WPW SYNDROMEWPW SYNDROMERavi Kumar,DM(Cardiology)

NIMS,Hyderbad-50082India

Historical perspectiveHistorical perspective

The earliest description of an accessory pathway was reported by Stanley Kent in 1893 who suggested that impulses can travel from the atrium to the ventricle over a node-like structure other than the atrioventricular (AV) node.

Cohn and Fraser reported the first case of pre-excitation syndrome in 1913

In 1930, Louis Wolff, Sir John Parkinson, and Paul Dudley White published a seminal article describing 11 young patients who suffered from attacks of tachycardia associated with an electrocardiographic pattern of bundle branch block with a short PR interval

Ohnell was the first to use the term “pre-excitation,” whereas Seters described the slurred initial component of the QRS complex as a “delta” wave.

Curative therapy of WPW syndrome was demonstrated in 1967 when Cobb et al successfully ablated an accessory pathway during open-hear surgery

The first successful catheter ablation of an accessory pathway by delivering direct current energy was reported by Morady and Scheinman in 1984.

In 1987, Borggrefe et al. successfully ablated a right-sided pathway by delivering RF current. Radiofrequency ablation of accessory pathways has become a first line therapy and is favoured over the medical treatment in most of the patients.

INTRODUCTIONINTRODUCTIONPatients with pre-excitation

syndromes have an additional or accessory pathway, which directly connects the atria and ventricles.

In the Wolff-Parkinson-White pattern, AV conduction through the bypass tract results in earlier activation (preexcitation) of the ventricles than if the impulse had travelled through the AV node

Classic accessory pathway is the AV bypass tract or bundle of kent in WPW

James fibres, AN tracts connect atrium to distal AV node

Brechenmacher fibres(atrio- hisian tracts) connect atrium to HIS bundle

Hisian -fascicular tracts(Mahaim fibres)

CONDUCTIONCONDUCTION

FrequencyFrequency

Delta waves detectable on an ECG have been reported to be present in 0.15% to 0.25% of the general population.

A higher prevalence of 0.55% has been reported in first-degree relatives of patients with accessory pathways. Wolff–Parkinson–White syndrome is more commonly diagnosed in men than in women, although this sex difference is not observed in children.

Among those with the Wolff–Parkinson–White syndrome, 3.4 percent have first-degree relatives with preexcitation.

The familial form is usually inherited as a mendelian autosomal dominant trait

Inherited form of WPW syndrome associated with familial hypertrophic cardiomyopathy has been recently described with the locus mapped to chromosome 7q33.

The term Wolff-Parkinson-White syndrome is used to describe individuals with ventricular pre-excitation and symptomatic tachycardias as originally described by Wolff, Parkinson and White.

The term Wolff-Parkinson-White pattern refers to the electrocardiographical finding of ventricular preexcitation.

VariantsVariants

Concealed Accessory Pathways Defined as pathways that are capable of

conduction only in the retrograde (VA) direction at rates similar or greater than the sinus rate.

The concealed accessory pathways are noted in between 15% to 42% of patients with accessory pathway.

Approximately one third of AVRTs are due to concealed accessory pathways.

The clinical presentation of patients who have a concealed accessory pathway is similar to the classic presentation of WPW syndrome with the exception that no preexcitation, rapid preexcited responses are not observed during AF.

Concealed pathways are more frequently localized to the left free wall (64%), and less frequently in Septal (31%) and right free wall locations.

Decremental Accessory Decremental Accessory pathwayspathways

The electrophysiologic properties of accessory pathways are similar to working myocardium.

Few accessory pathways may exhibit progressive delay in conduction in response to increased rate of pacing.

Decremental conduction can be seen in approximately 7% of the patients with WPW syndrome

Multiple accessory pathways are present in as many as 13 percent of patients

Most patients with accessory pathways do not have any structural cardiac abnormalities but as many as 10 percent of patients with Ebstein’s anomaly have one or more accessory pathways.

PathophysiologyPathophysiology

Accessory AV muscle bridges are normally presented in human fetal hearts but these connections are interrupted during growth of the fibrous annulus

Most accessory pathways consist of small fibers resembling ordinary myocardium crossing the AV groove.

The pathways insert directly into the atrial and basal ventricular myocardium but they may course through the AV groove at variable depth ranging from subepicardial to subendocardial locations.

Accessory pathways may have an oblique course rather than perpendicular to the transverse plane of the AV groove, resulting in an atrial insertion that may be transverse some distance from the ventricular insertion site.

The presence of very short AV nodal conduction times may cause the ventricular preexcitation to be invisible on the surface ECG.

Preexcitation can also be minimal when the accessory pathway is located on the lateral mitral ring relatively far from the origin of the sinus impulse.

It was postulated that preexcitation pattern with a PR interval >120ms typically indicates a left free wall accessory pathway.

