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Ventricular Septal Defect (view source)

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[[Image:VSD1.jpg|thumb|right|150px|<small><center><b>Ventricular septal defect</b>. Courtesy of A. Jefferies</center></small>]]  
 
[[Image:VSD1.jpg|thumb|right|150px|<small><center><b>Ventricular septal defect</b>. Courtesy of A. Jefferies</center></small>]]  
 
[[Image:VSD2.jpg|thumb|right|150px|<small><center><b>Ventricular septal defect</b>. Courtesy of A. Jefferies</center></small>]]  
 
[[Image:VSD2.jpg|thumb|right|150px|<small><center><b>Ventricular septal defect</b>. Courtesy of A. Jefferies</center></small>]]  
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Ventricular Septal Defect, also known as '''VSD''', is the most common congenital cardiac abnormality in large animals and the second most common congenital cardiac abnormality in cat. It does occur in dogs, but less frequently. Predisposed breeds include Keeshonds, English Springer Spaniel, English Bulldog and West Highland White Terrier.
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Ventricular defects are usually in the '''membranous area''' of the interventricular septum. On the right ventricle, the septal defect usually occurs below the septal leaflet of the tricuspid valve. On the left ventricle, the septal defect usually occurs under the aortic valve. 
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Ventricular septal defects (VSDs) are the most common congenital cardiac abnormality in large animals and the second most common congenital cardiac abnormality in cats. They less commonly occur in dogs.  
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Ventricular Septal Defects can occur alone or in combination with other congenital malformations. Usually blood flows from the higher pressure left ventricle through the shunt to the lower pressure right ventricle. Left to right shunting causes volume overload of the pulmonary circulation and consequently the left atrium and ventricle. The consequences of L-R shunting are [[Heart Failure, Left-Sided|left-sided congestive heart failure]] and [[Pulmonary Hypertension|pulmonary hypertension]]. Shunting can be reversed from L-R towards R-L if pulmonary hypertension increases the pressure on the right side of the heart and/or there is also [[Pulmonic Stenosis|pulmonic stenosis]] (Eisenmenger's Physiology see below). A R-L shunt would allow unoxygenated blood into the systemic circulation resulting in arterial hypoxaemia. Increased amounts of blood into the systemic circulation causes an increased right sided pressure load. The defect is often associated with other conditions e.g. [[Tetralogy of Fallot]].  
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The lesion is usually in the '''membranous area''' of the interventricular septum, just below the aortic valve and the septal tricuspid leaflet.  
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'''Eisenmenger's Syndrome''': chronic pulmonary overcirculation results in pulmonary hypertension and increased right-sided pressure. This facilitates right to left shunting and reduced lung perfusion, leading on to cyanosis.
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Ventricular Septal Defects can occur alone or in combination with other congenital malformations, such as [[Tetralogy of Fallot]]. Usually blood flows from the higher pressure left ventricle through the VSD to the lower pressure right ventricle during systole. Significant left-to-right shunting causes volume overload of the pulmonary circulation, increasing pulmonary venous return to the left atrium and consequently the left ventricle. This may result in volume overload of the left heart with consequent [[Heart Failure, Left-Sided|left-sided congestive heart failure]] and [[Pulmonary Hypertension|pulmonary hypertension]]. If chronic over-circulation of the pulmonary vasculature occurs, pulmonary hypertension may develop. Pulmonary hypertension causes increased right ventricular pressures and therefore right-to-left shunting during systole may occur; this is known as '''Eisenmenger's syndrome'''. Right-to-left shunting allows deoxygenated blood to enter the systemic circulation, resulting in arterial hypoxaemia and cyanosis.  
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== Clinical Signs ==
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Small VSDs provide high resistance to flow, as high pressure gradients between the left and right ventricle are maintained. These are known as '''restrictive''' or '''resistive''' VSDs, and are usually of no haemodynamic consequence. Larger VSDs offer little resistance to the shunting of blood and are more likely to result in haemodynamic consequences.
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Coughing, exercise intolerance, left-sided congestive heart failure, [[Heart Failure, Right-Sided|right-sided heart failure]] and cyanosis (with R-L shunt) are all possible clinical signs. With smaller defects, the condition can be asymptomatic.
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==Signalment==
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Predisposed breeds include the English Springer Spaniel, Cocker Spaniel, English Bulldog and West Highland White Terrier.
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== Diagnosis ==
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== History and Clinical Signs ==
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History and clinical signs would be presumptive of a heart condition.  
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A murmur is usually detected at the first health check, or primary vaccination. Most affected animals are asymptomatic, but large defects can result in [[Heart Failure, Left-Sided|left-sided congestive heart failure]]. Right-to-left shunting can cause stunted growth and exercise intolerance.  
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On physical examination, a '''holosystolic murmur over left apex and right sternal border''' (diagonal murmur) can be detected as well as a '''systolic murmur over pulmonic valve''' (pulmonic stenosis) and '''diastolic murmur over aortic valve''' (aortic regurgitation). There may also be a '''murmur''' from mitral regurgitation (caused by left ventricular dilation).
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== Diagnosis ==
