Coronary Artery Calcification in Type 1 Diabetes

BACKGROUND:

Approximately 10 percent of premature coronary artery disease (CAD) morbidity and mortality in the general population is due to insulin dependent diabetes mellitus (IDDM). By age 55, 35 percent of IDDM patents die of CAD, in contrast to only 8 percent of nondiabetic men and 4 percent of women. In the U.S., IDDM affects at least 750,000 persons and this number is growing rapidly as the effect of increasing incidence and improved survival. Tight blood glucose control can slow the development of microvascular complications but a protective effect on heart disease has not been convincingly demonstrated.

DESIGN NARRATIVE:

This observational population-based study evaluated cross- sectionally a population-based group of 656 IDDM patients aged 20-55 years and 764 of their non-diabetic spouse/partner controls using the electron-beam computed tomography (EBCT). Patients and controls were compared in terms of the amount and anatomical distribution of coronary artery calcium (CAC), a marker of atherosclerosis, and the left ventricular (LV) area, a marker of LV hypertrophy and diabetic cardiomyopathy. The demographic, metabolic, and behavioral factors associated with increased CACand LV area were defined. Standard epidemiological methods were used to determine the prevalence of clinical CAD, defined by previous MI, revascularization, or angina in the study population. In 100 asymptomatic high-risk IDDM patients (CAC greater than or equal to 20 or LV area greater than 60 cm2), in 50 low-risk patients (CAC and LV area below these cut-offs), and in 20 nondiabetic controls age-sex matched to the high-risk patients, ECG-gated rest-stress technetium-99m sestamibi single-photon emission computed tomographic imaging (MIBI SPECT) was performed. This helped to determine the presence of myocardial perfusion defects and to quantify myocardial perfusion reserve as well as to relate these findings anatomically to the distribution of CAC by EBCT. In addition, LV volumes, ejection fraction, wall motion and thickening were determined, and related to LV area by EBCT. Finally, the study cohort of 656 IDDM patients and 764 non diabetic spouses/partners were followed up for a period of 3 years to measure the change in CAC and LV area using a repeat EBCT and to identify the metabolic and behavioral risk factors for progression in these indices. Cause-specific mortality was monitored and all fatal and non-fatal cardiac events were ascertained. In the subgroup of 100 high-risk IDDM patients studied with the MIBI SPECT at the baseline and in all low-risk patients whose CAC increased by more than 50 during the follow-up, MIBI SPECT was used to evaluate the change in myocardial perfusion, LV volumes, ejection fraction, wall motion and thickening, as well as to relate these findings to the change in CAC and LV area by EBCT.

The study was extended to follow the cohort for an additional three years to achieve the following specific aims: 1. To determine, among type 1 diabetic (T1D) patients and comparable controls, the risk factors for: a. 6-year progression of electron-beam tomography (EBT) defined coronary calcification - marker of coronary atherosclerosis b. 6-year development of myocardial perfusion defects and changes in relative myocardial perfusion reserve defined using ECG-gated rest-stress technetium-99m MIBI SPECT imaging c. 6-year incidence of clinical CAD, defined by fatal and non-fatal MI, revascularization or angina, as well as stroke, peripheral artery disease and cause-specific mortality. 2. To develop a clinically useful measure of insulin sensitivity that is directly comparable between T1D patients and non-diabetic persons to more precisely determine the role of insulin resistance in development of premature CAC in type I diabetes.