AV reentrant tachycardias (AVRT) occur when two functionally different conduction pathways are present.

The effective refractory period of the accessory tract is usually longer than that of the normal AV nodal His-Purkinje tract.

orthodromic atrioventricular orthodromic atrioventricular reciprocating tachycardia reciprocating tachycardia (AVRT) (AVRT)

Preexcitation pathwaysPreexcitation pathways

Antidromic AVRTAntidromic AVRT

Patients with antidromic tachycardias have usually shorter refractoriness in the normal retrograde VA conduction system and the maintenance of tachycardia is favored by the greater distance from the normal AV node.

AVRT using two accessory pathways is a rare form of tachycardia with broad QRS complexes in which anterograde conduction is down one accessory pathway and retrograde conduction is up another.

The rate of the AVRT depends on the conduction times of all tissues involved in the reentrant circuit and on the autonomic tone modulation.

QRS complex alternans during supraventricular tachycardia is relatively specific for AVRT.

AFAFVentricular rates up to 350 bpm are

possible and the QRS morphology reflects varying degree of preexcitation due to conduction over the normal AV node as well as the accessory pathway.

A causal relationship between ventricular fibrillation and atrial fibrillation with rapid ventricular response has been documented

SymptomsSymptoms

The usual complaint of patients with WPW syndrome and recurrent tachycardia is usually rapid palpitations associated with chest discomfort, shortness of breath, lightheadedness or syncope.

The onset and offset are typically sudden. Some patients may report precipitating factors such as coffee, stress, menstrual periods or pregnancy but most usually the symptoms are sporadic and unpredictable.

Sudden death is rare but may sporadically be the initial presentation in previously asymptomatic individuals.

A history of syncope raises concerns regarding a very rapid arrhythmia with haemodynamic compromise.

The WPW pattern in symptomatic or asymptomatic infants usually disappears, especially in the first year of life.

However, once symptomatic recurrent tachycardias appear in adolescence or adulthood, the course is usually one of recurring episodes.

Sudden death in WPW Sudden death in WPW syndromesyndromeThe incidence of sudden cardiac death in

patients with the WPW syndrome has been estimated to range from 0.15% to 0.39%.

It is unusual for cardiac arrest to be the first symptomatic manifestation of WPW syndrome.

Risk factors identified for sudden death include,a shortest pre-excited R-R interval less than 250ms during spontaneous or induced AF, history of symptomatic tachycardia, multiple accessory pathways, Ebstein’s anomaly and familial WPW syndrome.

Findings suggestive of a low likelihood of sudden death include

preexcitation that is intermittent, the ability to produce anterograde

conduction block with drugs such as procainamide, and

the disappearance of preexcitation during exercise

In patients without manifest pre-excitation the initial activation of the septum is usually from the left to the right side producing a Q wave in lateral leads and R wave in lead aVR.

It was claimed that in the presence of a manifest accessory pathway the usual septal activation is masked and therefore the finding of a septal Q wave in lead excludes ventricular pre-excitation.

However, several other studies have reported the presence of the septal Q wave in lead V6 despite manifest pre-excitation.

46 to 60 percent of accessory pathways are found within the left free wall space

25 percent are within the posteroseptal space

13 to 21 percent of pathways are within the right free wall space

2 percent are within the anteroseptal space

AV ACCESSORY AV ACCESSORY PATHWAYSPATHWAYS

Localization of the accessory Localization of the accessory pathwaypathwaySeveral algorithms have been

proposed for anatomical localization of the accessory pathway.

Rosebaum in 1945 divided WPW into type A, left sided pathways (tall R

wave in lead V1, i.e. a positive delta wave), and

type B, right sided pathways (QS complex in lead V1, i.e. a negative delta wave)

Polarity of QRS

QRS AXIS

DELTA AXIS

V1 V2 V3

Antero septal - - - NORMAL NORMAL

Rt lat - - - LEFT

[ -60]LEFT[ -60]

Rt postseptal - + + LEFT [ -

30]LEFT[ -60]

Lt postseptal + + + LEFT[ -30] LEFT[ -60]

Lt lateral + + + INFERIOR

[+60 TO 90]

INFERIOR[+ 90 TO 120]

DELTA IN V1

QRS IN V1 QRS IN V2

RT POST SEPTAL

ISO or NEGATIVE

DOMINANTLY NEGATIVE

POSITIVE

LT POST SEPTAL

POSITVE [ALWAYS]

DOMINANTLY POSITIVE or equiphasic

positive

The predictive accuracy of all these algorithms is significantly reduced in the presence of multiple pathways.

Coexistent anomalies such as Acute MI or LVH may alter the QRS morphology

Electrophysiological Electrophysiological assessmentassessmentThe main indication for

electrophysiological testing is a decision to undergo catheter ablation or less frequently, diagnostic study for risk stratification.

