Measurement of Aortic Stiffness Essay

1. Background
Arterial stiffness (AS), among markers of arterial disease, has gained clinical importance. Several studies have demostrated that AS is an important parameter for the assessment of Cardiovascular (CV) risk1 and an indipendent predictor of Cardiovascular Diseases (CVD)2 and mortality in the general population3. The "gold standard" for assessing AS is the Pulse Wave Velocity4 (PWV). The prominent results from its use in the clinical routine and within the framework of epidemiological clinical and studies, has lead to its inclusion in ESH/ESC guidelines for the management of hypertension5. Different equipments are avaible for its evaluation but there are critical issues related to the reproducibility of the analysis that revealed intra- and inter-operator differences 6. Current noninvasive devices for assessing PWV in ambulatory conditions are based on the principles of applanation tonometry (e.g. the well-established SphygmoCor), oscillometric techniques and Doppler Ultrasound technique7. Recently, a new index derived from 24-h ambulatory blood pressure (BP) monitoring (ABPM) such as the Mobil-O-Graph, records oscillometric BP and pulse wave forms at the brachial artery and provides an estimate of aortic BP, augmentation index, and PWV in ambulatory conditions810. Nevertheless, studies comparing these two techniques are lacking. In a feasibility study the analysis of measurement provided by SphygmoCor comparing with those provided by Mobil-O-Graph, revealed, with the Bland and Altman's statistics, similar estimates for central systolic pressure and systolic augmentation, but slightly underestimated PWV with the oscillometric device (Mobil-O-Graph)11. Recent findings, however, in a sample of hemodialysis patients, showed with the Bland Altman Plots, acceptable agreement between two devices for systolic blood pressure and arterial index and no evidence of systemic bias for PWV12. Furthermore, findings from a Swiss multi-centre observational study confirmed the ability of this non-operator dependent device to estimate vascular aging in haemodialysis patients in clinical wards and showed that the vascular age of dialysis patients was, on average, older compared to a control group with a similar comorbidity profile but a less compromised renal function13. This results shed light on the importance of further validation of this oscillometric method in the general population and provide some insights whether these measurements could have additive prognostic value for CV risk stratification, beyond common brachial BP measurements or estimations of wave reflection and PWV at office. As previously stated, PWV is an indipendent predictor of CVD14. Studies, on a general population level, have associated the heart rate-corrected QT (QTc) interval, measured from the surface of electrocardiogram (ECG), with the risk of both all-cause and cardiovascular death15. QT measure is wildly used in clinical setting to describe cardiac abnormalities and to detect drug safety16 . Several studies underline that QT interval duration is a predictor of the occurrence of cardiovascular events and his prolongation carries an increase in the risk of CV death and sudden death also after adjustment for traditional cardiovascular risk factors17 . Few studies have addressed the association of QT interval with clinical or subclinical arterial disease. Findings from a Japanese study shows that there is an association between AS and QT Interval