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Congenital heart disease in adult patients
Simple cardiac shunts in adults: atrial septal defects, ventricular septal defects, patent ductus arteriosus
  1. Daniel Tobler1,
  2. Matthias Greutmann2
  1. 1 Cardiology, University Hospital Basel, Basel, Switzerland
  2. 2 Cardiology, University Hospital Zurich, Zurich, Switzerland
  1. Correspondence to Dr Daniel Tobler, Cardiology, University Hospital Basel, Basel 4031, Switzerland; daniel.tobler{at}

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Learning objectives

  • To understand the anatomy, pathophysiology and complications of simple septal defects and patent ductus arteriosus in adults.

  • To understand general management recommendations of simple shunt lesions.

  • To select patients for interventional and surgical repair.


Simple shunt lesions are among the most common forms of congenital heart disease.1 Depending on location and size of the shunts, haemodynamic effects and presentation vary considerably. For example, while haemodynamically relevant ventricular septal defects (VSDs) nowadays typically are managed during childhood, atrial septal defects (ASDs) often escape diagnosis in childhood and many patients are diagnosed in adult life.2 Therefore, general cardiologists are frequently confronted with diagnosis and management of interatrial communications. This article focuses on anatomy, pathophysiology, natural history and common complications of simple shunt lesions; discusses imaging techniques and invasive procedures to diagnose and manage ASDs and VSDs and provides a practical algorithm on how to manage patients with ASDs with and without pulmonary hypertension.

Anatomy and pathophysiology of simple shunt lesions

Atrial septal defects

​Anatomy of ASDs

ASD are defined as direct communications on the atrial level.

The ostium secundum ASD (figure 1A1) is located within the fossa ovalis but may extend in any direction. In contrast to a patent foramen ovale (PFO), which is a flap-valve of tissue formed by the septum primum and septum secundum, an ostium secundum ASD is characterised by a true tissue defect of variable size. Occasionally, there may be multiple defects or a combination of an ostium secundum ASD in addition to a PFO with or without an associated atrial septal aneurysm.

Figure 1

Anatomy and haemodynamic consequences of simple shunt lesions. Panels (1A and 1B) anatomy of secundum atrial septal defects and haemodynamic consequences of relevant left-to-right shunting in interatrial communications. Panels (2A and 2B) anatomy of muscular ventricular septal defects and haemodynamic consequences of relevant left-to-right shunting. Panels (3A and 3B) anatomy of patent ductus arteriosus and the consequences of relevant left-to-right shunting. AO, ascending aorta; LA, left atrium; PA, pulmonary arteries; PV, pulmonary veins; LV, left ventricle; RA, right atrium; RV, right ventricle; VC, vena cava. Illustration taken from

The ostium primum defect is part of the spectrum of atrioventricular septal defects (AVSD) (figure 2A). The anatomical key feature of AVSD is the common atrioventricular junction. Although an ostium primum ASD shares many pathophysiological features of an ostium secundum ASD, given the more complex anatomy, management differs from ostium secundum ASDs and therefore, is not discussed in this review.

Figure 2

Anatomy of atrial septal defects (ASD) type I and superior sinus venosus defect. Panel (A) ASD type I (ostium primum defect). Panel (B) superior sinus venosus defect with partial anomalous connections of the right upper and middle pulmonary veins.

Sinus venosus defects are extracardiac communications between the atria and caval veins (figure 2B). The anatomical key feature is overriding of the mouth of the superior or inferior caval veins across the intact muscular border of the oval fossa.3 Partial anomalous pulmonary venous return is frequently associated, mostly with the upper right pulmonary vein draining to the superior vena cava. The inferior sinus venosus defect (located at the entry of the inferior vena cava) is much rarer than the superior type.

The unroofed coronary sinus is rare and results from partial or complete unroofing of the tissue between the coronary sinus and the left atrium.

​Pathophysiology and clinical presentation of ASDs

The amount of shunting is dependent on defect size and pressure difference between left and right atrium. In most instances, there is predominant left-to-right shunting. Haemodynamically significant shunts lead to volume overload of the right heart with dilatation of right ventricle, right atrium and the pulmonary arteries (figure 1A2).

