Dysrhythmia and electrocardiographic changes in diabetes mellitus: pathophysiology and impact on the incidence of sudden cardiac death

Electrocardiological effects of ranolazine and lidocaine on normal and diabetic rat atrium

PURPOSE

Cellular changes occurring in diabetic cardiomyopathy include disturbances of calcium and sodium homeostasis. Voltage-gated sodium channels are responsible for the initiation of cardiac action potentials, and the excitability would create relevance. The effect of ranolazine as a sodium channel blocker on atrium electromechanical parameters is investigated and compared with lidocaine in streptozocin-treated diabetic rats.

METHODS

After an 8-week induction of diabetes type I, the effect of cumulative concentrations of ranolazine and lidocaine on the electrophysiology of isolated atrium was studied. Ranolazine's effects were evaluated on cardiac sodium current in normal- and high-glucose medium, with whole-cell patch-clamp technique.

RESULTS

Ranolazine at therapeutic concentrations had no significant statistical effect on refractory period in normal and diabetic isolated heart. Ranolazine (10 μM) caused a hyperpolarizing shift of V_1/2 for steady-state inactivation in normal media, while it significantly elicited a depolarizing shift in high-glucose media (p < 0.05).

CONCLUSION

It is concluded that in the isolated rat atrium preparation, ranolazine and lidocaine have no beneficial on diabetic cardiomyopathy. Although refractoriness and contractility were not much different in normal and diabetic atria, there was a definite effect of ranolazine and lidocaine on sodium current in varying concentrations. This may have significance in future therapeutics.

Inhibition of the sodium-glucose co-transporter 2 in the elderly: clinical and mechanistic insights into safety and efficacy

The prevalence of type 2 diabetes mellitus (T2DM) in the elderly grew sharply over the last decade. Reduced insulin sensitivity and secretory capacity, weight gain, sarcopenia, and elevated adiposity are all common metabolic and body changes in the aging population that favor an increased risk of hypoglycemia, frailty syndrome, falls, and cognitive dysfunction. First line antidiabetic therapy is frequently not safe in older individuals because of its high risk of hypoglycemia and prevalent co-morbid diseases, such as chronic kidney disease, osteoporosis, cardiovascular disease, and obesity. Sodium-glucose cotransporter 2 inhibitor (SGLT2i) is a new class of antidiabetic therapy that inhibits glucose and sodium reabsorption on renal proximal convoluted tubule. Its effect is well demonstrated in various clinical scenarios in the younger population. This review and metanalysis describe particularities of the SGLT2i on the elderly, with mechanistic insights of the potential benefit and remaining challenges about the use of these drugs in this important age group. Further, we will present a meta-analysis of the main effects of SGLT2i reported in post-hoc studies in which the median age of the subgroups analyzed was over 60 years. Despite the absence of specific clinical trials for this population, our findings suggest that SGLT2i therapy on older individuals is effective to lower glucose and maintain its effect on systolic blood pressure and body weight.

Comparative Safety of Sulfonylureas and the Risk of Sudden Cardiac Arrest and Ventricular Arrhythmia

OBJECTIVE

To examine the association between individual antidiabetic sulfonylureas and outpatient-originating sudden cardiac arrest and ventricular arrhythmia (SCA/VA).

RESEARCH DESIGN AND METHODS

We conducted a retrospective cohort study using 1999-2010 U.S. Medicaid claims from five large states. Exposures were determined by incident use of glyburide, glimepiride, or glipizide. Glipizide served as the reference exposure, as its effects are believed to be highly pancreas specific. Outcomes were ascertained by a validated ICD-9-based algorithm indicative of SCA/VA (positive predictive value ∼85%). Potential confounding was addressed by adjustment for multinomial high-dimensional propensity scores included as continuous variables in a Cox proportional hazards model.

