Ultrasound entropy may be a new non-invasive measure of pre-clinical vascular damage in young hypertensive patients.

BACKGROUND: The identification of pre-clinical microvascular damage in hypertension by non-invasive techniques has proved frustrating for clinicians. This proof of concept study investigated whether entropy, a novel summary measure for characterizing blood velocity waveforms, is altered in participants with hypertension and may therefore be useful in risk stratification. METHODS: Doppler ultrasound waveforms were obtained from the carotid and retrobulbar circulation in 42 participants with uncomplicated grade 1 hypertension (mean systolic/diastolic blood pressure (BP) 142/92 mmHg), and 26 healthy controls (mean systolic/diastolic BP 116/69 mmHg). Mean wavelet entropy was derived from flow-velocity data and compared with traditional haemodynamic measures of microvascular function, namely the resistive and pulsatility indices. RESULTS: Entropy, was significantly higher in control participants in the central retinal artery (CRA) (differential mean 0.11 (standard error 0.05 cms(-1)), CI 0.009 to 0.219, p 0.017) and ophthalmic artery (0.12 (0.05), CI 0.004 to 0.215, p 0.04). In comparison, the resistive index (0.12 (0.05), CI 0.005 to 0.226, p 0.029) and pulsatility index (0.96 (0.38), CI 0.19 to 1.72, p 0.015) showed significant differences between groups in the CRA alone. Regression analysis indicated that entropy was significantly influenced by age and systolic blood pressure (r values 0.4-0.6). None of the measures were significantly altered in the larger conduit vessel. CONCLUSION: This is the first application of entropy to human blood velocity waveform analysis and shows that this new technique has the ability to discriminate health from early hypertensive disease, thereby promoting the early identification of cardiovascular disease in a young hypertensive population. CLINICAL TRIAL REGISTRATION: Clinical Trials.gov, NCT01047423.

A Reappraisal of the Safety and Cost-Effectiveness of Statin Therapy in Primary Prevention.

Statins are among the most investigated drugs of all time. There is now a wealth of evidence supporting their use in the primary and secondary prevention arenas. The reduction in event recurrence has since been demonstrated across all levels of risk and in elderly patients. As a result, it is now accepted practice for statins to be prescribed universally in secondary prevention unless contraindicated. The extension of this policy into the primary prevention setting is more problematic, with moral and financial issues arising from the long-term treatment of many young apparently healthy individuals. For these reasons it is necessary to prove not only the financial sustainability of such a strategy but also the long-term safety of statins and the degree of benefit that might be expected.

Endothelial Function in Hypertension: Victim or Culprit?

Far from simply lining the inner surface of blood vessels, the cellular monolayer that comprises the endothelium is a highly active organ that regulates vascular tone. In health, the endothelium maintains the balance between opposing dilator and constrictor influences, while in disease, it is the common ground on which cardiovascular risk factors act to initiate the atherosclerotic process. As such, it is the site at which cardiovascular disease begins and consequently acts as a barometer of an individual's likely future cardiovascular health. The vascular endothelium is a very active organ responsible for the regulation of vascular tone through the effects of locally synthesized mediators, predominantly nitric oxide (NO), endothelial NO synthase (eNOS), and superoxide. NO is abundantly evident in normally functioning vasculature where it acts as a vasodilator, inhibits inflammation, and has an antiaggregant effect on platelets. Its depletion is both a sign and cause of endothelial dysfunction resulting from reduced activity of eNOS and amplified production of nicotinamide adenine dinucleotide oxidase, which, in turn, results in raised levels of reactive oxygen species. This cascade is the basis for reduced vascular compliance through an imbalanced regulation of tone with a predominance of vasoconstrictive elements. Further, structural changes in the microvasculature are a critical early step in the loss of normal function. This microvascular dysfunction is known to be highly predictive of future macrovascular events and is consequently a very attractive target for intervention in the hypertensive population in order to prevent cardiovascular events.