Detection of right-to-left shunts: Comparison between the international consensus and Spencer Logarithmic Scale criteria

BACKGROUND International Consensus Criteria (ICC) consider right-to-left shunt (RLS) present when Transcranial Doppler (TCD) detects even one microbubble (mu B). Spencer Logarithmic Scale (SLS) offers more grades of RLS with detection of >30 mu B 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 mu B), grade I (1-20 mu B), grade II (>20 mu B or "shower" appearance of mu B), and grade III ("curtain" appearance of mu B)] and SLS criteria [negative (no mu B), grade I (1-10 mu B), grade II (11-30 mu B), grade III (31100 mu B), grade IV (101300 mu B), grade V (>300 mu B)]. 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.