A potential role for glucagon in the treatment of drug-induced symptomatic bradycardia

Evidence for a lack of inotropic and chronotropic effects of glucagon and glucagon receptors in the human heart

BACKGROUND

Glucagon is thought to increase heart rate and contractility by stimulating glucagon receptors and increasing 3',5'-cyclic adenosine monophosphate (cAMP) production in the myocardium. This has been confirmed in animal studies but not in the human heart. The cardiostimulatory effects of glucagon have been correlated with the degree of cardiac dysfunction, as well as with the enzymatic activity of phosphodiesterase (PDE), which hydrolyses cAMP. In this study, the presence of glucagon receptors in the human heart and the inotropic and chronotropic effects of glucagon in samples of failing and nonfailing (NF) human hearts were investigated.

METHODS

Concentration‒response curves for glucagon in the absence and presence of the PDE inhibitor IBMX were performed on samples obtained from the right (RA) and left atria (LA), the right (RV) and left ventricles (LV), and the sinoatrial nodes (SNs) of failing and NF human hearts. The expression of glucagon receptors was also investigated. Furthermore, the inotropic and chronotropic effects of glucagon were examined in rat hearts.

RESULTS

In tissues obtained from failing and NF human hearts, glucagon did not exert inotropic or chronotropic effects in the absence or presence of IBMX. IBMX (30 µM) induced a marked increase in contractility in NF hearts (RA: 83 ± 28% (n = 5), LA: 80 ± 20% (n = 5), RV: 75 ± 12% (n = 5), and LV: 40 ± 8% (n = 5), weaker inotropic responses in the ventricular myocardium of failing hearts (RV: 25 ± 10% (n = 5) and LV: 10 ± 5% (n = 5) and no inotropic responses in the atrial myocardium of failing hearts. IBMX (30 µM) increased the SN rate in failing and NF human hearts (27.4 ± 3.0 beats min^-1, n = 10). In rat hearts, glucagon induced contractile and chronotropic responses, but only contractility was enhanced by 30 µM IBMX (maximal inotropic effect of glucagon 40 ± 8% vs. 75 ± 10%, in the absence or presence of IBMX, n = 5, P < 0.05; maximal chronotropic response 77.7 ± 6.4 beats min^-1 vs. 73 ± 11 beats min^-1, in the absence or presence of IBMX, n = 5, P > 0.05). Glucagon receptors were not detected in the human heart samples.

CONCLUSIONS

Our results conflict with the view that glucagon induces inotropic and chronotropic effects and that glucagon receptors are expressed in the human heart.

Cardiovascular and Adverse Effects of Glucagon for the Management of Suspected Beta Blocker Toxicity: a Case Series

BACKGROUND

Although glucagon use in beta blocker toxicity has been recommended for many years, evidence for its safety and efficacy in humans is limited. This study aims to determine the magnitude of effect of glucagon on heart rate (HR) and systolic blood pressure (SBP) in patients with suspected beta blocker toxicity and describe potential adverse effects of the medication.

METHODS

We conducted a retrospective, multi-center case series of patients greater than 12 years of age who received glucagon for suspected beta blocker toxicity. The primary outcome was the mean difference in HR from immediately pre- to 20-minutes post-glucagon administration. Secondary outcomes included the median difference in SBP, and occurrence of nausea, vomiting, and hyperglycemia.

RESULTS

A total of 107 patients met inclusion criteria accounting for 144 glucagon orders. The mean difference in HR from pre- to post-glucagon administration was 4 bpm ± 10.6 (95% CI [2.25-5.76], p < 0.001). The median difference (IQR) in SBP was 4.5 (- 6 to 16) mmHg (p = 0.004). Similar increases were observed when patients receiving concomitant vasopressors were excluded. A total of nine glucagon administrations (6.3%) were associated with nausea and 14 (9.7%) with vomiting; however, 52 doses (36.1%) were administered concomitantly with antiemetic medications. Fifteen administrations (10.4%) were associated with hyperglycemia.

CONCLUSION

Glucagon administration was associated with a statistically significant increase in HR, but a small absolute difference of uncertain clinical significance. A similar observation was noted for SBP. Few patients experienced adverse events.

