Acute hyperglycemia reduces myocardial blood flow reserve and the magnitude of reduction is associated with insulin resistance: a study in nondiabetic humans using contrast echocardiography

The Heart in Diabetic Ketoacidosis: A Narrative Review Focusing on the Acute Cardiac Effects and Electrocardiographic Abnormalities

Diabetic ketoacidosis (DKA) is a serious complication of diabetes mellitus. Hyperglycemia, acidosis, and electrolyte imbalances can directly affect the heart by inducing toxicity, impairing myocardial blood flow, autonomic dysfunction, and altering activation and conduction of electrical impulses throughout the heart, increasing the risk of arrhythmias and ischemia. The electrocardiogram is useful in monitoring patients during and after an episode of DKA, as it allows the detection of arrhythmias and guides metabolic correction. Unfortunately, reports on electrocardiographic abnormalities in patients with DKA are lacking. We found two electrocardiographic patterns that are frequently reported in the literature: a pseudo-myocardial infarction and a Brugada Phenocopy. Both are associated with DKA metabolic anomalies and they resolve after treatment. Because of their clinical relevance and the challenge they represent for clinicians, we analyzed the clinical characteristics of these patients and the mechanisms involved in these electrocardiographic findings.

An Experimental Series Investigating the Effects of Hyperinsulinemic Euglycemia on Myocardial Blood Flow Reserve in Healthy Individuals and on Myocardial Perfusion Defect Size following ST-Segment Elevation Myocardial Infarction

BACKGROUND

Incomplete restoration of myocardial blood flow (MBF) is reported in up to 30% of ST-segment elevation myocardial infarction (STEMI) despite prompt mechanical revascularization. Experimental hyperinsulinemic euglycemia (HE) increases MBF reserve (MBFR). If fully exploited, this effect may also improve MBF to ischemic myocardium. Using insulin-dextrose infusions to induce HE, we conducted four experiments to determine (1) how insulin infusion duration, dose, and presence of insulin resistance affect MBFR response; and (2) the effect of an insulin-dextrose infusion given immediately following revascularization of STEMI on myocardial perfusion.

METHODS

The MBFR was determined using myocardial contrast echocardiography. Experiment 1 (insulin duration): 12 participants received an insulin-dextrose or saline infusion for 120 minutes. MBFR was measured at four time intervals during infusion. Experiment 2 (insulin dose): 22 participants received one of three insulin doses (0.5, 1.5, 3.0 mU/kg/minute) for 60 minutes. Baseline and 60-minute MBFRs were determined. Experiment 3 (insulin resistance): five metabolic syndrome and six type 2 diabetes (T2DM) participants received 1.5 mU/kg/minute of insulin-dextrose for 60 minutes. Baseline and 60-minute MBFRs were determined. Experiment 4 (STEMI): following revascularization for STEMI, 20 patients were randomized to receive either 1.5 mU/kg/minute insulin-dextrose infusion for 120 minutes or standard care. Myocardial contrast echocardiography was performed at four time intervals to quantify percentage contrast defect length.

RESULTS

Experiment 1: MBFR increased with time through to 120 minutes in the insulin-dextrose group and did not change in controls. Experiment 2: compared with baseline, MBFR increased in the 1.5 (2.42 ± 0.39 to 3.25 ± 0.77, P = .002), did not change in the 0.5, and decreased in the 3.0 (2.64 ± 0.25 to 2.16 ± 0.33, P = .02) mU/kg/minute groups. Experiment 3: compared with baseline, MBFR increase was only borderline significant in metabolic syndrome and T2DM participants (1.98 ± 0.33 to 2.59 ± 0.45, P = .04, and 1.67 ± 0.35 to 2.14 ± 0.21, P = .05). Experiment 4: baseline percentage contrast defect length was similar in both groups but with insulin decreased with time and was significantly lower than in controls at 60 minutes (2.8 ± 5.7 vs 13.7 ± 10.6, P = .02).

CONCLUSIONS

Presence of T2DM, insulin infusion duration, and dose are important determinants of the MBFR response to HE. When given immediately following revascularization for STEMI, insulin-dextrose reduces perfusion defect size at one hour. Hyperinsulinemic euglycemia may improve MBF following ischemia, but further studies are needed to clarify this.

