The Asymptomatic Patient with the Wolff-Parkinson-White Electrocardiogram

HEIN J. WELLENS, LUZ MARIA RODRIGUEZ, CARL TIMMERMANS, andJOEP L. SMEETS

From the Academic: Hospital Maastricht, Maastricht, The Netherlands

WELLENS, H.J., ET AL.: The Asymptomatic Patient with the Wolff-Parkinson-White Electrocardiogram.Sudden death can be the first manifestation of the Wolff-Parkinson-White (WPW) syndrome. The under-lying mechanism being atrial fibrillation with a very high ventricular rate, because of a short anterograderefractory period of the accessory atrioventricular pathway (AP), deteriorating into ventricular fibrillation.Information on the anterograde refractory period of the AP is therefore important to recognize asymp-tomatic people with the WPW ECG at risk for dying suddenly. Several noninvasive tests are available toidentify the low risk patient. Decision making when to interrupt the AP in asymptomatic WPW patientsnot at low risk requires an invasive study to document the electrophysiological properties of the AP andto determine its exact location. (PACE 1997; 20[Pt. 111:2082-2086)

Wolff-Parkinson-White syndrome, sudden death, asymptomatic patient

Introduction

The usual presentation of the patient withpreexcitation is because of an arrhythmia, either aregular tachycardia based upon a circus move-ment tachycardia incorporating the atrioventricu-lar (AV) node-His pathway and the accessory AVconnection or atrial fibrillation. However, this ar-ticle addresses what to do when a person withoutany complaint suggesting an arrhythmia, presentswith an ECG showing ventricular preexcitation.

Incidence of the Asymptomatic Wolff-Parkinson-White ECG

The true incidence of preexcitation is notknown; the reported figures vary from0.1-3.0/1,000 ECGs.̂ '̂ The Wolff-Parkinson-White(WPW) syndrome is undoubtedly underdiagnosedbecause, as shown in Figures 1 and 2, the contribu-tion to ventricular activation over the accessorypathway may vary. What percentage of the WPWpatient is asymptomatic is understandably also un-known. Those cases may occur more frequently infamily members of symptomatic patients with theWPW syndrome. As pointed out by Vidaillet et al.,^

Address for reprints: Hein J. Wellens, Department of Cardiol-ogy, Academic Hospital Maastricht, PO Box 5800, 6202 AZMaastricht, The Netherlands. Fax: 31-43-387-5104

family members have a fourfold greater chance ofhaving the syndrome than do people without a fam-ily history. The authors suggest that the WPW syn-drome is inherited as an autosomal dominant trait.

Asymptomatic should also he discussed in re-lation to the age of the patient. As shown in TableI, the first episode of an arrhythmia may occurshortly after birth but also in the sixth decade."Therefore, most children with the WPW ECG mustbe asymptomatic!

The Importance of Identify ingthe Asymptomatic Patient

In the human heart, the ventricles are pro-tected by the refractory period of the AV nodeagainst a very high ventricular rate during a rapidatrial rhythm. In patients having an accessory AVpathway, atrial fibrillation can be an extremelydangerous arrhythmia if the accessory connectionhas a short anterograde refractory period. Underthose circumstances, the occurrence of ventricularfibrillation has been documented^ [see Fig. 3). Sev-eral studies have shown that sudden cardiac arrestdue to ventricular fibrillation can be the first mani-festation of the WPW syndrome.^-^ In that regard itis of interest that in the series of Timmermans etal./ cardiac arrest was the first arrhythmia mani-festation in 53% of their patients with aborted sud-den death. One of these patients was only 5-years

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ASYMPTOMATIC WOLFF-PARKINSON-WHITE ECG

Figure 1. Schematic drawings showing some of the fac-tors thot ploy a role in the degree of preexcitation in thepatient with an accessory AV pathway during sinusrhythm. In this example the accessory connection is left-sided. In the left panel, because of a shorter conductiontime from the sinus node to the ventricle over the acces-sory pathway (65 + 30 = 95 ms vs 35 + 80 -h 45 ^ 160msec over the normal AV conduction system), an im-portant part of the ventricle is preexcited resulting in onECG with a short PR interval, clear delta wave, and awidened QRS complex (top left panel). In contrast, in thepanel on the right, octivation of the ventricle starts si-multaneously over the normal AV conduction system(30 + 60 + 35 ^ 125 msec) and the accessory pathway(90 + 35 - 125 msec). This results in an ECG with alonger PR interval, hardly any delta wave, and a morenarrow QRS complex (top right panel).

old the other seven patients were age 20 years orolder. It is of importance, therefore, to be informedabout the anterograde refiractory period of the ac-cessory pathway in the asymptomatic patient.

Noninvasive Tests to Recognize the Patientwho is at Low Risk for Dying Suddenly

Three noninvasive techniques can give anidea about the approximate length of the refractoryperiod of the accessory pathway in anterograde di-rection. First, the finding of intermittent preexcita-tion (Fig. 4) indicates a long anterograde refractoryperiod of the accessory pathway." Second, asshown by Levy et al.,*̂ disappearance of preexcita-

tion during exercise points to a long anterograderefractory period of the accessory pathway. An ex-ample is giveti in Figure 5. One has to be carefulhowever, because sympathetic stimulation duringexercise will accelerate AV nodal conduction andmight thereby diminish the size of the area of theventricles preexcited over the accessory pathway.

