| 1. Embryologic Origin | The left atrium forms from two embryologic components: the primitive atrium and the pulmonary vein tissue. |
| 2. Smooth Posterior Wall | Derived from the incorporation of the common pulmonary vein into the atrial wall. This forms the smooth-walled portion. |
| 3. Trabeculated Anterior Wall | Formed from the primitive atrium and contains pectinate muscles. |
| 4. Left Atrial Appendage (LAA) | Derived from the primitive atrium; has a narrow neck and trabeculated interior (with pectinate muscles). |
| 5. Pulmonary Veins | The 4 pulmonary veins develop from the common pulmonary vein and become incorporated into the LA. |
| 6. Septum Formation | The septum primum and septum secundum divide the atria during development; the foramen ovale is located within the septum. |
| 7. Foramen Ovale | Normally closes after birth due to increased LA pressure; failure to close results in PFO. |
| 8. Position | Posterior and superior chamber of the heart; lies posterior to the right atrium. |
| 9. Relations (Posterior) | Directly related to the esophagus — important for transesophageal echocardiography (TEE). |
| 10. Relations (Anterior) | Lies posterior to the aortic root and interatrial septum. |
| 11. Chamber Shape | Irregular ovoid chamber with smooth posterior wall and more muscular anterior wall. |
| 12. Volume (Indexed) | Normal LA volume index is < 34 mL/m² (ASE/EACVI guideline). |
| 13. Main Functions | LA acts as: reservoir (during LV systole), conduit (early diastole), and booster pump (late diastole). |
| 14. Muscle Content | Contains pectinate muscles only in the appendage, unlike the RA. |
| 15. LAA Morphology | Variable: chicken wing, windsock, cauliflower, cactus types — relevant for thrombus risk. |
| 16. Blood Supply | Mostly supplied by the left circumflex artery (LCx) and branches from right coronary artery (RCA) to interatrial septum. |
| 17. Innervation | Autonomic innervation from the cardiac plexus; ganglionated plexi are involved in AF. |
| 18. Electrical Role | Plays a key role in atrial conduction and AF genesis, especially near the pulmonary veins. |
| 19. Clinical Relevance | LA enlargement associated with AF, stroke risk, heart failure, and diastolic dysfunction. |
| 20. Imaging Modalities | Best assessed by TEE, TTE, cardiac MRI, and CT angiography for anatomy and thrombus. |
