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A cura del Dr. Igino Contrafatto M.D. – Cardiac Electrophysiology – Salus Hospital – Reggio Emilia

Wolf-Parkinson-White Asymptomatic

Management of the asymptomatic pediatric and young adult patient (8-21 years) with a WPW ECG pattern (isolated ventricular preexcitation).

Since Wolff, Parkinson, and White published their sentinel paper in 1930, much has been learned about the anatomy, electrophysiology, and natural history of accessory connections exhibiting antegrade conduction.1 Classically, patients with Wolff-Parkinson-White (WPW) syndrome presented with palpitations or presyncope caused by an atrioventricular (AV) reciprocating tachycardia or, less commonly, a primary atrial tachycardia. Rapid conduction of atrial fibrillation (AF) over the accessory pathway resulting in ventricular fibrillation (VF) is rare but unfortunately may be the first manifestation of WPW syndrome, even in the young. Refinements in catheter ablation equipment and techniques have rendered ablation a highly effective therapy for WPW in children.

In recent years, the use of electrocardiograms (ECGs) for screening prior to sports participation, medical and surgical procedures, and initiation of some medications has identified increasing numbers of asymptomatic individuals with a WPW ECG pattern.

The optimum management of these patients is not known. Although successful catheter ablation is capable of eliminating the risk of sudden death in the asymptomatic child with a WPW ECG pattern, uniform referral of every child for an ablation could also result in serious and potentially life-threatening complications, possibly greater in number than the deaths averted from untreated disease.

In large-scale

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general population studies involving children and adults, the prevalence of WPW is estimated to be 1–3 in 1000 individuals.
Identification of the truly asymptomatic patient with WPW is difficult, as these individuals are by definition without palpitations, syncope, or other symptoms secondary to ventricular preexcitation. At present, it is estimated that approximately 65% of adolescents and 40% of individuals over 30 years with a WPW pattern on a resting ECG are asymptomatic.

The majority of patients with WPW have normal cardiac anatomy. Accessory pathways are thought to be an embryologic remnant, as substantiated by diagnosis of supraventricular tachycardia (SVT) in utero and by a greater prevalence of WPW in newborns and infants.

Although episodes of SVT often decrease in frequency in the first year of life (90% of patients), tachycardia recurs in approximately 30% at an average age of 7–8 years. Furthermore, there is evidence that in the first year of life the accessory pathway loses anterograde conduction in as many as 40% of patients, and SVT becomes noninducible in a similar percentage, suggesting loss of retrograde conduction as well.

If WPW and tachycardia coexist in an individual beyond 5 years of age, they continue to be present more than a decade later in more than 75% of individuals.
Young adults with WPW typically present with arrhythmia symptoms, but the prevalence of documented SVT is lower.
Up to 31% of adults may lose the capacity for ventricular preexcitation and anterograde conduction over a 5-year time period.
Rarely patients present with WPW due to the hemodynamic effects of preexcitation alone. This is presumed to be due to dyssynchronous ventricular contraction associated with a highly preexcited rhythm.
Most worrisome are the uncommon presentations of syncope or aborted sudden cardiac arrest as the first manifestation of WPW syndrome. The mechanism of sudden death in patients with WPW syndrome is very rapid conduction of atrial flutter and AF, which provokes VF. Although most WPW patients resuscitated from a sudden cardiac death (SCD) event have had prior symptoms, VF or a cardiac arrest may be the sentinel event, particularly in children.
Determining which WPW patients are at highest risk for life-threatening arrhythmia by history alone remains a dilemma, but in the absence of noninvasive and invasive testing the reported warning flags appear to be younger age (<30 years), male gender, history of AF, prior syncope, associated congenital or other heart disease, and familial WPW.

