The Ankle Brachial Index Measurement, Calculation, and Interpretation Limitations Ivan Casserly MD Denver VA Medical Center University of Colorado Hospital

Ankle Brachial Index Ankle brachial index (ABI) Ankle brachial pressure index (ABPI) Ankle arm index (AAI)

Ankle Brachial Index Why should we care? In clinical practice Aids in diagnosis and assessment of patients with symptoms suggestive of PAD Role in primary prevention since PAD is a powerful independent predictor of CV morbidity and mortality regardless of symptomatic status of PAD.

Ankle Brachial Index How good is it at diagnosing PAD? Using gold standard of DSA angiography >50% stenosis in lower extremity vessel

Ankle Brachial Index Diagnosis of PAD Niazi et al, Cath Cardiovasc Interv 2006;68:788-792

Ankle Brachial Index Role in Primary Prevention – Low incidence of classic claudication PAD Asymptomatic Atypical Symptoms Claudication Substrate for CLI of underlying PAD. Only 1-3% of all patients with PAD progress to CLI Clinical pathway to CLI is variable - Prior to presentation with CLI, most patients will have been asymptomatic – perhaps related to sedentary existence, only a minority with prior claudication. Some present with tissue loss (especially diabetics), others progress through rest pain and subsequent tissue loss. Stable PAD Rest Pain Tissue Loss CLI

Peripheral Arterial Disease Prevalence PARTNERS Program (PAD Awareness, Risk, and Treatment: New Resources for Survival) 350 Primary care sites Patients (n=~7,000) >70 yrs 50-69 yrs with history DM or smoking PVD diagnosis ABI <0.9 Previous documentation Abnormal vasc studies Prior revascularization Hirsch AT, JAMA 2001;286:1317-1324

Peripheral Arterial Disease Prevalence 24% 16% 13% Hirsch AT, JAMA 2001;286:1317-1324

Peripheral Arterial Disease Under-diagnosis in Primary Care Practice / Influence of assoc. diagnosis of CVD 10% 7% 6% 6% Hirsch AT, JAMA 2001;286:1317-1324

Peripheral Arterial Disease Impact of Diagnosis on Survival Normal Subjects Asymptomatic PAD Symptomatic PAD Severe Symptomatic PAD Survival Year 1.00 12 10 8 6 4 2 0.00 0.25 0.50 0.75 severe symptomatic PAD had the worst prognosis: analysis of this group revealed a 15-fold increase in rates of mortality due to cardiovascular disease and CHD. The study cited above categorized patients (n=565) into four groups: normals (n=318) and those with PAD (n=67). Evaluated were those with asymptomatic PAD (by Rose questionnaire) , those with symptomatic PAD (symptomatic and either abnormal ABI or diminished doppler flow velocities, not both) characterized by claudication, and those with PAD that was both symptomatic and severe (symptoms by Rose, and severity by both abnormal ABI and diminished doppler flow velocities). The graph shows the survival curves for the three groups of patients compared with the normal subjects. Patients with severe symptomatic PAD had by far the worst prognosis of the three groups of patients; only one in four was still alive at the end of the 10-year follow-up period. METHODS. We examined 565 men and women (average age, 66 years) for the presence of large-vessel peripheral arterial disease by means of two noninvasive techniques--measurement of segmental blood pressure and determination of flow velocity by Doppler ultrasound. We identified 67 subjects with the disease (11.9 percent), whom we followed prospectively for 10 years. RESULTS. Twenty-one of the 34 men (61.8 percent) and 11 of the 33 women (33.3 percent) with large-vessel peripheral arterial disease died during follow-up, as compared with 31 of the 183 men (16.9 percent) and 26 of the 225 women (11.6 percent) without evidence of peripheral arterial disease. After multivariate adjustment for age, sex, and other risk factors for cardiovascular disease, the relative risk of dying among subjects with large-vessel peripheral arterial disease as compared with those with no evidence of such disease was 3.1 (95 percent confidence interval, 1.9 to 4.9) for deaths from all causes, 5.9 (95 percent confidence interval, 3.0 to 11.4) for all deaths from cardiovascular disease, and 6.6 (95 percent confidence interval, 2.9 to 14.9) for deaths from coronary heart disease. The relative risk of death from causes other than cardiovascular disease was not significantly increased among the subjects with large-vessel peripheral arterial disease. After the exclusion of subjects who had a history of cardiovascular disease at base line, the relative risks among those with large-vessel peripheral arterial disease remained significantly elevated. Additional analyses revealed a 15-fold increase in rates of mortality due to cardiovascular disease and coronary heart disease among subjects with large-vessel peripheral arterial disease that was both severe and symptomatic. CONCLUSIONS. Patients with large-vessel peripheral arterial disease have a high risk of death from cardiovascular causes. Adapted from Criqui MH, et al. N Engl J Med. 1992;326:381-386. Criqui MH, Langer RD, Fronek A, et al. Mortality over a period of 10 years in patients with peripheral arterial disease. N Engl J Med. 1992;326:381-386.

