Effects of reduced coronary flow reserve on left ventricular function in type 2 diabetes

Diabetic cardiomyopathy: Clinical phenotype and practice

Diabetic cardiomyopathy (DCM) is a pathophysiological condition of cardiac structure and function changes in diabetic patients without coronary artery disease, hypertension, and other types of heart diseases. DCM is not uncommon in people with diabetes, which increases the risk of heart failure. However, the treatment is scarce, and the prognosis is poor. Since 1972, one clinical study after another on DCM has been conducted. However, the complex phenotype of DCM still has not been fully revealed. This dilemma hinders the pace of understanding the essence of DCM and makes it difficult to carry out penetrating clinical or basic research. This review summarizes the literature on DCM over the last 40 years and discusses the overall perspective of DCM, phase of progression, potential clinical indicators, diagnostic and screening criteria, and related randomized controlled trials to understand DCM better.

End-stage renal failure is associated with impaired coronary microvascular function

BACKGROUND

Cardiovascular disease is the leading cause of death in patients with chronic kidney disease. Studies investigating the disproportionate burden of cardiovascular disease have occurred predominantly in the peripheral vasculature, often used noninvasive imaging modalities, and infrequently recruited patients receiving dialysis. This study sought to evaluate invasive coronary dynamic vascular function in patients with end-stage renal failure (ESRF).

PATIENTS AND METHODS

Patients referred for invasive coronary angiography prior to renal transplantation were invited to participate. Control patients were recruited in parallel. Baseline characteristics were obtained. Coronary diameter (via quantitative coronary angiography) and coronary blood flow (via Doppler Flowire) were measured; macrovascular endothelial-dependent and independent effects were evaluated in response to intracoronary acetylcholine infusion (10 and 10 mol/l) and intracoronary glyceryl trinitrate, respectively. Microvascular function was evaluated by response to adenosine and expressed as coronary flow velocity reserve. Mean values were compared.

RESULTS

Thirty patients were evaluated: 15 patients with ESRF (mean age 52.1 ± 9, male 73%) and 15 control patients (mean age 53.3 ± 13, male 60%). Comorbidity profile, aside from ESRF, was well matched. Baseline coronary blood flow was similar between groups (101.6 ± 10.3 vs. 103.4 ± 9.1 ml/min, P = 0.71), as was endothelial-dependent response to acetylcholine (159.1 ± 16.9 vs. 171.1 ± 16.8 ml/min, P = 0.41). Endothelial-independent response to glyceryl trinitrate was no different between groups (14.3 ± 3.1 vs. 13.1 ± 2.3%, P = 0.73. A significantly reduced coronary flow velocity reserve was observed in the ESRF cohort compared to controls (2.34 ± 0.4 vs. 3.05 ± 0.3, P = 0.003).

CONCLUSION

Patients with ESRF had preserved endothelial-dependent function however compared to controls, demonstrated significantly attenuated microvascular reserve. An impaired response to adenosine may not only represent a component of the pathophysiological milieu in patients with ESRF but may also provide a basis for the suboptimal diagnostic performance of vasodilatory stress in this population.

Dobutamine Stress Echocardiography Unmasks Early Left Ventricular Dysfunction in Asymptomatic Patients with Uncomplicated Type 2 Diabetes: A Comprehensive Two-Dimensional Speckle-Tracking Imaging Study

BACKGROUND

Discrepancies are present in the literature on resting myocardial mechanics in patients with uncomplicated type 2 diabetes mellitus (T2DM). Data are noticeably sparse regarding circumferential function and torsional mechanics. Resting deformation imaging may not be sensitive enough to detect subtle dysfunctions. The aim of this study was thus to comprehensively evaluate myocardial mechanics in patients with T2DM at rest and to investigate whether dobutamine stress echocardiography could unmask functional alterations that would remain otherwise subtle at rest.

METHODS

Forty-four patients with T2DM and 35 healthy control subjects of similar age and sex were prospectively recruited. After conventional echocardiography, myocardial mechanics was evaluated at rest and during low-dose dobutamine stress echocardiography (target heart rate, 110 beats/min).

