I diopathic ventricular arrhythmias (VAs) arising from the left ventricle (LV) are often accessible for catheter ablation from the aortic sinuses of Valsalva or adjacent to the mitral annulus (MA). 1 The aortic and mitral valves are direct apposition and attach to an elliptical opening at the base of the LV known as the LV ostium. 2 The VAs arising from this region are being increasingly recognized as targets for catheter ablation. [3][4][5][6][7] This review describes the anatomic features of the LV ostium and the electrocardiographic, electrophysiological, and angiographic characteristics that are relevant to the mapping and ablation of these arrhythmias.
Anatomy of the LV OstiumThe dominant central structure of the heart is the junction of the aorta with the LV. Fundamental for understanding idiopathic VAs arising near the aortic and mitral valves are 2 concepts: first, these arrhythmias arise from the LV ostium ( Figure 1); and second, the LV ostium is covered by the aorto-ventricular membrane, a tough fibrous structure which is perforated by the aorta anteriorly and the mitral valve (MV) posteriorly ( Figure 2). The anatomic concept of the LV ostium and its covering, the aorto-ventricular membrane, are based on the pioneering work of McAlpine. 2
The Anterior Division of the Aorto-Ventricular Membrane Within the LV OstiumThe aorta is joined to the LV ostium at an angle of Ϸ30% above the horizontal plane with the noncoronary cusp (NCC) most inferiorly and the left coronary cusp (LCC) most superiorly (Figures 1 and 3A). Rather than a circular fibrous aortic annulus, in reality the anatomy is much more complex with 3 membranous attachments at the base of the right, left, and noncoronary cusps (Figure 2). These attachments consist of less than one half of the circumference of each aortic sinus cusp (ASC). The most anterior attachment of the aorta to the LV ostium is the right coronary cusp (RCC) (Figure 3B), which is in contact with the LV ostial myocardium over a distance of 16.5Ϯ3 mm ( Figure 4A). 2 When viewed from the superior aspect of the RCC, LV muscle can be seen at the base of the cusp. The RCC has an average depth of 23.2Ϯ2.7 mm with the ostium of the right coronary artery (RCA) located Ϸ15 mm from the nadir of the cusp ( Figure 3C). 2 The LCC forms the lateral and postero-lateral attachment of the aorta to the LV ostium (Figure 2). The LCC is in contact with the LV ostium in the antero-lateral portion of the cusp for 7.4Ϯ3 mm, significantly less than for the RCC. 2 The posterior portion of the LCC is not in direct contact with LV myocardium but apposes the left fibrous trigone (LFT), a tough membranous region joining the aorta to the anterior leaflet of the MV ( Figure 5A). Thus, a catheter positioned in the antero-lateral portion of the LCC will usually record a larger ventricular electrogram than atrial electrogram whereas a catheter positioned in the more posterior portion of this cusp will often record a larger atrial electrogram. The left main coronary artery ostium is located 15 to 20 mm above ...