Boutouyrie P, Revera M, Parati G.
Precise assessment of cardiovascular risk factors is a necessary step for the identification of patients at high risk of developing cardiovascular events. When setting the operating curve of the risk function, measurement of blood glucose and lipids, estimation of blood pressure (BP) levels, identification of smoking status, and assessment of existing organ damage represent the main determinants of the tendency to develop cardiac and vascular problems over and above the impact of nonmodifiable factors such as age and sex. Each of these classical risk factors is included in a risk function specific to a given population and aimed at yielding absolute quantitative values of cardiovascular risk [1,2]. Such an approach, in spite of its clinical usefulness, is affected by important limitations. This is because the importance of any modifiable risk factor and its ill effects is highly variable in individual patients, with most of their risk level depending on nonmodifiable characteristics and/or on the complex interaction between a variety of mechanisms. The usual and disappointing result of this classical approach to cardiovascular risk assessment is the possibility to target a very small number of patients at a very high risk only. This allows prevention of only a minority of the total burden of cardiovascular events, as most of them occur in the large majority of patients with only marginally elevated levels of risk . In this context, the quest for new markers of risk offering better identification of patients worth receiving preventive intervention is intense. When focusing on patients with arterial hypertension, markers of target organ damage, such as left ventricular hypertrophy and microalbuminuria, have demonstrated their predictive value, both at baseline and following treatment . More recently, large artery properties, such as intima–media thickness and arterial stiffness, have also been proposed as useful indices of hypertension target organ damage and, thus, as clinically relevant new risk factors. Several methods have been developed over the years to assess arterial stiffness in humans. Overall, three main groups of techniques can be identified: methods based on the analysis of arterial pressure pulse waveform, methods based on the quantification of pulse transit time, and methods based on a direct estimation of arterial stiffness through the assessment of arterial diameter and of the corresponding distending pressure . The method most commonly employed in this setting is the assessment of carotid–femoral pulse wave velocity (cf-PWV), which is also the method most frequently shown to carry prognostic information. Indeed, the predictive value of arterial stiffness, measured through cf-PWV, has been demonstrated in more than 11 independent studies, being beyond and above that of the classical risk factors . In particular, the prognostic value of arterial stiffness has been demonstrated in hypertension , type II diabetes , end-stage renal disease , and in the general population . Moreover, the prediction of cardiovascular risk was shown to be improved by inclusion of cf-PWV in the risk equation [10,11]. This has led arterial stiffness through cf-PWV to be recommended in the current European Society of Hypertension (ESH) and European Society of Cardiology (ESC) guidelines for risk assessment in hypertension . At the present time, the two most commonly employed noninvasive methods that allow the measurement of cf-PWV are those implemented in the Complior (Artech Medical, Pantin, France) and in the Sphygmocor (AtCor Medical, Sydney, Australia). These methods are considered as techniques of reference, although they differ according to certain aspects 
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