Atrial structure

Left Atrium (LA)

Diameter

Left atrium areas can be planimetered in the 4 chamber (HLA) view, 2 chamber (VLA) view and in the 3 chamber view, while longitudinal and transverse diameters can be measured in the HLA and VLA views (Alicia M. Maceira et al. 2010).

<figure> <img src="/latex/images/atrium/LA_size.png" id="fig:LA_size" alt="Measurement of LA parameters in the 2, 4, and 3 chamber views (A2C, A4C, A3C) (Alicia M. Maceira et al. 2010)" /><figcaption aria-hidden="true">Measurement of LA parameters in the 2, 4, and 3 chamber views (A2C, A4C, A3C) <span>(Alicia M. Maceira et al. 2010)</span></figcaption> </figure>

1. Longitudinal diameter

   • Definition: The maximal distance from the midpoint of the mitral annulus plane to the superior wall of the atrium in the long-axis view.

   • Acquisition Type: LAX

   • Reference Range:

     Study	Cohort Size	Imaging modality	Gender	Reference Value (cm)	Note
     (Kawel-Boehm et al. 2020)	185	VLA	male	(4.9, 0.7)
     	181	VLA	female	(4.6, 0.7)
     	66	3ch LAX	male	(5.5, 0.6)
     	69	3ch LAX	female	(5.4, 0.7)
     	126	HLA	male	(5.8, 0.6)
     	129	HLA	female	(5.5, 0.6)
     (Alicia M. Maceira et al. 2010)	60	VLA	male	3.6-6.4
     	60	VLA	female	3.1-6.0
     	60	HLA	male	4.5-7.2
     	60	HLA	female	4.1-6.9

   • ICC: 0.57 (VLA), 0.56 (HLA)

2. Transversal diameter

   • Definition: The maximal horizontal distance between the medial and lateral walls of the left atrium, measured perpendicular to the longitudinal axis.

   • Acquisition Type: LAX

   • Reference Range:

     Study	Cohort Size	Imaging modality	Gender	Reference Value (cm)	Note
     (Kawel-Boehm et al. 2020)	126	VLA	male	(4.4, 0.6)
     	129	VLA	female	(4.3, 0.5)
     	185	HLA	male	(4.3, 0.5)
     	181	HLA	female	(4.1, 0.5)
     (Alicia M. Maceira et al. 2010)	60	VLA	male	3.7-5.5
     	60	VLA	female	3.4-5.5
     	60	HLA	male	3.0-5.2
     	60	HLA	female	3.0-5.1

   • ICC: 0.70 (VLA), 0.71 (HLA)

3. Antero-posterior diameter*

   • Definition: The maximal distance between the posterior atrial wall and the posterior aspect of the aortic root or anterior atrial wall.

   • Acquisition Type: 3ch LAX

   • Reference Range:

     Study	Cohort Size	Imaging modality	Gender	Reference Value (cm)	Note
     (Kawel-Boehm et al. 2020)	185	3ch LAX	male	(3.0, 0.5)
     	181	3ch LAX	female	(3.0, 0.5)
     (Alicia M. Maceira et al. 2010)	60	3ch LAX	male	2.3-4.2
     	60	3ch LAX	female	2.1-4.1
     (Mulder et al. 2020)	110	CT		(3.52, 0.51)	51 males, 59 females, average age 58 years

• Clinical Associations: The maximal LA diameter is increased in patients with hypertrophic cardiomyopathy (HCM), particularly in those with the obstructive subtype (HOCM) (Anwar et al. 2008; Bi et al. 2022). This enlargement, referred to as left atrial enlargement, is recognized as an independent predictor of stroke or systemic embolism (SE) in patients with paroxysmal atrial fibrillation (AF) (Takahashi et al. 1982; Hamatani et al. 2016). The indexed LA antero-posterior diameter can also enhance discrimination and risk prediction for adverse outcomes in AF patients (Mantovani et al. 2025).

