Atrial Septal Defect

Atrial Septal Defect

1. Atrial Septal Defect Dr. Sayeedur Rahman Khan Rumi [email protected] MD (Cardiology) Final Part Student NHFH&RI

2. Definition An atrial septal defect is a communication between the atria resulting from a deficiency of tissue in the septum, as distinguished from a patent foramen ovale , where septum primum , though preserved, is not adherent to the superior limbic band of septum secundum .

3. Prevalence Atrial septal defect (ostium secundum defect) occurs as an isolated anomaly in 5% to 10% of all congenital heart defects (CHDs). Male:Female = 1:2 About 30% to 50% of children with CHDs have an ASD as part of the cardiac defect. Excluding bicuspid aortic valve and mitral valve prolapse, ASD is the most common form of congenital heart defect found among adults and is the most common acyanotic shunt lesion in adults as well.

4. EMBRYOLOGY

5. The primitive atrium is first partitioned into right and left atria by growth of the septum primum —a thin, crescent-shaped membrane that grows from the roof of the primitive atrium toward the endocardial cushions. Foramen primum , composed of the free edge of the septum primum and the endocardial cushions.

6. Fenestrations develop in the septum primum that coalesce to form the ostium secundum . As the septum primum then fuses with the endocardial cushions, the ostium secundum maintains a right-to-left atrial flow that is important in the fetal circulation. Failure of this fusion results in the development of a primum ASD.

7. A second septum, the septum secundum , then forms to the right of the septum primum , growing toward the endocardial cushions and usually closing the ostium secundum . Failure to close the ostium secundum results in the formation of a secundum ASD.

8. ANATOMY When viewed from its right aspect, the atrial septum is composed of interatrial and atrioventricular regions. The interatrial portion is characterized by the fossa ovalis , which is the anatomic hallmark of a morphologic right atrium. When viewed from the left atrium, the atrial septum is entirely interatrial because the atrioventricular component lies below the mitral annuls between the left ventricle and right atrium.

9. Anatomic Types Ostium secundum defects or secundum ASD Ostium primum defects or primum ASD Sinoseptal defects SVC type IVC type Coronary sinus ASD

10. Ostium secundum defects or secundum ASDs The most common type, 70% to 75% of ASDs. Location: in the midportion of the atrial septum, within or including the fossa ovalis . Defects result from a deficient septum primum or an abnormally large foramen secundum . Two times more common in female patients. Association: Mitral valve prolapse and other forms of congenital heart disease. It may also be associated with rheumatic mitral stenosis (i.e., Lutembacher syndrome).

11. Ostium primum defects or primum ASDs 15% to 20% of ASDs and are part of the spectrum of atrioventricular (AV) septal defects (also known as AV canal defects or endocardial cushion defects). Location: These defects occur in the inferior–anterior portion of the atrial septum. Association: Cleft in the anterior leaflet of the mitral valve, leading to varying degrees of mitral regurgitation. In their complete form, they include a large ventricular septal defect and a common AV valve. Most common ASD type associated with Down’s syndrome.

12. Sinoseptal defects Constitute the remaining 5% to 10% of septal defects. These lesions involve the portion of the atrial wall derived from the sinus venosus (i.e., there is no direct communication between the right and left atria) Location: Sinus venosus defects are typically at the orifice of the superior vena cava (SVC) at the junction of the right atrium or, less frequently, in the region of the inferior vena cava (IVC). Association: with partial anomalous pulmonary venous drainage of the right pulmonary veins

13. Abnormal Physiology With moderate to large defects, no resistance to blood flow across the defect is present, resulting in equalization of pressure between the 2 atria. A left-to-right shunt of blood occurs because : the right atrium is more distensible than the left, the tricuspid valve is normally more capacious than the mitral valve, and the thin-walled, compliant right ventricular chamber accommodates a larger volume of blood at the same filling pressure than does the left ventricle.

14. Natural History In patients with an ASD smaller than 3 mm in size diagnosed before 3 months of age, spontaneous closure occurs in 100% of patients at 1½ years of age. Spontaneous closure occurs more than 80% of the time in patients with defects between 3 and 8 mm before 1½ years of age. An ASD with a diameter larger than 8 mm rarely closes spontaneously. Spontaneous closure is not likely to occur after 4 years of age Most children with an ASD remain active and asymptomatic. Rarely, congestive heart failure (CHF) can develop in infancy.

