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Emergency Medicine > CARDIOVASCULAR
Wolff-Parkinson-White Syndrome
Article Last Updated: Jun 14, 2006
AUTHOR AND EDITOR INFORMATION
Section 1 of 10  
Author: Thomas J Hemingway, MD, Staff Physician, Department of Emergency Medicine, University of California at Los Angeles/Olive View
Thomas J Hemingway is a member of the following medical societies: American College of Emergency Physicians and Emergency Medicine Residents Association
Coauthor(s):
Eric Alexander Savitsky, MD, Associate Clinical Professor of Medicine, Department of Medicine, Division of Emergency Medicine, University of California at Los Angeles Medical Center;
Mel Herbert, MD, MBBS, Assistant Professor of Medicine and Nursing, Department of Emergency Medicine, Olive View-University of California at Los Angeles Medical Center;
Griffith Tully, MD, Staff Physician, Department of Emergency Medicine, University of California at Los Angeles Medical Center
Editors: Theodore J Gaeta, DO, MPH, FACEP, Clinical Associate Professor, Department of Emergency Medicine, Joan and Sanford Weill Medical College at Cornell University; Vice Chairman and Program Director of Emergency Medicine Residency Program, Department of Emergency Medicine, New York Methodist Hospital; Academic Chair, Adjunct Professor, Department of Emergency Medicine, St George's University School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Gary Setnik, MD, Chair, Department of Emergency Medicine, Mount Auburn Hospital; Assistant Professor, Division of Emergency Medicine, Harvard Medical School; John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center; Charles V Pollack, Jr, MD, MA, FACEP, Professor, Department of Emergency Medicine, University of Pennsylvania College of Medicine; Chairman, Department of Emergency Medicine, Pennsylvania Hospital
Author and Editor Disclosure
Synonyms and related keywords:
Wolff-Parkinson-White syndrome, preexcitation syndrome, atrioventricular reentrant tachycardia, AVRT, AVNRT, atrioventricular nodal reentrant tachycardia, AV nodal reentrant tachycardia, WPW syndrome, paroxysmal supraventricular tachycardia, PSVT, supraventricular tachycardia, SVT, heart disease
Background
Preexcitation was defined by Durrer et al in 1970 with the following statement, "Preexcitation exists, if in relation to atrial events, the whole or some part of the ventricular muscle is activated earlier by the impulse originating from the atrium than would be expected if the impulse reached the ventricles by way of the normal specific conduction system only." Of the various preexcitation syndromes, the most common is Wolff-Parkinson-White (WPW) syndrome. Emergency physicians should be familiar with this syndrome and the proper treatment of its associated dysrhythmias to minimize morbidity and mortality.
Pathophysiology
Accessory connections between the atrium and ventricle are the result of anomalous embryonic development of myocardial tissue bridging the fibrous tissues that separate the two chambers. This allows for electrical conduction between the atria and ventricles at sites other than the atrioventricular node (AVN). Passage through this accessory pathway circumvents the usual conduction delay between the atria and ventricles, which normally occurs at the AVN and predisposes the patient to develop tachydysrhythmias. Although dozens of locations for bypass tracts can exist in preexcitation, including atriofascicular, fasciculoventricular, intranodal, or nodoventricular, the most common bypass tract is an accessory atrioventricular (AV) pathway otherwise known as a Kent bundle. This is the anomaly seen in WPW syndrome. Conduction through a Kent bundle can be anterograde, retrograde, or both. Another common preexcitation syndrome, Lown-Ganong-Levine (LGL), also has an accessory pathway (the James fibers), whichconnect
the atria serially to the His bundle. The end result is the same, preexcitation and a predisposition to the development of tachydysrhythmias. Fortunately, the treatment of LGL parallels that of WPW, and they are discussed together.
Frequency
International
WPW syndrome affects approximately 0.15-0.2% of the general population. Of these individuals, 60-70% have no other evidence of heart disease.
Mortality/Morbidity
Death from WPW syndrome occurs secondary to the associated dysrhythmias or from mistreatment of these dysrhythmias with inappropriate medications. Little data are available regarding the mortality rate of such dysrhythmias, but most studies report the incidence of sudden death in the 0-4% range.
