The three musketeers of the parasternal long axis view
Identification of gross discrepancies in chamber size is one of the core competencies of focused cardiac ultrasound. In the parasternal long axis (PLAX) view, right ventricular outflow tract (RVOT), aorta (Ao) and left atrium (LA) roughly occupy one-third of the image and hence are nicknamed, ‘three musketeers’. When one of these structures enlarges, we can get a sense of severity by observing their relative proportions. In nephrology practice, it is not uncommon to see patients with pulmonary hypertension with a large RV and those with elevated left ventricular filling pressures with an enlarged LA. Absolute values of linear measurements are provided below but it is not necessary to memorize them for POCUS purposes.
Here are nice examples demonstrating severe enlargement of each of these musketeers. If you see enough images, you can pick up even mild abnormalities. It is also important to realize that over-reliance on linear measurements obtained from one view can be misleading.
Below image is obtained from a pregnant woman with pulmonary embolism and consequent right ventricular dilatation.
Here is an image demonstrating a large ascending aortic aneurysm measuring ~7cm!
Below image demonstrates severely dilated LA obtained from a patient with nephrotic syndrome. Found to have cardiac amyloidosis. Also note left ventricular hypertrophy.
Another example of dilated LA in a patient with severely reduced LVEF. Note the LV is barely contracting.