IVAs, including PVCs and VTs, are the most common arrhythmias and usually occur on patients without structural heart disease [1,2,3,4,5,6]. Although most of them can be safely and efficaciously treated with RFCA, VAs arising from left ventricular summit, which occupies the most superior LV portion, remain a challenge for RFCA7.
Anatomy of the LV summit
Epicardially, the LV summit is the area on the epicardium of the LV beneath the bifurcation of the left main coronary artery and superior to the horizon line of the first septal perforating branch, bounded by the left anterior descending artery (LAD) anteriorly and the left circumflex artery (LCX) laterally, the DGCV transversely bisects the LV summit into a superior portion, which is in close proximity to the proximal coronary arteries with epicardial fat overlaying it and inaccessible to catheter ablation, and an inferior portion that can be accessible by trans-DGCV or transpericardial approach [9]. Endocardially, it is an area within LVOT just below LCC, located anterosuperior of the AMC, and is accessible to endocardial catheter ablation [10].
The approaches for RFCA of VAs arising from LV summit
Previous studies described different ablation approaches for VAs arising from left ventricular summit. Yamada et al. reported that VAs origin in left ventricular endocardial summit just below LCC can be ablated by a retrograde transaortic approach with a catheter inversion technique [8], meanwhile, he also demonstrated that VA origin in the accessible area of left ventricular epicardial summit can be ablated by a trans-DGCV approach or a pericardial approach via suboxiphoid puncture [9]. Ouyang et al. recently reported that the left ventricular endocardial summit VAs can be better mapped and ablated via a transseptal approach with the ablation catheter reversed S curved [10]. Nonetheless, no matter which ablation approach mentioned above was chosen for left ventricular summit VAs ablation, its advantages and limitations should be taken into full consideration. The transaortic approach is usually firstly attempted for its relatively safe for there is no coronary artery endocardially, however, because of the relatively rigid aortic valve leaflets limiting catheter manipulation and vigorous movements of the aortic valves rendering a contact of the mapping catheter on the tissue in this region unstable, the area below the ASC is sometime insufficiently mapped, leading to unsuccessful ablation. Trans-DGCV approach should be attempted when an epicardial origin within DGCV was supposed, however, it is sometime difficult to place the tip of an ablation catheter in the narrow vascular lumen, meanwhile, high impedance produced during ablation limits the release of energy, and potentially fatal risks, like pericardial tamponade and coronary artery injury, may occur. Transseptal approach was recently proposed for left ventricular summit VAs ablation, by which access into the left ventricular endocardial summit below the ASCs and catheter manipulation in this area are thought easier, however, the transseptal procedure with a Brockenbrough needle is not always safe, catastrophic complications, including atrial rupture and acute mitral valve damage, may be induced by this approach. In addition, Yamada et al. demonstrated by catheter inversion technique via the retrograde transaortic approach, the looped mapping catheter looked the same as the distal half part of the reverse S curve with the antegrade transseptal approach [8], thus they thought inversion with the retrograde transaortic approach should be attempted before the transseptal approach. Pericardial approach via subxiphoid puncture was rarely adopted for its high risk of severe complications, such as heart rupture and pericardial tamponade, and it was forbidden in inaccessible area where lay the proximal coronary arteries and energy application can lead to fatal myocardial infarction. Thus, when VAs were suspected of a LV summit origin, taking full consideration about the ablation approach prior to the procedure was important, it may save the RFCA time and avoid serious complications.
ECG characteristics of LV summit ECG
Previous studies has described electrocardiographic characteristics criteria to identify the left ventricular summit VAs. Because the LV summit is located most superior in the LV beneath the LCC, VAs originating from this region exhibit high inferior lead R-wave amplitudes and no S wave in V5/V6. Left ventricular summit VAs of left bundle branch block morphology are a rare phenomenon. In our study, all VAs, no matter ablated endocardially and epicardially, had high inferior lead R-wave amplitudes, no S wave in V5/V6, most VAs had right bundle branch block pattern, which is consistent with previous reports [9].
PdW, IDT, MDI in approach selection
Although a series of ECG characteristics of LV summit VAs have been concluded to differentiate itself from the other sites of PVCs/IVTs origin, the ECG characteristics predicting which ablation approach adopted for LV summit VAs have not been studied. A series of electrocardiographic criteria were once put forward to help recognizing the epicardial origin of VAs and consistently suggested that epicardial VAs usually show prolonged PdW, IDT, MDI [1, 9]. The potential explanation for this electrocardiographic phenomenon is that the Purkinje network is primarily located in the subendocardium, thus excitation of an epicardial ectopy exactly needs more time to reach the Purkinje network to fire arrhythmias than that of an endocardial ectopy, resulting in a relative prolonged PdW, IDT, MDI in epicardial VAs than endocardial VAs. In the present study, we also found that for LV summit VAs, the prolonged PdW time and IDT time and MDI indicated an epicardial origin and trans-DGCV approach could be adopted firstly.
Catheter ablation of LV summit VAs by transseptal approach
Ouyang et al. described that LV summit VAs ablated by transseptal approach [10], for these VAs, earliest ventricular activation of target sites preceding the QRS onset by 39.5 ± 7.7 ms, pace mapping at the target site showed mismatch of QRS morphology to clinical VAs, radiofrequency resulted in rapid disappearance of VAs within 10 s. We also found the LV summit VAs ablated by transseptal approach showed poor pace match, however, opposed to Ouyang et al., we found the earliest ventricular activation of target sites preceding the QRS onset just by 28.61 ± 2.71 ms, and these VAs usually need more than 10 s’ energy discharging (less than 20 s). The relative delayed ventricular activation time and prolonged energy application, and the poor pace match of target sites by transseptal approach from endocardium, to some extent, suggested that the origin of VAs may be located subepicardially or intramurally. However, complete epicardial mapping via suboxiphoid approach was not performed in any of our patients, whether a much earlier local ventricular activation can be recorded epicardially is unknown.
Study limitations
In our study, complete mapping of LV summit before ablation by transaortic approach, by trans-DGCV approach, by transseptal approach and by pericardial approach respectively was not performed. The RFCA procedure in the present study was proceeded by transaortic approach and trans-DGCV approach firstly, followed by a transseptal approach. Pericardial approach was abandoned for its high risk of catastrophic complications. Thus where the exactly earliest local ventricular activation of PVCs/IVTs located was not fully investigated. However, for mapping in LV summit VAs, it is something different. The LV summit is the most common area where intramural VAs are located [12]. In the area, even complete mapping from both the endocardium and epicardium performed before ablation, we can not precisely locate the origins of VAs. In our study, as we were more concerned about safety and effectivity of RFCA procedure of LV summit VAs, we performed complete mapping and ablation by transaortic approach and trans-DGCV approach firstly, when failed, the more aggressive transseptal approach was proceeded, by our ablation strategy, a part patients can get away from severe RFCA complications.