Effect of canagliflozin on left ventricular diastolic function in patients with type 2 diabetes

This prospective single-center pilot study was performed to evaluate the effects of additional treatment with canagliflozin on left ventricular function in T2DM. Between July 2017 and December 2017, 38 diabetic patients who had inadequately controlled T2DM were consecutively recruited from outpatients at Tsuruoka Kyoritsu Hospital, Yamagata, Japan. All participants were evaluated at baseline and at 3 months after beginning additional treatment with canagliflozin. During the 6 months before the start of this study and the 3 months after the start of this study, participants had not changed their use of antidiabetic drugs or any other drugs that could affect glucose metabolism such as renin–angiotensin–aldosterone system (RAAS) inhibitors (angiotensin-converting enzyme inhibitors and/or angiotensin receptor blockers), beta blockers, diuretics, and statins. The inclusion criteria were as follows: (1) T2DM with HbA1c (NGSP) of ≥ 7.0%, < 10.5% and (2) experiencing no changes in antidiabetic drugs or any other drugs during the 6 months prior to the start of this study. Inclusion criteria also included (3) satisfaction of either (a) or (b) as follows: (a) age ≥ 45 and < 75 years without a history of CVD and with ≥ 2 of the following risk factors determined at the screening visit: duration of T2DM ≥ 10 years, systolic blood pressure (SBP) ≥ 140 mmHg (average of 3 readings at screening visit), taking at least one anti-hypertensive agent, current daily cigarette smoker (Brinkmann index ≥ 200), microalbuminuria or macroalbuminuria (microalbuminuria: urinary albumin excretion from 30 to 300 mg/g Cr; macroalbuminuria: urinary albumin excretion of ≥ 300 mg/g Cr); dyslipidemia (abnormal values for ≥ 1 among high-density lipoprotein [HDL] cholesterol < 40 mg/dL, low-density lipoprotein (LDL) cholesterol ≥ 120 mg/dL, and/or triglycerides (TG) ≥ 150 mg/dL); carotid intima media thickness ≥ 1.1 mm, and plaque positive; or (b) age ≥ 35 and < 75 years with a history of ≥ 1 of the following indicating CVD: old cerebral infarction, old myocardial infarction, hospital admission for unstable angina, chronic heart failure, coronary artery bypass graft, percutaneous coronary intervention (with or without stenting), peripheral revascularization (angioplasty or surgery), symptomatic with documented hemodynamically significant carotid or peripheral vascular disease, or amputation secondary to vascular disease. Patients were excluded based on: (1) age < 35 years or ≥ 75 years; (2) taking antipsychotics; (3) arrhythmia; (4) severe renal dysfunction (serum Cr ≥ 2.5 mg/dL); (5) severe liver dysfunction (3× upper limit of normal); (6) diabetic ketosis or diabetic coma; (7) insulin-dependent diabetes mellitus; (8) malignancy, or (9) acute heart failure or acute myocardial infarction. All participants underwent blood tests, including those for fasting plasma glucose, HbA1c, estimated glomerular filtration rate (eGFR), HDL cholesterol, LDL cholesterol, TG, brain natriuretic peptide (BNP), hemoglobin (Hb), and hematocrit (Hct). Clinical data (duration of diabetes; body mass index [BMI]; SBP; diastolic blood pressure [DBP]; heart rate [HR]; history of CVD; insulin therapy; and use of oral anti-diabetic drugs, anti-hypertensive agents, and lipid-lowering agents) were obtained from medical records and a questionnaire.

Thirty-seven patients were included in the analysis after excluding 1 with arrhythmias.

The study protocol was approved by the ethics committee of Tsuruoka Kyoritsu Hospital (approval number: 2017-01; date: 7th June, 2017), and the study was conducted according to the principles of the Helsinki Declaration II. This study was registered at the UMIN Clinical Trial Registry (UMIN000028141). All patients were informed of the purpose of the study after which consent was obtained.

Standardized transthoracic and Doppler echocardiographic examinations were performed in all participants using commercially available equipment (iE33, Philips, Amsterdam, Netherlands). Left atrial diameter and end-diastolic and end-systolic left ventricular internal diameters were measured on a 2-dimensional guided M-mode recording. Left ventricular ejection fraction (EF) was assessed by the modified Simpson’s Biplane Method. Using two-dimensional echocardiograms the left ventricular mass index was determined by the area-length method [20]. To assess diastolic function, the following mitral pulse wave Doppler and tissue Doppler parameters were measured: peak early (E) and late (A) diastolic filling velocities, E/A ratio, deceleration time of E wave (DT), septal early diastolic mitral annular tissue velocity (septal e′), and lateral early diastolic mitral annular tissue velocity (lateral e′). We also calculated the E/e′ ratio by dividing the transmitral E peak by e′ [21].

