Atrial Septal Defect (ASD): A Medical-Legal Guide for Attorneys

Introduction

Atrial septal defect (ASD) is among the most common congenital heart lesions, accounting for roughly 10% of all congenital heart defects, with the ostium secundum subtype representing approximately 75%–90% of cases (de Liyis et al., Journal of Endovascular Therapy, 2025; Oster et al., AHA/ACC, 2019). It is also one of the most litigated congenital heart lesions, for a reason that attorneys should understand at the outset: an ASD is frequently silent in childhood, is highly treatable when recognized, and carries serious but largely preventable long-term consequences when it is missed. That combination—a treatable defect, a long asymptomatic window, and a bad late outcome—creates the classic structure of a delayed-diagnosis claim.

At the same time, ASD is a field defined by nuance. Many small defects close on their own and never require intervention; closure is a scheduled, elective procedure rather than an emergency; and the closure devices themselves carry rare but catastrophic complications that generate a distinct category of procedural and product-liability litigation. A fair evaluation of any ASD case requires distinguishing the genuinely preventable injury from the natural history of the disease and from the known, disclosed risks of a properly performed procedure.

This article outlines what ASD is, how it is diagnosed and managed under current standards, the principal targets of litigation (including device-related claims), and the legitimate defenses that apply.

Clinical Vignette

The following scenario is entirely fictional and is provided for illustration only. It does not depict any actual patient or case.

A pediatrician follows a child from infancy. At several well-child visits a soft systolic murmur is noted and attributed to an "innocent flow murmur." No echocardiogram is ordered. Over the years the child is described as thin, with mild exercise intolerance that is attributed to being "not athletic." At age 11 the child is referred to cardiology for persistent murmur and is found to have a large secundum ASD with marked right ventricular dilation and early pulmonary hypertension. The defect is closed, but the child has residual right-heart changes and requires ongoing surveillance.

A plaintiff's theory in such a scenario would focus on whether the murmur and growth/exercise findings should have prompted earlier echocardiography and referral, and whether earlier closure—typically recommended at 3–5 years of age for a hemodynamically significant defect—would have prevented the right-heart remodeling and pulmonary vascular changes. A defense theory would examine whether the earlier murmur truly had pathologic features, whether the defect was hemodynamically significant earlier, and whether the ultimate outcome would have been materially different with earlier intervention. This vignette is used throughout only to illustrate the medical-legal issues, not to suggest how any real case should be resolved.

What Is an Atrial Septal Defect?

An ASD is an opening in the wall (septum) separating the heart's two upper chambers (the atria). It allows blood to flow from the left atrium to the right atrium (a "left-to-right shunt"). Over time, this extra flow volume-overloads the right heart and the lungs' circulation.

There are several anatomic types, and the distinction matters legally because it governs both treatability and the type of intervention:

• Ostium secundum — the most common type (roughly 75%–90%), located in the central septum. This is the type that can often be closed with a transcatheter device.
• Ostium primum — part of the spectrum of atrioventricular septal (canal) defects, typically requiring surgery.
• Sinus venosus — located near where the large veins enter the heart, often associated with anomalous pulmonary vein drainage; requires surgery.
• Coronary sinus defect — rare.

Importantly, no transcatheter device is currently designed to close the sinus venosus, primum, or coronary sinus types—these require surgery. Only secundum defects are candidates for device closure (Feltes et al., AHA, 2011; Turner et al., JACC, 2022).

Hemodynamic significance. Not every ASD matters clinically. A defect is considered hemodynamically significant when it produces a pulmonary-to-systemic flow ratio (Qp:Qs) of at least 1.5:1 and/or causes right ventricular dilation (Writing Committee/Sachdeva et al., ACC, 2026; Hanna, Practical Cardiovascular Medicine, 2022). Small defects without right-heart enlargement generally do not require closure.

Spontaneous closure. A crucial point for both liability and causation: many small secundum ASDs diagnosed in infancy close on their own, which is one reason that early, aggressive intervention is not always indicated and why watchful waiting is an accepted strategy (Writing Committee/Sachdeva et al., ACC, 2026).

Why ASD Is Easy to Miss

ASD is frequently silent, which is central to understanding delayed-diagnosis claims:

• Few or subtle symptoms in childhood. Most children with even a large ASD are minimally symptomatic in the first decades of life (Hanna, Practical Cardiovascular Medicine, 2022). Symptoms typically lag behind the objective evidence of cardiac dysfunction, meaning a child can have significant right-heart volume overload while appearing well (Oster et al., AHA/ACC, 2019).
• A soft or atypical murmur. The murmur of an ASD is not the loud, obvious murmur of some other defects; it can be easily attributed to an innocent flow murmur.
• Nonspecific findings. Mild exercise intolerance, fatigue, or poor weight gain can be attributed to other causes.

