Normal left atrial dimensions in indians by echocardiographyDR Kulkarni, AS Vengsarkar
Department of Cardiology, K.E.M.Hospital, Parel, Bombay-400012, India
Correspondence Address: Source of Support: None, Conflict of Interest: None PMID: 529177
Source of Support: None, Conflict of Interest: None
One hundred normal Indian subjects were studied to establish the normal left atrial dimension (LAD), left atrial dimension corrected to body surface area (LA index) and left atrium to aorta ratio (LA/AO) for this population. Normal mean LAD was 21.9 ± 3.6 mm (12 mm to 30 mm). Elderly subjects had higher mean LAD (25.2 ± 3.6 mm). The LA index for adults was 14.1 ± 2.5 mm. LA index for younger subjects was higher because of low body surface area. Mean LA/AO was 0.95± 0.22;LA/AO greater than 1.17 is suggested as a criterion for LA enlargement.
The left atrium is involved in an important manner in the various diseases of mitral valve apparatus,  so commonly seen in India. The left atrial dimension therefore has a diagnostic and prognostic significance in clinical cardiology.
Echocardiographically one can measure the left atrial dimensions in both anteroposterior and supero-inferior diameters by parasternal and suprasternal approach respectively.  As the left atrium enlarges equally in all diameters  any one diameter is a reliable reflection of left atrial enlargement. Various studies have shown good correlation between the left atrial size i.e. diameter, measured by echocardiography and angiography. ,
As the left atrial dimension has a wide normal range, it has been correlated to the body surface area in an attempt to increase the clinical utility. The ratio of left atrial dimension to the aortic dimension has also been devised for a more accurate assessment of left atrial size. 
All the values of normal and abnormal left atrial dimensions are established in the western population ,,,, These values are invalid for the Indian population on account of the lower body surface area related to the racial differences. So many of our enlarged left atria echocardiographically fall within the western normal limits. It is the object of this study to establish normal range of the left atrial dimension for Indian population. To our knowledge there are no reports on this subject in the literature.
One hundred normal subjects were studied. The age range was from 10 to 50 years; this appeared to match with the age of diseased population in so far as rheumatic heart disease is concerned. There were 8 five-year subgroups with a minimum of 10 patients in each subgroup. These subjects were examined thoroughly to rule out any disease likely to bear upon the heart directly or indirectly. The echoes were recorded with a Unirad sonograph machine. A non focused 2.25 mHz transducer of 13 mm diameter was used. The subjects were examined for mitral valve and left atrial echoes by methods routinely employed .  The left atrium was recorded at the level of aortic cusps; time gain compensation was used to yield optimum aortic wall echoes. These were recorded on a Honeywell strip chart recorder No. 1858. The left atrium was measured from the posterior edge of the posterior aortic wall to the anterior surface of the posterior left atrial wall at the end systole. The aorta was measured from the anterior surface of anterior wall to the anterior surface of posterior aortic wall at the end diastole  (See [Figure 1] on page 200 A). The height and weight were recorded in each patient and body surface area was calculated from the nomogram by Dubois  The various values calculated were (i) Left atrial dimension, (ii) Ratio of left atrial diamension to the aortic dimension and (iii) Left atrial index i.e. left atrial dimension/body surface area (sq. meters). The dimensions were measured in millimetres for absolute values but the mean values are expressed upto one decimal point because of statistical averaging.
The mean left atrial dimension of all the patients was (21.9 ± 3.6 mm) [Table 1]. Statistically there was no significant difference between the mean values of the first 7 subgroups (19.8 ± 3.6 mm to 22.5 ± 4.7 mm). But the last subgroup (46 years to 50 years) had a mean value (25.2 ± 3.6 mm) which was just significantly higher than 4 of the 7 subgroups.
The mean LA/AO ratio for all patients was (0.95 ± 0.22). There was no significant difference between the mean values of the subgroup.
The mean LA index of all patients was (15.0 ± 2.5 mm). The mean LA index for the first subgroup was significantly higher (21.2 ± 2.9 mm) than the remaining (12.6 ± 2.5 mm to 15.8 ± 3.2 mm).
The left atrium is involved in various left heart diseases  and in some left to right shunts e.g. Patent Ductus Arteriosus.  The measurement of left atrial dimension by echocardiography has an advantage over the angiographic measurements as the latter is an invasive procedure. 
The mean left atrial dimension in this study was 21.9 ± 3.6 mm. There was no significant difference between the mean value of younger subjects (21.3 ± 2.5 mm for 11 to 15 years and 19.8 ± 3.6 mm for 16 to 20 years subgroups); the mean value of the subgroup of 45 to 50 years had just significantly higher value (25.2 - 3.6 mm) which cannot be explained satisfactorily. Other reported normal mean values of LAD are Hirata et al  - 3.1 ± 0.5 cm (1.8 to 4 cm), Brown et al  -3.23 cm (2.3 to 4.4 cm), and Francis et al 
28.5 - 5.1 mm (16 to 40 mm). These values are obviously higher than those reported in the present study.
The clinical utility of these normal values is blighted by a large overlap between the normal and abnormal left atrial dimensions. The large scatter of normal LAD is thought to be the result of difference in the body surface area. Hirata et al  and Brown et al  have reported that LA index is significantly correlated to the body surface area whsle Hagan et al  and Francis et at  have reported to the contrary. In the present study no significant correlation was established. The mean LA index in the study was 15 ± 0.25 mm (9 mm to 21 mm). This was significantly higher in younger subjects of the 1st subgroup (21.2 ± 2.9 mm for 11 to 15 years). This was due to low body surface area with normal LAD. The adult LA index was 14.1 -±2.5mm (12.6± 2.5 mm to 15.6 ± 3.2 mm). Normal LA index in the study of Hirata et al  is 1 to 2 cm/m  while in Brown's  study it is 1.2 to 2 cm/m  . These values are identical with the values in this series.
As LAD and LA index have a significant overlap between normal and enlarged left atria, another index (LA/AO) is contemplated to be more specific and reliable for LA enlargement. Brown et al  has reported that LA/AO ratio as a measure of LA enlargement is much more sensitive than LAD or LA index as it has a minimal overlap with the normal population. He has suggested LA/AO greater than 1.17 plus a left atrium greater than 4.2 cm as a criterion for LA enlargement. The present study also had a mean LA/AO ratio 0.95 ± 0.22 (0.73 to 1.17); the upper limit is similar to that reported by Brown et al.