Peripheral artery disease (PAD) of the lower extremities is a common cause of impaired ambulation and is a leading cause of lower extremity wounds and amputations. It is also associated with atherosclerosis elsewhere in the body. Thus, individuals with PAD are at significantly increased risk of cardiovascular and cerebrovascular events and mortality. There is substantial evidence that the majority of cases of PAD go undetected in routine clinical practice. As a result, there is considerable interest in detection of PAD through routine screening. However, a systematic review of guidelines for peripheral artery disease screening found divergent recommendations among the eight screening guidelines identified from major organizations. In the absence of a randomized trial evaluating outcomes of screening in asymptomatic individuals, critical questions regarding the objectives of screening, appropriateness of screening, and optimal approach to screening need to be addressed.
Approximately 20 percent of adults older than 55 years have peripheral artery disease (PAD). It is well documented that undiagnosed PAD is common. In a study of almost 7000 primary care patients ages 70 years or older or 50 to 69 years with risk factors for atherosclerosis (history of cigarette use or diabetes), PAD was identified in 29 percent. Over half of these cases were new diagnoses found by ankle-brachial index (ABI) screening during the study.
The ankle-brachial index (ABI) is a simple, accurate, and relatively inexpensive test that assesses the ratio of systolic pressures in the lower versus upper extremities using hand-held Doppler ultrasound at the bedside. ABI was initially used to identify the presence and extent of peripheral vascular disease (PVD). In my residency, every patient with symptoms of PVD underwent an ABI. While some think this is difficult to do, every medical student learns to do this on their surgery rotation. The only requirements are a blood pressure cuff and a hand held Doppler probe. ABI is measured as the ratio of the systolic blood pressure in the foot/ ankle arteries (posterior tibial or dorsalis pedis arteries) over the systolic blood pressure in the arm artery (brachial artery). Both the arm pressures are measured and both the arteries in each leg. The higher leg pressure in each leg is then divided by the higher pressure recorded in the arm. If 1 is a normal value, then incremental reductions indicate worsening vascular disease.
In a definitive paper, after adjustments were made for age, LDL cholesterol, and carotid intimal medial thickness (CIMT), an ABI< 0.9 was shown to be an independent predictor of cardiovascular events. An ABI < 0.9 yielded a 90% sensitivity and 98% specificity for moderate-to-severe obstructive peripheral artery disease as determined by a confirmatory conventional angiogram. While ABI alone is not ideal to screen for mild disease, it is estimated that 40% of patients with positive ABI were asymptomatic, which would mean that it is an effective way to identify vascular disease before it is clinically apparent. A patient with symptoms and an abnormal ABI should then undergo an angiogram to identify the correct anatomic location of the arterial narrowing if surgical intervention is being contemplated.