Feasibility study of microbubble enhanced echocardiography in normal horses.

This study tested whether microbubble-enhanced echocardiography can be practically performed in healthy horses and which contrast volume provides better imaging. In 12 horses, a 60 ml microbubble infusion produced longer, clearer right-heart opacification than 25 ml, supporting the method’s feasibility for detecting intrapulmonary shunts in future clinical use.

What problem does the study address?

• Horses can develop intrapulmonary right-to-left shunting, which contributes to hypoxemia during anesthesia or with pulmonary/systemic disease.
• In human medicine, transthoracic microbubble-enhanced echocardiography is a standard bedside test to detect such shunts (notably in hepatopulmonary syndrome), but it has not been established for equine patients.
• The study asks whether this technique is feasible in normal horses and which injected microbubble volume provides sufficiently long and clear visualization to enable clinical interpretation.

How does microbubble-enhanced echocardiography work (conceptual background)?

• A sterile microbubble solution is injected into a peripheral vein; it reaches the right atrium and right ventricle, appearing as bright echo “contrast.”
• In intact pulmonary circulation, most microbubbles are filtered in the lungs and do not reach the left heart.
• If bubbles appear in the left heart, that indicates a right-to-left pathway:
  • Immediate (within the first 1–3 cardiac cycles) suggests an intracardiac shunt (e.g., septal defect in species where this is relevant).
  • Delayed (typically after several beats) suggests an intrapulmonary shunt or abnormally dilated intrapulmonary vessels.
• Prolonged, dense opacification of the right heart helps clinicians time any left-sided appearance and increases diagnostic confidence.

Study design and methods

• Population: Twelve healthy horses (normal, without known cardiopulmonary disease).
• Interventions (within-subject comparison):
  • Infusion of 25 ml of microbubble solution.
  • Infusion of 60 ml of microbubble solution.
• Preparation and administration:
  • Microbubble solution prepared using 60 ml syringes and a 3‑way stopcock (a standard method to create a fine bubble suspension).
  • Injection site: left external jugular vein.
• Imaging protocol:
  • Transthoracic echocardiographic recordings obtained during the subsequent cardiac cycles after each infusion.
  • Primary feasibility outcomes: immediacy and persistence (number of cardiac beats) of right‑sided contrast visualization.

Key findings

• Right-heart opacification:
  • Microbubbles appeared immediately in the right atrium and ventricle after injection for both volumes.
• Persistence (duration measured in cardiac beats):
  • 25 ml infusion: right-heart contrast persisted for approximately 5–9 beats.
  • 60 ml infusion: right-heart contrast persisted longer, for approximately 6.5–12.5 beats.
• Overall performance:
  • The 60 ml dose provided more prolonged visualization, allowing more detailed and reliable assessment.

Interpretation and significance

• Feasibility established: The technique is practical in healthy horses, producing immediate and robust right-heart opacification.
• Dose matters: A 60 ml microbubble volume extends the window of visualization across more cardiac cycles, which can be critical for timing and detecting any left-heart bubble appearance in clinical cases.
• Clinical potential: Because the method is minimally invasive, quick, and uses standard echocardiographic equipment, it could become a useful stall-side tool for investigating unexplained hypoxemia or suspected intrapulmonary shunting in equine practice.

What would constitute a positive test for intrapulmonary shunting (general principle)?

• A positive study (for intrapulmonary shunt) would be the delayed appearance of microbubbles in the left heart after initial right-heart opacification.
• Longer-lasting right-heart contrast (as seen with 60 ml) improves the clinician’s ability to count beats and distinguish:
  • Early left-sided bubbles (first 1–3 beats): more consistent with intracardiac pathways.
  • Delayed left-sided bubbles (after several beats): more consistent with intrapulmonary pathways.
• Note: This feasibility study focused on healthy horses and the right-heart contrast behavior; it did not report left-heart bubble passage in diseased states.

Practical implications for equine clinicians

• Setup: Standard transthoracic echocardiography with peripheral venous access (e.g., jugular) and a simple syringe/stopcock preparation for microbubbles.
• Workflow: Inject microbubbles while recording continuous cine loops to capture initial right-heart opacification and subsequent beats for timing analysis.
• Volume selection: The 60 ml infusion provided a longer and more stable contrast window in this study, which may enhance diagnostic confidence when assessing for shunts.
• Use cases: Horses with hypoxemia during anesthesia, suspected pulmonary vascular abnormalities, or systemic inflammatory states where intrapulmonary shunting is a concern.

Limitations and caveats

• Population: Only healthy horses were studied; diagnostic performance in diseased horses remains to be established.
• Outcomes: Feasibility (visualization and persistence) was assessed; sensitivity and specificity for detecting shunts were not determined.
• Measurement unit: Persistence reported in cardiac beats; because heart rate varies among horses, beat counts are not directly equivalent to time in seconds across individuals.
• Safety/tolerability: The abstract does not report adverse events; dedicated safety assessment, especially at higher volumes, would be valuable.
• Generalizability: Image quality and acoustic windows can vary among operators and horses; standardized protocols will be important for widespread adoption.

Future directions

• Clinical validation in horses with suspected or confirmed intrapulmonary shunting, comparing microbubble echocardiography to reference standards (e.g., arterial blood gases, advanced imaging, or nuclear medicine studies where available).
• Protocol optimization, including contrast volume, infusion rate, and imaging views to maximize sensitivity while ensuring safety.
• Defining interpretive criteria for equine patients (e.g., beat thresholds for delayed left-heart appearance) and assessing intra-/interobserver agreement.
• Assessment of utility during anesthesia and in various pulmonary or systemic inflammatory conditions common in equine practice.

Supplementary information

• The online version includes supplementary material (DOI: 10.1038/s41598-026-38819-7), which may contain additional methodological details, videos, or analysis supporting feasibility.