Effects of exercise training on carotid intima-media thickness in patients with type 2 diabetes and coronary artery disease. Influence of carotid plaques

This study is part of a randomized clinical trial investigating effects of exercise training on cardiovascular disease (CVD) risk factors and measures of atherosclerosis in patients with type 2 diabetes and CAD (ClinicalTrials.gov: NCT01232608). Patients with known type 2 diabetes and verified CAD by coronary angiography (n = 137) were included at the Department of Cardiology, Oslo University Hospital, Ullevål, Oslo, Norway between August 2010 and March 2012. The last follow-up was in March 2013. Exclusion criteria were presence of proliferative retinopathy, end stage renal disease, cancer, stroke or acute myocardial infarction within the last 3 months, unstable angina, uncompensated heart failure, serious arrhythmia, severe valvular disease, severe rheumatologic disease, chronic obstructive pulmonary disease stadium GOLD IV, thromboembolic disease, ongoing infections, severe musculoskeletal disorders and other disabilities limiting the ability for physical activity. All patients gave informed, written consent to participate in the study. The study was approved by The Regional Ethics Committee and was conducted according to the Declaration of Helsinki. At the time of inclusion the patients were randomized in a 1:1 ratio to either the exercise group or the control group. The control group continued with standard follow-up by their general practitioner. Study design and methods have also previously been reported [21].

The study participants randomized to the exercise group underwent a 12 months combined aerobic and resistance training program planned and conducted in collaboration with the Norwegian School of Sports Sciences, Oslo, Norway. The exercise program consisted of group-based exercise sessions of 60 min duration twice a week under supervision of qualified instructors throughout the intervention period, and a third weekly home-based individual exercise session. The total exercise volume was 150 min per week, of which approximately two-thirds was aerobic and one-third resistance exercises. The exercise sessions were guided by Borg’s scale of rated perceived exertion (RPE) and included parts of high intensity interval training (RPE ≥ 15) [21].

Body weight was measured with light clothing on the same weight before and after the intervention. Waist circumference was measured horizontally at the level of the iliac crest and at the end of a normal expiration. Arterial blood pressure (BP) was measured automatically in the brachial artery with patients in a supine position (Riester ri-champion^® N, Jungingen, Germany). Blood samples were drawn at inclusion and end of the study by standard venipuncture between 0800 and 1000 AM after overnight fast, without medication taken since the preceding evening and without exercise training the last 24 h. The final blood samples were taken within 1 week after the last exercise section. Total cholesterol, high-density lipoprotein (HDL) cholesterol, triglyserides were determined by conventional laboratory methods. Low-density lipoprotein (LDL) cholesterol was calculated by Friedewalds formula. HbA1c was measured by turbidimetric inhibition immunoassay (Roche, Basel, Switzerland) and CRP was determined by high sensitivity enzyme-linked immunosorbent assay (DRG Instruments, Marburg/Lahn, Germany).

We implemented a standardized protocol and strict quality control procedures to achieve reliable ultrasonic measurements of the carotid artery IMT [22]. The subjects were studied in the morning under standardized conditions (quiet room, comfortable temperature) and in the fasting state. One experienced sonographer who was blinded to the participants’ group status and risk factor levels did all the examinations. High-resolution ultrasonography was performed with a Zonare z.one ultra (Zonare medical Systems, Mountain View, CA, USA) ultrasound scanner equipped with electrocardiogram (ECG) and a linear array 5–10 MHz transducer, using 8 MHz as centre frequency and utilizing the harmonic frequencies. The participants were examined in the supine position with the head turned slightly to both sides. After identifying the bulb, longitudinal images of the common carotid artery (CCA) were obtained by combined B-mode and colour Doppler. The scan was focused on the far wall segment 20 mm proximal of the carotid bulb, where all measurements were done. All images were acquired by using an anterior oblique angle (30° from midline), and/or if needed, a lateral angle (100° from midline) [23, 24]. Measurements were taken during end-diastole (R-wave of the ECG) [25]. The CCA and the carotid bulb region were also scanned for the presence of atherosclerotic plaques, defined as a distinct area of the vessel protruding >50 % of the adjacent parts of the intima-media layer [26]. cIMT was measured at locations without atherosclerotic plaques, although plaques could be present in adjacent areas. The plaques’ volume and content (calcified, non-calcified, or mixed plaque) were analysed at baseline. Calculation of plaque volumes was based on manually set measurements of length, width and height of the plaques. All scans were digitally stored on the internal hard disk for subsequent off-line analysis using Osirix MD (v. 2.5.1) (Pixmeo, Geneva, Switzerland). Three end-diastolic frames were selected, and the mean cIMT was calculated for each subject as the average of maximum 9 (3 × 3) consecutive measurements on each side. A minimum of two measurements on one side were needed to be included in the baseline analyses and at least two measurements from the same side at both baseline and 12 months to be included in the interval analyses. The intrasonographer variability has been shown earlier [22] [correlation coefficient for mean cIMT 0.99 (0.977–0.999)].

The power calculations in the main study were based on an expected 10 % relative reduction of HbA1c in the exercise group while unchanged in the control group. Accounting for possible dropouts the calculations indicated a minimum of 68 patients in each arm of the study [21].

Demographic data are given as proportions, mean (±SD) or medians (25, 75 percentiles) with skewed data. Between group differences in baseline characteristics were calculated by independent-sample Students t-test, Chi square test or Mann–Whitney test as appropriate. Baseline associations were assessed by Pearson correlation or Spearman’s rank correlation as appropriate. Differences between the randomized groups in changes from baseline to 12 months were calculated by one-way ANCOVA. Skewed data distributions were log transformed before entering the model. Within group changes in cIMT was calculated by paired-samples Student’s t-test. Changes are presented as mean [95 % confidence interval (CI)]. Interactions between the exercise effect on cIMT and relevant baseline factors were investigated by two-way ANCOVA. Based on clinical judgement, the following factors were considered potential effect modifiers (continuous variables were dichotomized at median values): Gender, etnicity (caucasian), age (>64), body mass index (BMI) (>29 kg/m²), previous myocardial infarction, presence of carotid plaques, years of known diabetes (>9), presence of microvascular complications, baseline LDL (>2.0 mmol/L) and baseline HbA1c (>7.4 %). SPSS version 18.0 for Windows was used. p value < 0.05 was defined as statistically significant.