Digitalis glycosides: mechanisms and manifestations of toxicity. Part III

Successful management of massive digoxin overdose using DIGIFab and therapeutic plasma exchange: a case report

BACKGROUND

Despite the efficacy and safety of DIGIFab, it is relatively expensive and has limited availability. In addition, alternative interventions, such as therapeutic plasma exchange, may need to be considered in massive digoxin overdoses. Although few case reports describe its efficacy.

CASE PRESENTATION

We report a case of a 17-year-old white male patient brought by family members to our emergency department in Riyadh, Saudi Arabia. After intentionally ingesting 48 mg of digoxin tablets to commit suicide, the patient's initial digoxin serum level was 8.04 ng/mL. The patient was resuscitated in the emergency department. After admission to the intensive care unit, the patient underwent therapeutic plasma exchange, because of insufficient DIGIFab doses. Afterward, the serum digoxin levels drastically decreased, and his symptoms reverted. The patient was successfully managed and discharged 7 days after admission.

CONCLUSION

Despite insufficient evidence and a limited number of case reports describing the use of extracorporeal treatment in digoxin overdose, we noted the significant impact of therapeutic plasma exchange on our patient. However, therapeutic plasma exchange's use in routine treatment requires stronger evidence to confirm its benefits.

Digoxin Impact on Heart Failure Patients with Atrial Fibrillation

BACKGROUND

Digoxin is a cardiac glycoside, derived from the plant Digitalis purpurea. For many years digitalis has been widely used in the treatment of heart failure (HF), owing to its cardiotonic and neurohormonal effects and atrial fibrillation (AF), due to its parasympathomimetic effect on the AV node.

OBJECTIVE

The aim of this paper is to evaluate the available evidence on the safety and efficacy of digoxin in patients with HF and AF, by reviewing the pertinent literature.

METHODS

We conducted a PubMed/MEDLINE and SCOPUS search to evaluate the currently available evidence on the administration of digoxin and its association with all-cause mortality risk in patients with AF and HF.

RESULTS

Several observational analyses of clinical trials and meta-analyses have shown conflicting results on the safety and efficacy of digoxin administration in patients with AF and HF. According to these results, digoxin should be avoided in patients without HF, as it is associated with worse outcomes. On the other hand, in patients with AF and HF digoxin should be used with caution.

CONCLUSION

The impact of digoxin on all-cause mortality and adverse effects in these patients remains unclear based on the current evidence. More trials at low risk of bias evaluating the effects of digoxin are needed.

Improvement of Adequate Digoxin Dosage: An Application of Machine Learning Approach

Digoxin is a high-alert medication because of its narrow therapeutic range and high drug-to-drug interactions (DDIs). Approximately 50% of digoxin toxicity cases are preventable, which motivated us to improve the treatment outcomes of digoxin. The objective of this study is to apply machine learning techniques to predict the appropriateness of initial digoxin dosage. A total of 307 inpatients who had their conditions treated with digoxin between 2004 and 2013 at a medical center in Taiwan were collected in the study. Ten independent variables, including demographic information, laboratory data, and whether the patients had CHF were also noted. A patient with serum digoxin concentration being controlled at 0.5-0.9 ng/mL after his/her initial digoxin dosage was defined as having an appropriate use of digoxin; otherwise, a patient was defined as having an inappropriate use of digoxin. Weka 3.7.3, an open source machine learning software, was adopted to develop prediction models. Six machine learning techniques were considered, including decision tree (C4.5), k-nearest neighbors (kNN), classification and regression tree (CART), randomForest (RF), multilayer perceptron (MLP), and logistic regression (LGR). In the non-DDI group, the area under ROC curve (AUC) of RF (0.912) was excellent, followed by that of MLP (0.813), CART (0.791), and C4.5 (0.784); the remaining classifiers performed poorly. For the DDI group, the AUC of RF (0.892) was the best, followed by CART (0.795), MLP (0.777), and C4.5 (0.774); the other classifiers' performances were less than ideal. The decision tree-based approaches and MLP exhibited markedly superior accuracy performance, regardless of DDI status. Although digoxin is a high-alert medication, its initial dose can be accurately determined by using data mining techniques such as decision tree-based and MLP approaches. Developing a dosage decision support system may serve as a supplementary tool for clinicians and also increase drug safety in clinical practice.

Contemporary Controversies in Digoxin Use in Systolic Heart Failure

Digoxin remains one of the oldest therapies for heart failure; however, its safety and efficacy have been controversial since its initial use. Questions that remain include the clinical efficacy of digoxin when added to contemporary medical therapy, when and if it should be added, and how to minimize adverse effects. In this review, we will summarize recent data on the use of digoxin in systolic heart failure and address some of the controversies regarding the role of digoxin in the modern era of heart failure treatment.

