We thank Dr. Aboyans and colleagues for their interest in our study (1). They remark that our observation of a higher risk of death in patients with poorly compressible arteries (PCA) than in patients with peripheral arterial disease (PAD) may have been due to inclusion of patients with an abnormal post-exercise ankle-brachial index (ABI) and use of the lower ankle pressure to calculate the ABI. An ABI <0.9 after exercise is an established vascular laboratory criterion for PAD, and therefore such patients were included in our analyses. We used the lower of the 2 ankle pressures to calculate the ABI in each leg because such an approach identifies a greater number of patients at risk for adverse cardiovascular events than an ABI based on the higher ankle pressure (2- 3). Our inferences remained unchanged when we used the higher ankle pressure in calculating the ABI (1). Assigning patients who had PCA in one leg and a low ABI in the other leg to the PCA group is unlikely to have influenced our results because only 2.2% of the patients had both PCA and PAD.

Second, Dr. Aboyans and colleagues raise the issue of residual confounding. We performed a rigorous adjustment for potential confounders, including cardiovascular risk factors (age, sex, systolic blood pressure, hypertension, smoking, body mass index, and diabetes), comorbidities (coronary heart disease, cerebrovascular disease, congestive heart failure, chronic kidney disease, malignancy, and chronic obstructive pulmonary disease), medication use (statins and aspirin), and the presence of critical limb ischemia. The hypothesis that patients with PCA may not have been treated as aggressively as patients with PAD is interesting and will need to be addressed in future studies. With regard to the duration of diabetes, this is difficult to ascertain accurately, even in prospective studies, given the often long pre-symptomatic stage for this disease.

Finally, Dr. Aboyans and colleagues remark that we did not address whether patients with isolated PCA remained at increased risk of death compared with the PAD group. In fact, this analysis was reported in our study (1). The risk of death in patients with PCA but normal Doppler waveforms was higher than in those with normal ABI (fully adjusted hazard ratio: 1.4; 95% confidence interval: 1.2 to 1.6) and similar in those with PAD (fully adjusted hazard ratio: 0.9; 95 confidence interval: 0.8 to 1.1). However, the presence of abnormal Doppler waveforms in patients with PCA was associated with a significant increment in the risk of death, suggesting that the presence of atherosclerosis adds to the risk because of medial arterial calcification.