RESULTS

Of sulfonylurea users under study (N = 519,272), 60.3% were female and 34.9% non-Hispanic Caucasian, and the median age was 58.0 years. In 176,889 person-years of sulfonylurea exposure, we identified 632 SCA/VA events (50.5% were immediately fatal) for a crude incidence rate of 3.6 per 1,000 person-years. Compared with glipizide, propensity score-adjusted hazard ratios for SCA/VA were 0.82 (95% CI 0.69-0.98) for glyburide and 1.10 (0.89-1.36) for glimepiride. Numerous secondary analyses showed a very similar effect estimate for glyburide; yet, not all CIs excluded the null.

CONCLUSIONS

Glyburide may be associated with a lower risk of SCA/VA than glipizide, consistent with a very small clinical trial suggesting that glyburide may reduce ventricular tachycardia and isolated ventricular premature complexes. This potential benefit must be contextualized by considering putative effects of different sulfonylureas on other cardiovascular end points, cerebrovascular end points, all-cause death, and hypoglycemia.

Pro- and Antiarrhythmic Actions of Sulfonylureas: Mechanistic and Clinical Evidence

Sulfonylureas are the most commonly used second-line drug class for treating type 2 diabetes mellitus (T2DM). While the cardiovascular safety of sulfonylureas has been examined in several trials and nonrandomized studies, little is known of their specific effects on sudden cardiac arrest (SCA) and related serious arrhythmic outcomes. This knowledge gap is striking, because persons with DM are at increased risk of SCA. In this review, we explore the influence of sulfonylureas on the risk of serious arrhythmias, with specific foci on ischemic preconditioning, cardiac excitability, and serious hypoglycemia as putative mechanisms. Elucidating the relationship between individual sulfonylureas and serious arrhythmias is critical, especially as the diabetes epidemic intensifies and SCA incidence increases in persons with diabetes.

Early inner retinal thinning and cardiovascular autonomic dysfunction in type 2 diabetes

Background

To investigate changes in the neural retina according to the presence of retinal nerve fiber layer (RNFL) defects in type 2 diabetes, and to determine the association between inner retina thickness and the severity of diabetic complications.

Methods

We studied non-glaucomatous patients with type 2 diabetes and control subjects Circumpapillary RNFL and macula ganglion cell-inner plexiform layer (GCIPL) thicknesses were measured by spectral-domain optical coherence tomography. In patients with type 2 diabetes, a cardiovascular autonomic function test (AFT) was performed, which included the heart rate parameter of beat-beat variation—with deep breathing, in response to the Valsalva maneuver, and on postural change from lying to standing. The results of each test were scored as 0 for normal and 1 for abnormal. A total AFT score of 1 was defined as early cardiovascular autonomic neuropathy (CAN), and an AFT score≥ 2 as definite CAN.

Results

We compared control eyes (n = 70), diabetic eyes with RNFL defects (n = 47), and eyes without RNFL defects (n = 30). The average RNFL and GCIPL thicknesses were significantly different among groups (all, P<0.05). On post-hoc testing, diabetic eyes with RNFL defects had a significantly thinner average GCIPL thickness than those without RNFL defects. On multivariate analyses, significantly thinner average GCIPL was seen in early CAN staging (B = -4.32, P = 0.016) and in definite CAN staging (B = -10.33, P<0.001), compared with no CAN involvement, after adjusting for confounding parameters.

Conclusions

Cardiovascular autonomic dysfunction was associated with early neurodegenerative changes in type 2 diabetes.

Rosiglitazone increases cerebral klotho expression to reverse baroreflex in type 1-like diabetic rats