High-Dose Glucagon Has Hemodynamic Effects Regardless of Cardiac Beta-Adrenoceptor Blockade: A Randomized Clinical Trial

Background Intravenous high-dose glucagon is a recommended antidote against beta-blocker poisonings, but clinical effects are unclear. We therefore investigated hemodynamic effects and safety of high-dose glucagon with and without concomitant beta-blockade. Methods and Results In a randomized crossover study, 10 healthy men received combinations of esmolol (1.25 mg/kg bolus+0.75 mg/kg/min infusion), glucagon (50 µg/kg), and identical volumes of saline placebo on 5 separate days in random order (saline+saline; esmolol+saline; esmolol+glucagon bolus; saline+glucagon infusion; saline+glucagon bolus). On individual days, esmolol/saline was infused from -15 to 30 minutes. Glucagon/saline was administered from 0 minutes as a 2-minute intravenous bolus or as a 30-minute infusion (same total glucagon dose). End points were hemodynamic and adverse effects of glucagon compared with saline. Compared with saline, glucagon bolus increased mean heart rate by 13.0 beats per minute (95% CI, 8.0-18.0; P<0.001), systolic blood pressure by 15.6 mm Hg (95% CI, 8.0-23.2; P=0.002), diastolic blood pressure by 9.4 mm Hg (95% CI, 6.3-12.6; P<0.001), and cardiac output by 18.0 % (95% CI, 9.7-26.9; P=0.003) at the 5-minute time point on days without beta-blockade. Similar effects of glucagon bolus occurred on days with beta-blockade and between 15 and 30 minutes during infusion. Hemodynamic effects of glucagon thus reflected pharmacologic glucagon plasma concentrations. Glucagon-induced nausea occurred in 80% of participants despite ondansetron pretreatment. Conclusions High-dose glucagon boluses had significant hemodynamic effects regardless of beta-blockade. A glucagon infusion had comparable and apparently longer-lasting effects compared with bolus, indicating that infusion may be preferable to bolus injections. Registration Information URL: https://www.clinicaltrials.gov; Unique identifier: NCT03533179.

Pharmacological and mechanical management of calcium channel blocker toxicity

Cardiovascular instability associated with calcium channel blocker toxicity comprises a small percentage of overdose presentations, yet they are associated with a high mortality rate. We detail the management of a 64-year-old man who took an intentional overdose of 840 mg nimodipine. We include the treatment he received and highlight the scarcity of evidence behind the use of gastric decontamination, calcium, glucagon, intravenous lipid emulsion, high-dose insulin therapy, sodium bicarbonate, vasopressors and methylene blue in calcium channel blocker toxicity. Additionally, the article explores the use of electrical pacing and venoarterial extracorporeal membrane oxygenation (VA-ECMO). Following successful weaning of VA-ECMO, the patient was successfully extubated but remained neurologically impaired due to hypoxic-ischaemic brain injury, critical care polyneuropathy and renal failure requiring dialysis. He has cerebral performance category 3; he has mild cognitive impairment but able to perform some activities of daily living independently and communicate his thoughts and needs. He requires no respiratory or cardiovascular support.

Hemodynamic Effects of Glucagon: A Literature Review

CONTEXT

Glucagon's effects on hemodynamic parameters, most notably heart rate and cardiac contractility, are often overlooked. The glucagon receptor is a central target in novel and anticipated type 2 diabetes therapies, and hemodynamic consequences of glucagon signaling have therefore become increasingly important. In this review, we summarize and evaluate published studies on glucagon pharmacology with a focus on clinical hemodynamic effects in humans.

EVIDENCE ACQUISITION

PubMed, Embase, and the Cochrane Library were searched for clinical studies concerning hemodynamic effects of glucagon (no year restriction). Papers reporting effects of a defined glucagon dose on any hemodynamic parameter were included. Reference searches were conducted in retrieved articles.

EVIDENCE SYNTHESIS

Hemodynamic effects of glucagon have been investigated mainly in cohort studies of patients suffering from heart failure receiving large glucagon bolus injections. The identified studies had shortcomings related to restricted patient groups, lack of a control group, randomization, or blinding. We identified no properly conducted randomized clinical trials. The majority of human studies report stimulating effects of pharmacological glucagon doses on heart rate, cardiac contractility, and blood pressure. The effects were characterized by short duration, interindividual variation, and rapid desensitization. Some studies reported no measurable effects of glucagon.

CONCLUSIONS

The level of evidence regarding hemodynamic effects of glucagon is low, and observations in published studies are inconsistent. Actual effects, interindividual variation, dose-response relationships, and possible long-term effects of supraphysiological glucagon levels warrant further investigation.

