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Structure

Left atrium

Content last updated · 1 min read ·

This is the date the draft was written, not a medical review date.

The left atrium receives oxygenated blood from the four pulmonary veins and delivers it through the mitral valve to the left ventricle. It is the most posterior chamber of the heart, lying directly in front of the oesophagus.

Terminologia Anatomica (Latin): Atrium sinistrum · Open in the 3D atlas

Location

Posterior in the middle mediastinum, lying directly in front of the oesophagus and the descending aorta, with the tracheal bifurcation above. The left auricle projects anteriorly beside the pulmonary trunk.

Structure

The posterior wall is smooth and receives two right and two left pulmonary veins (no valves). Pectinate muscles are confined to the narrow, hooked auricle. The septal wall shows the valve of the foramen ovale; the wall is slightly thicker than in the right atrium.

Blood supply

Atrial branches of the left circumflex artery, with contributions from the right coronary artery; the left circumflex gives the sinoatrial nodal artery in a minority of people (about a quarter to a third in published series).

Innervation

Cardiac plexus (sympathetic and vagal). Ganglionated plexi near the pulmonary vein ostia modulate atrial electrophysiology.

Function

Serves as the reservoir, conduit and booster pump for left ventricular filling. Atrial contraction contributes a larger fraction of filling when the ventricle is stiff or the heart rate is high.

Clinical correlations

Atrial fibrillation often originates from the pulmonary vein ostia, and thrombus forms preferentially in the left atrial appendage, raising stroke risk. Mitral valve disease enlarges the atrium, which may compress the oesophagus (dysphagia) or recurrent laryngeal nerve. Transseptal puncture across the fossa ovalis is used to reach the left heart.

Common exam points

  • Most posterior chamber of the heart, directly in front of the oesophagus.
  • Four pulmonary veins enter the smooth posterior wall; no valves guard them.
  • Left atrial appendage is the commonest site of atrial thrombus in non-valvular atrial fibrillation.
  • Posterior relation to the oesophagus: transoesophageal echocardiography images the atrium well, and enlargement can cause dysphagia.

References

  1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)
  2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Wolters Kluwer, 8th edition (2018) — Tier 3 (textbook)
  3. 2020 ESC Guidelines for the diagnosis and management of atrial fibrillation developed in collaboration with the European Association for Cardio-Thoracic Surgery (EACTS). European Society of Cardiology (2020) — Tier 2 (guidelines / primary literature)

References are listed only where the article cites them. See the sources page for the full policy. How sources are chosen and credited

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