The use of digoxin in patients with worsening chronic heart failure: reconsidering an old drug to reduce hospital admissions

Digoxin is the oldest cardiac drug still in contemporary use, yet its role in the management of patients with heart failure (HF) remains controversial. A purified cardiac glycoside derived from the foxglove plant, digoxin increases ejection fraction, augments cardiac output, and reduces pulmonary capillary wedge pressure without causing deleterious increases in heart rate or decreases in blood pressure. Moreover, it is also a neurohormonal modulator at low doses. In the pivotal DIG (Digitalis Investigation Group) trial, digoxin therapy was shown to reduce all-cause and HF-specific hospitalizations but had no effect on survival. With the discovery of neurohormonal blockers capable of reducing mortality in HF with reduced ejection fraction, the results of the DIG trial were viewed as neutral, and the use of digoxin declined precipitously. Although modern drug and device-based therapies have dramatically improved the survival of ambulatory patients with HF, outcomes for patients with worsening chronic HF, defined as deteriorating signs and symptoms on standard therapy often leading to unscheduled clinic or emergency department visits or hospitalization, have largely remained unchanged over the past 2 decades. The available data suggest that a therapeutic trial of digoxin may be appropriate in patients with worsening chronic heart failure who remain symptomatic.

MONaKA, a novel modulator of the plasma membrane Na,K-ATPase

We have cloned and characterized mouse and human variants of MONaKA, a novel protein that interacts with and modulates the plasma membrane Na,K-ATPase. MONaKA was cloned based on its sequence homology to the Drosophila Slowpoke channel-binding protein dSlob, but mouse and human MONaKA do not bind to mammalian Slowpoke channels. At least two splice variants of MONaKA exist; the splicing is conserved perfectly between mouse and human, suggesting that it serves some important function. Both splice variants of MONaKA are expressed widely throughout the CNS and peripheral nervous system, with different splice variant expression ratios in neurons and glia. A yeast two-hybrid screen with MONaKA as bait revealed that it binds tightly to the beta1 and beta3 subunits of the Na,K-ATPase. The association between MONaKA and Na,K-ATPase beta subunits was confirmed further by coimmunoprecipitation from transfected cells, mouse brain, and cultured mouse astrocytes. A glutathione S-transferase-MONaKA fusion protein inhibits Na,K-ATPase activity from whole brain or cultured astrocytes. Furthermore, transfection of MONaKA inhibits 86Rb+ uptake via the Na,K-ATPase in intact cells. These results are consistent with the hypothesis that MONaKA modulates brain Na,K-ATPase and may thereby participate in the regulation of electrical excitability and synaptic transmission.

Mechanisms, manifestations, and management of digoxin toxicity in the modern era

Because of the common use of digoxin and because of its narrow therapeutic index, digoxin toxicity has been prevalent historically and, therefore, most clinicians are well aware of the classical dose/concentration-related signs and symptoms of toxicity. Yet, in the modern era the incidence of digoxin toxicity has been declining for a variety of reasons, including a new (lower) therapeutic range, the development of more effective drug therapies for heart failure, and more accurate dosing methods. In addition, digoxin toxicity, once commonly fatal, can now be quickly and effectively treated by the emergency administration of antidigoxin Fab fragments. Indeed, it may be possible to expand the use of Fab fragments to select patients with non-life-threatening digoxin toxicity, in order to save costs and improve patient comfort. Most cases of digoxin toxicity are caused by inappropriately high dosages, which are usually prescribed in the setting of renal dysfunction, while other cases can be attributed to system errors such as multiple prescriptions, poor patient counseling, or errors in transcribing. With modern computerized prescribing systems, such as direct physician order entry and prompts that alert the clinician to the potential for error, it is possible to decrease the incidence of digoxin toxicity even further. A realistic goal is to nearly eradicate once commonplace digoxin toxicity or at least make its occurrence a rare event.

Supraventricular tachycardia

Supraventricular tachycardias (SVT) comprise those tachycardias that originate above the bifurcation of the bundle of His. They can be classified broadly as AV node dependent and AV node independent. The mechanism and clinical manifestation of SVTs, which is essential to their correct diagnosis, is reviewed. The therapeutic management of SVTs, including acute and chronic drug therapy and catheter ablation, is discussed also.

Plasma exchange for the removal of digoxin-specific antibody fragments in renal failure: timing is important for maximizing clearance

Life-threatening digoxin toxicity may be effectively treated with digoxin-specific antibody fragments (Fab). However, in end-stage renal disease, the digoxin-Fab complexes persist in the circulation and dissociate, potentially resulting in rebounding free digoxin levels and the recurrence of symptomatic toxicity. To prevent this rebound phenomenon, plasma exchange (PE) has been implemented for the removal of the digoxin-Fab complexes in renal failure. However, there is only one case report describing its use in this setting. To better determine the optimal timing of PE after Fab administration, we performed two PE treatments (each preceded by Fab) in a patient with acute renal failure and acute digoxin poisoning. The admission serum digoxin level was 21 ng/mL. The timing of the PE treatments relative to Fab dosing was as follows: the first PE was performed 26 hours post-Fab, and the second PE was performed 2.5 hours post-Fab. The plasma ultrafiltrate digoxin concentration was 2.5-fold greater when PE was performed 2.5 hours versus 26 hours after Fab administration (19.9 versus 8.1 ng/mL). The combined total amount of digoxin removed in the ultrafiltrate plasma was minimal (0.13 mg), less than 1% of the total amount of ingested drug. We conclude that the optimal timing of PE is within the first 3 hours after Fab administration. Although PE is efficacious for removing digoxin-Fab complexes, thus preventing rebound digoxin toxicity, it is not efficacious for improving total digoxin clearance because of the large apparent volume of distribution of digoxin (5 to 8 L/kg).