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msecFigure 2. ECG examples of the two schematic drawingsshown in Figure 1. The ECCs on the left and right corre-spond to the left ond right panels of Eigure 1. The ECGon the left shows a much larger area of ventricular pre-excitation than the ECG on the right.

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Table I.

Age at Onset of First Episode of Tachycardia in 280Consecutive Patients with the WPW Syndrome

Years Number of Patients Percent

00-1011-2021-3031-4041-50> 50

358258504213

280

13302017155

100

It is important, therefore, to record several ECGleads simultaneously, and special attention shouldhe given to the ECG after exercise u'hen in case ofexercise-induced block in the accessory pathway,a sudden marked change in the ECG takes place onresumption of AV conduction over the accessoryconnection. Third, failure to produce completeblock in the accessory pathway hy intravenous in-jection of procainamide [10 mg/kg hody weightover a 5-min period) strongly suggests a short an-terograde refractory period of accessory pathway(of < 270 ms).^" An example of block in the acces-sory pathway following procainamide administra-tion is shown in Figure 6. Because procainamidemay also prolong the refractory period of the His-Purkinje system, this test should he done in a sur-rounding in which advanced heart block can bemanaged appropriately. By combining the differ-ent noninvasive tests, patients can usually be iden-

tified who are at low risk for sudden death becauseof a relatively long anterograde refractory period ofthe accessory pathway. "'^^

When to do Invasive Testing?

Ventricular fibrillation is a rare but lethalcomplication in patients with the WPW syn-drome. Natural history studies report a suddendeath incidence ranging from O^/o-O.eX/year/^"^'^and in the asymptomatic WPW patient the pres-ence of a short anterograde refractory period of theaccessory pathway is an obvious risk factor. Ifnoninvasive testing suspects a short anterograderefractory period of the accessory connection, isinvasive determination of the anterograde refrac-tory period indicated?

In the past, several studies suggested that, ingeneral, asymptomatic patients with a short an-terograde period have a good prognosis '̂̂ '̂'̂ ^" andthat no antiarrhythmic drugs should be pre-scribed. Ablation of the accessory pathway wasonly recommended for professional reasons, forexample, to be licensed to fly a commercial air-liner or to be insured as a professional athlete. Re-cently, the Federal Aviation Administration(FAA) of the United States has developed stan-dards for subjects with arrhythmias or the poten-tial for arrhythmias (e.g., asymptomatic WPW syn-drome), which were summarized in a jointstatement hy the American Heart Association andthe North American Society of Pacing and Eiec-trophysiology.^'' Ventricular preexcitation was

Figure 3. Example of deterioration ofatriai fibrillation into ventricular fib-rillation in a patient with the WPWsyndrome. The right panel shows theECG during sinus rhythm.

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ASYMPTOMATIC WOLFF-PARKINSON-WHITE ECG

400 msec

considered a disqualifying condition only if thereis a preceding history of arrhythmia or evidence ofstructural heart disease. The European Joint Avia-tion Authorities (lAA) standards are similar and

Figure 4. Intermittent preexcitation. During sinusrhythm, alternating QRS complexes show conductionnver both the accessory pathway and the AV nodewhile the others show AV conduction over the AV nodeonly.

require that patients found to have a WPW patternon the ECG undergo medical assessment.

In view of the low risk and high success ratesof radiofrequency (RF) catheter ahlation (whenperformed by an experienced operator), and theobservation that in half of our cardiac arrest pa-tients arrhythmia was the first manifestation ofWFW. we are currently inclined to advise RF ab-lalion of the accessory pathway if that structurehas a short anterograde refractory period.

This implies that an electrophysiological studyis advised to explore the actual anterograde refrac-tory period of the accessory connection and its lo-cation. The decision to perform RF ablation will bemade after explaining the (low) risks of the ahlationprocedure taking into account the location of theaccessory pathway. To ablate a para hissal acces-sory pathway in an asymptomatic patient is obvi-ously a much more difficuh decision than inter-rupting conduction over a left free-wall pathway.

In asymptomatic children, one very rarely hasto make decisions about RF ablation of accessorypathways simply because no ECGs are made whenthe child has no complaints suggestive of a cardiacailment. In the rare case of the accidental findingof an accessory pathway with a very short refrac-

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400 msec

Figure 5. Effect of exercise in a pa-tient with the WPW syndrome. Onreaching a critical sinus rate 1 : 1conduction over the accessory path-way disappears. Thereafter, only ev-ery third sinus beat is conductedover the accessory pathway untilcomplete block in the accessorypathway occurs.

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Figure 6. Example of the occurrence of complete blockin the accessory pathway after the intravenous admin-istration of procainamide. This indicates a long antero-grade refractory period of the accessory pathway.

tory period in a child, RF ablation should prefer-ably be postponed till the age of 10 years to pre-vent a large ablation lesion in a small heart.^"'̂ ^

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