15. If a large defect is untreated, CHF and pulmonary hypertension begin to develop in adults who are in their 20s and 30s, and it becomes common after 40 years of age. With or without surgery, atrial arrhythmias (flutter or fibrillation) may occur in adults. The incidence of atrial arrhythmias increases to as high as 13% in patients older than 40 years of age. Infective endocarditis does not occur in patients with isolated ASDs. Cerebrovascular accident, resulting from paradoxical embolization through an ASD, is a rare complication.

16. CLINICAL MANIFESTATIONS

17. History Infants and children with ASDs are usually asymptomatic Exercise intolerance with fatigue and dyspnea may occur Frequent pulmonary infections Palpitations Occasionally, a paradoxical embolus causing a stroke or transient ischemic attack (TIA) is the first clue to an ASD.

18. Physical Examination A relatively slender body build is typical. In the older child, prominence of the left anterior chest is common, and a hyperdynamic right ventricular systolic lift can be felt. A widely split and fixed S2 and a grade 2 to 3 of 6 systolic ejection murmur are characteristic findings of ASD in older infants and children.

19. If a shunt fraction ( Qp /Qs) of 2.5:1, there may be a diastolic murmur secondary to increased flow across the tricuspid valve. A loud P2 component of the second heart sound indicates the presence of pulmonary hypertension, which can affect up to 20% of patients; if cyanosis is present, this generally suggests advanced pulmonary hypertension with reversal of shunt flow ( Eisenmenger syndrome). Classic auscultatory findings of ASD are not present unless the shunt is reasonably large. The typical auscultatory findings may be absent in infants and toddlers, even in those with a large defect because the RV is poorly compliant.

20. Investigations

21. ECG Secundum ASD: RSR’ pattern in lead V1 QRS duration < 0.11 seconds (incomplete right bundle branch block) Right-axis deviation RV hypertrophy First-degree AV block (20%) RA enlargement (about 50%) with a prominent P wave in lead II Primum ASD: RSR’ pattern in lead V1 Left-axis deviation First-degree AV block, classically seen with right bundle branch block and left anterior fascicular block

22. Chest radiography Cardiomegaly with enlargement of the RA and right ventricle (RV) may be present. A prominent pulmonary artery (PA) segment and increased pulmonary vascular markings are seen when the shunt is significant.

23. CXR P/A & Lat views from a 10-year-old child with atrial septal defect. The heart is mildly enlarged with involvement of the RA (best seen in the P/A view) and the RV (best seen in the lateral view with obliteration of the retrosternal space). Pulmonary vascularity is increased, and the main pulmonary artery segment is slightly prominent.

24. Echocardiography A two-dimensional echocardiographic study is diagnostic. The study shows the position as well as the size of the defect, which can best be seen in the subcostal four chamber view. The SVC type of sinus venosus defect shows a defect in the posterosuperior atrial septum. In secundum ASD, a dropout can be seen in the midatrial septum. The primum type shows a defect in the lower atrial septum.

25. Indirect signs of a significant left-to-right atrial shunt include RV enlargement and RA enlargement, as well as dilated PA, which often accompanies an increased flow velocity across the pulmonary valve. Pulsed Doppler examination reveals a characteristic flow pattern with the maximum left-to-right shunt occurring in diastole. Color-flow mapping enhances the evaluation of the hemodynamic status of the ASD.

26. M-mode echocardiography may show increased RV dimension and paradoxical motion of the interventricular septum, which are signs of RV volume overload.

27. In older children and adolescents, especially in those with overweight, adequate imaging of the atrial septum may not be possible with the ordinary transthoracic echocardiographic study. Transesophageal echocardiography (TEE) may be used as an alternative.

28. Cardiac catheterization Typically not required for diagnostic purposes except to assess pulmonary pressures and resistance or as part of a planned transcatheter device closure. Oximetry measurements: Oximetry samples obtained during catheterization demonstrate a step-up within the right atrium due to shunting across the defect. Hemodynamic assessment: An important assessment is comparison of pulmonary artery pressure with systemic pressure and measurement of pulmonary vascular resistance . If pulmonary pressures are elevated, the response to oxygen or other vasodilators should be assessed. Alternatively, the ASD can be balloon occluded with assessment of hemodynamics to ensure that closure is safe.

29. Cardiac MRI Can be helpful, as it can provide additional information beyond echocardiography.

30. Management

31. Medical Exercise restriction is unnecessary. In infants with CHF, medical management (with a diuretic) is recommended. Rhythm disturbances such as atrial fibrillation require attention with respect to rate control and anticoagulation. Endocarditis antibiotic prophylaxis during dental procedures is not required in the setting of an isolated ASD before surgery, but it is warranted for 6 months after surgical or device closure (AHA/ACC class IIa ).

