Electrophysiological characteristics and ablation of ventricular arrhythmias originating from the intramural basal inferior septum

Figures

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  Figure 1. Representative ECG of BIS-VA. All patients exhibited a predominantly positive QRS complex in Leads I and avL, and a negative complex in inferior leads. VAs of RV-BIS featured with an LBBB pattern and a late precordial transition of ≥V3 (Cases 1 and 2), and VAs of LV-BIS exhibited as both RBBB (Case 3) and LBBB (Case 4) patterns with an early precordial transition of ≤V2, while the VAs of intramural origins also exhibited as both RBBB (Case 5) and LBBB (Case 6) patterns with an early precordial transition of ≤V2. BIS, basal inferior septum; ECG, electrocardiogram; Intra, intramural; LBBB, left bundle branch block; LV-BIS, left ventricle BIS; RBBB, right bundle branch block; RV-BIS, right ventricle BIS; VAs, ventricular arrhythmias.

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  Figure 2. The mapping and ablation of VA from LV-BIS. Initial mapping along the TA found the EAS at the mid-septum (A), but the local activation time precedes QRS by only 3 ms and unmatched QRS during pace mapping (E). Further mapping along the MA identified the EAS at LV-BIS (B) with the local activation time >20 ms earlier than QRS and matched slightly different from QRS morphology during pace mapping (D), and ablation at this site successfully terminated the VA within 5 s. Combined maps showed an earlier local activation time at the EAS of LV-BIS (C). Of note, the QRS of V1 was featured with an LBBB pattern in this case, and even the success ablation target was on the left site. AO, aorta; EAT, earliest activation time; His, His bundle; LBBB, left bundle branch block; LV, left ventricle; LV-BIS, LV basal inferior septum; MA, mitral annulus; RV, right ventricle; RV-BIS, RV basal inferior septum; TA, tricuspid annulus; VA, ventricular arrhythmia.

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  Figure 3. The mapping and ablation of VA from RV-BIS. VA from RV-BIS demonstrated significant EAT at the right-sided BIS with a perfectly matched QRS to the clinical VA (A and D). The later activation time was evident at the left-sided BIS with a poor-matched QRS during pace mapping (B, C and E). AO, aorta; EAT, earliest activation time; His, His bundle; LV, left ventricle; LV-BIS, LV basal inferior septum; MA, mitral annulus; RV, right ventricle; RV-BIS, RV basal inferior septum; TA, tricuspid annulus; VA, ventricular arrhythmia.

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  Figure 4. The mapping and ablation of VA of intramural origin. No adequate EAS was found at the two-sided BIS (A, B and C), and pacing at the breakouts produced the unmatched QRS to clinical VA (E). Further mapping was performed within the MCV and yielded similar results (D). Although a slightly earlier activation time was recorded in the ostium of the MCV, focal ablation on either side was futile, and extensive ablation was required to eliminate the VA. AO, aorta; BIS, basal inferior septum; CS, coronary sinus; EAT, earliest activation time; LV, left ventricle; MA, mitral annulus; MCV, middle cardiac vein; RV, right ventricle; TA, tricuspid annulus; VA, ventricular arrhythmia.

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  Figure 5. Flowchart of ablation outcome in the Intra group. BIS, basal inferior septum; EAS, earliest activation site; Intra, intramural; LV, left ventricle; MCV, middle cardiac vein; RF, radiofrequency; RV, right ventricle.

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  Figure 6. The anatomical configuration of the BIS region and adjacent structures under ICE view. The pyramid space (green) was a 3D structure displayed by ICE reconstruction. It was ‘sandwiched’ by the hinge line of the mitral and tricuspid valves and the inferior epicardial atrial-ventricular groove. When viewed from different projections, the pyramid served as the division of two-sided BIS with its vertices towards the upper septum and continuing with the muscular ventricular septum (A–F). Under the ICE fan, the pyramid space (red dashed line) was filled with adipose tissue with vessels passing through (red circles) (G and H). BIS, basal inferior septum; CS, coronary sinus; ICE, intracardiac echocardiography; LA, left atrial; LV, left ventricle; MCV, middle cardiac vein; RA, right atrial; RV, right ventricle.

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  Figure 7. The anatomical relationship among the BIS, cardiac crux, and PSP-LV. The pyramidal space, outlined in the yellow area in (A and B), is the confluence of all four cardiac chambers. It is featured with a broader base and tapering thickness towards the upper septum, thus showing as a triangle surface towards different orientations. To elucidate the anatomical relationship among the BIS, cardiac crux, and PSP-LV, the pyramidal space is further simplified into a tetrahedron in (C and D). The BIS and PSP-LV are segmented from the pyramidal space by the red and green lines. As shown by the blue portion, the BIS is the pedestal of the pyramidal space and also inherits the endocardial and epicardial aspects of the pyramid. But, the PSP-LV represents the left-sided pyramidal space, extending from the anterior to the inferior septum. There is a prominent overlap between the PSP-LV and the BIS in the left basal process of the pyramidal space. At the same time, the crux cordis mainly represents the posterior and inferior epicardial aspects of the pyramid. The red asterisk in (B) and the yellow sphere indicate the intramural foci of the BIS-VAs settled deeply within the PSP-LV and BIS. BIS,…