Severe thrombocytopenia caused by digitoxin intoxication in a patient with heart failure associated with Sjögren's syndrome

Congestive heart failure (CHF) related to Sjögren's syndrome is extremely rare. This report concerns a patient who presented with CHF and severe thrombocytopenia (5,000/microl). Serum concentrations of K, Mg and digitoxin were 3.2mmol/L, 1.4mg/L and 57.2ng/ml, respectively. Digitoxin intoxication was evident, seemingly evoked by hypokalemia, hypomagnesemia, hepatorenal dysfunction and hypothyroidism. The severe thrombocytopenia was considered to have been caused by this intoxication, as it disappeared soon after the digitoxin was discontinued and potassium was supplemented.

Digoxin-macrolide drug interaction

Macrolide antibiotics appear to be able to enhance the oral bioavailability of digoxin by altering the gastrointestinal flora that metabolize digoxin to less active dihydro metabolites, thus leading to increased serum digoxin concentrations and possible digoxin toxicity in select patients stabilized on digoxin therapy. This interaction may be of clinical importance in up to 10% of the population. Currently, the orally administered erythromycin, clarithromycin, and roxithromycin have been implicated. Although realistically this interaction may be encountered rarely, when it does occur, it can be of clinical significance.

Gitaloxin poisoning in a child

Gitaloxin is a digitalis glycoside used for the same indications as digoxin and digitoxin. The successful outcome for a 2 1/2-year-old boy who accidentally ingested 3 mg of gitaloxin (100 times the normal therapeutic dose) is reported. At admission the child presented with irregular heart rhythm. He subsequently started vomiting, even after continuous gastric feeding. Only 48 h after ingestion of gitaloxin he became somnolent and developed bradyarrhythmia. The symptoms disappeared 96 h later; the bradyarrhythmia, however, (second-degree atrioventricular block) decreased progressively only after 120 h. The initial clinical presentation of gitaloxin poisoning may be misleading and careful observation in a pediatric intensive care unit is mandatory. A cross-reaction between the fluorescence polarization immunoassay for digitoxin and the radioimmunoassay for gitaloxin was found and was used as a helpful, but rough, estimate of the severity of gitaloxin poisoning, in the absence of a specific measurement of gitaloxin.

Value of digoxin in heart failure and sinus rhythm: new features of an old drug?

Digoxin has been a controversial drug since its introduction >200 years ago. Although its efficacy in patients with heart failure and atrial fibrillation is clear, its value in patients with heart failure and sinus rhythm has often been questioned. In the 1980s, reports of some large-scale trials indicated that digoxin, with or without vasodilators or angiotensin-converting enzyme inhibitors, reduced signs and symptoms of congestive heart failure and improved exercise tolerance. This beneficial influence was mainly found in patients with more advanced heart failure and dilated ventricles, whereas the effect in those with mild disease appeared to be less pronounced. In the last few years, new data have shown that digoxin may also have clinical value in mild heart failure, either when used in combination with other drugs or when administered alone. As neurohumoral activation has increasingly been recognized to be a contributing factor in the disease progression of chronic heart failure, the modulating effects of digoxin on neurohumoral and autonomic status have received more attention. Also, there is evidence that relatively low doses of digoxin may be at least as effective as higher doses and have a lower incidence of side effects. Further, the recognition that the use of digoxin too early after myocardial infarction may be harmful and the development of other drugs, in particular angiotensin-converting enzyme inhibitors, have obviously changed the place of digoxin in the treatment of chronic heart failure. The large-scale survival trial by the Digitalis Investigators Group (DIG), whose preliminary results have recently been presented, has shown that although digoxin has a neutral effect on total mortality during long-term treatment, it reduces the number of hospital admissions and deaths due to worsening heart failure. The potentially new features of the old drug digoxin are discussed in this review.

New indole and pyridazinoindole analogs--synthesis and study as inhibitors of phosphodiesterases and as inhibitors of blood platelet aggregation

This paper presents the synthesis of new indole, pyridazino[4,5-b]-indole, and pyridazino[4,5-a]indole analogs as well as a study of their "in vitro" activity as inhibitors of different phosphodiesterases isolated from dog cardiac tissue, dog aorta, and bovine platelets; the study of their activity as inhibitors of platelet aggregation in guinea pig whole blood, with ADP and arachidonic acid (AA) as pro-aggregants, is also included. The selected compounds 8-benzyloxy-3,4-dihydro-1-(3,4,5-trimethoxy)benzylideneaminopyridazin o[4,5- b]indole 14g, and 8-benzyloxy-4-[(3,4-dimethyl)pyrazolyl]pyridazino[4,5-b]indo le 20 present an interesting profile as potential inodilators, with a complementary, beneficial activity as inhibitors of the aggregation, activities which could possibly be related to the inhibition of the PDE's. Among the other compounds studied, 8-benzyloxy-3,4-dihydro-1-[4-(methyl)piperazino]acetamidopyrida zino[4,5- b]indol-4-one 16c and 8-benzyloxy-3,4-dihydro-1-[4-(2- methoxyphenyl)piperazino]acetamidopyridazino[4,5-b]indol-4-o ne 16f stood out as inhibitors of platelet aggregation, with a mechanism that could possibly be related to the AA cascade.

