Introduction
Ablation of PVCs originating from the proximal LBB in the left ventricular outflow tract may easily damage normal conduction bundles, such as the atrioventricular block and left bundle branch block (LBBB). The His-bundle passes below the non-coronary cusp (NCC) and RCC and divides into right and left bundle branches. Herein, we present a successful case of ablation of PVCs originating from the proximal LBB through the RCC.
Case Report
A 70-year-old woman was admitted to our hospital because of palpitation. Her physical examination findings and vital signs and laboratory tests were unremarkable. No structural heart disease was detected on transthoracic echocardiography. Her electrocardiogram (ECG) showed a sinus rhythm with frequent PVCs. The PVCs showed narrow QRS and an incomplete RBBB morphology pattern with rs wave in II and AVF and qr wave in III (Figure 1). A total of 25290 monofocal PVCs, including 556 coupled beats, were detected by Holter ECG. From the ECG, we inferred that the PVCs probably originated from the proximal LBB. Because of the anatomic characteristics of the conduction bundle, ablation of arrhythmias may potentially increase the risk of injuring the conduction system, such as the atrioventricular block and LBBB. Activation mapping with a 3D navigation system (Carto 3™, Biosense Webster) was performed. The earliest activation site during PVCs was observed at the RCC (Figure 2). Radiofrequency energy was delivered with an initial power of 20 W, then was up-titrated to a maximum power of 30 W with an irrigation rate of 18–30 mL/min for almost 180 seconds while the surface ECG and conduction intervals were carefully monitored. The frequency of spontaneous PVCs gradually decreased. Ablation was stopped when RBBB occurred in a sinus rhythm.
A 12-lead electrocardiogram during sinus rhythm and premature ventricular contraction. The PR duration was 179 ms and the QRS duration was 94 ms in sinus rhythm and 118 ms in premature ventricular complexes.
Three-dimensional anatomic reconstruction and mapping of aorta cusps. The blue dot indicated ablation target and the red dots indicated ablation sits. Mapping and ablation of the premature ventricular complexes in right coronary cusp and the local potential precede the QRS by 26 ms during ventricular extrasystoles.
Incomplete RBBB remained after the operation, but the PR duration (178 ms) was not prolonged with respect to that before operation (179 ms; Figure 3). During follow-up, after 1 month, Holter ECG showed only eight PVCs, and incomplete RBBB was still observed, but no further aggravation of the atrioventricular block was present.
Discussion
In our patient, ECG showed typical incomplete RBBB in lead V1 and positive waves in lead I and II. According to a study by Im Si [1], PVCs can be inferred to have characteristics allowing for successful ablation from the RCC. Elizari’s study [2] has shown that the His-bundle penetrates the right fibrous trigone and emerges between the NCC and RCC. RBB appears to be a direct continuation of the His-bundle, and the LBB emerges at the inferior border of the membranous septum between the NCC and RCC of the aortic valve. Within 2 mm of its origin, the LBB subdivides into left anterior and left posterior branches. Chen et al. [3] have reported that the distance from the proximal left anterior fascicle origin to the RCC (3.9±0.8 mm) in the proximal group is shorter than 6 mm, thus theoretically making the penetration of radiofrequency induced conductive lesion to the proximal LBB. Previous research [4] has shown that the dead-end tract starting at the summit of the ventricular septum after the bifurcation of the bundle branches may be a possible source of ventricular arrhythmias, and can be mapped at or beneath the RCC. The RCC is close to the origin of these arrhythmias, and ablation within the RCC is an option providing better stability and easier manipulation. Left anterior hemiblock is still seen in 12.5% of patients during ablation within the RCC [3]. Incomplete RBBB persisted in our patient during the follow-up period, thus underscoring the need for caution regarding changes in atrioventricular conduction during ablation through the RCC. The RCC approach may be an effective strategy for ablation of PVCs originating from the proximal LBB.