Right atrium

Last revised by Dan Mahon on 7 Dec 2023

The right atrium (RA) (plural: atria) is one of the four chambers of the human heart, and is the first chamber to receive deoxygenated blood returning from the body, via the two venae cavae. It plays an important role in originating and regulating the conduction of the heart.

The right atrium receives deoxygenated blood from the superior vena cava (SVC), the inferior vena cava (IVC), the coronary sinus (covered by the Thebesian valve), and the Thebesian veins.

It is grossly the shape of an irregular ellipsoid, with the exception of the right atrial appendage (auricle), which arises anteriorly. The right atrial appendage overlies the aortic root and the proximal right coronary artery (RCA) 5.

The right atrium is separated from the left atrium by the interatrial septum. In cases of congenital cardiac malformations, the morphologic right atrium can be identified by the fossa ovalis in the interatrial septum 5.

The right atrium leads into the right ventricle through the tricuspid valve

  • superior end: SVC orifice 

  • inferior end: IVC orifice

  • posterior wall: interatrial septum, faces anterior and to the right, marked by depression (fossa ovalis) in lower part of the septum with crescenteric upper margin called the limbus)

  • anterior and right lateral wall: cardiac wall

  • left lateral extent: right atrioventricular ostium 

  • atrial cavity divided into 2 main parts by crista terminalis 

    • smooth muscular ridge (musculi pectini) from the roof just in front of and below the SVC opening (between SVC and right auricle) and extends along lateral wall to the anterior lip of IVC 5

  • sinus venarum cavarum 

    • cavity posterior to crista terminalis 

    • drains IVC and SVC

    • smooth wall 

  • atrium proper 

    • anterior half of the chamber (anterior to crista terminalis)

      • represents true auricular chamber of embryonic heart 

    • includes right auricle 

      • upper end of right atrium to the left of the SVC

      • overlaps commencement of aorta and clasps infundibulum of right ventricle 

    • wall is ridged by pectinate muscles fanning out from crista terminalis and also extending into the right atrial appendage 

      • the atrial lead of an external pacemaker is frequently located in these muscles

  • SVC opening superiorly 

    • superiorly to the right of the crista

  • IVC opening inferiorly 

    • guarded by ridge that extends from anterior lip of IVC (remains of valve of IVC / Eustachian valve)

  • coronary sinus opening inferiorly

    • medial to the IVC opening in posterior wall of right atrium

    • bordered by small fold (valve of coronary sinus / thebesian valve) 

  • right atrioventricular ostium

    • guarded by tricuspid valve

  • variable veins drain the atrial walls

  • tiny myocardial Thebesian veins drain directly into the right atrium

  • sinoatrial (SA) node

    • primary cardiac pacemaker 

    • subepicardial location near junction of SVC and right atrium

    • regulated by vagus nerve and cardiac sympathetic plexus

  • atrioventricular (AV) node

    • subendocardial location between coronary sinus ostium, septal leaflet of tricuspid valve and tendon of Todaro (which connects the Thebesian and eustachian valves), an area known as the Triangle of Koch

See innervation of the heart.

  • thickened Eustachian valve of the IVC 

    • thickened ridge due to incomplete regression of Eustachian valve 

  • chiari network

  • a prominent pectinate muscle is present in most people known as the taenia sagittalis

  • incomplete closure of the foramen ovale

  • variable size of the fossa ovalis 

  • coronary sinus may be doubled

  • coronary sinus may drain into the left atrium

  • SVC may be joined to the left atrium 

On contrast-enhanced chest CT and cardiac MRI, the right atrium when measured on axial slices can be considered enlarged when the transverse diameter is ≥67 mm (male) and ≥64 mm (female) 3.

Develops from the right horn of the sinus venosus. Originates as two chambers, an anterior and a posterior. See development of the heart.

CT evaluation of the right atrium:

  • the patient should be encouraged to avoid the Valsalva maneuver, which may bring unopacified blood from the IVC into the right atrium, and may mimic a thrombus

  • to avoid streak artifact from dense CT contrast, a multiphasic study with 100% contrast followed by a 20-50% contrast and saline chaser should be administered

Measurements of the right atrium are primarily acquired from the transthoracic apical four chamber view. While more time intensive, planimetry is preferred to estimations of area based on long/short axis dimensions. Measurements are obtained as follows 4:

  • major dimension

    • measured parallel to the interatrial septum from the center of the tricuspid annulus to the superior atrial wall

  • minor dimension

    • perpendicular to the long axis, measured from the interatrial septum to the atrial free wall

  • end-systolic area

    • the atrial endocardium is traced, spanning the lateral to septal aspects of the tricuspid annulus

The lower and upper limits of reference values for the right atrium are as follows:

  • major dimension: 3.4-5.3 cm

  • minor dimension: 2.6-4.4 cm

  • end-systolic area: 10-18 cm2

"Atrium" is the Latin word for "court", referring to the central area in a Roman house from which one could enter various chambers. It was entered through the "ostium" of a Roman house.

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Cases and figures

  • Case 1: labeled 76
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  • Case 2: labeled 30
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  • Figure 1
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  • Case 3: labeled 25
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  • Case 4: labeled 35
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  • Figure 2
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  • Figure 3: heart anterior surface (Gray's illustrations)
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  • Figure 4: right atrium and ventricle (Gray's illustration)
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