Digitalis cardiotoxicity

Drug-induced AF: Arrhythmogenic Mechanisms and Management Strategies

AF is a prevalent condition that is associated with various modifiable and unmodifiable risk factors. Drug-induced AF, despite being commonly under-recognised, can be relatively easy to manage. Numerous cardiovascular and non-cardiovascular agents, including catecholaminergic agents, adenosine, anti-tumour agents and others, have been reported to induce AF. However, the mechanisms underlying drug-induced AF are diverse and not fully understood. The complexity of clinical scenarios and insufficient knowledge regarding drug-induced AF have rendered the management of this condition complicated, and current treatment guidelines follow those for other types of AF. Here, we present a review of the epidemiology of drug-induced AF and highlight a range of drugs that can induce or exacerbate AF, along with their molecular and electrophysiological mechanisms. Given the inadequate evidence and lack of attention, further research is crucial to underscore the clinical significance of drug-induced AF, clarify the underlying mechanisms and develop effective treatment strategies for the condition.

Drug Interactions Affecting Antiarrhythmic Drug Use

Antiarrhythmic drugs (AAD) play an important role in the management of arrhythmias. Drug interactions involving AAD are common in clinical practice. As AADs have a narrow therapeutic window, both pharmacokinetic as well as pharmacodynamic interactions involving AAD can result in serious adverse drug reactions ranging from arrhythmia recurrence, failure of device-based therapy, and heart failure, to death. Pharmacokinetic drug interactions frequently involve the inhibition of key metabolic pathways, resulting in accumulation of a substrate drug. Additionally, over the past 2 decades, the P-gp (permeability glycoprotein) has been increasingly cited as a significant source of drug interactions. Pharmacodynamic drug interactions involving AADs commonly involve additive QT prolongation. Amiodarone, quinidine, and dofetilide are AADs with numerous and clinically significant drug interactions. Recent studies have also demonstrated increased morbidity and mortality with the use of digoxin and other AAD which interact with P-gp. QT prolongation is an important pharmacodynamic interaction involving mainly Vaughan-Williams class III AAD as many commonly used drug classes, such as macrolide antibiotics, fluoroquinolone antibiotics, antipsychotics, and antiemetics prolong the QT interval. Whenever possible, serious drug-drug interactions involving AAD should be avoided. If unavoidable, patients will require closer monitoring and the concomitant use of interacting agents should be minimized. Increasing awareness of drug interactions among clinicians will significantly improve patient safety for patients with arrhythmias.

Freshly isolated primary human proximal tubule cells as an in vitro model for the detection of renal tubular toxicity

Drug induced kidney injury (DIKI) is a common reason for compound attrition in drug development pipelines with proximal tubule epithelial cells (PTECs) most commonly associated with DIKI. Here, we investigated freshly isolated human (hPTECs) as an in vitro model for assessing renal tubular toxicity. The freshly isolated hPTECs were first characterized to confirm gene expression of important renal transporters involved in drug handling which was further corroborated by confirming the functional activity of organic cation transporter 2 and organic anion transporter 1 by using transporter specific inhibitors. Additionally, functionality of megalin/cubilin endocytic receptors was also confirmed. A training set of 36 compounds was used to test the ability of the model to classify them using six different endpoints which included three biomarkers (Kidney Injury Molecule-1, Neutrophil gelatinase-associated lipocalin, and Clusterin) and three non-specific injury endpoints (ATP depletion, LDH leakage, and barrier permeability via transepithelial electrical resistance) in a dose-dependent manner across two independent kidney donors. In general, biomarkers showed higher predictivity than non-specific endpoints, with Clusterin showing the highest predictivity (Sensitivity/Specificity - 65.0/93.8 %). By using the thresholds generated from the training set, nine candidate internal Takeda compounds were screened where PTEC toxicity was identified as one of the findings in preclinical animal studies. The model correctly classified four of six true positives and two of three true negatives, showing validation of the in vitro model for detection of tubular toxicants. This work thus shows the potential application of freshly isolated primary hPTECs using translational biomarkers in assessment of tubular toxicity within the drug discovery pipeline.

Serum digoxin concentrations and clinical signs and symptoms of digoxin toxicity in the paediatric population

BACKGROUND

Serum digoxin levels have limited utility for determining digoxin toxicity in adults. Paediatric data assessing the utility of monitoring serum digoxin concentration are scarce. We sought to determine whether serum digoxin concentrations are associated with signs and symptoms of digoxin toxicity in children.

