Why is a bubble study performed before Transjugular Intrahepatic Portosystemic Shunt (TIPS)?

Why Bubble Study is Performed Before TIPS

A bubble study (agitated saline contrast echocardiography) is performed before TIPS to detect right-to-left cardiopulmonary shunts that could increase the risk of complications during and after the procedure.

Purpose of Bubble Study Before TIPS

• Bubble studies help identify intracardiac shunts (particularly patent foramen ovale) or intrapulmonary shunts that could allow emboli to bypass the lungs and enter systemic circulation during TIPS 1, 2
• Detection of these shunts is critical as TIPS creates a direct connection between portal and systemic circulation, potentially increasing the risk of paradoxical embolism in patients with right-to-left shunts 2
• The procedure is part of the comprehensive cardiac assessment recommended in guidelines before TIPS placement 1, 3

Cardiac Assessment for TIPS Candidates

• Guidelines strongly recommend cardiac evaluation before TIPS due to significant hemodynamic changes that occur during the procedure 1
• After TIPS creation, cardiac output and right atrial pressures increase by approximately 50% and 100%, respectively, which can precipitate heart failure in susceptible patients 1
• Bubble studies complement other cardiac assessments including:
  • Echocardiography to evaluate systolic and diastolic function 1
  • Assessment for pulmonary hypertension 1
  • Evaluation of tricuspid regurgitation 1

Bubble Study Technique

• The procedure involves injecting agitated saline (microbubbles) intravenously while performing echocardiography 2
• Timing of bubble appearance in the left heart helps differentiate between:
  • Intracardiac shunts (bubbles appear within first 4 cardiac cycles) 4
  • Intrapulmonary shunts (bubbles appear at or after the 5th cardiac cycle) 4
• Three-dimensional echocardiography may have higher sensitivity for diagnosing intrapulmonary shunts compared to 2D echocardiography 4

Clinical Implications of Positive Findings

• Identification of significant right-to-left shunts may influence:
  • Decision to proceed with TIPS 1
  • Selection of stent size (smaller 8mm diameter may be preferred in high cardiac risk patients) 1
  • Post-procedure monitoring requirements 1
• In patients with moderate or severe portopulmonary hypertension, TIPS is approached with significant caution due to risk of right-sided heart failure 1

Safety Considerations

• Bubble studies are generally safe but rare complications can occur:
  • Transient ischemic attacks or strokes have been reported in approximately 0.1% of patients 5, 6
  • Complications are more likely in patients who already have right-to-left shunts 6
• Informed consent should be obtained given the small but real risk of cerebrovascular complications 5

Limitations and Pitfalls

• False positives can occur due to:
  • Congenital abnormalities 2
  • Mischaracterization of intrapulmonary shunts as intracardiac shunts 2
• False negatives can result from:
  • Inadequate injection technique 2
  • Respiratory variation 2
  • Elevated left atrial pressure 2

Bubble studies represent an important component of the comprehensive pre-TIPS evaluation aimed at reducing procedural risk and optimizing patient outcomes by identifying potential contraindications or modifications needed for the TIPS procedure 1.