Feasibility and Accuracy of Right-to-Left Shunt Detection in Children with Congenital Heart Defects by New Ultrasound Dilution Technique

Background: Ultrasound dilution technique (UDT), a novel indicator dilution (ID) method for cardiac output (CO) measurement, detects and quantifies shunts unrestricted by age and catheter location in intensive care patients. However, until now its accuracy and reproducibility in cardiac right-to-left-shunt (RLS) detection has not been investigated.

Methods: In a prospective observational study ID curves of children with congenital heart disease (CHD) and proven cardiac RLS were analyzed for appearance time (AT), curve morphology and central blood volume index (CBVI). Results were compared with controls without shunts.

Results: RLS were correctly identified by UDT in sixteen children with known RLS (median (range) age: 18months (1month to 15yr 6months) and excluded in twenty-six controls (74months [8months to 17yr 4months]). AT correlated well with age and body surface area in both groups and was significantly shorter in RLS (p < 0.05). By shortening of ≥1.69 second of a normally expected AT, a RLS can be detected with 93.8% sensitivity and 92.3% specificity. RLS ID curves can be subdivided into four morphological categories: I) Hump on upslope (n = 5); II) Double-hump (n = 3); III) Pseudonormal (n = 3); IV) Abnormal width (n = 5). No correlation was found between specific type of CHD and RLS categories. CBVI was significantly smaller in RLS categories I–III than in controls (p < 0.05).

Conclusion: Presence of cardiac RLS can be accurately and reliably detected by AT shortening and low CBVI. RLS categories determine measurements of CO and RLS fraction. On pediatric cardiac intensive care unit UDT is a valuable tool to monitor shunt magnitude and direction. Thereby, exemplary in fenestrated Fontan circulation, it may be used to optimize hemodynamic and respiratory therapy.