Sex
Men (60-70% cases) are affected more often than women. Typically, those affected are young, otherwise healthy individuals.
Age
Although this disease affects people of all ages, it is most commonly recognized in children and young adults presenting to the ED with a dysrhythmia. Conduction speed in the accessory pathway appears to attenuate with age.
History
- Patients may present with anything from mild chest discomfort or palpitations to severe cardiopulmonary compromise or cardiac arrest.
- Occasionally, electrocardiographic evidence of disease is discovered on routine electrocardiography (ECG), independent of a concurrent tachydysrhythmia.
- Patients commonly present with rapid heart rates in the 250 beats per minute (bpm) range, often with associated hypotension.
- Many patients are not aware of their underlying condition.
Physical
WPW has no specific examination features except for those that may accompany symptomatic dysrhythmias.
- Many young patients appear minimally symptomatic (eg, palpitations, weakness, mild dizziness) despite exceedingly fast heart rates.
- On physical examination, the patient may be cool, diaphoretic, and hypotensive.
- Crackles in the lungs are common, as the rapid heart rate may cause pulmonary vascular congestion due congestive heart failure.
Atrial Fibrillation
Atrial Flutter
Ventricular Tachycardia
Other Problems to be Considered
Supraventricular tachycardia
Other Tests
- Electrocardiogram
- The classic ECG morphology of Wolff-Parkinson-White (WPW) syndrome is described as a shortened PR interval and a widened QRS complex with a delta wave. In reality, the ECG morphology varies greatly.
- Depending upon the location of the accessory pathway in relation to the sinus node and the relative transmission characteristics of the accessory pathway and the AV node, the morphology of the ECG may vary from a classic presentation to near normal.
- In some cases, the electrical impulse's arrival at the ventricles occurs slightly earlier through the accessory pathway (by not undergoing the typical slowing through the AVN), creating preexcitation.
- The QRS interval is widened because the ventricles are initially activated via the accessory pathway, which lies outside the normal conducting system, producing an early, albeit relatively slow initial propagation of depolarization forces through the ventricular tissue. This produces the delta wave. The delta wave makes the QRS appear wider than expected and the PR interval somewhat shortened. This is known as a revealed accessory pathway because it is easily identifiable on ECG.
- WPW syndrome has been described by some as either type A or type B, depending on the appearance of the delta wave/QRS complex in the precordial leads. Type A WPW syndrome is described as having an upright positive delta wave in all precordial leads with a resultant R greater than S amplitude in lead V1. Type B has a predominantly negative delta wave and QRS complex in leads V1 and V2 and becomes positive in transition to the lateral leads resembling that of a left bundle-branch block (LBBB).
- LGL has a shortened PR interval due to the presence of the accessory pathway bypassing the AVN, but a normal QRS because the accessory pathway (James fibers) connects directly with the His bundle and do not depolarize the ventricles directly but do so through the typical conduction pathway through the His-Purkinje system.
- In other WPW syndrome cases, arrival of the electrical impulse to the ventricle occurs nearly simultaneously through both the accessory pathway and the AV node.
- When this occurs, preexcitation is absent and ECG appears normal.
- Thus, the morphology of the ECG depends directly upon the degree of preexcitation (ie, relative conduction speeds).
- An accessory pathway that does not manifest on ECG is revealed when the rate exceeds the refractory period of the AV node. This has been described as latent accessory pathway.
- A latent accessory pathway can conduct both anterograde and retrograde transmissions.
- An accessory pathway in which only retrograde transmission of impulses can occur is called concealed and is used only during circus movement tachycardias (CMT).
- Although many types of dysrhythmias can occur in a patient with WPW syndrome, the two most common are CMT and atrial fibrillation (AFib). CMT is the more common dysrhythmia of the two.
- A critically timed premature atrial beat that occurs during the refractory period of the accessory pathway typically initiates CMT. The impulse, therefore, travels solely down the AV node but returns retrograde through the accessory pathway, resulting in CMT (orthodromic conduction).