Volume

The LA has a structure composed of three parts, each derived from different embryologic origin: the anterior LA, the posterior (venous) LA, and the LA appendage (LAA) (Sun and Park 2021). Quantifying LA size is difficult, in part because left atrium’s complex geometry and intricate fiber orientation and the variable contribution of its appendage and pulmonary veins (Hoit 2014). It is not consistently defined if the left atrial appendage must be included in the measurements of the left atrial volume. While some investigators consider it to be part of the LA volume, other studies exclude the LAA (Wandelt et al. 2017).

<figure> <img src="/latex/images/atrium/LA_phase1.png" id="fig:LA_phase2" alt="Left atrial phasic function and the temporal relationship between LA volume and ECG. Red arrows represent blood flow, blue arrows represent myocardial deformation (Alfuhied et al. 2021)." /><figcaption aria-hidden="true">Left atrial phasic function and the temporal relationship between LA volume and ECG. Red arrows represent blood flow, blue arrows represent myocardial deformation <span>(Alfuhied et al. 2021)</span>.</figcaption> </figure>

<figure> <img src="/latex/images/atrium/LA_phase2.png" id="fig:LA_phase2" alt="Left atrial phasic function and the temporal relationship between LA volume and ECG. Red arrows represent blood flow, blue arrows represent myocardial deformation (Alfuhied et al. 2021)." /><figcaption aria-hidden="true">Left atrial phasic function and the temporal relationship between LA volume and ECG. Red arrows represent blood flow, blue arrows represent myocardial deformation <span>(Alfuhied et al. 2021)</span>.</figcaption> </figure>

• Definition:

  1. Maximal volume LAV_max: Volume at left ventricular end-systole, just before mitral valve opening (Hoit 2014; Wandelt et al. 2017).

  2. Volume immediately before atrial contraction LAV_{pre − A}: Volume at left ventricular end-diastole when the mitral valve closes (Hoit 2014).

  3. Minimal volume LAV_min: Volume at left ventricular diastole immediately prior to LA contraction (P-wave in electrocardiographic) (Hoit 2014; Wandelt et al. 2017).

• Calculation: In addition to Simpson’s method, biplane area-length formula is also frequently used to determine the LA volume: $V=0.85\times \frac{A_{2ch}\times A_{4ch}}{L}$ where A_2c**h, A_4c**h are LA areas measured in the 2-chamber and 4-chamber view; L corresponds to the shorter long-axis length of the LA either from the 2-chamber or 4-chamber view (Nacif et al. 2012; Hoit 2014; Wandelt et al. 2017). When compared to Simpson’s method in transversal slices, The biplane area-length method leads to an overestimation of volume and underestimation of phasic function (Wandelt et al. 2017).

• Acquisition Type: LAX

• Reference Range:

  • Maximal volume

    Study	Cohort Size	Gender	Reference Value (mL)	Note
    (Kawel-Boehm et al. 2020)	734	male	(72, 20)	biplane area-length method, LAA excluded
    	841	female	(64, 18)	biplane area-length method, LAA excluded
    	66	male	(70, 15)	Simpson’s method, LAA excluded
    	69	female	(66, 13)	Simpson’s method, LAA excluded
    	256	male	(78, 18)	Simpson’s method, LAA included
    	298	female	(66, 14)	Simpson’s method, LAA included
    (Truong et al. 2019)	45	male	(86.7, 23.7)	average age 43 years
    	67	female	(72.7, 15.8)	average age 41 years
    (Hudsmith et al. 2005)	63	male	(103, 30)
    	45	female	(89, 21)
    (Petersen et al. 2017)	368	male	30-104	measured in VLA
    	432	female	24-90	measured in VLA
    	368	male	36-124	measured in HLA
    	432	female	36-108	measured in HLA
    	368	male	37-108	biplane area-length method
    	432	female	33-93	biplane area-length method
    (Le Ven et al. 2016)	196	male	(79, 19)	average age 26.7 years
    	238	female	(64, 14)	average age 25.8 years

