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Pre-excitation syndromes in children

This article discusses the various types of pre-excitation syndromes in children, including their causes, symptoms, and management. It explores the different types of accessory pathways and their association with congenital heart defects.

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Pre-excitation syndromes in children

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  1. Pre-excitation syndromes in children Dr.K.Mahesh

  2. Introduction

  3. What are “Pre-excitation syndromes” ? • Term coined by Ohnell • A group of ECG and Electrophysiological abnormalities in which • The atrial impulses are conducted partly or completely, PREMATURELY, to the ventricles via a mechanism other than the normal AV-node * • Associated with a wide array of tachycardias with both normal QRS and prolonged QRS durations *Moss & Adams

  4. RE-ENTRANT V. regular Abrupt onset/cessation Easily initiated Easily terminated Responsive to drugs AUTOMATIC Wide variation “Warm-up, cool-down” Not so Not so Atypical responses Re-entrant Vs Automatic Tachycardias

  5. Origin of the Accessory pathways ? • In early stages of cardiac development, there is direct physical and electrical contact between the atrial and ventricular myocardium • ….disrupted by susequent in-growth of the AV sulcus tissue and formation of the annulus fibrosus • Defects in this annulus results in accessory pathhways

  6. Most of these connections are of ventricular myocardial origin, rather than of atrial issue origin • May be found anywhere across the tricuspid or mitral valve annulus – whether endocardial or epicardial • Most common pathways in children are Left Free Wall followed by Posteroseptal and Right Free Wall ; Midseptal and Anteroseptal are least common * *Calkin et al, Circulation 1999

  7. AP mediated SVTs account for > 70% of all SVTs in children who have not undergone surgical repair of CHDs * *Burchell et al – 1986, Ko JK et el - 1992

  8. Atrio-ventricular Accessory Pathways & the Ventricular Pre-excitation Syndromes

  9. Understanding the variations in “Pathway – electrophysiology – the key to understanding variations in presentations and management issues • Number , Location , Direction of Propagation & Propagation velocities

  10. WPW - ORT

  11. Antidromic WPW

  12. ORT - URAP

  13. PJRT

  14. Mahaim

  15. WPW Syndrome

  16. 1930 : Wolf, Parkinson & White described a syndrome that consisted of • Short PR-interval (<0.12 sec) • Bundle branch block on surface QRS • Paroxysmal tachycardia • 1932: Wolferth and Wood – hypothesized Extra-nodal AV connections to be the basis for this syndrome • 1969: Sealy et al surgically confirmed. • Characteristic appearance on surface ECG during Sinus Rhythm: • Short PR interval • Slurred initial QRS ( ‘Delta wave’ ) resulting in broadening of the QRS complex , without widening the duration from beginning of P to end of QRS

  17. WPW Syndrome • The most common cardiac pre-excitation syndrome. • Overall incidence in a population study of Olmstead County, Minnesota : 3.96/100,000 persons/year. (*Munger et al. Circ 1993) • Exact cause unknown. • Most cases sporadic. • Bimodal age distribution – 1st year, then young adulthood. • 3% of Probands have an affected 1st-deg relative. • Familial occurrence reported – autosomal dominant inheritance. • Recent report – Chr 7q3 in a family with WPW / HCM / HB. • Tuberin and Hamartin gene mutations in WPW + Tuberous Sclerosis • Myo Binding Prot / cardiac troponin gene mutations in WPW + HCM

  18. Accessory Pathways and CHD APs in CHD have a strong association with the TV Multiple APs are common

  19. Generally, AV conduction through the accessory pathway is faster than through the AV Node. • Thus, some part of the ventricle is “pre-excited” by this eccentric spread of activation • Surface ECG in Sinus Rhythm depends upon the balance between ventricular depolarization occuring through the AV node vs the Accessory Pathway • Greater the contribution of the Accessory Pathway to ventricular depolarization, smaller the PR interval, more prominent the Delta Wave

  20. Electrophysiological characteristics • Short or negative H-V interval on His-Bundle electrogram • Atrial pacing enhances pre-excitation • AV block results in maximum pre-excitation • Faster AV conduction ( Exercise / Isoproterenol) decreases the pre-excitation • Pre-excitation is lost when RR interval shortens below the AP effective refractory period (ERP)