- This circus movement tachycardia pattern is termed orthodromic conduction. It results in a narrow complex heart rhythm limited by the refractory period of the AV node. The QRS interval is narrow because the impulses travel antegrade (orthodromically) through the AV node and regular because circus movement occurs at a regular rate.
- Differential diagnosis of this type of WPW dysrhythmia (orthodromic conduction) includes paroxysmal supraventricular tachycardia (PSVT). Differentiating between the two in an acutely symptomatic patient with a regular rhythm, narrow complex tachycardia is difficult. Cardiac dysrhythmias with rates greater than 220 bpm in adults suggest the dysrhythmia is bypassing the AV node and is suggestive of an accessory pathway or ventricular tachycardia.
- Orthodromic CMTs are 10-15 times more likely than antidromic CMTs.
- Antidromic CMTs are wide and potentially faster because of the relatively short refractory period of most accessory pathways. They are termed antidromic because anterograde transmission occurs down the accessory pathway, creating preexcitation of the ventricle adjacent to it. These dysrhythmias are regular due to the nature of the circus movement.
- The accessory pathways in antidromic CMTs conduct anterograde from the atria to the ventricles and are likely to have the classic delta wave appearance of the QRS on the resting ECG.
- Differential diagnoses include ventricular tachycardia (V tach), which also is regular (unless it is torsade de pointes) or PSVT with aberrancy. Consider any regular wide-complex tachycardia to be V tach until proven otherwise; however, as in regular narrow-complex tachycardias.
- Most cases of regular wide-complex CMT associated with WPW syndrome that are treated with adenosine consequently are converted to sinus rhythm.
- AFib in patients with WPW is very common and has an incidence of 11-38%. It also is the deadliest arrhythmia for these patients because of the possibility of deterioration into ventricular fibrillation (V fib).
- In normal hearts, an individual is protected from exceptionally high ventricular rates by the relatively long refractory period of the AV node. In patients with WPW, however, the accessory pathway often has a much shorter anterograde refractory period, allowing for much faster transmission of impulses and correspondingly higher rates.
- In addition, sympathetic discharge secondary to hypotension may lead to further shortening of the refractory period and subsequent increases in the ventricular rate. If the rate becomes too high, V fib may result.
- Note that AFib through an accessory pathway appears as a bizarre, wide-complex, irregular tachycardia on ECG, with rates often in the 250 bpm range or higher.
Prehospital Care
Therapy in the prehospital setting depends upon the patient's degree of stability and the specific dysrhythmia.
Emergency Department Care
Upon presentation, immediately place an IV line in the patient and connect him or her to cardiac, blood pressure, and pulse oximetry monitors. Administer oxygen if the patient is hypoxic. Immediately perform cardioversion on a patient who is grossly unstable. Otherwise, a defibrillator should be readily available. If a patient is in cardiac arrest, treat according to advanced cardiac life support (ACLS) guidelines. Treat dysrhythmias associated with Wolff-Parkinson-White (WPW) syndrome with caution. Although a therapeutic trial of adenosine had previously been advocated by some for both irregular and regular tachycardias and in some cases to distinguish SVT with aberrancy from ventricular tachycardia, this has fallen out of favor recently because of the possibility of degradation of the rhythm to ventricular fibrillation when used indiscriminately.
- Treatment of AFib associated with WPW is necessarily different than for a patient with a normal heart. AFib is an irregular rhythm as opposed to the regular rhythm seen in CMTs.
- The basic treatment principle in WPW AFib is to prolong the anterograde refractory period of the accessory pathway relative to the AV node. This slows the rate of impulse transmission through the accessory pathway and, thus, the ventricular rate. This is in direct contradistinction to the goal of treatment of non-WPW AFib, which is to slow the refractory period of the AVN.
- If AFib were treated in the conventional manner by drugs that prolong the refractory period of the AV node (eg, calcium channel blockers, beta-blockers, digoxin), the rate of transmission through the accessory pathway likely would increase, with a corresponding increase in ventricular rate. This could have disastrous consequences, possibly causing the arrhythmia to deteriorate into V fib.
