Tetralogy of Fallot pathophysiology: Difference between revisions

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==Overview==
==Overview==
Tetralogy of Fallot is a congenital heart lesion characterized by a constellation of four morphologic abnormalities present in the newborn heart. These features include a ventricular septal defect, overriding aorta, pulmonary stenosis, and right ventricular hypertrophy. The obstruction of right ventricular outflow in tetralogy of Fallot causes [[blood]] to [[shunt]] or flow from the right to left side of heart through the [[ventricular septal defect]].  This causes [[right ventricular hypertrophy]] and eventual [[right sided heart failure]].  There is flow of deoxygenated venous blood from the right side of the [[heart]] to the [[systemic circulation]] resulting in [[cyanosis]].
Tetralogy of Fallot is a [[Congenital heart defect|congenital heart lesion]] characterized by a constellation of four [[Morphology|morphologic]] [[abnormalities]] present in the [[newborn]] [[heart]]. It is understood that tetralogy of fallot is the result of improper positioning of the outlet [[septum]]. In the normal [[heart]], the outlet septum is an indistinguishable component of the crista supraventricularis that communicates with the [[Septomarginal trabecula|septomarginal trabeculae]] to divide the [[Right ventricle|right]] and [[Left ventricle|left]] [[Ventricle|ventricular cavities]]. In Tetralogy of Fallot, proper [[Ventricle (heart)|ventricular]] septation is perturbed by anterocephalad displacement of the outlet [[Septum (disambiguation)|septum]] relative to the [[septomarginal trabecula]]. These features include a ventricular septal defect, overriding aorta, pulmonary stenosis, and right ventricular hypertrophy. The obstruction of right ventricular outflow in tetralogy of Fallot causes [[blood]] to [[shunt]] or flow from the [[Right-to-left shunt|right to left]] side of heart through the [[ventricular septal defect]].  This causes [[right ventricular hypertrophy]] and eventual [[right sided heart failure]].  There is [[Blood flow|flow]] of deoxygenated [[venous blood]] from the right side of the [[heart]] to the [[systemic circulation]] resulting in [[cyanosis]].


==Pathophysiology==
==Pathophysiology==
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====Embrylogy====
====Embrylogy====


