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Stockholm, Sweden - The ankle-brachial blood-pressure index (ABI), even if measured simply by palpation of the foot arteries, is a strong predictor for future cardiovascular events and for all-cause mortality, a new analysis of the HOPE study shows.1
In a paper published in the January 2004 issue of the European Heart Journal, a team led by Dr Jan stergren (Karolinska Hospital, Stockholm, Stockholm) concludes that: "Even a relatively crude method of assessing a diminished circulation to the foot has great predictive value and is widely applicable in clinical practice to identify individuals at high risk."
The authors explain that ABI is known to be a predictor for mortality in the general population, but in the epidemiological studies indicating this, ankle blood pressure was measured by ultrasound Doppler, a technique not readily available in most general practices. If a simpler measurement of the ABI using routine blood-pressure measurement in the arm and palpation of the foot pulse were shown to have predictive value, this would have wide practical applicability, they note.
In the HOPE study, patients at high risk for cardiovascular events were randomized in a 22 factorial design to treatment with ramipril or placebo and vitamin E or placebo and followed for 4.5 years. The main results of the study showed a significant reduction in the primary end point of cardiovascular death, MI, or stroke with ramipril but no effect of vitamin E.
ABI was measured, mainly by digital palpation of the foot pulse, at baseline in 8986 patients. The ABI was subnormal (below 0.9) in 3099 patients and normal in 5887 patients. Noting that the prevalence of a low ABI in this study may seem high, the authors point out that peripheral arterial disease (PAD) was one of the inclusion criteria in the HOPE study.
Results showed that a low ABI was a strong predictor of morbidity and mortality during follow-up, even in patients with no clinical symptoms of PAD. This was so for the primary outcome of the studycardiovascular death, MI, strokeand for all-cause mortality.
Outcome according to ankle-brachial blood-pressure index|
Outcome |
ABI >0.9 (%) |
ABI 0.6-0.9 (%) |
ABI <0.6 (%) |
p |
|
CV death/MI/stroke | 13.1 | 18.2 | 18.0 | <0.0001 |
|
All-cause mortality | 8.5 | 12.4 | 14.2 | <0.0001 |
As expected, patients with clinical PAD showed a higher rate of cardiovascular events, but even in those without clinical PAD, lower ABI levels (<0.9) increased the risk of future events (from 13.1% to 18.2%) suggesting that even a simple marker of peripheral arterial disease has substantial prognostic value, the researchers comment. "Given that digital palpation of ankle pulse to record BP is relatively crude, our data are probably underestimating the true relationship between ABI and outcome had we used more sensitive methods such as ultrasound," they add.
Benefits of ramipril
They say there are two important findings related to the use of ramipril in this study. First, ramipril prevented clinical events in both patients with and without clinical evidence of PAD. In particular the relative benefit was similar in patients subdivided by levels of ABI.
Relative reduction in cardiovascular events with ramipril according to ABI|
Risk |
ABI >0.9 |
ABI 0.6-0.9 |
ABI <0.6 |
p |
|
RR in CV events | 0.83 | 0.75 | 0.79 | NS |
They note, however, that as the event rates were higher in those with an ABI below 0.9, the absolute benefits were about twice as large in this group (50 per 1000 events prevented) compared with those with an ABI above 0.9 (24 per 1000 events prevented). Second, therefore, "this suggests that in patients with CAD and no clinical evidence of PAD, utilizing the ABI is a simple method to further identify high-risk patients who can benefit from preventive strategies," they say.
They conclude that "measuring ankle-arm BP ratio either by the simple approach that we have used (or when available by more precise methods) should be considered in the planning of future large cardiovascular prevention trials and epidemiological studies."
In an accompanying editorial, Dr Daniel Duprez(University of Minneapolis, MN) says that not enough attention has been paid to the measurement of the ABI in cardiovascular risk detection.2 This study is important as it shows that, in these times of major healthcare budget burden, ABI can be used with little or no additional costs to further stratify patients who may benefit to a greater extent from preventive treatments, he adds.