Effects of a novel cardiotonic agent, Org 9731, on force and aequorin light transients in intact ventricular myocardium of the dog: involvement of a cyclic AMP-mediated mechanism and myofibrillar responsiveness to Ca2+ ions

The action of a novel cardiotonic agent, Org 9731 (4-fluoro-N-hydroxy-5, 6-dimethoxy-benzo[b]thiophene-2-carboximidamide methanesulphonate), on intracellular aequorin light transients and isometric contractions was investigated in ventricular trabeculae isolated from dogs. The positive inotropic effect of Org 9731 at 3 microM and higher (up to 0.1 mM) was associated with an increase in the amplitude of the intracellular Ca2+ transient, but the effect of the compound at 0.3 and 1 mM was accompanied by a decrease of the transient. The maximum inotropic response to Org 9731 was approximately 70% of the maximum response to isoproterenol, while the maximum increase in the amplitude of Ca2+ transients produced by Org 9731 was about 30% of the maximum increase induced by isoproterenol. The duration of isometric contractions was prolonged by Org 9731 at 0.3 and 1 mM, with accompanying prolongation of the duration of light transients. The concentration-response curve for the positive inotropic effect of Org 9731 was markedly shifted by carbachol (3 microM), being moved to the right and downward, and the maximum response to Org 9731 was about 10% of that to isoproterenol in the presence of carbachol. Carbachol abolished the increase in the light transient and the accumulation of adenosine 3',5'-cyclic monophosphate (cyclic AMP) induced by Org 9731. These results indicate that Org 9731 increases cardiac contractility, mainly through the accumulation of cyclic AMP up to a concentration of 0.1 mM and also by increasing the responsiveness of myofibrils to Ca2+ ions at 0.3 mM and higher in association with the attenuation of Ca2+ transients. The structure-activity relationship implies that the introduction of a fluorine atom at position 4 of the benzothiophene ring of Org 30,029 attenuated its Ca(2+)-sensitizing action but markedly increased the activity of mechanisms dependent on cyclic AMP.

Disturbances of potassium homeostasis in poisoning

Unless renal function is impaired or rhabdomyolysis is severe, hyperkalemia is a relatively uncommon metabolic complication of poisoning. In contrast, marked hypokalemia is a more common problem and may have serious sequelae. Most potassium disturbances in acute poisoning are due to disruption of extra-renal control mechanisms, notably the activity of Na+/K+ ATPase and K+ channels. Hypokalemia occurs because of increased Na+/K+ ATPase activity (e.g. beta 2 agonist, theophylline or insulin poisoning), competitive blockade of K+ channels (e.g. barium or chloroquine poisoning), gastrointestinal losses and/or alkalosis. Hyperkalemia follows inhibition of Na+/K+ ATPase activity (e.g. by digoxin), increased uptake of potassium salts, disruption of intermediary metabolism (e.g. cyanide poisoning), activation of K+ channels (e.g. fluoride poisoning), and the presence of acidosis and rhabdomyolysis, particularly if the latter is complicated by renal failure. Hypokalemia results in generalized muscle weakness, paralytic ileus, ECG changes (flat or inverted T waves, prominent U waves, ST segment depression) and cardiac arrhythmias (atrial tachycardia +/- block, AV dissociation, VT, VF). Hyperkalemia is associated with abdominal pain, diarrhea, muscle pain and weakness, ECG changes (tall peaked T waves, ST segment depression, prolonged PR interval, QRS prolongation) and cardiac arrhythmias (VT, VF). Significant disturbances of potassium homeostasis are often unrecognized and may cause considerable morbidity and mortality. Prompt recognition and appropriate treatment of these disturbances could be life-saving.

Acute digitalis intoxication--is pacing still appropriate?

Over a six year period, 92 patients intoxicated with either digitoxin or digoxin were admitted to our ICU. Fifty-one patients were treated with cardiac pacing and/or Fab fragments, and the mortality rate was 13% (14 were intoxications with digoxin, 36 with digitoxin, 1 was mixed). Forty-five cases were suicide attempts; six were accidental overdosages. Since cardiac pacing may trigger fatal arrhythmia or delay the administration of Fab fragments, we conducted a retrospective study to determine whether fatal outcomes could be related either to cardiac pacing or to unsatisfactory use of immunotherapy. In our study, prevention of life-threatening arrhythmia failed in 8% of cases with Fab and in 23% with pacing. Though Fab tended to be more effective, this difference was not significant. In our study, the main obstacles to the success of Fab were pacing-induced arrhythmias and delayed or insufficient administration of Fab. Iatrogenic accidents of cardiac pacing were frequent (14/39, 36%) and often fatal (5/39, 13%). In contrast, immunotherapy was not associated with any serious adverse effects (0/28, 0%) and was safer than cardiac pacing (p < 0.05). In conclusion, during digitalis intoxication, the pacemaker has limited preventive and curative effects, is difficult to handle, and exposes patients to severe iatrogenic accidents. Fab fragments act as a powerful antidote and are safer and much easier to use than pacing. These results encourage us to prescribe Fab fragments as first-line therapy during acute digitalis intoxication.