Risk stratification in WPW
In current practice the intent of risk stratification in asymptomatic children with a WPW ECG pattern is to identify which individuals are at risk for a lethal cardiac arrhythmia.
In its simplest form, risk stratification utilizes noninvasive testing (Holter or exercise stress test) to ascertain true loss of preexcitation at physiological heart rates. Inability to clearly demonstrate absolute loss of manifest preexcitation warrants consideration for more invasive EP testing. The critical obligatory condition for VF is the presence of a short anterograde functional refractory period of the accessory pathway as reflected in the shortest R-R interval between preexcited beats in AF. Invasive EP testing should include measurement of the shortest preexcited R-R interval during induced AF in addition to determination of the number and location of accessory pathways, the anterograde and retrograde characteristics of the accessory pathway(s) and AV node, and the effective refractory period of the accessory pathway(s) (APERP) and of the ventricle at multiple cycle lengths.

Noninvasive evaluation of WPW patients
ECG
The ECG during preexcited AF affords a “true” assessment of the anterograde characteristics of the accessory pathway. The measurement of the Shortest Pre-Excited R-R Interval (SPERRI) has been used to determine accessory pathway properties; however, much of the literature is based on invasive studies. A SPERRI of 220–250 ms and especially less than 220 ms is more commonly seen in patients with WPW who have experienced cardiac arrest.
Conversely, intermittent loss of preexcitation during sinus rhythm suggests that the risk of cardiac arrest is low. The variation can be within a few beats, captured on a single ECG or at disparate points in time, determined on ambulatory monitoring or serial ECGs. Although intermittent preexcitation is a predictor of poor anterograde conduction through the accessory pathway, it has been observed, on rare occasions, in some patients with cardiac arrest. Intermittent preexcitation does not exclude patients from developing SVT.
The presence of multiple accessory pathways has been identified as a risk factor for VF. The appearance of different preexcited morphologies on an ECG or ambulatory monitoring confers higher risk and individuals are less likely to be asymptomatic. Approximately 5%–10% of patients with a WPW pattern may present with preexcited tachycardia, allowing for an understanding of the anterograde conduction properties of the accessory pathway.

Medication challenge
Although no longer routinely utilized, sodium channel blocking agents have been used to determine the properties of an accessory pathway.

Exercise testing
Disappearance of preexcitation during exercise testing has been proposed as a surrogate method of assessing the accessory pathway refractory period. Delta wave behavior during exercise is dependent upon the relative effects of sympathetic stimulation on accessory pathway refractoriness and AV nodal conduction. More rapid AV nodal conduction at higher exertion levels may mask persistent preexcitation through a left-sided accessory pathway, even when subtle clues for WPW are sought. It is deemed that only abrupt and complete loss of preexcitation during exercise can predict a long anterograde APERP.

In the absence of a clear understanding of the accessory pathway anterograde characteristics by noninvasive testing, invasive testing should be considered (Electrophysiology Study). The purpose of such an invasive EP study in asymptomatic patients with a WPW ECG pattern is to identify a potential subgroup of patients who may be at increased risk for lethal cardiac arrhythmias and in whom the risk-to-benefit ratio favors ablation. In adults with asymptomatic preexcitation, 70% of electrophysiologists recently surveyed supported risk stratification and prophylactic ablation. In a separate survey of 43 pediatric electrophysiologists, 84% used some form of an EP study to risk-stratify asymptomatic children with WPW, with 77% affirming RFA would be indicated when the shortest preexcited R-R interval in AF is <240 ms.

In clinical studies of adult WPW patients, a SPERRI <220–250 ms during AF has been shown to be the best discriminator of those at risk of VF. The sensitivity of SPERRI in AF is 88%–100% for identifying symptomatic adults at risk for VF, but because of the low incidence of cardiac arrest in these patients, the positive predictive value of a SPERRI <220 ms in adults is only 19%–38%.

Reference:
PACES/HRS Expert Consensus Statement on the Management of the Asymptomatic Young Patient with a Wolff-Parkinson-White (WPW, Ventricular Preexcitation) Electrocardiographic Pattern (2012)