P.041 Validation of Sphygmocor-Processed Augmentation Index Using Carotid Artery Distension Waveform

Abstract

Arterial tonometry (AT), used for measurement of augmentation index (AI) at the central level, has been criticized because of artefacts induced by hand motion and deformation of the artery. We hypothesized that carotid distension waveforms, obtained with high definition echotracking device (walltrack system WTS-AI) could be used to derive augmentation index, a measure of wave reflection, and that those values were comparable with AT, either performed at carotid (CSP-AI) or on the radial artery (RSP-AI), using the generalized transfer function (GTF) of Sphygmocor system.

A group of 48 subjects with various diseases was studied. For WTS-AI, inflexion point was determined from the 0 crossing of the 3^rd derivative. For CSP and RSP-AI, standard reports of Sphygmocor were used. WTS-AI could be determined with good precision from all tracings in all patients. Agreement between WTS-AI and CSP-AI was good (R² = 0.83, RMSE = 5.8), with a 35% systematic underestimation by Sphygmocor: slope = 0.65 [0.56–0.73]). A weaker agreement between WTS-AI and RSP-AI was observed (R² = 0.71, RMSE = 6.9), with comparable underestimation. This underestimation was not due to GTF, but to the applanation process since bypassing GTF had no influence on it and because AI, estimated with another type of tonometer, was correctly scaled with CSP-AI (slope 0.93 [0.81–1.05). CSP-AI and RSP-AI were not in good agreement (R² = 0.66, RMSE = 10.7), but correctly scaled (slope = 0.87 [0.81–1.05].

In conclusion, wave reflections can be assessed from distension waveforms with good accuracy. Lower values for AI resulted from overestimation with applanation techniques rather than from underestimation with distension waveforms.