The aorta must be understood as part of the central cardiac anatomy rather than as an isolated arterial tube. Its root is interposed between the cardiac chambers, the ascending segment occupies a central position within the pericardium, and its branches establish close relationships with the conduction tissues, pulmonary arteries, atrial walls, and epicardial structures. These relationships are fundamental when catheters are positioned within the aortic sinuses or when imaging is used to define an arrhythmic substrate. [1-3]

1  Aortic root and ventriculoarterial junction

The aortic root extends from the basal attachments of the aortic valvar leaflets to the sinotubular junction. It contains the valvar leaflets, their semilunar attachments, the aortic sinuses, and the interleaflet triangles. The haemodynamic junction between the left ventricle and aorta is defined by the leaflet attachments, whereas the anatomical ventriculoarterial junction follows the transition between ventricular myocardium and arterial wall. These two boundaries are not coincident. [1,2]

The basal ring formed by joining the lowest points of leaflet attachment is a useful imaging construct, but it is not a discrete anatomical annulus. Between the semilunar hinge lines, triangular extensions of the left ventricular outflow tract reach distally towards the sinotubular junction. These interleaflet triangles are fibrous and extracardiac in their potential relationships despite lying within the overall crown-shaped root.

2  Aortic sinuses and coronary origins

The right and left aortic sinuses give rise to the corresponding coronary arteries, while the third is the non-coronary sinus. The coronary ostia usually arise below the sinotubular junction, but their height, shape, and precise position vary. The right coronary sinus is related to the right ventricular outflow tract, and the left coronary sinus is related mainly to the left ventricular myocardium and the left atrial roof region. [1-3]

The non-coronary sinus occupies the posterior and rightward portion of the root in attitudinal orientation. It is closely related to the interatrial septal region and central fibrous body. These relations explain why mapping within different aortic sinuses can record ventricular, atrial, or His-bundle signals depending on catheter position.

3  Ascending aorta and proximal arch

The ascending aorta arises centrally and passes superiorly, with a slight rightward and posterior course before becoming the arch. It is enclosed with the pulmonary trunk within the arterial pericardial reflection. Posteriorly it is related to the transverse pericardial sinus and the superior aspect of the left atrium; rightward it approaches the superior caval vein and right atrial appendage.

The arch passes superiorly, posteriorly, and leftward over the left pulmonary artery and left main bronchus. Its principal branches are the brachiocephalic trunk, left common carotid artery, and left subclavian artery. Variations in branching are common and are principally important to this atlas when they affect vascular access or the interpretation of cross-sectional imaging.

4  Myocardial extensions above the aortic valve

Ventricular myocardium can extend a short distance beyond the anatomical ventriculoarterial junction into the bases of the aortic sinuses. These extensions are most often associated with the right coronary sinus and the adjacent part of the left coronary sinus; myocardium is not distributed uniformly around the root. Examination of large series of human hearts confirms substantial individual variability. [3]

Such myocardial crescents provide an anatomical explanation for ventricular arrhythmias mapped above the valvar hinge line. Their presence does not mean that the arterial wall itself is muscular throughout. Precise correlation between the leaflet hinge, the sinuses, adjacent ventricular outflow tracts, and coronary ostia is necessary before ablation.

5  Relations with the conduction system

The membranous septum and central fibrous body lie beneath the region between the right and non-coronary aortic sinuses. The penetrating atrioventricular bundle passes through this fibrous area before becoming the branching bundle on the ventricular side. The conduction axis is therefore closest to the basal septal region of the root rather than to all three sinuses equally. [1,2]

This relationship is central to transcatheter aortic valve implantation and to ablation near the aortic root. Device depth, the dimensions of the membranous septum, and the location of the muscular septal crest influence the risk of atrioventricular conduction injury.

6  Relevance for mapping and intervention

The aortic sinuses offer access to arrhythmic sites that may be separated from an endocardial target by only a thin fibrous or muscular partition. Mapping can help identify outflow-tract arrhythmias, para-Hisian pathways, and some atrial tachycardias. Coronary angiography or equivalent imaging is required whenever energy delivery may approach a coronary ostium or proximal coronary artery.

Aortic root geometry should always be interpreted in attitudinal orientation and in relation to the pulmonary root, ventricular septum, atrial septal region, and fibrous skeleton. Detailed ablation technique belongs in the relevant procedural chapters.