Atrial Septal Defect & Patent Foramen Ovale

Key Features

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

Clinical Findings

• 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 ...