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{{Atrial septal defect}}
{{CMG}}; '''Associate Editor(s)-In-Chief:''' [[Priyamvada Singh|Priyamvada Singh, M.B.B.S.]] [mailto:psingh13579@gmail.com];  '''Assistant Editor(s)-In-Chief:''' [[Kristin Feeney|Kristin Feeney, B.S.]] [mailto:kfeeney@elon.edu]


{{CMG}}
==Overview==
 
In a normal [[heart]], the typical path of [[blood flow]] is to flow from right-to-left allowing for [[blood]] to leave the deoxygenated right system and become oxygenated in the left system. In patients with an atrial septal defect, the typical path of blood flow is disrupted by the [[septal]] opening. This results in blood shunting from [[atrial septal defect left-to-right shunt|left-to-right]]. The severity of circulatory complications depends largely on the size of the defect. The larger the defect between the septal walls, the greater the amount of mixing between deoxygenated and [[oxygenated blood]].  Flow from the [[left atrium]] into the [[right atrium]] increases flow through the pulmonary circuit increasing the load on the [[right ventricle]] and slowly injuring the pulmonary vasculature over time.
{{EH}}


==Pathophysiology==
==Pathophysiology==
In unaffected individuals, the chambers of the left side of the heart make up a higher pressure system than the chambers of the right side of the heart. This is because the [[left ventricle]] has to produce enough pressure to pump blood throughout the entire body, while the [[right ventricle]] only has to produce enough pressure to pump blood to the [[lung]]s.
===Left-Sided Versus Right-Sided Pressures===
In unaffected individuals, the chambers of the left side of the [[heart]] make up a higher pressure system than the chambers of the right side of the heart. This is because the [[left ventricle]] has to produce enough pressure to pump blood throughout the entire body, while the [[right ventricle]] only has to produce enough pressure to pump blood to the [[lung]]s.


In the case of a large [[ASD]] (>9mm), which may result in a clinically remarkable ''[[left-to-right shunt]]'', blood will shunt from the [[left atrium]] to the [[right atrium]] causing excessive interatrial communication (In the case of hemodynamically significant [[ASD]] (Qp:Qs > 1.5:1), the patient is often found to be notably symptomatic and [[ASD]] repair may be indicated). This extra blood from the left atrium may cause a volume overload of both the [[right atrium]] and the [[right ventricle]], which if left untreated, can result in enlargement of the right side of the heart and ultimately heart failure.
===Calculation of the Pulmonary to Systemic Flow Ratios===
In the case of a large ASD (>9 mm), which may result in a clinically significant [[atrial septal defect left-to-right shunt|left-to-right shunt]], [[blood]] will shunt from the [[left atrium]] to the [[right atrium]] causing excessive mixing of the blood between the two [[atria]].  In a hemodynamically significant [[ASD]], Qp is the pulmonary flow and Qs is the systemic flow and the Qp:Qs > 1.5:1).  If the Qp:Qs is > 1.5:1, then the patient is often symptomatic, and a repair of the [[ASD]] may be indicated. This extra blood from the [[left atrium]] may cause a volume overload of both the [[right atrium]] and the [[right ventricle]], which if left untreated, can result in enlargement of the right side of the heart and ultimately [[right-sided heart failure]].


===Impact of Changes in Left Ventricular Loading Conditions===
Any process that increases the pressure in the [[left ventricle]] can cause worsening of the left-to-right shunt. This includes [[hypertension]], which increases the pressure that the [[left ventricle]] has to generate in order to open the [[aortic valve]] during ventricular [[systole]], and [[coronary artery disease]] which increases the stiffness of the [[left ventricle]], thereby increasing the filling pressure of the left ventricle during ventricular [[diastole]].
Any process that increases the pressure in the [[left ventricle]] can cause worsening of the left-to-right shunt. This includes [[hypertension]], which increases the pressure that the [[left ventricle]] has to generate in order to open the [[aortic valve]] during ventricular [[systole]], and [[coronary artery disease]] which increases the stiffness of the [[left ventricle]], thereby increasing the filling pressure of the left ventricle during ventricular [[diastole]].


