Mapping and ablation
Electrophysiological study and ablation were performed after discontinuation of all antiarrhythmic drugs for at least five half-lives. A 6F decapolar catheter (4-mm interelectrode spacing) was inserted from the right internal jugular vein and placed in the coronary sinus. If clinical arrhythmias failed to occur spontaneously, intravenous isoproterenol infusion (2–5 mg/min) was administered. An irrigated-tip ablation catheter was advanced to the right ventricle and coronary venous system via antegrade transvenous approach and to the left ventricle via retrograde aortic approach. The RVOT, LV endocardium, aortic cusp, and DGCV-AIV were mapped with the ablation catheter to identify the earliest site of ventricular activation during VAs. Activation mapping was preferentially used to identify the origin during the procedure. Pace-mapping was also performed to capture the ventricular myocardium at the site of earliest activation. A suitable target for ablation was selected based on the earliest activation times during the arrhythmia combined with pace mapping. Once the origin of VAs was found within ASCs or PSCs, RFCA would be attempted by the irrigated-tip catheter in a power-controlled mode with a maximum temperature of 43 °C, preset power of 35 W, and flow rate of 17 ml/min. For DGCV-AIV, the irrigated-tip was applied with a flow rate of 30-60 ml/min, preset power of 25-30 W. CAG was performed in all cases to investigate distance from the catheter tip to adjacent coronary arteries before RFCA. Energy delivery was forbidden when the distance was less than 5mm. Coronary blood supply was routinely evaluated before and after ablation. If VAs were terminated or accelerated during the initial 10 s, radiofrequency delivery would be continued for 60 to 180 s. Otherwise, other targets were sought.
After successful ablation, intravenous administration of isoproterenol and programmed stimulation were performed to induce clinical VA. Acute success was defined as both absence of spontaneous or provoked clinical VA at the end of the procedure and the latter 48-hours period post-ablation on ECG Holter.
Swartz sheath support approach and non-Swartz sheath support approach
When the DGCV-AIV was considered the origin of ventricular arrhythmias, detailed mapping in DGCV-AIV was performed. For mapping and ablation in DGCV-AIV, two catheter manipulation approaches could be adopted, and shown in Figure1 . The conventional approach, non-Swartz sheath support (NS) approach, was facilitated by delivering the tip of ablation catheter directly from the ostium of coronary sinus to DGCV-AIV to perform mapping and ablation. The Swartz sheath support (SS) approach was facilitated by engagement of Swartz sheath in GCV from the ostium of coronary sinus by ablation catheter. Then the ablation catheter and Swartz sheath were advanced alternately in GCV to reach the distal portion of DGCV-AIV to perform mapping and ablation. If the Swartz sheath still could not go through the GCV, the hydrophilic coated guide wire and Judkins’ 4-left coronary catheter-guided deep engagement of Swartz sheath in GCV was conducted to support ablation catheter.