Atrial Septal Defect

Atrial septal defect (ASD) is a congenital malformation characterized by a communication between the atrial chambers of the heart.

This disease is associated with congenital processes.

Presentation

History

ASDs are usually asymptomatic in infancy and childhood. In most cases, the symptoms manifest by the third decade of life. Due to paucity of symptoms, most times ASDs go undetected in childhood. Most cases of ASD, even moderate to large ASDs, do not manifest symptoms during childhood. Some cases of ASD may show common symptoms like fatigue, dyspnoea on exertion, exercise intolerance and frequent respiratory infections during childhood. In childhood, an accidental finding of a heart murmur on routine examination or an abnormal finding on chest radiograph or echocardiogram (ECG) may help to diagnose ASD.

Signs and symptoms

The signs and symptoms are dependent on various other factors like pulmonary arterial hypertension, atrial arrhythmias and other ASD complications. As age progresses, the heart musculature too ages leading to manifestation of signs and symptoms. In adults, common symptoms include shortness of breath, exhaustion, palpitations, atrial arrhythmia, syncope and stroke.

Complications

These include infective endocarditis, hypertrophy of the right atrium and the right ventricle, pulmonary arterial hypertension, paradoxical embolization, stroke, cardiac failure especially right side failure, arrhythmias, palpitations secondary to supra-ventricular arrhythmias, or recurrent respiratory infections. In rare cases, it may lead to reversal of the shunting that is from right to left (Eisenmenger syndrome).

Workup

On physical examination, there is presence of right ventricular pulsation due to higher diastolic filling and increased stroke volume. The pulmonary artery is dilated and hence, its pulsations are palpable. S2 is widely split and fixed in most cases of ASD.

Moderate to large, left to right shunt produces a systolic ejection murmur in the second inter-costal space at the upper left sternal border. Increased flow across the tricuspid valve causes a mid-diastolic rumbling murmur in cases with large left to right shunt.

An apical systolic murmur of mitral regurgitation may be present in cases with primum ASD. In cases of severe pulmonary arterial hypertension, atrial shunt reversal (Eisenmenger syndrome) may occur which leads to cyanosis and clubbing.

Electrocardiography

In ostium secundum ASD, the electrocardiogram shows right axis deviation and right bundle branch block. In ostium primum ASD, it shows left axis deviation and right bundle branch block. In sinus venosus ASD, it shows left axis deviation and a negative P wave in lead III.

Imaging

The chest X-ray shows a dilated pulmonary artery, prominent pulmonary vascular markings, and enlarged right atrial and ventricular chambers in patients with significant left to right shunting.

Doppler echocardiography and contrast echocardiography provide details of the defect. It has been found that Doppler echocardiography may be inaccurate often in estimating the pulmonary artery pressure and cardiac output while evaluating patients with pulmonary hypertension as sequelae to ASD [4]. Transthoracic echocardiography (TTE) is a non-invasive imaging procedure for ostium primum and ostium secundum ASDs. For sinus venosus, the imaging procedure of choice is transesophageal echocardiography (TEE).

Use of non-invasive tools like echocardiography, right heart catheterization (RHC) and tissue Doppler imaging (TDI) for detecting pulmonary hypertension and right heart dysfunction are absolutely essential [5]. MRI and CT can be useful in the evaluation of patients with ASDs. Cardiac catheterization will aid in the diagnosis when the non-invasive techniques are not conclusive of the diagnosis [6].

Treatment

Small ASDs may close spontaneously. Larger defects require surgical intervention. Medical therapy can be used to treat the symptoms of ASD, but surgical intervention is a must for the closure of the defect. The operation for closure of Sinus venosus ASD has low mortality as well as low morbidity with improvement occurring irrespective of the age at which the surgery is performed [7].

Transcatheter closure of ASD secundum defect using Occlutech Figull-N occlude is safer and more efficient in severely symptomatic patients less than 2 years of age [8].

Prognosis

ASDs with small defects may close spontaneously in some children. Larger defects require surgical intervention. Medical therapy can be used to treat the symptoms of ASD, but surgical intervention is a must for the closure of the defect. The operation for closure of Sinus venosus ASD has low mortality as well as low morbidity with improvement occurring irrespective of the age at which the surgery is performed [7].

Transcatheter closure of ASD secundum defect using Occlutech Figulla-N occlude is safer and more efficient in severely symptomatic patients less than 2 years of age [8].

If left untreated, there is a high risk of developing atrial arrhythmias and morbidity at later ages, making closure of defects with significant hemodynamic changes a necessary choice [9].

Chance of survival of patients with untreated ASD beyond third or fourth decade of their life is less than 50%. Given risks associated with surgery, it is advisable to repair the defect as early as possible to avert hemodynamic sequelae [10].

Etiology

ASDs mostly occur due to genetic mutations. Along with a genetic predisposition, certain maternal environmental factors (for example alcohol, drugs or metabolic diseases) can be responsible for the defects.

When problems occur in the development of the heart and its structures, it can result in ASDs. The different types of ASDs are formed due to incomplete fusion of certain parts of heart musculature as seen in the four type explained above.

Epidemiology

ASDs account for 10% of all congenital heart diseases. Incidence of ostium secundum ASDs is 75%, of ostium primum is 15-20% & of sinus venosus is 5-10%. Coronary ASDs are rare.

The incidence of ASDs in females is twice as those in males.

Sex distribution
Age distribution

Pathophysiology

The extent of the left to right atrial shunting will depend on the size of the defect, the relative ventricular compliance, vascular resistance and accompanying congenital defects. When the ASD is small, the shunting is not significant.

