What is the difference in appearance between Atrial Septal Defect (ASD) and Patent Foramen Ovale (PFO) on echocardiography (echo)?

From the Guidelines

Atrial septal defects (ASDs) and patent foramen ovale (PFO) can be distinguished on echocardiography based on their appearance, with ASDs typically showing a fixed, persistent opening in the interatrial septum and PFOs appearing as a potential channel between septum primum and secundum that opens intermittently. The key differences in their appearance are due to their distinct anatomical characteristics, as outlined in the 2019 ACC/AHA/ASE key data elements and definitions for transthoracic echocardiography 1. Some of the main types of ASDs include:

• Secundum ASD, which is the most common type and is characterized by a deficiency of septum primum in the region of the fossa ovalis 1
• Primum ASD, which is a variant of an atrioventricular septal defect with an interatrial communication just above the atrioventricular valve 1
• Sinus venosus defect, which involves a vena cava and/or pulmonary vein(s) that overrides the atrial septum or septum secundum producing an interatrial or anomalous venoatrial communication 1 In contrast, a PFO is characterized by a small interatrial communication (or potential communication) confined to the region of the fossa ovalis, with no deficiency of septum primum and a normal limbus with no deficiency of the septum secundum 1. The use of bubble contrast echocardiography can be particularly useful in detecting PFOs, where microbubbles crossing from right to left atrium within 3-5 cardiac cycles after injection indicate a PFO, as noted in the context of guidelines for managing adults with congenital heart disease 1. Transesophageal echocardiography provides better visualization of both defects compared to transthoracic echocardiography due to its closer proximity to the interatrial septum and higher resolution imaging. Overall, accurate identification and characterization of ASDs and PFOs on echocardiography are crucial for guiding management decisions, including the potential need for surgical or device closure, as recommended in the 2018 AHA/ACC guideline for the management of adults with congenital heart disease 1.

From the Research

Echocardiographic Appearance of ASD and PFO

• The appearance of atrial septal defects (ASD) and patent foramen ovale (PFO) on echocardiography can be distinct, with ASD typically presenting as a direct communication between the two atrial chambers 2.
• PFO, on the other hand, is a normal variant present in up to 25% of the population, and its appearance on echocardiography may vary depending on the presence of a right-to-left shunt 3.
• Transesophageal echocardiography (TEE) is often used to diagnose and guide the closure of ASD and PFO, but it may have limitations such as the need for general anesthesia and possible trauma from endotracheal intubation 4.

Diagnostic Accuracy of Echocardiography

• The diagnostic accuracy of contrast-enhanced transthoracic echocardiography (CE-TTE) for the diagnosis of PFO and ASD has been shown to be favorable, with a sensitivity of 96.9% and specificity of 95.1% compared to transcranial Doppler (TCD) 5.
• CE-TTE may be recommended as an adjunct diagnostic modality for patients with a high pre-test probability of PFO/ASD and right-to-left shunt, as it may identify patients who may be missed if only TCD is used 5.
• Intracardiac echocardiography (ICE) has also been shown to be a safe and high-quality imaging technique for guiding transcatheter ASD and PFO occlusion, and can detect cardiac abnormalities that are not identified with TEE during the initial diagnostic investigation 4.

Comparison of ASD and PFO

• ASD and PFO have distinct clinical presentations and management strategies, with ASD typically resulting in right heart volume overload and PFO being associated with paradoxic embolism and embolic stroke 3.
• The prevalence of ASD and PFO in patients with cryptogenic strokes has been shown to be 1.3% and 36.8%, respectively, with ASD being a rare stroke risk factor for cryptogenic strokes 6.
• The characteristics of patients with ASD and PFO may vary, with ASD patients being older and more often female, and having more cardiovascular risk factors and silent strokes compared to patients with high-likelihood PFO-related stroke 6.