METHODS

We carried out a retrospective review of patients 2 ng/ml).

RESULTS

There were 87 patients who met study criteria (male 46%, mean age 8.4 years). CHD was present in 67.8% and electrocardiograms were performed in 72.4% of the patients. The most common indication for digoxin toxicity was heart failure symptoms (61.5%). Toxic serum digoxin concentrations were present in 6.9% of patients (mean 2.6 ng/ml). Symptoms associated with digoxin toxicity occurred in 48.4%, with nausea/vomiting as the most common symptom (36.4%), followed by tachycardia (29.5%). Compared with those without toxic serum digoxin concentrations, significantly more patients with toxic serum digoxin concentrations were female (p=0.02). The presence of electrocardiogram abnormalities and/or signs and symptoms of digoxin toxicity was not significantly different between patients with and without serum digoxin concentrations (p>0.05).

CONCLUSION

Serum digoxin concentrations in children are not strongly associated with signs and symptoms of digoxin toxicity.

Bidirectional ventricular tachycardia due to coronary allograft vasculopathy a unique presentation

Bidirectional ventricular tachycardia (BVT) is an uncommon type of polymorphic ventricular tachycardia (PVT) with alternating polarity of the QRS complex most commonly described digitalis toxicity. Recent data has demonstrated the possible molecular basis of this electrocardiographic phenomenon. To our knowledge this is the first reported case of BVT in a patient with orthotopic cardiac transplantation and coronary allograft vasculopathy.

Digitalis toxicity: a fading but crucial complication to recognize

Digoxin usage has decreased in the treatment of congestive heart failure and atrial fibrillation as a result of its inferiority to beta-adrenergic inhibitors and agents that interfere with the deleterious effects of the activated renin-angiotensin-aldosterone system. As a result of reduction of usage and dosage, glycoside toxicity has become an uncommon occurrence but may be overlooked when it does occur. Older age, female sex, low lean body mass, and renal insufficiency contribute to higher serum levels and enhanced risk for toxicity. Arrhythmias suggesting digoxin toxicity led to its recognition in the case presented here.

Toxicogenomic Analysis of Cardiotoxicity in Rats

Evidence of cardiotoxicity in the preclinical testing of drugs will often lead to compound attrition. The standard method for identifying cardiotoxic compounds involves histopathological analysis of tissue sections, a resource intensive process. In an effort to reduce attrition and capture safety endpoints early within the drug discovery paradigm, a more rapid assessment of target organ effects is desired. Here we describe the results of a preliminary study in which a group of common genes were affected by in vivo exposure to compounds known to cause dose-dependant cardiotoxicity. Adult male Sprague-Dawley rats were treated intraperitoneally with a single dose of digoxin (20 mg/kg), doxorubicin (30 mg/kg), isoproterenol (70 mg/kg), lipopolysaccharide (10 mg/kg) or carbon tetrachloride (800 mg/kg) and euthanized either 6 or 24 hours post-dose. Digoxin, doxorubicin, isoproterenol, and lipopolysaccharide were chosen for this study based on their diverse mechanisms of cardiotoxicity. Carbon tetrachloride, a known liver toxicant, was chosen as a non-cardiotoxic negative control. Genes commonly affected by all four cardiotoxic compounds were grouped together as a list of potential biomarkers. Gene expression changes were subsequently quantified using quantitative PCR. These genes were compared to those affected by novel experimental compounds previously shown to cause cardiotoxicity in rats. These compounds also affected over half of the genes on the biomarker list, whereas the non-cardiotoxic control compound did not affect any genes on the biomarkers list. These data indicate that measuring changes in gene expression could aid in the prioritization of compounds before they are tested in more resource intensive studies.

Digoxin therapy and the risk of primary cardiac arrest in patients with congestive heart failure: effect of mild-moderate renal impairment

BACKGROUND AND OBJECTIVE

The cardiac safety of digoxin therapy for congestive heart failure (CHF) is a source of concern, especially among those with renal impairment.

METHODS

Using a case-control design, we examined the risk of primary cardiac arrest (PCA) associated with digoxin therapy within three levels of renal function.

RESULTS

After adjustment for other clinical characteristics, digoxin therapy for CHF was not associated with an increased risk of PCA [odds ratio (OR)=0.97, 95% confidence interval (CI) 0.59-1.62] among patients with normal renal function (serum creatinine </=1.1 mg/dL). In contrast, digoxin therapy was associated with a modest increase in risk (OR=1.58, CI 0.89-2.80) among patients with mild renal impairment (serum creatinine=1.2-1.4 mg/dL); and a twofold increase in risk (OR=2.39, CI 1.37-4.18) among patients with moderate renal impairment (serum creatinine=1.5-3.5 mg/dL).