Reduced baroreflex sensitivity (BRS) is widely observed in diabetic human and animals. Rosiglitazone is one of the clinically used thiazolidinediones (TZD) known as PPARγ agonist. Additionally, the klotho protein produced from choroid plexus in the central nervous system is regulated by PPARγ. In an attempt to develop the new therapeutic strategy, we treated streptozotocin-induced diabetic rats (STZ) with rosiglitazone (STZ + TZD) orally at 10 mg/kg for 7 days. Also, STZ rats were subjected to intracerebroventricular (ICV) infusion of recombinant klotho at a dose of 3 μg/2.5 μL via syringe pump (8 μg/hr) daily for 7 days. The BRS and heart rate variability were then estimated under challenge with a depressor dose of sodium nitroprusside (50 μg/kg) or a pressor dose of phenylephrine (8 μg/kg) through an intravenous injection. Lower expression of klotho in medulla oblongata of diabetic rats was identified. Cerebral infusion of recombinant klotho or oral administration of rosiglitazone reversed BRS in diabetic rats. In conclusion, recovery of the decreased klotho in brain induced by rosiglitazone may restore the impaired BRS in diabetic rats. Thus, rosiglitazone is useful to reverse the reduced BRS through increasing cerebral klotho in diabetic disorders.

Characteristics of single large-conductance Ca2+-activated K+ channels and their regulation of action potentials and excitability in parasympathetic cardiac motoneurons in the nucleus ambiguus

Large-conductance Ca2(+)-activated K+ channels (BK) regulate action potential (AP) properties and excitability in many central neurons. However, the properties and functional roles of BK channels in parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus (NA) have not yet been well characterized. In this study, the tracer X-rhodamine-5 (and 6)-isothiocyanate (XRITC) was injected into the pericardial sac to retrogradely label PCMNs in FVB mice at postnatal 7-9 days. Two days later, XRITC-labeled PCMNs in brain stem slices were identified. Using excised patch single-channel recordings, we identified voltage-gated and Ca(2+)-dependent BK channels in PCMNs. The majority of BK channels exhibited persistent channel opening during voltage holding. These BK channels had a conductance of 237 pS and a 50% opening probability at +27.9 mV, the channel open time constant was 3.37 ms at +20 mV, and dwell time increased exponentially as the membrane potential depolarized. At the +20-mV holding potential, the [Ca2+]50 was 15.2 μM with a P0.5 of 0.4. Occasionally, some BK channels showed a transient channel opening and fast inactivation. Using whole cell voltage clamp, we found that BK channel mediated outward currents and afterhyperpolarization currents (IAHP). Using whole cell current clamp, we found that application of BK channel blocker iberiotoxin (IBTX) increased spike half-width and suppressed fast afterhyperpolarization (fAHP) amplitude following single APs. In addition, IBTX application increased spike half-width and reduced the spike frequency-dependent AP broadening in trains and spike frequency adaption (SFA). Furthermore, BK channel blockade decreased spike frequency. Collectively, these results demonstrate that PCMNs have BK channels that significantly regulate AP repolarization, fAHP, SFA, and spike frequency. We conclude that activation of BK channels underlies one of the mechanisms for facilitation of PCMN excitability.

Influence of fluvastatin on cardiac function and baroreflex sensitivity in diabetic rats

AIM

To investigate whether fluvastatin is able to ameliorate the impaired cardiac function or baroreflex sensitivity (BRS) in rats with type 1 diabetes.

METHODS

Type 1 diabetic rats were induced by intraperitoneal injection of streptozotocin (STZ) and then administered fluvastatin (1.5, 3.0, and 6.0 mg·kg(-1)·d(-1)) for 30 d. Food and drink intake was recorded every day. Fasting blood glucose (FBG) level, blood lipid level, cardiac function and BRS were measured in diabetic rats after fluvastatin treatment for 30 d.

RESULTS

The polydipsia, polyphagia and abnormal biochemical indexes of blood were significantly ameliorated by the the 3.0- and 6.0-mg doses of fluvastatin in STZ-induced diabetic rats. FBG was decreased in diabetic rats after fluvastatin treatment for 30 d. The left ventricular systolic pressure (LVSP) and the maximum rate of change of left ventricular pressure in the isovolumic contraction and relaxation period (±dp/dt(max)) were elevated, and left ventricular diastolic pressure (LVEDP) was decreased by fluvastatin. The attenuated heart rate responses to arterial blood pressure (ABP) increase induced by phenylephrine (PE) and ABP decrease induced by sodium nitroprusside (SNP) were reversed by the 3.0-mg dose of fluvastatin.