The rational pharmacology of digoxin

Although digoxin remains one of the most widely prescribed drugs in the United States, potential pharmacodynamic and pharmacokinetic interactions between this compound and other drugs, diseases, and events commonly encountered in the perioperative period remain largely unappreciated. Furthermore, the therapeutic benefit of discontinuing or initiating digoxin treatment preoperatively remains unclear. We present a basic review of current knowledge regarding digoxin pharmacology and examine those concepts from the perspective of clinical anesthesiologists.

Digitalis toxicity. Using immunotherapy when supportive care isn't enough

Significant digitalis toxicity, although uncommon, is a medical emergency. Recognition of the problem and good supportive care (eg, administration of activated charcoal and binding resins, correction of potassium levels, restoration of heart rhythm) are the cornerstones of treatment. If indicated, immunotherapy with digoxin immune Fab (Digibind) is a valuable and effective tool.

Protective action of clonidine against the arrhythmogenic and lethal effects of ouabain in guinea-pigs

1. Clonidine (1.25, 2.5 and 5.0 micrograms kg-1) was studied for its effect on the cardiac arrhythmias and lethality induced by slow intravenous infusion of ouabain in guinea-pigs. 2. Clonidine produced significant delays in the onset of the arrhythmic stages and lethality. However, clonidine did not offer any such protection in reserpinised guinea-pigs, whereas its effects were unaltered in atropinized guinea-pigs. 3. Idazoxan (100 micrograms kg-1, i.v.) abolished the antiarrhythmic effect of clonidine whereas corynanthine (1 mg kg-1, i.v.) had no such effect. 4. Clonidine inhibited the rate of the ouabain-induced rise in blood pressure and the peak pressor response. 5. In isolated paced left atria of the guinea-pig, clonidine (3.75 x 10(-4) M) did not offer any protection against rapid and/or irregular extrasystolic contractions induced by ouabain. 6. It is concluded that the antiarrhythmic effect of clonidine is due to its effects on the indirect neural components of digitalis toxicity mediated by the stimulation of alpha 2-adrenoceptors, without any direct antiarrhythmic effect on the myocardium.

The influence of potassium concentration on the inhibitory effect of amiodarone on guinea-pig microsomal Na(+)-K(+)-ATPase activity

The effects of varying incubation K+ concentration on the inhibitory action of amiodarone on the Mg(2+)-dependent ATP hydrolysis by myocardial Na(+)-K(+)-ATPase (EC 3.6.1.3) were studied in guinea pig heart preparations. In the first part of the study, it was established that the activity of the enzyme increased with growing concentrations up to approximately 20 mM K+. The concentration-response relationships for amiodarone were investigated in incubation media containing 2.5, 5.0 and 10 mM K+ respectively. Amiodarone exhibited similar concentration-dependent inhibitory effects in the range of 0.01 nM-80 microM at 2.5 mM, 0.13-150 microM at 5.0 mM and 0.3-700 microM at 10.0 mM K+. The corresponding IC50 values were 10.4 +/- 3.2 microM, 28.3 +/- 7.6 microM at 5.0 mM and 33.3 +/- 9.2 microM at 10.0 mM K+, respectively. Thus, reduction in the K+ concentration from the "standard" 5.0 to 2.5 mM was accompanied by a significant right-to-left shift in the inhibitory potency of amiodarone, the effective concentrations being shifted from microM into nM ranges. Increasing K+ concentration to 10 mM on the other hand attained opposite but less remarkable effects. The results show that the in vitro inhibition of myocardial Na(+)-K(+)-ATPase activity by amiodarone is related to the K+ concentration of the incubation medium. These effects may be pertinent to the mechanism by which this drug interferes with the electrogenic Na+/K+ pump activity of the enzyme, thereby probably contributing to the mechanism(s) responsible for some of its cardiac actions.

Digitalis and beta-blocking agents: effects on depression following myocardial infarction

Depression is frequently seen in patients following myocardial infarction (MI), many of whom are receiving digitalis glycosides, beta-blockers, or other agents that may exert central nervous system (CNS) effects. In a prospective study of the clinical significance of post-MI depression, 335 patients were assessed using a standardized diagnostic interview for depression at 8 to 10 days, and 190 were reinterviewed at 3 to 4 months. Patients prescribed digitalis, beta-blockers, or other cardioactive medications at hospital discharge were identified. Logistic regression analyses were performed to determine the contribution of these agents to depression at 3 to 4 months, controlling for medical and sociodemographic factors as well as for baseline depression. Treatment with digitalis predicted depression at 3 to 4 months (p less than 0.05); no other medications, including beta-blockers, predicted depression (p greater than 0.10). Digitalis may have CNS effects that contribute to depression post-MI and this finding should be considered in the differential diagnosis of depression in cardiac patients.