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===Physical Examination===
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Radiographs would show a generally normal heart with small defects such as pulmonary overcirculation, left or right sided heart enlargement (due to which side the shunt went) and enlargement of the pulmonary arteries.
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* '''Systolic''' murmur with point of maximum intensity on the '''right''' hemithorax (blood shunts to the right) The murmur can also be detected on the left side, either due to radiation of the primary murmur or the relative pulmonic stenosis caused by the increased blood flow across the pulmonic valve.
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* Murmur grade is inversely proportional to the size of the defect, as smaller defects provide more resistance and therefore produce louder murmurs
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Echocardiography with doppler would show blood shunting through defect.
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* Cyanosis may be present with right-to-left shunts
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===Thoracic Radiographs===
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* Left ventricular enlargement
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* Left atrial enlargement
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* Right ventricular enlargement
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* Pulmonary over-circulation may be present if the left-to-right shunting is significant
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===Echocardiography===
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* Left atrial dilation
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* Left ventricular dilation (eccentric hypertrophy)
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* Hyperkinetic left ventricle
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* May be able to visualise large defects
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* Spectral or colour flow Doppler can be used to interrogate the right ventricular side of the VSD and should demonstrate left-to-right flow
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* Velocity of blood flow accross the VSD can be measured, using Doppler, to assess the pressure gradient. High velocity flow is associated with small defects.
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* Mitral regurgitation is common
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* Aortic regurgitation can occur if the aortic valve prolapses into the VSD
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An Electrocardiograph (ECG) will show left sided enlargement (L-R shunt), right ventricular hypertrophy (R-L shunt), arrhythmias and a wide or notched Q wave showing abnormal septal depolarization.
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== Management ==
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== Treatment ==
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Treatment may be unnecessary, as the defect may close on its own. Treatment is also not necessary for small VSDs that are of no haemodynamic significance.
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Treatment may be unnecessary as the defect may close on its own (or is small enough not to cause any clinical signs). Severe cases will usually need medications; drugs to decrease volume through the shunt (arterial vasodilators for R-L shunt) and drugs to combat heart failure. Surgery may also be necessary in these cases to close the septal defect (open heart surgery rarely performed in veterinary patients) or to perform pulmonary artery banding (palliative surgical procedure to decrease left to right shunting).
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In severe cases, [[Heart Failure, Left-Sided|congestive heart failure]] should be appropriately managed. The principle palliative surgical procedure described is pulmonary artery anding, in order to protect the pulmonary vascular bed and therefore prevent the development of pulmonary hypertension. Transcatheter closure of VSDs using an Amplatzer device has also been described in a dog.  
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The use of vasodilators and the surgical procedures above are contraindicated with a right to left shunt.
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If significant right to left shunting  with resultant '''polycythaemia''' is present, occlusion of the VSD is contraindicated.  
    
== Prognosis ==
 
== Prognosis ==
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In mild to moderate cases the prognosis is excellent. In severe cases, the prognosis is guarded (L-R shunts) and poor (R-L shunts).
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In mild to moderate cases the prognosis is excellent. In severe cases, the prognosis is guarded to poor.  
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{{Learning
 
{{Learning
 
|flashcards = [[Cardiovascular Developmental Pathology Flashcards]]  
 
|flashcards = [[Cardiovascular Developmental Pathology Flashcards]]  
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== References ==
 
== References ==
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Merck &amp; Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial
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Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier.
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{{review}}
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{{OpenPages}}
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[[Category:Cardiovascular_System_-_Developmental_Pathology]] [[Category:Expert_Review]] [[Category:Cardiac_Diseases_-_Dog]] [[Category:Cardiac_Diseases_-_Cat]] [[Category:Cardiac_Diseases_-_Horse]] [[Category:Cardiac_Diseases_-_Cattle]] [[Category:Cardiac_Diseases_-_Pig]]
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[[Category:Cardiology Section]]
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Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier.
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Pasquini, C, Pasquini, S, Woods, P (2005) Guide to Equine Clinics Volume 1: Equine Medicine (Third edition), SUDZ Publishing.
       
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