Current concepts and treatment of digitalis toxicity

Extreme digitalis intoxication

A case of massive digoxin intoxication is described. The concentration of digoxin in plasma, 15.5 ng/ml, is one of the highest observed in an individual not having heart diease who survived the intoxication. During the first two days there was complete heart block but only moderate hyperkalaemia. The advantage of temporary pacemaker treatment under these conditions is emphasized.

Difficulties in maintaining potassium homeostasis in patients with heart failure

Potassium (K) concentration plays a significant role in cell metabolism and membrane excitability. The imbalance of serum potassium is important because it can lead to life-threatening events. Potassium balance may be lost both through the neurohormonal mechanisms involved in cardiovascular diseases and through the drugs used in the treatment of this illness. Avoiding both hypo- and hyperkalemia is beneficial in several cardiovascular diseases, especially heart failure. Electrolyte abnormalities are frequently seen complications in subjects with heart failure. Malignant ventricular arrhythmias and sudden cardiac death are particularly feared complications in K+ instability.

Potential Roles of Electrogenic Ion Transport and Plasma Membrane Depolarization in Apoptosis

Apoptosis is characterized by the programmed activation of specific biochemical pathways leading to the organized demise of cells. To date, aspects of the intracellular signaling machinery involved in this phenomenon have been extensively dissected and characterized. However, recent studies have elucidated a novel role for changes in the intracellular milieu of the cells as important modulators of the cell death program. Specially, intracellular ionic homeostasis has been reported to be a determinant in both the activation and progression of the apoptotic cascade. Several apoptotic insults trigger specific changes in ionic gradients across the plasma membrane leading to depolarization of the plasma membrane potential (PMP). These changes lead to ionic imbalance early during apoptosis. Several studies have also suggested the activation and/or modulation of specific ionic transport mechanisms including ion channels, transporters and ATPases, as mediators of altered intracellular ionic homeostasis leading to PMP depolarization during apoptosis. However, the role of PMP depolarization and of the changes in ionic homeostasis during the progression of apoptosis are still unclear. This review summarizes the current knowledge regarding the causes and consequences of PMP depolarization during apoptosis. We also review the potential electrogenic ion transport mechanisms associated with this event, including the net influx/efflux of cations and anions. An understanding of these mechamisms could lead to the generation of new therapeutic approaches for a variety of diseases involving apoptosis.

Na+, K+-ATPase: the new face of an old player in pathogenesis and apoptotic/hybrid cell death

The Na(+), K(+)-ATPase is a ubiquitous membrane transport protein in mammalian cells, responsible for establishing and maintaining high K(+) and low Na(+) in the cytoplasm required for normal resting membrane potentials and various cellular activities. The ionic homeostasis maintained by the Na(+), K(+)-ATPase is also critical for cell growth, differentiation, and cell survival. Although the toxic effects of blocking the Na(+), K(+)-ATPase by ouabain and other selective inhibitors have been known for years, the mechanism of action remained unclear. Recent progress in two areas has significantly advanced our understanding of the role and mechanism of Na(+), K(+)-ATPase in cell death. Along with increased recognition of apoptosis in a wide range of disease states, Na(+), K(+)-ATPase deficiency has been identified as a contributor to apoptosis and pathogenesis. More importantly, accumulating evidence now endorses a close relationship between ionic homeostasis and apoptosis, namely the regulation of apoptosis by K(+) homeostasis. Since Na(+), K(+)-ATPase is the primary system for K(+) uptake, dysfunction of the transport enzyme and resultant disruption of ionic homeostasis have been re-evaluated for their critical roles in apoptosis and apoptosis-related diseases. In this review, instead of giving a detailed description of the structure and regulation of Na(+), K(+)-ATPase, the author will focus on the most recent evidence indicating the unique role of Na(+), K(+)-ATPase in cell death, including apoptosis and the newly recognized "hybrid death" of concurrent apoptosis and necrosis in the same cells. It is also hoped that discussion of some seemingly conflicting reports will inspire further debate and benefit future investigation in this important research field.

