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Right atrium

The right atrium is one of the four chambers of the heart, located on the right anterior side. It receives systemic venous return from the superior vena cava, inferior vena cava, and coronary sinus. Internally, it is divided into a smooth-walled posterior part (sinus venarum) and an anterior muscular part (atrium proper) marked by pectinate muscles. The two regions are separated by the crista terminalis. The interatrial septum forms the medial wall and bears the fossa ovalis, a remnant of the fetal foramen ovale. The right atrium empties blood into the right ventricle through the tricuspid valve.

Synonyms

  • Atrium dextrum

  • Right atrial chamber

  • Right cardiac atrium

Function

  • Collects deoxygenated blood from systemic venous return

  • Acts as a reservoir and conduit for right ventricular filling

  • Generates atrial contraction (“atrial kick”), contributing to ventricular preload

  • Coordinates with sinoatrial (SA) node to regulate cardiac rhythm

Arterial Supply

  • Primarily supplied by branches of the right coronary artery (RCA)

  • Sinoatrial nodal artery (from RCA in ~60%, from left circumflex artery in ~40%) supplies the SA node region

  • Small atrial branches from the left circumflex artery (LCx) may contribute

Venous Drainage

  • Right atrial myocardium drains into the coronary sinus

  • Small cardiac veins and anterior cardiac veins also empty directly into the right atrium

Nerve Supply

  • Parasympathetic innervation: via the vagus nerve (CN X), regulating atrial contractility and nodal conduction

  • Sympathetic innervation: via cardiac branches from the thoracic sympathetic trunk, enhancing contractility and conduction

  • Rich autonomic plexuses around the SA and AV nodes coordinate rhythm

MRI Appearance

T1-weighted images:

  • Blood in the right atrium appears as intermediate to low signal depending on flow (flow void may be present)

  • Atrial walls are low signal intensity relative to myocardium and fat

  • Surrounding pericardial fat is hyperintense, outlining the chamber

T2-weighted images:

  • Blood pool appears variable but often hyperintense depending on flow dynamics

  • Myocardial wall remains low to intermediate signal

  • Pericardial effusion (if present) is bright hyperintense

STIR (Short Tau Inversion Recovery):

  • Suppresses fat, improving visualization of edema, myocarditis, or infiltration of atrial wall

  • Pathology (inflammation, tumor, infarction) appears hyperintense, while normal atrial wall remains low signal

T1 Post-Contrast (Gadolinium-enhanced):

  • Atrial wall shows subtle enhancement; pathology (scar, tumor, inflammation) demonstrates focal or heterogeneous enhancement

  • Late gadolinium enhancement (LGE) sequences highlight fibrosis or atrial scarring (e.g., in atrial fibrillation or myocarditis)

CT Appearance

Non-contrast CT:

  • Right atrium appears as a low attenuation cavity with thin walls

  • Calcifications (rare) may be identified in the atrial wall or around the tricuspid annulus

Contrast-enhanced CT (CECT / CTA):

  • Contrast opacifies the right atrial chamber, making it appear bright hyperdense

  • Clearly shows venous inlets (SVC, IVC, coronary sinus) and the tricuspid valve orifice

  • Excellent for evaluating atrial masses, thrombus, congenital anomalies, and relationship to venous catheters

MRI images

Right atrium anatomy MRI coronal image -img-00000-00000

CT image

Right atrium anatomy CT axial image -img-00000-00000