Road to the Summit May Follow an Eccentric Path

he left ventricular (LV) ostium or LV summit is the most superior aspect of the LV outflow tract (LVOT). Ventricular arrhythmias (VAs) arising from this region represent one of the most common sites of origin of idiopathic VAs. ] 6] ECG findings are consistent with the more septal and superior location of the basal LV summit in relationship to the apical LV summit. Compared with the apical segment, arrhythmias originating from the basal segment typically have a left bundle branch block pattern, shorter QRS duration (175 ms), greater R-wave amplitude in the inferior leads, smaller R-wave ratio in III/II and Q wave ratio in aVL/aVR, and a later precordial transition. direct ablation approach through the cardiac venous system is usually recommended when an early ventricular activation is recorded within the distal GCV. This approach can be problematic secondary to difficulty in passing the ablation catheter to the site of interest, inability to achieve adequate power, and proximity to coronary arteries. Alternatively, an anatomic approach from the adjacent endocardial site closest to the LV summit arrhythmia origin can be used, such as from the aortomitral continuity, LVOT, or coronary cusps. Predictors of successful ablation using an anatomic approach include a Q-wave ratio of <1.45 in leads aVL/aVR and a close anatomic distance <13.5 mm from the earliest activation site in the GCV. 8 Importantly, anatomic proximity and not activation timing dictates the success of an anatomic approach. 11 Finally, a percutaneous epicardial approach can be considered when a direct or anatomic ablation approach is unsuccessful. Unfortunately, this approach is only successful in a minority of patients (14%-17%), limited by proximity to major coronary arteries, the left atrial appendage, and poor energy delivery due to the presence of thick epicardial fat.