RESULTS

Patients with T2DM presented with altered global diastolic function but preserved systolic function. Deformation imaging indexes were similar between groups at rest, but significant differences were noticed under dobutamine infusion for longitudinal strain (-21.2 ± 2.4% vs -24.2 ± 2.5%, P < .001), circumferential strain (apex, -32.3 ± 5.3% vs -36.3 ± 5.3%, P = .002; papillary muscle, -25.6 ± 3.2% vs -28.0 ± 3.6%, P = .001; base, -23.2 ± 3.6% vs -25.3 ± 3.8%, P = .03), apical (11.2 ± 4.4° vs 14.1 ± 6.3°, P = .020) and basal (-12.2 ± 3.3° vs -14.3 ± 3.9°, P = .021) rotation, and twist (21.9 ± 5.9° vs 26.8 ± 8.3°, P = .007). Multivariate analysis identified epicardial fat, dyslipidemia, and fasting glycaemia as significant contributors to the changes from rest to dobutamine.

CONCLUSIONS

These findings demonstrate the usefulness of dobutamine stress echocardiography in establishing impairments in myocardial mechanics in patients with uncomplicated T2DM. Systemic metabolic disturbances and epicardial fat act as the main contributors to the blunted response to dobutamine stress in these patients.

EMPA-REG OUTCOME: The Cardiologist's Point of View

Cardiologists could view empagliflozin as a cardiovascular drug that also has a beneficial effect on reducing hyperglycemia in patients with type 2 diabetes mellitus (T2DM). The effects of empagliflozin in lowering the risk of cardiovascular death and hospitalization for heart failure in T2DM patients with high cardiovascular risk during the recent Empagliflozin Cardiovascular Outcome Event Trial in Type 2 Diabetes Mellitus Patients-Removing Excess Glucose (EMPA-REG OUTCOME) trial may be explained principally in terms of changes to cardiovascular physiology; namely, by the potential ability of empagliflozin to reduce cardiac workload and myocardial oxygen consumption by lowering blood pressure, improving aortic compliance, and improving ventricular arterial coupling. These concepts and hypotheses are discussed in this report.

EMPA-REG OUTCOME: The Cardiologist's Point of View

Cardiologists could view empagliflozin as a cardiovascular drug that also has a beneficial effect on reducing hyperglycemia in patients with type 2 diabetes mellitus (T2DM). The effects of empagliflozin in lowering the risk of cardiovascular death and hospitalization for heart failure in T2DM patients with high cardiovascular risk during the recent Empagliflozin Cardiovascular Outcome Event Trial in Type 2 Diabetes Mellitus Patients-Removing Excess Glucose (EMPA-REG OUTCOME) trial may be explained principally in terms of changes to cardiovascular physiology; namely, by the potential ability of empagliflozin to reduce cardiac workload and myocardial oxygen consumption by lowering blood pressure, improving aortic compliance, and improving ventricular arterial coupling. These concepts and hypotheses are discussed in this report.

Bimodal Pattern of Coronary Microvascular Involvement in Diabetes Mellitus

Background

The contribution of functionally disturbed coronary autoregulation and structurally impaired microvascular vasodilatory function to reduced coronary flow velocity reserve, reflecting impaired coronary microcirculation in diabetes mellitus (DM), has not been clearly elucidated. The objective of this study was to identify the mechanism of coronary microvascular impairment in DM in relation to duration of disease.