Because symptoms cannot be relied upon to guide therapy, objective imaging is what establishes the diagnosis and significance.

Current Standards of Care

Diagnosis

The diagnosis is made by echocardiography, which demonstrates the shunt and, critically, evaluates for right ventricular volume overload and any associated anomalies (Hari et al., Echocardiography, 2015). Indirect indicators of a significant shunt include right ventricular dilation on echocardiogram, cardiomegaly or increased pulmonary markings on chest x-ray, and right ventricular hypertrophy on ECG (Writing Committee/Sachdeva et al., ACC, 2026). In children with good imaging windows, transthoracic echocardiography is usually adequate; in adults, transesophageal echocardiography is often required (Turner et al., JACC, 2022).

Indications and Timing of Closure

Under the 2026 ACC concise clinical guidance, ASD closure is indicated when there is a hemodynamically significant shunt (Qp:Qs ≥1.5:1), right ventricular dilation, or both (Writing Committee/Sachdeva et al., ACC, 2026). Closure is performed to prevent well-recognized late complications, including pulmonary hypertension, atrial arrhythmias, right ventricular dysfunction, paradoxical embolism (stroke), and significant tricuspid regurgitation.

On timing, it is generally accepted that hemodynamically significant defects diagnosed early in life should be closed before the child is school-aged—typically at 3–5 years of age—but frequent follow-up before that window is not necessary, and an evaluation at 3–5 years for intervention planning is appropriate (Writing Committee/Sachdeva et al., ACC, 2026). This timing point is often central to causation analysis: the standard contemplates a planned, elective closure, not an emergency.

Surveillance

Surveillance intervals are defect-size dependent: small secundum ASDs may be followed every 3–5 years to reassess for right ventricular dilation, while larger defects warrant evaluation at 3–5 years of age for intervention planning (Writing Committee/Sachdeva et al., ACC, 2026). After closure, periodic long-term surveillance is indicated—in part because some devices carry a risk of late erosion (Writing Committee/Sachdeva et al., ACC, 2026).

Consequences of a Truly Missed or Untreated Significant ASD

The downstream consequences of an uncorrected, significant ASD are the damages engine of these cases. Historic natural-history data on large unoperated defects showed substantial excess mortality over a lifetime, and even surgically repaired ASDs may be associated with reduced survival when repair is performed later in adulthood (Oster et al., AHA/ACC, 2019). Recognized late complications include atrial arrhythmias (which carry stroke risk even after repair), right heart failure, paradoxical embolism, and—in a minority of cases—progressive pulmonary vascular disease culminating in Eisenmenger syndrome, an irreversible condition of fixed pulmonary hypertension with shunt reversal and cyanosis (Konstam et al., AHA, 2018; Arvanitaki et al., JACC, 2022). Notably, severe pulmonary vascular disease develops in under 10% of ASD patients and is less common than with ventricular septal defects, a point that cuts against overstated causation theories (Hanna, Practical Cardiovascular Medicine, 2022).

Targets for Litigation

1. Delayed or Missed Diagnosis

The most common ASD claim. Typical allegations:

• Failure to work up a persistent or pathologic murmur with echocardiography.
• Failure to recognize right-heart findings on chest x-ray or ECG.
• Failure to refer to pediatric cardiology.
• Attributing exercise intolerance, poor growth, or fatigue to benign causes without investigation.

The strength of such a claim turns on whether the clinical findings at the time actually warranted further evaluation under the standard of care, and whether the defect was hemodynamically significant during the window in question.

2. Failure to Treat / Delayed Closure

Where an ASD was diagnosed but closure was delayed, allegations may focus on failure to close a hemodynamically significant defect within the recommended window (typically before school age), allowing preventable right-heart remodeling, arrhythmia, or pulmonary vascular disease to develop.

3. Inadequate Surveillance

Failure to maintain appropriate follow-up—either of a known small defect being observed, or after closure—can be alleged where a progressing defect or a late device complication goes undetected.

4. Procedural and Device-Related Claims

Discussed in detail in the next section—these are the most concrete, provable targets because the alleged negligence is a discrete act rather than an outcome-based "should have treated sooner" theory.

5. Informed-Consent and Selection Claims

Allegations that the family was not adequately counseled on the pros and cons of surgical versus transcatheter closure, on device-specific risks (erosion, embolization), or that an anatomically unsuitable patient was selected for device closure.