The magnitude of left-to-right shunt may change during life related to changes of the size of the defect and the compliance of the ventricles and hence atrial pressures.4

Clinical signs may be subtle. On auscultation, the hallmark is a fixed split second heart sound, often in association with a soft pulmonic systolic ejection murmur caused by increased blood flow across the pulmonic valve. ECG often shows right axis deviation and partial right bundle branch block but may be normal. Chest X-ray may show right heart dilatation and pulmonary hypercirculation (figure 3A).

Figure 3

Chest X-ray with pulmonary overcirculation and Eisenmenger syndrome. Panel (A) chest X-ray of a patient with large atrial septal defect (quantification of pulmonary to systemic blood flow ratio=4.0) without pulmonary hypertension. Typical signs of pulmonary overcirculation. Panel (B) Chest X-ray of a patient with large atrial septal defect and severe, irreversible pulmonary arterial hypertension and shunt reversal (Eisenmenger syndrome). The arrow points to massively enlarged central pulmonary arteries. There is peripheral rarefaction of pulmonary vessels with typical peripheral vascular ‘pruning’ (arrowhead).

Ventricular septal defects

​Anatomy of VSDs

VSDs are defined as direct communications in the ventricular septum. Classification of VSDs is based on size and location of the defects.5 The perimembranous VSD is located within the membranous septum in direct continuity to aortic and tricuspid valves. Due to the anatomical proximity to the aortic valve, aortic valve cusps may prolapse into the defect and thus may lead to (progressive) aortic regurgitation. Muscular VSDs are located within the muscular portion of the interventricular septum and are entirely surrounded by muscular tissue (figures 1B1). An important subtype of muscular VSD is the subpulmonary or doubly committed VSD. It is located within the outlet portion of the muscular interventricular septum. Inlet VSDs or atrioventricular septal-type VSDs are part of the spectrum of AVSDs.

​Pathophysiology and clinical presentation of VSDs

VSDs vary in size, ranging from small defects without haemodynamical significance to large communications leading to complications in early childhood. A decrease in shunt size or even spontaneous closure of VSDs is common during early childhood, either by growth of the muscular interventricular septum (muscular VSDs) or by tricuspid valve tissue in case of perimembranous defects. In the latter, formation of a membranous septum aneurysm is common. Usually, the direction of the shunt in VSDs is left to right and the magnitude of shunting depends on the size of the defect and the vascular resistance within the pulmonary and the systemic circulation. In contrast to ASDs, haemodynamically significant VSDs lead to dilatation of the left heart chambers (figures 1B2). In the absence of pulmonary hypertension, the right ventricle is not enlarged in VSDs because the magnitude of shunt flow occurs during ventricular systole.

Depending on size and physiology of VSDs, clinical presentation and findings vary considerably. Small defects, leading to high-velocity turbulent flow between left and right ventricle typically cause a loud, pansystolic murmur, often associated with a palpable thrill. In large defects with equalisation of pressures between ventricles, no murmur is audible. Patients with elevated pulmonary vascular resistance and shunt reversal show signs of central cyanosis with clubbing of hands and feet and chest X-ray may show signs of pulmonary arterial hypertension (figure 3B).

Patent ductus arteriosus

​Anatomy of PDA

The ductus arteriosus, an important part of the fetal circulation, connects the proximal left pulmonary artery near the bifurcation of the main pulmonary artery to the descending aorta distal to the left subclavian artery (figures 1C1). Usually, the lumen of the ductus arteriosus obliterates within the first 48 hours of life in about 90% of full-term infants due to contraction of the ductus vascular smooth muscle. Failure of spontaneous closure leads to persistent shunting between pulmonary artery and aorta. Sizes and shapes of a PDA and hence, the haemodynamic impact vary widely.

