Confusable diagnoses · PANCE / PANRE

Patent Ductus Arteriosus vs Atrial Septal Defect

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

Patent Ductus Arteriosus and Atrial Septal Defect are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.

Patent Ductus Arteriosus vs Atrial Septal Defect at a glance

  • Patent Ductus Arteriosus: Persistent fetal connection between aorta and pulmonary artery producing a continuous machinery murmur and L-to-R shunt.
  • Atrial Septal Defect: Opening in the interatrial septum producing left-to-right shunt, fixed split S2, and risk of paradoxical embolism.

Try two board-style questions on Patent Ductus Arteriosus vs Atrial Septal Defect

Real questions from the FirstPassPA bank, with the full explanation. Pick an answer — no signup, no email.

Question 1CardiovascularEasy
A 6-week-old term girl is brought in for poor weight gain. Her mother reports she tires and sweats during feeds and breathes rapidly. On exam she is tachypneic with a hyperdynamic precordium, bounding peripheral pulses, and a wide pulse pressure. A continuous "machinery" murmur is best heard at the left infraclavicular area, peaking around the second heart sound. Which of the following is the most appropriate next diagnostic test to confirm the diagnosis?
  • ATransthoracic echocardiography, Doppler
  • BTwo-view plain chest radiograph series
  • CCardiac catheterization with angiography
  • DTwelve-lead surface electrocardiography
Reveal answer & full explanation
Correct answer: A — Transthoracic echocardiography, Doppler
  • ATransthoracic echocardiography, Doppler✓
  • BTwo-view plain chest radiograph series
  • CCardiac catheterization with angiography
  • DTwelve-lead surface electrocardiography

Why Transthoracic echocardiography, Doppler is correct

  • The continuous machinery murmur at the left infraclavicular area with bounding pulses and a wide pulse pressure is classic for a patent ductus arteriosus (PDA).
  • Echocardiography with color Doppler is the diagnostic study of choice: it directly visualizes the ductus, shows the direction and velocity of the shunt, and quantifies left atrial and left ventricular enlargement from chronic volume overload.
  • It is noninvasive, available at the bedside, and confirms the anatomic lesion.

Why the others are wrong

  • Two-view plain chest radiograph series may show cardiomegaly and prominent pulmonary vascularity in a moderate-to-large shunt, but these findings are nonspecific and cannot distinguish a PDA from other left-to-right shunts.
  • Twelve-lead surface electrocardiography can reveal left atrial enlargement and LVH with a large shunt, but it is normal with small defects and never identifies the anatomic lesion.
  • Cardiac catheterization with angiography is invasive and reserved for measuring pulmonary vascular resistance when pulmonary hypertension is suspected before closure, not for initial confirmation of the diagnosis.
Question 2CardiovascularMedium
A 44-year-old woman presents with several months of progressive exertional dyspnea and intermittent palpitations. She reports no prior cardiac history. Vital signs are normal. On auscultation there is a soft mid-systolic ejection murmur at the upper left sternal border and wide splitting of S2 that does not vary with respiration. A right ventricular heave is palpable at the lower left sternal border. ECG shows an incomplete right bundle branch block with right axis deviation, and chest radiograph reveals an enlarged right atrium and right ventricle with increased pulmonary vascular markings. Which of the following is the most likely diagnosis?
  • APulmonary valve stenosis
  • BVentricular septal defect
  • CSecundum atrial defect
  • DPatent ductus arteriosus
Reveal answer & full explanation
Correct answer: C — Secundum atrial defect
  • APulmonary valve stenosis
  • BVentricular septal defect
  • CSecundum atrial defect✓
  • DPatent ductus arteriosus

Why Secundum atrial defect is correct

  • Wide and fixed splitting of S2 that does not vary with respiration is the auscultatory hallmark of an atrial septal defect; the left-to-right shunt augments right atrial volume so right ventricular ejection time stays prolonged in both inspiration and expiration.
  • The soft pulmonic flow murmur (from increased flow across the pulmonic valve), the right ventricular heave, and right heart enlargement with increased pulmonary vascular markings all reflect chronic right-sided volume overload from the shunt.
  • An atrial septal defect is the most common congenital heart defect first diagnosed in adulthood, classically in a middle-aged woman presenting with dyspnea, palpitations or atrial arrhythmia, or unexplained right heart enlargement.
  • An ECG with incomplete right bundle branch block and right axis deviation is typical of the secundum subtype, which accounts for roughly 75% of atrial septal defects.

