Atrial Septal Defect

Atrial septal defect

Dr. Md. Rezwanul HoqueMBBS, MS, FCPS, FRCSG, FRCSEdAssociate ProfessorDepartment of cardiac surgeryBSMMU, Dhaka, Bangladesh

IntroductionAtrial septal defect (ASD) is a form of congenital heart defect that enables blood flow between the left and right atria via the interatrial septum.Depending on the size of the defect, size of the shunt, and associated anomalies, this can result in a spectrum of disease from no significant cardiac sequelae to right-sided volume overload, pulmonary arterial hypertension, and even atrial arrhythmias.The 3 major types of atrial septal defect (ASD) account for 10% of all congenital heart disease and as much as 20-40% of congenital heart disease presenting in adulthood. More than 60% of healthy full-term infants have a PFO.A PFO is present in one third of people under 29 years of age, one fourth of those 30 to 79, and one fifth of persons older than 80 .Secundum ASD occurs in 1 in 1500 live births, accounting for 10% to 15% of congenital heart defects in children and 20% to 40% of defects discovered in adults. Women are affected twice as often as men. A significant number of ASDs close spontaneously within the first few years of life, but spontaneous closure after age 3 to 4 is rare and one fifth of persons older than 80.

Sellke: Sabiston & Spencer Surgery of the Chest, 7th ed., Copyright © 2005 Saunders

Natural history

Although life expectancy is not normal for patients with atrial septal defect (ASD), patients generally survive into adulthood without surgical or percutaneous intervention, and many patients live to advanced age.Natural survival beyond age 40-50 years is less than 50%, and the attrition rate after 40 years of age is about 6% per year.Advanced pulmonary hypertension seldom occurs before the third decade.Late complications are stroke and atrial fibrillation.

Atrial Partitioning

By the time the heart tube has formed the bulboventricular loop , the two primitive right and left atria have fused to form a common atrium. Note that it now lies cranial to the primitive ventricle and dorsal to the bulbus cordis. The truncus arteriosus lies on the roof of the common atium causing a depression and indicates where septation of the atrium will occur. AS = Aortic sac BC = Bulbus cordis CC = Conus cordis LA = Left atrium LV = Left ventricle RA = Right atrium SV = Sinus venosus TA = Truncus arteriosus

Atrial Partitioning- contd

The partitioning of the atrium begins with the appearance of septum primum at about the 28th day. This is a crest of tissue that grows from the dorsal wall of the atrium towards the endocardial cushions - - the ostium (opening) formed by the free edge of septum primum is the ostium primum.


Before the septum primum fuses with the endocardial cushions, perforations appear in the upper portion of the septum primum. These perforations will coelasce to form the ostium secundum. SAO = Sinoatrial oriface SS = Septum spurium S1 = Septum primum Perf = Perforations O1 = Ostium secundum EC = Endocardial cushions


Unlike the septum primum, septum secundum does not fuse with the endocardial cushions. Its free edge forms the foramen ovale. The left venous valve and the septum spurium, located on the dorsal wall of the right atrium, fuse with the septum secundum as it grows. EC = Endocardial cushions LVV = Left venous valve O1 = Ostium secundum SS = Septum spurium S1 = Septum primum S2 = Septum secundum


At the end of the seventh week the human heart has reached its final stage of development. Because the fetus does not use its lungs, most of the blood is diverted to the systemic circulation. This is accomplished by a right to left shunting of blood that occurs between the two atria. The foramen ovale and the septum primum control this right and left communication. The septum primum acts as a valve over the foramen ovale. At birth the child will use its lungs for the first time and consequently more blood will flow into the pulmonary circulation. The pressure increase in the left atrium (where the pulmonary veins empty) will force septum primum to be pushed up against septum secundum. Shortly thereafter the two septa fuse to form a common atrial septum. O1 = Ostium primum S1 = Septum primum FO = Foramen ovale S2 = Septum secundum

Types of ASD,


Types of ASD Patent foramen ovale (PFO)

Denotes a failure of the septum primum and septum secundum to fuse. A failure of fusion results in either a valve-competent “probe patent” PFO or valvular incompetence with or without an aneurysm of the septum primum component .

Secundum defect (75%)Lies within the boundaries of the fossa ovalis, widely ranging in morphology from the slit like PFO at the superior aspect of the fossa, to defects involving part or all of the remainder of the fossa with a single or multiply fenestrated communication. Form as a result of underdevelopment of the septum secundum or an abnormal pattern of septum primum resorption .

