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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 10  |  Issue : 4  |  Page : 236-239

Morphological variations of pulmonary veins draining into left atrium: A detailed cadaveric study


1 Assistant Professor, Department of Anatomy, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India
2 Assistant Professor, Department of Anatomy, Shri Shankaracharya Institute of Medical Sciences, Bhilai, Chhattisgarh, India
3 Research Scholar, Department of Anatomy, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India
4 Professor, Department of Anatomy, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India

Date of Submission22-Oct-2020
Date of Decision09-Mar-2021
Date of Acceptance10-Jul-2021
Date of Web Publication28-Oct-2021

Correspondence Address:
Prasenjit Bose
Department of Anatomy, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/NJCA.NJCA_65_20

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  Abstract 


Introduction: During pulmonary vein isolation ablation procedure, the knowledge of number and position of pulmonary veins with thickness of posterior wall of left atrium (LA) is of invaluable significance. The objective of the study was to determine the left atrial wall thickness (LAWT) and its relationship with number and variations of right pulmonary veins (RPVs) and left pulmonary veins (LPVs). Methodology: In an observational study, carried out in the Department of Anatomy, All India Institute of Medical Sciences, Raipur (Chhattisgarh), morphological variations of pulmonary veins among 75 formalin-fixed hearts were noted. The thickness of posterior wall of LA was measured in each specimen studied. The number of RPVs and LPVs was counted. Any sexual differences in these numbers were noted. Results: Normal anatomical description of two RPVs and two LPVs opening the LA was observed in 63 out of 75 heart specimens (84%). The posterior LAWT is ranged 1.28–1.48 mm where two RPVs and two LPVs enter LA. The remaining 12 specimens (16%) showed variation in the number of veins opening into LA ranging between 1 and 5 veins of either side. The posterior LAWT ranged between 1.01 and 2.53 mm in these 12 specimens. The mean posterior LAWT thickness with 3, 4, and 5 RPVs was 1.47, 1.94, and 2.43 mm, respectively. Conclusion: The thickness of posterior wall of LA increases as the number of RPVs increases. Twelve specimens (16%) showed variation in the number of veins opening into LA ranging between 1 and 5 veins of either side.

Keywords: Atrial fibrillation, left atrium, pulmonary vein isolation, wall thickness


How to cite this article:
Bose P, Choudhary U, Singh P, Singh B, Singh R. Morphological variations of pulmonary veins draining into left atrium: A detailed cadaveric study. Natl J Clin Anat 2021;10:236-9

How to cite this URL:
Bose P, Choudhary U, Singh P, Singh B, Singh R. Morphological variations of pulmonary veins draining into left atrium: A detailed cadaveric study. Natl J Clin Anat [serial online] 2021 [cited 2021 Dec 8];10:236-9. Available from: http://www.njca.info/text.asp?2021/10/4/236/329500




  Introduction Top


Atrial fibrillation is the most common arrhythmia noted with advancement of age.[1] In the pathophysiology of atrial fibrillation, pulmonary veins have a very crucial role and its anatomical variants are often associated with increased arrhythmogenic potential.[2],[3] Especially, atrial myocardium sleeves projecting into the pulmonary veins are identified as a major cause of ectopic arrhythmogenic foci.[4],[5] Superior pulmonary veins are implicated in persistent atrial fibrillation more than the inferior pulmonary veins. Radiofrequency ablation procedures are commonly done for atrial fibrillation. Pulmonary vein isolation ablation is delivering a microwave energy to the LA musculature and scarring the tissues. This results in cessation of ectopic firing from the atrial tissue leading to symptomatic improvement in atrial fibrillation.[4],[6] During this electrophysiological procedure, the knowledge of number and position of pulmonary veins with left atrial wall thickness (LAWT) is of invaluable significance.

