Acebutolol-induced ventricular tachycardia reversed with sodium bicarbonate

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.

ECG Manifestations: The Poisoned Patient

Despite that drugs have widely varying indications for therapeutic use, many unrelated drugs share a common cardiac pharmacologic effect if taken in overdose. The purpose of this article is to group together agents that cause similar electrocardiographic effects,review their pharmacologic actions, and discuss the electrocardiographic findings reported in the medical literature.

Pharmacology, Pathophysiology and Management of Calcium Channel Blocker and ??-Blocker Toxicity

Calcium channel blockers (CCB) and beta-blockers (BB) account for approximately 40% of cardiovascular drug exposures reported to the American Association of Poison Centers. However, these drugs represent >65% of deaths from cardiovascular medications. Yet, caring for patients poisoned with these medications can be extremely difficult. Severely poisoned patients may have profound bradycardia and hypotension that is refractory to standard medications used for circulatory support.Calcium plays a pivotal role in cardiovascular function. The flow of calcium across cell membranes is necessary for cardiac automaticity, conduction and contraction, as well as maintenance of vascular tone. Through differing mechanisms, CCB and BB interfere with calcium fluxes across cell membranes. CCB directly block calcium flow through L-type calcium channels found in the heart, vasculature and pancreas, whereas BB decrease calcium flow by modifying the channels via second messenger systems. Interruption of calcium fluxes leads to decreased intracellular calcium producing cardiovascular dysfunction that, in the most severe situations, results in cardiovascular collapse.Although, CCB and BB have different mechanisms of action, their physiological and toxic effects are similar. However, differences exist between these drug classes and between drugs in each class. Diltiazem and especially verapamil tend to produce the most hypotension, bradycardia, conduction disturbances and deaths of the CCB. Nifedipine and other dihydropyridines are generally less lethal and tend to produce sinus tachycardia instead of bradycardia with fewer conduction disturbances.BB have a wider array of properties influencing their toxicity compared with CCB. BB possessing membrane stabilising activity are associated with the largest proportion of fatalities from BB overdose. Sotalol overdoses, in addition to bradycardia and hypotension, can cause torsade de pointes. Although BB and CCB poisoning can present in a similar fashion with hypotension and bradycardia, CCB toxicity is often associated with significant hyperglycaemia and acidosis because of complex metabolic derangements related to these medications. Despite differences, treatment of poisoning is nearly identical for BB and CCB, with some additional considerations given to specific BB. Initial management of critically ill patients consists of supporting airway, breathing and circulation. However, maintenance of adequate circulation in poisoned patients often requires a multitude of simultaneous therapies including intravenous fluids, vasopressors, calcium, glucagon, phosphodiesterase inhibitors, high-dose insulin, a relatively new therapy, and mechanical devices. This article provides a detailed review of the pharmacology, pathophysiology, clinical presentation and treatment strategies for CCB and BB overdoses.

Electrocardiographic changes associated with beta-blocker toxicity

STUDY OBJECTIVE

We sought to characterize the ECG changes associated with symptomatic beta-blocker overdose.

METHODS

The study population consisted of a prospective cohort of patients reporting to 2 regional poison centers with beta-blocker overdose. Each patient received an ECG on presentation and a structured follow-up. The inclusion criteria for symptomatic overdose included heart rate of less than 60 beats/min or systolic blood pressure of less than 90 mm Hg; symptoms consistent with decreased end-organ perfusion; therapeutic intervention with cardioactive medication; and corroboration by 2 of the authors that this was a clear-cut case of symptomatic beta-blocker overdose with cardiovascular toxicity. Exclusion criteria included cardioactive coingestants, age younger than 6 years, and no available ECG.

RESULTS

Of 167 patients, 13 were determined to have symptomatic exposures. First-degree heart block (>200 ms) was the most common ECG finding (10/12) and also had the greatest likelihood ratio (5.31) when comparing those with symptomatic exposures with those with asymptomatic exposures. Comparing the asymptomatic with the symptomatic groups, the mean PR interval was 167 ms (95% confidence interval [CI] 162 to 171 ms) versus 216 ms (95% CI 193 to 238 ms), the mean QRS interval was 89 ms (95% CI 87 to 91 ms) versus 112 ms (95% CI 92 to 132 ms), the mean QTc interval was 422 ms (95% CI 417 to 428) versus 462 ms (95% CI 434 to 490 ms), and the mean heart rate was 72 beats/min (95% CI 69 to 74 beats/min) versus 66 beats/min (95% CI 59 to 73 beats/min). Two cases of symptomatic acebutolol exposure appeared unique by demonstrating disproportionate prolongation of the QTc interval, an RaVR height of 3 mm or greater, and associated ventricular tachydysrhythmia.

CONCLUSION

The majority of clinically significant beta-blocker intoxications demonstrate negative dromotropic effects on ECG. Several ECG differences in acebutolol intoxication might reflect unique pathophysiologic processes relative to other beta-blockers.

In vivo rates of skeletal muscle protein synthesis in rats are decreased by acute ethanol treatment but are not ameliorated by supplemental alpha-tocopherol

Some studies have shown that reductions in tissue protein synthesis, under a variety of cytotoxic conditions, are ameliorated by alpha-tocopherol (ATC) supplementation. We have also shown evidence of increased oxidative stress and reduced protein synthesis rates in alcohol-exposed muscle. Serum levels of ATC fall and rates of muscle protein synthesis are reduced in patients with alcoholic myopathy. We therefore tested the hypothesis that treatment with ATC could ameliorate the ethanol-induced changes in muscle protein synthesis, a contributory event in the pathogenesis of alcoholic muscle disease. Studies were carried out on gastrocnemius (Type II fiber-predominant and usually considered representative of the musculature as a whole), soleus (Type I fiber-predominant) and plantaris (Type II fiber-predominant) muscles. For comparative purposes, we also investigated the liver. Young male Wistar rats (90 g body weight) were injected intraperitoneally (i.p.) daily with ATC (30 mg/kg body weight) in Intralipid fat emulsion (0.1 mL/100 g body, i.p.) for 5 d. Controls were similarly injected with the Intralipid vehicle alone. After ATC supplementation, rats were given ethanol (75 mmol/kg body weight, i.p., 2.5 h) or saline (0.15 mol/L NaCl, i. p.). Fractional rates of tissue protein synthesis (i.e., the percentage of the tissue protein pool renewed each day, k(s), %/d) and RNA activities [i.e., the amount of protein synthesis each day per unit RNA, k(RNA), mg protein/d/mg RNA)] were then measured. Supplementation increased ATC concentrations in plasma, gastrocnemius and liver. There was no effect of ATC supplementation alone on k(s) in any of the tissues. ATC supplementation in the absence of alcohol increased k(RNA) in the plantaris muscle. In nonsupplemented groups, acute ethanol treatment reduced skeletal muscle (soleus, plantaris and gastrocnemius) k(s). Hepatic k(s) was not altered by ethanol, although ATC concentrations in this tissue increased due to ethanol. However, none of the changes in muscle k(s) or k(RNA) due to ethanol were significantly affected by ATC supplementation. In conclusion, ATC supplementation does not appear beneficial in ameliorating acute alcohol toxicity in skeletal muscle as defined by reductions in protein synthesis.