REVIEW

The Wolf-Parkinson-White ECG Pattern – Assessingthe Mortality Risk

Emoke Posan, MD

The presence of a Wolf-Parkinson-White (WPW) pattern is notuncommonly discovered on a life insurance applicant’s ECG. Howdoes one determine the appropriate mortality risk in thispopulation? This article will discuss the risk of sudden cardiacdeath (SCD), the interpretation of electrophysiology testing results,and risk-stratification both for asymptomatic individuals and thosewho have had ablation treatment.

Address for Correspondence:London Life, Great West life,Canada Life Insurance Company,255 Dufferin Ave T150, LondonOntario, Canada N6A 4K1;emoke.posan@londonlife.com.

Correspondent: Emoke Posan,MD, PhD, Assistant Medical,Director.

Key words: WPW, preexcitation,accessory pathway, suddencardiac death, mortality, lifeinsurance.

Received: October 8, 2014

Accepted: November 10, 2014

TWO HYPOTHETICALCASE SCENARIOS

While you are reading ECGs, you comeacross two tracings showing WPW patterns.The first ECG (Figure 1) is on a 23-year-oldmale client (case #1). The second ECG(Figure 2) is on a 45-year-old woman (case#2). Both individuals are applying fora million dollar life insurance policy.

Case #1

There is no disclosed medical history bythe 23-year-old male client, who has a WPWpattern on his ECG (Figure 1). The ECGshows sinus rhythm at 60 bpm; the PRinterval is short, and there is slurring of the

upstroke of the QRS (delta wave) making theQRS wide. There are QS complexes in lead IIIand AVF. The QRS axis is leftward (approx-imately -50 degrees). The QRS and deltawave transition is between V1 and V2.Repolarization is basically normal.

Case #2

The 45-year-old woman disclosed a historyof palpitations for which she was seen bya cardiologist 15 years ago. Her ECG(Figure 2) shows sinus rhythm at 94 bpm.There are 2 populations of QRS complexes.The narrow QRS complexes are preceded bya normal PR interval; repolarization isnormal, and the QRS transition is in V3.

REVIEW

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Figure 1. ECG of a 23-year-old male with WPW pattern.

Figure 2. ECG of a 45-year-old female with intermittent preexcitation.

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The wide QRS complexes are also precededby sinus P waves at the same rate as thosewith narrow QRS complexes. There is slur-ring on the upstroke of the QRS, and thereare minor repolarization abnormalities. TheQRS complex in V1 is positive. The differen-tial diagnosis for alternating wide andnarrow QRS complexes is intermittent pre-excitation or ventricular extrasystoles withlong coupling intervals. This ECG is consis-tent with intermittent preexcitation, and thepositive QRS complex in V1 suggests a left-sided accessory pathway.

Individuals who have a WPW pattern ontheir ECG have an abnormal accessoryconduction connection between the atriaand the ventricles, which bypasses theatrioventricular node (AV node). Histologi-cally, this accessory pathway has a patternconsistent with normal working ventricularmyocardium, not specialized conductiontissue. Importantly, it does not share therate-slowing properties of the AV node. Theaccessory pathway (AP) is, therefore, capableof conducting antegradely to the ventriclewith conduction faster than the AV nodeduring sinus rhythm. Thus, the AV node andthe accessory pathway are in competition todepolarize the ventricle when a supraventric-ular beat is initiated. The fusion of thesecompeting paths results in the WPW pattern,consisting of a delta wave, which is theslurring of the initial upstroke of the QRS(also making the QRS wide) and a short PRinterval (Figure 3). The accessory pathwaycan also predispose the patient to supraven-tricular tachycardia (SVT) – primarily AVreentry tachycardia (AVRT) – as well as veryrapid ventricular rates during other supra-ventricular tachyarrhythmias such as atrialfibrillation (AF) (Figure 5).