ASD Closure Devices and Device-Specific Litigation Targets

Device closure is now the dominant approach for suitable secundum defects—more than 80% of isolated secundum ASDs in the United States are treated by catheterization, with surgery reserved for defects unsuitable for a device (Turner et al., JACC, 2022). Successful closure rates exceed 95%, with serious adverse events in 5% or fewer (Turner et al., JACC, 2022). Because the procedure is common, elective, and device-dependent, it is a focused source of litigation.

Patient selection and anatomic suitability. Candidacy for a device depends on defect size, adequacy of the septal rims, and patient size; most centers perform elective device closure at a weight above 15 kg and age 3–5 years to minimize procedural risk (Turner et al., JACC, 2022). Device closure is contraindicated in advanced pulmonary vascular disease (pulmonary pressures or resistance exceeding two-thirds systemic, or net right-to-left shunting) (Turner et al., JACC, 2022). Selection claims arise when a patient with deficient rims, an oversized defect, or advanced pulmonary vascular disease is nonetheless taken for device closure.

Recognized device complications (Turner et al., JACC, 2022; Feltes et al., AHA, 2011):

• Device erosion into the aortic root or through the atrial wall—a rare (approximately 0.1%–0.3%) but potentially catastrophic complication that can cause tamponade and death. Erosion is associated with device oversizing and deficiency of septal rims, particularly the retro-aortic rim, and can present within days or even months to years after implantation. This has led some operators to favor particular device families. Erosion is a leading device-litigation target, often framed as negligent sizing/selection, product liability, or failure to recognize and respond to a post-implant presentation.
• Device embolization/migration—associated with undersizing and flimsy or deficient rims. Embolized devices may be retrievable by catheter but sometimes require surgical removal, especially if they embolize to the left heart.
• Cardiac perforation/tamponade, arrhythmia, and atrioventricular block.
• Thromboembolism, including stroke, and vascular injury at the access site.
• Residual shunt requiring further intervention.
• Nickel allergy (rare) and, with certain older devices, wire-frame fracture.

In one pediatric AMPLATZER series, the overall complication rate was 7.2%, with a major complication rate of 1.6% (including device embolism requiring surgical removal) and a minor rate of 6.1% (Feltes et al., AHA, 2011).

Surgical versus transcatheter risk profile. A 2025 meta-analysis of nearly 9,700 pediatric patients found that surgical closure carried significantly higher odds of cardiac arrhythmia, pericardial effusion, and pulmonary complications, and a longer hospital stay, while closure success and residual shunting rates were comparable; surgery showed advantages in residual-shunt rates for defects over 15 mm and in children under 8 (de Liyis et al., Journal of Endovascular Therapy, 2025). This comparative risk data is frequently invoked on both sides of selection and informed-consent disputes.

Endocarditis prophylaxis. Antibiotic prophylaxis is recommended for the first 6 months after closure, until the device or prosthetic material endothelializes (Writing Committee/Sachdeva et al., ACC, 2026)—a discrete standard whose breach can be a focused allegation.

Medical Causation

Causation is often the decisive and most contested issue in ASD litigation, and several features of the disease cut in both directions:

• For the plaintiff: When a hemodynamically significant defect was missed for years and the child developed right-heart remodeling, atrial arrhythmia, or pulmonary vascular disease, the argument is that timely, elective closure—an effective, low-risk procedure—would more probably than not have prevented the injury. Historic data showing excess mortality and reduced survival with later repair support this framing (Oster et al., AHA/ACC, 2019).
• For the defense: Several realities temper causation. Many small defects close spontaneously, so a defect seen early may not have warranted intervention (Writing Committee/Sachdeva et al., ACC, 2026). Severe pulmonary vascular disease/Eisenmenger syndrome develops in under 10% of ASD patients, making it a low-probability outcome that cannot simply be assumed (Hanna, Practical Cardiovascular Medicine, 2022; Arvanitaki et al., JACC, 2022). Much of the right ventricular dysfunction associated with ASD is driven by volume overload and ventricular geometry and is reversible after closure, which can rebut claims of permanent injury (Konstam et al., AHA, 2018). And for device complications, erosion and embolization are recognized, disclosed risks of a correctly performed procedure, not necessarily evidence of negligence.

The central causation questions are therefore: Was the defect hemodynamically significant during the window in question? Would earlier recognition and elective closure, more likely than not, have changed the outcome? Is the claimed injury (e.g., Eisenmenger syndrome) actually attributable to the delay, given its low baseline incidence? And for a device complication, was it a failure of technique/selection or a materialization of a known risk?

