Atrial Septal Defect & Patent Foramen Ovale

For further information, see CMDT Part 10-06: Atrial Septal Defect & Patent Foramen Ovale

Essentials of Diagnosis

• Often asymptomatic and discovered on routine physical examination

• With an atrial septal defect (ASD) and left-to-right shunt: RV lift; S₂ widely split and fixed

• Echocardiography/Doppler is diagnostic

• ASDs should be closed if there is evidence of an RV volume overload regardless of symptoms

• A patent foramen ovale (PFO), present in 25% of the population, rarely can lead to paradoxical emboli

General Considerations

• Persistence of the ostium secundum in the mid-septum is most common form of ASD (80% of cases)

• Persistence of the ostium primum (low in the septum) is a less common abnormality

• In most patients with an ostium primum defect, there are mitral or tricuspid valve “clefts” as well as a ventricular septal defect (VSD) as part of the atrioventricular (AV) septal defect

• In all cases, normally oxygenated blood from the higher-pressure LA shunts into the RA, increasing RV output and pulmonary blood flow

• As the RV compliance worsens from the chronic volume overload, the RA pressure may rise and the degree of left-to-right shunting may decrease over time

• If the RA pressure exceeds the LA, the shunt may reverse and be primarily right-to-left; when this happens, systemic cyanosis appears

• The pulmonary pressures are modestly elevated in most patients with an ASD due to the high pulmonary blood flow

• Severe pulmonary hypertension with cyanosis (Eisenmenger physiology) is unusual, occurring in only about 15% of the patients with an ASD alone

• If pulmonary hypertension does occur, the 2018 guidelines recommend that the shunt should still be closed as long as the

  • Left-to-right shunt is still > 1.5:1

  • Systolic PA pressure is < 1/2 the systemic arterial pressure

  • Pulmonary vascular resistance (PVR) calculation is less than one-third systemic vascular resistance

• Patients with a small or moderate ASD or with a PFO are asymptomatic unless a complication occurs

• There is only trivial shunting in a PFO unless the RA pressure increases for some other reason or the atrial septum is distorted

• Exertional dyspnea or heart failure may develop in patients with larger ASD shunts, most commonly in the fourth decade of life or later

• Prominent RV and PA pulsations are then readily visible and palpable

• A moderately loud systolic ejection murmur can be heard in the second and third interspaces parasternally as a result of increased flow through the pulmonary valve

• The left-to-right shunt across the defect decreases with inspiration (as the RA pressure increases) and then increases with expiration (as the RA pressure decreases), thus keeping the RV stroke volume relatively constant in inspiration and expiration; S₂ is widely split and does not vary with respiration (“fixed” splitting)

• A tricuspid rumble may be heard in very large left-to-right shunts due to the high flow across the tricuspid valve in diastole

• PFOs are usually not associated with significant shunting, and therefore the patients are hemodynamically asymptomatic and the heart size is normal

• After age 40 years, cardiac arrhythmias (especially atrial fibrillation) and heart failure occur with increased frequency due to the chronic right heart volume overload

• PFOs can be responsible for paradoxical emboli and are a possible cause of cryptogenic strokes in patients under age 55 years

• ECG

  • Right axis deviation or RVH may be present depending on the size of the RV volume overload

  • Incomplete or complete right bundle branch block is present in nearly all cases of ASD

  • Superior axis deviation (left anterior fascicular block) is noted in the complete AV septal defect, where complete heart block is often seen as well

• Chest radiography

  • Shows large pulmonary arteries, increased pulmonary vascularity, an enlarged RA and RV, and a small aortic knob as with all pre-tricuspid valve cardiac left-to-right shunts

  • The LA is not traditionally enlarged due to an ASD shunt because the chamber is being decompressed

• Both CT and MRI can

  • Elucidate the atrial septal anatomy

  • Detect multiple fenestrations

  • Demonstrate associated lesions, such as anomalous pulmonary venous connections

• Echocardiography

  • Demonstrates evidence of RA and RV volume overload

  • Echocardiography with saline injection (bubble contrast) can demonstrate the right-to-left component of the shunt

  • Both pulsed and color flow Doppler flow studies can demonstrate shunting in either direction

  • Transesophageal echocardiography (TEE) is helpful when transthoracic echocardiography quality is not optimal because it improves the sensitivity for detection of small shunts and provides a better assessment of PFO or ASD anatomy

• Cardiac catheterization can

  • Define the size and location of the shunt

  • Determine the pulmonary pressure and PVR

• Guidelines suggest that closure of all left-to-right shunts > 1.5:1 should be accomplished by either a percutaneous device or surgery

• For ostium secundum ASDs, percutaneous closure by use of a variety of devices is preferred over surgery when the anatomy is appropriate

• Patients who have hypoxemia should have the PFO closed if no other cause for hypoxemia is evident and there is right-to-left shunting demonstrated through the PFO

• For patients with cryptogenic stroke or TIA, whether closure of the PFO, either by open surgical or percutaneous techniques, has any advantage over anticoagulation remains uncertain; atrial fibrillation may be the real risk factor in some patients

Follow-Up

• If the RA and RV sizes remain normal, serial echocardiography should be performed every 3–5 years

Prognosis

• Patients with small atrial shunts live a normal life span with no intervention

• Large shunts usually cause disability by age 40 years

When to Refer

• All patients with an ASD should be evaluated by a cardiologist with expertise in adult congenital disease to ensure no other structural disease is present and to investigate whether the RV is enlarged

• If the RA and RV volumes are increased, then referral to a cardiologist who performs percutaneous closure is warranted