Evaluation of the Left Atrium
Common Causes of Left Atrial Enlargement
- Mitral valve disease (e. g., mitral stenosis, mitral regurgitation)
- Ventricular septal defect
- Patent ductus arteriosus
- Left ventricular failure
- Constrictive pericarditis
- Valvular aortic stenosis
- Atrial fibrillation
- Cardiac transplantation
- Parasternal long-axis view
- Parasternal short-axis view of the aortic valve
- Modified parasternal short-axis view of the aortic valve (to visualize the left atrial appendage)
- Apical four-, five-, two-chamber and long-axis views
- Subcostal four-chamber and short axis views
- Suprasternal long- and short axis views
- Transesophageal echocardiography has greatly enhanced visualization of the left atrium, especially the left atrial appendage
Left Atrial Dimensions
- The left atrium is at its largest dimension at end-systole. M-mode measurement of the left atrium is made easier by observing the distinct motion of the left atrial posterior wall: anterior motion with atrial systole, posterior motion with ventricular systole and anterior motion with ventricular diastole.
- The left atrium may be compared to the aorta in a qualitative fashion to determine left atrial enlargement, with the LA/Ao ratio equal to 1: l. This ratio is not valid in the presence of aortic dilatation.
- Measuring the left atrium by 2-D echocardiography is helpful and probably more accurate than by M-mode because the left atrium may be visualized in so many different views.
Normal Left Atrial Parameters : Left atrial dimensions:
- Normal : 19 to 40 mm
- Mild enlargement : 40 to 50 mm
- Moderate enlargement : 50 to 60 mm
- Severe enlargement : 60 to 70 mm
- Giant left atrium :>70 mm
Important to Note
The modified parasternal short-axis view of the aortic valve is used to visualize the left atrial appendage. To obtain this view, the transducer is first oriented for the standard parasternal short-axis view at the aortic valve level. The plane of the beam is then tilted superiorly with lateral angulation of the transducer, so that the pulmonary and aortic valves, but not the tricuspid, are imaged. Positioning the transducer in a high intercostal space is sometimes helpful for optimal imaging of the left atrial appendage.