Methods and Results

Coronary flow velocities in the anterior descending coronary artery were assessed by transthoracic echocardiography following angiography revealing normal epicardial coronary arteries in 55 diabetic and 47 nondiabetic patients. Average peak flow velocities, coronary flow velocity reserve, and microvascular resistance in baseline and hyperemic conditions (baseline and hyperemic microvascular resistance, respectively) were assessed. Reduced coronary flow velocity reserve in patients with short duration (<10 years) of DM compared with nondiabetic patients was primarily driven by increased baseline average peak flow velocity (26.50±5.6 versus 22.08±4.31, P=0.008) in the presence of decreased baseline microvascular resistance (3.69±0.86 versus 4.34±0.76, P=0.003). In contrast, decreased coronary flow velocity reserve in patients with long‐standing (≥10 years) DM compared with nondiabetic patients was predominantly driven by reduced hyperemic average peak flow velocity (41.57±10.01 versus 53.47±11.8, P<0.001) due to increased hyperemic microvascular resistance (2.13±0.42 versus 1.69±0.39, P<0.001).

Conclusions

Both altered coronary autoregulation and impaired microvascular vasodilatory function contribute to DM‐related coronary microvascular impairment in a time‐dependent manner. DM‐induced early functional microvascular autoregulatory impairment seems to evolve into structural microvascular impairment in the initially overperfused microvascular territory at the later stage of disease.

RhoA/rock signaling mediates peroxynitrite-induced functional impairment of Rat coronary vessels

Background

Diabetes-induced vascular dysfunction may arise from reduced nitric oxide (NO) availability, following interaction with superoxide to form peroxynitrite. Peroxynitrite can induce formation of 3-nitrotyrosine-modified proteins. RhoA/ROCK signaling is also involved in diabetes-induced vascular dysfunction. The study aimed to investigate possible links between Rho/ROCK signaling, hyperglycemia, and peroxynitrite in small coronary arteries.

Methods

Rat small coronary arteries were exposed to normal (NG; 5.5 mM) or high (HG; 23 mM) D-glucose. Vascular ring constriction to 3 mM 4-aminopyridine and dilation to 1 μM forskolin were measured. Protein expression (immunohistochemistry and western blot), mRNA expression (real-time PCR), and protein activity (luminescence-based G-LISA and kinase activity spectroscopy assays) of RhoA, ROCK1, and ROCK2 were determined.

Results

Vascular ring constriction and dilation were smaller in the HG group than in the NG group (P < 0.05); inhibition of RhoA or ROCK partially reversed the effects of HG. Peroxynitrite impaired vascular ring constriction/dilation; this was partially reversed by inhibition of RhoA or ROCK. Protein and mRNA expressions of RhoA, ROCK1, and ROCK2 were higher under HG than NG (P < 0.05). This HG-induced upregulation was attenuated by inhibition of RhoA or ROCK (P < 0.05). HG increased RhoA, ROCK1, and ROCK2 activity (P < 0.05). Peroxynitrite also enhanced RhoA, ROCK1, and ROCK2 activity; these actions were partially inhibited by 100 μM urate (peroxynitrite scavenger). Exogenous peroxynitrite had no effect on the expression of the voltage-dependent K⁺ channels 1.2 and 1.5.

Conclusions

Peroxynitrite-induced coronary vascular dysfunction may be mediated, at least in part, through increased expressions and activities of RhoA, ROCK1, and ROCK2.

The effects of good glycaemic control on left ventricular and coronary endothelial functions in patients with poorly controlled Type 2 diabetes mellitus

OBJECTIVE

Diabetics are at risk for developing overt heart failure and subclinical left ventricular (LV) dysfunction. Also, impaired coronary flow reserve (CFR) reflecting coronary microvascular dysfunction is common in diabetics. However, no substantial data regarding the effects of good glycaemic control on subclinical LV dysfunction and CFR are available.

CONTEXT

To investigate whether good glycaemic control had favourable effects on subclinical LV dysfunction and CFR.

DESIGN

Prospective, open-label, follow-up study.

PATIENTS

Diabetics (n = 202) were classified based on baseline HbA1C levels: patients with good (group 1) (<7·0%) and poor glycaemic control (≥7·0%).

MEASUREMENTS

All patients underwent echocardiographic examination at baseline evaluation, and it was repeated at months 6 and 12. Based on HbA1C levels obtained at month 6, the patients with poor glycaemic control were divided into two groups: achieved (group 2) and not achieved good glycaemic control (group 3).