The [[right ventricle]] will have to push out more blood than the [[left ventricle]] due to the left-to-right shunt. This constant overload of the right side of the heart will cause an overload of the entire pulmonary vasculature. Eventually the pulmonary vasculature will develop [[pulmonary hypertension]] to try to divert the extra blood volume away from the lungs.
===Right Heart Failure as a Consequence of Left Right Shunting===
The [[right ventricle]] will have to push out more blood than the [[left ventricle]] due to the left-to-right shunt. This constant overload of the right side of the heart will cause an overload of the entire pulmonary vasculature. Eventually the pulmonary vasculature will develop [[pulmonary hypertension]] as a result of the extra blood flow through the lungs.


The [[pulmonary hypertension]] will cause the [[right ventricle]] to face increased [[afterload]] in addition to the increased [[Preload (cardiology)|preload]] that the shunted blood from the left atrium to the right atrium caused. The [[right ventricle]] will be forced to generate higher pressures to try to overcome the [[pulmonary hypertension]]. This may lead to [[heart failure|right ventricular failure]] (dilatation and decreased [[systole|systolic]] function of the right ventricle) or elevations of the right sided pressures to levels greater than the left sided pressures.
The resulting [[pulmonary hypertension]] will cause the [[right ventricle]] to face increased pressure or increased [[afterload]] in addition to the increased [[Preload (cardiology)|preload]] (higher volume coming into the right side of the heart) as a result of the shunted blood flowing from the [[left atrium]] into the [[right atrium]]. The [[right ventricle]] will be forced to generate higher pressures to try to overcome the [[pulmonary hypertension]]. This may lead to [[heart failure|right ventricular failure]] (dilatation and decreased [[systole|systolic]] function of the right ventricle).  Eventually the right-sided pressures may exceed left-sided pressures.


===Equalization of Left and Right Atrial Pressures===
When the pressure in the right atrium rises to the level in the left atrium, there will no longer be a pressure gradient between these heart chambers, and the left-to-right shunt will diminish or cease.
When the pressure in the right atrium rises to the level in the left atrium, there will no longer be a pressure gradient between these heart chambers, and the left-to-right shunt will diminish or cease.


If left uncorrected, the pressure in the right side of the heart will be greater than the left side of the heart. This will cause the pressure in the right atrium to be higher than the pressure in the left atrium. This will reverse the pressure gradient across the [[ASD]], and the shunt will reverse; a '''right-to-left shunt''' will exist. This phenomenon is known as [[Eisenmenger's syndrome]].
===Development of Right-to-Left Shunting or Eisenmenger's Syndrome===
If left uncorrected, the pressure in the right side of the heart will be greater than the left side of the heart. This will cause the pressure in the right atrium to be higher than the pressure in the left atrium. This will reverse the pressure gradient across the [[ASD]], and the shunt will reverse; a right-to-left shunt will exist. This phenomenon is known as [[Eisenmenger's syndrome]]. Once right-to-left shunting occurs, a portion of the oxygen-poor blood will get shunted to the left side of the heart and ejected to the peripheral vascular system. This will cause signs of [[cyanosis]].  once [[Eisenmenger's syndrome]] develops, the patient can no longer benefit from [[surgery]] to correct the defect.
 
===Gross Pathology===
<div align="left">
<gallery>
Image:Congenital heart defect 0053.jpg|Atrial Septal Defect, Septum Primum; View from Right Atrium (a 4 month old baby)
Image:Congenital heart defect 0054.jpg|Atrial Septal Defect, Septum Primum; Also Cleft in Anterior Cusp of Mitral Valve
</gallery>
</div>
 
[http://www.peir.net Images courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology]


Once right-to-left shunting occurs, a portion of the oxygen-poor blood will get shunted to the left side of the heart and ejected to the peripheral vascular system. This will cause signs of [[cyanosis]].
===Associated Conditions===
Secundum ASD is seen in [[Holt-Oram (heart-hand) syndrome|Holt-Oram Syndrome]] with obvious limb malformations.