The Use of Glucagon and other Antidotes in a Case of Beta-Blocker and Calcium Channel Blocker Overdose

We report a case of metoprolol and nifedipine overdose complicated by hypotension which responded to intravenous boluses of calcium chloride and glucagon. The blood pressure was subsequently stabilised by continuous glucagon infusion with the aid of an insulin-dextrose drip. The discussion is focused on the role of antidotes and catecholamine inotropes in the management of beta-blocker and calcium channel blocker poisoning.

Experts Consensus Recommendations for the Management of Calcium Channel Blocker Poisoning in Adults

OBJECTIVE

To provide a management approach for adults with calcium channel blocker poisoning.

DATA SOURCES, STUDY SELECTION, AND DATA EXTRACTION

Following the Appraisal of Guidelines for Research & Evaluation II instrument, initial voting statements were constructed based on summaries outlining the evidence, risks, and benefits.

DATA SYNTHESIS

We recommend 1) for asymptomatic patients, observation and consideration of decontamination following a potentially toxic calcium channel blocker ingestion (1D); 2) as first-line therapies (prioritized based on desired effect), IV calcium (1D), high-dose insulin therapy (1D-2D), and norepinephrine and/or epinephrine (1D). We also suggest dobutamine or epinephrine in the presence of cardiogenic shock (2D) and atropine in the presence of symptomatic bradycardia or conduction disturbance (2D); 3) in patients refractory to the first-line treatments, we suggest incremental doses of high-dose insulin therapy if myocardial dysfunction is present (2D), IV lipid-emulsion therapy (2D), and using a pacemaker in the presence of unstable bradycardia or high-grade arteriovenous block without significant alteration in cardiac inotropism (2D); 4) in patients with refractory shock or who are periarrest, we recommend incremental doses of high-dose insulin (1D) and IV lipid-emulsion therapy (1D) if not already tried. We suggest venoarterial extracorporeal membrane oxygenation, if available, when refractory shock has a significant cardiogenic component (2D), and using pacemaker in the presence of unstable bradycardia or high-grade arteriovenous block in the absence of myocardial dysfunction (2D) if not already tried; 5) in patients with cardiac arrest, we recommend IV calcium in addition to the standard advanced cardiac life-support (1D), lipid-emulsion therapy (1D), and we suggest venoarterial extracorporeal membrane oxygenation if available (2D).

CONCLUSION

We offer recommendations for the stepwise management of calcium channel blocker toxicity. For all interventions, the level of evidence was very low.

Guidelines for the Establishment of Appropriate beyond Use Dating of Sterile Compounded Admixtures

To support compounding of products that are sterile and chemically stable, beyond use dating of admixtures must include a thorough evaluation of appropriate resources. In most instances, resources provide documentation of a specific compounded admixture, at a specific concentration and storage parameters, that does not coincide with current operations or patient-specific requirements. To meet the operational demands of a pharmacy, institutions employ a referenced guideline approach to guide decision making for safe sterile admixing. Often these guidelines are established and maintained at individual practicing locations with varying levels of detail and accuracy. In an effort to improve sterile compounding across a multihospital system, we developed and implemented beyond use dating guidelines to improve consistency and patient safety while meeting regulatory concerns.

Extracorporeal Life Support in Severe Propranolol and Verapamil Intoxication

Combined poisoning with calcium-channel blockers and β-blockers is usually associated with severe heart failure. This report shows the effectiveness of emergency extracorporeal life support in treating life-threatening simultaneous propranolol and verapamil intoxication. A 15-year-old girl presented in cardiogenic shock after alcohol consumption and a propranolol and verapamil overdose; plasma concentrations: propranolol, 0.53 m/mL; verapamil, 1.06 mg/mL. She was successfully resuscitated with extracorporeal life support. Therapeutic plasma exchange was initiated. Extracorporeal support was discontinued 70 hours later. The patient made a full recovery. Simultaneous verapamil and propranolol overdoses can cause severe hemodynamic compromise and arrest of electrical and mechanical function of the heart. Emergency extracorporeal life support can successfully maintain vital organ blood flow and allows time for drug metabolism, redistribution, and removal. Therapeutic plasma exchange may reduce the time of emergency extracorporeal life support. Emergency extracorporeal life support should be considered early in cases of near-fatal intoxications with cardiodepressive drugs.