​Pathophysiology and clinical presentation of PDA

In the absence of elevated pulmonary vascular resistance there is continuous left-to-right shunting. The magnitude of shunting is dependent on the pressure difference between the aorta and the pulmonary artery (related to cardiac output and both the resistances of the pulmonary and systemic circulation) and the size and shape of the ductus itself. The haemodynamic impact of a large PDA is pulmonary hypercirculation and enlargement of the pulmonary artery, the left atrium, the left ventricle and the ascending aorta (figure 1C2).

The typical clinical feature of small-sized and medium-sized PDAs is a continuous murmur, reflecting high-velocity systo-diastolic left-to-right shunting from the aorta into the pulmonary artery. In large defects with equalisation of pressures and bidirectional shunting the typical murmur is absent and these patients may exhibit differential cyanosis .6

Late complications of repaired and unrepaired simple shunt lesions in adults

Atrial septal defects

Whereas small ASDs tend to become smaller and may close spontaneously over the first years of life, ASDs with a diameter of >8 mm rarely close spontaneously and even tend to increase in size.7 8

Unrepaired ASDs: life expectancy in patients with large defects is reduced due to an increased risk of right-sided heart failure, progressive right ventricular dilatation often associated with progressive tricuspid regurgitation, stroke due to paradoxical embolism, recurrent pneumonia or pulmonary hypertension.9–11 Atrial flutter and atrial fibrillation are the most frequent cardiac complications in unrepaired ASDs with increasing incidence rates after age 30 years.12 Patients with an unrepaired ASD have twofold to threefold increased risk of stroke regardless of the presence of atrial fibrillation.13 Heart failure tends to occur after the fifth decade of life in the setting of progressive diastolic dysfunction of the left ventricle with increasingly elevated left atrial pressures subsequently leading to an increase of the left-to-right shunting. While progressive right heart failure typically occurs in moderate-sized to large-sized defects, paradoxical embolism may occur in small defects. Elevated pulmonary pressures in patients with an ASD may be caused by elevated pulmonary blood flow, elevated pulmonary vascular resistance or a combination of both. Although a relevant/irreversible increase in pulmonary arterial resistance is rare in patients with an ASD (occurring in only about 5% of affected patients), the identification of these patients is of paramount importance for their management (see below).

Repaired ASD: the long-term outcome after defect repair is good and most patients have a normal life expectancy. Long-term complications may, however, occur and appropriate counselling and patient education is important.13–16 Similarly, good long-term results after transcatheter closure of ASDs are expected.17 Adult patients seem to benefit from closure even after the age of 40 years in regard to survival and cardiac morbidity compared with medical treatment alone.11 18 However, after late repair, there may be an increased risk for the persistence or occurrence of atrial arrhythmias (particular atrial flutter or atrial fibrillation).19 20 Device migration or erosion are rare complications after transcatheter repair of an ASD.

Late complications of VSDs

Spontaneous closure of VSDs occur relatively often in childhood, more frequently in small defects. In adults, spontaneous closure is rare.21 Adult cardiologists are usually confronted with either small restrictive VSDs or repaired VSDs. Most adults with unoperated large VSDs will have developed pulmonary vascular obstructive disease resulting in irreversible pulmonary vascular disease, typically with progressive shunt reversal (Eisenmenger syndrome). These patients should be followed at specialist centres and their management will not be discussed in this review.

Restrictive unrepaired VSDs: these patients have an excellent long-term outcome.22 In most patients, defect closure will not be required during life and patients remain asymptomatic. The risk of infective endocarditis is, however, substantial, 11-fold to 15-fold higher than in the general population23 accounting for an estimated lifetime risk of 2%–10%.12 21 24 Progressive aortic regurgitation due to valve prolapse is rare in adulthood (up to 3%).24

Repaired VSDs: patients with early repair, without postoperative persistence of elevated pulmonary pressures have an excellent prognosis with a low risk of long-term complications.

