Atrial septal defect overview: Difference between revisions
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==Pathophysiology== | ==Pathophysiology== | ||
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]]. | 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]]. | ||
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 | 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. | ||
==Causes== | ==Causes== | ||
Revision as of 17:09, 3 January 2013
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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] Assistant Editor(s)-In-Chief: Kristin Feeney, B.S. [4]
Overview
Atrial septal defects (ASD) refer to a group of congenital heart diseases that involve the inter-atrial septum. The inter-atrial septum is the tissue that separates the right and left atria from each other. This tissue prevents arterial and venous blood from mixing with each other. If there is a defect in this septum, a direct communication between the atria can occur, which allows shunting, resulting in mixing of arterial and venous blood. It is possible for blood to travel from the left side of the heart to the right side of the heart, or vice versa. Shunting can result in cyanosis. The excess flow to the right atrium and the right ventricle causes enlargement of these organs, and the increased flow through the pulmonary artery eventually causes pulmonary hypertension.
Anatomy
The embryological development of human fetal heart takes place as early as 4th week of intrauterine life. The normal septal development requires a proper alignment and fusion of the two interatrial septums i.e. septum primum and septum secundum. Failure to do so may lead to the development of atrial septal defects.
Classification
The normal septal development requires a proper alignment and fusion of the two interatrial septums i.e. septum primum and septum secundum. Failure to do so may lead to a patent fossa ovalis and the development of atrial septal defects (ASDs). Atrial septal defects are classified into various types based on their location and the nature of the embryological defect. The types of atrial septal defects that can occur are: ostium primum, ostium secundum, sinus venosus, common or single atrium and coronary sinus defects. Patent foramen ovale, commonly associated with atrial septal defects, is a sister condition involving communication between the two atria. Patent foramen ovale is not a true atrial septal defect as flap like tissue that functions usually like a one way valve is present in a PFO.
Pathophysiology
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.
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.
Causes
Often an ASD occurs sporadically. However, ASD has been associated with genetic disorders such as the Holt-Oram syndrome (heart-hand syndrome) , Down syndrome, Noonan syndrome,Treacher Collins syndrome, and the thrombocytopenia-absent radii (TAR) syndrome.
Epidemiology and Demographics
Ostium secundum ASD is the most common type of atrial septal defect. Atrial septal defect are common congenital heart defects and comprises approximately 7% of all the congenital heart disorders. [1]. ASD is associated with a slight 2:1 female preponderance.
Natural History, Complications and Prognosis
The natural history of atrial septal defect depends on the location, the size of the defect, the amount of shunting of blood and the presence of associated congenital anomalies. A small atrial septal defect may remain asymptomatic throughout life and/or may close spontaneously in infants. Patients with isolated atrial septal defects generally survive to adulthood. An ASD can also present in adulthood with the insidious development of symptoms. Complications like pulmonary hypertension, atrial fibrillation, right heart failure and stroke can develop if large sized defects are left uncorrected. The mortality rate associated with surgical repair is less than 1% for patients under the age of 45, who have no history of heart failure or pulmonary artery hypertension. Virtually all ASD patients develop symptoms by the age of 60. An ASD that is repaired early in life is associated with no reduction in life expectancy.
Pregnancy causes an increase in cardiac output and stroke volume. This can cause an increased left-to-right shunting of blood. Despite the increased workload on heart, females with isolated asymptomatic atrial septal defects tolerate the pregnancy well. Pregnant females with an atrial septal defect may have increased frequencies of some complications for instance arrhythmias, thromboembolism, and bleeding. Despite this, there are no studies suggesting that pregnancy requires different indications for closure in pregnant females with atrial septal defect compared to a non-pregnant female with atrial septal defect. The ACC/AHA guidelines, however, do dictate clear deviations in course of treatment in certain special circumstances. Pregnancy in patients with ASD and severe PAH (Eisenmenger syndrome) is not recommended owing to excessive maternal and fetal mortality and should be strongly discouraged.
Diagnosis
History and Symptoms
Atrial septal defect patients may present with symptoms that are due to left-to-right shunting of blood. Symptoms such as difficulty breathing, exercise intolerance, and fatigue may be seen.
Physical Examination
Volume overload of the right side of heart can lead to right heart failure that may present with symptoms of swelling of the extremities, difficulty breathing and signs such as hepatomegaly and an elevated jugular venous pulse. On cardiovascular examinations there is a fixed splitting of second heart sound. Also, a systolic ejection murmur that is attributed to the increased flow of blood through the pulmonic valve can be heard.
Electrocardiogram
The ECG findings may show a prolonged PR interval (first degree heart block). The prolongation of the PR interval is probably due to the enlargement of the atria that is common in ASD. Other findings include right bundle branch block (RBBB), right axis deviation, right ventricular hypertrophy (RVH), atrial fibrillation and atrial flutter.
Echocardiography
Echocardiography along with doppler ultrasound are the preferred imaging modalities to diagnose atrial septal defect. On transthoracic echocardiography, an atrial septal defect may be seen on color flow imaging as a jet of blood from the left atrium to the right atrium. Usually transesophageal echocardiography is a better tool for diagnosing atrial septal defects than transthoracic echo. Trials have demonstrated that transesophageal echocardiography is superior to transthoracic echocardiography in diagnosing sinus venosus ASD[2].
Treatment
Atrial septal defects can remain asymptomatic until the fourth decade of life. The treatment can involve either a medical or surgical approach. Surgical closure further could be divided into percutaneous repair or open heart surgery involving either suture or patch closure.
Medical Therapy
Medical therapy has a limited role in the definitive treatment of ASD. Medical therapy consists rate control of atrial fibrillation and anticoagulation to reduce the risk of embolization among patients with atrial fibrillation.
Interventional or Surgical Therapy
Percutaneous Closure
Percutaneous closure is commonly performed for ostium secundum ASDs. This procedure is still not FDA approved for the treatment of other types of atrial septal defects like sinus venosus ASD, coronary sinus ASD, or primum ASD. With appropriate patient selection, percutaneous closure of an ostium secundum ASD has been demonstrated to be as successful, safe and effective as surgical closure. Additionally, percutaneous closure has been associated with fewer complications and a reduced average length of hospital stay compared to surgical care.
Surgical Closure
Surgical closure is the most common treatment method for atrial septal defect patients and has been the gold standard for many years. It is still the most popular method for repair of defects like sinus venosus ASD, coronary sinus ASD, or primum ASD. However, surgery is contraindicated in patients with severe irreversible pulmonary artery hypertension, Eisenmenger's syndrome and no evidence of a left-to-right shunt.
References
- ↑ Feldt RH, Avasthey P, Yoshimasu F, Kurland LT, Titus JL (1971). "Incidence of congenital heart disease in children born to residents of Olmsted County, Minnesota, 1950-1969". Mayo Clin Proc. 46 (12): 794–9. PMID 5128021.
- ↑ Kronzon I, Tunick PA, Freedberg RS, Trehan N, Rosenzweig BP, Schwinger ME (1991). "Transesophageal echocardiography is superior to transthoracic echocardiography in the diagnosis of sinus venosus atrial septal defect". J Am Coll Cardiol. 17 (2): 537–42. PMID 1991912.