Detection of Right‐to‐Left Shunts: Comparison between the International Consensus and Spencer Logarithmic Scale Criteria

Publisher Website
Google Scholar
Abstract
BACKGROUND International Consensus Criteria (ICC) consider right‐to‐left shunt (RLS) present when Transcranial Doppler (TCD) detects even one microbubble (μB). Spencer Logarithmic Scale (SLS) offers more grades of RLS with detection of >30 μB corresponding to a large shunt. We compared the yield of ICC and SLS in detection and quantification of a large RLS. SUBJECTS AND METHODS We prospectively evaluated paradoxical embolism in consecutive patients with ischemic strokes or transient ischemic attack (TIA) using injections of 9 cc saline agitated with 1 cc of air. Results were classified according to ICC [negative (no μB), grade I (1‐20 μB), grade II (>20 μB or “shower” appearance of μB), and grade III (“curtain” appearance of μB)] and SLS criteria [negative (no μB), grade I (1‐10 μB), grade II (11‐30 μB), grade III (31100 μB), grade IV (101300 μB), grade V (>300 μB)]. The RLS size was defined as large (>4 mm) using diameter measurement of the septal defects on transesophageal echocardiography (TEE). RESULTS TCD comparison to TEE showed 24 true positive, 48 true negative, 4 false positive, and 2 false negative cases (sensitivity 92.3%, specificity 92.3%, positive predictive value (PPV) 85.7%, negative predictive value (NPV) 96%, and accuracy 92.3%) for any RLS presence. Both ICC and SLS were 100% sensitive for detection of large RLS. ICC and SLS criteria yielded a false positive rate of 24.4% and 7.7%, respectively when compared to TEE. CONCLUSIONS Although both grading scales provide agreement as to any shunt presence, using the Spencer Scale grade III or higher can decrease by one‐half the number of false positive TCD diagnoses to predict large RLS on TEE.