Differential Diagnosis of Atrial Septal Defect (ASD) and Patent Ductus Arteriosus (PDA)

Clinical Examination Findings

The American Heart Association recommends that ASD presents with a fixed split S2 and systolic pulmonary flow murmur with normal pulses, while PDA presents with a continuous "machinery" murmur at the left infraclavicular area with bounding pulses and wide pulse pressure 1, 2
Patients with ASD may exhibit precordial lift indicating right ventricular volume overload 3
Systolic pulmonary flow murmur (not continuous) is a characteristic finding in ASD 3
Fixed splitting of the second heart sound is pathognomonic when present in ASD 3
Diastolic flow rumble across the tricuspid valve with large shunts may be observed in ASD 3
Normal peripheral pulses (no bounding quality) are typically seen in ASD 3
PDA is characterized by a continuous "machinery-type" murmur heard best at the left infraclavicular area and left upper sternal border 1, 2
Bounding peripheral pulses with increased pulse amplitude are a hallmark of PDA 1
Wide pulse pressure when the PDA is moderate to large is a significant finding 1, 2

Right-axis deviation is a common finding in ASD 3
Right atrial enlargement may be observed in ASD 3
Incomplete right bundle-branch block (secundum ASD) is a characteristic ECG pattern 3
Superior left-axis deviation (primum ASD) is due to anatomic position of conduction bundles, not bifascicular block 3
Abnormal P-wave axis (superiorly located sinus venosus ASD) may be seen in ASD 3
Normal ECG if the ductus is small in PDA 1
Left atrial enlargement and LV hypertrophy with moderate left-to-right shunt may be observed in PDA 1
RV hypertrophy when pulmonary arterial hypertension develops is a significant finding in PDA 1

RV and right atrial enlargement are characteristic radiographic findings in ASD 3
Prominent pulmonary artery segment and increased pulmonary vascularity may be observed in ASD 3
Cardiomegaly (variable, depending on shunt size) and increased pulmonary vascular markings reflecting magnitude of left-to-right shunt are significant findings in PDA 1

Transthoracic echocardiography is the primary diagnostic modality for ASD 3
Visualize atrial septum from parasternal, apical, and subcostal views with color Doppler demonstration of shunting in ASD 3
Direct visualization of PDA by color Doppler in parasternal short-axis view is a characteristic finding 1, 4
Continuous wave Doppler to measure transpulmonary gradient and estimate pulmonary artery pressure is useful in PDA 1, 4
Left ventricular volume overload indicated by dilated left atrium and left ventricle (not right-sided chambers) may be observed in PDA 1

Always check oxygen saturation in all four extremities when evaluating suspected PDA to detect differential cyanosis (lower saturation in feet compared to right hand) indicating right-to-left shunting at the ductal level with Eisenmenger physiology 1, 4

Right ventricular volume overload is the primary hemodynamic consequence in ASD 3
Pulmonary vascular obstructive disease develops much later than with high-pressure shunts like VSD or PDA in ASD 3
Paradoxical embolism risk from right-to-left shunting across the atrial septum is a significant concern in ASD 3
Left ventricular volume overload is the primary hemodynamic consequence in PDA 1, 4
Small PDA: No LV volume overload, normal pulmonary artery pressure 1
Moderate PDA: Either predominant LV volume overload OR pulmonary arterial hypertension 1
Large PDA: Eisenmenger physiology with shunt reversal, differential cyanosis affecting lower extremities 1

NOT indicated in younger patients with uncomplicated ASD when imaging is adequate 3
Can be useful to rule out coronary artery disease in older patients at risk with ASD 3
Can be useful to assess pulmonary arterial hypertension and test vasoreactivity in ASD 5
NOT indicated for uncomplicated PDA with adequate noninvasive imaging 5
Indicated when PAP appears high on echocardiography to measure pulmonary vascular resistance in PDA 1
Indicated for determining operability when PAP >2/3 systemic pressure or PVR >2/3 SVR in PDA 1