Transposition of the great vessels pathophysiology: Difference between revisions

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==Overview==
==Overview==
R[[right atrium|ight atrium]] ([[RA]]) is connected to a morphologic [[right ventricle]] ([[RV]]). The morphologic [[left atrium]] ([[LA]]) is connected to the morphologic [[left ventricle]] ([[LV]]). This is called '''atrio-ventricular concordance'''. In a normal heart, the great arteries ([[aorta]] and [[pulmonary arteries]]) are concordant with the morphologic [[LV]] and [[RV]]. This is termed '''ventriculo-arterial concordance'''. In addition, the aorta and pulmonary trunk ascend in a '''spiral''' relationship. In the TGA the [[aorta]] arises from the morphologic [[right ventricle]] via a subaortic infundibulum and the [[pulmonary artery]] arises from the morphologic [[left ventricle]], without a subpulmonary infundibulum. These ventriculoarterial connection is known as '''ventriculoarterial discordance'''. The abnormal origin of the great arteries results in an altered spiral relationship resulting in parallel circulation.
<br />
==Anatomy==
==Anatomy==
====== Embryology ======
* In the fifth week of gestation, opposing pairs of ridges form in the [[truncus arteriosus]].<ref name="Levin1977">{{cite journal|last1=Levin|first1=Daniel L.|title=d-Transposition of the Great Vessels in the Neonate|journal=Archives of Internal Medicine|volume=137|issue=10|year=1977|pages=1421|issn=0003-9926|doi=10.1001/archinte.1977.03630220061015}}</ref><ref name="Rashkind1966">{{cite journal|last1=Rashkind|first1=William J.|title=Creation of an Atrial Septal Defect Without Thoracotomy|journal=JAMA|volume=196|issue=11|year=1966|pages=991|issn=0098-7484|doi=10.1001/jama.1966.03100240125026}}</ref><ref name="pmid10569681">{{cite journal |vauthors=Hornung TS, Bernard EJ, Celermajer DS, Jaeggi E, Howman-Giles RB, Chard RB, Hawker RE |title=Right ventricular dysfunction in congenitally corrected transposition of the great arteries |journal=Am. J. Cardiol. |volume=84 |issue=9 |pages=1116–9, A10 |date=November 1999 |pmid=10569681 |doi=10.1016/s0002-9149(99)00516-0 |url=}}</ref>
* These ridges are termed the right superior truncus swelling and the left inferior truncus swelling.
* The right superior truncus swelling grows distally and to the left while the left inferior truncus swelling grows distally and to the right.
* The result is twisting of the swellings around each other and the foreshadowing of the anatomically normal spiral septum.  
* Simultaneously, swellings in the dorsal and ventral walls of the conus cordis appear and grow toward each other and distally.
* Eventually, these swellings fuse with each other, as well as the truncus septum, thus dividing the conus cordis into anterolateral (right ventricular outflow tract) and posteromedial (left ventricular outflow tract) portions.
* Equally important to septal formation, is the migration of neural crest cells through pharyngeal arches three, four, and six, and to the heart.
* There, they contribute to endocardial cushion formation in the truncus arteriosus and conus cordis, as well as lengthening of the outflow tracts.
*<nowiki/>Any insult to the migration of neural crest cells can cause [[Tetralogy of Fallot|tetralogy of Fallo]]<nowiki/>t, [[truncus arteriosus]], and [[TGA]].


'''Normal Heart'''
'''Normal Heart'''
*R[[right atrium|ight atrium]] ([[RA]]) is connected to a morphologic [[right ventricle]] ([[RV]]). The morphologic [[left atrium]] ([[LA]]) is connected to the morphologic [[left ventricle]] ([[LV]]). This is called '''atrio-ventricular concordance'''.
*R[[right atrium|ight atrium]] ([[RA]]) is connected to a morphologic [[right ventricle]] ([[RV]]).  
*In a normal heart, the great arteries ([[aorta]] and [[pulmonary arteries]]) are concordant with the morphologic [[LV]] and [[RV]]. This is termed '''ventriculo-arterial concordance'''.  
**The morphologic [[left atrium]] ([[LA]]) is connected to the morphologic [[left ventricle]] ([[LV]]). This is called '''atrio-ventricular concordance'''.
*In a normal heart, the great arteries ([[aorta]] and [[pulmonary arteries]]) are concordant with the morphologic [[LV]] and [[RV]].  
**This is termed '''ventriculo-arterial concordance'''.
*In addition, the aorta and pulmonary trunk ascend in a '''spiral''' relationship.
*In addition, the aorta and pulmonary trunk ascend in a '''spiral''' relationship.


