Discussion
Idiopathic ventricular arrhythmia (VA) from the ostium of the left ventricle could be eliminated by the radiofrequency (RF) application within the aortic sinus cusps (ASCs). The VA originating from the junction between the left and right coronary cusp was rare, however, the elimination needs to the RF application below the aortic cusps.[1] Of interest, this VA had a unique electrocardiographic characteristic of a qrS pattern in at least one of the leads V1–V3 or abrupt V3 transition (Figure 1A).[2, 3] The tip of the ablation catheter should be positioned at this site by deflecting the loop of the ablation catheter in the left ventricle cavity or on the non-coronary cusp, but this technique was relatively difficult to stabilize the ablation catheter due to the limited anatomical space. In the current case, although electrogram at the ablation catheter was sub-optimal, RF application at the left coronary cusp (LCC) – right coronary cusp (RCC) junction above ACSs could eliminate the VA (Figure 1C). The local electrogram at the successful ablation site showed a tiny dull ventricular potential with low R wave amplitude. The distal tip of the ablation catheter in the fluoroscopy was located behind the coronary sinus catheter in the right anterior oblique view (Figure 1B, C). These findings suggest the ablation catheter is more likely to be located close to the LCC-RCC junction above the ASCs.
To identify radiofrequency lesion extension, high-resolution late-gadolinium enhancement magnetic resonance imaging (LGE-MRI) was performed three months after the catheter ablation. The LGE-MRI of ASC and left ventricle was acquired using a 3D inversion recovery, respiration navigated, electrocardiogram-gated, T1-FFE sequence in the transverse plane 15 minutes after the contrast injection, as previously reported. The typical parameters were as follows: repetition time/echo time = 4.7 / 1.5 ms, voxel size = 1.43 × 1.43 × 2.40 mm (reconstructed to 0.63 × 0.63 × 1.20 mm), flip angle = 15°, SENSE = 1.8, and 80 reference lines. The inversion time (TI) was set at 280 – 320 ms using a Look-Locker scan. LGE-MRI could demonstrate that the strong LGE could be found at the ventricular myocardium beyond the LCC – RCC junction, so-called myocardial crescents. However, we have clearly demonstrated that the LCC – RCC junction does not involve the myocardial crescents.[4] The resign corresponds to the myocardium beneath the interleaflet triangle, which is located within the left ventricle. Therefore, it is better reached from the below ASC approach with caution to the thin interleaflet triangle. In the current case, fortunately, RF lesion could extent from the myocardial crescent beneath the LCC – RCC junction to the myocardium beneath the interleaflet triangle (Figure 2). In case when the accurate mapping and catheter stability was difficult beneath the ASCs, careful mapping and RF application at the LCC – RCC junction above the ASCs might be acceptable option to eliminate the VA arising from the myocardium beneath the interleaflet triangle.