Patent ductus arteriosus

Patients with small shunts usually are not at risk for haemodynamic deterioration or pulmonary hypertension and apart from a small risk of endarteritis, their long-term prognosis is normal.9 25 Even in moderate shunts, adults may remain asymptomatic, but some may develop congestive heart failure, atrial arrhythmias, pulmonary hypertension and rarely ductus aneurysm.26 27

Tools for diagnosis and evaluation of cardiac shunt lesions

Echocardiography is the main diagnostic tool for diagnosis of lesion type, associated complications and management planning. Bubble-contrast echocardiography, transoesophageal echocardiography and advanced imaging with cardiac MRI or CT may be required in selected patients. Cardiac catheterisation allows quantification of cardiac haemodynamics and particularly the precise assessment of pulmonary artery pressures and pulmonary vascular resistance.

Cardiac catheterisation and cardiac MRI allow the quantification of pulmonary to systemic blood flow ratio. A ratio of >1.5 is usually considered haemodynamically significant and is typically associated with enlargement of affected heart chambers.

Management and treatment of simple shunt lesions

General management recommendations

Patients at increased risk of infective endocarditis require repeated counselling of preventive measures (dental and skin hygiene) and education about signs and symptoms of infective endocarditis and appropriate measures when such symptoms occur (early medical assessment, liberal use of blood cultures, etc). In patients with Eisenmenger syndrome and during the first 6 months after surgical repair or device closure and in patients with residual VSDs after surgical patch closure or device closure, antibiotic prophylaxis for dental procedures is still recommended according to current European guidelines (but not according to the National Institute for Health and Care Excellence guidelines).28–30

Patients with intracardiac right-to-left shunting (most patients with an unrepaired ASD and those with Eisenmenger physiology) benefit from the use of air bubble filters for intravenous lines and careful prophylaxis against thromboembolism to reduce the risk of paradoxical embolism.

Periodic counselling and education about arrhythmias is important, as timely recognition, diagnosis and treatment of arrhythmias prevent adverse outcomes, such as tachymyopathy or strokes.31

Atrial septal defects

​Repaired ASDs

Although guidelines suggest that patients repaired before the age of 25 years without important haemodynamic sequelae do not require regular follow-up, in our experience it may be prudent to keep even such patients in loose follow-up as they have an increased risk of late atrial arrhythmias.16

​Unrepaired ASDs

The aim of repair in patients with haemodynamically significant ASDs is to improve symptoms of exercise intolerance and to decrease the risk of long-term complications. An algorithm supporting decision-making on treatment of patients with an ASD is provided in figure 4. Although long-term results after surgical ASD closure are excellent, given the lower morbidity of transcatheter interventions, device closure—when technically feasible—is the preferred treatment option by most experts.30 Device closure is only possible in secundum type ASDs, without associated lesions. The technical feasibility of device closure is determined by defect size and appropriate tissue rims, particularly in the infero-posterior aspect of the defect. In adults, this usually requires assessment by transoesophageal echocardiography with careful delineation of tissue rims all along the entire circumference of the defect, which is much more important for procedure planning than three-dimensional images of the defect itself.32

Figure 4

Algorithm of management of secundum ASD. ACC, American College of Cardiology; AHA, American Heart Association; AICD, automatic intracardiac defibrillator; ASD, atrial septal defect; CMR, cardiac MRI; PASP, pulmonary artery systolic pressure; PCWP, pulmonary capillary wedge pressure; PHT, pulmonary hypertension; PVR, pulmonary vascular resistance; Qp:Qs, pulmonary-systemic blood flow ratio; RA, right atrium; RV, right ventricle; SVR, systemic vascular resistance; TEE, transoesophageal echocardiography; WU, Woods units. *For patients with pulmonary vascular resistance between 3 and 5 WU. See considerations in section on management of ASDs in ‘Patients with pulmonary hypertension’. Some centres use MRI for delineation of tissue rims of ASDs.

Given that some complications of device closure, such as device embolisation or device erosion may be catastrophic events, patients with non-straightforward defect anatomy benefit from specialist review and device closure at expert centres. We strongly recommend echocardiographic guidance of device closure. This can be achieved by transoesophageal or intracardiac echocardiography, while some centres use guidance by transthoracic echocardiography, depending on local expertise. Patients with an ASD, who suffered paradoxical embolism, also qualify for defect closure, regardless of defect size.