'''Transposition of the great vessels'''   
'''Transposition of the great vessels'''   
*In the TGA the [[aorta]] arises from the morphologic [[right ventricle]] via a subaortic infundibulum and the [[pulmonary artery]] arises from the morphologic [[left ventricle]], without a subpulmonary infundibulum. These ventriculoarterial connection is known as '''ventriculoarterial discordance'''. As a consequence, there is a a fibrous continuity between the mitral and [[pulmonary valve]], but no continuity between the [[tricuspid]] and [[aortic valve]].
*In the TGA the [[aorta]] arises from the morphologic [[right ventricle]] via a subaortic infundibulum and the [[pulmonary artery]] arises from the morphologic [[left ventricle]], without a subpulmonary infundibulum.
*The abnormal origin of the great arteries results in an altered spiral relationship. Therefore, the aorta and pulmonary artery run parallel to each other
*These ventriculoarterial connection is known as '''ventriculoarterial discordance'''.  
*In normal heart thus the circulation is in series. However, in transposition of the great vessels circulation is in parallel
*As a consequence, there is a a fibrous continuity between the mitral and [[pulmonary valve]], but no continuity between the [[tricuspid]] and [[aortic valve]].
*The abnormal origin of the great arteries results in an altered spiral relationship.  
*Therefore, the aorta and pulmonary artery run parallel to each other
*In normal heart thus the circulation is in series.  
*However, in transposition of the great vessels circulation is in parallel


{| class="wikitable"
{| class="wikitable"
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==Pathophysiology==
==Pathophysiology==


*'''Fetal Ciculation'''→'''Oxygen-rich blood from placenta'''(drains to)→'''Umbilical vein''' (drains to)→'''Right atrium''' (drains to) →'''Fossa ovalis'''(drains to)→'''Left ventricle''' (drains to)→'''The pulmonary artery'''(drains to)→'''Ductus arteriosus'''(drains to)→'''Descending aorta'''
*The fetus circulation in-utero is different compared to the extra-uterine circulation.<ref name="pmid17159076">{{cite journal |vauthors=Warnes CA |title=Transposition of the great arteries |journal=Circulation |volume=114 |issue=24 |pages=2699–709 |date=December 2006 |pmid=17159076 |doi=10.1161/CIRCULATIONAHA.105.592352 |url=}}</ref>
 
* The fetus circulation in-utero is different compared to the extra-uterine circulation.
* The fetus tolerates a D-TGA well in-utero due to this difference in circulation.
* The fetus tolerates a D-TGA well in-utero due to this difference in circulation.
* The high resistance in the pulmonary circulation compared to the placenta, allows the blood to flow to the descending aorta rather than to the lung.
* The high resistance in the pulmonary circulation compared to the placenta, allows the blood to flow to the descending aorta rather than to the lung.
* Due to this the fetus gets blood with a higher oxygen tension.
* Due to this the fetus gets blood with a higher oxygen tension.


[[Image:D-TGA.jpg|center|400px|Normal heart anatomy compared to d-TGA]]'''Pathophysiology in Dextro-TGA in extra-uterine life'''-
[[Image:D-TGA.jpg|center|400px|Normal heart anatomy compared to d-TGA]]
 
* '''Fetal Ciculation'''→'''Oxygen-rich blood from placenta'''(drains to)→'''Umbilical vein''' (drains to)→'''Right atrium''' (drains to) →'''Fossa ovalis'''(drains to)→'''Left ventricle''' (drains to)→'''The pulmonary artery'''(drains to)→'''Ductus arteriosus'''(drains to)→'''Descending aorta'''.'''Pathophysiology in Dextro-TGA in extra-uterine life'''-


