The challenges of identifying cardiovascular risk
Despite numerous tools, calculators and algorithms to assess cardiovascular risk, many individuals at apparently low to moderate risk continue to suffer major cardiovascular events. The greatest concern is that a significant proportion of cardiovascular deaths occur in the absence of well-established risk factors such as hypertension, diabetes, obesity, raised lipids or smoking.
At the other end of the spectrum, modestly raised blood pressure is possibly treated unnecessarily as a precaution. New cardiovascular biomarkers such as C-reactive protein, N-terminal pro-atrial natriuretic peptide and homocysteine have only added moderately to standard risk factors for risk assessment1.
Over the past 20 years, arterial stiffness, as measured by aortic pulse wave velocity (aPWV), is being increasingly recognized as a promising biometric to help predict major cardiovascular events and death. The test is likely to be most useful in younger adults with low to moderate cardiovascular risk2. Underwriters will find the aPWV test particularly relevant as a significant proportion of insurance applicants are in this risk group.
Arterial stiffness, also known as hardening of the arteries, is a well-known precursor to cardiovascular disease, including coronary heart disease, stroke and heart failure. Recent evidence suggests arterial stiffness precedes both hypertension and target organ damage. Measurement of arterial stiffness is therefore emerging as a method to predict cardiovascular disease.
Arteriosclerosis and atherosclerosis are separate pathological entities, driven largely by different mechanisms (Figure 1, page 51). Measuring arterial stiffness is primarily focused on arteriosclerosis rather than atherosclerosis. Arteriosclerosis involves loss of elasticity and dilatation of the large arteries, while atherosclerosis (a form of arteriosclerosis) is characterised by patchy thickening of the inner lining of the artery walls.
Direct measurement of arterial stiffness is technically challenging, requires invasive investigations and is expensive. Instead, aPWV can be used to estimate arterial stiffness and is being increasingly recognised as a reliable technique. Using a complex mathematical formula relating to large-artery haemodynamics, aPWV can be estimated using relatively cheap, noninvasive techniques.
What is pulse wave velocity?
With each heartbeat, a wave, or pulse, travels along arterial vessels. PWV is the speed at which this arterial pulse transmits through the circulatory system. The velocity of this pulse wave is related to the stiffness of the arteries; a higher PWV corresponds to lower arterial distensibility and compliance. In other words, the pulse wave travels faster if the arteries are stiffer.
Carotid-femoral PWV (cfPWV) is regarded as the gold standard measurement methodology, as it includes the aorta and other large arteries that are at highest risk of stiffening. cfPWV is usually measured by placing a non-invasive pressure sensor over the carotid and femoral arteries and then calculating the time difference in the arrival of the pulse (expressed in metres per second). However, measuring cfPWV is not always practical as it requires special equipment and trained technicians. Other disadvantages of cfPWV include the need to measure the distance between the carotid and femoral artery, the patient’s need to undress to allow access to the femoral artery, and finding the pulse in the presence of obesity.
Accurate and reproducible techniques to measure aPWVNewer techniques to measure aPWV have become available in recent years. Devices that use a cuff around the brachial artery are quicker, more practical and require minimal training. As the technology advances, the cost of measuring aPWV is likely to decrease, allowing it to be used for insurance underwriting assessment at paramedical examinations. Studies have shown cuff-based device measurements to be accurate and reproducible4 (Figure 2, see pdf). Using the brachial pulse wave to derive aPWV has been validated in low- and high-risk cohorts5,6 and is highly reproducible7.
Aortic PWV can also be measured using sophisticated ultrasonography or MRI-based approaches. However, these are considered too expensive and time-consuming for routine clinical medicine.
In the future it may be possible to estimate aPWV with low-cost optical methods using photoplethysmography, i.e., measuring light absorption through blood. However, these devices are at an early stage of validation. Such novel solutions are showing encouraging results and could allow the measurement of arterial stiffness to become part of routine clinical medicine8.Read More +