Anatomically, left atrium (LA) has superior, posterior, left lateral, septal, and anterior walls. LA is located posteriorly and superiorly relative to the right atrium (RA). Usually, four pulmonary veins enter through the posterior wall of LA. Left pulmonary veins (LPVs) are located superior to the right pulmonary veins (RPVs). The wall of the LA is relatively smooth walled than the RA. However, the walls are not uniformly thick. The thickness of the muscle was reported to range between 1 and 6 mm in the formalin-fixed specimens from cadavers.[7],[8] In general, the vestibule of LA is thin and lateral wall is thick.[9] The estimation of the LAWT is by cardiac tomography and is observer dependent.[10] The number and relative position of the pulmonary veins are said to influence the LAWT.[11],[12],[13] Therefore, the present study is designed to evaluate the relation of the number of RPVs and LPVs and determine any relationship with the LAWT.

The objective of the study was to determine the LAWT and its relationship with number and variations of RPVs and LVPs.


  Methodology Top


In an observational study, carried out in the Department of Anatomy, All India Institute of Medical Sciences, Raipur (Chhattisgarh), morphological variations of pulmonary veins were noted. The study spanned out over a period of 7 months starting from December 2018 to July 2019. Seventy-five human hearts were taken from formalin-preserved and well-embalmed cadavers. Out of 75 heart samples, 60 were obtained from the Department of Anatomy, Institute of Medical Sciences, Banaras Hindu University, Varanasi (Uttar Pradesh). The age of cadavers was ranging between 30 and 80 years. The cause of death was unknown in most of the cadavers. The study protocol was approved by the Institutional Ethics Committee (Letter no. Dean/2014-15/EC/442 , Dated – 18/02/2014). The gender of the cadaver and the number of veins draining into LA were noted. All hearts with overt congenital malformations were excluded from the study. Dissected hearts where LA was not having clearly delineated walls were also excluded.

The LA of each heart was exposed by making incision extending from pulmonary vein. The left atrial chambers were cleaned under running water to remove clots present. The thickness of posterior wall of LA was measured in each specimen studied. The number of RPVs and LPVs was counted. Any sexual differences in these numbers were noted. All measurements were done using calibrated Vernier caliper.


  Results Top


Normal anatomical description of two RPVs and two LPVs opening the LA was observed in 63 out of 75 heart specimens (84%). The remaining 12 specimens (16%) showed variation in the number of veins opening into LA ranging between 1 and 5 veins of either side [Table 1] and [Figure 1], [Figure 2]. The posterior wall of LA thickness ranged between 1.01 and 2.53 mm in these 12 specimens [Table 1]. All these 12 specimens had consistent variations in the RPVs. Only two specimens had variations on the LPVs. Variations in both RPV and LPV were found only in two specimens (2.67%). Both these hearts had three RPVs and one LPV. The mean thickness of LA in these specimens was 1.76 mm which was higher than the normal thickness of other specimens. Among these 12 specimens, 9 were male hearts and 3 were female hearts.
Table 1: Heart specimens with variation in number of right and left pulmonary veins arranged in increasing thickness of posterior wall of left atrium, n=12

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Figure 1: Dissected hearts showing the variations in the number of right pulmonary veins (colored pins) draining into left atrium. (a) Three right pulmonary veins and (b) four right pulmonary veins

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Figure 2: Dissected hearts showing the variations in the number of pulmonary veins (arrows) (a) five right pulmonary veins (b) one left pulmonary vein draining into left atrium

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The mean thickness of posterior wall of LA is ranged 1.28–1.48 mm where two RPVs and two LPVs enter LA. The mean LAWT thickness with 3, 4, and 5 RPVs was 1.47, 1.94, and 2.43 mm, respectively. As the number of RPV increases, the thickness of the posterior wall of LA also increases [Table 1].


