“Symptomatic” Pre-excitation in Pediatrics: Review of Two Cases

Introduction

Although a classical arrhythmic substrate in the pediatric electrophysiology realm, Wolff-Parkinson-White (WPW) syndrome can still pose a challenge for diagnostic and therapeutic management. Children five years of age or older presenting with “palpitations” and a WPW EKG pattern are typically offered an electrophysiology study, with catheter ablation as first-line therapy. This practice is based on the fact that most children with symptomatic WPW will have inducible supraventricular tachycardia, and only a minority will exhibit weak antegrade accessory pathway (AP) properties such that the future risk of pre-excited atrial fibrillation will be negligible.^1,2 

We present two cases of “symptomatic” pre-excitation in which the pre-excitation variant was incapable of supporting any arrhythmia, and in which catheter ablation would be unnecessary or contraindicated.

Case #1

A 19-year-old female presented with a long history of symptomatic palpitations in the setting of pre-excitation on surface ECG (Figure 1). She had undergone three previous EP studies at another center for ablation of a right anteroseptal accessory pathway without inducible sustained tachycardia. Her procedures showed antegrade pre-excitation with weak antegrade conduction but with persistent pre-excitation. During previous procedures, the antegrade pathway conduction was mapped to the earliest ‘V’ and the retrograde pathway was mapped to the earliest ‘A’. Conservative ablation of the antegrade pathway signal with a 6 mm cryocatheter resulted in transient suppression of pre-excitation. However, the patient continued to have symptomatic palpitations during follow-up after each successive attempt of ablation of the right anteroseptal pathway. Ablation of the retrograde limb was not attempted due to inability to monitor the AV node conduction properties. 

The patient was eventually referred for a second opinion for persistent symptomatic pre-excitation. Repeat event monitoring revealed palpitations occurring during periods of sinus tachycardia with and without pre-excitation, and there was no evidence for SVT. After reviewing previous EP study documentations, comprehensive maneuvers were not performed which could assist in further differentiation of the etiology of pre-excitation. Due to patient preference, the patient was brought to the EP lab for her fourth EP study and possible catheter ablation of a high-risk septal WPW pathway.

Approach

At baseline, the patient had sinus rhythm with pre-excitation at a cycle length of 940 ms. The A1-H1 interval was 63 milliseconds and the H1-V1 interval was short, but not negative, at 9 milliseconds. 

During antegrade AV conduction maneuvers, there was no dual AV node physiology elicited. Atrial extrastimulus testing was performed from the coronary sinus at a cycle length of 600 ms. The A2-H2 interval was decremental, measuring 86 ms at 600/450 ms to a maximum of 151 ms at 600/310 ms. At 600/300 ms, there was AV nodal effective refractory period (ERP), but atrial ERP was not encountered. Accessory pathway ERP was seen above 600/500 ms, and there was no inducible echo beats or non-sustained supraventricular tachycardia. Decremental atrial pacing was performed, which revealed an AV nodal Wenckebach at a pace cycle length of 300 ms. 

Retrograde V-A conduction maneuvers were performed that revealed a V-A Wenckebach at a cycle length of 500 ms with a central retrograde activation pattern, suggesting no retrograde or minimal retrograde AP conduction properties. 

Epinephrine Infusion

An epinephrine infusion was administered at 2 mcg/min and then increased to 4 mcg/min to facilitate any accessory pathway conduction. During this period, paired base-to-apex pacing showed a V-A interval of 75 ms from the RV base compared to 117 ms from the RV apex. This is suggestive of a basal insertion of an accessory pathway; however, during para-Hisian pacing, the narrow QRS complex had a V-A interval of 65 ms and the wide QRS complex had a V-A interval of 128 ms (Figure 2), which is inconsistent with the presence of a septal accessory pathway. 

