Surface projections of the heart
The surface projections of the heart are the anatomical points that medical professionals use to orientate themselves on the human thorax when noninvasive clinical examinations are being performed on the heart, such as observation, palpation, percussion and auscultation. This article will highlight the main points which are essential for locating the borders of the heart when it is covered by bones, muscles, vessels and skin. Two parts of the heart are projected onto the chest, the borders of the heart and the anulus fibrosus or fibrous skeleton of the heart.
Borders of the Heart
The superior border of the heart is a convex line that runs from the inferior border of the second left costal cartilage to the superior border of the third right costal cartilage.
The right border of the heart is a convex line that runs from the third right costal cartilage to the sixth right costal cartilage.
The inferior border of the heart is a convex line that runs from the sixth right costal cartilage to the fifth intercostal space close to the left midclavicular line.
The left border of the heart is a convex line that runs from the fifth intercostal space close to the left midclavicular line to the inferior border of the second left costal cartilage.
On an x-ray, the heart can be seen as an outline with several convexities on each side. On the right side, there are three convexities running in the craniocaudal direction. These include the superior vena cava, the right atrium and the inferior vena cava which is the smallest and most inferior convexity as it directly enters the diaphragm.
On the left side of the heart there are four convexities. In a craniocaudal order they appear as the aortic arch, the pulmonary trunk, the left auricle or atrium and the left ventricle. At the point where the left side of the heart touches the diaphragm, the apex can be located.
The Anulus Fibrosus
Upon the diagram that is constructed by using an x-ray to outline the borders of the heart, when two convex lines are drawn connecting the lower right corner of the heart to the upper left corner, the right and left limit of the coronary groove is pinpointed. These two lines embody the surface projections of the anulus fibrosus which contains the heart valves.
The Heart Valves
Using the markings that locate the area of the anulus fibrosus and moving in the same direction from lower right to upper left, the four heart valves can also be located. First is the right atrioventricular valve, which is the most lateral of the valves on the right side of the heart. Next is the left atrioventricular valve which is equivalent to the right valve in that it is the most lateral of the left cardiac valves and it is also deeper than the aortic valve and pulmonary valve. In third place is the aortic valve, which superiorly borders the right ventricle and is more superficial than the right atrioventricular valve. Lastly, the pulmonary valve due to the fact that the pulmonary trunk is situated on the left side of the ascending aorta and is slightly posterior to it.