Revisiting the anatomy of the left ventricle in the light of knowledge of its development

Despite centuries of investigation, certain aspects of left ventricular anatomy remain either controversial or uncertain. We make no claims to have resolved these issues, but our review, based on our current knowledge of development, hopefully identifies the issues requiring further investigation. When first formed, the left ventricle had only inlet and apical components. With the expansion of the atrioventricular canal, the developing ventricle cedes part of its inlet to the right ventricle whilst retaining the larger parts of the cushions dividing the atrioventricular canal. Further remodelling of the interventricular communication provides the ventricle with its outlet, with the aortic root being transferred to the left ventricle along with the newly formed myocardium supporting its leaflets. The definitive ventricle possesses inlet, apical and outlet parts. The inlet component is guarded by the mitral valve, with its leaflets, in the normal heart, supported by papillary muscles located infero-septally and supero-laterally. There is but a solitary zone of apposition between the leaflets, which we suggest are best described as being aortic and mural. The trabeculated component extends beyond the inlet to the apex and is confluent with the outlet part, which supports the aortic root. The leaflets of the aortic valve are supported in semilunar fashion within the root, with the ventricular cavity extending to the sinutubular junction. The myocardial-arterial junction, however, stops well short of the sinutubular junction, with myocardium found only at the bases of the sinuses, giving rise to the coronary arteries. We argue that the relationships between the various components should now be described using attitudinally appropriate terms rather than describing them as if the heart is removed from the body and positioned on its apex. The image shows how the left ventricle of the human heart can be assessed in terms of its inlet, apical and outlet components. The ventricle has been opened through a superior incision parallel to the anterior interventricular groove. The roof of the ventricle is formed by the area of fibrous continuity between the leaflets of the aortic and mitral valves, which is thickened at its ends to form the right and left fibrous trigoes (white triangles with black borders). The outlet component is complex, extending beyond the so-called echocardiographic 'annulus', which in reality is no more than a virtual basal ring, to reach the level of the sinutubular junction. Note the infero-septal recess of the outflow tract, which interposes between the leaflets of the mitral valve and the septum.image