Why the others are wrong

  • Ventricular septal defect produces a holosystolic murmur at the lower left sternal border with a normally splitting S2, not a wide fixed split; large defects typically cause pulmonary congestion and heart failure in infancy rather than first presenting in adulthood.
  • Patent ductus arteriosus produces a continuous machinery murmur with a wide pulse pressure and bounding pulses, none of which are present here.
  • Pulmonary valve stenosis gives a systolic ejection murmur at the upper left sternal border with an ejection click; significant stenosis delays and softens P2, so the split S2 is wide but still varies with respiration. It is an isolated valvular lesion and does not produce a fixed split S2 or a left-to-right shunt with right heart volume overload.
🔒 Free preview limit reached

Keep comparing — start your free trial

You've used your 2 free previews. Create your free account to see the full Patent Ductus Arteriosus vs Atrial Septal Defect comparison — plus all 514 diagnosis outlines, 7,200+ board-style questions, and an AI tutor. Your 7-day free trial includes everything, no credit card required.

Start your 7-day free trial → Sign in
Free to start · No credit card · Cancel anytime

Side-by-side comparison

FeaturePatent Ductus ArteriosusAtrial Septal Defect
At a glancePersistent fetal connection between aorta and pulmonary artery producing a continuous machinery murmur and L-to-R shunt.Opening in the interatrial septum producing left-to-right shunt, fixed split S2, and risk of paradoxical embolism.
Classic presentationContinuous machinery murmur with wide pulse pressure and bounding pulses in a child; differential cyanosis is pathognomonic when shunt reversal develops.; Small PDA: asymptomatic, found incidentally on auscultation; Moderate-to-large PDA in infancy: poor feeding, diaphoresis with feeds, failure to thrive, tachypnea, recurrent pulmonary…Wide and fixed split S2 with pulmonic flow murmur in an otherwise asymptomatic adult.; Often asymptomatic in childhood; diagnosed in adulthood after decades of right heart volume overload; Exertional dyspnea, fatigue, palpitations (atrial arrhythmias); Recurrent respiratory infections in larger defects; Cryptogenic stroke or TIA…
Workup / key labsBMP, CBC; Genetic evaluation if features suggest a syndrome (Down, rubella exposure history)Hemodynamically significant ASD warranting closure: right heart (RA/RV) enlargement on imaging with Qp/Qs ≥1.5, without severe pulmonary hypertension. Closure may also be considered after documented paradoxical embolism or for platypnea-orthodeoxia. Closure is generally contraindicated if pulmonary vascular resistance is severely…
ImagingTransthoracic echocardiography with color Doppler — diagnostic; visualizes the ductus, direction and velocity of shunt, and chamber size; ECG: normal if small; LA enlargement and LVH with large shunts; biventricular hypertrophy with pulmonary HTN; CXR: cardiomegaly, prominent pulmonary vasculature, dilated proximal pulmonary arteries in…Transthoracic echocardiography with agitated saline (bubble study) and color Doppler — visualizes defect, direction and magnitude of shunt, RA/RV size, RV function, and estimates pulmonary pressures; Transesophageal echocardiography for better characterization of sinus venosus and sinus coronarius defects and to evaluate suitability for…
First-line treatmentPremature infants: expectant management for most PDAs in the first 2 weeks (many close spontaneously), since prophylactic or early medical closure has not improved outcomes. Persistent hemodynamically significant PDA: pharmacologic closure with a COX inhibitor (ibuprofen or indomethacin) or acetaminophen; if unsuccessful, transcatheter…Secundum ASD: percutaneous transcatheter device closure (e.g., Amplatzer septal occluder) is the preferred approach when anatomy is suitable (adequate rims, defect <38 mm); Primum, sinus venosus, and unroofed coronary sinus defects, as well as secundum defects with inadequate rims: surgical patch closure; Antiplatelet therapy for about…

Drill Patent Ductus Arteriosus vs Atrial Septal Defect questions on FirstPassPA

Turn this comparison into retention. 7,200+ board-style questions with an AI tutor that explains every answer — free to start, no card required.

Answer the 2 free questions above → Get today's free question →

Full outlines

Patent Ductus Arteriosus (PDA) Atrial Septal Defect (ASD) All 514 diagnoses

Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.