The Revised Sonographic NASCET Index: A New Hemodynamic Parameter for the Assessment of Internal Carotid Artery Stenosis

Abstract

Purpose: A previously described Doppler parameter, the sonographic NASCET index (SNI), was derived to be more directly analogous to the North American Symptomatic Carotid Endarterectomy Trial (NASCET) methodology for assessing carotid artery stenosis. However, this index does not account for complex changes affecting the Doppler waveform. We propose a revised SNI (rSNI) in an effort to improve predicting carotid stenosis.

Materials and Methods: 25 carotid bifurcations with stenoses ranging from 40 – 92 % were analyzed. For each vessel, the rSNI and original SNI were calculated. The peak systolic velocity (PSV), rSNI, and original SNI were correlated with angiography using linear regression analysis and relative accuracies were compared at two thresholds.

Results: A correlation between rSNI and angiography was found to be significantly better than that between PSV or internal carotid artery-common carotid artery (ICA-CCA) peak velocity ratio and angiography (r² = 0.47 vs. 0.22; r² = 0.47 vs. 0.16). The accuracy of PSV in predicting high-grade stenosis was 68 % and 72 %, compared with 80 % and 88 % for rSNI, at each of two thresholds. The original SNI better correlated with angiography compared to the rSNI (r² = 0.55 vs. 0.47), but with slightly lower accuracy in predicting high-grade stenosis (76 % vs. 80 %).

Conclusion: The revised SNI correlates more closely with angiographic stenosis than either the PSV or the ICA-CCA ratio, and is more accurate in predicting high-grade stenosis. However, it is overall comparable to the original SNI, suggesting that the previously unaccounted for effects over the remainder of the cardiac cycle do not significantly improve the ability to sonographically predict significant stenosis.

Zusammenfassung

Ziel: Der in der Literatur beschriebene Doppler-Parameter „sonografischer NASCET-Index (SNI)“ wurde zur besseren Vergleichbarkeit der Graduierung von Karotisstenosen analog der NASCET Studien Methodologie entwickelt. Allerdings berücksichtigt dieser Index keine komplexen Änderungen des Doppler Spektrums. Wir evaluierten einen revidierten SNI (rSNI), der den Grad einer Karotisstenose besser vorhersagen soll.

Material und Methoden: 25 Karotisbifurkationen mit Stenosen zwischen 40 und 92 % wurden analysiert. Für jedes Gefäß wurden der rSNI und der SNI berechnet. Die systolische Maximalgeschwindigkeit (PSV), der rSNI und der SNI wurden mit der Angiografie anhand linearer Regressionsanalysen korreliert und die relative Genauigkeit für zwei Grenzwerte verglichen.

Ergebnisse: Die Korrelation zwischen dem rSNI und der Angiografie war signifikant besser als die zwischen der PSV oder der A. carotis interna – A. carotis communis (ICA-CCA) PSV Ratio und der Angiografie (r² = 0,47 vs. 0,22; r² = 0,47 vs. 0,16). Die Genauigkeit der PSV zur Prädiktion einer hochgradigen Stenose lag bei 68 % und 72 %, verglichen mit 80 % und 88 % für den rSNI an den beiden Grenzwerten. Der originale SNI korrelierte besser mit der Angiografie im Vergleich zum rSNI (r² = 0,55 vs. 0,47), aber hatte eine etwas geringere Genauigkeit zur Vorhersage hochgradiger Stenosen (76 % vs. 80 %).

Schlussfolgerung: Der revidierte SNI korreliert besser mit der angiografisch gemessenen Stenose als die PSV oder die ICA-CCA Ratio und ist akkurater in der Prädiktion hochgradiger Stenosen. Allerdings ist er insgesamt vergleichbar mit dem originalen SNI, was dafür spricht, dass die zuvor nicht berücksichtigten Effekte des restlichen Herzzyklus’ keinen signifikanten Einfluss auf die sonografische Vorhersagbarkeit signifikanter Stenosen haben.

Key words

ultrasound spectral Doppler - ultrasound Doppler - angiography - vascular - carotid arteries

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