RESULTS

The groups were comparable with respect to diastolic function parameters including left atrium diameter, mitral E/A, Sm , Em /Am , E/E' and Tei index, and these parameters did not significantly change at follow-up in the groups. At baseline, CFR was slightly higher in group 1 than in group 2 and group 3, but it did not reach statistically significant level. At follow-up, CFR remained unchanged in group 1 (P = 0·58) and group 3 (P = 0·86), but increased in group 2 (P = 0·02: month 6 vs baseline and P = 0·004: month 12 vs baseline).

CONCLUSIONS

Diabetics with poor and good glycaemic control were comparable with respect to echocardiographic parameters reflecting subclinical LV dysfunction, and good glycaemic control did not affect these parameters. However, good glycaemic control improved CFR.

Acute Rho-kinase inhibition improves coronary dysfunction in vivo, in the early diabetic microcirculation

OBJECTIVES

Activation of RhoA/Rho-kinase (ROCK) is increasingly implicated in acute vasospasm and chronic vasoconstriction in major organ systems. Therefore we aimed to ascertain whether an increase in ROCK activity plays a role in the deterioration of coronary vascular function in early stage diabetes.

METHODS

Synchrotron radiation microangiography was used to determine in vivo coronary responses in diabetic (3 weeks post streptozotocin 65 mg/kg ip) and vehicle treated male Sprague-Dawley rats (n = 8 and 6). Changes in vessel number and calibre during vasodilator stimulation before and after blockade of nitric oxide synthase and cyclooxygenase were compared between rats. Acute responses to ROCK inhibitor, fasudil (10 mg/kg iv) was evaluated. Further, perivascular and myocardial fibrosis, arterial intimal thickening were assessed by histology, and capillary density, nitrotyrosine and ROCK1/2 expressions were evaluated by immunohistochemical staining.

RESULTS

Diabetic rats had significantly elevated plasma glucose (P < 0.001 vs control), but did not differ in fibrotic scores, media to lumen ratio, capillary density or baseline visible vessel number or calibre. Responses to acetylcholine and sodium nitroprusside stimulation were similar between groups. However, in comparison to control rats the diabetic rats showed more segmental constrictions during blockade, which were not completely alleviated by acetylcholine, but were alleviated by fasudil. Further, second order vessel branches in diabetic rats were significantly more dilated relative to baseline (37% vs 12% increase, P < 0.05) after fasudil treatment compared to control rats, while visible vessel number increased in both groups. ROCK2 expression was borderline greater in diabetic rat hearts (P < 0.053).

CONCLUSIONS

We found that ahead of the reported decline in coronary endothelial vasodilator function in diabetic rats there was moderate elevation in ROCK expression, more widespread segmental constriction when nitric oxide and prostacyclin production were inhibited and notably, increased calibre in second and third order small arteries-arterioles following ROCK inhibition. Based on nitrotyrosine staining oxidative stress was not significantly elevated in early diabetic rats. We conclude that tonic ROCK mediated vasoconstriction contributes to coronary vasomotor tone in early diabetes.

Effects of prediabetes and diabetes on left ventricular and coronary microvascular functions

BACKGROUND

Coronary flow reserve (CFR) provides independent prognostic information in diabetic patients with known or suspected coronary artery disease. However, there have been no substantial data to evaluate CFR in prediabetics. Accordingly, we aimed to evaluate CFR in subjects with prediabetes using second harmonic transthoracic Doppler echocardiography.

