Cardiology · Congenital Heart Disease
The facts most likely to be tested
The hallmark physical exam finding is a fixed split S2 that does not vary with respiration.
The most common type of ASD is the ostium secundum defect, located at the site of the foramen ovale.
A systolic ejection murmur is typically heard at the left upper sternal border due to increased flow across the pulmonic valve.
Chronic left-to-right shunting leads to right ventricular volume overload, which may eventually cause pulmonary hypertension and Eisenmenger syndrome.
The ostium primum defect is associated with Down syndrome and often involves the mitral valve (cleft mitral valve).
Transthoracic echocardiogram with bubble study is the diagnostic test of choice to visualize the shunt and assess right-sided heart chambers.
Surgical or percutaneous transcatheter closure is indicated for symptomatic patients or those with a Qp:Qs ratio > 1.5:1.
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A 28-year-old female presents for a routine physical examination. She reports no significant past medical history but notes occasional exercise intolerance. On cardiac auscultation, a grade 2/6 systolic ejection murmur is heard at the left upper sternal border, and the second heart sound (S2) is widely split and fixed throughout the respiratory cycle. An ECG reveals right axis deviation and an incomplete right bundle branch block. A transthoracic echocardiogram confirms a large defect in the interatrial septum.
What is the most likely underlying anatomical defect?
Ostium secundum atrial septal defect
The clinical presentation of a fixed split S2 and a systolic ejection murmur at the left upper sternal border is classic for an ASD, with the ostium secundum being the most common variant.
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Etiology / Epidemiology
Most common congenital heart defect in adults; often associated with fetal alcohol syndrome or Down syndrome.
Clinical Manifestations
Presents with a fixed split S2 and a systolic ejection murmur at the pulmonic area.
Diagnosis
The transthoracic echocardiogram is the diagnostic test of choice to visualize the shunt.
Treatment
Surgical or percutaneous transcatheter closure is indicated for symptomatic patients or significant shunts.
Prognosis
Untreated defects lead to pulmonary hypertension and Eisenmenger syndrome.
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Epidemiology & Etiology
ASD is the most common congenital heart lesion presenting in adulthood. It is frequently associated with ostium secundum defects, which account for 75% of cases. Genetic associations include Down syndrome and Holt-Oram syndrome.
Pertinent Anatomy
The defect involves an abnormal opening in the atrial septum, allowing communication between the left and right atria. The ostium secundum type is located at the fossa ovalis, while ostium primum defects are located near the atrioventricular valves.
Pathophysiology
The defect causes a left-to-right shunt, leading to chronic right ventricular volume overload. This increased flow across the pulmonic valve creates the characteristic systolic murmur. Over time, the volume overload causes pulmonary vascular remodeling and potential reversal of the shunt.
Clinical Manifestations
Patients are often asymptomatic until adulthood, presenting with exercise intolerance or palpitations. The hallmark is a fixed split S2 that does not vary with respiration. A systolic ejection murmur is heard at the left upper sternal border due to increased flow across the pulmonic valve. Paradoxical emboli are a risk due to the potential for right-to-left shunting.
Diagnosis
The transthoracic echocardiogram is the gold standard for diagnosis and shunt quantification. A bubble study (agitated saline) may be used to confirm the shunt. A Qp:Qs ratio > 1.5:1 is the standard threshold for surgical intervention.
Treatment
Asymptomatic small defects may be monitored. Transcatheter device closure is the preferred treatment for ostium secundum defects. Surgical repair is required for ostium primum defects or those with complex anatomy. Do not delay closure if there is evidence of right heart enlargement or pulmonary hypertension.
Prognosis
Untreated patients are at risk for atrial arrhythmias, heart failure, and Eisenmenger syndrome. Once pulmonary vascular resistance becomes fixed, the condition is often irreversible and carries a poor prognosis.
Differential Diagnosis
Ventricular Septal Defect: holosystolic murmur at the left lower sternal border
Pulmonic Stenosis: harsh systolic ejection murmur with a soft S2
Patent Ductus Arteriosus: continuous 'machine-like' murmur
Mitral Regurgitation: holosystolic murmur radiating to the axilla
Tetralogy of Fallot: cyanotic presentation with a single S2