  21. In WPW Syndrome, Accessory Pathways are usually capable of conducting in both directions • Usually the APs are “Non-decremental” in nature • Can potentially result in several different types of tachycardias • Orthodromic reciprocating tachycardia (ORT) with retrograde AP conduction is the commonest • ORT is also commonly seen in patients without manifest pre-excitation – “ Concealed Pathways “ • Antidromic tachycardia (ART) is seen as well, but seldom in isolation without ORT

  22. Risk of sudden death from rapid Ventricular response to Atrial Fibrillation

  23. Per se, WPW refers to patients with pre-excitation in ECG + symptomatic episodes of tachycardia – “Manifest Pathways” • Asymptomatic patients with pre-excitation pattern are simply described as having “VPE pattern” • Patients with Accessory Pathways, but no pre-excitation are described as having “Concealed Pathways”. Pathways may become manifest during episodes of tachycardia

  24. WPW - ORT

  25. WPW - ORT

  26. ORT • The most common manifestation of WPW in children • Accounting for almost 90% of SVTs • Large peak in infancy • Smaller peak between 6-8 years • Though the most common SVT in patients with manifest WPW, only 27-35% of patients with ORT have pre-excitation

  27. ORT occurs paroxysmally – with or without exercise • Manifest as self-limited episodic palpitations with shortness of breath, fatigue or dizziness • Syncope is uncommon but worrisome • Usually well tolerated • Can cause ventricular dysfunction / hemodynamic collapse if undetected for hours / days, especially in infants • Faster rates (>250 BPM) and poorer condition at presentation are seen in younger children • Severe symptoms occur in only about 1% older children and adult patients • ECG Features: • Narrow QRS @ 215 – 350 BPM in infants ; lower rates in older children • Tachycardia rate largely determined by AV nodal conduction • Rate-related BBB may occur especially at initiation of tachycardia ; can help in localization of the Accessory Pathway as left / right • Retrograde ‘P’s usually occur during T-wave

  28. Electrophysiological Study for confirmation of ORT • Premature ventricular beat placed when the His Bundle is refractory results in blocking-off of the Accessory Pathway resulting in termination of the tachycardia without atrial activation • Ventriculo-Atrial (VA) interval is prolonged by introduction of a premature VPB when the His is refractoy • Retrograde atrial activation pattern demonstrating eccentric atrial conduction, identically matching that during ventricular pacing • BBB during tachycardia results in persistent lengthening of the tachycardia cycle-length • VA prolongation occurs with BBB aberration when AP is ipsilateral to the BBB

  29. Initiation of Tachycardia • Critically timed Atrial premature stimulus that blocks anterograde in the Accessory connection, and encounters an appropriate delay in AV Node conduction so that AP and Atria are excitable when the re-entrant wave-front reaches them • That is, at an interval < ERP of the AP • Isoproterenol • Other intiating events : High catecholamine states, exercise, sinus acceleration, junctional beats (conducting antegrade only in AVN) , VPBs ( conducting retrograde, only in the AP)

  30. Termination of tachycardia • Spontaneous OR drug-induced block in either the AVN OR AP • OR placement of a critically timed APC that encounters AVN or AP when they are refractory • Spontaneous termination occurs more frequently with AVN due to increases in the vagal tone • When the last beat of the tachycardia is manifest as an atrial stimulus without the following ventricular stimulus = Termination in the AVN • When the last beat of the tachycardia is manifest as a ventricular stimulus without the following atrial stimulus = Termination in the AP

  31. Electrophysiological features for differentiating ORT from AVNRT • Atrial recording ( INTRACARDIAC or ESOPHAGEAL ) • ORT : VA interval > 95 milliseconds (intracardiac recording) or > 70 milliseconds ( esophageal recording) in ORT • Typical AVNRT : VA interval < 70 milliseconds by either method • { Positive predictive value 94% ; Negative predictive value 100% ; Sensitivity 100% ; Specificity 92% } • ORT via ‘Septal pathways’ Vs AVNRT - Para-Hissian pacing • Comparison of the VA intervals with high-output & low-output pacing • { Hight output captures both His and the ventricle ; low output only captures the ventricle } Unchanged VA makes Septal pathway more likely • Premature VPB when His is refractory confirms presence of Acc Pathway

  32. Likelihood of recurrence of ORT increases with age at presentation • ** Data derived from studies including both treated and untreated patients ** • Recurrence rate in ‘untreated’ patients unknown, but likely to be higher than in treated patients • Recurrence rates are independent of whether pre-excitation is ‘manifest’ or NOT.