Antidote Use in the Critically Ill Poisoned Patient

The proper use of antidotes in the intensive care setting when combined with appropriate general supportive care may reduce the morbidity and mortality associated with severe poisonings. The more commonly used antidotes that may be encountered in the intensive care unit ( N-acetylcysteine, ethanol, fomepizole, physostigmine, naloxone, flumazenil, sodium bicarbonate, octreotide, pyridoxine, cyanide antidote kit, pralidoxime, atropine, digoxin immune Fab, glucagon, calcium gluconate and chloride, deferoxamine, phytonadione, botulism antitoxin, methylene blue, and Crotaline snake antivenom) are reviewed. Proper indications for their use and knowledge of the possible adverse effects accompanying antidotal therapy will allow the physician to appropriately manage the severely poisoned patient.

Glucagon Increases Beating Rate but Not Contractility in Rat Right Atrium. Comparison with Isoproterenol

This study evaluated the chronotropic and inotropic responses to glucagon in spontaneously beating isolated right atria of rat heart. For comparison, we also investigated the effects resulting from stimulating β-adrenoceptors with isoproterenol in this tissue. Isoproterenol increased both atrial frequency and contractility but glucagon only enhanced atrial rate. The transcript levels of glucagon receptors were about three times higher in sinoatrial node than in the atrial myocardium. Chronotropic responses to glucagon and isoproterenol were blunted by the funny current (If) inhibitor ZD 7288. Inhibitors of protein kinase A, H-89 and KT-5720 reduced the chronotropic response to glucagon but not to isoproterenol. Inhibition of ryanodine receptors and calcium/calmodulin dependent protein kinase II (important regulators of sarcoplasmic reticulum Ca2⁺ release), with ruthenium red and KN-62 respectively, failed to alter chronotropic responses of either glucagon or isoproterenol. Non selective inhibition of phosphodiesterase (PDE) with 3-isobutylmethylxantine or selective inhibition of PDE3 or PDE4 with cilostamide or rolipram respectively did not affect chronotropic effects of glucagon or isoproterenol. Our results indicate that glucagon increases beating rate but not contractility in rat right atria which could be a consequence of lower levels of glucagon receptors in atrial myocardium than in sinoatrial node. Chronotropic responses to glucagon or isoproterenol are mediated by If current but not by sarcoplasmic reticulum Ca2⁺ release, neither are regulated by PDE activity.

Treatment for calcium channel blocker poisoning: a systematic review

CONTEXT

Calcium channel blocker poisoning is a common and sometimes life-threatening ingestion.

OBJECTIVE

To evaluate the reported effects of treatments for calcium channel blocker poisoning. The primary outcomes of interest were mortality and hemodynamic parameters. The secondary outcomes included length of stay in hospital, length of stay in intensive care unit, duration of vasopressor use, functional outcomes, and serum calcium channel blocker concentrations.

METHODS

Medline/Ovid, PubMed, EMBASE, Cochrane Library, TOXLINE, International pharmaceutical abstracts, Google Scholar, and the gray literature up to December 31, 2013 were searched without time restriction to identify all types of studies that examined effects of various treatments for calcium channel blocker poisoning for the outcomes of interest. The search strategy included the following Keywords: [calcium channel blockers OR calcium channel antagonist OR calcium channel blocking agent OR (amlodipine or bencyclane or bepridil or cinnarizine or felodipine or fendiline or flunarizine or gallopamil or isradipine or lidoflazine or mibefradil or nicardipine or nifedipine or nimodipine or nisoldipine or nitrendipine or prenylamine or verapamil or diltiazem)] AND [overdose OR medication errors OR poisoning OR intoxication OR toxicity OR adverse effect]. Two reviewers independently selected studies and a group of reviewers abstracted all relevant data using a pilot-tested form. A second group analyzed the risk of bias and overall quality using the STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) checklist and the Thomas tool for observational studies, the Institute of Health Economics tool for Quality of Case Series, the ARRIVE (Animal Research: Reporting In Vivo Experiments) guidelines, and the modified NRCNA (National Research Council for the National Academies) list for animal studies. Qualitative synthesis was used to summarize the evidence. Of 15,577 citations identified in the initial search, 216 were selected for analysis, including 117 case reports. The kappa on the quality analysis tools was greater than 0.80 for all study types.