Intracellular calcium and ventricular fibrillation. Studies in the aequorin-loaded isovolumic ferret heart

To elucidate the role of changes in [Ca2+]i in the induction of ventricular fibrillation (VF), Ca2+i signals, epicardial electrical potentials, and isovolumic left ventricular pressure were simultaneously recorded in isolated intact ferret hearts loaded with aequorin, a bioluminescent protein. When the preparations were perfused with 3 microM acetylstrophanthidin and 8 mM Ca2+, or with a low Na+ solution (18 mM Na+, 100 mM Li+), spontaneous transitions to the VF state were consistently observed within a short period of time. The initiation of spontaneous VF was preceded by development of a Ca2+i overload state, coincidental with the ascending phase of diastolic Ca2+i oscillations, and was followed by further elevation in Ca2+i levels, which were associated with augmented Ca2+i oscillations of a saw-toothed pattern. Pretreatment with 10 microM ryanodine, which blocked Ca2+i oscillations in the preparation, did not eliminate inducibility of VF by means of AC electrical stimulations; however, VF no longer occurred spontaneously, and the threshold for VF induction increased markedly. In the absence of a state of Ca2+i overload, spontaneous defibrillation occurred within a minute after the initiation of VF. We conclude that 1) VF can be induced in the absence of Ca2+i oscillations; however, 2) Ca2+i oscillations play a crucial role as a trigger for VF and therefore are an important determinant of the vulnerability to VF; and 3) the augmented Ca2+i oscillations after the transition to VF state may support the maintenance of this type of arrhythmia.

Relationship between red blood cell potassium and plasma digitoxin concentrations in intoxicated patients

After severe acute self-poisoning by cardiac glycosides, significant and persistent depletion of red blood cell K+ due to inhibition of Na+K+ ATPase is seen. Because of a delay between the time course of plasma digitalis concentrations and that of red blood cell K+ depletion, no direct relation exists between the two, and RBC K+ has hitherto not been considered useful as prognostic indicators of clinical outcome. In an effort to solve this problem, red blood cell K+ was measured by atomic absorption spectrophotometry and plasma digitoxin concentration assayed in six patients admitted to an intensive care unit after digitoxin self-poisoning. Using the effect compartment model of Sheiner, a relationship based on a sigmoid Emax model was able to relate the digitoxin concentration at the action site to red blood cell K+ depletion. Thus the duration of red blood cell K+ depletion could be predicted from two relative simple in vitro assays. Since RBC K+ is a marker of the inhibition of Na+K+ ATPase by digitoxin, this method could be of use for the management of patients self-poisoned with digitalis.

Recognition and management of digitalis intoxication: implications for emergency medicine

Digitalis intoxication is among the most common serious adverse drug reactions in clinical medicine. While the recent development of a radioimmunoassay to accurately measure serum concentrations of digoxin has been of assistance, digitalis intoxication remains a difficult diagnosis to make with certainty. The difficulty in diagnosing digitalis intoxication arises from the nonspecificity of its associated signs and symptoms. The most common symptoms include fatigue, weakness, nausea, and anorexia. These symptoms can occur with many illnesses other than digitalis intoxication. Similarly, the electrocardiographic disturbances caused by cardiac glycosides may be nondiagnostic. The arrhythmias commonly associated with digitalis toxicity are often nonspecific and can be a reflection of the patient's underlying heart disease. The measurement of serum digoxin levels is useful, but studies have demonstrated overlap of the levels between groups with and without toxicity. Due to the modulation of the cardiac effects of digitalis glycosides by such clinical variables as underlying myocardial or renal disease, electrolyte and acid-base imbalances, and other factors, the correlation of toxicity with particular serum digoxin concentrations may vary. Because of the inherent difficulties in confirming the diagnosis of digitalis intoxication in some cases, digoxin-specific Fab antibodies may play a role as a diagnostic tool. Certainly, digoxin-specific Fab antibodies play a significant part in the treatment of digitalis intoxication. Fab antibodies have been successfully used to reverse the effects of digoxin, digitoxin, and oleander poisoning. These antibodies are useful in the treatment of acute and chronic digitalis intoxication in all age groups, including geriatric and pediatric populations.(ABSTRACT TRUNCATED AT 250 WORDS)

Risk factors and manifestations of digoxin toxicity in the elderly

The incidence of digoxin toxicity increases with age, largely because the two most common conditions that benefit from use of digoxin, congestive heart failure and atrial fibrillation, are markedly more prevalent in old age. Whether the elderly are more sensitive to the effects of digoxin because of age per se is unclear. However, several other factors render the elderly more susceptible to digoxin toxicity. These include an age-related decline in renal function and a decrease in volume of digoxin distribution. There is also an increase in the number of comorbid conditions, including cardiovascular and chronic obstructive pulmonary disease, which heighten susceptibility to digoxin toxicity. Moreover, treatment of these diseases with such interactive medications as quinidine and calcium channel blockers may increase the serum level of digoxin. Similarly, such electrolyte imbalances as hypokalemia and hypomagnesemia occur more frequently in the elderly as a result of diuretic therapy. However, recent data suggest that manifestations of digoxin toxicity among younger and older patients do not differ. Similar incidences of cardiac toxicity, gastrointestinal toxicity, and altered mental status are found in both patient populations. Treatment of digitalis toxicity in the elderly is the same as for younger patients. Response rates to Digibind are not diminished in the elderly.

