Response to Letter Regarding Article, “Different Calculations of Ankle Brachial Index and Their Impact on Cardiovascular Risk Prediction”
We thank Jaquinandi et al for their interest in our publication. We want to stress that the patient population of the AtheroGene study is not comparable with the patient populations reported in the articles from Lee et al and Kreitner et al, which included only patients with known advanced peripheral arterial disease.1,2 The AtheroGene study includes primarily patients with coronary artery disease, no patient had rest pain or peripheral ulcers and only 52 patients (6.3%) had intermittent claudication.3 In addition, patients with incompressible ankle arteries with suspected media sclerosis have been excluded.
Jaquinandi et al conclude that we had no patients with infrapopliteal occlusion because the lowest ABI was 0.1. In fact, the lowest ankle pressure that we measured was 10 mm Hg in 1 of the 2 ankle arteries, and no patient had missing values. Nevertheless, it cannot be concluded that a patient with a detectable ankle pressure doesn’t have infrapopliteal peripheral occluded arteries. If at least 1of the 3 lower-limb arteries is patent, this vessel usually feeds the pedal distal part of the occluded tibial arteries and thus a reduced postocclusive ankle pressure can be measured.4 In the case of complete occlusion of all lower-limb arteries, no peripheral pressure can be measured and we see the clinical situation of an advanced critical limb ischemia. Our patient population includes only patients without symptoms or with only mild symptoms of peripheral arterial disease. Therefore, we suggest that a low percentage of our patients have occlusions of 1 lower-limb artery with good clinical compensation due to collateralization from another patent lower-limb artery because the tibial vessels show connecting side branches, especially at the ankle level. In fact, the exact number of patients with infrapopliteal occlusions cannot be given because we didn’t performed consequent duplex scanning of the limb arteries in all patients.
Moreover, it is known that measurement of ankle pressure is, like all ultrasound methods, investigator dependent.5 In our study, all measurements were performed by only 2 very experienced investigators with a low interobserver variability. In addition, a continuous-wave Doppler ultrasound device was used instead of a hand-held Doppler system for ankle pressure measurement, which might be more sensitive in the detection of very low ankle pressures, especially in the hands of an experienced investigator. Finally, in our opinion, the fact of “absent missing values” in our patient populations is thereby explained and does not influence the main result of the article.
Kreitner KF, Kalden P, Neufang A, Duber C, Krummenauer F, Kustner E, Laub G, Thelen M. Diabetes and peripheral arterial occlusive disease: prospective comparison of contrast-enhanced three-diemtional MR angiography with conventional digital substraction angiography. AJR. 2000; 174: 171–179.
Espinola-Klein C, Rupprecht HJ, Bickel C, Lackner K, Savvidis S, Messow CM, Munzel T, Blankenberg S, for the AtheroGene Investigators. Different calculations of ankle brachial index and their impact on cardiovascular risk prediction. Circulation. 2008; 118: 961–967.
Fowkes FG, Housley E, Macintyre CC, Prescott RJ, Ruckley CV. Variability of ankle and brachial systolic pressures in the measurement of atherosclerotic peripheral arterial disease. J Epidemiol Community Health. 1998; 42: 128–133.