* Embryologic studies show that tetralogy of Fallot is a result of anterior malalignment of the conal septum, resulting in the clinical combination of a [[ventricular septal defect]] ([[VSD]]), [[pulmonary stenosis]], and an [[overriding aorta]].  
*[[Embryology|Embryologic]] studies show that tetralogy of Fallot is a result of anterior misalignment of the conal septum, resulting in the clinical combination of a [[ventricular septal defect]] ([[VSD]]), [[pulmonary stenosis]], and an [[overriding aorta]].
* [[Right ventricular hypertrophy]] is secondary to this combination of abnormalities, which causes resistance to [[blood flow]] from the [[right ventricle]].
* [[Right ventricular hypertrophy]] is secondary to this combination of [[abnormalities]], which causes resistance to [[blood flow]] from the [[right ventricle]].
* Tetralogy of Fallot results in [[cyanosis]], ([[hypoxia]] or [[low oxygenation]]) of the blood due to mixing of deoxygenated venous blood from the [[right ventricle]] with oxygenated blood in the [[left ventricle]] through the [[ventricular septal defect]] and preferential flow of both oxygenated and deoxygenated blood from the ventricles through the [[aorta]] because of obstruction to flow through the [[pulmonary valve]].  
* Tetralogy of Fallot results in [[cyanosis]], ([[hypoxia]] or [[low oxygenation]]) of the blood due to mixing of [[Venous blood|deoxygenated venous blood]] from the [[right ventricle]] with [[oxygenated blood]] in the [[left ventricle]] through the [[ventricular septal defect]] and preferential flow of both [[Oxygenated blood|oxygenated]] and deoxygenated [[blood]] from the [[Ventricle (heart)|ventricles]] through the [[aorta]] because of obstruction to flow through the [[pulmonary valve]].
*This is known as a [[right-to-left shunt]].   
*This is known as a [[right-to-left shunt]].   
*If pulmonary blood flow is dramatically reduced, pulmonary blood flow may depend on a [[patent ductus arteriosus]] ([[PDA]]) or bronchial collaterals.
*If [[Pulmonary valve|pulmonary]] [[blood flow]] is dramatically reduced, [[Pulmonary valve|pulmonary]] [[blood flow]] may depend on a [[patent ductus arteriosus]] ([[PDA]]) or [[bronchial]] collaterals.
* If obstruction of the right ventricular outflow tract is minimal, the intracardiac shunt may be mostly from left to right, and this may result in what is termed a pink tet or pink tetralogy.
* If obstruction of the [[right ventricular outflow tract]] is minimal, the intracardiac [[Shunt (medical)|shunt]] may be mostly from left to right, and this may result in what is termed a pink tet or pink tetralogy.
*Although [[cyanosis]] is absent on clinical exam, laboratory testing will often show systemic oxygen desaturation.
*Although [[cyanosis]] is absent on [[Clinical examination|clinical exam]], [[laboratory]] testing will often show [[systemic]] [[oxygen]] [[desaturation]].
* Children with tetralogy of Fallot may develop acute severe [[cyanosis]] or [[hypoxic]] [[tet spells]].  
*[[Children]] with tetralogy of Fallot may develop [[Acute (medicine)|acute]] severe [[cyanosis]] or [[hypoxic]] [[tet spells]].
*The mechanism underlying these episodes is not entirely clear, but may be due to spasm of the infundibular septum and the right ventricular outflow tract.
*The mechanism underlying these episodes is not entirely clear, but may be due to [[spasm]] of the infundibular septum and the [[right ventricular outflow tract]].
*Whatever the mechanism, there is an increase in resistance to blood flow to the [[lung]]s with increased preferential flow of desaturated [[blood]] to the systemic circulation.  
*Whatever the mechanism, there is an increase in [[resistance]] to [[blood flow]] to the [[lung]]s with increased preferential flow of desaturated [[blood]] to the [[systemic circulation]].
*The child will often squat during a [[tet spell]] to improve venous return to the right side of the [[heart]].  
*The [[child]] will often squat during a [[tet spell]] to improve [[venous return]] to the right side of the [[heart]].
*Squatting increases the [[systemic vascular resistance]] and thereby [[shunt]]s flow to pulmonary circuit.
*Squatting increases the [[systemic vascular resistance]] and thereby [[shunt]]s flow to [[Pulmonary circulation|pulmonary circuit]].
*These spells can be fatal, and can occur in patients who are not cyanotic.
*These spells can be [[fatal]], and can occur in [[patients]] who are not [[cyanotic]].