Age-Related Difference in the Effect of Acute Hyperglycemia on Myocardial Ischemia-Reperfusion Injury

Age and acute hyperglycemia are known risk factors of myocardial ischemia-reperfusion injury. We investigated age-related difference in the effect of acute hyperglycemia on myocardial ischemia-reperfusion injury in Sprague-Dawley rats (young, 3 months; middle-aged, 10-12 months; and old, 22-24 months). The rats received 1.2 g/kg dextrose or normal saline and were subjected to coronary artery occlusion for 45 minutes followed by reperfusion for 240 minutes. Infarct size and ejection fraction were measured. The levels of apoptosis-related proteins (C-PARP, Bcl-2, Bax, and cytochrome c) and autophagy-related proteins (Bnip3, Beclin-1, Atg5, and LC3B-II) were evaluated. Infarct size increased with acute hyperglycemia in young and middle-aged rats but not in old rats, whereas the reduction of ejection fraction after ischemia-reperfusion was aggravated by acute hyperglycemia in all age groups. Acute hyperglycemia increased Bnip3 and Beclin-1 expressions after ischemia-reperfusion in young and middle-aged rats but not in old rats, whereas it increased the expression of Bax, cytochrome c, Atg5, and LC3B-II only in young or middle-aged rats. Conclusively, acute hyperglycemia does not aggravate myocardial ischemia-reperfusion injury in old rats, unlike in young and middle-aged rats. This heterogeneity may be due to attenuated changes in protein signaling after ischemia-reperfusion injury under acute hyperglycemia in old rats.

Myocardial Perfusion and Function Are Distinctly Altered by Sevoflurane Anesthesia in Diet-Induced Prediabetic Rats

Preservation of myocardial perfusion during surgery is particularly important in patients with increased risk for perioperative complications, such as diabetes. Volatile anesthetics, like sevoflurane, have cardiodepressive effects and may aggravate cardiovascular complications. We investigated the effect of sevoflurane on myocardial perfusion and function in prediabetic rats. Rats were fed a western diet (WD; n = 18) or control diet (CD; n = 18) for 8 weeks and underwent (contrast) echocardiography to determine perfusion and function during baseline and sevoflurane exposure. Myocardial perfusion was estimated based on the product of microvascular filling velocity and blood volume. WD-feeding resulted in a prediabetic phenotype characterized by obesity, hyperinsulinemia, hyperlipidemia, glucose intolerance, and hyperglycemia. At baseline, WD-feeding impaired myocardial perfusion and systolic function compared to CD-feeding. Exposure of healthy rats to sevoflurane increased the microvascular filling velocity without altering myocardial perfusion but impaired systolic function. In prediabetic rats, sevoflurane did also not affect myocardial perfusion; however, it further impaired systolic function. Diet-induced prediabetes is associated with impaired myocardial perfusion and function in rats. While sevoflurane further impaired systolic function, it did not affect myocardial perfusion in prediabetic rats. Our findings suggest that sevoflurane anesthesia leads to uncoupling of myocardial perfusion and function, irrespective of the metabolic state.

Glucagon-like peptide-1 protects against ischemic left ventricular dysfunction during hyperglycemia in patients with coronary artery disease and type 2 diabetes mellitus

Background

Enhancement of myocardial glucose uptake may reduce fatty acid oxidation and improve tolerance to ischemia. Hyperglycemia, in association with hyperinsulinemia, stimulates this metabolic change but may have deleterious effects on left ventricular (LV) function. The incretin hormone, glucagon-like peptide-1 (GLP-1), also has favorable cardiovascular effects, and has emerged as an alternative method of altering myocardial substrate utilization. In patients with coronary artery disease (CAD), we investigated: (1) the effect of a hyperinsulinemic hyperglycemic clamp (HHC) on myocardial performance during dobutamine stress echocardiography (DSE), and (2) whether an infusion of GLP-1(7-36) at the time of HHC protects against ischemic LV dysfunction during DSE in patients with type 2 diabetes mellitus (T2DM).