Association of perioperative myocardial ischemia with cardiac morbidity and mortality in men undergoing noncardiac surgery. The Study of Perioperative Ischemia Research Group

BACKGROUND

Adverse cardiac events are a major cause of morbidity and mortality after noncardiac surgery. It is necessary to determine the predictors of these outcomes in order to focus efforts on prevention and treatment. Patients undergoing noncardiac surgery sometimes have postoperative cardiac events. It would be helpful to know which patients are at highest risk.

METHODS

We prospectively studied 474 men with coronary artery disease (243) or at high risk for it (231) who were undergoing elective noncardiac surgery. We gathered historical, clinical, laboratory, and physiologic data during hospitalization and for 6 to 24 months after surgery. Myocardial ischemia was assessed by continuous electrocardiographic monitoring, beginning two days before surgery and continuing for two days after.

RESULTS

Eighty-three patients (18 percent) had postoperative cardiac events in the hospital that were classified as ischemic events (cardiac death, myocardial infarction, or unstable angina) (15 patients), congestive heart failure (30), or ventricular tachycardia (38). Postoperative myocardial ischemia occurred in 41 percent of the monitored patients and was associated with a 2.8-fold increase in the odds of all adverse cardiac outcomes (95 percent confidence interval, 1.6 to 4.9; P less than 0.0002) and a 9.2-fold increase in the odds of an ischemic event (95 percent confidence interval, 2.0 to 42.0; P less than 0.004). Multivariate analysis showed no other clinical, historical, or perioperative variable to be independently associated with ischemic events, including cardiac-risk index, a history of previous myocardial infarction or congestive heart failure, or the occurrence of ischemia before or during surgery.

CONCLUSIONS

In high-risk patients undergoing noncardiac surgery, early postoperative myocardial ischemia is an important correlate of adverse cardiac outcomes.

Treatment of digitalis intoxication with emphasis on the clinical use of digoxin immune Fab

Many studies and cases of digitalis intoxication have been reported since the time of William Withering's first publication in 1785. Recognition and management of digitalis toxicity is challenging. Before digoxin immune Fab was commercially available, treatment consisted of managing the signs and symptoms of toxicity until the digitalis was eliminated. Digoxin immune Fab offers a safe, effective, and specific method of quickly reversing digitalis toxicity. Factors that must be considered with the clinical use of this agent include the dosage calculation, administration technique, postdose monitoring, pharmacokinetics, mechanism of action, interference with commercially available digoxin assays, partial neutralizing dosing, rebound of free digoxin, and indications for use. For severe, life-threatening toxicity, digoxin immune Fab is the treatment of choice.

Treatment of 150 cases of life-threatening digitalis intoxication with digoxin-specific Fab antibody fragments. Final report of a multicenter study

One hundred fifty patients with potentially life-threatening digitalis toxicity were treated with digoxin-specific antibody fragments (Fab) purified from immunoglobulin G produced in sheep. The dose of Fab fragments was equal to the amount of digoxin or digitoxin in the patient's body as estimated from medical histories or determinations of serum digoxin or digitoxin concentrations. The youngest patient received Fab fragments within several hours of birth, and the oldest patient was 94 years old. Seventy-five patients (50%) were receiving long-term digitalis therapy, 15 (10%) had taken a large overdose of digitalis accidentally, and 59 (39%) had ingested an overdose of digitalis with suicidal intent. The clinical response to Fab was unspecified in two cases, leaving 148 patients who could be evaluated. One hundred nineteen patients (80%) had resolution of all signs and symptoms of digitalis toxicity, 14 (10%) improved, and 15 (10%) showed no response. After termination of the Fab infusion, the median time to initial response was 19 minutes, and 75% of the patients had some evidence of a response by 60 minutes. There were only 14 patients with adverse events considered to possibly or probably have been caused by Fab; the most common events were rapid development of hypokalemia and exacerbation of congestive heart failure. No allergic reactions were identified in response to Fab treatment. Of patients who experienced cardiac arrest as a manifestation of digitalis toxicity, 54% survived hospitalization.(ABSTRACT TRUNCATED AT 250 WORDS)

Diltiazem attenuates the inotropic and peripheral vascular effects of cardiac glycosides

The influence of diltiazem on the hemodynamic effects of ouabain in 10 preinstrumented awake dogs was studied. Mean aortic pressure increased from 102 to 119 mm Hg with ouabain (p less than 0.05), an effect that was attenuated by pretreatment with diltiazem. The increase in systemic vascular resistance of 30% with ouabain was ablated by prior diltiazem. Heart rate did not significantly change with ouabain or with diltiazem plus ouabain, but intravenous diltiazem alone produced a reflex increase in heart rate of 26%. Left ventricular (LV) end-diastolic dimension was significantly greater with ouabain alone, but not with ouabain after pretreatment with diltiazem. LV dP/dt max increased by 40% with ouabain alone, but by only 23% (p less than 0.001) after pretreatment with diltiazem plus ouabain. When observed at matched preload and heart rate, diltiazem markedly attenuates the positive inotropic and peripheral arterial constrictive effects of acute ouabain administration in the conscious animal with normal LV function.