  33. WPW - ART

  34. Antidromic WPW

  35. ART • 10% of SVTs in Adults and < 5% SVTs in children • Rates similar to ORT but dizziness / syncope more common than in ORT ( due to more uncoordinated ventricular depolarization) • Wide complex tachycardia • Maximal Pre-excitation – ventricular activation entirely through AP • Retrograde P-waves – axis about -120 degrees • Multiple APs (33%) account for variations in patterns of SVTs

  36. Requirements for occurrence of ART • AVN anterograde conduction be blocked, while it continues in the AP , i.e. • Anterograde ERP of AP < ERP of AVN • Requirements for maintenance of ART • Retrograde RP of AVN < tachycardia cycle length • Infrequency of both of these occurring makes it an infrequent tachyarrhythmia

  37. Electrophysiological features for differentiating ART from other Wide-QRS tachycardias • Regularity of ART rules out Pre-excited atrial fibrillation • Termination of tachycardia with a VPB that does not depolarize the atria or His rules-out Pre-excited atrial flutter and EAT • Ventricular Tachycardia ruled out by • An Atrial premature beat that terminates the tachycardia without conducting to the ventricle • APB can advance the tachycardia cycle-length with the SAME QRS pattern • AVNRT with antegrade conduction down a ‘bystander’ AP ruled out by • APB that advances the tachycardia, but next atrial actrivation occurs with the same VA interval and same retrograde atrial activation • In general, the VA interval is shorter in AVNRT

  38. Immediate management of SVT with WPW Syndrome

  39. Verapamil consistently effective but contraindicated in infants Both Dig & Verapamil ABSOLUTELY contraindicated in WPW with Atrial fibrillation or flutter

  40. Digoxin and Verapamil can decrease the ERP of the AP and thereby increase the rate of conduction of Atrial impulses to the Ventricles Infants have under-developed Sarcoplasmic Reticulum and may have severe hemodynamic collapse resulting from blocking off of the trans-membrane Ca2+ channels by Verapamil

  41. WPW with Pre-excited Atrial Fibrillation / Flutter

  42. Pre-excited Atrial Fibrillation or Flutter in WPW • It is the presenting symptom in 25% of older patients with WPW • Risk of atrial fibrillation in adults with WPW – 10% to 38% • Spontaneous Atrial fibrillation is rare in children with WPW and even rarer in infants • Presence of extremely rapid conducting APs in infants has potential for disaster if atrial fibrillation DOES occur • Can potentially result in rapid ventricular activation, even ventricular fibrillation, depending upon conduction times and ERPs of the AVN and the AP

  43. Why does Atrial Fibrillation occur?

  44. Why does the ventricular rhythm degenerate during Atrial Fibrillation ?

  45. PRIMARY ATRIAL ACTIVITY AS A CAUSE FOR ATRIAL FIBRILLATION IN WPW • Jais et al (Circulation 1997) suggested rapidly firing focal atrial activity as the trigger for Atrial fibrillation in a subset of young patients without structural heart disease • Basso et al in Circulation Jan 2001 reported the presence of histopathological evidence of ‘focal atrial myocarditis’ in 4 of 8 (50%) patients with WPW Syndrome out of a total series of 273 children and young adults (<35 years) who had Sudden Cardiac Death • Lymphocytic infiltrates in 75% • Polymorphous infiltrates in 25%

  46. Arrhthmogenic Atrial Myocraditis

  47. Why does the ventricular rhythm degenerate during Atrial Fibrillation ? Atrial fibrillation SCD Ventricular fibrillation

  48. Irregularly irregular rhythm in Atrial fibrillation, strictly regular in flutter Variable fusion between AVN and AP conduction resulting in varying QRS morphologies Presence of two distinct QRS patterns suggests multiple APs EP Risk factors Inducible atrial fibrillation H/o ventricular fibrillation RR interval < 250ms and antegrade AP ERP < 340ms In children, atrial fibrillation may be difficult to induce, so response of APs to rapid atrial pacing may suffice ECG features EP Factors

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