Atrial extrastimulus testing was repeated with single and double extrastimuli in the presence of epinephrine, and there was no induction of tachycardia or retrograde atrial echo beats. However, there was a junctional beat that occurred coincidentally simultaneous to an atrial-paced beat that failed to capture that was still pre-excited, proving the presence of an infra-Hisian variant of pre-excitation known as a fasciculoventricular pathway (FVP) (Figure 4). There should be no pre-excited junctional complex in the setting of a conventional annular AP. 

A retrograde right atrial 3D activation map was constructed during slow ventricular pacing. The earliest retrograde atrial sites were seen diffusely at the His bundle position, suggesting either a para-Hisian AP or normal retrograde AV node conduction, or both. A Marinr catheter (Medtronic) was positioned in series with the His bundle catheter from a superior internal jugular vein approach, such that a continuous His recording was achieved from proximal to distal, beginning with the ablation catheter and ending with the distal pole of the His catheter (Figure 5). The most proximal portion showed an AH interval of 61 ms followed by the septal pre-excitation with a short H-V interval. Differential pacing from multiple sites in the right atrium showed a consistent H-V interval relationship with no negative HV interval values recorded. These findings are not consistent with a conventional tricuspid annular accessory pathway, but rather an FVP.

Adenosine Challenge

Adenosine was administered in consecutive boluses of 6 mg, 12 mg, and 18 mg doses during pre-excited sinus rhythm. After the 18 mg bolus of adenosine, there was a diagnostic change visualized on the His catheter where the A1-H1 interval increased from 61 ms to 102 ms, followed by a return to the baseline 61 ms. The H-V interval began at 11 ms and reached a minimum of 0 ms, and then returned to the baseline again with a short, but never a negative, HV interval (Figure 6). With an increase in the A-H interval, an associated unchanged infranodal H-V interval is not consistent with a septal accessory pathway. 

Conclusion

With this criteria, we demonstrated normal AH physiology, the presence of a septal, right-sided infranodal (FVP) pathway, and only normal retrograde AV node physiology via para-Hisian pacing. The data suggest a right septal infra-Hisian FVP bystander pre-excitation that is incapable of supporting conventional supraventricular tachycardia or malignant pre-excited atrial fibrillation. The procedure was concluded and no intervention was required. It is important to differentiate FVP from WPW, as only the latter is associated with sudden cardiac death risk, and attempted ablation of this structure carries a fairly high risk of iatrogenic heart block due to its obligatory proximity to the normal AV node complex. Our hypothesis of this patient’s FVP as to why there is discrepancy between the base-to-apex pacing and para-Hisian pacing is that para-Hisian pacing is not dependent upon the location of the catheter position at time of stimulus, whereas, base-to-apex pacing is dependent on the location of the catheters due to the varying location and conduction properties of the His-Purkinje system. If a FVP exists, base-to-apex pacing can potentially delineate whether the FVP is a discrete fiber or a hole in the insulation of the right bundle branch (Figure 3). The previous ablations resulting in transient attenuation of the pathway suggests that FVP, at least in this case, is a discrete fiber rather than a hole in the conduction system. Further investigation of FVPs comparing para-Hisian pacing and base-to-apex pacing would be interesting and beneficial.  

Key points to help differentiate an FVP and annular accessory pathway: 

1)    The H-V interval was short, but never negative, confirming that with FVPs, pre-excitation is constant despite differential pacing. 

2)    FVP retrograde conduction sequence reveals a decremental A-H interval with a short, consistent H-V interval. 

3)    FVP should not significantly change after an adenosine challenge, as it is infra-Hisian. 

4)    Para-Hisian pacing should be valid because the insertion site of the FVP should be below the AV node. 

5)    Base-to-apex pacing in the setting of FVPs may reveal varying responses depending on the insertion location of the FVP and its conduction properties. Comparing para-Hisian pacing and base-to-apex pacing in such cases requires further investigation. 

Case #2

A 9-year-old boy presented with palpitations and pre-excitation on resting electrocardiogram (Figure 7). Although ambulatory ECG monitoring revealed no supraventricular tachycardia or arrhythmias, it did reveal clear pre-excitation at lower heart rates. He was brought in for an elective EP study and catheter ablation attempt under general anesthesia.