The term WPW syndrome refers to pre-excitation seen on an ECG associated withthe clinical symptoms, ie, palpitations andtachyarrhythmias. Not all patients with theWPW pattern will develop clinical tachy-cardias and not all patients with AVRTtachycardia will have preexcitation apparent

on the surface ECG. The terms preex-citation and Wolff-Parkinson-White syn-drome are used interchangeably in thisarticle, even though there are other formsof preexcitation.

WPW ARRHYTHMIAS ANDMECHANISM OF SUDDEN

CARDIAC DEATH

Accessory pathways may conduct ante-gradely only, retrogradely only or mayconduct bi-directionally (ie, both antegradelyand retrogradely). Accessory pathways canbe present without an obvious WPW patternon the ECG. Supraventricular tachycardia isnot uncommon in patients with WPW(,20%). Tachyarrhythmias associated withaccessory pathways are most often a narrowcomplex AVRT regardless of the overtpresence of preexcitation on the ECG. Theantegrade limb of the tachycardia circuit isdown the AV node and the retrograde limbis up the accessory pathway. The other formof AVRT is less common (wide QRS tachy-cardia) in which the antegrade limb of the

Figure 3. Impulse from Sinus Node is conducted via AVnode and Accessory pathway (in competition) tothe ventricle.

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circuit is down the accessory pathway andthe retrograde limb is up the AV node.Rarely the accessory pathway plays the roleof a bystander only during other forms ofSVTs (ie, atrial tachycardia, AVNRT, atrialflutter, atrial fibrillation).

The mortality concern with a Wolff-Par-kinson-White ECG pattern is the risk forsudden cardiac death due to the develop-ment of rapidly conducting, preexcited atrialfibrillation that may degenerate into ventric-ular fibrillation (VF) and sudden cardiacdeath.1-3 This life-threatening arrhythmiaoccurs when the accessory pathway hasa short anterograde effective refractory peri-od (ERP), resulting in a ‘‘wide window’’allowing many atrial impulses during atrialfibrillation to be conducted to the ventricle.This will result in very high ventricular rateswith possible deterioration into ventricularfibrillation and sudden cardiac death. A longantegrade effective refractory period of theaccessory pathway does not exclude thepossibility of a SVT, but the individual isnot at risk of sudden death if atrial fibrilla-tion occurs.

Epidemiological data indicates that theprevalence of a WPW pattern on a routineECG is 0.1% to 0.3% in the general popula-tion4,5 meaning that every year approximate-ly 3 new cases are found in a population of100,000. It is also known that there is a 4-foldincrease of this finding in family members ofWPW patients.6 The risk of ventricularfibrillation and sudden death in symptomaticindividuals with WPW syndrome is estimat-ed to be approximately 0.25% per year or 3%to 4% over a lifetime.2 However, suddendeath rarely may be the first event inindividuals with asymptomatic preexcitation.3

Recently there have been advocates forperforming invasive electrophysiologic as-sessment and catheter ablation therapy inasymptomatic individuals with Wolff-Parkin-son-White ECG patterns based on the find-ing by some investigators of higher mortalityrates in these individuals.7-9 This approachhas triggered multiple publications with

several rebuttals. Should life insurance med-ical directors reevaluate our approach toWolff-Parkinson-White ECG findings? Well,first, let’s leave this debate for the electro-physiologist community. Second, the riskof sudden cardiac death in a populationwith Wolff-Parkinson-White ECG pattern isexceedingly small.