CONCLUSION

Fluvastatin regulates blood lipid levels and decreases the FBG level in diabetic rats. These responses can protect the diabetic heart from complications by improving cardiac function and BRS.

Small conductance Ca2+-activated K+ channels regulate firing properties and excitability in parasympathetic cardiac motoneurons in the nucleus ambiguus

Small conductance Ca(2+)-activated K(+) channels (SK) regulate action potential (AP) firing properties and excitability in many central neurons. However, the functional roles of SK channels of parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus have not yet been well characterized. In this study, the tracer X-rhodamine-5 (and 6)-isothiocyanate (XRITC) was injected into the pericardial sac to retrogradely label PCMNs in FVB mice at postnatal days 7-9. Two days later, XRITC-labeled PCMNs in brain stem slices were identified. With the use of whole cell current clamp, single APs and spike trains of different frequencies were evoked by current injections. We found that 1) PCMNs have two different firing patterns: the majority of PCMNs (90%) exhibited spike frequency adaptation (SFA) and the rest (10%) showed less or no adaptation; 2) application of the specific SK channel blocker apamin significantly increased spike half-width in single APs and trains and reduced the spike frequency-dependent AP broadening in trains; 3) SK channel blockade suppressed afterhyperpolarization (AHP) amplitude following single APs and trains and abolished spike-frequency dependence of AHP in trains; and 4) SK channel blockade increased the spike frequency but did not alter the pattern of SFA. Using whole cell voltage clamp, we measured outward currents and afterhyperpolarization current (I(AHP)). SK channel blockade revealed that SK-mediated outward currents had both transient and persistent components. After bath application of apamin and Ca(2+)-free solution, we found that apamin-sensitive and Ca(2+)-sensitive I(AHP) were comparable, confirming that SK channels may contribute to a major portion of Ca(2+)-activated K(+) channel-mediated I(AHP). These results suggest that PCMNs have SK channels that significantly regulate AP repolarization, AHP, and spike frequency but do not affect SFA. We conclude that activation of SK channels underlies one of the mechanisms for negative control of PCMN excitability.

Impairment of baroreflex control of heart rate in conscious transgenic mice of type 1 diabetes (OVE26)

Baroreflex control of heart rate (HR) is impaired in human type 1 diabetes mellitus. The goal of this study is to use a transgenic mouse model of type 1 diabetes (OVE26) to assess the diabetes-induced baroreflex impairment in the conscious state. OVE26 transgenic mice (which develop hyperglycemia within the first three weeks after birth due to the specific damage of beta cells) and normal control mice (FVB) 5-6months of age were anesthetized, and the left femoral artery and both veins were catheterized. On the second day after surgery, baroreflex-mediated HR responses to arterial blood pressure (ABP) changes that were induced by separate microinfusion of phenylephrine (PE) and sodium nitroprusside (SNP) at different doses (0.03-0.4microg/min) were measured in the conscious state. Compared with FVB control, we found that in OVE26 diabetic mice 1) mean ABP (MABP) and HR were decreased (p<0.05). 2) PE-induced MABP increases were comparable to those in FVB mice (p>0.05). 3) Baroreflex-mediated bradycardia was attenuated (p<0.05). 4) SNP-induced MABP decreases was reduced (p<0.05). 5) Baroreflex-mediated tachycardia was attenuated (p<0.05). Since baroreflex control of HR in conscious OVE26 mice is impaired in a similar fashion to human diabetes mellitus, we suggest that OVE26 mice may provide a useful model to study the neural mechanisms of diabetes-induced baroreflex impairment.

