Abstract
A 13-year-old-girl presented with one episode of pre-syncope while standing in a train. Her ECG was suggestive of preexcitation. Echocardiography revealed structurally normal heart without any ventricular hypertrophy. During electrophysiology study, her ventriculo-atrial (VA) conduction was absent even on isoprenaline. However, a para-Hisian pacing maneuver (PHP) revealed consistent VA conduction with a nodal response. This finding indicated that the VA dissociation at baseline was at infra-Hisian (VH) level and conduction at HA level was intact. In addition, this finding is coherent with a speculation of a fasciculo-ventricular pathway (FVP) resulting in such an ECG pattern in her. Pacing from various atrial sites (right atrium, coronary sinus) exhibited nearly fixed preexcitation and short non-varying HV interval confirmatory of FVP. Testing for a PRKAG mutation was advised for her.
Keywords: VA conduction, Ventriculo-atrial conduction, Para-Hisian pacing, Fasciculo-ventricular accessory pathway
1. Case
A 13-year-old girl presented with one episode of pre-syncope while standing in a train. Her ECG was suggestive of a preexcitation pattern corroborative of a septal accessory pathway (AP) (Fig. 1A, inadvertently taken in 1 mV = 20 mm gain setting). Echocardiography revealed structurally normal heart without any ventricular hypertrophy. She was planned for an electrophysiology study. She was not on any anti-arrhythmic medication. Three catheters were placed in right atrium (RA)/coronary sinus (CS), right ventricle (RV) and His region. However, the coronary sinus catheter could not be placed properly inside CS due to a thebesian valve and the distal CS could reach only upto the mid CS (near 6-0-clock of mitral annulus). HV interval was 0 ms (Fig. 1B). During retrograde study her VA conduction was consistently absent at baseline starting from 700 ms pacing cycle length down till 350 ms (Fig. 1C). This was repeated on isoprenaline and still the VA conduction was absent. Antegrade study during atrial pacing demonstrated a fixed HV interval with non-varying preexcitation until the block. A para-Hisian pacing (PHP) maneuver was performed keeping only antegradely conducting atrioventricular AP vs fasciculo-ventricular AP as differentials. It revealed a nodal response (showed in Fig. 2AB) as the VA time was longer during wider myocardial only capture beat. What could be the mechanism behind this type of conduction during a PHP response despite consistent VA block noted at baseline and can we conclude on the type of AP based on these findings?
Fig. 1.
1A: Baseline ECG (at 1 mV = 20 mm gain setting), 1B: HV interval was 0 ms. C: VA conduction was absent. AA interval shows that atrium was dissociated from ventricular pacing. (HRA = hight right atrium, LRA = low right atrium).
Fig. 2.
2A: Catheter position before para-Hisian pacing was started. The CS catheter was partly inside the CS. The distal CS bi-pole in mid CS into a branch of CS. (HISd = distal His region. HRAd = high right atrium distal). 2B: The first and third beat have H + V capture. Pure His capture was excluded as no isoelectric interval noted. The second beat have exclusive V (myocardial) capture and longer VA (208 ms). Possibly the retrograde His signal is also visible in the local electrogram as a distinct spike (marked by red arrow). The VH time was 31 ms. HA time was constant 177–178 ms all 3 beats.
2. Commentary
The resurgence of VA conduction during PHP in absence of baseline VA conduction suggests that the level of VA block is at infra-His level [1]. Had it been at supra-His level, the VA dissociation would have prevailed even during PHP [1]. The likely cause of the preexcitation on her ECG was due to a FVP as the preexcitation remained fixed.
Firstly, there is certainly an antegradely conducting accessory pathway as HV interval was 0 ms. There was only a minimal change in preexcitation from various atrial site pacing without any change in HV interval. This confirmed an FVP. As expected, it did not have any VA conduction hence could not result in an atrio-ventricular reentrant tachycardia (AVRT).
The para-Hisian pacing revealed a nodal response as a surprise. However, this is well known in cases with FVPs [2]. Therefore, the level of initial VA block was ascertained to be at infra-His level (VH level). What actually perplexed us was why there would be at all a VA conduction even during PHP during the isolated myocardial captured beats (second and third beat in Fig. 2) as there was no VA conduction during RV apical pacing at baseline. It could be related to the loss of insulation near His bundle (HB)/right bundle (RB) region in cases with FVP. We postulate that higher output pacing near the HB/RB could overcome the small amount of myocardium to reach the conduction tissue (RB/HB which is uninsulated in FVP), however took longer time as compared to when His bundle was directly captured. This finally resulted in a nodal response during the PHP. To overcome the small amount of intervening myocardial tissue between the pacing site and RB capture could be explained by a source-sink mismatch [3,4].
This case highlights the importance of careful analysis of maneuvers to avoid unwarranted ablation of FVP, one of the pre-excitation mimickers on baseline ECG. In a study by Sternick et al. comparing the ECG findings of FVP and WPW with anteroseptal AP, QRS transition in the precordial leads occurred earlier mainly in lead V2, and QRS width and PR interval were shorter in patients with FVP like our case [5,6].
For the index patient no ablation was attempted. Her presyncope was attributed a neurocardiogenic syncope also supported by a subsequent tilt table test. Her cardiac MRI was unremarkable. A testing for PRKAG mutation was advised for her.
Funding
None.
Consent has been taken from the patient.
Data availability statement
All raw data are available for review.
Declaration of competing interest
We are submitting a device round article titled as ‘Absent ventriculo-atrial conduction during apical right ventricular pacing but nodal response during Para-Hisian pacing – what is the mechanism?’ and we have no conflict of interest.
Footnotes
Peer review under responsibility of Indian Heart Rhythm Society.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
All raw data are available for review.