Septum primum defect(15%) Is a persistence of the ostium primum, and is most commonly associated with an atrioventricular septal defect .

Types of ASD cont. Sinus venosus interatrial defect (8-10%)

Always associated with a partial anomalous pulmonary venous connection. The more common superior variant is an interatrial communication lying posterior and superior to the true atrial septum, and the superior vena cava (SVC) overrides the defect. The right upper pulmonary veins, usually two or more, drain to the right atrium at the superior cavoatrial junction or enter the SVC directly .The less common inferior sinus venosus defect is a communication inferior and posterior to the fossa ovalis with the right pulmonary veins entering the right atrium near the inferior cavoatrial junction. A PFO or secundum ASD may additionally be present.

Embryologically, the right wall of the common pulmonary vein contributes to the posterior part of the atrial septum. A deficiency in the common wall between the sinus venosus in the right atrium and the common pulmonary vein results in the development of the sinus venosus defect, associating right pulmonary veins with the right atrium.

Types of ASD cont. Coronary sinus type ASD

The uncommon coronary sinus–type ASD results from a complete or partial unroofing of the coronary sinus along its course through the floor of the left atrium. A communication of the coronary sinus with the left atrium results in an interatrial communication at the level of the coronary sinus ostium, the size of which is determined by the extent of unroofing and the size of the ostium . The diagnosis can be made by injecting contrast agent into left upper extremity; coronary sinus opacification precedes right atrial opacification.

Types ASD cont.

Common (or single) atrium Is a failure of development of the embryologic components that contribute to the atrial septal complex. It is frequently associated with heterotaxy syndrome.

Mixed atrial septal defectThe inter atrial septum can be divided in to 5 septal zones. If the defect involves 2 or more of the 5 septal zones, then the defect is termed a mixed atrial septal defect.

http://en.wikipedia.org/wiki/Atrial_septal_defect


Schematic drawing showing the location of different types of ASD, the view is into an opened right atrium. HV: right ventricle; VCS: superior caval vein; VCI: inferior caval vein; 1: upper sinus venosus defect; 2: lower sinus venosus defect; 3: secundum defect; 4: defect involving coronary sinus; 5; primum defect.



Associated lesionVSD, PDA, PS,AS, MS, Coarctation of aorta.Mitral stenosis( rheumatic/ nonrheumatic) with pulmonary artery dilation in association with ASD, is known as Lutembacher’s syndrome. A cleft anterior mitral leaflet, typically associated with a primum ASD, uncommonly with secundum ASD. Mitral regurgitation is found in 2.5% to 10% of adults with a large ASD. Mitral prolapse may be present in 20% of cases, with a distribution increasing with age.Mitral or Tricuspid valve prolapse –usually functional, recovers after closure of ASD.


GeneticsAtrial septal defect (ASD) may occur on a familial basis. Holt-Oram syndrome characterized by an autosomal dominant pattern of inheritance and deformities of the upper limbs (most often, absent or hypoplastic radii) has been attributed to a single gene defect in TBX5. The penetrance is nearly 100% for Holt-Oram syndrome. Approximately 40% of Holt-Oram cases are due to new mutations.Ellis van Creveld syndrome is an autosomal recessive disorder associated with skeletal dysplasia characterized by short limbs, short ribs, postaxial polydactyly, dysplastic nails and teeth, and a common atrium, occurring in 60% of affected individuals.Mutations in the cardiac transcription factor NKX2.5 have been attributed to the syndrome familial ASD associated with progressive atrioventricular block. This syndrome is an autosomal dominant trait with a high degree of penetrance but no associated skeletal abnormalities.

http://emedicine.medscape.com/article/162914-overview#a0102

http://emedicine.medscape.com/article/162914-overview

left to right shuntIn newborn and infant, pulmonary resistance is high, left and right ventricular compliances are similar, and net shunting through an ASD is typically slight. The magnitude of the left-to-right shunt across the ASD depends on the defect size, the relative compliance of the ventricles, and the relative resistance in both the pulmonary and systemic circulation. As the left ventricle matures postnatally, it becomes thicker and less compliant in diastole than the right and accounts for higher left atrial pressure than right. Shunting across the interatrial septum is usually left-to-right and occurs predominantly in late ventricular systole and early diastole. A transient and small right-to-left shunt can occur, especially during respiratory periods of decreasing intrathoracic pressure, even in the absence of pulmonary arterial hypertension.The functional loss in the left and right ventricles is normalized 6 months following ASD closure in the child and young adult.

