Anatomic characteristics and radiofrequency ablation lesions of the left ventricular summit

For ventricular arrhythmias originating from the left ventricular summit (LVS), the anatomical characteristics of ablation sites may influence lesion formation and ablation outcome.

Dissection was performed on 12 swine hearts to investigate anatomical characteristics of the LVS. Radiofrequency ablation was conducted in 17 swine hearts at 6 distinct sites, including the great cardiac vein (GCV), accessible area of the LVS, inaccessible area of the LVS, left coronary cusp (LCC), left ventricular outflow tract (LVOT) and right ventricular outflow tract (RVOT), for the purpose of evaluating ablation lesions.

Anatomically, the LVS apex carried a thicker epicardial-fat pad and a thinner myocardial wall than its base. The great cardiac vein/anterior interventricular vein (GCV/AIV) was separated from underlying myocardium by 2.54 mm (1.43, 3.86 mm) of epicardial fat. Between the LCC and myocardium, a 1.51 ± 0.82 mm layer of fibrous tissue was consistently found. Among 263 radiofrequency applications, 29 (11.0 %) produced steam pops; 17 of these (58.6 %) occurred in the accessible area. Seventy lesions (26.6 %) left no discernible myocardial necrosis; the vast majority of these ineffective applications were delivered to the inaccessible area, the accessible area, within the GCV, or on the LCC. Mean lesion depth in the inaccessible area (1.52 ± 0.28 mm), accessible area (1.64 ± 0.99 mm), GCV (2.16 ± 0.70 mm) and LCC (2.60 ± 0.72 mm) was significantly shallower than in the LVOT (4.43 ± 0.57 mm) or RVOT (4.15 ± 0.52 mm) (P < 0.05).

At the apex of the LVS, epicardial fat is thickest and the underlying myocardium thinnest. Consequently, epicardial ablation produces markedly shallower lesion and a significantly higher incidence of steam pop than endocardial ablation.