Coronary Artery Plaque Burden in Asymptomatic Danish Men Aged 65-75 Years and the Relation to Glycemic Status.

Background

Cardiovascular disease: Cardiovascular disease (CVD) is still one of the leading causes of death in the Western Society. Despite extensive research, risk estimation based on traditional risk factors predicts risk in the general population but may not give an adequate individual risk, and can thereby under- or overestimate the risk of future cardiovascular event and therefore lead to either over- or undertreatment of a not ignorable part of the population.

T2DM/dysglycemia and atherosclerosis: The prevalence of type 2 diabetes mellitus (T2DM) is rising rapidly. Furthermore, one study has reported that the prevalence of dysglycemia or undiagnosed diabetes were as high as 43.8% among 60-year-old men. T2DM is known to be strongly associated with an increased risk of CVD, but also dysglycemia has been associated with an increased risk of CVD. Thus, it is possible that there is a linear relationship between stepwise dysregulated glycemic status and increased coronary plaque burden, but the relationship has not been fully explored.

CCTA: Coronary CT Angiography (CCTA) can be performed with or without contrast. Contrast enhanced CCTA has been found to be a valid and reproducible method of evaluation of both extent and characteristics of atherosclerotic plaques. Motoyama et al. reported spotty calcification, positive remodeling, and LAP (non-calcified plaque) to be associated with an increased risk of development of AMI, especially when two or more patterns were co-localized in the plaques. Thus, it might be possible that this type of plaque morphology is associated with vulnerable plaques.

Echocardiography and T2DM/Dysglycemia: T2DM is correlated to a higher incidence of diastolic dysfunction, which is thought to predispose to diabetic cardiomyopathy. In addition, subtle left ventricular systolic dysfunction assessed by 2D speckle-tracking (also termed impaired strain) was found in patients with diabetes and normal systolic function. To our knowledge only few studies have investigated diastolic dysfunction and 2D speckle-tracking in patients with dysglycemia and their results were mostly diverging.

To our knowledge no studies have investigated coronary artery plaque burden and morphology in asymptomatic men aged 65-75 years with focus on the influence of glycemic status in individuals without known T2DM. Due to the expectance of increasing number of patients with T2DM and dysglycemia the coming years, it must be foreseen that the number of patients with CVD will increase in this group of patients. It is mandatory that we increase our knowledge, especially about the development of coronary atherosclerosis and left ventricular function. We expect that this study will bring further light on these important aspects of dysglycemia and hopefully give information to improve treatment and prophylaxis.

Methods

Study population: We plan to recruit 500-800 participants from the DANCAVAS study. More detailed description of the Study population can bee read in "Eligibility". Based on one oral glucose tolerance test (OGTT) per participant, this population will be divided into three groups; normal glucose tolerance (NGT), dysglycemia (impaired fasting glucose (IFG) or impaired glucose tolerance (IGT)) and diabetic OGTT without known T2DM. We use the WHO definitions in dividing the participants into the mentioned three groups of different glycemic status. To date the use of OGTT in diagnosing T2DM, demands two measurements at two separate days. Because of the measurement of only one OGTT in this study, the participants with diabetic OGTT does not per se fulfil the criteria for diabetes.

Data acquisition

1. OGTT: Patients will be instructed in 8-12 hours fasting before the OGTT. Fasting plasma glucose (FPG) will be measured. Thereafter, 75 gram glucose will be ingested over five minutes. 120 minutes later plasma glucose (120-PG) will be measured and patients will be categorized according to mentioned definitions.

2. Echocardiography: Echocardiography standard measurements of left ventricular (LV) systolic and diastolic function:

   • LV and left atrial volumes will be estimated using Simpson's biplane method of discs in the 4 and 2-chamber views, and LV ejection fraction will be calculated.
   • The mitral inflow pattern will be estimated in the apical 4-chamber view, and the peak early (E) and peak atrial(A) velocities will be measured. Peak early mitral annular velocities (e') will be estimated using tissue Doppler imaging. The E/e´ratio will be obtained by dividing E by average value of e´.

   Global left ventricular longitudinal strain (GLS):

   • Longitudinal systolic strain will be measured using 2D speckle tracking echocardiography. This measurement will be obtained from views with an optimized focus on the LV and a frame rate of about 60-80 frames/sec. Subsequently LV will be divided into 18 segments. GLS will be calculated by the software as the mean value of the peak systolic longitudinal strain of the 18 segments.

3. CCTA: The CCTA scan GE revolution will be used. CAC score will be evaluated using non contrast scans from the DANCAVAS study. In our study, contrast enhanced scans using 256-slice, ECG-gated, will be performed. In order to regain optimal results, patients with pulse >60 beat/min will be given intravenous Beta-blockers and sublingual Nitroglycerin spray just before the examination if not contraindicated. Depending on BMI, tube voltage will be 120 or 100 kV and tube current 350-650 mAs. The collimation is 256×0,23mm with a gantry rotation time of 280 ms with 16 centimeters axial coverage per rotation. The estimated total radiation dose for one contrast enhanced CCTA is 1-6 mS. To reduce risk of contrast related affection of the kidney function a recent eGFR must be obtained before scanning and patients will be sufficiently hydrated.

   CCTA analysis:

   Plaque burden The major proximal coronary segments; 1,2,3-5,6,7-11,12,13 are analyzed.

   Per vessel analysis of:

   • Percent atheroma volume (PAV):(Total vessel volume-total lumen volume/total vessel volume×100%)
   • Total atheroma volume (TAV):(Total vessel volume-total lumen volume)
   • Normalized atheroma volume (NAV):(Total vessel volume-total lumen volume/mean segment length)

   Plaque morphology

   Per plaque analysis of:

   • LAP: defined as a non-calcified plaque (HU\<150) with a lipid core of \<30 HU.
   • Remolding indices (RI): calculated by lesion diameter/reference diameter, where the reference diameter is from a normal appearing proximal segment.
   • Spotty calcifications (SC): defined as small calcified nodules \<3mm in length and \<=90 degrees of the coronary arch.
   • Degree of stenosis: a significant stenosis is defining as >70% of the luminal area.

   All CTTA scans will be assessed by an observer blinded to patient characteristics. Semi quantitative method using dedicated plaque software (QAngioCT Research Edition version 2.0, Medis Medical Imaging Systems, Leiden, Holland) will be used to assess the plaque analysis.

4. Population characteristics: Baseline data will be collected from journal system and questionnaires and includes demographic, former CVD disease, presence of T2DM and information regarding the traditional risk factors (e.g. hypertension, hypercholesterolemia, obesity and smoking).
5. Blood sample: Blood sample includes e.g.cholesterol profile, HbA1c, Creatinine, C-Peptide, Insulin etc. Additionally, totally 30 ml blood will be collected to form a biobank for future research on the influence of inflammatory markers on atherosclerosis and glycemic status.