Ventricular Preexcitation Syndrome

Not all patients are symptomatic or have a prior diagnosis; 1–3% of diagnoses are made following ECG in previously asymptomatic individuals.

WPW syndrome affects 0.1–0.3% of the population, is more prevalent in males, and is characterized by symptomatic arrhythmias and an ECG showing a short PR interval (<120 ms) with a widened QRS (>100 ms) and often, but not always, δ waves, representing fusion of early and late depolarization via the accessory pathway and AV node. Abnormal conduction occurs via a bundle-of-Kent accessory pathway between atria and ventricles. Risk of SCD is estimated to be 0.25% per annum in WPW syndrome.

LGL syndrome affects 0.5% of adults, is more prevalent in women, and reflects abnormal conduction through the James bundle (atria to bundle of His). Characterized by a short PR interval, normal QRS, and no δ waves, it manifests through reentrant type PSVT or atrial fibrillation/flutter. No studies have shown an increased risk of SCD in LGL.

The Mahaim type is a rarer form of preexcitation, caused by Aps in the right ventricle, called Mahaim fibers. It is characterized by a normal PR interval, long QRS, and δ waves and may trigger episodes of SVT.

General or regional anesthesia may unmask ventricular preexcitation syndromes.

Asymptomatic individuals with a WPW ECG pattern may present no added risk. Symptomatic individuals with WPW syndrome are prone to PSVT (up to 75%), or less commonly to atrial fibrillation (15–30%) and flutter (5%); rapid ventricular rates may occasionally deteriorate to VT or VF.

There is a danger of misrecognition of WPW ECG patterns for BBB (wide QRS); myocardial infarction (negative δ waves simulating pathologic Q waves); other tachyarrhythmias (including VT). All prompt inappropriate treatment.

Drugs used to suppress AV conduction (to slow the ventricular rate in treatment of atrial fibrillation/flutter) may dangerously accelerate the rate in WPW.

Periop nausea, gagging, hypothermia, pneumoperitoneum, and pregnancy can all accentuate conduction via abnormal APs. Hyperadrenergic states, overstimulation (including laryngoscopy), and other interactions can also provoke or aggravate tachyarrhythmias.

High spinal anesthesia may block sympathetic cardiac accelerator nerves and suppress normal AV conduction. Alongside relative parasympathetic predominance, this may further facilitate conduction by the APs, resulting in preexcitation and tachyarrhythmias.

Cholinergic medications, such as suxamethonium and reversal agents, along with other AV-nodal blocking drugs (diltiazem, digoxin) may enhance conduction via APs, worsening tachyarrhythmias.

Potential of WPW-related PSVT to deteriorate into atrial fibrillation or flutter, with danger of extremely rapid ventricular rates and ensuing VT and VF.

The presence of a short PR interval, often with a δ wave, reflects the underlying early depolarization of ventricles and defines preexcitation syndrome.

The extent of preexcitation may change depending upon the conduction characteristics of the abnormal AP, AV node, and autonomic tone. The majority of pathways allow dual conduction, both anterograde (i.e., atrial to ventricular) and retrograde (i.e., ventricular to atrial). Retrograde-only conduction occurs in 15% and anterograde only is rare.

Pts with a ventricular preexcitation syndrome have an abnormal AP that bypasses the AV node to electrically connect atria and ventricle. The majority of these APs generate fast action potentials due to rapid sodium current influx, resulting in faster conduction of electrical impulses to the ventricle than the slower calcium current–dependent AV nodal route. This electrochemical distinction means that the onset of ventricular activation occurs earlier than if impulses had conducted through the AV node; hence preexcitation. Additionally, at faster atrial rates, progressive prolongation of AV nodal conduction is also bypassed, meaning that atrial tachycardias may deteriorate into VF.

A range of arrhythmias may occur in preexcitation syndromes, from SVTs (more common) to life-threatening ventricular arrhythmias (less common).

OAVRTs are due to abnormal circuits, in which anterograde conduction occurs via the AV node and retrograde conduction via the AP. Since the normal AV pathway is used for ventricular depolarization, QRS complexes are narrow and no δ waves are present. This accounts for most tachyarrhythmias in WPW syndrome (70%).

Antidromic tachycardias derive from anterograde ventricular activation via an AP, with retrograde current reentering atria via the AV nodal route. Wide QRS and δ waves are present on the ECG.

The first episode of PSVT in many pts appears before the age of 20 y, rarely in middle age, and infrequently after age 50. The frequency of episodes of PSVT increases with age in WPW syndrome.

APs are congenital in origin, and preexcitation syndromes may be hereditary.

Associated with congenital cardiac defects (most commonly tricuspid value lesions) and acquired cardiac defects (e.g., cardiomyopathy, idiopathic hypertrophic subaortic stenosis, asymmetric septal hypertrophy).