Why Pulmonologists Order Limited Echo with Bubble Study
A pulmonologist orders a limited echocardiogram with bubble study primarily to detect intracardiac shunts (particularly patent foramen ovale) and pulmonary arteriovenous malformations that can complicate pulmonary hypertension, cause unexplained hypoxemia, or increase risk in patients with pulmonary embolism. 1, 2
Primary Indications in Pulmonary Practice
Detection of Intracardiac Shunts in Pulmonary Hypertension Workup
Pulmonologists routinely screen for shunts when evaluating patients with elevated right ventricular systolic pressure (RVSP > 45 mmHg) as part of comprehensive pulmonary hypertension assessment. 1
If there is any suggestion of a shunt—such as history of childhood murmurs, cyanosis, clubbing, or flow murmurs on examination—an echocardiogram with bubble study is performed to identify patent foramen ovale or other intracardiac communications. 1
Intracardiac shunts can contribute to or complicate pulmonary hypertension, making their identification essential for proper disease classification and treatment planning. 2
Risk Stratification in Pulmonary Embolism
In patients with pulmonary embolism, the presence of a patent foramen ovale significantly increases the risk of death, stroke, and peripheral arterial embolism through paradoxical embolism. 1, 2
The American Heart Association recommends screening for PFO with an echocardiogram with agitated saline bubble study in patients with massive or submassive pulmonary embolism for risk stratification (Class IIb recommendation). 1
Detection of impending paradoxical embolism (thrombus trapped within a PFO) may warrant consideration for surgical embolectomy or more aggressive therapeutic options. 1
Echocardiography is reasonable for risk-stratification in non-high risk pulmonary embolism and for guiding therapeutic options in patients with pulmonary embolism at intermediate risk. 1
Evaluation of Unexplained Hypoxemia
Bubble studies help distinguish between cardiac and non-cardiac causes of dyspnea when clinical and laboratory findings are ambiguous. 1
The test can identify pulmonary arteriovenous malformations, particularly in patients with hereditary hemorrhagic telangiectasia, with transthoracic echocardiography with contrast showing 98-99% sensitivity for detecting PAVMs. 2, 3
Right-to-left shunting through either intracardiac or intrapulmonary routes can cause refractory hypoxemia that doesn't respond to supplemental oxygen, making bubble study essential for diagnosis. 2
Technical Advantages for Pulmonary Patients
Feasibility in Lung Disease
Patients with pulmonary disease are often not ideal candidates for standard echocardiographic examination because hyperinflated lung is a poor conductor of ultrasound, but the subxiphoid/subcostal view can usually visualize the heart well. 1
Between transthoracic windows and transesophageal echocardiography, it is possible to obtain diagnostic images in almost all patients with primary lung disease. 1
Comprehensive Pulmonary Vascular Assessment
Echocardiography allows simultaneous assessment of right ventricular function, pulmonary artery pressures, and detection of shunts in a single study. 1, 4
The test provides rapid, noninvasive, portable evaluation that can be performed at the bedside in critically ill patients. 5, 6
Clinical Decision Points
When Bubble Study Changes Management
Only 31% of patients with detected PFO have subsequent changes in management, emphasizing the importance of appropriate patient selection. 7
Management changes may include alteration of antiplatelet/anticoagulant therapy or referral for PFO closure, particularly in patients with cryptogenic stroke or recurrent paradoxical embolism. 2, 3, 7
Important Caveats
The bubble study should not be ordered routinely in all patients with lung disease without clinical suspicion of cardiac involvement. 1
Transesophageal echocardiography provides higher sensitivity (51% vs. 32%) for detecting shunts compared to transthoracic echocardiography, and may be necessary when transthoracic studies are non-diagnostic. 2, 3
The procedure carries a very low complication rate (0.1% risk of TIA), but informed consent is warranted. 7
A PAsP >60 mmHg suggests a more chronic process rather than acute pulmonary embolism, as the right ventricle can only generate up to 60 mmHg acutely. 1