==References==
==References==
{{reflist|2}}
{{reflist|2}}


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Latest revision as of 16:08, 11 July 2017

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Atrial Septal Defect Microchapters

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Overview

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Ostium Secundum Atrial Septal Defect
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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]; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S. [3]

Overview

In a normal heart, the typical path of blood flow is to flow from right-to-left allowing for blood to leave the deoxygenated right system and become oxygenated in the left system. In patients with an atrial septal defect, the typical path of blood flow is disrupted by the septal opening. This results in blood shunting from left-to-right. The severity of circulatory complications depends largely on the size of the defect. The larger the defect between the septal walls, the greater the amount of mixing between deoxygenated and oxygenated blood. Flow from the left atrium into the right atrium increases flow through the pulmonary circuit increasing the load on the right ventricle and slowly injuring the pulmonary vasculature over time.

Pathophysiology

Left-Sided Versus Right-Sided Pressures

In unaffected individuals, the chambers of the left side of the heart make up a higher pressure system than the chambers of the right side of the heart. This is because the left ventricle has to produce enough pressure to pump blood throughout the entire body, while the right ventricle only has to produce enough pressure to pump blood to the lungs.

Calculation of the Pulmonary to Systemic Flow Ratios

In the case of a large ASD (>9 mm), which may result in a clinically significant left-to-right shunt, blood will shunt from the left atrium to the right atrium causing excessive mixing of the blood between the two atria. In a hemodynamically significant ASD, Qp is the pulmonary flow and Qs is the systemic flow and the Qp:Qs > 1.5:1). If the Qp:Qs is > 1.5:1, then the patient is often symptomatic, and a repair of the ASD may be indicated. This extra blood from the left atrium may cause a volume overload of both the right atrium and the right ventricle, which if left untreated, can result in enlargement of the right side of the heart and ultimately right-sided heart failure.

Impact of Changes in Left Ventricular Loading Conditions

Any process that increases the pressure in the left ventricle can cause worsening of the left-to-right shunt. This includes hypertension, which increases the pressure that the left ventricle has to generate in order to open the aortic valve during ventricular systole, and coronary artery disease which increases the stiffness of the left ventricle, thereby increasing the filling pressure of the left ventricle during ventricular diastole.

Right Heart Failure as a Consequence of Left Right Shunting

The right ventricle will have to push out more blood than the left ventricle due to the left-to-right shunt. This constant overload of the right side of the heart will cause an overload of the entire pulmonary vasculature. Eventually the pulmonary vasculature will develop pulmonary hypertension as a result of the extra blood flow through the lungs.

The resulting pulmonary hypertension will cause the right ventricle to face increased pressure or increased afterload in addition to the increased preload (higher volume coming into the right side of the heart) as a result of the shunted blood flowing from the left atrium into the right atrium. The right ventricle will be forced to generate higher pressures to try to overcome the pulmonary hypertension. This may lead to right ventricular failure (dilatation and decreased systolic function of the right ventricle). Eventually the right-sided pressures may exceed left-sided pressures.

Equalization of Left and Right Atrial Pressures

When the pressure in the right atrium rises to the level in the left atrium, there will no longer be a pressure gradient between these heart chambers, and the left-to-right shunt will diminish or cease.

Development of Right-to-Left Shunting or Eisenmenger's Syndrome

If left uncorrected, the pressure in the right side of the heart will be greater than the left side of the heart. This will cause the pressure in the right atrium to be higher than the pressure in the left atrium. This will reverse the pressure gradient across the ASD, and the shunt will reverse; a right-to-left shunt will exist. This phenomenon is known as Eisenmenger's syndrome. Once right-to-left shunting occurs, a portion of the oxygen-poor blood will get shunted to the left side of the heart and ejected to the peripheral vascular system. This will cause signs of cyanosis. once Eisenmenger's syndrome develops, the patient can no longer benefit from surgery to correct the defect.

Gross Pathology

Images courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology

Associated Conditions

Secundum ASD is seen in Holt-Oram Syndrome with obvious limb malformations.

References


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