CONCLUSIONS

These findings suggest that the risks of digoxin may offset the benefits among patients with moderately impaired renal function, but not among patients with normal renal function.

Electrocardiographic manifestations: digitalis toxicity

Toxicity from the digitalis family of cardiac glycoside medications remains common. Successful treatment depends on early recognition; however, the diagnosis of potentially life-threatening toxicity remains difficult because the clinical presentation is often nonspecific and subtle. The hallmark of cardiac toxicity is increased automaticity coupled with concomitant conduction delay. Though no single dysrhythmia is always present, certain aberrations such as frequent premature ventricular beats, bradydysrhythmias, paroxysmal atrial tachycardia with block, junctional tachycardia, and bidirectional ventricular tachycardia are common. Treatment depends on the clinical condition rather than serum drug level. Management varies from temporary withdrawal of the medication to administration of digoxin-specific Fab fragments for life-threatening cardiovascular compromise.

Hemodynamic follow-up of cardiac allografts from poisoned donors

BACKGROUND

The current shortage of donor organs, combined with an increasing demand for cardiac allografts, means that extended donor criteria are becoming more and more accepted. The use of cardiac allografts for transplantation from donors after acute poisoning is still under discussion; few data are currently available in the medical literature. We describe our experience with 19 orthotopic heart transplant recipients of organs from donors after acute intoxication with different agents.

METHODS

Between March 1989 and December 1997, 883 orthotopic heart transplantations were performed at our transplant unit. Within this group, we accepted donor hearts after ethanol intoxication (n=1), benzodiazepine (n=1), alkylphosphate (E 605) in combination with beta-blocker intoxication (n=1), carbon monoxide poisoning (n=5), digitalis (n=1), digitalis/glibenclamide (n=1), chlormethiazole (n=1), propoxyphene (n=1), alkylphosphate (E 605) (n=1), insulin (n=2), neprobamate/ thiocyacide/flurazepam (n=1), paracetamol (n=1), carbamazepine (n=1), and cyanide (n=1) intoxication. At the time of organ explantation, hemodynamic data were available from all patients.

RESULTS

Early mortality in this group was 11%; cumulative survival after 5 years was 74%.

CONCLUSIONS

Based on our limited experience, cardiac allografts from donors exposed to different kinds of poisons can be transplanted in selected cases. If the donor organ is not hemodynamically compromised, showing regular filling pressures on low or mild inotropic support just before explantation, and if there are no electrocardiographic changes in combination with elevation of the transaminases, cardiac allograft transplantation seems to be a safe and life-saving procedure.

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.

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.

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.

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.

Which cardiac disturbances should be treated with digoxin immune Fab (ovine) antibody?

Digoxin excess can produce characteristic bradyarrhythmias, tachyarrhythmias, and hyperkalemia. The bradyarrhythmias, which consist of disturbances in conduction and block at the level of the atrioventricular and sinus nodes, are mediated by a direct and vagotonic effect. The vagotonic effect of excess digoxin may also result in a marked slowing of the sinus rate in the setting of severe toxicity. Digoxin increases automatic and triggered electrical activity in atrial muscle, His-Purkinje system, and ventricular muscle, which predisposes to tachycardias. Many of the tachyarrhythmias are relatively specific for the toxic effects of digoxin. Atrial tachycardias with variable atrioventricular block, accelerated junctional rhythms (especially in the setting of atrial fibrillation), and fascicular tachycardias are characteristic digoxin toxic rhythms. Digoxin-specific antibody fragments should be considered the treatment of choice for any digoxin toxic arrhythmia associated with hemodynamic compromise or the threat of hemodynamic compromise. Hyperkalemia, when due to acute severe digoxin toxicity, is also an appropriate indication for digoxin-specific Fab fragment therapy. When assessing the risk:benefit ratio for using digoxin-specific Fab fragment therapy, one needs to determine, in addition to the electrocardiographic manifestations and patient's hemodynamic status (1) the severity of toxicity, as indexed by the amount ingested and/or the serum digoxin concentration; (2) the expected time course for reversal of toxicity, which is usually determined by the status of renal function; (3) the need for digoxin to provide ventricular rate control or improved ventricular contractility and therapeutic alternatives to digoxin; (4) the presence of a strong allergy history; (5) the presence of such factors as increased age and severity of heart disease that may predispose to digoxin toxicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of calcium and the calcium channel in the initiation and maintenance of ventricular fibrillation