==Genetics==
==Genetics==


* Genes involved in the pathogenesis of tetralogy of fallot include:<ref name="pmid17008524">{{cite journal| author=Olson EN| title=Gene regulatory networks in the evolution and development of the heart. | journal=Science | year= 2006 | volume= 313 | issue= 5795 | pages= 1922-7 | pmid=17008524 | doi=10.1126/science.1132292 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17008524  }} </ref><ref name="pmid24000169">{{cite journal| author=Yang YQ, Gharibeh L, Li RG, Xin YF, Wang J, Liu ZM et al.| title=GATA4 loss-of-function mutations underlie familial tetralogy of fallot. | journal=Hum Mutat | year= 2013 | volume= 34 | issue= 12 | pages= 1662-71 | pmid=24000169 | doi=10.1002/humu.22434 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24000169  }} </ref><ref name="pmid18288184">{{cite journal| author=Bruneau BG| title=The developmental genetics of congenital heart disease. | journal=Nature | year= 2008 | volume= 451 | issue= 7181 | pages= 943-8 | pmid=18288184 | doi=10.1038/nature06801 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=18288184  }} </ref><ref name="pmid24526674">{{cite journal| author=Bruneau BG, Srivastava D| title=Congenital heart disease: entering a new era of human genetics. | journal=Circ Res | year= 2014 | volume= 114 | issue= 4 | pages= 598-9 | pmid=24526674 | doi=10.1161/CIRCRESAHA.113.303060 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24526674  }} </ref><ref name="pmid11431700">{{cite journal| author=Hiroi Y, Kudoh S, Monzen K, Ikeda Y, Yazaki Y, Nagai R et al.| title=Tbx5 associates with Nkx2-5 and synergistically promotes cardiomyocyte differentiation. | journal=Nat Genet | year= 2001 | volume= 28 | issue= 3 | pages= 276-80 | pmid=11431700 | doi=10.1038/90123 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11431700  }} </ref><ref name="pmid12845333">{{cite journal| author=Garg V, Kathiriya IS, Barnes R, Schluterman MK, King IN, Butler CA et al.| title=GATA4 mutations cause human congenital heart defects and reveal an interaction with TBX5. | journal=Nature | year= 2003 | volume= 424 | issue= 6947 | pages= 443-7 | pmid=12845333 | doi=10.1038/nature01827 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12845333  }} </ref><ref name="pmid24182332">{{cite journal| author=Sheng W, Qian Y, Wang H, Ma X, Zhang P, Diao L et al.| title=DNA methylation status of NKX2-5, GATA4 and HAND1 in patients with tetralogy of fallot. | journal=BMC Med Genomics | year= 2013 | volume= 6 | issue=  | pages= 46 | pmid=24182332 | doi=10.1186/1755-8794-6-46 | pmc=PMC3819647 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24182332  }} </ref>
*[[Genes]] involved in the [[pathogenesis]] of tetralogy of fallot include:<ref name="pmid17008524">{{cite journal| author=Olson EN| title=Gene regulatory networks in the evolution and development of the heart. | journal=Science | year= 2006 | volume= 313 | issue= 5795 | pages= 1922-7 | pmid=17008524 | doi=10.1126/science.1132292 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17008524  }} </ref><ref name="pmid24000169">{{cite journal| author=Yang YQ, Gharibeh L, Li RG, Xin YF, Wang J, Liu ZM et al.| title=GATA4 loss-of-function mutations underlie familial tetralogy of fallot. | journal=Hum Mutat | year= 2013 | volume= 34 | issue= 12 | pages= 1662-71 | pmid=24000169 | doi=10.1002/humu.22434 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24000169  }} </ref><ref name="pmid18288184">{{cite journal| author=Bruneau BG| title=The developmental genetics of congenital heart disease. | journal=Nature | year= 2008 | volume= 451 | issue= 7181 | pages= 943-8 | pmid=18288184 | doi=10.1038/nature06801 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=18288184  }} </ref><ref name="pmid24526674">{{cite journal| author=Bruneau BG, Srivastava D| title=Congenital heart disease: entering a new era of human genetics. | journal=Circ Res | year= 2014 | volume= 114 | issue= 4 | pages= 598-9 | pmid=24526674 | doi=10.1161/CIRCRESAHA.113.303060 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24526674  }} </ref><ref name="pmid11431700">{{cite journal| author=Hiroi Y, Kudoh S, Monzen K, Ikeda Y, Yazaki Y, Nagai R et al.