Cardiac Structures Best Visualized in the Parasternal Long-Axis View
The aortic root, left ventricular outflow tract (LVOT), left atrium, and mitral valve are the cardiac structures best visualized in the parasternal long-axis (PLAX) view, making option C (Aorta and left atrium) the correct answer.
Structures Visualized in the Parasternal Long-Axis View
The parasternal long-axis view provides excellent visualization of several key cardiac structures:
- Aortic root and valve: Clearly visualized in the right upper portion of the image
- Left atrium: Well-visualized posterior to the aortic root
- Left ventricular outflow tract: Clearly seen connecting to the aortic valve
- Left ventricle: Visualized in long axis
- Mitral valve and inflow tract: Well-demonstrated between the left atrium and left ventricle
- Right ventricle: Anterior portion visible
- Interventricular septum: Clearly visualized
- Pericardial spaces: Both anterior and posterior pericardial spaces can be assessed
According to the American College of Emergency Physicians guidelines 1, the PLAX view is typically obtained using the third, fourth, and fifth intercostal spaces, immediately to the left of the patient's sternum. The probe marker is directed to the patient's left hip (approximately 4-o'clock position).
Advantages of the PLAX View
The PLAX view is particularly valuable for:
- Assessing the aortic root dimensions and morphology
- Evaluating left atrial size and function
- Examining mitral valve morphology and function
- Measuring left ventricular wall thickness and dimensions
- Detecting pericardial effusions
Research has demonstrated that the PLAX view in isolation is highly sensitive and specific for identifying left ventricular dysfunction and moderate to large pericardial effusions 2. This makes it one of the most useful single views in focused cardiac ultrasound.
Comparison with Other Echocardiographic Views
While other echocardiographic views have their own strengths:
Parasternal short-axis view: Better for visualizing the papillary muscles, mitral valve in cross-section, and left ventricular function at various levels
Apical four-chamber view: Superior for visualizing all four cardiac chambers simultaneously, including the right atrium and tricuspid valve (option B)
Subcostal four-chamber view: Better for visualizing the right atrium and IVC junction (option D)
The PLAX view remains superior specifically for visualizing the aorta and left atrium (option C) in combination, as well as the mitral valve apparatus and left ventricular outflow tract.
Clinical Implications
The European Association of Echocardiography guidelines 1 highlight that the functional integrity of the subvalvular mitral apparatus can be particularly well appreciated from left ventricular long-axis cut planes, which includes the PLAX view. This makes the PLAX view especially valuable for evaluating mitral valve pathologies.
The PLAX view is often the first view obtained in a focused cardiac ultrasound examination due to its high diagnostic yield and relative ease of acquisition in most patients.