Successful ablation of premature ventricular contraction originating from the proximal left anterior fascicle using selective fascicular capture pace mapping with a small-electrode multipolar catheter

Key Teaching Points.

• •Using a multipolar catheter with small, closely spaced electrodes allows for selective capture of the conduction system. Even in the absence of spontaneous premature ventricular contractions (PVCs), pace mapping with the small-electrode catheter represents an advanced diagnostic and therapeutic strategy for fascicular PVCs.
• •This case highlights the retro-aortic root branch as a dead-end tract, distinct from the proximal left anterior fascicle (LAF). Electrophysiological findings confirm that PVCs originating from the proximal LAF can be differentiated from retro-aortic root branch origins through precise pace mapping.
• •PVCs arising from the proximal LAF can be safely and successfully ablated from the right coronary cusp without causing permanent conduction system damage.

Introduction

Although there are few reports on the ablation of premature ventricular contractions arising from the left anterior fascicle (LAF-PVCs), several previous studies have identified that the earliest presystolic fascicular potential of the PVC is an effective target for catheter ablation.1, 2, 3 However, the strategy requires the appearance of clinical PVCs during the procedure. Pace mapping is reportedly ineffective in diagnosing the origin of fascicular PVCs.⁴ Currently, no studies have identified the origin of LAF-PVCs through pace mapping alone using electrode catheters. Herein, we report a case of successful evaluation and treatment of an LAF-PVC via detailed pace mapping using a small-electrode, tight-distance, multipolar, paddle-design catheter to depict the excitatory conduction of the stimulating conduction system by specifically capturing the local fascicular only.

Case report

A 35-year-old man with no notable medical history was referred to our hospital with a chief symptom of palpitations. Echocardiography revealed no evidence of structural heart disease, and a 12-lead electrocardiogram showed frequent PVCs with a narrow QRS morphology (duration, 90 ms) closely resembling that observed during sinus rhythm (Figure 1A). The QRS morphology of the PVC was compatible with that of a PVC originating from the LAF region: rS in leads I and aVL and qR in the inferior leads.¹ Bisoprolol (2.5 mg) was started daily, but was ineffective. A 24-hour Holter electrocardiogram showed 20,495 PVCs per day (19.8%). Catheter ablation was performed as a curative treatment for drug-resistant symptomatic PVCs. The CARTO™ 3 System (Biosense Webster, Irvine, CA) was used as a 3-dimensional mapping system. Unfortunately, once the patient entered the catheterization room, the appearance of the PVCs was almost completely suppressed. Adenosine triphosphate (5 mg) and phenylephrine (0.2 mg) were administered, but PVCs were not observed. After continuous infusion of isoproterenol (1 μg/min) and burst pacing from the right atrium, 1 beat clinical PVC appeared (Figure 1B), which was recorded as a reference. Because treatment based on PVC activation mapping was considered difficult, we first generated an activation map during sinus rhythm. The anterior and posterior branches of the left fascicle were visualized by adjusting the window of interest to precede the QRS complex on the body surface. Pace mapping of the LAF was subsequently performed. The mapping procedure employed the Optrell™ Mapping Catheter (Biosense Webster), characterized by small (460 μm) electrodes with tight spacing (2.4 × 2.4 mm) via a trans-aortic approach. During sinus rhythm, the left fascicular potential was recorded at the F5–6 electrode of the Optrell (Figure 2). Low-output pacing (1.2 mA/2.0 ms) was conducted from the Optrell catheter. The intracardiac electrogram indicated that pacing from the Optrell catheter selectively activated the LAF, which was conducted antegrade to the left ventricular anterior wall and retrograde through the His bundle to the right bundle branch (Figure 2). These findings demonstrated that local fascicular capture could be achieved with low-output pacing from the Optrell catheter. Subsequent pace mapping was conducted in the LAF region using low-output pacing (1–1.5 mA, 2.0 ms) from the Optrell catheter. The paced QRS complex was compared with the clinical PVC morphology using the PaSo software module for the CARTO 3 System to localize the site of origin of the PVC. The pace mapping results for the LAF area are shown in Figure 3. Pacing from the proximal LAF (Figure 3; proximal LAF3) produced a perfectly paced map (PaSo score = 0.953). Based on the pace mapping results, the origin of the PVCs was determined to be the proximal LAF. Previous studies have documented successful treatment of PVCs originating in the proximal LAF using ablation from the right coronary cusp (RCC).⁵ The perfect pace mapping site was located 4.8 mm from the RCC, and multiple radiofrequency applications (35 W/60 seconds) were applied from the RCC side (Figure 4A–4C). Junctional beats occurred during ablation and transient suppression of LAF conduction was noted; however, no permanent damage to the conduction system was observed (Figure 4D). Isoproterenol was administered, and atrial burst pacing was attempted; however, no PVCs were induced. A follow-up Holter ECG performed 3 and 6 months after the procedure showed no recurrence of PVCs.

