an ancillary test and may be used to (1) reproduce a transient paroxysmal arrhythmia, (2) document the relationship of exercise to the onset of tachycardia, (3) evaluate the efficacy of therapy, and (4) assess adverse responses.
  • A bicycle ergometer or standard treadmill can be used.
  • Thallium or echocardiographic imaging is not necessary unless an ischemic etiology is considered as a potential cause or trigger of the onset of arrhythmia.
  • Stress testing may also provide some general insight into the refractory periods of accessory pathways in patients with WPW syndrome but is unreliable because exercise also alters the competing conduction properties of the AV node.

Procedures

• Intracardiac EP studies
  • EP studies are performed in a cardiac electrophysiology laboratory. Using multicatheter electrode systems, recordings from many intracardiac sites can be performed simultaneously, facilitating delineation of the sequence of depolarization and impulse conduction in the atria, AV junction, and ventricle.¹
  • EP studies can be used in patients with WPW syndrome to determine the following:
    • The mechanism of the clinical arrhythmia
    • EP properties (eg, conduction capability, refractory periods) of the accessory pathway and the normal conduction system
    • The number and locations of accessory pathways (which is necessary for catheter ablation)
    • The response to pharmacologic or ablation therapy
• Indications for EP studies in patients with WPW syndrome according to the American College of Cardiology/American Heart Association guidelines
  • Class I indications include the following:
    • Patients being evaluated for catheter ablation or surgical ablation of an accessory pathway
    • Patients with ventricular preexcitation who have survived cardiac arrest or who have unexplained syncope
    • Symptomatic patients in whom determination of the mechanism of arrhythmia or knowledge of the EP properties of the accessory pathway and normal conduction system would help in determining appropriate therapy
  • Class II indications include the following:
    • Asymptomatic patients with a family history of sudden cardiac death or with ventricular preexcitation but no spontaneous arrhythmia who engage in high-risk occupations or activities and in whom knowledge of the EP properties of the accessory pathway or inducible tachycardia may help determine recommendations for further activities or therapy
    • Patients with ventricular preexcitation who are undergoing cardiac surgery for other reasons
  • Class III indications include asymptomatic patients with ventricular preexcitation, except those in class II.
• EP features of preexcitation
  • If a Kent bundle (AV)–type accessory bypass tract conducts in an antegrade fashion, 2 parallel paths can potentially carry the impulse. The first is the natural one, which comes with inherent physiological delay over the AV node. The second is the bypass tract (Kent bundle), which allows the impulse to pass directly without delay from the atrium to the ventricle.
  • This dual-path mechanism produces a unique QRS complex that is a form of fusion beat due to depolarization of the ventricle from these 2 pathways.
  • The delta wave results from ventricular activation by the impulse traveling over the accessory pathway.
  • The extent of contribution to ventricular depolarization by the wavefront over each route varies, as follows:
    • If delay in AV nodal conduction occurs from either rapid atrial pacing or a premature atrial complex, a greater proportion of the ventricle activates via the bypass tract and the QRS becomes more abnormal in shape.
    • On the other hand, if the bypass tract is far from the sinus node (as in the presence of a left lateral pathway) or if AV nodal conduction is rapid, a larger proportion of the ventricle activates via the normal pathway.
    • The normal fusion beat during sinus rhythm has a short or negative HV interval. This occurs because the His bundle activation begins later than the ventricular activation from the bypassing impulse, while the impulse traveling over the AV node just reaches the His bundle. Pacing the atrium rapidly at premature intervals accentuates the abnormal ventricular depolarization and further shortens the HV interval.
• Recognition and localization of accessory pathways using EP studies
  • When retrograde atrial activation during tachycardia occurs over an accessory pathway that connects the left atrium to the left ventricle, the earliest retrograde activity is recorded from a left atrial electrode (usually positioned in the coronary sinus). This is a left lateral pathway.
  • When retrograde atrial activation during tachycardia occurs over an accessory pathway that connects the right ventricle to the right atrium, the earliest retrograde atrial activity is generally recorded from a lateral right atrial electrode. This is a right ventricular free wall pathway.
  • Participation of a septal accessory pathway creates earliest retrograde atrial activation in the low-right atrium situated near the septum, anterior or posterior, depending on the insertion site.
  • Mapping procedures with intravenous catheter electrodes placed at the time of surgery may help provide accurate assessments of the position of the accessory pathway. Recording electrical activity directly from the accessory pathway obviously provides the most precise localization, but the proxy of atrial and ventricular fusion together with earliest conduction in the target chamber provides an alternative. In some pathways, conduction can be slow enough that atrial and ventricular fusion is never observed, reflecting electrically silent conduction delay in the accessory connection.
• Retrograde atrial activation over the accessory pathway on EP studies
  • This can be confirmed by inducing premature ventricular complexes during tachycardia to determine whether retrograde atrial excitation can occur from the ventricle at a time when the His bundle is refractory.
  • Because VA conduction cannot occur over the normal conduction system because the His bundle is refractory, an accessory pathway must be present for the atria to become excited and most likely is participating in the tachycardia circuit.
  • The following parameters may be helpful:
    • Patients with a reciprocating tachycardia due to an accessory AV bypass tract almost always have a VA interval of greater than 70 milliseconds measured from the onset of ventricular activation to the onset of atrial activity recorded on an esophageal lead or greater than 95 milliseconds when measured to the high-right atrium.
    • In contrast, in most patients with AVNRT, the interval from the onset of ventricular activity to the earliest onset of atrial activity is characteristically shorter than 70 milliseconds.
• Intraoperative (multiarray) epicardial mapping and endocardial catheter mapping using EP studies
  • Mapping of the pathways and sites of origin for both ventricular and supraventricular tachyarrhythmias has led to tremendous improvements in surgical outcomes, which has given way to catheter techniques for ablation procedures.⁴
  • Multiple electrode arrays allow simultaneous recordings from several intracardiac sites during the same cardiac cycle, generating maps of wave activation. This technology allows the clinical electrophysiologist and surgeon to identify target areas for surgical ablation.
  • Although quite successful in prior years, intraoperative mapping for WPW syndrome has now been replaced by catheter mapping during EP studies and ablation procedures.

Histologic Findings

Histologic findings of accessory bypass pathways have been described with careful dissection of the AV space.

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