Cardiac Valves: Assessment and Identification
Atrial Septal Defects

The different types of atrial septal defect (ASDs) are: sinus venosus, secondum and primum. In order to remember the anatomic locations of the atrial septal defects one can remember the letters "VSP" which localized each atrial septal defect from cranial/top of the atria to caudal/bottom of the atria: V- venosus, S - secondum, P -primum

- Sinus venosus ASDs are seen with PAPVR

- Secundum ASDs are the commonest type

- Primum ASDs are seen with Down syndrome

Ventricular Septal Defects

There are four major locations of ventricular septal defects: membranous, muscular, anterior and posterior.

The membranous ventricular septal defects are more common (80%) and occur in the fibrous portion of the septum closer to the base of the heart. The muscular ventricular septal defects exist in the muscular portion of the septum closer to the apex of the heart.

Prosthetic Cardiac Valves

Localizing cardiac prosthetic valves can be difficult. There are a number of strategies that can be employed to aid in characterizing the type of prosthetic valve. The best strategy involves assessing the location of the valve and then determining the orientation and direction of flow. Additional aids which serve as adjunts are the statistical nature of valve replacement and including patient history.

The location of the cardiac valves is best determined on the lateral radiograph. A line is drawn on the lateral radiograph from the carina to the cardiac apex. The pulmonic and aortic valves generally sit above this line and the tricuspid and mitral valves sit below this line. Keep in mind that sometimes the aortic root can be inferiorly displaced which will shift the aortic valve below this line.

The aortic and pulmonic valves are generally above the red line and the mitral and tricuspid valves generally lie below it.

A second technique to further localize prosthetic valves involves drawing a second line which is perpendicular to the patient's upright position which bisects the cardiac silouette. The aortic valve projects in the upper quadrant, the mitral valve in the lower quadrant and the tricuspid valve in the anterior quadrant. The pulmonary valve projects in the superior portion of the posterior quadrant which is illustrated in the below images:

Lateral chest radiograph: A second line is drawn which bisects the cardiac silouette. Blue: aortic valve, pink: mitral valve, green: pulmonic valve, yellow: tricuspid valve.

An alternative method, which is less reproducible, involves the frontal radiograph. On the frontal chest radiograph (either the AP or PA view) cardiac valvular prostheses can be localized by drawing a longitudinal line through the mid sternal body. Use this line to bisect the sternum in the sagittal plane and then draw a perpendicular line dividing the heart horizontally. The aortic valve should overlie the intersection of these two lines. The mitral valve will lie in the lower left quadrant (the patient’s left). The tricuspid valve would lie in the lower right corner (the patient's right) and the pulmonic valve will lie in the upper left corner (the patient's left).

Frontal chest radiograph: A longitudinal line bisects the sternum and a perpendicular line is drawn thereafter. Blue: aortic valve, pink: mitral valve, green: pulmonic valve, yellow: tricuspid valve.

A word of warning pertains to the above strategies. Patients with cardiac valves often have chamber enlargement and cardiac rotation which can displace the positions of the valves as well as create difficulty when drawing lines through the cardiac silhouette. These rules are meant as a guideline to better localize cardiac valves although they do not always work.

If we apply these rules to a chest radiograph in a patient with known aortic and mitral prosthetic valves:

The aortic valve is above the red line and the mitral valve lies below it.

The aortic valve is usually superior to the mitral valve as depicted in this chest radiograph as a second example.

Aortic valve is usually placed superiorly on the frontal chest radiograph over the lower mitral valve.

Sometimes the aortic valve may be low lying which makes localization of the valve difficult, especially on the frontal radiograph. A low lying aortic valve can appear projecting over the expected location of the mitral valve on the frontal projection.

One additional pearl in determining the location of cardiac valves includes localizing the direction of flow. Some bioprosthetic valves have components that determine the direction of flow which helps localize the valve prosthesis. If the direction of flow is from inferior to superior and then an aortic valve is likely. If the direction of flow is from superior to inferior in the left chest then the valve is likely a mitral valve.

Direction of flow can help determine if the valve is atrial or in the outflow tract. In this case this Carpentier-Edwards aortic valve's direction of flow is into the aortic outflow tract.

Sometimes there are cardiac prosthetic valves which are partial ring shaped. Caution must be taken if there is consideration of a partially broken ring as recognition of partial annuloplasty rings needs to be considered. Partial annuloplasty rings show up as a partial metallic ring-like density. These rings are used to buttress the leaflets of a regurgitant valve. Ideally, when repairing a valve, it is favourable to use as little foreign material as possible. Hence, partial annuloplasty rings were developed in order to minimize the amount of foreign material while being able to remedy a regurgitant valve. A partial annuloplasty ring of the mitral and aortic valves are seen below:

Lateral chest radiograph: Aortic and mitral valve partial annuloplasty rings.

An adjunctive strategy involves the incidence of valve replacement. Mitral valve replacement is the commonest valve to be replaced followed by the aortic valve and then the tricuspid valve. The pulmonic valve is the least common valve to be replaced. Hence, if unsure regarding the type of valve but the valve is above the diagonal line drawn from the carina to the cardiac apex on the lateral chest radiograph then the valve is likely either an aortic valve or a pulmonic valve. Since the aortic valve is much more frequently replaced than the pulmonic valve, the valve in question is likely an aortic valve.

Despite these strategies it can still be difficult to characterize the type of cardiac valve. If there is no clinical information to help one can simply dictate "valvular prosthesis" to indicate that there is a cardiac valve present but the type of valve is uncertain with the limited information provided.