What does the Left Atrium Do?

The left atrium is one of the 4 chambers of the heart and occurs on the upper posterior upper right side of the heart. After the entry of oxygen-rich blood from the pulmonary veins into the left atrium, it directly pumps the blood into the left ventricle. The left circumflex coronary artery provides most of the blood supply that is received by the left atrium. There is partial drainage of the veins via the oblique vein of the left atrium.

• Functions: The main functions of the left atrium are to store the blood received by the blood flowing from the lungs and to the pump such blood to other sections of the heart. It may be noted that the left atrial walls are somewhat thicker than the right atrial walls. Oxygenated blood returning from the lungs enter the left atrium via the pulmonary vein. The blood is then pumped by the left atrium into the heart’s left ventricle chamber via the mitral valve. The oxygen-rich blood is now ready to get pumped to different tissues of the body.
• Problems: Some common cardiac conditions associated with the left atrium include mitral valve prolapse marked by incomplete closure of the mitral valve between the left ventricle and the left atrium, thereby causing backward leakage of blood into the left atrium; and mild, severe, or moderate enlargement or dilation of the left atrium.

Enlargement or dilation of the left atrium

Left atrial dilation or left atrial enlargement/LAE is a type of cardiomegaly marked by enlargement of the left atrium. It is commonly caused due to heart valve problems, obesity, hypertension, atrial fibrillation, obstructive sleep apnea, and cardiac failure.

• Heart valve problems: Vulvular heart disorders can cause LAE. The left ventricle is separated from the left atrium by the mitral valve. Mitral regurgitation can occur if the mitral valve has excessive leaks prompting backward flow of the blood into the left atrium and eventually causing LAE. Likewise, mitral stenosis or constriction of the mitral valve can cause buildup of blood in left atrium, thereby causing it to enlarge.
  • The flow of blood from the left ventricle of the heart into the aorta and then to different parts of the body is facilitated by the aortic valve. Narrowing, constriction, or stenosis of the aortic valve causes the heart to pump harder against increased pressure to transfer blood to other parts of the body. Pumping against such elevated pressure and resistance finally triggers enlargement of the left ventricle and then the left atrium.
• Obesity: Obesity is considered as one of the most common factors among the general population which can increase the risk to left atrial enlargement. It may also be noted that LAE has close co-relation to the size of the body which means that people with a naturally large body are also vulnerable to developing the cardiac condition, irrespective of whether or not they are obese.
• Hypertension: Uncontrolled high blood pressure causes the heart to work harder so as to be able to pump blood to the rest of the body. The heart being a muscle tend to enlarge when pumping against increased pressures. The left ventricle usually enlarges at first. Increase in the left ventricle pressure then causes the left atrium to also start enlarging slowly. LAE associated with hypertension carriers an increased risk to occurrence of stroke and cardiac arrest.
• Atrial fibrillation: Atrial fibrillation is a condition of anomalous heart beats that trigger irregular beating of the heart. The ventricles and atria in healthy people generally beat together in a synchronous manner and atrial fibrillation interferes and unsettles this process.
  • Atrial fibrillation usually occurs in older individuals, but can also affect people of all ages. Heart failures and mitral stenosis marked enlargement of the left atrium often result in atrial fibrillation. Atrial fibrillation and LAE often occur together, but the former may also occur without the latter. However, chronic atrial fibrillation can eventually cause enlargement and dilation of the atria.
  • Non-treatment of LAE and atrial fibrillation can trigger the development of blood clots which can migrate to the brain, thereby causing a stroke. Hence, affected individuals are given blood thinners to decrease the susceptibility of stroke.
• Obstructive sleep apnea: Some cases of left atrial enlargement may occur due to OSA or obstructive sleep apnea. During an OSA episode, patients try to breathe with a blocked respiratory tract and there is sudden reduction of internal chest pressure. Such negative intra-thoracic pressure can trigger expansion and stretching of the left atrial walls, during each episode of OSA. With time, recurrent left atrial stretching can lead to persistent enlargement of the left atrium.
• Heart failure: Inability of the heart to effectively pump blood to other areas of the body is termed as cardiac failure. It can occur due to coronary artery disease, unregulated hypertension, alcohol and drug abuse, and diabetes, etc. Progressive weakening of the heart causes the blood to accumulate in the lungs and heart, thereby triggering enlargement of the left ventricle and left atrium. Non-treatment of heart failure can then trigger abnormalities of the right side of heart by the excess volume of blood, eventually causing enlargement of the right atrium and right ventricle.

Diagnosis of left atrium enlargement

• An ECG or electrocardiogram with a visible notch in P wave is normally used to detect left atrial enlargement. However, P wave is not present in case the patient also suffers from atrial fibrillation. Both conditions can however be measures and diagnosed with the help of an ECHO or echocardiogram.
• Doctors prefer to measure the left atrium size as per its volume rather than one linear dimension. This is because enlargement or dilation can be different for varied directions.

Clinical significance

• In addition to other factors, the size of left atrium can be used by doctors to predict the mortality occurring due to cardiovascular conditions as well as all other causes of death.
• Studies indicate that an echo-cardiograph measurement of the left atrium size may help identify the prognosis for preclinical cardiovascular illness. However, doctors who believe that LAE can be used as a predicting tool for mortality have also suggested that a more standard measurement option for left atrium size is needed, as echo-cardiogram measurements are insufficient and not so conclusive.