Right-to-left shunts (RLS) allow unfiltered venous blood to pass into the systemic arterial circulation, exposing patients to paradoxical embolism. Patent foramen ovale (PFO), the most frequent cause of RLS, is implicated in a significant proportion of cryptogenic strokes, particularly among younger individuals. Accurate detection of these shunts is essential to guide management, especially percutaneous closure procedures. Transcranial Doppler (TCD) is considered the reference technique, but its use may be limited by the absence of an adequate temporal acoustic window. This study aimed to assess the diagnostic performance of carotid Doppler ultrasound (CDU) with contrast injection for RLS detection and grading, compared with reference methods (TCD and transthoracic echocardiography–TTE).

A retrospective, single-center study was conducted in the vascular medicine department of Dijon University Hospital between July 2024 and June 2025. Eighty-three patients who simultaneously underwent CDU at the level of the internal carotid artery and TCD when a temporal window was available and/or TTE for the detection of RLS were included. The standardized protocol involved two microbubble injections, at rest and during the Valsalva maneuver. Patient data and imaging reports (CDU, TCD, TTE) were retrospectively analyzed using the DxCare software.

An RLS was identified in 50 patients, 82% of which were related to a PFO. CDU demonstrated a sensitivity of 98% and a specificity of 100%. Excellent agreement was observed between CDU and TCD for RLS grading, both at rest and during Valsalva, with high kappa and Spearman correlation coefficients. In several symptomatic patients, CDU led to diagnostic reconsideration and subsequent referral for percutaneous PFO closure when TTE had failed to detect the shunt.

These findings suggest that CDU is a reliable alternative for RLS detection, particularly in patients without an adequate temporal acoustic window. Its simplicity, availability, and reproducibility strengthen its value as a routine diagnostic tool in vascular practice.

Contrast-enhanced carotid Doppler ultrasound is a high-performing, non-invasive, and complementary method for screening and quantifying right-to-left shunts, contributing to improved diagnostic and therapeutic management of patients at risk for paradoxical embolism.