In cases of larger defects, the extent of the shunting is significant and can lead to volume overload of the right atria and right ventricle. This raises the filling pressure of the right side of the heart causing the right ventricle to pump out more blood as compared to the left ventricle.

The overloading of the right side of the heart will cause an overload of the entire pulmonary circulation leading to pulmonary hypertension eventually. This will further force the right ventricle to generate higher pressures to overcome the pulmonary hypertension which may even lead to right ventricular failure.

In cases where ASD is left untreated, the increased pressure on the right side of the heart causes reversal of the shunt i.e. right to left shunting (Eisenmenger syndrome). This will cause mixing of the oxygenated and non-oxygenated blood in the heart. Once in circulation, this inevitably leads to cyanosis.

Prevention

There are no guidelines for prevention of ASD.

Summary

Atrial septal defect (ASD) is a congenital defect in the septum between the two atria of the heart. ASD results in pulmonary venous return going directly to the right atrium from the left atrium [1] [2] [3]. The significance of the complications of ASD will depend on the size of the defect and shunt. The presence of any associated anomalies will lead to further complications.

There are four types of ASD, depending on where these defects are found. The most common is Ostium Secundum defect which occurs in the middle of the atrial septum. It can be associated with partial anomalous pulmonary venous return. The second type of ASD is Ostium Primum defect which is a form of atrioventricular septal defect with shunting at atrial level. It can be associated with mitral regurgitation. The least common type of ASD is Sinus Venosus defect which occurs in the superior aspect of the atrial septum involving the superior vena cava. A variation of this involves the inferior vena cava. The rarest type of ASD is Coronary sinus defect. It involves direct communication of the coronary sinus and the left atrium.

Patient Information

Atrial septal defect (ASD) is a heart defect present since birth in which there is a hole in the wall that separates the upper heart chambers (atria) from the ventricles/other atrium.

The septal defects are located in different parts of the atrial septum and they can be of different sizes. A "shunt" is the presence of a net flow of blood through the defect, either from left to right or right to left.

The size of the defect, size of the shunt, and associated anomalies, can lead to a range of diseases from no significant cardiac complication to right-sided volume overload, pulmonary arterial hypertension or even atrial arrhythmias.

ASDs are usually asymptomatic in infancy and childhood. In most cases the symptoms appear by the third decade of life. Most cases of ASD, even moderate to large ASDs do not manifest symptoms during childhood. Hence, ASDs go undetected in childhood due to lack of symptoms.

Cardiac murmurs can be detected on auscultation in some cases which may be a clue that a child has an ASD. Common symptoms include dyspnoea, easy fatigue, palpitations, exercise intolerance and recurrent respiratory infections. The significance of the complications will depend on the size of the defect and shunt. The presence of any associated anomalies will lead to further complications.

ASDs once diagnosed can be treated successfully with few or no complications. Transthoracic echocardiography and transesophageal echocardiography are common non-invasive imaging techniques used to diagnose ASDs. Cardiac catheterization is the invasive technique used.

Small ASDs may close naturally after birth. If the ASD is left untreated it may lead to arrhythmias, pulmonary arterial hypertension, reversal of shunting and heart failure. Larger defects are treated through surgery. Medical therapy can be used to treat the symptoms of ASD, but surgical intervention is a must for the closure of the defect. 

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References

  1. Braunwald E. Atrial septal defect. In: Braunwald E, ed. Heart Disease: A Text of Cardiovascular Medicine. 1992. 4th ed. Philadelphia, Pa: WB Saunders; 1992:906-8
  2. Goldman L, Braunwald E. Primary Cardiology. Philadelphia, Pa: WB Saunders; 1998:394-411. 
  3. Child J, Friedman W. Harrison’s Principles of Internal Medicine. 16th ed. McGraw Hill. Chapter 218. Congenital Heart Disease in the adult.
  4. Fisher MR, Forfia PR et al. Accuracy of Doppler Echocardiography in the Hemodynamic assessment of Pulmonary Hypertension. Am J Respir Crit Care Med. 2009 April 1; 179(7): 615–621.
  5. Constantinescu T, Magda SL, et al. New Echocardiographic Tehniques in Pulmonary Arterial Hypertension vs. Right Heart Catheterization – A Pilot Study. Maedica (Buchar). 2013 June; 8(2): 116–123.
  6. Davidson CJ, Bonow RO. In: Bonow RO, Mann DL, Zipes DP, Libby P, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 9th ed. Saunders; Philadelphia: 2011. Chapter 20. Cardiac catheterization.
  7. Jost CH, Connolly HM, Danielson GK, et al. Sinus venosus atrial septal defect: long-term postoperative outcome for 115 patients. Circulation. Sep 27 2005; 112(13):1953-8.
  8. Ammar RI, Hegazy RA. Transcatheter closure of secundum ASD using Occlutech Figulla-N device in symptomatic children younger than 2 years of age. J Invasive Cardiol. 2013 Feb; 25(2):76-9.
  9. Feltes TF, Bacha E, Beekman RH 3rd, et al. Indications for cardiac catheterization and intervention in pediatric cardiac disease: a scientific statement from the American Heart Association. American Heart Association Congenital Cardiac Defects Committee of the Council on Cardiovascular Disease in the Young; Council on Clinical Cardiology; Council on Cardiovascular Radiology and Intervention. Circulation. 2011; 123(22):2607-2652.
  10. Lakhdhar R, Drissa M Drisa H. Natural history of atrial septal defect in the sixth decade: study of 5 cases. Tunis Med. 2013 Apr; 91(4):243-7.

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