All analyses except the recent Italianstudies have shown very low event rates.Unfortunately, we do not get ECGs on allasymptomatic individuals, so we do notknow the cause and the true incidence ofsudden cardiac death. It is also known thatmany patients with Wolff-Parkinson-Whitetend to lose accessory pathway conductionover time.10 A recent metaanalysis hasshown that asymptomatic individuals havea low incidence of sudden cardiac death, andthe risks associated with an invasive pro-cedure such as ablation therapy are similar tothe risk of sudden cardiac death in asymp-tomatic individuals. This argues againstroutine invasive management in mostasymptomatic individuals with the Wolff-Parkinson-White ECG pattern.11 The majorconclusion of this meticulous review is thatthe available evidence is insufficient tojustify the use of catheter ablation in theasymptomatic patient. ‘‘The risk of suddencardiac death was statistically significantlylower in the non-Italian compared to theItalian studies’’.11

In summary: though some recent Italianstudies had showed somewhat higher mor-tality rate in asymptomatic individuals,based on available evidence, the mortalityrisk in insured populations is no differentthan was believed in the past, and thus theapproach should probably remain the same.

RISK STRATIFICATION OFINDIVIDUALS WITH WPW

In absence of any tests, important risk factors(‘‘red flags’’) are: younger age (,30y), malesex, history of palpitations, syncope or atrialfibrillation, history of congenital heart dis-

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ease and family history of WPW.12 Thepurpose of risk stratification is to identifyindividuals with a Wolff-Parkinson-WhiteECG pattern who are at risk for lethalarrhythmias. The obligatory condition forventricular fibrillation is an accessory path-way with short antegrade refractory period(as reflected by the shortest R-R intervalbetween preexcited QRS complexes duringatrial fibrillation (Figure 5) or the effectiverefractory period measured during EPstudy). Non-invasive and invasive (electro-physiology) tests are used for risk assess-ment.

NONINVASIVE TESTING

In general, these tests look for evidence ofan accessory pathway that fails to be able toconduct at rapid rates, either in sinus rhythmor during AF. These tests include restingECGs, Holter monitoring, exercise testingand medication challenge to induce a blockin the accessory pathway in sinus rhythm.These tests can reveal intermittent preexcita-tion during sinus rhythm. Intermittent pre-excitation is present when 2 consecutivesinus beats show the presence and absenceof preexcitation (Figure 2). This findingindicates a long antegrade refractory periodof the accessory pathway resulting in verylow risk of sudden cardiac death.13,14

During preexcited atrial fibrillation, theantegrade characteristics of the accessorypathway are assessed by the measurementof the shortest preexcited R-R interval (SPERRI)(Figures 4 and 5). A SPERRI of 220-250 ms,especially if ,220 ms indicates high risk forventricular fibrillation and cardiac arrest.15-17

The appearance of different preexcitedmorphologies on an ECG or serial monitor-ing is suggestive of multiple accessory path-ways, which has been identified as a riskfactor for ventricular fibrillation and suddencardiac death.9,16,18

Serial monitoring also helps to find epi-sodes of supraventricular tachycardia or atrialfibrillation in asymptomatic individuals. In

a prospective study of 184 asymptomaticchildren with WPW followed for 5 years with2 Holter monitor per year, 12% had paroxys-mal atrial fibrillation, an incidence signifi-cantly higher than seen in asymptomaticadults with WPW.15

The best indicator of low risk is the suddendisappearance of pre-excitation during exer-cise, first described by Levy et al.19 Thisindicates a long antegrade effective refracto-ry period of the accessory pathway. Sympa-thetic stimulation occurring during exercisewill shorten the duration of the effectiverefractory period of the accessory pathway.20

When the effective refractory period of theaccessory pathway is reached during exer-cise, as manifested by sudden block in theaccessory pathway and normalization of theECG, it is a good indicator that the patient isnot at risk for ventricular fibrillation evenduring sympathetic stimulation.21,22 Onemust be careful, however, to distinguishtrue block in the accessory pathway fromdiminution of the degree of preexcitationover that produced by sympathetic stimu-lation during exercise, which will shortenthe trans-AV nodal conduction time. There-fore, several leads are taken simultaneously,and special attention is given to the suddenoccurrence of block in the accessory path-way during exercise and to the ECG afterexercise. This is because, in exercise-in-duced block in the accessory pathway,a sudden marked change in the ECG takesplace since there is an exclusive conductionover the AV node (rather than fusionconduction over the AVN and the accessorypathway). The inability to clearly demon-strate the sudden and absolute loss ofmanifest PRX during exercise warrantsinvasive electrophysiology testing.