| title=Tbx5 associates with Nkx2-5 and synergistically promotes cardiomyocyte differentiation. | journal=Nat Genet | year= 2001 | volume= 28 | issue= 3 | pages= 276-80 | pmid=11431700 | doi=10.1038/90123 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11431700  }} </ref><ref name="pmid12845333">{{cite journal| author=Garg V, Kathiriya IS, Barnes R, Schluterman MK, King IN, Butler CA et al.| title=GATA4 mutations cause human congenital heart defects and reveal an interaction with TBX5. | journal=Nature | year= 2003 | volume= 424 | issue= 6947 | pages= 443-7 | pmid=12845333 | doi=10.1038/nature01827 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12845333  }} </ref><ref name="pmid24182332">{{cite journal| author=Sheng W, Qian Y, Wang H, Ma X, Zhang P, Diao L et al.| title=DNA methylation status of NKX2-5, GATA4 and HAND1 in patients with tetralogy of fallot. | journal=BMC Med Genomics | year= 2013 | volume= 6 | issue=  | pages= 46 | pmid=24182332 | doi=10.1186/1755-8794-6-46 | pmc=PMC3819647 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24182332  }} </ref>
** The cellular processes that underlie cardiogenesis are extensively regulated in the developing heart.
** The [[cellular]] processes that underlie cardiogenesis are extensively regulated in the developing [[heart]].
** Proper cardiac development requires the complex orchestration of cardiac transcription factors and signaling pathways in a spatiotemporal specific manner.
** Proper [[Heart|cardiac]] development requires the complex orchestration of [[cardiac]] [[Transcription factor|transcription factors]] and [[Signaling pathway|signaling pathways]] in a spatiotemporal specific manner.
** Previous genetic studies demonstrated that mutations in numerous genes encoding cardiac transcription factors and cell signaling proteins have a role in the development of Tetralogy of Fallot.
** Previous [[Genetics|genetic]] studies demonstrated that [[mutations]] in numerous [[genes]] encoding [[Heart|cardiac]] [[transcription factors]] and [[cell]] [[Signaling protein|signaling proteins]] have a role in the [[development]] of Tetralogy of Fallot.
** Specifically, heterozygous mutations in NKX2-5, HAND1, TBX5, and GATA4 have been reported in familial forms of disease.
** Specifically, [[Heterozygous|heterozygous mutations]] in [[NKX2-5]], [[HAND1]], [[TBX5 (gene)|TBX5]], and [[GATA4]] have been reported in familial forms of [[disease]].
** Many of these single gene mutations result in haploinsufficiency and suggest a dose dependent relationship between genetic expression and disease.
** Many of these single [[Gene mutation|gene mutations]] result in [[haploinsufficiency]] and suggest a dose dependent relationship between [[genetic]] expression and [[disease]].
** While the mechanistic basis of this relationship is currently poorly understood, it is hypothesized that disruption of the direct protein-protein interactions that allow these transcription factors to work synergistically impedes the activation of downstream targets and signaling pathways central to cardiac morphogenesis.
** While the mechanistic basis of this relationship is currently poorly understood, it is hypothesized that disruption of the direct [[protein]]-[[protein]] interactions that allow these [[transcription factors]] to work synergistically impedes the activation of downstream targets and [[signaling pathway]]<nowiki/>s central to [[cardiac]] morphogenesis.
** In addition, recent whole-exome sequencing investigations have introduced a novel role for epigenetic dysregulation in the pathogenesis of Tetralogy of Fallot.
** In addition, recent whole-exome sequencing investigations have introduced a novel role for [[Epigenetics|epigenetic]] dysregulation in the [[pathogenesis]] of Tetralogy of Fallot.
** Aberrant epigenetic modifications are thought to provide an alternative mechanism to perturb normal spatiotemporal expression of these essential developmental genes.
** Aberrant [[epigenetic]] modifications are thought to provide an alternative mechanism to perturb normal spatiotemporal expression of these essential [[developmental]] [[genes]].