  Discussion Top


In attempt to comprehend the anatomical variation of pulmonary veins in the LA, a detailed embryological knowledge is required. The development of the lung begins at around 26 days of gestation. It evolves as a respiratory diverticulum that emerges from a primitive foregut.[14] Drainage of lower lobe of right lung is mainly done by lower RPV. Drainage of upper lobe and lingula of the left lung is chiefly done by upper LPV. The lower lobe of left lung is drained by LPV on the lower side. In 60%–70% of the population, this arrangement is usually seen. It is very common to find an extensive variation in pulmonary venous drainage.[15] When the upper and lower veins on the same side merge together until both flow into LA, the conjoined vein is developed and is primarily seen on the left part. For such cases, a single ostium is constructed.[16] Accessory veins are present in addition to the upper and lower pulmonary veins. These accessory veins open in the LA with a separate ostium and are narrower. The accessory pulmonary veins open with a separate ostium in the LA and are narrower. In 30% of the population, it is mainly present and usually noticed on the right side draining middle lobe.[17]

In our study, we found that in 16% of heart samples, 3–5 ostia were noted on the right side, while in 2.67% of heart samples, a solitary ostium was observed on the left side, but no accessory left sided pulmonary vein was observed. In one study, 28% of patients reported 3–5 ostia in the right part while 2% reported a solitary ostium on the right side. According to Marom et al, in their study, the majority of patients (71%) reported 2 ostias in the right part and 86 per cent reported 2 ostias in the left part for both upper lobe veins as well as lower lobe veins. While remaining 14 percent had a single ostium.[18] During embryologic development, accessory or supernumerary PVs may appear which lead to additional, distinct openings of the LA with typically narrower arteriovenous junctions.[19]

Although the majority of the left atrial wall is far more uniform in thickness than the right atrium, the posterior wall and dome are thicker. Its anterior wall is thinner in comparison to the posterior wall. An “unsafe zone” of thin myocardium facing the transverse sinus has already been described by Mc-Alpine.[20] In the present research, we found that the mean LAWT increases with increase in the RPVs. We also found that there was more variability in numbers of pulmonary veins draining into left atrial chamber seen in males than in females. A correlation has been found in one study between the presence of the middle pulmonary vein and the higher incidence of cardiac arrhythmia.[21] Our findings are significant for clinical purposes and also in line with previous papers. Our results could help the cardiac surgeons and clinicians to better recognize potentially dangerous variations and could also enable them to better prepare for catheter ablation or surgery.


  Conclusion Top


The thickness of posterior wall of LA increases as the number of RPVs increases. Twelve specimens (16%) showed variation in the number of veins opening into LA ranging between 1 and 5 veins of either side.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Díez-Villanueva P, Alfonso F. Atrial fibrillation in the elderly. J Geriatr Cardiol 2019;16:49-53.  Back to cited text no. 1
    
2.
Hussein A, Das M, Riva S, Morgan M, Ronayne C, Sahni A, et al. Use of ablation index-guided ablation results in high rates of durable pulmonary vein isolation and freedom from arrhythmia in persistent atrial fibrillation patients: The PRAISE study results. Circ Arrhythm Electrophysiol 2018;11:e006576.  Back to cited text no. 2
    
3.
Vivek YR, Petr N, Jacob SK, Jan P, Moritoshi F, Hubert C, et al. Pulsed field ablation for pulmonary vein isolation in atrial fibrillation. J Am Coll Cardiol 2019;74:315-26.  Back to cited text no. 3
    
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Yorgun H, Canpolat U, Kocyigit D, Çöteli C, Evranos B, Aytemir K. Left atrial appendage isolation in addition to pulmonary vein isolation in persistent atrial fibrillation: One-year clinical outcome after cryoballoon-based ablation. Europace 2017;19:758-68.  Back to cited text no. 4
    
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Voskoboinik A, Moskovitch JT, Harel N, Sanders P, Kistler PM, Kalman JM. Revisiting pulmonary vein isolation alone for persistent atrial fibrillation: A systematic review and meta-analysis. Heart Rhythm 2017;14:661-7.  Back to cited text no. 5
    
