Unusual QRS complexes associated with the simultaneous presence of a right-sided accessory pathway, fasciculoventricular pathway, and incomplete right bundle branch block

Abstract

A 52-year-old man presented with delta waves on a body surface electrocardiogram, which suggested the presence of a right-sided accessory pathway (AP). Patients with right-sided APs generally have an rS pattern in leads V1–2, while he had an rS in lead V1 but an Rs in lead V2, which could not rule out the possibility of the presence of a septal AP or fasciculoventricular pathway (FVP). On the other hand, patients with septal APs or FVPs generally have a QS pattern in lead V1 instead of an rS pattern. An electrophysiological study demonstrated that the simultaneous presence of a right-sided posterolateral AP and FVP with incomplete right bundle branch block (ICRBBB) generated those unusual QRS complexes. The FVP arose distal to the site with ICRBBB, and the ICRBBB delayed the initiation of the FVP conduction. The delayed QS and Rs waves in leads V1–2 generated by the FVP conduction with ICRBBB appeared to produce rS and Rs patterns in leads V1–2, respectively. A radiofrequency application along the posterolateral tricuspid annulus eliminated the right-sided AP conduction. If the localization of APs based on the QRS morphology is difficult, multiple APs or an FVP with a conduction system disturbance should be noted.

Learning objective

Patients with right-sided posterolateral accessory pathways (APs) generally have an rS pattern in lead V2, while patients with fasciculoventricular pathways (FVPs) generally have a QS pattern in lead V1. The present case with a suspected right-sided posterolateral AP had unusual QRS complexes, an rS in lead V1, Rs in lead V2, and monophasic R in leads V3–6, which were associated with the simultaneous presence of a right-sided posterolateral AP, FVP, and incomplete right bundle branch block.

Introduction

The polarity of delta waves on the body surface electrocardiogram (ECG) can estimate the location of an accessory pathway (AP). We present a case with a suspected right-sided posterior or posterolateral AP based on a localization algorithm of atrioventricular (AV) APs [1]. The present case had an rS pattern in lead V1, Rs in lead V2, and monophasic R in leads V3–6 on the body surface ECG during sinus rhythm, which could not rule out the possibility of the presence of a septal AP or fasciculoventricular pathway (FVP), however, lead V1 did not exhibit a QS pattern. Therefore, the possible mechanism for the formation of those QRS complexes and the location of the AP remained unclear. An electrophysiological study (EPS) demonstrated that the simultaneous presence of a right-sided posterolateral AP, FVP, and incomplete right bundle branch block (ICRBBB) generated those unusual QRS complexes.

Case report

A 52-year-old man presented with recurrent palpitations and ventricular preexcitation on a body surface ECG (Fig. 1). The localization algorithm of the APs suggested that he had a right-sided posterior or posterolateral AP [1]. Patients with right-sided posterior or posterolateral APs generally have an R/S ratio of <1 in leads V1–2 [2]. However, the precordial leads in the present case exhibited a very early R-wave progression: an rS pattern in lead V1, Rs in lead V2, and monophasic R in leads V3–6, which could not rule out the possibility of the presence of a septal AP or FVP. On the other hand, patients with septal APs or FVPs generally have a QS pattern in lead V1 [1], [3], [4], [5], [6], but the present case had an rS pattern in lead V1. Therefore, it was difficult to localize the AP based on the QRS morphology. He underwent an EPS and radiofrequency catheter ablation.

Fig. 1.

Pre-ablation 12‑lead electrocardiogram during sinus rhythm.

The baseline EPS demonstrated a short AV interval with delta waves during sinus rhythm (Fig. 2A). Programmed atrial extrastimulation revealed a gradual increase in the preexcitation and no prolongation of the AV interval. The QRS morphology after preexcitation maximization suggested the presence of a right-sided posterior AP (Fig. 2B) [7]. When the S1-S2 interval was shortened from 300 to 290 ms, the AV interval prolonged from 65 to 136 ms, delta waves disappeared, and His-bundle electrogram became unmasked (Fig. 2C). When the S1-S2 interval was further shortened in a stepwise fashion from 290 to 220 ms, the following findings were observed: (1) no delta waves, (2) gradual prolongation of the AH interval from 136 to 195 ms, (3) a short and fixed HV interval of 18 ms, and (4) no significant change in the QRS morphology (Fig. 2D). Those findings suggested the presence of two APs: one a right-sided posterior or posterolateral AP with antegrade and non-decremental AV conduction, and the other an FVP [3], [4], [5], [6]. Right ventricular pacing revealed decremental ventriculoatrial (VA) conduction, and para-Hisian pacing exhibited a VA conduction pattern through the AV node, which indicated the absence of retrograde VA conduction via the right-sided AP. No AV reciprocating tachycardia could be induced by any atrial or ventricular pacing. During the EPS, spontaneous atrial fibrillation with a wide QRS complex occurred repeatedly, which was considered to be the cause of his palpitations. A radiofrequency application targeting fused atrial and ventricular bipolar electrograms and a P-QS pattern unipolar electrogram along the posterolateral tricuspid annulus using a contact force-sensing irrigated ablation catheter (TactiCath SE, Abbott, Minneapolis, MN, USA) successfully eliminated the right-sided posterolateral AP conduction (Fig. 3). After the elimination of the right-sided posterolateral AP conduction, an intravenous bolus of 40 mg of adenosine during atrial pacing induced transient AV block. A post-ablation ECG during transient occurrence of complete right bundle branch block (CRBBB) exhibited a normal HV interval of 42 ms and rsR’ pattern in leads V1–2, while that during the ICRBBB exhibited a short HV interval of 26 ms and rS pattern in leads V1–2 (Fig. 2E and F). Therefore, the simultaneous presence of a right-sided posterolateral AP and FVP with ICRBBB made it difficult to predict the localization of the AP and FVP based on the pre-ablation QRS morphology.

