This cross-sectional study was conducted between 2019 and 2020. The inclusion criterion was new patient referred to Professor Kojuri Cardiovascular Clinic in Shiraz, Iran (email: [email protected], webpage: http://kojuriclinic.com). The exclusion criteria were deep vein thrombosis, lower extremity injury that caused severe pain, and inability to remain supine. Patients with ABI more than 1.4 were also excluded.
Complete history was noted and physical examination findings were recorded for all patients. Risk factors such as smoking, hypertension, dyslipidemia, diabetes mellitus, age and gender were considered. We also recorded triglycerides, total cholesterol, LDL cholesterol, HDL cholesterol, HbA1c and hs-CRP for all patients, and documented blood pressure and electrocardiographic findings for all patients.
Dyslipidemia was defined as high total or LDL cholesterol, or high triglycerides, or low HDL cholesterol. Diabetes mellitus was diagnosed according to the 2019 ADA guidelines [22]. Hypertension were defined according to the ACC/AHA 2017 guidelines [23].
Triglyceride levels higher than 200 mg/dL, total cholesterol more than 200 mg/dL, LDL cholesterol more than 100 mg/dL, HDL cholesterol less than 40 mg/dL in men and less than 50 mg/dL in women, HbA1c more than 6.5% and hs-CRP more than 2 mg/L were considered abnormal. Patients with hs-CRP more than 10 mg/L were excluded due to the possibility of acute inflammation. Smoking was defined as regular tobacco smoking or past history of smoking within 3 months before the study [24–29].
If noninvasive studies yielded no evidence of abnormal findings, this was considered absence of CAD. Patients with strongly positive results in noninvasive studies underwent selective coronary angiography via radial artery approach by an expert interventional cardiologist. Angiography videos were reviewed by a team of expert cardiologists. Based on the results, patients were classified as having proven mild CAD if stenosis was less than 50%, or proven severe CAD if stenosis was more than 50%.
ABI was determined in all patients with the Huntleigh Dopplex Ability Automatic Ankle Brachial Index System (Cardiff, UK), which uses Doppler ultrasound to measure blood pressure. The appropriate cuffs were selected for each patient, and the patient lay supine for 30 min before starting the test. The ankle and arm cuffs were attached directly to the patient’s skin. Blood pressure was recorded in both the left and right limbs. An ABI less than 0.9 was considered abnormal, and values between 0.9 and 1.4 were considered normal. Patients with both right and left ABI between 0.9 and 1.4 were classified as having normal ABI. Patients with a right and/or left ABI less than 0.9 were considered to have abnormal ABI. We also calculated inter-arm systolic pressure difference for each patient; a difference greater than 10 mmHg was considered abnormal.
The study was double-blinded. The team of cardiologists who recorded the results of coronary angiography were blinded to the patients’ ABI. The statisticians did not receive information about the ABI values or coronary angiography findings. For blinding, we used alphabetical order for each group of patients with or without coronary artery disease. Patients with proven mild CAD were designated with the letter A, and patients with proven severe CAD were designated with the letter B. We also used alphabetical order for normal or abnormal ABI. Patients with abnormal ABI were designated with the letter C, and patients with normal ABI were designated with the letter D.
For statistical analyses we used IBM SPSS software version 25. Independent-sample t tests and one-way ANOVA were used for parametric variables. The Mann-Whitney U test and Kruskal-Wallis test were used for nonparametric data. Values of p < 0.05 were considered significant.
All patients were informed about the details of this research, and provided their written informed consent. Patients who declined to participate in the study were excluded. The protocol was approved by the Ethics Committee of Shiraz University of Medical Sciences under code number: IR.SUMS.MED.REC.1398.437. All methods were performed in accordance with the Helsinki ethics guidelines and regulations.