The cellular events during the initiation and maintenance of ventricular fibrillation (VF) are poorly understood. We developed a nonischemic, isolated, perfused rabbit Langendorff preparation in which sustained VF could be induced by alternating current (AC) and which allowed changes in perfusate composition. We also used Na(+)-K+ pump inhibition (10 microM ouabain or K(+)-free perfusate) to induce VF. AC stimulation or Na(+)-K+ pump inhibition always initiated VF. Calcium channel blockade by verapamil or nitrendipine uniformly inhibited the initiation of VF in both models. During Na(+)-K+ pump inhibition, 1) VF was prevented by calcium channel blockade, despite evidence of Ca2+ overload, and 2) abolition of spontaneous sarcoplasmic reticulum-generated cytosolic Ca2+ oscillations by ryanodine or Na+ channel blockade with tetrodotoxin did not prevent VF initiation. Lowering extracellular [Ca2+] to 80 microM uniformly prevented the initiation of VF due to Na(+)-K+ pump inhibition but not that due to AC stimulation. VF maintenance also was studied using 1) reduction in perfusate [Ca2+], 2) blockade of Ca2+ channels, or 3) electrical defibrillation. Decreasing the perfusate [Ca2+] to 80 microM resulted in defibrillation during VF whether induced by AC or Na(+)-K+ pump inhibition. Verapamil or nitrendipine also resulted in defibrillation regardless of the initiation method. Electrical defibrillation was successful only in AC-induced VF. The results demonstrate that VF can be initiated and maintained in a nonischemic rabbit Langendorff preparation. The data suggest that increases in slow channel Ca2+ flux, as opposed to increases in cytosolic Ca2+ per se, were necessary for the initiation and maintenance of VF. The data, however, do not exclude an important role for cytosolic Ca2+ in the modulation of VF.

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.

How effective is digitalis in the treatment of congestive heart failure?

The evidence suggests that digitalis glycosides do indeed improve ventricular performance through a sustained but moderate positive inotropic effect. This effect is more marked in failing than in nonfailing myocardium. The clinical studies suggest a moderate salutary effect in patients with chronic CHF who are in sinus rhythm. The drug can be given safely to patients with CAD and in combination with other medications when the physician is aware of those factors leading to increased sensitivity to digitalis.

Role of prostaglandins in the arrhythmogenic effects of ouabain on isolated guinea pig hearts

We examined the hypothesis that endogenous prostaglandins participate in the arrhythmogenic influence of ouabain in guinea pig hearts. Addition of ouabain (10 ng/ml) resulted in a 5-fold increase in the release of 6-keto-prostaglandin F1 alpha in the coronary effluent. Ten of 13 hearts studied (77%) demonstrated arrhythmic activity with a mean time to the onset of arrhythmias of approximately 35 min. The nonsteroidal antiinflammatory drugs indomethacin and acetylsalicylic acid which significantly inhibited the efflux of 6-keto-prostaglandin F1 alpha also reduced the incidence of arrhythmias to 10 of 30 hearts studied. In those hearts in which arrhythmias occurred, the time to onset was significantly increased to approximately 50 and 55 min for acetylsalicylic acid and indomethacin, respectively. In contrast, exogenous prostaglandin F2 alpha (0.1 and 1 ng/ml) and prostacyclin (0.1 and 10 ng/ml) increased the incidence of arrhythmias to 100% (10 of 10 hearts studied) and decreased the time to onset to approximately 10 min. These prostaglandin pretreatments were also able to reverse the protective actions of both acetylsalicylic acid and indomethacin. Other concentrations (10 ng/ml prostaglandin F2 alpha and 1 ng/ml prostacyclin) had no influence either on the incidence of arrhythmias or their time to onset. Prostaglandin E2 (0.1 ng/ml) produced a modest but not significant decrease in the time to onset of arrhythmias although this concentration was significantly effective in reversing the nonsteroidal antiinflammatory drug effects. The inotropic, chronotropic and coronary constricting actions of ouabain were unaffected either by nonsteroidal antiinflammatory drug or prostaglandin pretreatment. These studies suggest that prostaglandins are involved, at least in part, in the arrhythmogenic actions of ouabain in the isolated guinea pig heart.

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.