==Associated Conditions==
==Associated Conditions==


* Conditions associated with tetralogy of fallot include:<ref name="pmid7349946">{{cite journal |vauthors=Dabizzi RP, Caprioli G, Aiazzi L, Castelli C, Baldrighi G, Parenzan L, Baldrighi V |title=Distribution and anomalies of coronary arteries in tetralogy of fallot |journal=Circulation |volume=61 |issue=1 |pages=95–102 |date=January 1980 |pmid=7349946 |doi=10.1161/01.cir.61.1.95 |url=}}</ref><ref name="Satyanarayana RaoAnderson1971">{{cite journal|last1=Satyanarayana Rao|first1=B.N.|last2=Anderson|first2=Ray C.|last3=Edwards|first3=Jesse E.|title=Anatomic variations in the tetralogy of Fallot|journal=American Heart Journal|volume=81|issue=3|year=1971|pages=361–371|issn=00028703|doi=10.1016/0002-8703(71)90106-2}}</ref><ref name="MusterPaul1973">{{cite journal|last1=Muster|first1=Alexander J.|last2=Paul|first2=Milton H.|last3=Nikaidoh|first3=Hisashi|title=Tetralogy of Fallot Associated with Total Anomalous Pulmonary Venous Drainage|journal=Chest|volume=64|issue=3|year=1973|pages=323–326|issn=00123692|doi=10.1378/chest.64.3.323}}</ref><ref name="SaifiMatsumoto2012">{{cite journal|last1=Saifi|first1=Comron|last2=Matsumoto|first2=Hiroko|last3=Vitale|first3=Michael G.|last4=Roye|first4=David P.|last5=Hyman|first5=Joshua E.|title=The incidence of congenital scoliosis in infants with tetralogy of Fallot based on chest radiographs|journal=Journal of Pediatric Orthopaedics B|volume=21|issue=4|year=2012|pages=313–316|issn=1060-152X|doi=10.1097/BPB.0b013e3283536872}}</ref>
* Conditions associated with tetralogy of fallot include:<ref name="pmid7349946">{{cite journal |vauthors=Dabizzi RP, Caprioli G, Aiazzi L, Castelli C, Baldrighi G, Parenzan L, Baldrighi V |title=Distribution and anomalies of coronary arteries in tetralogy of fallot |journal=Circulation |volume=61 |issue=1 |pages=95–102 |date=January 1980 |pmid=7349946 |doi=10.1161/01.cir.61.1.95 |url=}}</ref><ref name="Satyanarayana RaoAnderson1971">{{cite journal|last1=Satyanarayana Rao|first1=B.N.|last2=Anderson|first2=Ray C.|last3=Edwards|first3=Jesse E.|title=Anatomic variations in the tetralogy of Fallot|journal=American Heart Journal|volume=81|issue=3|year=1971|pages=361–371|issn=00028703|doi=10.1016/0002-8703(71)90106-2}}</ref><ref name="MusterPaul1973">{{cite journal|last1=Muster|first1=Alexander J.|last2=Paul|first2=Milton H.|last3=Nikaidoh|first3=Hisashi|title=Tetralogy of Fallot Associated with Total Anomalous Pulmonary Venous Drainage|journal=Chest|volume=64|issue=3|year=1973|pages=323–326|issn=00123692|doi=10.1378/chest.64.3.323}}</ref><ref name="SaifiMatsumoto2012">{{cite journal|last1=Saifi|first1=Comron|last2=Matsumoto|first2=Hiroko|last3=Vitale|first3=Michael G.|last4=Roye|first4=David P.|last5=Hyman|first5=Joshua E.|title=The incidence of congenital scoliosis in infants with tetralogy of Fallot based on chest radiographs|journal=Journal of Pediatric Orthopaedics B|volume=21|issue=4|year=2012|pages=313–316|issn=1060-152X|doi=10.1097/BPB.0b013e3283536872}}</ref>
**Left superior vena cava
**Left [[superior vena cava]]
**Anomalies of the mitral valve
**[[Anomaly|Anomalies]] of the [[mitral valve]]
**Anomalies of the tricuspid valve
**[[Anomaly|Anomalies]] of the [[tricuspid valve]]
**[[pulmonic stenosis|Stenosis of the left pulmonary artery]], in 40% of patients
**[[pulmonic stenosis|Stenosis of the left pulmonary artery]], in 40% of [[Patient|patients]]
** A bicuspid [[pulmonary valve]], in 40% of patients
** A bicuspid [[Pulmonic regurgitation|pulmonary valve]], in 40% of [[patients]]
** Right sided aortic arch, in 25% of patients
** Right sided [[aortic arch]], in 25% of [[patients]]
** Coronary artery anomalies, in 10% of patients
**[[Coronary artery anomalies]], in 10% of [[patients]]
** An [[atrial septal defect]], in which case the syndrome is sometimes called a [[pentalogy of Fallot]].
** An [[atrial septal defect]], in which case the [[DRESS syndrome|syndrome]] is sometimes called a [[pentalogy of Fallot]].
** An [[atrioventricular septal defect]]
** An [[atrioventricular septal defect]]
** Partially or totally [[anomalous pulmonary venous return]]
** Partially or totally [[anomalous pulmonary venous return]]
** Forked ribs and [[scoliosis]]
** Forked ribs and [[scoliosis]]
**Associated abnormalities include [[cleft lip]], [[cleft palate]], [[hypospadias]], skeletal and craniofacial abnormalities.
**Associated [[abnormalities]] include [[cleft lip]], [[cleft palate]], [[hypospadias]], [[Skeleton|skeletal]] and [[craniofacial]] [[abnormalities]].


==Gross Pathology==
==Gross Pathology==


* On gross pathology characteristic features findings of tetralogy of fallot include:
* On [[gross pathology]] characteristic features findings of tetralogy of fallot include:
** Right ventricular hypertrophy
**[[Right ventricular hypertrophy]]
** VSD
**[[VSD]]
**Overriding aorta
**[[Overriding aorta]]
**Subpulmonic stenosis
**Subpulmonic stenosis
**  
**  


[[File:PLC Fallots tetralogy.jpg|300px|none|thumb|https:// by Jurgennizer| https://en.wikipedia.org/wiki/File:PLC_Fallots_tetralogy.jpg]]<br />
[[File:PLC Fallots tetralogy.jpg|300px|none|thumb|https:// by Jurgennizer| https://en.wikipedia.org/wiki/File:PLC_Fallots_tetralogy.jpg]]<br />
== Microscopic Pathology ==
== Microscopic Pathology ==
There is no characteristic findings of tetralogy of fallot on microscopic histopathological analysis.  
There is no characteristic findings of tetralogy of fallot on microscopic [[histopathological]] analysis.  