Peripheral Arterial Disease Impact of Diagnosis on Survival Data from the Strong Heart Study, n=4393. 1988-1999. Strong heart study Circ 2004;109:733-39. Only 25 patients with ABI<0.6 Background—The associations of low (0.90) and high (1.40) ankle brachial index (ABI) with risk of all-cause and cardiovascular disease (CVD) mortality have not been examined in a population-based setting. Methods and Results—We examined all-cause and CVD mortality in relation to low and high ABI in 4393 American Indians in the Strong Heart Study. Participants had bilateral ABI measurements at baseline and were followed up for 8.32.2 years (36 589 person-years). Cox regression was used to quantify mortality rates among participants with high and low ABI relative to those with normal ABI (0.90 ABI 1.40). Death from all causes occurred in 1022 participants (23.3%; 27.9 deaths per 1000 person-years), and of these, 272 (26.6%; 7.4 deaths per 1000 person-years) were attributable to CVD. Low ABI was present in 216 participants (4.9%), and high ABI occurred in 404 (9.2%). Diabetes, albuminuria, and hypertension occurred with greater frequency among persons with low (60.2%, 44.4%, and 50.1%) and high (67.8%, 49.9%, and 45.1%) ABI compared with those with normal ABI (44.4%, 26.9%, and 36.5%), respectively (P0.0001). Adjusted risk estimates for all-cause mortality were 1.69 (1.34 to 2.14) for low and 1.77 (1.48 to 2.13) for high ABI, and estimates for CVD mortality were 2.52 (1.74 to 3.64) for low and 2.09 (1.49 to 2.94) for high ABI. Conclusions—The association between high ABI and mortality was similar to that of low ABI and mortality, highlighting a U-shaped association between this noninvasive measure of peripheral arterial disease and mortality risk. Our data suggest that the upper limit of normal ABI should not exceed 1.40. (Circulation. 2004;109:733-739.) Resnick et al. Circulation 2004;109;733-739

Peripheral Arterial Disease Impact of Diagnosis on Survival – Polyvascular Disease Hospitalization events: Transient ischemic attack, unstable angina, or worsening of PAD. Adjusted for sex and age. Adapted from PG Steg et al. JAMA.2007;297:1197-1206.

ABI and Primary Prevention Algorithm Doobay AV et al. Arterioscler Thromb Vasc Biol.2005;25:1463-1469.

Ankle Brachial Index Performance Calculation Interpretation

Ankle Brachial Index Performance - Equipment

Ankle Brachial Index Performance Hiatt WR, N Engl J Med 2001;344:1608-1621

Ankle Brachial Index Performance CLINICAL DEMONSTRATION

Ankle Brachial Index Performance - Review Patient Position No activity for 4-5 minutes Supine position

Ankle Brachial Index Performance – Arm Pressure Appropriate cuff size Doppler over brachial artery NOT STETHESCOPE (underestimate SBP) NOT OVER RADIAL ARTERY Record right AND left arm brachial pressures Why?

Ankle Brachial Index Performance – Ankle Pressure Cuff Appropriate size Appropriate location Lower leg above malleoli NOT OVER BULK OF CALF MUSCLES Doppler over DP AND PT NOT STETHESCOPE

Ankle Brachial Index Calculation ABI Numerator – Ankle pressures Higher of the two pedal pressures Brachial Denominator – Brachial pressure Higher of the two arm pressures Best reflects aortic pressure

Ankle Brachial Index Calculation - Rationale Patient DP 100, PT 150, Highest brachial 150 Method 1. Higher of the two pressures ABI 150/150 = 1 Sensitivity ↓ Specificity ↑ Method 2. Lower of the two pressures ABO 100/150 = 0.66 Sensitivity ↑ Specificity ↓

Ankle Brachial Index High versus Low Ankle Pressure (HAP vs LAP) Niazi et al, Cath Cardiovasc Interv 2006;68:788-792

Ankle Brachial Index Interpretation What is a normal ABI?

