Reservoir for the oxygen rich blood returning from the lungs via the pulmonary veins.
Holds about 50 cc and partially empties into the left ventricle during diastole.
They posterior most chamber of the heart, and is almost a mid line structure.
The normal size of left atrium is about 4 X 4 cm.
Normal left atrial volume is 46ml in men and 38 ml in women .
A difficult structure to identify in the X ray chest as it does not form the cardiac border, except as a small circumference of left atrial appendage.
Can enlarge in multiple directions, but dilates in the path of least resistance.
Its size measured best by echocardiogram.
It is directly exposed to left ventricular pressure during diastole through the open mitral valve.
Its shape determined by the same factors that influence diastolic left ventricular filling.
LA size as evaluated by echocardiography and is strongly associated with mortality.
Left atrial volume index predicts mortality risk independent of left ventricle geometry.
In patients with preserved LV systolic function, left atrial volume index is strongly associated with all cause mortality, with mortality risk increasing with worsening LA volume index (Patel DA et al).
LA enlargement associated with cardiovascular and all cause mortality in population based studies and in patients with dilated cardiomyopathy, LV dysfunction, atrial arrhythmias, and acute myocardial infarction.
The left atrial appendage enlarges early, and USB seen as a fullness beneath the pulmonary artery shadow.
The left atrial appendage enlargement is the earliest finding of left atrial enlargement (LAE) in X ray, and may appear as straight left heart border.
The left atrial appendage enlargement is not necessarily in proportion with LAE.
Posterior enlargement of the LA pushes the esophagus towards the spine, and is visible only in barium swallow examinations.
Then LA can enlarge either to left or right.
If the LA enlarges superiorly it lifts the left main bronchus and widens they subcarinal angle which is normally less than 75 degrees.
LA can enlarge anteriorly sometimes and can produce a left parasternal lift.
The upper limit of normal LA size is around 4.5cm, and enlargement is seen with mitral stenosis, regurgitation, hypertensive heart disese, and cardiomyopathy.
In the presence of atrial fibrillation LA size increases.
Atrial myopathy refers to a range of abnormalities associated with disease of the left atrium with or without atrial fibrillation.
Findings in atrial myopathy include left atrial enlargement, impaired atrial systole, abnormal P wave terminal force in lead V1, atrial fibrosis for atrial flow abnormalities detectable by echocardiography or cardiac MRI.
Lower left atrial function is associated with adverse cardiovascular outcomes in the general population and worse prognosis among those with cardiovascular disease.
Greater maximal LA volume index and greater minimal left atrial volume index are also risk factors for cardiovascular events.
Findings in atrial myopathy include left atrial enlargement, impaired atrial systole, abnormal P wave terminal force in lead V1, atrial fibrosis for atrial flow abnormalities detectable by echocardiography or cardiac MRI: Such abnormalities can occur in the absence of atrial fibrillation.
Atrial myopathy may account for stroke, even in the absence of atrial fibrillation due to blood stasis in a hypercoagulable state associated with atrial fibrosis and inflammation.
Lower LA reservoir function has been associated with silent brain infarcts and white matter hyperintensities.
Atrial myopathy may be an independent risk factor for an ischemic stroke and therefore may contribute to dementia risk.
Atrial myopathy is a precursor to atrial fibrillation and the latter is associated with dementia.
Atrial myopathy may alter cardiac output and therefore cerebral perfusion.