* In normal cardiac anatomy, the aorta is positioned posterior and to the right of the main pulmonary artery.  
* In normal cardiac anatomy, the aorta is positioned posterior and to the right of the main pulmonary artery.  
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[[Image:CompleteTGA.jpg|center]]
[[Image:CompleteTGA.jpg|center]]
<br clear="left"/>
<br clear="left"/>
* Levo-TGA (L-TGA) is a lesser known form of TGA.
* The [[left ventricle]] is positioned to the right of the [[right ventricle]] (opposite sides of the heart).
* The [[pulmonary trunk]] and [[aorta]] arise in their anatomically correct orientations, however, since the [[ventricles]] are reversed, the [[aorta]] is fused with the [[right ventricle]], and the [[pulmonary trunk]] is combined with the [[left ventricle]].
* The resultant flow of [[blood]] in a patient with L-TGA is as follows:
** Deoxygenated blood enters the anatomically correct [[right atrium]], passes through the [[mitral valve]] into the [[left ventricle]], and is pumped into the [[pulmonary trunk]] to the [[Lung|lungs]].
** From the [[Lung|lungs]], the oxygenated [[blood]] enters the [[left atrium]], passes through the [[tricuspid valve]], and into the [[right ventricle]] where [[blood]] is then pumped into the [[aorta]].
** Since the flow of blood in patients with L-TGA passes through the normal systemic and pulmonary circuits, L-TGA is sometimes termed anatomically correct TGA.


===Associated Conditions===
===Associated Conditions===
*Ventricular septal defect
Conditions associated with TGA include:
*Pulmonary stenosis
 
*[[Ventricular septal defect]]
*[[Pulmonary stenosis]]
*Left atrioventricular valve regurgitation (tricuspid or systemic)
*Left atrioventricular valve regurgitation (tricuspid or systemic)
*complete heart block
*[[Complete heart block]]


==References==
==References==

Latest revision as of 19:07, 21 February 2020

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [2]; Cafer Zorkun, M.D., Ph.D. [3]; Keri Shafer, M.D. [4]; Kristin Feeney, B.S. [5]

Overview

Right atrium (RA) is connected to a morphologic right ventricle (RV). The morphologic left atrium (LA) is connected to the morphologic left ventricle (LV). This is called atrio-ventricular concordance. In a normal heart, the great arteries (aorta and pulmonary arteries) are concordant with the morphologic LV and RV. This is termed ventriculo-arterial concordance. In addition, the aorta and pulmonary trunk ascend in a spiral relationship. In the TGA the aorta arises from the morphologic right ventricle via a subaortic infundibulum and the pulmonary artery arises from the morphologic left ventricle, without a subpulmonary infundibulum. These ventriculoarterial connection is known as ventriculoarterial discordance. The abnormal origin of the great arteries results in an altered spiral relationship resulting in parallel circulation.

Anatomy

Embryology
  • In the fifth week of gestation, opposing pairs of ridges form in the truncus arteriosus.[1][2][3]
  • These ridges are termed the right superior truncus swelling and the left inferior truncus swelling.
  • The right superior truncus swelling grows distally and to the left while the left inferior truncus swelling grows distally and to the right.
  • The result is twisting of the swellings around each other and the foreshadowing of the anatomically normal spiral septum.  
  • Simultaneously, swellings in the dorsal and ventral walls of the conus cordis appear and grow toward each other and distally.
  • Eventually, these swellings fuse with each other, as well as the truncus septum, thus dividing the conus cordis into anterolateral (right ventricular outflow tract) and posteromedial (left ventricular outflow tract) portions.
  • Equally important to septal formation, is the migration of neural crest cells through pharyngeal arches three, four, and six, and to the heart.
  • There, they contribute to endocardial cushion formation in the truncus arteriosus and conus cordis, as well as lengthening of the outflow tracts.
  • Any insult to the migration of neural crest cells can cause tetralogy of Fallot, truncus arteriosus, and TGA.

Normal Heart

  • Right atrium (RA) is connected to a morphologic right ventricle (RV).
  • In a normal heart, the great arteries (aorta and pulmonary arteries) are concordant with the morphologic LV and RV.
    • This is termed ventriculo-arterial concordance.
  • In addition, the aorta and pulmonary trunk ascend in a spiral relationship.

