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Review -
Wolff-Parkinson-White (WPW) Syndrome
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Chris Talluto, MD
A 25-year-old man presents to the emergency room with palpitations,
shortness of breath, and a feeling of lightheadedness.
A 12 lead EKG shows a SVT and adenosine is administered.
The tachycardia resolves and a repeat EKG shows a shortened
PR interval, a widened QRS complex, and a delta wave. A
diagnosis of Wolff-Parkinson-White (WPW) Syndrome is made.
In 1970 Durrer et al clarified that “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 WPW syndrome which occurs in about 0.15%- 0.2% of the general
population with men being affected 60-70% more commonly than women. It can
affect people of all ages, but usually is recognized in children and young
adults presenting with an arrhythmia. It is thought that there is a congenital
accessory pathway between the atrium and ventricles. There are many different
locations for the bypass tracts including atriofascicular, fasciculoventricular,
intranodal, or nodoventricular, but the most common bypass tract is an accessory
atrioventricular pathway often referred to as the bundle of Kent. This is
the congenital anomaly seen in WPW.
Typically patients present to the emergency room with mild
symptoms of chest discomfort or palpitations, but can also present in full
cardiopulmonary arrest secondary to an associated arrhythmia. Small children
often present with irritability, vomiting of feeds, and decreased oral intake.
Typically the heart rates are approximately 250 for older individuals, whereas
babies can present with heart rates in the 300’s. On physical exam the patient
may be cool, diaphoretic and hypotensive and crackles in the lungs can be
heard because of diastolic heart failure secondary to the tachycardia. In
babies, the physical exam can be completely normal except for the isolated
tachycardia. The differential diagnosis at this time includes atrial fibrillation,
atrial flutter, ventricular tachycardia, or supraventricular tachycardia.
A diagnosis of WPW syndrome can be made when you have both preexcitation of
the EKG and paroxysmal tachycardias.
EKG findings are particularly helpful in making an initial
diagnosis, although the diagnosis of WPW syndrome can not usually be made
until the tachycardia resolves. The classic EKG morphology of WPW is a shortened
PR interval of less than 0.12sec., a slurred upstroke of the QRS complex (delta
wave), and a wide QRS complex.
This typical pattern is seen with antegrade conduction activating
the ventricles from both the bypass tract and AV nodal His-Purkinje system.
Depending upon the location of the accessory pathway in relation to the sinus
node, the relative transmission characteristics of the accessory pathway and
the AV node, the morphology of the EKG may vary from the classic presentation
to near normal. An accessory pathway that does not have EKG changes is usually
revealed when the rate exceeds the refractory period of the AV node. This
“latent” accessory pathway can conduct both anterograde and retrograde. There
is an accessory pathway in which only retrograde transmission of the impulses
can occur, and this is called concealed. This concealed accessory pathway
can lead to circus movement tachycardias; one of the most common types of
arrhythmias seen in WPW syndrome. The other most common arrhythmia is atrial
fibrillation.
Patients presenting with paroxysmal supraventricular tachycardia,
the impulse is usually conducted antegradely over the normal
AV system and retrogradely through the bypass tract. Rarely
(approximately 5% of patients) there is antegrade conduction
through the bypass tract and retrograde conduction through
the normal AV system. This produces a wide complex QRS complex
in which the ventricles are stimulated by the accessory
pathway. If there is a premature atrial beat that occurs
during the refractory period of the accessory pathway,
the impulse could travel down the AV nodal pathway, but
then return via the accessory pathway resulting in circus
movement tachycardias (CMT). This orthodromic tachycardia
is a narrow complex and is rate limited by the refractory
period of the AV node. Differentiating CMT from PSVT is
unnecessary because the treatment for both is IV adenosine.
It is important to remember that any regular wide-complex
tachycardia should be considered V-Tach until proven otherwise,
however a stable patient with a wide complex tachycardia
can be treated with adenosine.
Afib in a patient with
WPW occurs in 11-40% of patients, and can be fatal because of the anatomy
involved. Patients with WPW have the accessory pathway with a shorter anterograde
refractory period allowing for much faster transmission of impulses. This
can lead to a 1:1 transmission from the atria to the ventricles leading to
hypotension and if the rate becomes too high, V fib. The typical EKG pattern
of A Fib through an accessory pathway appears as a wide-complex, irregular
tachycardia.
Treatment of patients with WPW differs depending upon the
presentation. Patients who are unstable may need cardioversion or ACLS resuscitation.
Treatment of A Fib in a patient with WPW is different than a patient with
a normal heart. If treated with conventional drugs, the prolongation of
the refractory period of the AV node would increase the rate of transmission
through the accessory pathway and increase ventricular rate, therefore cardioversion
is the preferred method of treatment. Treating CMT/PSVT is similar and is
accomplished by prolonging the refractory period of the AV node. Adenosine
6mg IV push, should be the first line of treatment. In children, a dose of
0.1mg/kg/dose is used with a max dose of 6mg initially. If this fails, increase
the dose to 12mg via IV push. Adenosine can be used regardless of whether
the complex is wide or narrow as long as the patient is stable.
Of importance is the regularity of the QRS. A regular QRS
distinguishes CMT/PSVT from Fib, which has irregular QRS
patterns. A regular QRS either narrow or wide can be treated
with adenosine. If the QRS is irregular its more likely
to be AFib, and adenosine should not be used and either
cardioversion or procanamide should be used. When in doubt
it is safer to err on the side of treating for AFib.
REFERENCES
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Garratt C, Antoniou A, Ward D, et al.
Misuse of verapamil in pre-excited atrial fibrillation.
Lancet 1989 Feb 18; 1(8634): 367-9.
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Herbert M, Tully G, et al. Wolff-Parkinson-White
Syndrome. E-medicine 2001 December; 1-9.
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Sharma AD, Klein, GJ, Yee R. Intravenous adenosine
triphosphate during wide QRS complex tachycardia: safety,
therapeutic efficacy, and diagnostic utility. Am J
Med 1990 Apr; 88(4)); 337-43.
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