Common Misconceptions

• "Any heart murmur in a child is malpractice if a defect is later found." False. Innocent murmurs are extremely common and benign; conversely, a significant ASD may produce only a soft murmur. The question is whether the murmur had pathologic features warranting workup.
• "A normal-appearing child cannot have a significant heart defect." False. Children with even large ASDs are often minimally symptomatic for years; symptoms lag behind objective dysfunction (Oster et al., AHA/ACC, 2019).
• "Every ASD must be closed." False. Small defects without right-heart enlargement generally do not require closure, and many close spontaneously (Writing Committee/Sachdeva et al., ACC, 2026).
• "A device complication proves the operator was negligent." False. Erosion, embolization, and arrhythmia are recognized complications that can occur despite appropriate technique; many are associated with anatomic factors (rim deficiency) rather than operator error.
• "Closure must happen immediately upon diagnosis." False. For an asymptomatic child, closure of a significant defect is typically a planned, elective procedure around 3–5 years of age (Writing Committee/Sachdeva et al., ACC, 2026).

Long-Term Outcomes and Damages

Potential injuries alleged in ASD cases include:

• Atrial arrhythmias (and associated stroke risk), which can persist even after repair.
• Right heart failure and right ventricular dysfunction.
• Paradoxical embolism and stroke.
• Progressive pulmonary hypertension and, rarely, irreversible Eisenmenger syndrome.
• Reduced long-term survival when repair occurs late.
• For device cases: tamponade, emergency surgery, need for device retrieval, residual shunt, or death.

A balanced damages analysis accounts for the fact that timely closure generally restores a normal or near-normal life expectancy in otherwise healthy patients, so the measure of harm is typically the incremental injury attributable to the delay or complication—not the existence of the defect itself.

Medical Records That Matter

• Serial well-child and growth records (documentation of murmur characteristics over time).
• Any ECGs and chest x-rays (right-heart findings).
• All echocardiograms (defect type, size, rim anatomy, right ventricular size/function, pulmonary pressures, Qp:Qs).
• Cardiology consultation notes and referral timing.
• Cardiac catheterization and operative/device-implant reports (device type, size, sizing method, rim assessment).
• Post-procedure imaging and surveillance records (residual shunt, erosion/migration monitoring).
• Informed-consent documentation (disclosure of surgical vs. device options and device-specific risks).
• Records addressing exercise tolerance and symptom progression.

The Role of Pediatric and Congenital Cardiology Expertise

ASD cases require expertise that general pediatrics or adult cardiology alone may not provide. A pediatric/congenital cardiology expert can determine whether a murmur warranted workup, whether a defect was hemodynamically significant during the relevant period, whether closure timing met the standard, whether device selection and sizing were appropriate for the anatomy, whether a device complication reflects technique or a known risk, and whether the claimed long-term injury is causally attributable to the alleged breach. Because management has shifted substantially toward transcatheter closure and conservative observation of small defects, standard-of-care opinions must be anchored to the era of care.

Key Takeaways for Attorneys

• ASD is common and highly treatable, but often silent in childhood—making delayed-diagnosis claims structurally common.
• Only hemodynamically significant defects (Qp:Qs ≥1.5:1 and/or right ventricular dilation) warrant closure; many small defects close spontaneously.
• For significant defects diagnosed early, closure is typically a planned, elective procedure at 3–5 years of age—not an emergency.
• Only secundum defects are device-eligible; primum, sinus venosus, and coronary sinus defects require surgery.
• Device closure now predominates (>80% of secundum defects) with >95% success and ≤5% serious complications.
• Device-specific complications—erosion (0.1%–0.3%, potentially fatal), embolization/migration, AV block, perforation—are the most concrete procedural and product-liability targets, and are often linked to rim deficiency and device sizing.
• Erosion and embolization are recognized, disclosable risks; their occurrence does not by itself establish negligence.
• Causation is the pivotal issue: Eisenmenger syndrome occurs in under 10% of ASD patients, and much ASD-related right-heart dysfunction is reversible after closure.
• Informed-consent and patient-selection/anatomic-suitability issues are frequent and provable targets.
• Standard-of-care opinions must be anchored to the era of care, given the rapid shift toward transcatheter closure.

References

• Arvanitaki et al., JACC, 2022
• Feltes et al., AHA, 2011
• Hanna, Practical Cardiovascular Medicine, 2022
• Hari et al., Echocardiography, 2015
• Konstam et al., AHA, 2018
• Oster et al., AHA/ACC, 2019
• Turner et al., JACC, 2022
• Writing Committee/Sachdeva et al., ACC, 2026
• de Liyis et al., Journal of Endovascular Therapy, 2025