In the past, sodium channel blockingagents (ajmaline, procainamide, etc.) wereused to determine properties of the accessorypathway.23-25 The specificity of loss of pre-excitation after drug administration waspoor, and this technique is no longer utilizedfor risk assessment.

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Figure 4. Preexcited ECG; sinus rhythm with conduction competing over AP and AV node; all QRS complexes arepreexcited (fused).

Figure 5. Preexcited AF with rapid conduction over the AP. The Shortest preexcited R-R interval (SPERRI) is 240 ms.

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INVASIVEELECTROPHYSIOLOGY TESTING

Invasive electrophysiology testing also canbe used for risk stratification as an alternativeapproach to noninvasive risk stratification forasymptomatic patients. An electrophysiologystudy is recommended in asymptomaticpatients when non-invasive testing is ambig-uous or uncertain regarding the risk. When anelectrophysiology study reveals high risk inan asymptomatic patient, mapping of theaccessory pathway’s location and ablationtherapy are usually performed (as a potential-ly definitive treatment) of the accessorypathway. Invasive electrophysiology testingis also strongly indicated in certain asymp-tomatic patients with a WPW pattern whenthere is a coexistent cardiac abnormality. It isalso recommended when multiple accessorypathways are suspected. For symptomaticpatients with palpitations/tachycardia, anelectrophysiology study with ablation is clear-ly recommended. Invasive electrophysiologytesting is usually not recommended in anindividual over age 40 to identify stratify risk.

During the electrophysiology study, theinducibility of tachycardias is assessed aswell as the conduction characteristics of theaccessory pathway. The antegrade conduc-tion property is measured by the effectiverefractory period of the accessory pathway(or also defined by the shortest preexcited R-R interval [SPERRI], as discussed earlier). Inchildren, SPERRI ,220 ms carry a threefoldincrease in risk of sudden cardiac deathcompared to the general WPW population.17

Long anterograde ERP/SPERRI (.250 ms) ofthe accessory pathway indicates limitedcapability of anterograde conduction viaaccessory pathway and indicates low riskfor ventricular fibrillation and sudden cardi-ac death. The sensitivity and negative pre-dictive value of SPERRI (# 220 ms) is highand well established,26-29 but the specificityand positive predictive values of predictingsudden cardiac death are low.30,31 The verylow event rates of ventricular fibrillation

challenge the accuracy of electrophysiologytesting to predict sudden cardiac death.32

MANAGEMENT

Radiofrequency Ablation Therapy

In symptomatic WPW syndrome, radio-frequency (RF) ablation therapy is the well-established first line of therapy. It is alsoindicated in some occupations in which thedevelopment of symptoms would put them-selves or others at risk (eg, truck drivers orairline pilots, some athletes).

In asymptomatic patients, ablation of theaccessory pathway decreases the incidence ofpotential future symptomatic arrhythmias;however, studies are not powered to detectreduction in mortality.22 A decision to pro-ceed with ablation in asymptomatic cases isrecommended when risk stratification revealshigh risk features. It can be also consideredwhen the WPW pattern is associated withstructural heart disease. Otherwise it is madeon a case-by-case basis with careful discussionbetween the clinician and the well-informedpatient who balances a very small immediateablation risk with a very small longer-termrisk without ablation.32 Low-risk patientswith WPW on the ECG require reassurance.

For the procedure, 3-4 diagnostic cathetersand 1 ablation catheter are inserted via thetransvenous route and positioned at specificsites in cardiac chambers in order to recordintracardiac electrograms during the pacingguided electrophysiology study. With pacingmaneuvers, the accessory pathway propertiesare defined, potential tachycardias are in-duced, accurate mapping (localization) of theaccessory pathway is achieved and radio-frequency ablation is employed. Under specialcircumstances other energy sources are used(ie, cryoablation). Permanent disappearanceof the accessory pathway and non-inducibilityof tachycardia define acute success.