Using the spontaneous sequence method, the beat-to-beat BP was measured for 15 min after 15 min of supine rest as the slope of the relationship between spontaneous changes in SBP and the pulse interval. Measurement was made using the second and third fingers of the right hand by the vascular unloading technique (Task Force Monitor, CNSystems, Graz, Austria). For calculation of BRS, the relative changes in SBP (mmHg) and the R–R interval (msec), which is expressed as the distance between corresponding QRS complexes, were considered according to the sequence method with cut-off points of 1 mmHg and 3 ms, respectively [22].

A 3-lead ECG with a sampling frequency of 1000 Hz was recorded for 15 min after the participant had rested for 15 min. The HRV was calculated during the test and included all recorded R–R intervals. HRV was calculated by the frequency domain method using a power spectral analysis of rhythmic oscillations of the R–R interval. The relative contributions of the low frequency (LF) power (0.04–0.15 Hz), high frequency (HF) power (0.15–0.4 Hz), and very-low-frequency (VLF) power (0–0.04 Hz) to total power were calculated as follows: LF normalized units (LFnu%) = LF absolute power (ms²)/total power (ms²) − VLF power (ms²)×100 and HFnu% = HF absolute power (ms²)/total power (ms²) − VLF (ms²)×100. The LFnu%/HFnu% ratio was considered to indicate sympathetic/vagal tone. All calculations were performed using the Task Force Monitor (CNSystems, Graz, Austria) [23].

The primary study outcome was a change in the septal E/e` as a parameter of left ventricular diastolic function. Secondary endpoints included changes in the following variables at the end of the 12-week treatment relative to the baseline: (1) echocardiographic parameters: left atrial diameter, left ventricular end-diastolic diameter, left ventricular end-systolic diameter, EF, left ventricular mass index, E, A, E/A, DcT, septal e′, lateral e′, and lateral E/e′; (2) autonomic function: BRS and LF/HF; (3) glycemic control variables: fasting plasma glucose and HbA1c level; (4) lipid metabolism variables: TG, LDL cholesterol, and HDL cholesterol; (5) BMI; (6) SBP and DBP, (7) HR; (8) BNP; (9) Hb and Hct; and (10) eGFR.

Because there has been no report on the effect of SGLT-2 inhibitors to improve the septal E/e′, we used information from a previous report on the effect of another drug on the septal E/e′ (approximately a 1.5 reduction) to estimate the required sample size [12]. Sample size estimates were based on the following: standard deviation, 3; α-level, 0.05; and power, 80%. Sample size was estimated to be 33 people. Assuming a dropout rate of 10%, the target number of patients was therefore set at 38 patients.

Data analyses were performed using the Statistical Package for the Social Sciences 22.0 software (IBM, Armonk, NY, USA). Patients’ characteristics and results are presented as mean ± SD, mean ± standard error, or median with interquartile range (IQR) as appropriate according to the data distribution. Comparison of variables between baseline and 3 months after treatment were made using the paired t test or Wilcoxon signed-rank test (Table 2). Pearson’s correlation analysis or Spearman’s rank correlation coefficient test was used for single correlations (Table 3). Multiple-linear regression was used to assess individual and cumulative effects of ΔHb, age, sex, SBP, eGFR, and HR on the Δseptal E/e′ ratio. Independent variables were selected among variables that were significantly correlated with the Δseptal E/e′ ratio (Table 4). The delta (∆) values for BRS and LF/HF were calculated according to values at 3 months after treatment-value at baseline. All other delta values were calculated as [(value at 3 months after treatment-value at baseline) × 100]/value at baseline (%). As shown in Fig. 2 and Table 5, the baseline septal E/e′ ratio was divided into tertiles (T1 < 12, T2 ≥ 12- < 16, T3 ≥ 16). The Jonckheere trend test was used to test for linear trends in Δseptal E/e′ ratio in relation to baseline septal E/e′ ratio tertiles. The analysis of variance (ANOVA) was used to compare Δseptal E/e′ ratios among participants with various baseline septal E/e′ ratio tertiles. In ANOVA, the Tukey post hoc test was also used to compare Δseptal E/e′ ratios among different baseline septal E/e′ ratio groups. As shown in Table 6, the effects of canagliflozin on Δseptal E/e′ ratios were analyzed for the following subgroups: sex, history of hypertension, presence of CVD, insulin use, sulfonylurea use, metformin use, DPP-4 inhibitor use, calcium channel blocker use, RAAS inhibitor use, beta blocker use, and diuretic use. In the subgroup analysis, mean Δseptal E/e′ was compared using Student’s t test. Hypertension was defined as follows: SBP ≥ 140 mmHg, DBP ≥ 90 mmHg and/or the use of at least one anti-hypertensive agent. CVD was considered to be present if any of the following had occurred: cerebral infarction, myocardial infarction, hospital admission for unstable angina, heart failure, coronary artery bypass graft, percutaneous coronary intervention (with or without stenting), peripheral revascularization (angioplasty or surgery), symptoms consistent with documented hemodynamically significant carotid or peripheral vascular disease, and/or amputation secondary to vascular disease. As shown in Additional file 1: Table S1, participants were divided into a primary prevention group without a history of CVD, a secondary prevention group with a history of CVD, and an overall population group. In each group, comparison of variables between baseline and 3 months after treatment were made using the paired t test. The Student’s t test was used to compare mean Δseptal E/e′ in the primary prevention group and secondary prevention group. A p value < 0.05 was considered significant.