Special considerations

​Patients with atrial arrhythmias

In adults, the diagnosis of an ASD is often preceded by atrial arrhythmias. If left atrial arrhythmias are suspected to be the dominant arrhythmia, ablation procedures, if appropriate, prior to device closure are recommended as access to the left atrium may be challenging after closure of the defect.

​Patients with interatrial communications requiring pacemakers

Patients with intracardiac shunts and transvenous pacemaker or defibrillator leads are at increased risk of paradoxical embolism, even on anticoagulation treatment.33 Careful assessment for intracardiac shunts (ie, bubble-contrast echocardiography) and defect closure prior to implantation of transvenous leads may prevent such devastating complications.

​Patients with pulmonary hypertension

In most patients with a large ASD, elevated pulmonary pressures are mainly caused by elevated pulmonary blood flow. Some may, however, have pulmonary arterial hypertension with elevated pulmonary vascular resistance. It is important to identify these patients. While the European guidelines recommend closure of an ASD in patients with pulmonary vascular resistance of <5 Wood units, the American College of Cardiology/American Heart Association guidelines recommend defect closure in patients with pulmonary pressures <50% of systemic pressures or pulmonary vascular resistance of less than one-third of systemic vascular resistance.29 34 In borderline cases (ie, patients with pulmonary vascular resistance between 3 and 5 Wood units), one should always be reminded that the estimation of pulmonary blood flow using the Fick method bears a substantial potential for error. This is important, as survival in patients with persistent pulmonary arterial hypertension after defect closure is decreased.35 36 Patients with borderline pulmonary vascular resistance values may benefit from specialist review by a dedicated multidisciplinary team before defect closure.37

After closure of ASDs, periodic monitoring for persistent or recurrent pulmonary hypertension may allow early initiation of specific treatment.

In patients with severe pulmonary hypertension and right heart failure with elevated right ventricular filling pressures, there is typically right-to-left shunting across the defect with central cyanosis (Eisenmenger syndrome). It is important to differentiate Eisenmenger physiology from conditions with predominant right-to-left-shunting in the absence of pulmonary hypertension, typically caused by geometrical changes of the interventricular septum (eg, plathypnoe-orthodeoxy syndrome). Such patients may benefit from closure of the interatrial communication.

​Left ventricular diastolic dysfunction

Patients with left ventricular diastolic dysfunction are at increased risk of pulmonary congestion and even pulmonary oedema after closure of ASDs. Careful haemodynamic assessment prior to defect closure (eg, test occlusion with a balloon-catheter with simultaneous monitoring of pulmonary artery wedge pressures) will identify patients at risk. In such patients, pretreatment with diuretics or even fenestrated defect closure may be appropriate.

Ventricular septal defects

​Patients after spontaneous closure of VSDs

Patients after spontaneous closure of VSDs in childhood usually do not require follow-up and do not have an increased risk for long-term complications. Exceptions are patients with a large septum membranaceum aneurysm that may cause right ventricular outflow tract obstruction or patients with aortic valve prolapse associated with aortic regurgitation.

​Repaired VSDs

Patients with repaired defects typically have a favourable long-term outcome. However, depending on timing and type of repair (eg, transatrial or transventricular repair), there may be an increased risk of late pulmonary hypertension and an increased risk of arrhythmias. Hence, we recommend periodic follow-up with an emphasis on patient education even in patients without residual haemodynamic sequelae.

​Unrepaired VSDs

Most patients with unrepaired VSDs in adult cardiology have either small, haemodynamically not significant defects or large defects with irreversible pulmonary arterial hypertension (Eisenmenger syndrome). The latter require care by multidisciplinary specialist teams and defect closure is contraindicated.

