Is a bubble study done with a regular echocardiogram (echo) or a transesophageal echocardiogram (TEE)?

Bubble Study: Transthoracic vs. Transesophageal Echocardiography

Bubble studies can be performed with both regular transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE), but TTE is the standard first-line approach for screening, while TEE is reserved for cases where TTE is non-diagnostic or when higher sensitivity is required. 1, 2, 3

Standard Approach: Start with TTE

• Transthoracic echocardiography with agitated saline bubble study is the initial screening test for detecting right-to-left shunts, including patent foramen ovale (PFO) and pulmonary arteriovenous malformations. 1, 2, 3

• TTE bubble studies are non-invasive, widely available, do not require sedation, and carry minimal risk (adverse events <1%). 3, 4

• The test involves injecting agitated saline containing microbubbles intravenously while performing echocardiography to identify intracardiac or intrapulmonary shunts. 1, 2

When to Escalate to TEE

TEE should be considered when TTE is non-diagnostic, when higher sensitivity is needed, or when detailed anatomical assessment of the atrial septum is required for procedural planning. 5, 6, 2, 3

TEE Advantages:

• TEE provides significantly higher sensitivity (51%) compared to TTE (32%) for detecting shunts. 2, 3

• TEE offers superior visualization of the atrial septum, atrial appendages, systemic and pulmonary venous connections, and is as accurate as CT for assessing secundum atrial septal defect size and rim length when planning PFO closure. 6, 2

• TEE can provide new or altered diagnoses (14%) or new information (56%) in adults with congenital heart disease that TTE misses. 6

TEE Limitations and Risks:

• TEE is semi-invasive and requires conscious sedation, which may affect hemodynamics and valvular flow assessment. 7

• The examination may be unsuccessful in 3-5% of patients due to inability to tolerate the probe, and another 4-5% require general anesthesia. 6

• TEE has specific blind spots: limited visualization of the right ventricular outflow tract, pulmonary valve, distal right pulmonary artery, proximal left pulmonary artery, and apical-anterior septum. 6, 2

• Mortality rate is extremely low (0.0098%) but complications can occur, including pulmonary, cardiac, or bleeding events (0.88% interruption rate). 8

Diagnostic Performance Characteristics

TTE Bubble Study:

• TTE has low sensitivity (46%) but extremely high specificity (99%), making it an excellent "rule-in" test but poor "rule-out" test. 4

• A positive TTE for right-to-left shunt has 95% probability of being a true positive in cryptogenic stroke patients. 4

• Positive likelihood ratio of 20.85 means a positive TTE dramatically increases the probability of true shunt presence. 4

TEE Bubble Study:

• TEE has sensitivity of 89.2% and specificity of 91.4% for detecting PFO when compared to surgical or autopsy confirmation. 9

• Even TEE can miss some PFOs, so highly sensitive screening tests like transcranial Doppler may be used in conjunction before scheduling PFO closure. 9

Clinical Decision Algorithm

For suspected intracardiac shunt (cryptogenic stroke, pulmonary hypertension evaluation):

1. Start with TTE bubble study as initial screening 2, 3
2. If TTE is positive → proceed with clinical management decisions 4
3. If TTE is negative but clinical suspicion remains high → perform TEE bubble study 2, 3, 4
4. If TEE is also negative but suspicion persists → consider transcranial Doppler 9

For pre-procedural planning (PFO closure):

• TEE is preferred for detailed anatomical assessment of atrial septum, defect size, and rim measurements. 6, 2

Common Pitfalls to Avoid

• Do not routinely order bubble studies in patients with already-established non-cryptogenic stroke etiologies or in patients >60 years old, as this represents diagnostic overuse not supported by guidelines. 10

• In one study, 62.3% of bubble studies were performed in non-cryptogenic stroke patients, yielding no change in management and contributing to healthcare waste. 10

• Ensure proper Valsalva maneuver or provocative maneuvers during the study, as inadequate provocation can lead to false-negative results. 4, 9

• Remember that TTE may be technically limited in patients with poor acoustic windows (obesity, emphysema, narrow intercostal spaces), necessitating TEE. 6