Figure 1.

A: 12-lead electrocardiogram (ECG) showing frequent premature ventricular contractions (PVCs) with a narrow QRS morphology (duration, 90 ms) closely resembling that observed during sinus rhythm. B: The intracardiac ECG of the PVC. Early excitatory potentials were recorded on the His bundle electrogram (HIS) 3–4 electrodes, suggesting that the PVCs originated near the left anterior fascicular. PVC = premature ventricular contraction; RVA = right ventricle apex; SR = sinus rhythm.

Figure 2.

Local fascicular capture with low-output pacing from the Optrell™ Mapping Catheter (Biosense Webster, Irvine, CA). Low-output pacing (1.2 mA/2.0 ms) was conducted from the Optrell catheter at the site where the left middle fascicle (LMF) potential was identified. The intracardiac electrogram indicated that pacing from the Optrell catheter selectively activated the LAF, which conducted antegradely to the left ventricular anterior wall and retrogradely through the His bundle to the right bundle branch. AP = anterior-posterior; LAF = left anterior fascicle; LV = left ventricle; RCC = right coronary cusp; RV = right ventricle.

Figure 3.

A: Results of the pace mapping of the left anterior fascicle (LAF) region. A perfect pace map (PaSo score = 0.958) was obtained at the site of proximal LAF3. B: Fascicular-ventricular (FV) interval and Stim-QRS interval in retro-aortic root branch (RARB). The FV interval during sinus rhythm was 39 ms in the RARB, and the S-QRS interval, with local fascicular capture, was prolonged to 49 ms. LMF = left middle fascicle; LP = left posterior fascicle.

Figure 4.

A, B: Fluoroscopic image during ablation from right coronary cusp (RCC). C: 3-dimensional mapping image during ablation. The distance between the ablated site at RCC and the site of perfect pace mapping was 4.8 mm. D: 12-lead electrocardiogram (ECG) after catheter ablation. Postoperative ECG showed no premature ventricular contractions and no conduction system disturbances.

Discussion

We presented a case in which a proximal LAF-PVC was successfully diagnosed and treated by pace mapping alone using Optrell, a multipolar catheter with small, closely spaced electrodes. Pacing was performed at a low output from the small electrodes, selectively capturing the specialized conduction system. The conducting potentials were also observed.

Previous studies have suggested that ablation at the earliest activation site may be ineffective for fascicular PVC.1, 2, 3 Instead, ablation targeting the presystolic fascicular potential, typically in the proximal fascicle, is recommended. In this case, identifying the earliest activation site and assessing the presystolic fascicular potential were challenging because clinical PVCs rarely appeared after the procedure began. Therefore, pace mapping has become the primary diagnostic method.