A total of 37 patients (25 males and 12 females) were included in the analysis. Table 1 shows the baseline clinical, anthropometric, and pharmacologic data on the study participants. Mean age of participants was 64.2 ± 8.1 years (mean ± SD), mean duration of diabetes was 13.5 ± 8.1 years, and mean HbA1c was 7.9 ± 0.7%. Of the participants, 86.5% had hypertension, 100% had dyslipidemia, and 32.4% had CVD. At baseline, 32.4% of patients were on insulin, 37.8% on sulfonylureas, 54.1% on metformin, 43.2% on DPP-4 inhibitors, 45.9% on calcium-channel blockers, 45.9% on RAAS inhibitors (angiotensin-converting enzyme inhibitors and/or angiotensin receptor blockers), 13.5% on beta blockers, 10.8% on diuretics, 48.6% on statins, and fibrates on 2.7%.

Compared to baseline levels, decreases were found at 3 months in mean fasting plasma glucose (146.3 ± 28.8 mg/dL to 125.9 ± 24.6 mg/dL, p = 0.001), mean HbA1c (7.9 ± 0.7% to 7.1 ± 0.6%, p < 0.001), mean SBP (134.1 ± 14.3 mmHg to 130.3 ± 15.1 mmHg, p = 0.028), mean left ventricular mass index (82.0 ± 15.8 g/m² to 77.3 ± 16.4 g/m², p = 0.003), mean septal E/e′ ratio (13.7 ± 3.5 to 12.1 ± 2.8, p = 0.001), and mean lateral E/e′ ratio (9.7 ± 2.9–8.3 ± 1.9, p < 0.001). Increases after 3 months of treatment were identified in mean Hb (13.9 ± 1.2 g/dL to 14.7 ± 1.4 g/dL, p < 0.001) and mean Hct (40.7 ± 3.3% to 44.0 ± 3.7%, p < 0.001). There were no differences from baseline values to the end of the 3-month treatment period in median BNP (11.4 [IQR 9.1–20.6] pg/mL to 10.6 [IQR 6.3–15.8] pg/dL, p = 0.061), mean EF (65.7 ± 5.0% to 65.3 ± 5.5%, p = 0.652), median BRS (9.6 [IQR 6.3-12.5] ms/mmHg to 7.9 [IQR 5.4–11.4] ms/mmHg, p = 0.592), and median LF/HF (1.3 [IQR 0.9–2.3] to 1.2 [IQR 0.7–2.0], p = 0.202) (Fig. 1, Table 2).

Correlation analysis showed that the Δseptal E/e′ ratio was correlated with the baseline septal E/e′ ratio (r = − 0.618, p = 0.000), age (r = − 0.464, p = 0.004), baseline SBP (r = − 0.335, p = 0.042), baseline HR (r = 0.359, p = 0.029), baseline eGFR (r = 0.355, p = 0.031), and ΔHb (r = − 0.496, p = 0.002) (Table 3).

Multiple regression analysis showed that ΔHb were inversely related to the Δseptal E/e′ ratio. These findings remained after adjusting the Δseptal E/e′ ratio for age, sex, SBP, eGFR, and HR (Table 4).

Figure 2 and Table 5 show the comparisons of Δseptal E/e′ ratio among participants with various baseline septal E/e′ ratios according to tertiles based on ANOVA. There was a significant difference in Δseptal E/e′ ratios among these three groups. The results were then analyzed by the Tukey post hoc test. The T2 (p = 0.03) and T3 (p = 0.009) groups had decreased septal E/e′ ratios in comparison with the T1 group. This observation was confirmed by the Jonckheere trend test: Δseptal E/e′ ratio (p = 0.008) was significantly correlated with tertiles of baseline septal E/e′ ratios.

The septal E/e′ ratio was significantly improved in patients using sulfonylurea (p = 0.006) or a DPP-4 inhibitor (p = 0.014) at baseline. However, there was no significant difference in patients grouped according to sex, history of hypertension, presence of CVD, insulin use, metformin use, calcium channel blocker use, RAAS inhibitor use, beta blocker use, and diuretic use (Table 6).