Electrophysiological studies utilize the placement of a decapolar catheter to the coronary sinus and three quadripolar catheters to the high right atrium, right ventricular apex and His bundle region.

The presence of an accessory AV connection is confirmed by the presence of a delta wave on the surface ECG and increased preexcitation and shortening of HV interval during incremental and programmed atrial pacing.

Indications of Indications of ElectrophysiologicalElectrophysiological Studies Studies in WPWin WPW 1) Sudden deaths have the peculiarity to occur

during exercise, hence all competitive athletes with WPW syndrome should be studied.

2) Patient with high responsibility profession such as professional pilot (plane, truck, bus, train)

3) The indications in children are more controversial, the conductionin accessory pathway and normal AV conduction system are more rapid, probably without a clinical significance.

The indications should be liberal in children who are competitive athletes and in all children above the age of 10 years.

4) In elderly, the propensity for atrial fibrillation increases hence the risk of occurrence of a potentially severe arrhythmia in an asymptomatic WPW patient should not be underestimated.

Atrial pacing from the sites closer to the accessory pathway will preferentially conduct over this pathway with enhanced preexcitation.

Therefore, in a patient with a left-sided accessory pathway, the stimulus to delta wave will be shorter during pacing from the coronary sinus than during right atrial pacing. This is especially useful in exposing left-sided pathways with minimal preexcitation on the surface ECG.

Multipolar catheters located in the coronary sinus are useful for accurate localization of the left sided accessory pathways as the coronary sinus runs in the epicardial fat in the posterior groove around the posterior and lateral aspects of the mitral valve.

The coronary sinus ostium empties into the junction of the inferior and medial walls of the right atrium and approximates the inferoposterior corner of the interatrial septum.

Mapping on the tricuspid ring is more difficult and preformed sheaths to facilitate contact, multipolar “halo” catheters to record signals along the tricuspid ring or catheters for mapping within the right coronary artery are available.

The distal portion of the catheter recording the His bundle electrogram approximates the superior limit of the atrial septum where it joins the tricuspid valve.

Exact localization of an accessory pathway may be limited by the possible occurrence of multiple pathways.

It may also be difficult to distinguish between retrograde atrial activation due to a midseptal pathway and atypical AV node reentry.

The use of pharmacologic agent that selectively slows conduction over the AV node, such as adenosine, may be useful to accentuate accessory pathway conduction during atrial pacing.

Left lat APLeft lat AP

Diag criteriaDiag criteria

Antidromic tachycardiaAntidromic tachycardiaObligatory 1:1 AV relationship.QRS morphology in tachycardia

consistent with max preexitation.Tachycardia QRS morphology

reproduced by atrial pacing near pathway insertion.

Advanced ventricular activation by atrial extrastimuli near insertion with advancement of subsequent His activation.

Changes in V –His interval precede changes in cycle length.

The presence of an accessory pathway participating in the tachycardia circuit can be confirmed by prolongation of the cycle length with ipsilateral bundle branch block and termination of tachycardia after a premature ventricular extrastimulus that does not conduct to the atria and occurs when the His bundle is refractory.

Differentiation between atrial tachycardia and AVRT is best accomplished by dissociating the ventricles from the tachycardia.

The demonstration of a VA-AV response after termination of ventricular pacing that entrains the atrium excludes an AVRT and confirms atrial tachycardia

For left free wall accessory pathways, the diagnosis of AVRT can be mimicked by antrioventricular nodal reentry with eccentric atrial activation or by atrial tachycardias arising from the CS musculature or the ligament of Marshall.

The differential diagnosis of an antidromic tachycardia includes ventricular tachycardia that should be diagnosed by the dissociation of the atrium from the ventricle or a variable His-to-atrium timing relationship without alteration of the tachycardia cycle length.

Antidromic tachycardia is diagnosed by demonstrating the reproduction of tachycardia QRS morphology by atrial pacing at the presumed accessory pathway insertion site and advancement of the ventricular and subsequent His activation by a premature atrial stimulus near the accessory pathway site.

VA conduction indices : Using ventricular-induced atrial pre-excitation, Miles et al  devised pre-excitation index

Progressively premature right ventricular extrastimuli were introduced during tachycardia and the difference between the TCL and the longest stimulation interval at which atrial pre-excitation occurred 

pre-excitation indexpre-excitation index

Atrial preexcitation at >90% TCL means the presence of a septal or right sided BT

If PEI is <25 then Anteroseptal or Right Free Wall

If PEI is > 75 then Left Lateral or AVNRT

More than 75 ms – left free wallLess than 45 ms- septal tracts

The new index was computed (AV conduction time during SVT)

+ (ventriculoatrial conduction time during ventricular pacing at the SVT cycle length) -(SVT cycle length). 

new index could differentiate AV reentrant tachycardia (index 60 ms,) from AV nodal reentrant tachycardia ( 100 ms ).