Usefulness of the Optrell in fascicular pace mapping

To selectively capture the LAF, the Optrell catheter, with its small (460 μm) electrodes and a 2.4-mm pole-to-pole distance, was used for low-output (1.0–1.5 mA/2.0 ms) pace mapping. Electrode size and spacing significantly affect conduction capture, and standard ablation catheters, which have a larger pole-to-pole distance of 4 mm, are considered unsuitable for selective pacing. The smaller the electrode length, the higher the current density during pacing, which increases pacing efficiency.⁶ We were able to use this catheter to selectively supplement the stimulus conduction system rather than the working myocardium. Small-electrode catheters are also useful for pace mapping because they can selectively capture a smaller area. Moreover, the Optrell catheter, designed as a paddle-type multipolar catheter, facilitates the detailed pace mapping of fascicular PVCs. Its planar structure enables a detailed assessment of conduction after the pacing supplements the conduction system. In addition, the Optrell can deliver stimulation from multiple electrodes and improve pace mapping efficiency, reducing the need for extensive removal of the catheter.

Is the origin of this PVC the proximal LAF or the retro-aortic root branch?

Several reports have discussed PVCs originating from the proximal LAF. Chen and colleagues⁵ described the successful treatment of proximal LAF-PVCs originating from the RCC. In 2022, Zhang and colleagues⁷ identified the retro-aortic root branch (RARB) as a histologically dead-end tract and noted that proximal LAF-PVCs had a 46% treatment success rate when treated from the RCC. They argued that the PVCs treated with ablation from the RCC originated from the RARB.⁷ In this case, the fascicular-ventricular interval during sinus rhythm was 39 ms in the RARB, whereas the S-QRS interval, with local fascicular capture, was prolonged to 49 ms (Figure 3). This finding suggests that there was no connection from the RARB to the myocardium, but conduction toward the LAF led to the excitation of the left ventricular myocardium. This may serve as electrophysiological evidence that the RARB is a dead-end tract. In contrast, in the LAF and the left posterior fascicle connected to the left ventricular myocardium, the fascicular-ventricular interval during SR matched the S-QRS interval. In the proximal LAF3, where perfect pace mapping was obtained, the fascicular-ventricular interval was equivalent to the S-QRS interval, indicating that pacing captured the LAF rather than the RARB. The paced QRS waveform in the areas with high PaSo scores showed that the R wave changed to an RS wave as it moved from the RARB to the proximal LAF in lead I (Figure 5). Furthermore, in pacing from the distal LAF, the S wave deepened, and the PaSo score dropped significantly. These fine changes in the QRS morphology caused by local fascicular selective pacing suggest that the PVC originated immediately after the bifurcation of the proximal LAF from the RARB.

Figure 5.

Comparison of paced QRS morphology at each pace map site. In lead I, the R wave changed to an RS wave as the pacing site moved from the retro-aortic root branch to the proximal left anterior fascicle (LAF). Furthermore, in pacing from distal LAF, the S wave deepened and the PaSo score dropped significantly.

As reported in previous studies, RF application from the RCC side can treat PVCs in the proximal LAF without affecting the conduction system.⁵ The PVC of the proximal LAF origin was ablated from the RCC. A transient conduction block of the left anterior branch was observed during ablation, but treatment was achieved without permanent damage. The success of the treatment without causing a conduction block, despite the LAF origin, may be attributed to the multiple fibrous structures of the LAF and the origin of the PVCs in its small branches. By performing only pace mapping using the Optrell catheter, we were able to diagnose a PVC originating from the proximal LAF in this case. Although previous studies have highlighted the limitations of pace mapping for fascicular PVCS,^1,8 the use of small-electrode catheters may improve the identification of appropriate ablation sites within the conduction system. This case demonstrates the effective use of detailed pace mapping with a small-electrode multipolar catheter to treat PVCs originating from the LAF. However, the generalizability of these findings is limited, and future large-scale multicenter trials are needed to evaluate the broader applicability and influencing factors of this technique.

Conclusion

Pace mapping with a multipolar catheter featuring small, closely spaced electrodes is a promising strategy for evaluating and treating fascicular PVCs, particularly when spontaneous PVCs are not present during evaluation.

Disclosures

The authors have no conflicts of interest to disclose.