Fig. 2.

Body surface and intracardiac electrocardiograms during (A) sinus rhythm, programmed atrial extrastimulation with an S1-S2 interval of (B) 300 ms, (C) 290 ms, and (D) 220 ms before the ablation, and sinus rhythm after the ablation with (E) complete right bundle branch block and (F) incomplete right bundle branch block.

A, atrial electrogram; CS, coronary sinus; H, His-bundle electrogram; HBE, His-bundle electrogram recording area; HRA, high right atrium; RVA, right ventricular apex; V, ventricular electrogram.

Fig. 3.

(A) Body surface and intracardiac electrocardiograms (ECGs) showing fused atrial and ventricular bipolar electrograms and a P-QS pattern unipolar electrogram recorded by an ablation catheter placed at the site with the successful elimination of the accessory pathway (AP) conduction along the posterolateral tricuspid annulus. (B) Elimination of the AP conduction within 1 s after commencing the radiofrequency application. The antegrade atrioventricular conduction via the right-sided posterolateral AP was present during the first to third beats, while that was absent during the fourth and fifth beats and the QRS morphology changed to a complete right bundle branch block pattern. (C) Fluoroscopic images showing the ablation catheter placed at the site with the successful elimination of the AP conduction in the left anterior oblique (LAO) 45-degree (upper panel) and right anterior oblique (RAO) 35-degree (lower panel) views. (D) Post-ablation 12‑lead ECG during sinus rhythm.

ABL, ablation catheter; ABL 1–2 and 3–4; distal and proximal recordings by the ablation catheter; ABL-uni, unipolar recording by the ablation catheter; A, atrial electrogram; CS, coronary sinus; H, His-bundle electrogram; HBE, His-bundle electrogram recording area; HRA, high right atrium; RVA, right ventricular apex; V, ventricular electrogram.

Discussion

This case report described the mechanism for the formation of unusual QRS complexes with delta waves, which was associated with both a right-sided posterolateral AP with antegrade AV conduction and an FVP with ICRBBB.

An FVP is generally characterized by a normal PR interval, shortened and fixed HV interval, and slight ventricular preexcitation manifested by delta waves [8]. Lead V1 exhibits a QS pattern in general septal AP or FVP patients [3], [4], [5], [6], but exhibited an rS pattern in the present case. Further, lead V2 exhibits an rS pattern in general right-sided free wall AP patients [2], but exhibited an R/S ratio of ≥1 in the present case. The reason for the presence of the “r” wave in lead V1 appeared to be that the FVP arose distal to the site with incomplete conduction block along the right bundle branch, and the initiation of the QRS formation by the FVP conduction was delayed due to the ICRBBB. Thus, the “r” and “S” waves in lead V1 appeared to be derived from the initial component of the ICRBBB and delayed QS wave generated by the FVP conduction with the ICRBBB, respectively. As a result, lead V1 exhibited an rS pattern instead of a QS pattern. The finding that no delta waves were observed despite the presence of the FVP conduction after the ablation of the right-sided posterolateral AP could also be explained by the delayed FVP conduction due to the ICRBBB. FVP patients can have various patterns of the QRS morphology in lead V2: a QS, rS, or Rs pattern [4], [5], [6]. The Rs pattern in lead V2 and notched latter component of the QRS complex in leads V2–6 on the pre-ablation ECG, as in Fig. 1, may have reflected the presence of both the FVP conduction and ICRBBB.

During the post-ablation EPS, when CRBBB transiently occurred, leads V1–2 exhibited an rsR’ pattern and normal HV interval of 42 ms. That finding that the FVP conduction was present during ICRBBB, but was not during CRBBB also suggested that the FVP arose distal to the site with ICRBBB. The ventricular attachment site of the FVP could not be mapped in the present case because CRBBB repeatedly occurred after the ablation of the right-sided posterolateral AP and masked the FVP conduction.

The coexistence of an AV-AP, FVP, and conduction system disturbance is a rare occurrence. Sternick et al. reported four case series of FVPs, including two patients with both an AV-AP and FVP [4]. A case report by Valentino et al. [9] described a 20-year-old man with four AV-APs with antegrade conduction and an FVP. Further, Yang et al. reported a 30-year-old man with an FVP and ICRBBB [10]. However, to the best of our knowledge, no previous reports have described the simultaneous presence of an AP with antegrade AV conduction, FVP, and ICRBBB. The present case may suggest that if the localization of APs is difficult based on the polarity of the delta waves and QRS morphology on the body surface ECG, multiple APs or an FVP with a conduction system disturbance should be noted.

Funding sources

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Declaration of competing interest

No author has a real or perceived conflict of interest.