Transposition of the great vessels

  • In the TGA the aorta arises from the morphologic right ventricle via a subaortic infundibulum and the pulmonary artery arises from the morphologic left ventricle, without a subpulmonary infundibulum.
  • These ventriculoarterial connection is known as ventriculoarterial discordance.
  • As a consequence, there is a a fibrous continuity between the mitral and pulmonary valve, but no continuity between the tricuspid and aortic valve.
  • The abnormal origin of the great arteries results in an altered spiral relationship.
  • Therefore, the aorta and pulmonary artery run parallel to each other
  • In normal heart thus the circulation is in series.
  • However, in transposition of the great vessels circulation is in parallel
dextro-Transposition of the great vessels Referred to as complete or uncorrected transposition of the great arteries identifying the single discordance between ventricles and great arteries
levo-Transposition of the great vessels Referred to as congenitally corrected transposition, identifying a double discordance (atrioventicular and ventriculo arterial)


Pathophysiology

  • The fetus circulation in-utero is different compared to the extra-uterine circulation.[4]
  • The fetus tolerates a D-TGA well in-utero due to this difference in circulation.
  • The high resistance in the pulmonary circulation compared to the placenta, allows the blood to flow to the descending aorta rather than to the lung.
  • Due to this the fetus gets blood with a higher oxygen tension.
Normal heart anatomy compared to d-TGA
Normal heart anatomy compared to d-TGA
  • Fetal CiculationOxygen-rich blood from placenta(drains to)→Umbilical vein (drains to)→Right atrium (drains to) →Fossa ovalis(drains to)→Left ventricle (drains to)→The pulmonary artery(drains to)→Ductus arteriosus(drains to)→Descending aorta.Pathophysiology in Dextro-TGA in extra-uterine life-
  • In normal cardiac anatomy, the aorta is positioned posterior and to the right of the main pulmonary artery.
  • Aorta being positioned anterior and slightly rightward of the pulmonary artery.
  • These changes cause the aorta to arise from the right ventricle and the pulmonary artery from the left ventricle (ventriculoarterial discordance).
  • In Uncorrected D-TGA the systemic and pulmonary circulations are parallel circuits which means that the deoxygenated systemic venous blood comes to the right ventricle and inplace of going to the lungs, drains back to the systemic circulation via the aorta.
  • Similarly, oxygenated pulmonary venous blood is recirculated to the lungs via the pulmonary artery.
  • This parallel circulation is incompatible to life.
  • For a child with dextro-TGA to survive, a communication between the two parallel circuits is necessary.
  • Various connections that allow mixing in these patients are: patent foramen ovale, ventricular septal defect, atrial septal defect,patent ductus arteriosus or the bronchopulmonary collateral circulation.
    • Ventricular septal defect (VSD) occurs (in about 50%) of patients with D-TGA. Patients with a VSD may have other cardiac anomalies like pulmonary stenosis or atresia, overriding of atrioventricular valve, and coarctation of aorta.
    • Left ventricular outflow tract obstruction is common in D-TGA and is present in up to 25 percent of patients.


Below is an image depicting the abnormal flow in the large vessels of the heart.


Associated Conditions

Conditions associated with TGA include:

References

  1. Levin, Daniel L. (1977). "d-Transposition of the Great Vessels in the Neonate". Archives of Internal Medicine. 137 (10): 1421. doi:10.1001/archinte.1977.03630220061015. ISSN 0003-9926.
  2. Rashkind, William J. (1966). "Creation of an Atrial Septal Defect Without Thoracotomy". JAMA. 196 (11): 991. doi:10.1001/jama.1966.03100240125026. ISSN 0098-7484.
  3. Hornung TS, Bernard EJ, Celermajer DS, Jaeggi E, Howman-Giles RB, Chard RB, Hawker RE (November 1999). "Right ventricular dysfunction in congenitally corrected transposition of the great arteries". Am. J. Cardiol. 84 (9): 1116–9, A10. doi:10.1016/s0002-9149(99)00516-0. PMID 10569681.
  4. Warnes CA (December 2006). "Transposition of the great arteries". Circulation. 114 (24): 2699–709. doi:10.1161/CIRCULATIONAHA.105.592352. PMID 17159076.

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