Patient characteristics
Of 1,935 patients included in DIAST-CHF, 1,085 patients were analysed, of whom 637 had an OGTT. A minority of these (13 patients) had a previous diagnosis of type 2 diabetes mellitus and were being treated with glucose-lowering medication. Overall, 465 patients had a history of diabetes mellitus at inclusion, of whom four with probable type 1 diabetes were excluded from analyses. Of the remaining 461 patients with known type 2 diabetes mellitus, 178 were treated with insulin and 283 with diet and/or oral glucose-lowering drugs.
Among those undergoing glucose tolerance testing, 343 participants (55.0%) had normal glucose metabolism, 229 (36.7%) had prediabetes and 52 (8.3%) had newly diagnosed diabetes mellitus (Fig. 1).
Clinical characteristics for patients with normal, prediabetic and diabetic glucose metabolism are shown in Table 1. Glucose and lipid metabolism variables are shown in Table 2. Overall, prediabetes tended to be an intermediate stage between normal and diabetic groups with regard to many indicators of metabolic disturbance and end-organ disease, while patients with insulin-treated type 2 diabetes had the highest rates of end-organ disease or comorbidities. Groups did not differ with regard to age, systolic blood pressure and prevalence of hypertension. Patients with diabetes were treated more intensively than those with prediabetes or normal glucose metabolism. Treatments were with typical cardiovascular drugs with a significant trend towards ACE inhibitors, loop diuretics, aldosterone antagonists, statins, acetylic salicylic acid and vitamin K antagonists.
Table 1 Clinical characteristics of patients with normal, prediabetic or diabetic glucose metabolism
Table 2 Metabolic characteristics of patients with normal, prediabetic or diabetic glucose metabolism
Consistent with the process of group allocation, prediabetic participants had significantly higher FPI and FPG than non-diabetic participants, as well as higher 1 h-PG and 2 h-PG, reflected also in AUCGlu0–120 and normalised AUCGlu0–120. Insulin resistance as approximated by HOMA was higher, and insulin sensitivity as approximated by QUICKI and Gutt index lower in prediabetic participants. Prediabetes also displayed an intermediate state in between normal and type 2 diabetic patients on oral glucose-lowering medication. LDL-cholesterol was paradoxically lower in this group and in insulin-treated type 2 diabetic patients, while HDL-cholesterol decreased with severity of glucose metabolism disturbance. This phenomenon is probably due to the fact that LDL-cholesterol is effectively lowered by statin therapy, which was more prevalent in diabetic patients, while low HDL-cholesterol is less amenable to pharmacological treatment.
Prevalence of diastolic dysfunction
Diastolic function could not be analysed or classified in 61 participants (5.6%) due to presence of atrial fibrillation or missing echocardiographic variables critical for classification. Accordingly, 1,024 participants were included in the analysis of diastolic function. Echocardiographic variables are listed in Table 3.
Table 3 Echocardiographic characteristics of patients with normal, prediabetic or diabetic glucose metabolism
Prevalence of any degree of diastolic dysfunction increased with impairment in glucose metabolism, i.e. the highest prevalence was found among insulin-treated type 2 diabetic patients (87.3%) or those on oral glucose-lowering therapy (88.4%) as compared with those with prediabetes (86.7%) or normal glucose metabolism (76.0%, p < 0.001 test for trend). Participants with prediabetes represented an intermediate between normal (p = 0.009 for difference) and diabetic patients with regard to diastolic dysfunction. This is also evidenced by trends in structural variables that are indicative of diastolic dysfunction, but not used as criteria for classification, e.g. left atrial diameter or LVMI. While prevalence of diastolic dysfunction of any grade was very similar between prediabetes and diabetes, the distribution across grades 1 to 3 of diastolic dysfunction was shifted to the right for diabetes as compared with prediabetes (Fig. 2), reflected by a statistically significant χ
2 test of the correspondent 3 × 4 table (p < 0.001). Only a small number of patients were identified as having severe diastolic dysfunction, none of whom had normal glucose metabolism; therefore patients with moderate or severe diastolic dysfunction were placed in one group for the above analysis.
Status of glucose metabolism remained significantly associated with prevalence of diastolic dysfunction in logistic regression analysis adjusted for the significantly associated variables heart rate, systolic blood pressure, and presence or history of heart failure. Furthermore, an odds ratio of 1.77 (95% CI 1.10–2.86) for having diastolic dysfunction was estimated for the prediabetes group compared with the normal glucose metabolism group.
Impairment in glucose metabolism and severity of diastolic dysfunction
As a functional variable indicative of left ventricular end-diastolic pressure, E:e′ was similar in prediabetes compared with normal glucose metabolism, but was significantly higher (p = 0.002) in diabetes than in the other groups. In the whole cohort, E:e′ correlated significantly with HbA1c (r = 0.20, p < 0.001), as well as with several other markers of glucose metabolism, namely 2 h-PI, normalised AUCGlu0–120 and ISI0,120. Importantly, the association between E:e′ and HbA1c remained significant when including only patients with HbA1c in the normal range, i.e. ≤4.2% (r = 0.16, p < 0.05).
In multivariate linear analysis including sex, CHD, CHF, history of myocardial infarction, age, log(BMI), heart rate, systolic and diastolic blood pressure, cardiovascular medications and HbA1c as predictors, HbA1c remained significantly (p < 0.001) associated with log(E:e′). When modelling status of glucose metabolism in place of HbA1c in a general linear model with log (E:e′) as dependent variable, status of glucose metabolism was a significant predictor, together with sex, age, log (BMI), heart rate, systolic and diastolic blood pressure, and both beta blocker and aldosterone antagonist intake. These associations remained significant with Bonferroni–Holm adjustment for multiple testing.
LVMI and left atrial diameter as structural markers of diastolic function correlated significantly with HbA1c and also with AUCGlu0–120, normalised AUCGlu0–120, 1 h- and 2 h-PG, HOMA, QUICKI and ISI0,120. In contrast to E:e′, these structural variables also correlated with FPG and FPI. However, in multivariate analysis associations of LVMI and left atrial diameter with HbA1c lost significance. Interestingly, there was also a highly significant negative correlation of HDL-cholesterol with left atrial diameter and LVMI. No significant correlation of structural variables with HbA1c was observed in patients with HbA1c ≤ 4.2%. Nevertheless, when including only patients with normal glucose metabolism or prediabetes, the above-mentioned correlations remained statistically significant except those between left atrial diameter and HbA1c, and LVMI and 2 h-PG or HbA1c, respectively. While the two type 2 diabetes treatment groups (oral glucose-lowering medication, insulin) had a similar prevalence of diastolic dysfunction and similar distribution across grades of diastolic dysfunction, E:e′ was significantly higher in the insulin-treated than in the other group (10.7 vs 9.5, p < 0.05).
E:e′, left atrial diameter or LVMI did not correlate with duration of diabetes or daily insulin dose.
Diabetes, diastolic dysfunction and physical impairment
The distance walked in 6 min as a simple indicator of exercise capacity decreased along the diabetic continuum (Table 1). Both grade of diastolic dysfunction (r = −0.29, p < 0.001) and E:e′ (r = −0.17, p < 0.001) correlated significantly with the distance walked in 6 min. Ejection fraction did not differ significantly between groups and there was only a very weak correlation between ejection fraction and distance walked in 6 min (r = 0.09, p < 0.01).