Latest revision as of 01:40, 23 February 2020

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editors-In-Chief: Fahimeh Shojaei, M.D., Priyamvada Singh, M.B.B.S. [2], Keri Shafer, M.D. [3]; Omar Toubat; Assistant Editor-In-Chief: Kristin Feeney, B.S. [4]

Overview

Tetralogy of Fallot is a congenital heart lesion characterized by a constellation of four morphologic abnormalities present in the newborn heart. It is understood that tetralogy of fallot is the result of improper positioning of the outlet septum. In the normal heart, the outlet septum is an indistinguishable component of the crista supraventricularis that communicates with the septomarginal trabeculae to divide the right and left ventricular cavities. In Tetralogy of Fallot, proper ventricular septation is perturbed by anterocephalad displacement of the outlet septum relative to the septomarginal trabecula. These features include a ventricular septal defect, overriding aorta, pulmonary stenosis, and right ventricular hypertrophy. The obstruction of right ventricular outflow in tetralogy of Fallot causes blood to shunt or flow from the right to left side of heart through the ventricular septal defect. This causes right ventricular hypertrophy and eventual right sided heart failure. There is flow of deoxygenated venous blood from the right side of the heart to the systemic circulation resulting in cyanosis.

Pathophysiology

Physiology

The normal physiology of heart development can be understood as follows:

https://en.wikipedia.org/wiki/File:2037_Embryonic_Development_of_Heart.jpg


Pathogenesis

https://en.wikipedia.org/wiki/File:Tetralogy_of_Fallot.svg


Anatomy

https://en.wikipedia.org/wiki/File:Heart_tetralogy_fallot.svg
  • This defect in outlet septum in turn leads to the four characteristic features:
  • A: Pulmonic Stenosis
    • Pulmonic stenosis is a right ventricular outflow tract obstruction
      • A narrowing at (valvular stenosis, seen in approximately 20-25% case) or just below (infundibular stenosis, seen in around 50% of cases) the pulmonary valve.
      • The stenosis is mostly the result of hypertrophy of the septoparietal trabeculae,[4] however the deviated outlet septum is believed to play a role.
      • The stenosis is the major cause of the malformations, with the other associated malformations acting as compensatory mechanisms to the pulmonic stenosis.[5]
      • The degree of stenosis varies between individuals with TOF, and is the primary determinant of symptoms and severity. This malformation is infrequently described as sub-pulmonary stenosis or subpulmonary obstruction.[6]
      • Tetralogy of Fallot with pulmonary atresia or pseudotruncus arteriosus is a severe variant in which there is complete obstruction of the right ventricular outflow tract and absence of the pulmonary trunk. In these individuals, there is complete right-to-left shunting of blood. The lungs are perfused via extensive collaterals from the systemic arteries.
  • B: Overriding Aorta
  • C: Ventricular Septal Defect
    • Ventricular septal defect is a hole between the two bottom chambers (ventricles) of the heart. The defect is centered around the outlet septum, the most superior aspect of the septum, and in the majority of cases is single and large. In some cases septal hypertrophy can narrow the margins of the defect.[4]
  • D: Right Ventricular Hypertrophy
    • The right ventricle is more muscular than normal, causing a characteristic coeur-en-sabot (boot-shaped) appearance as seen by chest x-ray. Due to the misarrangement of the external ventricular septum, the right ventricular wall increase in size to deal with the increased obstruction to the right outflow tract. This feature is now generally agreed to be a secondary anomaly, as the level of hypertrophy generally increases with age.[7]
  • There is anatomic variation between the hearts of individuals with tetralogy of Fallot.
  • The degree of right ventricular outflow tract obstruction varies between patients and is generally determines clinical symptoms and disease progression.

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Embrylogy

Genetics

Associated Conditions

Gross Pathology

https://en.wikipedia.org/wiki/File:PLC_Fallots_tetralogy.jpg


Microscopic Pathology

There is no characteristic findings of tetralogy of fallot on microscopic histopathological analysis.


References

  1. Anderson RH, Jacobs ML (2008). "The anatomy of tetralogy of Fallot with pulmonary stenosis". Cardiol Young. 18 Suppl 3: 12–21. doi:10.1017/S1047951108003259. PMID 19094375.
  2. Bashore TM (2007). "Adult congenital heart disease: right ventricular outflow tract lesions". Circulation. 115 (14): 1933–47. doi:10.1161/CIRCULATIONAHA.105.592345. PMID 17420363.
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