Delayed elimination of digoxin antidotum determined by radioimmunoassay

An observation of a treatment with digitalis antibodies (Fab-fragments) in a young child is presented. The elimination of this antidotum proved to be much slower than normally expected. In the patient's history, the disappearance of the Fab-fragments out of the blood lasted 142 days with a half-life of 15.6 days, whereas an elimination with a T1/2 of 28 hours is accepted. Probably there has been intracellular penetration of the antibodies into the liver, caused by concomitant diseases (Hepatitis A and B infections). An "in vitro" experiment is reported. It demonstrates the equimolar binding of the Fab-fragments for digoxin and shows that the elimination of the Fab-fragments can be established by a routine radioimmunoassay of digoxin, in an indirect way.

Acute digoxin overdose: use of digoxin-specific antibody fragments

An acute ingestion of 6 to 7 mg digoxin as a suicidal gesture in a 76-year-old man with chronic heart disease is presented. The patient arrived in the emergency department approximately 5 hours after ingestion with a normal serum potassium and increasing numbers of multifocal premature ventricular contractions. Digoxin-specific antibody fragments were administered. The patient developed ventricular tachycardia and ventricular fibrillation and was eventually stabilized 35 minutes after the Fab fragments were infused. A review of the pharmacology and indications for use of digoxin-immune Fab fragments is also presented.

Calcium oscillations in digitalis-induced ventricular fibrillation: pathogenetic role and metabolic consequences in isolated ferret hearts

The pathophysiology of the ventricular fibrillation that complicates digitalis intoxication was investigated. In this and other calcium-overload states, oscillations of the intracellular free calcium concentration ([Ca2+]i) have been implicated as the cause of ventricular tachyarrhythmias. We addressed two questions: 1) Are [Ca2+]i oscillations obligatory in the pathogenesis of ventricular fibrillation during digitalis toxicity? 2) What are the metabolic consequences of [Ca2+]i oscillations? Ferret hearts (n = 20) were Langendorff-perfused at constant flow with oxygenated HEPES-buffered Tyrode's solution at 37 degrees C. Isovolumic left ventricular pressure was measured along with the extracellular electrogram or with simultaneous phosphorus nuclear magnetic resonance spectra. When strophanthidin (20 microM) was added during pacing at 3 Hz, the positive inotropic effect soon gave way to a decrease in developed force. The decrease in force was accompanied by an increase in inorganic phosphate concentration, a decrease in phosphocreatine concentration, and a slight acidosis. The rhythm changed to ventricular fibrillation after 12-25 minutes. This change was initially accompanied by further metabolic deterioration, but all metabolites reached steady state within 12-18 minutes of the onset of ventricular fibrillation. Fast Fourier transformation revealed the existence of periodic oscillations at 7-10 Hz in both the extracellular electrogram and the ventricular pressure during ventricular fibrillation. Ryanodine, an inhibitor of [Ca2+]i oscillations, abolished the pressure oscillations but not the voltage oscillations. Exposure to ryanodine significantly decreased the inorganic phosphate concentration and increased the phosphocreatine concentration (p less than 0.05) despite continuing exposure to strophanthidin. The results indicate that oscillations of [Ca2+]i are not required to sustain ventricular fibrillation, but when present, such oscillations contribute importantly to metabolic deterioration.

Treatment of adverse digitalis effects by hemoperfusion through columns with antidigoxin antibodies bound to agarose polyacrolein microsphere beads

Ten patients with an array of moderate to severe adverse effects resulting from digitalis were effectively treated by hemoperfusion through small columns which contained antidigoxin antibodies bound to polyacrolein microspheres in agarose macrospheres (APAMB). The procedure was well tolerated. There was no detectable damage to formed blood elements and no changes in electrolytes, liver enzymes, or other related biochemical parameters. Despite some theoretic considerations to the contrary, the removal of a relatively small load of digoxin resulted in amelioration of the clinical symptoms and ECG abnormalities associated with digitalis. No rebound phenomena of intoxication or posthemoperfusion increase in digoxin serum levels were noted over the subsequent 5 to 6 days. A further increase in the capacity of the columns may render this method a safe and convenient emergency procedure for patients with digitalis toxicity.

Physical assessment and differential diagnosis of the poisoned patient

The rapid diagnosis and immediate intervention required in patients with serious drug overdose or poisoning makes toxicological screening of limited value to the emergency department physician. Instead, a careful clinical evaluation using the history, physical examination, and the more readily available laboratory tests may allow a tentative diagnosis and the initiation of life-saving treatment. Laboratory tests should include serum osmolality, electrolytes, glucose, BUN and an estimation of the anion and osmolar gaps. The ECG can also provide useful information. Clinical findings of important include altered blood pressure, pulse, respiration and body temperature, the presence of coma, agitation, delirium or psychosis, and muscular weakness. An ophthalmological examination is also of importance in the acutely poisoned patient. Oral burns or dysphagia may occur following ingestion of any strongly reactive substance, but the absence of oral burns does not preclude the possibility of oesophageal or stomach injury. Odours and skin colour may also contribute to the diagnosis. Comprehensive toxicology screening may not be immediately available, or may be inaccurate, thus adding little to the information obtained during the initial evaluation of the poisoned patient.