Idiopathic ventricular arrhythmias (VAs) originating in the vicinity of the His bundle (HB) are uncommon and ablation in this area carries a risk of atrioventricular (AV) block (AVB), leading to a failed outcome. In a recent study published in JACC clinical electrophysiology, Yue-Chun et al have shown that the RIII/SIII ratio was a helpful predictor of the successful ablation of para-hisian VAs.
The present study included 134 consecutive patients undergoing catheter ablation of para-Hisian VAs. The electrocardiographic characteristics in these patients were retrospectively evaluated with successful ablation and failed ablation. Before radiofrequency (RF) catheter ablation (RFCA), a 12-lead ECG was obtained, and 24 h of ambulatory ECG monitoring (Holter) was carried out at least once. VAs were considered to originate near the HB region based on the criteria that earliest activation was recorded in the presence of a HB potential or within 10-mm distance from the S1 under the guidance of the 3D mapping system.
The target site of RFCA was determined by the earliest local bipolar activation preceding the QRS complex. A unipolar electrogram was simultaneously recorded. Bipolar pacing was performed at an output just greater than the diastolic threshold from the distal electrode pair during sinus rhythm. If the earliest ventricular activation was observed in the vicinity of the HB, RF energy was cautiously delivered at least 5 mm away from the site recording the largest HB potential (S1), using an initial power of 10Wwith gradual increase to a maximum power of 30 W.
Successful ablation was achieved in 115 (85.8%) of the 134 patients. There was no significant difference in QRS duration between the successful and the failed ablation groups.
The ablation success rate was significantly lower for para-Hisian VAs with a predominantly positive R wave in lead III than those with a predominantly negative S wave in lead III. The significant factor associated with successful ablation was the RIII/SIII ratio. The RIII/SIII ratio ≤ 1.1 predicted the successful ablation of para-Hisian VAs with high sensitivity (80.9%) and specificity (94.7%).
Also, the RIII/SIII ratio of >1.2 had high sensitivity (100.0%) and specificity (82.8%) to predict the distance <5 mm from the site of origin of para-Hisian VAs to the site recording the largest HB potential. This may be useful for planning ablation of para-Hisian VAs and minimizing the risk of inadvertent AVB.
In this study, it was found that when the origin of the para-Hisian VAs shifted from midseptum to anteroseptum of the tricuspid annulus or mitral annulus, R-wave amplitude increased, and S wave amplitude decreased in leads II, III, and aVF. The amplitude of r or R was usually largest in lead II, next largest in lead aVF, and smallest in lead III (II> aVF >III), and the amplitude of s or S was usually largest in lead III, next largest in lead aVF, and smallest in lead II (III> aVF >II). The HB was located at the anteroseptum. Therefore, the greater the R or r wave in lead III, the closer the site of origin of para-Hisian VAs to the HB.
Data on the electrocardiographic characteristics and outcomes of catheter ablation of idiopathic VAs originating near the HB are insufficient. The RIII/SIII ratio was a helpful predictor of the successful ablation of para-Hisian VAs. This may be useful for planning ablation of para-Hisian VAs and minimizing the risk of inadvertent atrioventricular block.
Source: JACC Clinical electrophysiology: https://www.jacc.org/doi/full/10.1016/j.jacep.2020.10.012