Prevalence and Impact of Diabetes Mellitus in Patients With Acute Myocardial Infarction: A 10-year Experience

Background: Diabetes mellitus is associated with a higher incidence of acute myocardial infarction. Objective: To study the prevalence and outcome of patients with diabetes among patients with acute myocardial infarction. Methods: Retrospectively, patients who presented with acute myocardial infarction in a 10-year period were identified from the coronary care unit database. Results: A total of 1598 Qatari patients were admitted with acute myocardial infarction, 863 (54%) of them had diabetes mellitus (females 68.5% vs males 48.3%; P < .001). In-hospital mortality rate was non-significantly higher in diabetic patients (18% vs 15% P = .15). Aspirin (odds ratio 2.39, 95% confidence interval 1.96-2.90, P = .003] and β-blocker use (odds ratio 1.75, 95% CI 1.21-2.52, P = .0001) were independently associated with reduced mortality risk. Conclusions: The prevalence of diabetes mellitus among patients with acute myocardial infarction in a geographically defined population in the developing world is high with a trend for poor outcomes. However, mortality was not significantly higher in diabetes mellitus than non-diabetes mellitus patients.

Patients with a history of diabetes have a lower survival rate after in-hospital cardiac arrest

AIM

To describe the association between a history of diabetes and outcome among patients suffering an in-hospital cardiac arrest.

METHOD

All patients suffering an in-hospital cardiac arrest in whom cardiopulmonary resuscitation (CPR) was attempted at Sahlgrenska University Hospital in Göteborg between 1994 and 2006 and at nine further hospitals in Sweden between 2005 and 2006.

RESULTS

In all, 1810 patients were included in the survey, 395 (22%) of whom had a previous history of diabetes. Patients with a history of diabetes differed from those without such a history by having a higher prevalence of previous myocardial infarction, stroke, heart failure and renal disease. They were more frequently treated with anti-arrhythmic drugs during resuscitation. Whereas immediate survival did not differ between groups (51.7% and 53.1%, respectively), patients with diabetes were discharged alive from hospital (29.3%) less frequently compared with those without diabetes (37.6%). When correcting for dissimilarities at baseline, the adjusted odds ratio for being discharged alive (diabetes/no diabetes) was 0.57 (95% CL 0.40-0.79).

CONCLUSION

Among patients suffering an in-hospital cardiac arrest in Sweden in whom CPR was attempted, 22% had a history of diabetes. These patients had a lower survival rate, which cannot simply be explained by different co-morbidity.

Functional changes in baroreceptor afferent, central and efferent components of the baroreflex circuitry in type 1 diabetic mice (OVE26)

Baroreflex control of heart rate (HR) is impaired in diabetes mellitus. We hypothesized that diabetes mellitus induced functional changes of neural components at multiple sites within the baroreflex arc. Type 1 diabetic mice (OVE26) and FVB control mice were anesthetized. Baroreflex-mediated HR responses to sodium nitroprusside- (SNP) and phenylephrine- (PE) induced mean arterial blood pressure (MAP) changes were measured. Baroreceptor function was characterized by measuring the percent (%) change of baseline integrated aortic depressor nerve activity (Int ADNA) in response to SNP- and PE-induced MAP changes. The HR responses to electrical stimulation of the left aortic depressor nerve (ADN) and the right vagus nerve were assessed. Compared with FVB control mice, we found in OVE26 mice that (1) baroreflex-mediated bradycardia and tachycardia were significantly reduced. (2) The baroreceptor afferent function in response to MAP increase did not differ, as assessed by the parameters of the logistic function curve. But, the inhibition of Int ADNA in response to MAP decrease was significantly attenuated. (3) The maximum amplitude of bradycardic responses to right vagal efferent stimulation was augmented. (4) In contrast, the maximum amplitude of bradycardic responses to left ADN stimulation was decreased. Since Int ADNA was preserved in response to MAP increase and HR responses to vagal efferent stimulation were augmented, we conclude that a deficit of the central mediation of baroreflex HR contributes to the overall attenuation of baroreflex sensitivity in OVE26 mice. The successful conduction of physiological experiments on the ADN in OVE26 mice may provide a foundation for the understanding of cellular and molecular mechanisms of diabetes-induced cardiac neuropathy.