Methods

In study 1, twelve patients underwent two DSEs with tissue Doppler imaging (TDI)—one during the steady-state phase of a HHC. In study 2, ten patients with T2DM underwent two DSEs with TDI during the steady-state phase of a HHC. GLP-1(7-36) was infused intravenously at 1.2 pmol/kg/min during one of the scans. In both studies, global LV function was assessed by ejection fraction and mitral annular systolic velocity, and regional wall LV function was assessed using peak systolic velocity, strain and strain rate from 12 paired non-apical segments.

Results

In study 1, the HHC (compared with control) increased glucose (13.0 ± 1.9 versus 4.8 ± 0.5 mmol/l, p < 0.0001) and insulin (1,212 ± 514 versus 114 ± 47 pmol/l, p = 0.01) concentrations, and reduced FFA levels (249 ± 175 versus 1,001 ± 333 μmol/l, p < 0.0001), but had no net effect on either global or regional LV function. In study 2, GLP-1 enhanced both global (ejection fraction, 77.5 ± 5.0 versus 71.3 ± 4.3%, p = 0.004) and regional (peak systolic strain −18.1 ± 6.6 versus −15.5 ± 5.4%, p < 0.0001) myocardial performance at peak stress and at 30 min recovery. These effects were predominantly driven by a reduction in contractile dysfunction in regions subject to demand ischemia.

Conclusions

In patients with CAD, hyperinsulinemic hyperglycemia has a neutral effect on LV function during DSE. However, GLP-1 at the time of hyperglycemia improves myocardial tolerance to demand ischemia in patients with T2DM.

Trial Registration: http://www.isrctn.org. Unique identifier ISRCTN69686930

Relationship between glycosylated hemoglobin A1c and coronary flow reserve in patients with Type 2 diabetes mellitus

Type 2 diabetes mellitus patients are at increased risk for macrovascular and microvascular complications. Both in vivo and in vitro studies of small arteries and arterioles of diabetic subjects demonstrate impaired endothelial function without anatomic lesions. Coronary flow reserve (CFR) is a surrogate marker of coronary microcirculatory endothelial function in diabetic patients without significant stenosis of the associated epicardial coronary artery. Glycosylated hemoglobin A1c is related to likelihood of occurrence of microvascular events. The objective of this article is to report on recent developments in multiple noninvasive techniques to assess CFR and their use in aiding the understanding of the relationship of CFR, glycemic control and cardiovascular outcomes.

Admission glucose and left ventricular systolic function in non-diabetic patients with acute myocardial infarction

Carbohydrate metabolism disorder in patients hospitalized due to acute ST-segment elevation myocardial infarction (STEMI) is associated with poor outcome. The association is even stronger in non-diabetic patients compared to the diabetics. Poor outcome of patients with elevated parameters of carbohydrate metabolism may be associated with negative impact of these disorders on left ventricular (LV) function. The aim of the study was to determine the impact of admission glycemia on LV systolic function in acute phase and 6 months after myocardial infarction in STEMI patients treated with primary angioplasty, without carbohydrate disorders. The study group consisted of 52 patients (9 female, 43 male) aged 35-74 years, admitted to the Department of Cardiology and Internal Medicine, Collegium Medicum in Bydgoszcz, due to the first STEMI treated with primary coronary angioplasty with stent implantation, without diabetes in anamnesis and carbohydrate metabolism disorders diagnosed during hospitalization. Echocardiography was performed in all patients in acute phase and 6 months after MI. Plasma glucose were measured at hospital admission. In the subgroup with glycemia ≥7.1 mmol/l, in comparison to patients with glycemia <7.1 mmol/l, significantly lower ejection fraction (EF) was observed in acute phase of MI (44.4 ± 5.4 vs. 47.8 ± 6.3 %, p = 0.04) and trend to lower EF 6 months after MI [47.2 ± 6.5 vs. 50.3 ± 6.3 %, p = 0.08 (ns)]. Higher admission glycemia in patients with STEMI and without carbohydrate metabolism disturbances, may be a marker of poorer prognosis resulting from lower LV ejection fraction in the acute phase and in the long-term follow-up.