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Bradley CJ, Haines DE. Pulsed field ablation for pulmonary vein isolation in the treatment of atrial fibrillation. J Cardiovasc Electrophysiol 2020;31:2136-47.  Back to cited text no. 6
    
7.
Sun JY, Yun CH, Mok GS, Liu YH, Hung CL, Wu TH, et al. Left atrium wall-mapping application for wall thickness visualisation. Sci Rep 2018;8:4169.  Back to cited text no. 7
    
8.
Tan HW, Wang XH, Shi HF, Zhou L, Gu JN, Liu X. Left atrial wall thickness: Anatomic aspects relevant to catheter ablation of atrial fibrillation. Chin Med J (Engl) 2012;125:12-5.  Back to cited text no. 8
    
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Sánchez-Quintana D, Cabrera JA, Climent V, Farré J, Mendonça MC, Ho SY. Anatomic relations between the esophagus and left atrium and relevance for ablation of atrial fibrillation. Circulation 2005;112:1400-5.  Back to cited text no. 9
    
10.
Karim R, Blake LE, Inoue J, Tao Q, Jia S, Housden RJ, et al. Algorithms for left atrial wall segmentation and thickness – Evaluation on an open-source CT and MRI image database. Med Image Anal 2018;50:36-53.  Back to cited text no. 10
    
11.
Ho SY, Cabrera JA, Sanchez-Quintana D. Left atrial anatomy revisited. Circ Arrhythm Electrophysiol 2012;5:220-8.  Back to cited text no. 11
    
12.
Thomsen AF. Left atrial wall thickness and pulmonary vein size are increased in patients with atrial fibrillation compared to healthy controls – A multidetector computed tomography study. Int J Clin Cardiol 2017;4:1-9.  Back to cited text no. 12
    
13.
Whiteman S, Saker E, Courant V, Salandy S, Gielecki J, Zurada A, et al. An anatomical review of the left atrium. Transl Res Anat 2019;17:100052.  Back to cited text no. 13
    
14.
Moore KL, Persuad TV. The cardiovascular system. In: The Developing Human-Clinically Oriented Embryology. 7th ed. Philadelphia, Pennyslvania: Saunders, Elsevier; 2004. p. 345-7.  Back to cited text no. 14
    
15.
Prasanna LC, Praveena R, D'Souza AS, Bhat KM. Variations in the pulmonary venous ostium in the left atrium and its clinical importance. J Clin Diagn Res 2014;8:10-1.  Back to cited text no. 15
    
16.
Kaur A, Sharma A, Sharma M. Variations in the number of pulmonary veins draining into left atrium and its clinical significance. Int J Med Dent Sci 2017;6:1413-6.  Back to cited text no. 16
    
17.
Agarwal PP, Seely JM, Matzinger FR. MDCT of anomalous unilateral single pulmonary vein. AJR Am J Roentgenol 2004;183:1241-3.  Back to cited text no. 17
    
18.
Marom EM, Herndon JE, Kim YH, Mcadams HP. Variations in pulmonary venous drainage to the left atrium: Implications for radiofrequency ablation. Radiology 2004;230:824-9.  Back to cited text no. 18
    
19.
Rajesh S, Kumar SV, Reddy VM. A study on pulmonary venous ostia pattern in the left atrium and its clinical applications. Natl J Clin Anat 2018;7:201-4.  Back to cited text no. 19
  [Full text]  
20.
McAlpine WA: Heart and CoronaryArteries.Springer-Verlag, Berlin. 1975;58-9.  Back to cited text no. 20
    
21.
Wannasopha Y, Oilmungmool N, EuathrongchitJ. Anatomical variations of pulmonary venous drainage in Thai people: Multidetector CT study. Biomed Imaging Interv J 2012;8:e4.  Back to cited text no. 21
    


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