There is little doubt that PAD is a major cause of morbidity and diminished quality of life, and a major risk factor for adverse CV events including mortality. The ABI is a well-validated tool for categorizing disease severity and assessing CV risk.
Previous studies have assessed the use of the vascular physical examination for detecting PAD; however, some studies (22
) included only symptomatic patients, some (24
) included only asymptomatic patients, and other studies (28
) exclusively studied patients with diabetes mellitus. Disparities in the reference standard for disease detection (ie, ABI cut-off) also make consensus on the usefulness of the vascular physical examination difficult (32
). Current data concerning the accuracy of the physical examination to detect an ABI of 0.90 or lower in a heterogeneous population are lacking.
Our study included a large number of men and women, both with and without diabetes, and both symptomatic and asymptomatic. Only 171 patients (13.8%) were referred for PAD testing due to symptoms associated with PAD, whereas 890 patients (72%) referred had factors associated with increased vascular risk.
Claudication alone had a relatively poor accuracy to detect an abnormal ABI, and was a poor predictor of an abnormal ABI. Only 34.7% of patients with claudication had an ABI of 0.90 or lower. These data are not surprising and, in accordance with previous studies (29
), reflect the fact that claudication is dependent on the functional demand of the circulation and lower limb pain may be masked by adequate collateral circulation.
The most striking finding from our data was the very high specificity, NPV and accuracy for all pulses present in the absence of a femoral bruit in predicting a normal ABI. The high specificity (98.3%) indicates that patients with an abnormal vascular physical examination should be directed toward ABI measurement. The rather high positive likelihood ratio (odds of an abnormal ABI in a patient with an abnormal versus a normal vascular physical examination) of 34.2 also indicated that patients lacking both DP and PT pulses in the presence of a femoral bruit would likely benefit from having their ABI measured. Previous studies (24
) have examined combinations of pulse palpation for detecting an abnormal ABI; however, we are unaware of previous studies investigating a combination of both an abnormal pulse and a femoral bruit. Previous studies (32
) investigating combinations of pulse palpation alone have found more modest positive likelihood ratios – similar to those observed in our study.
Conversely, the high NPV indicates that 94.9% of patients with a normal vascular physical examination have a normal ABI. The overall accuracy of an abnormal vascular physical examination was 93.8%. Therefore, our data suggest that a complete vascular physical examination can exclude patients from redundant ABI testing, and ABI measurement should be focused toward patients with an abnormal vascular physical examination.
Although the Kingston Heart Clinic is a community-based outpatient cardiac facility, it is a major outpatient cardiac referral centre for CVD in southeastern Ontario. As such, there is a higher prevalence of peripheral vascular disease in those patients referred. Although there is a higher prevalence of PAD, we do not believe this should detract from the most important finding, which is the importance of a complete peripheral arterial examination that includes all four pedal pulses and the auscultation for a femoral bruit before embarking on the measurement of the ABI.
Another issue is the experience of the person (CT) who performed the majority of the clinical examinations and, therefore, the general application of our data to the practicing physician. Surely, this is the wrong message to be sending. The message should be that with the same application and dedication to the peripheral arterial physical examination, anyone can reliably expect to achieve similar results. The registered nurse (CT) had no expertise in the peripheral arterial examination and the first 85 cases were performed under the supervision of a physician (MFM). We believe that anyone can be taught this examination and eliminate unnecessary ABI measurements. We also believe that most physicians have the necessary expertise and all that is needed is the application.
There could be some concern regarding the exclusion of patients with a high ABI (greater than 1.30). First, we would simply say that our intention was to compare a normal ABI (0.91 to 1.30) with an ABI that clearly indicates obstructive PAD (ie, an ABI of 0.90 or lower). Second, there is overwhelming evidence that an ABI of 0.90 or lower has a high sensitivity and specificity for a stenosis of greater than 50% somewhere in the leg proximally, usually the aorto-iliac or superficial femoral systems on the affected side. Third, there is no evidence from our data that a high ABI is associated with obstructive PAD disease proximally. This is supported by showing that a completely normal toe-brachial index (TBI) (0.72 or greater with a strict definition) that is not affected by peripheral arterial calcification was seen in approximately 85% of our high ABI patients. Using the more conservative definition of a normal TBI (0.66 or greater), this percentage of normal TBIs in the high ABI group increases to almost 93%. Furthermore, these percentages are not significantly different from the normal ABI group, and the high ABI group had a similar profile to the normal ABI group including the physical examination (). It is well known that patients with a high ABI have a higher CV risk, but we believe this is most likely explained by the higher prevalence of diabetes and the higher mean age in this group (). Therefore, we believe that including the high ABI in the normal ABI group would be methodologically wrong and, even if we had, it would not have affected the overall results of the physical examination.