Pulmonary hypertensionPulmonary hypertension associated with an isolated ASD is rare in childhood, though 35% to 50% of patients with unrepaired ASD.One third demonstrated an elevation in PVR before 20 years of age, one third between 20 and 40, and the remainder after 40 years of age have elevated pulmonary resistance by age 40. The chronic significant left-to-right shunt can alter the pulmonary vascular resistance leading to pulmonary arterial hypertension, even reversal of shunt and Eisenmenger syndrome. Because of an increase in plasma volume during pregnancy, shunt volume can increase, leading to symptoms. Pulmonary artery pressure usually remains normal.

Clinical presentation

Great majority of ASDs are asymptomaticCommon presenting symptoms include dyspnea, easy fatigability, palpitations, sustained atrial arrhythmia, syncope, stroke, and/or heart failure (less common<40 years).SOBE, Recurrent respiratory infection , features of PHT, Eisenmenger syndrome. Mitral valve insufficiency leads to further increase in left atrial pressure and a higher degree of left-to-right shunt.

Clinical deterioration

Several mechanisms:First, an age-related decrease in left ventricular compliance augments the left-to-right shunt.Second, atrial arrhythmias, especially atrial fibrillation, but also atrial flutter or paroxysmal atrial tachycardia, increase in frequency after the fourth decade and can precipitate right ventricular failure.Third, most symptomatic adults older than 40 years have mild-to-moderate pulmonary arterial hypertension in the presence of a persistent large left-to-right shunt; therefore, the aging right ventricle is burdened by both pressure and volume overload.



Physical findingHyperdynamic right ventricular impulse due to increased diastolic filling and large stroke volume.Palpable pulsation of the pulmonary artery and an ejection click due to dilated PA.S1 is typically split, and the second component may be increased in intensity, reflecting forceful right ventricular contraction and delayed closure of the tricuspid leaflets.S2 is often widely split and fixed because of reduced respiratory variation due to delayed pulmonic valve closure (seen only if pulmonary artery pressure is normal and pulmonary vascular resistance is low). This characteristic abnormality is found in almost all patients with large left-to-right shunts.



Physical finding cont.Blood flow across the ASD does not cause a murmur at the site of the shunt because no substantial pressure gradient exists between the atria. However, ASD with moderate-to-large left-to-right shunts result in increased right ventricular stroke volume across the pulmonary outflow tract creating a crescendo-decrescendo systolic ejection murmur. This murmur is heard in the second intercostal space at the upper left sternal border. Patients with large left-to-right shunts often have a rumbling middiastolic murmur at the lower left sternal border because of increased flow across the tricuspid valve.Auscultatory findings of the ASD may resemble those of mild valvular or infundibular pulmonic stenosis and idiopathic dilatation of the pulmonary artery. These disorders all manifest as a systolic ejection murmur, but they differ from the ASD by movement of the S2 with respiration, a pulmonary ejection click, or the absence of a tricuspid flow murmur.



Physical finding cont.In patients with an ostium primum defect and an associated cleft of the mitral valve, an apical systolic regurgitant murmur of mitral regurgitation may be present.In patients who develop pulmonary arterial hypertension and right ventricular hypertrophy, a right ventricular S4 may be present. In such cases, the midsystolic pulmonic murmur is softer and shorter, the tricuspid flow murmur is not present, the splitting of S2 is narrowed with accentuated pulmonic component, and murmur of pulmonic regurgitation may become apparent.ASD is an acyanotic lesion. Thus, the patient should be normally saturated. In the rare case of severe pulmonary arterial hypertension, atrial shunt reversal (Eisenmenger syndrome) may occur, leading to cyanosis and clubbing.





Laboratory Studies

Routine laboratory studies should be performed in patients undergoing intervention for ASD:Complete blood countType and screenMetabolic profile or chemistryCoagulation studies (prothrombin time [PT] and activated partial thromboplastin time [aPTT])




Chest radiography

Cardiomegaly because of dilatation of the right atrium and right ventricular chamber.Pulmonary artery is prominent, and pulmonary vascular markings are increased in the lung fields.Left atrial enlargement is rare only if clinically significant mitral regurgitation. Proximal dilatation of the superior vena cava can be seen in sinus venosus defect.





