Cardiology · Arrhythmias
The facts most likely to be tested
The hallmark ECG finding of Wolff-Parkinson-White (WPW) syndrome is a short PR interval (<120 ms) combined with a delta wave representing early ventricular activation.
The underlying pathophysiology involves an accessory conduction pathway known as the Bundle of Kent that bypasses the AV node.
Patients with WPW who present with atrial fibrillation and a rapid ventricular response are at high risk for ventricular fibrillation due to the accessory pathway's lack of rate-limiting properties.
The first-line treatment for hemodynamically unstable patients with WPW-associated tachycardia is synchronized cardioversion.
In stable patients with orthodromic AV reciprocating tachycardia, vagal maneuvers or adenosine are the preferred initial interventions to terminate the arrhythmia.
AV nodal blocking agents such as beta-blockers, calcium channel blockers, digoxin, and adenosine are contraindicated in patients with WPW presenting with atrial fibrillation because they can paradoxically increase conduction through the accessory pathway.
The definitive treatment for symptomatic or high-risk patients with WPW is radiofrequency catheter ablation of the accessory pathway.
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A 22-year-old male presents to the emergency department with palpitations and lightheadedness. He reports similar episodes in the past that resolved spontaneously. On physical exam, he is tachycardic with a heart rate of 180 bpm and is hemodynamically stable. An ECG reveals a narrow-complex tachycardia with no visible P waves. After the administration of adenosine, the rhythm converts to sinus rhythm, revealing a short PR interval and a slurred upstroke of the QRS complex.
What is the most likely diagnosis and the underlying anatomical abnormality?
Wolff-Parkinson-White syndrome caused by a Bundle of Kent.
The patient's ECG findings of a short PR interval and delta wave (slurred upstroke) are pathognomonic for WPW, which is caused by the accessory Bundle of Kent.
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Etiology / Epidemiology
Congenital accessory pathway (Bundle of Kent) bypasses the AV node. Affects 0.1-0.3% of the population.
Clinical Manifestations
Often asymptomatic; presents with palpitations, syncope, or delta wave on ECG.
Diagnosis
ECG shows short PR interval (<0.12s) and wide QRS with slurred upstroke.
Treatment
Stable: Procainamide. AV nodal blockers (Adenosine, Beta-blockers, CCBs) are contraindicated.
Prognosis
Risk of sudden cardiac death due to rapid conduction during atrial fibrillation.
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Epidemiology & Etiology
WPW is a congenital pre-excitation syndrome caused by an accessory electrical pathway. It is more common in males and often presents in young adults. While many remain asymptomatic, the presence of the pathway creates a substrate for re-entrant tachycardias.
Pertinent Anatomy
The Bundle of Kent is an abnormal muscular connection between the atria and ventricles. This bypasses the normal delay provided by the AV node, allowing premature ventricular activation.
Pathophysiology
The accessory pathway conducts impulses faster than the AV node, resulting in ventricular pre-excitation. This creates a re-entrant circuit, most commonly leading to orthodromic AVRT. If atrial fibrillation occurs, the pathway can conduct impulses at dangerously high rates, leading to ventricular fibrillation.
Clinical Manifestations
Patients may report palpitations, dizziness, or syncope during episodes of tachycardia. The delta wave is the pathognomonic ECG finding representing early ventricular activation. Syncope in a patient with known WPW is a red flag for high-risk accessory pathway conduction.
Diagnosis
The ECG is the primary diagnostic tool, demonstrating a PR interval <0.12 seconds and a wide QRS complex with a slurred upstroke. The electrophysiology study (EPS) is the gold standard for mapping the accessory pathway location. A delta wave is classically present in sinus rhythm.
Treatment
For stable wide-complex tachycardia, procainamide is the drug of choice. AV nodal blocking agents (Adenosine, Digoxin, Verapamil, Beta-blockers) are strictly contraindicated as they promote conduction down the accessory pathway. Definitive treatment is radiofrequency catheter ablation.
Prognosis
Most patients have a benign course, but the risk of sudden cardiac death exists if the accessory pathway has a short refractory period. Patients with symptomatic arrhythmias require radiofrequency ablation to eliminate the pathway.
Differential Diagnosis
AVNRT: lacks delta wave and pre-excitation
Lown-Ganong-Levine syndrome: short PR but normal QRS
Ventricular tachycardia: usually associated with structural heart disease
Atrial fibrillation with aberrancy: lacks delta wave in sinus rhythm
Hypertrophic cardiomyopathy: can mimic pre-excitation on ECG