- Thus, standard treatments for non-WPW AFib must be avoided and replaced by cardioversion with the possibility of procainamide as a potential medical therapeutic alternative. Patients presenting with Afib in WPW syndrome are typically very tachycardic and often hypotensive with evidence of hypoperfusion, thus given this unstable state, primary synchronized cardioversion should be the first-line treatment.
- If the patient is stable, medical therapy with procainamide may be tried. Procainamide (17 mg/kg IV infusion, not to exceed 50 mg/min; hold for hypotension or 50% QRS widening) blocks the accessory pathway, but it has the added effect of increasing transmission through the AV node. Thus, although procainamide may control the AFib rate through the accessory pathway, it may create a potentially dangerous conventional AFib that may require treatment with other medications and/or cardioversion. Prompt cardioversion of patients with WPW syndrome and AFib may be required for any patient who is deteriorating or failing to improve.
- Medical management may be a viable option in some patients, but it may have unpredictable results. Note that cardioversion is always the treatment of choice in unstable patients. If medical management is recommended it should be under the direction of a cardiologist.
- Treatment of CMTs (regular and generally narrow complex tachycardias) associated with WPW syndrome yields several treatment approaches. Unfortunately, there is a paucity of literature and controlled studies, which makes the chosen treatment less definitively advocated. The two common approaches include cardioversion and the use of adenosine. If adenosine is chosen, all preparations for immediate cardioversion and appropriate resuscitation should be in order in the event of degeneration of the rhythm after adenosine-induced AV nodal blockade
- In a stable patient with a regular narrow complex tachycardia (not known to be a result of WPW syndrome), adenosine (6 mg rapid IV push; if unsuccessful, 12 mg rapid IV push) should be the first-line treatment. (Adenosine is contraindicated in heart transplant patients and should be used with caution in patients with severe obstructive pulmonary disease and in patients with a wide QRS complex, unless the diagnosis of PSVT with aberrancy is certain.) When WPW syndrome is known or highly likely, adenosine should be used with caution and preparation for cardioversion/defibrillation should be immediately available.
- Once the circus movement is broken, the patient usually converts to sinus rhythm. Note that whether the QRS complex is regular or irregular distinguishes CMTs from AFib on ECG.
- If the QRS complex is regular and narrow, the arrhythmia may be treated with adenosine as if it were CMT or PSVT, as long as preparations for cardioversion/defibrillation are immediately available.
- If the QRS complex is irregular, the arrhythmia is likely AFib. In this case, adenosine theoretically could increase the rate and cause clinical deterioration and should not be used.
- Cardioversion, or in some cases, procainamide, are the treatment choices in these situations (ie, irregular QRS complex), providing the necessary rate control.
- If in doubt about the regularity of the rhythm, it is safer to err on the side of treating for AFib in the context of WPW syndrome with direct cardioversion.
Consultations
Consult a cardiologist for patients presenting with WPW dysrhythmias.
The goal of pharmacologic therapy is to break the cyclical transmission of impulses using antiarrhythmics. Drugs such as adenosine and procainamide have proven useful to achieve this goal.
Drug Category: Antiarrhythmic agents
Alter the electrophysiologic mechanisms responsible for arrhythmia.
| Drug Name | Adenosine (Adenocard) |
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| Description | Slows conduction time through the AV node, can interrupt reentry pathways through the AV node, and can restore normal sinus rhythm in PSVT, including PSVT associated with WPW syndrome. |
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| Adult Dose | Initial dose: 6-mg rapid IV bolus over 1-2 seconds
If no response within 1-2 min, administer 12-mg rapid IV bolus
Repeat 12-mg dose a second time prn
Doses >12 mg not recommended |
|---|
| Pediatric Dose | 0.1 mg/kg IV; repeat at 0.2 mg/kg if first dose not effective; not to exceed 12 mg
Alternative: Administer 0.05 mg/kg IV; if not effective within 2 min, increase dose by 0.05 mg/kg increments q2min; not to exceed 0.25 mg/kg |
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| Contraindications | Documented hypersensitivity; second- or third-degree AV block or sick sinus syndrome (except in patients with functioning artificial pacemaker), heart transplant patients, atrial flutter, AFib, and V tach |
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| Interactions | Coadministration with carbamazepine may produce higher degrees of heart block; dipyridamole may potentiate effects; methylxanthines may antagonize effects |
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| Pregnancy | C - Safety for use during pregnancy has not been established.
