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1049.e2 Wolff-Parkinson-White Syndrome

Wolff-Parkinson-White Syndrome Client Education
Sheet
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complex because conduction follows the
BASIC INFORMATION
it can lead to tachycardia-induced cardiomy-
normal rapid intraventricular depolarization • If a tachyarrhythmia is frequent or sustained,
Definition system. opathy, a dilated, poorly contractile heart
Wolff-Parkinson-White syndrome (WPW) is • Concealed AP: capable only of retrograde that can be indistinguishable from idiopathic
the combination of ventricular pre-excitation conduction (ventricle to atrium). There is dilated cardiomyopathy (DCM), except
during sinus rhythm and paroxysmal tachyar- no ventricular pre-excitation during sinus that it can be reversible with control of the
rhythmias. The underlying defect is an accessory or an atrial-based rhythm. Concealed APs tachyarrhythmia.
pathway (AP) or additional conductive fiber can participate as the retrograde limb of a • Pathways capable of rapid antegrade conduc-
connecting the atria and ventricles, separate tachyarrhythmia. tion can conduct atrial tachyarrhythmias
from the normal atrioventricular (AV) node– rapidly to the ventricles, bypassing the
bundle of His connection. Many APs are HISTORY, CHIEF COMPLAINT normal delay imposed by the AV node.
capable only of retrograde conduction and Related to resultant tachyarrhythmias: Atrial fibrillation can quickly degenerate into
are known as concealed APs. They are able to • Decreased exercise tolerance/weakness/ ventricular fibrillation, causing sudden death.
participate as the retrograde limb of a narrow lethargy
QRS complex tachyarrhythmia but do not • Vomiting, diarrhea DIAGNOSIS
produce ventricular pre-excitation during sinus • Decreased appetite
rhythm, technically not fulfilling the definition • Syncope, presyncope Diagnostic Overview
of WPW. • Racing heart/pulsing ears or head Electrocardiographic identification of ventricular
• Dyspnea/coughing pre-excitation during sinus rhythm and an atrial
Synonyms • Abdominal distention tachycardia definitively identifies an AP. This
• The extra conductive pathway itself: accessory • Acute collapse is not found with concealed APs. A narrow
AV pathway (AP, or bypass tract) • Sudden death complex, regular tachyarrhythmia with specific
• Premature activation of the ventricles by electrocardiographic (ECG) features is sugges-
an atrial impulse conducting over the AP: PHYSICAL EXAM FINDINGS tive, but electrophysiologic study is required
ventricular pre-excitation Patient may be completely normal at the time for confirmation of an AP.
• Macroreentrant narrow complex tachycardia: of exam or may show any of the following signs:
orthodromic AV reciprocating tachycardia • Tachyarrhythmia Differential Diagnosis
(OAVRT) • Decreased femoral pulse quality • ECG: narrow complex, regular tachyar-
• Tachypnea/dyspnea rhythmias: automatic or reentrant atrial
Epidemiology • Heart murmur (usually caused by secondary tachycardias, AV nodal reentrant tachycardia,
SPECIES, AGE, SEX AV valve regurgitation) junctional tachycardias. Pre-excited tachyar-
Any; most commonly first identified in dogs • Abdominal fluid wave rhythmias: ventricular tachycardias, atrial or
< 6 years old • Mucous membrane pallor ± slow capillary junctional tachycardias conducted with right
refill time or left bundle branch block
GENETICS, BREED PREDISPOSITION • Radiographic/echocardiographic (in cases
Any breed can develop WPW, but Labrador Etiology and Pathophysiology progressing to tachycardia-induced cardio-
retrievers, golden retrievers, and brachycephalic • The AP is composed of working myocardial myopathy): idiopathic DCM
breeds appear to be predisposed. fibers that exist outside the confines of the
normal conduction system and connect atrial Initial Database
ASSOCIATED DISORDERS and ventricular myocardium. • ECG
In people, APs are associated with Ebstein’s • Antegrade (atria-to-ventricles) conduction ○ Ventricular pre-excitation may be seen
anomaly and heterotaxy syndrome. The vast of a sinus nodal or atrial impulse over the during sinus rhythm: PR interval often
majority of dogs with APs have no evidence AP activates a portion of the ventricular but not always shortened (<0.06 second);
of congenital heart disease but may have a myocardium early and then spreads in a initial portion of the QRS slurred (i.e.,
secondary form of reversible cardiomyopathy myocyte-to-myocyte fashion. The result is a slowly rises or descends [delta wave]); QRS
known as tachycardia-induced cardiomyopathy. short PR interval and a wide, abnormal QRS duration often prolonged (>0.06 second);
complex (i.e., ventricular pre-excitation). QRS axis may be abnormal
Clinical Presentation The extent of PR interval shortening and ○ Tachyarrhythmias: tend to be narrow
DISEASE FORMS/SUBTYPES widening of the QRS depend on how much complex (QRS < 0.06 second), 240-
• Manifest AP: capable of antegrade (atrium- of the ventricular myocardium is activated 400+ beats/min; when patients are not
to-ventricle) conduction, bypassing the AV by the AP and how much is activated by on antiarrhythmic drugs. The ECG may
node. The result is ventricular pre-excitation the normal conduction system because the have a visible deflection in ST segment
during normal sinus rhythm. These pathways QRS represents a fusion between these two (retrograde P wave). Tachyarrhythmias
most often are also capable of conducting in wave fronts. are often intermittent, and they are not
the retrograde (ventricle-to-atrium) direction. • Retrograde (ventricles to atria) conduc- necessarily captured on a baseline ECG.
Manifest APs can participate as the antegrade tion of a ventricular impulse over the AP Holter monitoring (p. 1120) is more
or retrograde limb of a tachyarrhythmia. If activates a portion of the atria and then helpful than a single baseline ECG but
the AP is the antegrade limb, the tachycardia spreads in a cell-to-cell fashion, eventually may still be normal on a given day.
has a wide QRS complex because conduction reaching the AV node. If the AV node • Echocardiogram
spreads from ventricular cell to ventricular conducts the impulse to the ventricles, the ○ May be normal
cell rather than through the normal rapid cycle can be repeated in a self-perpetuating ○ May mimic DCM
conduction system. If it is the retrograde loop and result in a narrow QRS complex ○ Assess for congenital heart defects,
limb, the tachycardia has a narrow QRS tachyarrhythmia. particularly tricuspid valve dysplasia.

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