RESULTS

The only observational study in humans examined high-dose insulin and extracorporeal life support. The risk of bias across studies was high for all interventions and moderate to high for extracorporeal life support. High-dose insulin. High-dose insulin (bolus of 1 unit/kg followed by an infusion of 0.5-2.0 units/kg/h) was associated with improved hemodynamic parameters and lower mortality, at the risks of hypoglycemia and hypokalemia (low quality of evidence). Extracorporeal life support. Extracorporeal life support was associated with improved survival in patients with severe shock or cardiac arrest at the cost of limb ischemia, thrombosis, and bleeding (low quality of evidence). Calcium, dopamine, and norepinephrine. These agents improved hemodynamic parameters and survival without documented severe side effects (very low quality of evidence). 4-Aminopyridine. Use of 4-aminopyridine was associated with improved hemodynamic parameters and survival in animal studies, at the risk of seizures. Lipid emulsion therapy. Lipid emulsion was associated with improved hemodynamic parameters and survival in animal models of intravenous verapamil poisoning, but not in models of oral verapamil poisoning. Other studies. Studies on decontamination, atropine, glucagon, pacemakers, levosimendan, and plasma exchange reported variable results, and the methodologies used limit their interpretation. No trial was documented in humans poisoned with calcium channel blockers for Bay K8644, CGP 28932, digoxin, cyclodextrin, liposomes, bicarbonate, carnitine, fructose 1,6-diphosphate, PK 11195, or triiodothyronine. Case reports were only found for charcoal hemoperfusion, dialysis, intra-aortic balloon pump, Impella device and methylene blue.

CONCLUSIONS

The treatment for calcium channel blocker poisoning is supported by low-quality evidence drawn from a heterogeneous and heavily biased literature. High-dose insulin and extracorporeal life support were the interventions supported by the strongest evidence, although the evidence is of low quality.

Management of calcium channel blocker overdoses

Calcium channel blockers (CCBs) are some of the most commonly used medications in clinical practice to treat hypertension, angina, cardiac arrhythmias, and some cases of heart failure. Recent data show that CCBs are the most common of the cardiovascular medications noted in intentional or unintentional overdoses.(1) Novel treatment approaches in the form of glucagon, high-dose insulin therapy, and intravenous lipid emulsion therapies have been tried and have been successful. However, the evidence for these are limited to case reports and case series. We take this opportunity to review the various treatment options in the management of CCB overdoses with a special focus on high-dose insulin therapy as the emerging choice for initial therapy in severe overdoses.

Management of beta-adrenergic blocker and calcium channel antagonist toxicity

State-of-the-art therapy for beta-adrenergic receptor blocker and calcium channel antagonist toxicity is reviewed in the light of new insights into drug-induced shock. A brief discussion of pathophysiology, including cardiac, hemodynamic, and metabolic effects of cardiac drug toxicity, provides a foundation for understanding the basis of therapy. The major focus of this review is a critical evaluation of antidotal use of calcium, glucagon, catecholamines, insulin-euglycemia, and other novel therapies based on investigational studies and cumulative clinical experience.

Compromising bradycardia: management in the emergency department

AIM OF THE STUDY

Bradycardia may represent a serious emergency. The need for temporary and permanent pacing is unknown.

METHODS

We analysed a registry for the incidence, symptoms, presenting rhythm, underlying mechanism, management and outcome of patients presenting with compromising bradycardia to the emergency department of a university hospital retrospectively during a 10-year period.

RESULTS

We identified 277 patients, 173 male (62%), median age 68 (IQR 58-78), median ventricular rate 33 min(-1) (IQR 30-40). The leading symptoms were syncope [94 (33%)], dizziness [61 (22%)], collapse [46 (17%)], angina [46 (17%)] and dyspnoea/heart failure [30 (11%)]. The initial ECG showed high grade AV block [134 (48%)], sinus bradycardia/AV block [46 (17%)], sinuatrial arrest [42 (15%)], bradycardic atrial fibrillation [39 (14%)] and pacemaker-failure [16 (6%)]. The underlying mechanisms were primary disturbance of cardiac automaticity and/or conduction [135 (49%)], adverse drug effect [58 (21%)], acute myocardial infarction [40 (14%)], pacemaker failure [16 (6%)], intoxication [16 (6%)] and electrolyte disorder [12 patients (4%)]. In 107 (39%) patients bed rest resolved the symptoms. Intravenous drugs to increase ventricular rate were given to 170 (61%) patients, 54 (20%) required additional temporary transvenous/transcutaneous pacing. Two severely intoxicated patients could be stabilised only by cardiopulmonary bypass. A permanent pacemaker was implanted in 137 patients (50%). Mortality was 5% at 30 days.

