Tongue capillary refill time and imaging parameters for acute coronary syndrome identification: A prospective ED study

Rapid identification of acute coronary syndrome (ACS) in emergency department (ED) patients with chest pain remains challenging. Tongue capillary refill time (CRT) and tongue imaging may reflect systemic perfusion, but their value in ACS is unknown.

To evaluate the diagnostic performance of standardized tongue-derived perfusion, macroscopic, and imaging parameters for identifying ACS.

This prospective observational study enrolled 208 consecutive adult ED patients presenting with chest pain. Standardized tongue imaging and tongue CRT were assessed. A separate 20-patient pilot assessed interobserver reliability using ICC and kappa coefficients. Blinded ACS adjudication used clinical findings, serial high-sensitivity troponin measurements, electrocardiography, imaging studies, specialist consultations, and follow-up data. ROC analysis and multivariable logistic regression were performed.

Among 208 patients, 61 (29.3%) had ACS: 16 STEMI, 41 NSTEMI, and four unstable angina cases. Tongue CRT was significantly prolonged in ACS patients (2.6 [2.2-2.9] vs. 1.3 [1.1-1.6] seconds; p<0.001). Tongue CRT demonstrated excellent discrimination for ACS (AUC 0.941, 95% CI 0.903-0.980), outperforming the HEART score (0.860), admission troponin (0.831), and TIMI score (0.788). A CRT threshold ≥2s yielded 86.9% sensitivity and 93.2% specificity. Tongue CRT and macroscopically dry tongue remained associated with ACS after adjustment (both p<0.001). Quantitative RGB and HSV parameters showed no significant between-group differences.

Standardized tongue CRT showed excellent discrimination for ACS in this cohort, in which most ACS cases were myocardial infarction. Its diagnostic value in unstable angina and incremental clinical utility remain unestablished. External validation is required before routine clinical use.