The success rate with catheter-based ablationis approximately 90% to 95%, depending uponthe location of the accessory pathway and theprecision of pathway localization.33,34 The

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recurrence rate of the accessory pathway isaround 8%. However, this depends on thelocation of the accessory pathway andthe possibility of multiple accessory pathways.This can increase the recurrence rate to 21%.Recurrences are often seen within 12-24 hours,or rarely later, usually within 2-3 months.35-37

The procedure carries a small risk ofcomplications. The incidence of major pro-cedural complications associated with elec-trophysiology studies and ablations has beenreported to be approximately 2%. Mostcommon are cardiac perforation with tam-ponade, advanced AV block, coronary arteryinvolvement and thromboembolic events.Other adverse events also can occur (hema-toma at entry site, RBBB, LBBB, valvularregurgitations, etc.). Mortality rates are re-ported to be 0.07% - 0.19%.35,38,39

DRUG THERAPY

Less frequently antiarrhythmic drugs are usedfor preventing tachycardia (SVT/AVRT). Effi-cacy is related to their ability to alter theelectrophysiologic properties of the circuit,rendering the circuit incapable of sustainingreentry. Some features and co-morbidities (ie,overt preexcitation, concomitant structuralheart disease, ischemia, etc) need to be consid-ered to choose the proper medication. Chronicand acute therapy for accessory pathway-related arrhythmia management and preven-tion requires careful decision making.

REVISITING THE CASES

Case # 1

The 23-year-old male client has no dis-closed medical history. His ECG showsa WPW pattern, and the mortality risk isunclear at this point. In the absence of anytests, the ‘‘red flags’’ in his case are theyounger age, male sex, and the lack ofinformation about symptoms. Since this in-dividual has persistent preexcitation on hisECG, clinical assessment will be helpful forhim to be able to get insurance. We noticed

QS complexes in lead III and AVF. Q waves/QS complexes can be seen on Wolff-Parkin-son-White pattern ECGs. This pattern isa nonpathological cause of Q waves.

Case # 2

The 45-year-old woman has a clear historyof palpitations. Her ECG reveals intermittentpreexcitation. Without any tests, her risk canbe considered low based on her age, sex andparticularly based on the intermittent patternof the preexcitation, which suggests pooranterograde conduction capability of theaccessory pathway. In addition, she admittedcardiac investigations for palpitation in thepast and was advised to undergo observa-tion only. Her mortality risk is low, probablyidentical to the insured population risk. Shedoesn’t require any further evidence toindicate that she is insurable.

SUMMARY

In summary, the Wolff-Parkinson-Whitesyndrome requires an assessment, re the needfor an electrophysiology study and possibleablation therapy. Asymptomatic patientsneed clinical assessment. If careful historytaking reveals symptoms, noninvasive assess-ment is indicated and electrophysiologystudy may be indicated. In the case of trulyasymptomatic patients with WPW pattern ontheir ECG, non-invasive testing may beconsidered. ‘‘Low-risk’’ individuals are usu-ally followed without invasive testing as longas they remain asymptomatic. Intermittentpreexcitation suggests low risk for life threat-ening events. High risk features or ambiguousfindings require invasive assessment. Keep inmind that very low event rates of ventricularfibrillation challenge the accuracy of electro-physiology studies to predict sudden cardiacdeath. The negative predictive value of theSPERRI .250 ms is well established, but thepositive predictive value of the SPERRI topredict sudden cardiac death remains low.For insurance purposes, patients over age 40

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with an asymptomatic WPW pattern on theirECG have a minimal risk for serious events.Younger patients with WPW pattern on theirECG require assessment.

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