CONCLUSION

In our cohort, about 20% of the patients presenting with compromising bradycardia required temporary emergency pacing for initial stabilisation, in 50% permanent pacing had to be established.

Antidotes for acute cardenolide (cardiac glycoside) poisoning

BACKGROUND

Cardenolides are naturally occurring plant toxins which act primarily on the heart. While poisoning with the digitalis cardenolides (digoxin and digitoxin) are reported worldwide, cardiotoxicity from other cardenolides such as the yellow oleander are also a major problem, with tens of thousands of cases of poisoning each year in South Asia. Because cardenolides from these plants are structurally similar, acute poisonings are managed using similar treatments. The benefit of these treatments is of interest, particularly in the context of cost since most poisonings occur in developing countries where resources are very limited.

OBJECTIVES

To determine the efficacy of antidotes for the treatment of acute cardenolide poisoning, in particular atropine, isoprenaline (isoproterenol), multiple-dose activated charcoal (MDAC), fructose-1,6-diphosphate, sodium bicarbonate, magnesium, phenytoin and anti-digoxin Fab antitoxin.

SEARCH STRATEGY

We searched MEDLINE, EMBASE, the Controlled Trials Register of the Cochrane Collaboration, Current Awareness in Clinical Toxicology, Info Trac, www.google.com.au, and Science Citation Index of studies identified by the previous searches. We manually searched the bibliographies of identified articles and personally contacted experts in the field.

SELECTION CRITERIA

Randomised controlled trials where antidotes were administered to patients with acute symptomatic cardenolide poisoning were identified.

DATA COLLECTION AND ANALYSIS

We independently extracted data on study design, including the method of randomisation, participant characteristics, type of intervention and outcomes from each study. We independently assessed methodological quality of the included studies. A pooled analysis was not appropriate.

MAIN RESULTS

Two randomised controlled trials were identified, both were conducted in patients with yellow oleander poisoning. One trial investigated the effect of MDAC on mortality, the relative risk (RR) was 0.31 (95% confidence interval (CI) 0.12 to 0.83) indicating a beneficial effect. The second study found a beneficial effect of anti-digoxin Fab antitoxin on the presence of cardiac dysrhythmias at two hours post-administration; the RR was 0.60 (95% CI 0.44 to 0.81). Other benefits were also noted in both studies and serious adverse effects were minimal. Studies assessing the effect of antidotes on other cardenolides were not identified. One ongoing study investigating the activated charcoal for acute yellow oleander self-poisoning was also identified.

AUTHORS' CONCLUSIONS

There is some evidence to suggest that MDAC and anti-digoxin Fab antitoxin may be effective treatments for yellow oleander poisoning. However, the efficacy and indications of these interventions for the treatment of acute digitalis poisoning is uncertain due to the lack of good quality controlled clinical trials. Given pharmacokinetic differences between individual cardenolides, the effect of antidotes administered to patients with yellow oleander poisoning cannot be readily translated to those of other cardenolides. Unfortunately cost limits the use of antidotes such as anti-digoxin Fab antitoxin in developing countries where cardenolide poisonings are frequent. More research is required using relatively cheap antidotes which may also be effective.

Cardiac function in mice lacking the glucagon-like peptide-1 receptor

Glucagon-like peptide-1 (GLP-1) acts via its G protein-coupled receptor (GLP-1R) to regulate blood glucose. Although the GLP-1R is widely expressed in peripheral tissues, including the heart, and exogenous GLP-1 administration increases heart rate and blood pressure in rodents, the physiological importance of GLP-1R action in the cardiovascular system remains unclear. We now show that 2-month-old mice with genetic deletion of the GLP-1R (GLP-1R(-/-)) exhibit reduced resting heart rate and elevated left ventricular (LV) end diastolic pressure compared with CD-1 wild-type controls. At the age of 5 months, echocardiography and histology demonstrate increased LV thickness in GLP-1R(-/-) mice. Although baseline hemodynamic parameters of GLP-1R(-/-) did not differ significantly from those of wild type, GLP-1R(-/-) mice displayed impaired LV contractility and diastolic function after insulin administration. The defective cardiovascular response to insulin was not attributable to a generalized defect in the stress response, because GLP-1R(-/-) mice responded appropriately to insulin with increased c-fos expression in the hypothalamus and increased circulating levels of glucagon and epinephrine. Furthermore, LV contractility after exogenous epinephrine infusion was also reduced in GLP-1R(-/-) mice. These findings provide new evidence implicating an essential role for GLP-1R in the control of murine cardiac structure and function in vivo.