New milrinone analogues: in vitro study of structure-activity relationships for positive inotropic effect, antagonism towards endogenous adenosine, and inhibition of cardiac type III phosphodiesterase

Two mechanisms are responsible for the positive inotropic effect of the cardiotonic drug milrinone, i.e., inhibition of type III cAMP phosphodiesterase (PDE III), and displacement of endogenous adenosine from A(1) inhibitory receptor. Since PDE III inhibition may increase the likelihood of cardiac arrhythmias by increasing cAMP content, our attention focused on the synthesis of new compounds with more pronounced characteristics as adenosine antagonists. In this work, four new milrinone analogues were studied, in comparison with the parent drug, for their effects on the contractility of guinea pig isolated atrial preparations, their ability to antagonize endogenous adenosine at the level of A(1) receptor, and to inhibit the activity of PDE III partially purified from guinea pig heart. The new compounds present various chemical substitutions with respect to the parent drug: in compounds SF397 (methyl 5-cyano-2-methyl-6-oxo-1,6-dihydropyridine-3-carboxylate) and SF399 (benzyl 5-cyano-2-methyl-6-oxo-1,6-dihydropyridine-3-carboxylate), the 4-pyridil moiety of milrinone was replaced with a methoxycarbonyl and a benzyloxycarbonyl group, respectively; the same structural modifications were also associated with the replacement of the cyano-group in 5-position with an acetyl group in compounds SF416 (methyl 5-acetyl-2-methyl-6-oxo-1,6-dihydropyridine-3-carboxylate) and SF419 (benzyl 5-acetyl-2-methyl-6-oxo-1,6-dihydropyridine-3-carboxylate). All the new compounds had a marked positive inotropic effect, most of them also being more active and more potent than milrinone. When their affinity for A(1) receptor was assessed as the displacement of [(3)H] 8-cyclopentyl-1,3-dipropylxanthine ([(3)H]DPCPX) from cardiac membranes, SF397 and SF399 showed affinity (K(i) of about 600 nM) similar to that of milrinone (K(i) 550 nM). By contrast, SF416 and SF419 had very low (K(i) of about 10000 nM) or scarce (K(i) of about 2000 nM) anti-adenosine component, respectively. All the new compounds inhibited PDE III activity, their K(i) values proceeding in the following order: milrinone (3.80 microM) <SF397 (7.00 microM) <SF399 (8.80 microM) <SF416 (35.00 microM) SF419< (155.00 microM). To better characterize the mechanisms responsible for the positive inotropic response of the new compounds, we also investigated the effects of new analogues on some systems (ATP-dependent Ca(2+) uptake, Ca(2+)ATPase, Na(+)/K(+)ATPase, Na(+)/Ca(2+) exchange carrier) or a receptor (beta-adrenoceptor) mainly involved in the control of cardiac contractility. None of the tested compounds inhibited enzyme or transport systems; however, SF397, SF399 and SF416, although to different extents, had a direct beta-adrenergic action. Indications about structure-activity relationships are tentatively discussed, in order to obtain useful information for the design of new analogues with better pharmacological profiles.

Subcellular mechanism of the positive inotropic effect of a new quinolinone derivative OPC-8490 on the dog ventricular myocardium

OPC-8490 [3,4-dihydro-6-[4-(4-oxo-4-phenylbutyl)-1- piperazinylcarbonyl]-2(1H)-quinolinone citrate] elicited a positive inotropic effect in a concentration-dependent manner on the isolated dog ventricular trabeculae electrically driven at 0.5 Hz in Krebs-Henseleit solution bubbled with 95% O2-5% CO2 at 37 degrees C. The beta-adrenoceptor antagonist, bupranolol (3 x 10(-7) mol/l), did not influence the effect of OPC-8490. The maximal effect of OPC-8490 was 0.19 compared with isoproterenol (1.0). The time course of the increase in contractile force coincided with that of the concomitant cyclic AMP accumulation induced by OPC-8490. The concentration-response curve for the OPC-8490-induced increase in contractile force was superimposable on that of the elevation of cyclic AMP levels. OPC-8490 (10(-5) mol/l) shifted the concentration-response curve for isoproterenol to the left and upward. These results imply that the accumulation of cyclic AMP induced by OPC-8490 through an inhibition of peak III PDE may be responsible for its positive inotropic effect. However, the OPC-8490-induced increase in the contractile force was not abolished by carbachol (3 x 10(-6) mol/l) when the cyclic AMP accumulation caused by the compound was completely inhibited by carbachol. In addition, OPC-8490 did cause a change in the time course of isometric contractions characteristic of cyclic AMP accumulation. These findings indicate that both the cyclic AMP-dependent (peak III PDE inhibition) and the cyclic AMP-independent mechanisms (prolongation of action potential duration by inhibition of K+ conductance) may be involved in the positive inotropic effect of OPC-8490 on the dog ventricular muscle.