  • Volume immediately before atrial contraction

    Study	Cohort Size	Gender	Reference Value (mL)	Note
    (Truong et al. 2019)	45	male	(53.3, 14.8)	average age 43 years
    	67	female	(43.7, 10.6)	average age 41 years

  • Minimal volume

    Study	Cohort Size	Gender	Reference Value (mL)	Note
    (Truong et al. 2019)	45	male	(36.6, 10.2)	average age 43 years
    	67	female	(29.5, 7.3)	average age 41 years
    (Hudsmith et al. 2005)	63	male	(46, 14)
    	45	female	(41, 11)
    (Le Ven et al. 2016)	196	male	(32, 9)	average age 26.7 years
    	238	female	(24, 7)	average age 25.8 years

• Clinical Associations: In HCM patients, maximum and minimum LA volumes, as well as volumes measured just before atrial contraction, are elevated (Williams et al. 2015; Anwar et al. 2008; Bi et al. 2022; Grassedonio et al. 2015). Similarly, increased maximal and minimal LA volumes have been reported in individuals who later developed heart failure, as demonstrated in a MESA cohort sub-study (Barison et al. 2022). In patients with dilated cardiomyopathy (DCM), maximal LA volume serves as a predictor of death or heart transplantation in the absence of AF (Hoit 2014).

  Indexed maximal and minimal LA volumes are independently predictive of cardiovascular events (first acute MI, coronary re-vascularization, AF, congestive heart failure (CHF), transient ischemic attack, cerebrovascular accident, or cardiovascular death) (Hoit 2014). They are also significantly higher in individuals with incident HF (Habibi et al. 2014), persistent AF (Habibi et al. 2015), as well as systemic and pulmonary hypertension (Gupta et al. 2013; Gard et al. 2023). LA size is positively associated with the severity of diastolic dysfunction and can predict the presence of left atrial appendage (LAA) thrombus in patients with persistent AF (Mehrzad, Rajab, and Spodick 2014). However, indexed LA volume lost its ability in predicting all-cause mortality when controlling for the degree of diastolic dysfunction, meaning that it provides no incremental predictive benefit (Hoit 2014). In patients undergoing mitral valve surgery, the maximal indexed LA volume is an independent predictor of post-operative AF (Hoit 2014).

• ICC:

  • Maximal volume: 0.76

  • Volume immediately before atrial contraction: 0.72

  • Minimal volume: 0.73

Sphericity Index

• Definition: LA maximal volume divided by the volume of a sphere whose diameter is the maximal LA length diameter among atrial length and transverse length (Nakamori et al. 2018).

• Acquisition Type: LAX

• Reference Range:

  Study	Cohort Size	Gender	Reference Value	Note
  (Mulder et al. 2020)	110		(0.839, 0.024)	51 males, 59 females, average age 58 years
  (Truong et al. 2019)	45	male	(0.67, 0.10)	average age 43 years
  	67	female	(0.65, 0.10)	average age 41 years

• Clinical Associations: Increased left atrial sphericity, measured prior to pulmonary vein isolation (PVI), has been identified as an independent predictor of AF recurrence after AF ablation, suggesting its potential value in selecting optimal candidates for the procedure (Bisbal et al. 2013; Nakamori et al. 2018).

• ICC: 0.53

<figure> <img src="/latex/images/atrium/sphericity_index.png" id="fig:LA_sphericity_index" alt="Measurements of LA maximal volume and sphericity. The volumetric LA sphericity index is calculated as the ratio of LA maximum volume to the volume of a sphere with maximum LA length diameter among atrial length and transverse length from the 2- and 4-chamber image (Nakamori et al. 2018)." /><figcaption aria-hidden="true">Measurements of LA maximal volume and sphericity. The volumetric LA sphericity index is calculated as the ratio of LA maximum volume to the volume of a sphere with maximum LA length diameter among atrial length and transverse length from the 2- and 4-chamber image <span>(Nakamori et al. 2018)</span>.</figcaption> </figure>