CXR-ASD

Electrocardiography ASD secundum- normal sinus rhythm, right-axis deviation, and an rSR' pattern in V1, an interventricular conduction delay or right bundle branch block (which represents delayed posterobasal activation of the ventricular septum and enlargement of the right ventricular outflow tract).ASD primum- Left-axis deviation and an rSR' pattern in V1, an interventricular conduction delay or right bundle branch block.Sinus venosus ASD- Left-axis deviation and negative P wave in lead III.A prolonged P-R interval can be seen in familial ASD or ostium primum defect.





ASD 20- ECG

EchocardiographyTypes of ASDs, including evaluation of the right atrium, right ventricle, and pulmonary arteries, as well as other associated abnormalities detected. TTE - Subcostal view better, TEE better for sinus venosus defect. With ASD, particularly a sinus venosus defect, anomalies of systemic venous connection should be soughtDoppler echocardiography may be helpful in demonstrating flow across the atrial septum. It typically shows a biphasic (systolic and diastolic) pattern with a small right-to-left shunt at the beginning of systole.TEE is also useful in guiding device placement during catheter ASD occlusion procedures and in providing immediate intraoperative assurance that defect closure is accomplished.Continuous-wave Doppler echocardiography is valuable for estimating right ventricular (and pulmonary arterial when there is no associated right ventricular outflow tract obstruction) systolic pressure when a tricuspid regurgitant jet is present. This technique is also useful in evaluating patients for obstruction to pulmonary venous return.Contrast echocardiography can provide additional confirmation. A right-to-left shunt can be detected by visualizing microcavitation bubbles in the left atrium and the left ventricle. A left-to-right shunt can be detected as a negative contrast washout effect in the right atrium.





ASD- echocardiography/ operative view

Cardiac catheterizationWith uncomplicated ASD in a child, routine cardiac catheterization for diagnosis is unnecessary.Cardiac catheterization may be useful if the clinical data are inconsistent, if clinically significant pulmonary arterial hypertension is suspected, or if concurrent coronary artery disease must be assessed in patients older than 40 years. Catheterization is also a viable alternative for intervention for secundum ASD.The diagnosis of ASD may be confirmed by directly passing the catheter through the defect. Serial oxygen saturation measurements can be used to estimate the magnitude of the shuntIn young patients, right heart pressures are often normal despite a large shunt.If high oxygen saturation is present in the superior vena cava or if the catheter enters a pulmonary vein directly from the right atrium, sinus venosus type is likely.




Indication for intervention/surgeryElective closure of ASD is generally recommended when the Qp:Qs is 1.5:1 or greater, ideally performed at age 2 to 5 years, before exercise capacity changes, while chest wall compliance is optimal, and before school age. An echo diagnosis of a significant defect with right ventricular volume overload is common and sufficient indication to close an ASD.


Contraindication Irreversible pulmonary hypertension is the only contraindication to ASD closure. Irreversible pulmonary hypertension is characterized by a pulmonary vascular resistance (PVR) 8–12 wood units/m2, with Qp:Qs <1.2:1, despite a vasodilator challenge.Moderate pulmonary hypertension with a reactive component is not a contraindication to ASD closure, though pulmonary hypertension may progress in these patients regardless of closure. Generally, the PVR must fall below 7 u/m2 with vasodilator therapy at cardiac catheterization for ASD closure risk to be less than prohibitive. Vasodilators used at cardiac catheterization to determine the reversible component of pulmonary hypertension include hyperoxia, inhaled nitric oxide, and isoproterenol.

Percutaneous transcatheter closure(Device closure)

These devices are placed through a femoral venous approach and are deployed like an umbrella to seal the septal defect. These devices work best for centrally located secundum defects( started in 1970).

4 major devices have become available: CardioSEAL , Amplatzer septal occluder , HELEX septal occluder and Sideris patch . The ASO is currently the most widely used device (since it’s first use in 1995).Defects unsuitable for device closure include those that have failed attempted device closure, common atria or those without sufficient septal rim(<5mm) to engage the device, and sinus venosus defects for which device closure would threaten obstruction of pulmonary veins, IVC, or SVC. Anterior-inferior septal( ostium primum) deficiency can be prohibitive of device closure, as the device can interfere with the tricuspid valve, mitral valve, or coronary sinus. Transcatheter closure of ASDs is now established practice at most cardiac centers. It is proven safe in experienced hands, it is cost-effective, and it favorably compares to surgical closure with successful implantation rates of more than 96%.