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)

The cardiovascular pharmacology of ICI 170777 ((6RS)-6-methyl-5-(pyrid-4-yl)-3H,6H-1,3,4- thiadiazin-2-one) a novel compound with positive inotropic and vasodilator effects

1. This paper describes the cardiovascular effects of ICI 170777, a novel compound which enhances cardiac contractility and causes arterial and venous dilatation. 2. The positive inotropic effects of ICI 170777 on the heart were demonstrated by an increase in left ventricular dP/dtmax in the anaesthetized and conscious dog, and by an increase in tension development in isolated papillary muscles from the cat. 3. In the anaesthetized dog, the positive inotropic effects of ICI 170777 and of isoprenaline were attenuated by atenolol (5 mg kg-1, i.v.). Atenolol displaced the dose-response curve to ICI 170777 to the right by 4 fold but displaced the isoprenaline dose-response curve to the right by 247 fold. In vitro, however, atenolol (10 microM) had no significant effect on the positive inotropic response to ICI 170777. In the ganglion-blocked anaesthetized dog, infusion of a low dose of ICI 170777 which had no effect on the basal left ventricular dP/dtmax, selectively potentiated the positive inotropic effects of isoprenaline. These results indicate that ICI 170777 has both a non-adrenoceptor-mediated positive inotropic effect on the heart and also facilitates the beta-adrenoceptor-mediated control of contractility. 4. In the denervated and perfused hind-limb of the dog, ICI 170777 reduced arterial perfusion pressure and increased limb circumference at a constant arterial flow and venous pressure. This indicates that ICI 170777 has direct dilator actions on both arterial and venous vessels. In this preparation, diazoxide exerted an arterial selective vasodilator effect and sodium nitroprusside was a relatively selective venous dilator. ICI 170777 exhibited a balanced arterial and venous dilator effect which was intermediate in profile between that of diazoxide and that of sodium nitroprusside. 5. In the conscious dog, low doses (2-5 mgkg -, orally) of ICI 170777 evoked an increase in left ventricular dP/dt,,, with no significant effect on heart rate or blood pressure. At a higher dose (10mg kg 1, orally) it also reduced blood pressure and caused a significant increase in heart rate. The duration of the positive inotropic effect of 5mg kg- (orally) of ICI 170777 was 10-12 hours. This response did not diminish following repeated administration of the compound. 6. The positive inotropic action and balanced arterial and venous dilator effect of ICI 170777 indicate that the compound may be useful in the treatment of congestive heart failure, a disorder that is characterized by decreased cardiac contractility and enhanced arterial and venous constrictor tone.

Pharmacokinetic profile of OPC-8212 in humans: a new, nonglycosidic, inotropic agent

OPC-8212, a new inotropic agent, was administered orally as a single 7.5-, 15-, 30-, 60-, 120-, or 240-mg dose in a sequentially ascending order to 21 male healthy volunteers to determine the pharmacokinetic profile. Each volunteer received one of the six doses after an overnight fast. After the single-dose study was completed and the safety and tolerability were ascertained, 3 of the 21 volunteers participated in a 15-day repeated-dose (30 mg once daily) study to determine the steady-state kinetic profile. The AUC0-infinity and Cmax values were proportional to doses (mg or mg/kg, P less than .001). The mean elimination t1/2, apparent oral clearance (CL/F) and percentage fraction of dose excreted unchanged in urine up to 336 hours postdose (fe0-336) appeared to be comparable among the six single doses examined. The overall mean (+/- SEM) kinetic parameters obtained from the 21 subjects were: 44.7 +/- 1.2 hours for t1/2, 0.284 +/- 0.018 L/hr or 4.49 +/- 0.28 mL/hr/kg for CL/F, and 17.7 +/- 0.9% for fe0-336. A steady state of the drug appeared to be attained by about day 9 after the initiation of the repeated dosing: the mean postdose 2- and 24-hour plasma drug concentrations observed during days 9 to 15 ranged from 6.3 +/- 0.5 micrograms/mL to 6.9 +/- 0.6 micrograms/mL and from 3.6 +/- 0.7 micrograms/mL to 4.0 +/- 0.6 micrograms/mL, respectively. The mean fraction of the daily dose excreted unchanged in urine over the dosing interval (fe0-r) during days 9 to 15 ranged from 19.2 +/- 1.4% to 25.6 +/- 0.6%.(ABSTRACT TRUNCATED AT 250 WORDS)

