A Comparison Of Different Time Windows For The Detection Of Cardiac Right-To-Left Shunt Using Contrast-Enhanced Transcranial Doppler Ultrasonography

Objective: Contrast-enhanced transcranial Doppler ultrasonography(c-TCD)is highly sensitive for detecting cardiac right-to-left shunt(RLS).However,the time window to be used with c-TCD for cardiac shunt detection is yet to be standardized.The aim of our study was to standardize the time window to enable easy and widespread use of c-TCD for cardiac shunt detection.Method: A total of 239 consecutive patients with suspected cardiac RLS were subjected to simultaneous c-TCD and contrast-enhanced transthoracic echocardiography(c-TTE).Contrast studies were repeated thrice,once at rest and twice with the patient performing Valsalva maneuver(VM).RLS was estimated based on the highest number of microbubbles(MBs)detected in each case during VM.Cardiac RLS was considered when at least three MBs appeared in the left atrium within three cardiac cycles following the complete opacification of the right atrium in c-TTE.We evaluated time windows of 15-,20-,25-,30-,35-,and 40-s duration for cTCD.Receiver operating characteristic(ROC)curve analyses and Spearman’s rho rank correlations were performed for the different time windows to calculate the areas under the curve(AUC)and Spearman’s rho.All data were processed using IBM SPSS Statistics 20.0.Result: 1、There were no significant differences in the AUCs between the different time windows,with patients at rest(P > 0.05).2、On VM,the AUC for the 15-s window(0.667;95% confidence interval [CI],0.598–0.737)was significantly smaller than the AUCs for the other time windows(P < 0.05).3、Although the AUCs for the 20-,25-,30-,35-,and 40-s windows during VM were similar(P > 0.05),diagnostic accuracy for cardiac shunt detection was best with the 25-s window(AUC,0.746;95% CI,0.684–0.809).This time window had the largest AUC during VM.4、We analyzed the correlation between RLS categorization by cTCD and c-TTE at different time windows during VM.The Spearman’s coefficient of rank correlation was 0.627(95% CI,0.534–0.708)at 25 s.The correlation between c-TCD and c-TTE appeared to be better at the 25-s window than at the other time windows.5、Among the 186 positive tests,in 180(96.8%),the first MBs were detected within 25 s following the injection.During VM,MBs appeared beyond the 25-s window in only 4(3.7%)of the 109 patients who had positive tests;2 of them had a single MB detected in only one of the three tests.Conclusion: 1、There were no significant differences in the diagnostic accuracy between the different time windows,with patients at rest.2、There was a significant reduction in the predictive competence and reliability of results at the 15-s time window during VM,suggesting a low diagnostic accuracy.The results obtained at 25 s were the most accurate.Our results recommend the 25-s time window for c-TCD-aided detection of cardiac RLS.3、We found a moderate correlation between c-TCD and c-TTE for the time windows ranging from 15 s to 40 s,with the 25-s window demonstrating the highest correlation.