From the Guidelines
For diagnosing pulmonary AVMs versus cardiac shunts using bubble echo, the key differentiator is the timing of bubble appearance in the left atrium, with pulmonary AVMs typically showing bubbles after 3 to 8 cardiac cycles, as evidenced by the 2024 study published in the Journal of the American College of Radiology 1. This distinction is crucial because the management strategies for these conditions differ significantly.
- Pulmonary AVMs may require embolization,
- whereas cardiac shunts might need surgical or catheter-based closure depending on their size and hemodynamic significance. The appearance of bubbles in the left atrium after 3 to 8 cardiac cycles in patients with an intrapulmonary shunt, as noted in the study 1, is a diagnostic feature that helps differentiate pulmonary AVMs from cardiac shunts. In contrast, cardiac shunts such as atrial septal defects or patent foramen ovale demonstrate early appearance of bubbles in the left heart, usually within 1-3 cardiac cycles after right heart opacification. The grading system based on the appearance of bubbles in the left atrium, as described in the study 1, correlates well with the diagnosis of PAVM and can predict treatment outcomes. Therefore, the timing of bubble appearance, specifically after 3 to 8 cardiac cycles for pulmonary AVMs, is a critical diagnostic feature that guides management decisions.
From the Research
Cardiac Cycles for Bubble Echo
- The number of cardiac cycles for bubble echo to differentiate between pulmonary AVM and cardiac shunt is crucial for accurate diagnosis.
- A study by 2 found that if bubbles appear in the left heart within the first 4 cardiac cycles, it is most likely a patent foramen ovale (PFO), while bubbles appearing at or after the 5th cardiac cycle most accurately determine an intra-pulmonary shunt (IPS).
- The study suggests that the 4th cardiac cycle rule differentiates PFO and IPS most optimally by 2D and 3D transthoracic echocardiography (TTE).
Diagnosis of Pulmonary AVM
- Contrast echocardiography is a useful screening tool for detecting pulmonary arteriovenous malformations (PAVMs) in patients with hereditary hemorrhagic telangiectasia (HHT) 3, 4, 5, 6.
- A study by 6 found that transthoracic contrast echocardiography (TTCE) has an excellent diagnostic value for PAVMs, with a sensitivity of 97% and a negative predictive value of 99%.
- However, the high false-positive rate of TTCE may represent microscopic pulmonary arteriovenous malformations.
Comparison of Diagnostic Methods
- A study by 3 compared contrast echocardiography with pulmonary angiography and pulmonary vein saturations for detecting PAVMs, and found that contrast echocardiography correlates poorly with angiography and pulmonary vein saturation.
- A study by 4 compared pulse oximetry and contrast echocardiography as screening tools for PAVMs, and found that contrast echocardiography is a more sensitive screening tool.
- A study by 2 compared 2D and 3D TTE for diagnosing PFO and IPS, and found that 3D TTE appears to have higher sensitivity for diagnosing IPS, while both methods are similar for diagnosing PFO.