METHODS AND RESULTS

We measured CFR of 65 subjects with prediabetes, 45 patients with overt type 2 diabetes, and 43 sex and age matched normoglycemic healthy subjects with normal glucose tolerance. Ages, gender, existence of hypertension or hypercholesterolemia, smoking status were similar among the groups. CFR was significantly lower in diabetics (2.15 ± 0.39) than in prediabetics (2.39 ± 0.45) and controls (2.75 ± 0.35); in addition, it was significantly lower in prediabetics than controls. Only 2 (5%) of control subjects had abnormal CFR (<2) but 11 (17%) prediabetic subjects and 19 (42%) diabetic patients had abnormal CFR. We found that only age (β=-0.31, P<0.01) and presence of the diabetes (β=-0.57, P<0.01) were significant predictors of lower CFR in a multivariable model that adjusted for other variables. CFR was significantly and inversely correlated with age (r=-0.15, P=0.04), fasting glucose level (r=-0.27, P=0.001), postprandial glucose level (r=0.43, P<0.001), hemoglobin A1C level (r=-0.34, P<0.001), LDL cholesterol level (r=0.22, P=0.009), mitral A velocity (r=-0.27, P=0.001) and Tei index (r=-0.19, P=0.02), whereas mitral E/A ratio, mitral Em (r=0.18, P=0.02), mitral Em/Am ratio (r=0.23, P=0.004) were significantly and positively correlated with CFR.

CONCLUSION

CFR is impaired in subjects with prediabetics, but this impairment is not as severe as that in diabetics.

The limited clinical value of a specific diabetic cardiomyopathy

AIMS

Diabetic patients show a higher likelihood of developing heart failure (HF), independently of the atherosclerotic process, than their nondiabetic counterparts. This suggests the presence of an intrinsic vulnerability of the heart in patients with diabetes mellitus.

DATA SYNTHESIS

A cardiomyopathy specific to the diabetic patient was first hypothesized by Rubler and co-workers, in 1972 and recognized as a nosologic entity by the World Health Organization (WHO) in 1995. All patients falling under Rubler's definition had ascertained diabetic glomerusclerosis, but were unaffected by major coronary artery disease (CAD). Notably, the mean plasma glucose in those patients was 417 ± 209 mg/dl. Since then, several studies conducted in both animals and in humans have focused on pathogenetic mechanisms, clinical manifestations, diagnostic as well as therapeutic approaches utilized for the treatment of diabetic cardiomyopathy (DCM). Despite the large body of literature available, the clinical entity and significance of this diabetic complication continue to be elusive.

CONCLUSIONS

In the present report, recent pathophysiological findings and diagnostic strategies to treat DCM are reviewed. Particular attention is dedicated to the clinical manifestation of DCM, that is to heart failure (HF), and to the implications of co-morbidities and metabolic control on its evolution.

Selective endothelin A-receptor blockade attenuates coronary microvascular dysfunction after coronary stenting in patients with type 2 diabetes

BACKGROUND

Endothelin-1 may be involved in the development of diabetic microangiopathy. We studied the effect of endothelin-1 blockade on myocardial microcirculation during coronary stenting.

PATIENTS AND METHODS

Patients with type 2 diabetes and stable coronary artery disease undergoing elective percutaneous coronary intervention (PCI) were randomized to bolus dose of 500 mg bosentan (n = 4), a dual endothelin receptor blocker, or intracoronary administration of 0.03 mmol BQ123 (n = 6), a selective endothelin A-receptor blocker, or placebo (n = 5), respectively. Coronary flow reserve (CFR) was measured immediately post-PCI. CFR was also measured in five nondiabetic controls post-coronary stenting.

RESULTS

Patients in the placebo group had (P < 0.05) lower values of CFR (2.3 +/- 1.2) as compared to those who received endothelin blockade (n = 10; 3.1 +/- 0.7) and nondiabetic controls (4.9 +/- 2.3). Patients who received BQ123 showed significantly higher CFR (3.3 +/- 0.5; P < 0.05) as compared to those on placebo. Nondiabetic patients had significantly higher CFR as compared to patients with diabetes (4.9 +/- 2.3 and 2.8 +/- 1.0, respectively; P < 0.05).

CONCLUSION

Coronary microvascular dysfunction is present during coronary stenting in patients with type 2 diabetes and may be reversed by selective endothelin A-receptor blockade. Targeting endothelin system may be of importance in protecting the myocardium against ischemic events during elective PCI in type 2 diabetic patients.