STOCKHOLM – People with a normal ankle:brachial index at rest may still have clinically significant peripheral artery disease that only appears after they walk for a few minutes, according to an analysis of more than 2,100 patients.
Dr. Inge I. de Liefde
An abnormally low ankle:brachial index (ABI) following nonstrenuous exercise proved as prognostic for subsequent mortality as a low ABI at rest, Dr. Inge I. de Liefde said at the European Society of Cardiology Congress 2010. In both cases, an ABI of less than 0.9 identified patients with a greater than twofold risk of dying during 5 years of follow-up, compared with those in the study who had an exercise ABI of at least 1.1. Her analysis also showed that 35% of the people in the study with a resting ABI of 0.9 or greater had an exercise ABI below 0.9, showing that this type of patient is common, said Dr. de Liefde, an anesthesiologist working in the department of vascular medicine at Erasmus University in Rotterdam, the Netherlands.
“Treadmill exercise ABI adds additional, important prognostic information on long-term mortality in patients with a normal resting ABI. Based on our results, we recommend that at least patients suspected for PAD [peripheral artery disease], with a resting ABI of 0.9 or greater who are at least 50 years old and have hypertension undergo treadmill exercise [ABI] testing,” she said.
The people in her study went to Erasmus for evaluation of known or suspected PAD and were all 50 or older with hypertension. But Dr. de Liefde added that exercise ABI provided a simple and inexpensive diagnostic tool that could also help evaluate a wider adult population.
“Many people have silent PAD that could be diagnosed with the exercise test,” she said in an interview. “It’s a really important and easy test to perform. People with PAD are not always identified by their resting ABI. If exercise ABIs are not measured, you can miss 30%-40% of patients with PAD.”
Although not widely used elsewhere, exercise ABI tests have been done at Erasmus for at least 20 years, she said. Their protocol does not specify a target heart rate. After evaluation for resting ABI, patients walked on a level surface for 5-6 min at 4 km/hour, followed by a repeat ABI measure. The Erasmus staff recorded ankle pressure as the highest systolic pressure measured at either the anterior or posterior tibular arteries, matched against the highest systolic pressure recorded at the arm.
The 2,164 patients referred to Erasmus during 1993-2005 averaged 63 years old, two-thirds were men and follow-up averaged 5 years. The all-cause mortality rate during follow-up ranged from a low of 5% in patients with a resting ABI of 0.9 or greater and an exercise ABI of at least 1.1, to a high of 26% in patients with a resting ABI of at least 0.9 but an exercise ABI of less than 0.9. The highest follow-up mortality rate, 35%, occurred in patients diagnosed with PAD by a resting ABI below 0.9.
In an analysis that adjusted for cardiovascular risk factors and medication use at the time of ABI measurement, patients with an exercise ABI below 0.9 had a 2.56-fold increased rate of death during follow-up compared with patients with an exercise ABI of at least 1.1. This increased risk closely matched the 2.73-fold higher rate of death in patients diagnosed with PAD by a resting ABI of less than 0.9. In both cases the increased risk was statistically significant, Dr. de Liefde said. In contrast, patients without PAD at rest and an exercise ABI of 0.9-1.09 had no significantly increased mortality rate compared with the reference group.
Dr. de Liefde had no disclosures.