Approach

At baseline, the patient had a sinus rhythm with pre-excitation physiology at a cycle length of 720 ms. The PR interval was 105 ms, with a QRS duration of 101 ms and QT interval of 397 ms. The A1-H1 interval was 73 ms and the H1-V1 interval was short, but not negative, at 5 ms. The delta wave was in a WPW type B distribution, suggesting a right-sided septal AP (Figure 8).

During atrial extrastimulus testing at 600 ms, there was subtle pre-excitation throughout the drive but loss of delta wave at an S2 coupling interval of 440 ms (Figure 9). There was no evidence of dual AV node physiology in the absence of catecholamines.

Retrograde ventricular pacing was performed at a cycle length of 700 ms, 600 ms, and 500 ms. There was VA dissociation with unchanged A-A sinus intervals at all paced cycle lengths, indicating antegrade-only pre-excitation (Figure 10).

Adenosine Challenge

Bolus of adenosine of 6 mg rapid push was given during sinus rhythm, which produced a larger delta wave, but still with a H-V interval of 0 ms.

Epinephrine Infusion

Epinephrine infusion began at 4 mcg/minute, and atrial extrastimuli testing was repeated. In the presence of epinephrine, there was evidence of dual AV node physiology with an A2-H2 interval of 81 ms at 600/400 ms, reaching a maximum of 156 ms at 600/270 ms. At 600/260, there was a jump to 232 ms with a maximum A2-H2 interval of 24 ms at 600/230 ms. However, despite the A2-H2 jump, there were no retrograde atrial echo beats or inducible AV node re-entry. Decremental atrial pacing showed Wenckebach at a pace cycle length of 320 ms with a maximum A1-H1 interval of 155 ms, and again, with no evidence of dual AV node physiology at baseline.

A 3D electroanatomic map was performed of the tricuspid valve annulus during sinus rhythm with pre-excitation. The earliest ventricular signals were seen at the 4 o’clock position on the tricuspid valve annulus at the expected position of the AV node. 

In the presence of an epinephrine infusion, there was evidence of a local ‘V’ before the His recording on the distal His catheter pole. However, by applying pressure to the His catheter, a transient suppression of pre-excitation occurred with a normal H-V interval, which is suggestive of the absence of an FVP (Figure 11). Another bolus of 6 mg of adenosine was repeated with continuation of the epinephrine infusion. The delta wave was monitored closely on the deflectable catheter. Under these conditions, the H-V interval became clearly negative, measuring -16 to -22 ms compared to the surface delta wave, excluding an infranodal FVP (Figure 12).

Despite differential pacing being performed from the coronary sinus and from several sites around the tricuspid valve annulus, the delta wave remained small and fairly constant.

Conclusion

We concluded that a true annular mid-septal accessory pathway existed with a weak antegrade and absent retrograde AP conduction incapable of supporting reentrant supraventricular tachycardia or pre-excited atrial fibrillation. Once again, the procedure was concluded and no intervention was required. 

Discussion

These cases illustrate benign variants of pre-excitation that in the first case resulted in three unnecessary EP studies due to “symptomatic” pre-excitation, but was in fact an unrecognized FVP incapable of supporting arrhythmia. The second case illustrated the unusual circumstance of a true annular accessory pathway with only antegrade conduction, also incapable of supporting conventional reentrant supraventricular tachycardia or pre-excited atrial fibrillation. Both of these cases of “symptomatic” pre-excitation presented with symptomatic palpitations not confirmed to be tachycardia by ambulatory ECG monitoring and a right-sided septal pre-excitation pattern on resting ECG. These benign variants of pre-excitation represent the “sheep in wolf’s clothing” and should not be missed.

Disclosures: The authors have no conflicts of interest to report regarding the content herein.  

Reference

1. Tsao S, Deal BJ. Management of symptomatic Wolff-Parkinson-White syndrome in childhood. Prog Pediatr Cardiol. 2013;35(1):7-15.