Glucagon in β‐Blocker and Calcium Channel Blocker Overdoses: A Systematic Review

BACKGROUND

Glucagon is usually accepted as part of the standard treatment in the management of patients with beta-blocker and calcium channel blocker overdoses.

METHODS

A systematic review was done in order to evaluate the evidence supporting glucagon use in beta-blocker and calcium channel blocker overdoses. Studies evaluating glucagon for those uses were identified using the Cochrane Database of Systematic Reviews, the Cochrane Controlled Trials Register, MedLine, ToxLine, and EMBASE searches, as well as reviewing medical toxicology textbooks and references of identified articles. Only controlled studies of human or animal studies were included, the latter only when it was an in vivo model of acute poisoning. The quality of the included studies was assessed.

RESULTS

The search found no study in humans but identified 30 in animals. In the five studies of animal models of beta-blocker overdose included, glucagon appeared to consistently increase the heart rate at least transiently but appeared to have no effect on mean arterial pressure even though it possibly increased cardiac output. Its effect on the survival rate in animal models of beta-blocker overdose was unclear. In the six studies of animal models of calcium channel blocker overdose included, glucagon appeared to increase heart rate and cardiac output and reverse second and third degree AV blocks, all at least transiently. There appeared to be no effect of glucagon on mean arterial pressure although it did increase in one model. Glucagon appeared to have no effect on survival rate. The included studies for both overdoses were not blinded, had limited numbers of animals, and some had inadequate glucagon regime.

CONCLUSION

The evidence supporting the use of glucagon in the management of patients with beta-blocker and calcium channel blocker overdoses is limited to animal studies.

Management of calcium channel antagonist overdose

Calcium channel antagonists are used primarily for the treatment of hypertension and tachyarrhythmias. Overdose of calcium channel antagonists can be lethal. Calcium channel antagonists act at the L-type calcium channels primarily in cardiac and vascular smooth muscle preventing calcium influx into cells with resultant decreases in vascular tone and cardiac inotropy and chronotropy. The L-type calcium channel is a complex structure and is thus affected by a large number of structurally diverse antagonists. In the setting of overdose, patients may experience vasodilatation and bradycardia leading to a shock state. Patients may also be hyperglycaemic and acidotic due to the blockade of L-type calcium channels in the pancreatic islet cells that affect insulin secretion. Aggressive therapy is warranted in the setting of toxicity. Gut decontamination with charcoal, or whole bowel irrigation or multiple-dose charcoal in the setting of extended-release products is indicated. Specific antidotes include calcium salts, glucagon and insulin. Calcium salts may be given in bolus doses or may be employed as a continuous infusion. Care should be exercised to avoid the administration of calcium in the setting of concomitant digoxin toxicity. Insulin administration has been used effectively to increase cardiac inotropy and survival. The likely mechanism involves a shift to carbohydrate metabolism in the setting of decreased availability of carbohydrates due to decreased insulin secretion secondary to blockade of calcium channels in pancreatic islet cells. Glucose should be administered as well to maintain euglycaemia. Supportive care including the use of phosphodiesterase inhibitors, adrenergic agents, cardiac pacing, balloon pump or extracorporeal bypass is frequently indicated if antidotal therapy is not effective. Careful evaluation of asymptomatic patients, including and electrocardiogram and a period of observation, is indicated. Patients ingesting a nonsustained-release product should be observed in a monitored setting for 12 hours, while those who ingest a sustained-release preparation should be observed for no less than 24 hours. Charcoal should be given to the asymptomatic patient with a history of calcium channel antagonist overdose.

Anesthesia for a patient with catecholaminergic polymorphic ventricular tachycardia

IMPLICATIONS

A patient with catecholaminergic polymorphic ventricular tachycardia required anesthesia for implantation of a defibrillator. The diagnostic criteria, treatment, and anesthetic considerations for this rare, familial dysrhythmia are described.