Complication of device closure The reported overall complication rate following catheter-deployed ASD closure devices is about 8%. Included among cardiac complications are device malposition or dislocation, early or late embolization, arrhythmia, pericardial effusion, left or right atrial thrombus, atrial or ventricular perforation, mitral or tricuspid regurgitation, aortoatrial fistula, eustachian valve entrapment, and sudden death. Mitral or tricuspid regurgitation can result from device entrapment within chordae, chordal rupture, or leaflet perforation by the device or the delivery system. Reported noncardiac complications include iliac vein dissection, retroperitoneal or groin hematoma, and leg ischemia. Thromboembolic events were seen in 20% of patients with thrombus. In 80-85%, thrombus resolved with heparin and warfarin. Risk factors for thrombogenesis on the device were the type of device, postprocedural atrial fibrillation, incomplete neoendothelialization of the surface of the device, insufficient antithrombotic treatment, and previously undiagnosed hypercoagulability disorders (including aspirin resistance and persistent interatrial septal aneurysm). For prophylaxis, aspirin given for 6 months is a common practice. When combined with clopidogrel, no thrombus was noted at 4 weeks and 6 months in one study.

ASD- device closure

Minimally invasive approaches

In most cases, the size of the incision is simply decreased with different approaches to cardiopulmonary bypass. Examples include partial or full submammary skin incision, hemisternotomy( lower), and limited thoracotomy( Right anterolateral, bilateral anterior). Thoracoscopic approach/ Robotic surgeryThe goal is to improve better cosmetic results because these approaches are not associated with decreased morbidity or mortality.Risk- phrenic nerve palsy, lung herniation, scoliosis, and breast or chest muscle deformity.

Surgical closureMedian sternotomy, bicaval cannulation, aortic cannulation, root cardioplegiaDirect closure, Pericardial patch closure, PTFE patch, dacron, portion of atrial wall may be used as patch In Sinus venosus type, the ASD must be patched in such a way as to ensure that the anomalous pulmonary venous drainage is diverted into the left atrium. In an Ostium primum defect, the patch must be attached to the septum at the juncture of the mitral and tricuspid valves. Mitral valve repair( replacement rarely), including closure of the cleft mitral leaflet and, possibly annuloplasty, may be necessary to correct or prevent mitral insufficiency.

Repair of superior sinus venosus atrial septal defect. A, A lateral atriotomy provides exposure to the anomalous right upper pulmonary vein. B, A pericardial baffle is constructed to direct right upper pulmonary vein flow to the left atrium, through a created or enlarged secundum defect. C, Completed intraatrial baffle. D, A patch plasty of the atriotomy extends sufficiently cephalad on the superior vena cava to avert caval obstruction. IVC, inferior vena cava; RuPV, right upper pulmonary vein(s); SVC, superior vena cava.

Transcaval repair of sinus venosus ASD Gajjar et al, J Card Surg 2011;26:429-434

The principles of the technique were longitudinal incision over the lateral aspect of superior vena cava (SVC) atthe entry point of anomalous right pulmonary veins, use of a single autologous untreated pericardial patch,and finally closure of the caval incision in such away that the patch gets sandwiched between two caval lips.

Complication of surgeryEarly- or late-patch dehiscence, thromboembolism, and arrhythmias such as heart block, sinus node dysfunction, and atrial fibrillation or flutter. In ASD closure with pulmonary hypertension, systemic venous hypertension, right ventricular failure, and low cardiac output can result acutely, necessitating a return to cardiopulmonary bypass to fenestrate the closure.Though early sinus node dysfunction occurs in 9% of patients undergoing repair of superior sinus venosus defects by either Warden procedure or baffle and SVC patch, 8-year follow-up data show no persistent late sinus node dysfunction following these procedures.

Prior to ASD closure, >60% of patients older than 40 are NYHA class III to IV, whereas after ASD closure, >80% are NYHA class I to II.Patients older than 60 show functional class improvement, immediate and late reduction in pulmonary artery pressure, and improved 5- and 10-year survival after ASD closure, by comparison to medical management.These data support a strategy of ASD closure regardless of age for the symptomatic patient, though some controversy remains over the closure of the asymptomatic ASD after age 40, as functional class deterioration and arrhythmia has been observed in this group after ASD closure.

Prognosis after surgical closure

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Atrial Septal Defect