|
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| Precautions | Bronchoconstriction in patients with asthma may occur |
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| Drug Name | Procainamide (Procanbid, Pronestyl) |
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| Description | Increases refractory period of the atria and ventricles (effectively the bypass tract). Myocardiac excitability is reduced by an increase in the threshold for excitation and inhibition of ectopic pacemaker activity. |
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| Adult Dose | Use continued IV infusion rates of 20 mg/min until arrhythmia is suppressed, the patient becomes hypotensive, the QRS widens 50% above baseline, or a maximum dose of 17 mg/kg is administered; once arrhythmia is suppressed, may be infused at a continuous rate of 1-4 mg/min |
|---|
| Pediatric Dose | 15-50 mg/kg/d PO divided q3-6h; not to exceed 4 g/d
3-6 mg/kg/dose IV infused over 5 min; not to exceed 100 mg/dose; may repeat q5-10min up to 15 mg/kg/load
20-30 mg/kg/d IM divided q4-6h; not to exceed 4 g/d
Maintenance dose: 20-80 mcg/kg/min IV; not to exceed 2 g/d continuous infusion |
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| Contraindications | Documented hypersensitivity; complete heart block or second- or third-degree heart block, if a pacemaker is not in place; torsade de pointes; systemic lupus erythematosus |
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| Interactions | Expect increased levels of procainamide metabolite NAPA in patients taking cimetidine, ranitidine, beta-blockers, amiodarone, trimethoprim, and quinidine; may increase effect of skeletal muscle relaxants, quinidine, and lidocaine and neuromuscular blockers; ofloxacin inhibits tubular secretion of procainamide and may increase bioavailability; when taken concurrently with sparfloxacin, may increase risk of cardiotoxicity |
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| Pregnancy | C - Safety for use during pregnancy has not been established.
|
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| Precautions | Long-term use of this drug leads to development of a positive antinuclear antibody test in a significant number of patients; these effects may significantly increase the incidence of lupus erythematosus?like syndrome in those patients; monitor for hypotension in patients receiving this drug; plasma concentration of procainamide and its active metabolite, NAPA, may be increased in renal failure; high or toxic concentrations may induce AV block or abnormal automaticity; caution in complete AV block, digitalis intoxication, bone marrow suppression, organic heart disease, renal disease, and hepatic insufficiency |
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Further Inpatient Care
- Arrange consultation with a cardiologist for patients admitted with Wolff-Parkinson-White (WPW) syndrome because these patients are at high risk of sudden death if they develop AFib. Consider radiofrequency ablation of the accessory pathway in all patients.
Further Outpatient Care
- Education is the most important aspect of outpatient care for patients with WPW. Urge patients to carry a sample ECG in sinus rhythm and a medical identification bracelet in case of cardiac arrest.
- Follow-up with a cardiologist and cardiac electrophysiologist is recommended in the patient with any worrisome features (eg, syncope, significant symptomatic tachyarrhythmias, uncertain diagnosis in those with wide-complex tachycardia, associated structural heart disease, WPW syndrome with a family history of sudden death, recurrent atrial fibrillation or flutter)
In/Out Patient Meds
- Ongoing therapy of patients with WPW syndrome is generally interventional (radiofrequency ablation). Patients should receive ongoing pharmacologic therapy only under the supervision of an experienced cardiologist.
Prognosis
- Patients with WPW syndrome have an excellent prognosis when treated with ablation of the accessory pathway.
Medical/Legal Pitfalls
- Failure to recognize this dysrhythmia and treatment with agents leading to deterioration (eg, beta-blockers, calcium channel blockers, digoxin) can lead to medicolegal vulnerability.
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Wolff-Parkinson-White Syndrome excerpt Article Last Updated: Jun 14, 2006
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