Final answer:
For evaluating an aortic valve, a TTE is usually the first choice due to its non-invasive nature. If more detail is needed, a TEE is preferable due to its ability to provide clearer images. The chordae tendineae are critical for atrioventricular valves to prevent backflow during ventricular contraction.
Step-by-step explanation:
To determine which is preferable for evaluating an aortic valve, between a Transthoracic Echocardiogram (TTE) or a Transesophageal Echocardiogram (TEE), it's important to understand the specifics of each procedure. A TTE is non-invasive and provides good images of the heart, often sufficient to evaluate the aortic valve. However, if the TTE images are not clear or if more detailed images are needed, a TEE might be performed. The TEE is more invasive than the TTE, as a probe is inserted down the esophagus, but it provides a much closer and clearer view of the aortic valve. Consequently, TEE is often used when the most detailed images are necessary, such as evaluating for infective endocarditis, prosthetic valves, or in pre-surgical assessment.
Considering the anatomy of the heart valves, the chordae tendineae's presence is more critical for the atrioventricular valves (tricuspid and mitral) compared to the semilunar valves (aortic and pulmonary). This is because the atrioventricular valves are under greater pressure to prevent backflow from the ventricles to the atria during ventricular contraction. The chordae tendineae and the papillary muscles to which they attach help prevent the valve leaflets from inverting or prolapsing into the atria, which would allow backflow. The semilunar valves, on the other hand, have a different mechanism, involving pocket-like folds of endocardium reinforced with connective tissue that closes the valves when pressure changes as the ventricles relax.