Why do doctors insist of checking cholesterol levels and blood pressure in their patients? At least part of the rationale is that these measurements will help identify individuals at heightened risk of things like heart disease and death, and appropriate steps might then be taken to reduce their risk. The value of ‘traditional risk factors’ in this endeavour is not assured however. We know, for example, that the much-maligned form of cholesterol known as LDL-cholesterol is not a particularly strong predictor of future health or longevity.
The fact is, measuring cholesterol levels is a poor proxy for the levels of arterial disease or general health in the body. A better measurement might be to, say, attempt to measure the degree of gumming up (atherosclerosis) of the arteries with tests like ‘Doppler scanning‘ of the major arteries in the neck, angiography (injection of dye into the coronary arteries), or something known as calcium scanning.
Another possibly fruitful avenue might be to assess the functioning of the heart and cardiovascular system, with an exercise test. Traditionally, this is done by getting people to exercise on a treadmill until they can exercise no more, get symptoms such as chest pain, or have changes on the ‘heart trace’ that suggest their heart muscle is starved of oxygen.
However, a recent study suggests that a simpler, cheaper and useful exercise tool is simply to measure how far an individual can walk in 6 minutes (the ‘6-minute walk test’) [1]. In the study in question, 556 individuals with known (but stable) heart disease underwent a 6-minute walk test and were followed over an average of 8 years. Cardiovascular events (heart failure, heart attack and death) were logged over this time.
During the study, about 40 per cent of people had one or more cardiovascular event. The distance covered in the 6-minute walk test was found to be a strong predictor of risk of having cardiovascular event. Individuals at the low end of the spectrum (87-419 metres in 6 minutes) had more the four times the risk of a cardiovascular event compared to those at the top end of the spectrum (544-837 metres) For every approximately 100 metres reduction in distance, there was a 55 per cent increased risk of a cardiovascular event.
The researchers also sought to take into account traditional risk factors such as blood pressure, body mass index and smoking, as well as measures of cardiovascular function and disease severity at the start of the study. Even after these adjustments, the results remained significant, although the association was somewhat reduced (each roughly 100 metre reduction in walking distance was associated with a 30 per cent increased risk of a cardiovascular event). When added to traditional risk factors, the 6-minute walk test improved the predictability of cardiovascular events by about 40 per cent, and has about the same usefulness in this respect as more conventional exercise testing.
In an accompanying comment piece [2], Dr David Nash (Department of Medicine, Syracuse Preventive Cardiology, State University of New York Upstate Medical Center, New York, US) states:
Given the greater ease and lesser cost of the 6MWT [6-minute walk test] compared with cardiovascular stress testing, I would recommend that physicians interested in improving their patients’ level of fitness use the 6MWT as a means of getting the patient started on regular exercise. Once the patients become familiar with the ease and safety of the 6MWT, they can be encouraged to repeat the 6MWT more frequently, even on a daily basis. It is then possible to lengthen the walk at appropriate intervals.
The 6MWT allows convenient assessment of the patient’s cardiovascular disease risk factors and can help guide personalized risk factor reduction based on lifestyle measures—diet, physical activity, and control of blood pressure and lipid levels.
References:
1. Beatty AL, et al. Six-Minute Walk Test as a Prognostic Tool in Stable Coronary Heart Disease: Data From the Heart and Soul Study. Arch Int Med epub 18 June 2012
2. Nash DT. Time for a 6-Minute Walk?Comment on Six-Minute Walk Test as a Prognostic Tool in Stable Coronary Heart Disease. Arch Int Med epub 18 June 2012
