Left ventricular outflow tract

The left ventricular outflow tract (LVOT) consists of the region of the left ventricle that extends from the basal interventricular septum and anterior mitral leaflet to the aortic valve annulus. The LVOT is bounded anteriorly by the interventricular septum and posteriorly by the anterior leaflet of the mitral valve, with the left ventricular free wall forming the lateral boundary. The tract begins just below the aortic valve and ends at the ventricular cavity, within 5 mm of the aortic annulus.

Morphologically, the LVOT is not uniformly circular; it is more elliptical at the proximal (ventricular) end and becomes more circular as it approaches the aortic valve (distal LVOT).The anterior-posterior diameter is generally smaller than the transverse diameter, and the shape changes dynamically during the cardiac cycle, being more circular in systole. The LVOT supports the aortic root, with the myocardial-arterial junction terminating at the bases of the aortic sinuses, not extending to the sinotubular junction.

The LVOT is clinically significant due to its role in conditions such as LVOT obstruction, which may be influenced by septal hypertrophy, mitral valve anatomy, and the presence of subaortic structures. The LVOT is widely studied and described in cardiology imaging for TAVI measurements and some peculiarities has to be known:

• The left ventricular outflow tract (LVOT) is the region of the left ventricle that lies between the anterior cusp of the mitral valve and the ventricular septum: as the ventricular septum lies at an angle of 45 degrees to the median plane, the “anterior” wall of the outflow tract is therefore anteromedial and the “posterior” wall is posterolateral.

• In the anterior wall are both the muscular and membranous parts of the ventricular septum. The outflow septal myocardium is smooth-walled. At the junction of the muscular and membranous parts of the septum lies the atrioventricular bundle.

• The posterior wall of the outflow tract is formed not only by the anterior mitral cusp but also by the 'intervalvar septum' and, in its upper part, by a curtain formed by the fusion of the anterior and posterior mitral cusps.

• There is no line of demarcation on its anterior (septal) wall to indicate the lower border of the tract. This is indicated on its posterior wall by the free lower border of the anterior cusp of the mitral valve.