Patients with small defects are at increased risk of infective endocarditis, often involving the tricuspid valve. Therefore, we recommend periodic follow-up even in patients with small VSDs for repeated patient education. Rarely, patients with a small perimembranous VSD or more commonly with supracristal defects develop progressive aortic regurgitation caused by aortic valve prolapse and may benefit from surgical repair, even in the absence of significant shunting. The occurrence of right ventricular muscle bundles, leading to (progressive) midventricular obstruction of the right ventricle (so-called double-chambered right ventricle) is a rare complication in patients with small VSDs and may require surgical repair.

Adult patients presenting with moderate-sized VSDs with evidence of haemodynamic significance is rare. Most of these patients will have some extent of elevated pulmonary pressures. Careful haemodynamic assessment before defect closure is mandatory to assess the potential risk of persistent postoperative pulmonary arterial hypertension.29 34

Patent ductus arteriosus

​Repaired PDA

Patients with repaired PDA (either surgically or after device closure) without residual pulmonary hypertension or obstruction of pulmonary arteries do not require follow-up and have no increased risk of long-term complications.

​Unrepaired PDA

Unrepaired PDA in adults are usually small and haemodynamically not significant. Such patients are at slightly increased risk of infective endarteritis and thus require appropriate counselling and education about endarteritis/endocarditis. Given the small lifetime risk of complications, routine closure of small PDAs is not recommended.

Patients with large PDAs have often developed irreversible pulmonary hypertension until adult life. These patients typically exhibit differential cyanosis—normal systemic arterial oxygen saturation in upper extremities and low oxygen saturations in the lower extremities with typical clubbing of toes (figure 5).6 Thus, in every adult patient with newly detected pulmonary arterial hypertension in the absence of an obvious intracardiac congenital defect, simple measurement of oxygen saturation in feet and both hands may lead to the diagnosis.

Figure 5

Differential clubbing and cyanosis in patent ductus arteriosus and Eisenmenger syndrome. Panel (A) clubbing of the toes; no evidence of clubbing of the fingers. Panel (B) differential cyanosis confirmed by using the same pulse oximeter model simultaneously at the fingers and the toes. Illustrations taken by Moccetti et al,6 with permission.

In the rare adult patient with a moderate-sized to large-sized PDA with persistent predominant left-to-right shunting, careful haemodynamic assessment is required to identify patients who may still benefit from PDA closure. This often requires temporary occlusion of the defect at times of invasive haemodynamic assessment.

In adults qualifying for PDA closure, device closure is the preferred method of intervention as calcification of ductal tissue typically increases the risk of surgery. The appropriate choice of closure device depends on size and anatomy of the PDA (ie, window-like or tubular).

Key messages

  • The hallmark of significant left-to-right shunts is pulmonary overcirculation.

  • Whereas interatrial communications lead to enlargement of the right atrium and the right ventricle, in ventricular septal defects (VSDs) and patent ductus arteriosus (PDA) the left heart chambers are enlarged.

  • Infective endocarditis is a serious complication in unrepaired VSD and repaired VSDs with residual left-to-right shunting.

  • Preventive strategies should be encouraged (meticulous dental and skin hygiene).

  • Repeated patient education is key for early diagnosis and is important.

  • Most patients with repaired or unrepaired shunt lesions are at increased long-term risk of arrhythmias and periodic monitoring and—more importantly—appropriate patient education about these risks is important.

  • In patients with an ASD, early repair likely reduces the long-term risk of atrial arrhythmias.

  • Patients with small shunts do not require shunt closure; exemptions may be patients with small shunts and associated complications, such as progressive aortic valve regurgitation in patients with VSDs or patients with paradoxical systemic embolism in the setting of a small ASD.

  • Patients with haemodynamically significant shunts benefit from repair to improve symptoms of exercise intolerance and prevention of long-term complications such as heart failure and pulmonary hypertension.

  • Patients with pulmonary hypertension require careful assessment to identify patients with advanced pulmonary vascular disease in whom shunt closure may impair long-term prognosis.

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  • Contributors Both authors have contributed to the manuscript equally.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Commissioned; externally peer reviewed.

  • Author note References which include a * are considered to be key references.

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