32. Surgical or transcatheter therapy Timing: For asymptomatic infants and children, closure is recommended at approximately 5 years of age Indications: If there is evidence of hemodynamically significant shunt ( Qp /Qs ≥ 1.5:1), evidence of right heart dilation, evidence of probable paradoxical embolism associated symptoms.

33. Contraindications: Defect is too small to be hemodynamically significant Pulmonary vascular resistance more than one-half of the systemic vascular resistance or An indexed pulmonary vascular resistance > 7 Wood units/m2 Severe LV dysfunction, where ASD is acting as a “pop-off” valve for the left ventricle In most cases where ASD is diagnosed in pregnancy, closure can be postponed until 6 months after delivery

34. Transcatheter closure Any patient with an isolated secundum ASD may be suitable for transcatheter closure. Transcatheter device closure of secundum type ASD was first performed in 1976 by Mills and King In the United States, currently only the Amplatzer septal occluder and Helex septal occluder are approved for secundum ASD closure. The use of the closure device may be indicated to close a secundum ASD measuring ≥ 5 mm in diameter (but less than 32 mm for Amplatzer device and less than 18 mm for Helex device)

35. There must be enough rim (4 mm) of septal tissue around the defect for appropriate placement of the device. The defect must be located centrally with adequate room for the device to be positioned, without interference of other intracardiac structures such as the AV valves, coronary sinus, or pulmonary veins.

36. The Amplatzer Septal Occluder (AGA Medical Corporation, Golden Valley, MN) approved in December 2001. The Amplatzer device consists of two disks made of Nitinol wire mesh filled with polyester fabric and separated by a narrower waist, which is appropriately fitted by balloon sizing

37. The Helex Septal Occluder (WL Gore & Associates, Flagstaff, AZ) approved in August 2006. The Helex device is also disklike and consists of expanded polytetrafluoroethylene ( ePTFE ) patch material supported by a single Nitinol wire frame.

38. Complications Complications are extremely rare (major complication rate of 1.6%, including device embolism with surgical removal). The overall risk of the procedure is 7.2% Probably the most feared complication with the Amplatzer device (but not with the Helex device) is early or late erosion of the device into the aortic root, with subsequent pericardial tamponade and rare death. It may be related to the oversizing of devices and deficiency of the anterosuperior (or retroaortic ) rim. Release of nickel from the device (with peak at 1 month after implant) is a rare cause of significant allergic reaction

39. Postdevice Closure Follow-up After closure, antiplatelet therapy, frequently aspirin and clopidogrel , is prescribed for a minimum of 6 months, after which time the device is generally believed to have endothelialized . Postprocedure echocardiographic studies check for a residual atrial shunt and unobstructed flow of pulmonary veins, coronary sinus, and venae cavae , and proper function of the mitral and tricuspid valves. If 1-month and 1-year follow-up echocardiographic findings are normal then yearly or biennial follow-up will suffice.

40. Surgical closure Indications: Surgical closure is indicated only when device closure is not considered appropriate. It is the treatment of choice for ostium primum and sinus venosus defects. Patients with secundum ASDs and anatomy that is not amenable to percutaneous closure: ASD diameter > 35 mm inadequate septal rims to permit device deployment close proximity to AV valves, coronary sinus, or venae cavae are also candidates for open surgical closure.

41. Timing Surgery is usually delayed until 2 to 4 years of age because the possibility of spontaneous closure exists. If CHF does not respond to medical management, surgery is performed during infancy (if device closure is considered inappropriate)

42. Procedure: Depending on the defect size and location, the secundum ASD can be closed by primary suture or, if needed, by the use of an glutaraldehyde treated autologous pericardial or synthetic patch.

43. Ostium primum defects require patch closure as well as repair of the cleft mitral valve.

44. Repair of sinus venosus defects is technically more challenging, as the pulmonary veins often have anomalous drainage and require rerouting.

45. Preoperative risk factors: Older age at operation, Presence of atrial fibrillation, and Elevated pulmonary pressure and resistance. Mortality: < 0.5% Complications: Cerebrovascular accident Postoperative arrhythmias may develop in the immediate postoperative period. Postpericardiotomy syndrome

46. Postoperative Follow-up Cardiomegaly on chest radiographs and enlarged RV dimension on echo as well as the wide splitting of the S2 may persist for 1 or 2 years after surgery. The ECG typically demonstrates RBBB (or RV conduction disturbance). Atrial or nodal arrhythmias occur in 7% to 20% of postoperative patients. Occasionally, sick sinus syndrome, which occurs especially after the repair of a sinus venosus defect, may require antiarrhythmic drugs, pacemaker therapy, or both.

47. Thank you