Right Atrium (RA)

Diameter

<figure> <img src="/latex/images/atrium/RA_size.png" id="fig:RA_size" alt="Panel B: Measurement of RA diameters in the 2 and 4 views. Longitudinal diameter is obtained from the posterior wall of the RA to the center of the tricuspid plane, and transverse diameter is obtained perpendicular to the longitudinal diameter, at the mid-level of the RA. Panel C: Measured areas in the 2 and 4 views. (Alicia M. Maceira et al. 2013)" /><figcaption aria-hidden="true">Panel B: Measurement of RA diameters in the 2 and 4 views. Longitudinal diameter is obtained from the posterior wall of the RA to the center of the tricuspid plane, and transverse diameter is obtained perpendicular to the longitudinal diameter, at the mid-level of the RA. Panel C: Measured areas in the 2 and 4 views. <span>(Alicia M. Maceira et al. 2013)</span></figcaption> </figure>

1. Longitudinal diameter

   • Definition: The maximal length from the midpoint of the line connecting the lateral and septal (or superior and inferior) attachments of the tricuspid valve to the atrial roof (Alicia M. Maceira et al. 2013).

   • Acquisition Type: LAX

   • Reference Range:

     Study	Cohort Size	Imaging modality	Gender	Reference Value (cm)	Note
     (Kawel-Boehm et al. 2020)	126	VLA	male	(5.5, 0.6)
     	129	VLA	female	(5.1, 0.6)
     	126	HLA	male	(5.3, 0.6)
     	129	HLA	female	(5.1, 0.6)

   • ICC: 0.81

2. Transversal diameter

   • Definition: The distance measured perpendicular to the longitudinal axis at the mid-level of the right atrium (Alicia M. Maceira et al. 2013).

   • Acquisition Type: LAX

   • Reference Range:

     Study	Cohort Size	Imaging modality	Gender	Reference Value (cm)	Note
     (Kawel-Boehm et al. 2020)	126	VLA	male	(4.2, 0.9)
     	129	VLA	female	(4.1, 0.9)
     	126	HLA	male	(4.8, 0.6)
     	129	HLA	female	(4.3, 0.6)

   • ICC: 0.73

Volume

• Definition:

• Acquisition Type: SAX, LAX

• Reference Range:

  • Maximal volume

    Study	Cohort Size	Gender	Reference Value (mL)	Note
    (Kawel-Boehm et al. 2020)	66	male	(65, 20)	biplane area-length method, RAA excluded
    	69	female	(53, 14)	biplane area-length method, RAA excluded
    	66	male	(89, 22)	Simpson’s method, RAA excluded
    	69	female	(77, 16)	Simpson’s method, RAA excluded
    	256	male	(108, 25)	Simpson’s method, RAA included
    	298	female	(85, 18)	Simpson’s method, RAA included
    (Petersen et al. 2017)	363	male	43-143
    	432	female	38-101

  • Minimal volume

    Study	Cohort Size	Gender	Reference Value (mL)	Note
    (Kawel-Boehm et al. 2020)	66	male	(32, 12)	biplane area-length method, RAA excluded
    	69	female	(23, 7)	biplane area-length method, RAA excluded
    	66	male	(46, 16)	Simpson’s method, RAA excluded
    	69	female	(35, 9)	Simpson’s method, RAA excluded
    	256	male	(50, 17)	Simpson’s method, RAA included
    	298	female	(33, 11)	Simpson’s method, RAA included

• Clinical Associations: RA volume is smaller hin patients with HFpEF compared with HFpEF-PH than those with PAH (Van Wezenbeek et al. 2022). Even after adjusting for left atrial parameters, RA volumes remain independently associated with incident AF (Lang et al. 2022), and the maximal RA volume has also demonstrated predictive value for identifying severe functional tricuspid regurgitation (TR) (Muraru et al. 2021).

• ICC:

  • End-diastolic: 0.81

  • End-diastolic: 0.80

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