Ankle Brachial Index Interpretation Normal ankle pressure is 8-15% higher than arm pressure Epidemiological studies have used ABI of 0.9 as cutoff of normal from abnormal for diagnosis of PAD.

Ankle Brachial Index Interpretation – High ABI – Non-compressible vessels

Ankle Brachial Index Interpretation Hirsch AT et al, J Am Coll Cardiol 2006;47:1239-1312

Study 17 volunteers 1st year n=10 2nd year n=4 3rd year n=3

Feedback from Study Part A – Performance of ABI Measure ABI for right leg on patient

Measure Right ABI Feedback – Arm Measurement

Measure Right ABI Feedback – Leg Measurement * Obtained accurate Doppler signal from DP and PT

Feedback from Study Part B – Calculation of ABI Right brachial Left brachial Right PT Right DP Left PT Left DP 150mmHg 140mmHg 100mmHg 130mmHg 120mmHg 105mmHg A B C D E F Right ABI = D/A Left ABI = E/A

ABI Calculation Feedback Errors Brachial:Ankle index Same leg/arm Right ankle/right arm Left ankle/left arm Lower brachial pressure Use of DP alone Use of PT alone N=1

Feedback from Study Part C – Interpretation of ABI 1.6 1.2 1.0 0.8 0.4 A – non-compressible B – normal C – mild D – Moderate E - Severe

ABI Interpretation Feedback

Ankle Brachial Index Interpretation

Ankle Brachial Index Limitations Localization of disease Non-compressible ABI Pseudo-normal ABI Resting versus exercise ABI Role in diagnosis of critical limb ischemia (CLI) Hypertensive patient

ABI and Localization of Disease Segmental Limb Pressures Brachial Upper Thigh Upper Calf Ankle Toe Aorto-Iliac, CFA, Prox SFA Mid/distal SFA and Popliteal Tibial Small Vessel Disease

ABI and Localization of Disease Pulse Volume Recordings Measures volume change in limb with each pulsation Volume of tissue and venous blood relatively constant Change in volume due to arterial inflow Cuffs inflated to ~60mmHg Volume change presented on spectral display Similar to arterial pulse wave tracing Stenosis indicated by loss of amplitude during systole

Non-Compressible ABI

Non-Compressible ABIs Role of Toe Pressure Great toe 32mHg 2nd toe 35mmHg 3rd toe 17mmHg 4th toe 19mmHg 5th toe absent Value of toe pressure in patients with non-compressible tibial vessels and supranormal ABI - Normal toe-brachial index > 0.7

Non-invasive Hemodynamic Evaluation Toe Pressure

Pseudonormal ABI PAD Vessel Ca 2+ ABI

Resting versus Exercise ABI Exercise Testing ABI at baseline 2 mph at 12% grade, 5 minutes ABI post-exercise, 1 minute, then q 2 minutes Post-exercise ankle systolic pressure Falls >20% from baseline Takes longer than 3 minutes to recover

Resting versus Exercise ABI Exercise Testing Resting ABI Exercise ABI N=396 symptomatic patients with PAD.

Resting versus Exercise ABI Exercise Testing 58 year old male Right buttock claudication Classic description

Non-invasive Hemodynamic Evaluation Exercise Testing

ABI in Patients with Critical Limb Ischemia Limitation Delete n=49 ABI Delete

ABI in Patients with Critical Limb Ischemia Importance of Indication for Assessment Hemodynamic findings are usually confirmatory – However exceptions exist as illustrated in this case. Ankle Pressure 140mmHg ABI 0.99 Toe Pressure 92mmHg Right Heel

Popliteal and Tibial Angiography AT PT Peroneal AT Emphasizing the point that anatomic definition is sometimes required to confirm the diagnosis. PT Peroneal

Conclusions ABI Helpful in diagnosis and assessment of patients with symptomatic PAD Useful in primary prevention of CV morbidity and mortality, especially in asymptomatic patients or patients with atypical symptoms. Requires training in order to perform correctly and calculate ABI Has limitations that should be understood