Curing experimental Bryophyllum tubiflorum poisoning of cattle with activated carbon, electrolyte replacement solution and antiarrhythmic drugs

A slurry of activated carbon (activated charcoal) in electrolyte replacement solution given by stomach tube and antiarrhythmic drugs given parenterally cured 9 of 11 calves dosed 7 to 24 h previously with a lethal amount (20g/kg) of Bryophyllum tubiflorum flower heads. Two of another 4 calves treated 26 to 36 h after dosing with flowers survived. B. tubiflorum toxins are bufadienolides (cardiac glycosides). Activated carbon was effective at a single dose of 5 g/kg. Calves were rehydrated with oral electrolyte replacement solution at 150 ml/kg in divided doses over 24 h. Tachycardia was treated with intravenous lignocaine (200 mg doses) or propranolol (5 mg doses) and atrioventricular block with atropine (0.5 mg/kg).

Acute hemodynamic effects of a new inotropic agent (OPC-8212) in patients with congestive heart failure

The acute effects of OPC-8212, a newly synthesized orally effective inotropic agent, were assessed clinically. Eleven patients with moderate congestive heart failure received a single mean dose of 6.5 mg/kg body weight of the drug. Eight hours after administration, the cardiac and stroke work indexes increased by 11% (p less than 0.01) and 20% (p less than 0.005), respectively, with concomitant decreases in the diastolic pulmonary artery (25%, p less than 0.005) and right atrial pressures (33%, p less than 0.01). There were no significant changes in blood pressure or heart rate. The contractile state of the left ventricle was also assessed by the shift of the Starling curve. To construct the function curve, lower body negative pressure was used to regulate the venous return to the heart. An inotropic effect of the agent was confirmed by the shift of this function curve upward and to the left, even when an augmentation of the cardiac output was masked by the marked reduction in preload. The hemodynamic and clinical effects of OPC-8212 were encouraging and the drug appears to be promising for the treatment of congestive heart failure.

Magnesium deficiency: pathogenesis, prevalence, and clinical implications

Hypomagnesemia is probably the most underdiagnosed electrolyte deficiency in current medical practice. Patients with cardiovascular disease who are at greatest risk for the development of magnesium deficiency are those treated with diuretics or digitalis. Both potassium and magnesium deficiencies are associated with increased ventricular ectopy and may increase the risk of sudden unexpected death. Refractory potassium repletion can be caused by concomitant magnesium depletion, and can be corrected with magnesium supplementation. Routine serum magnesium determination is recommended whenever the testing of electrolyte levels is required, especially in patients taking diuretic drugs or digitalis. Because hypomagnesemia is not necessarily present in a magnesium-deficient state, it is recommended that both potassium and magnesium be repleted in patients with hypokalemia. Potassium-/magnesium-sparing diuretics may be helpful in the prevention of these electrolyte deficiencies.

Magnesium and cardiac arrhythmias: nutrient or drug?

The antiarrhythmic potency of Mg has been described repeatedly since 1935, both as a factor in human disease and in animal experiments. Nevertheless, this therapeutic efficacy is rarely mentioned in textbooks. Both the pharmacological effect of Mg and the correction of Mg deficiency have been used in treatment of digitalis toxicity, variant angina, Torsades de Pointes, as well as in arrhythmia of unknown origin. Mg-deficiency can be caused by malabsorption or by excessive urinary loss. Both situations can occur on a congenital basis. The most frequent cause is probably alcoholism. Iatrogenic factors include digitalis, diuretics, gentamicin, as well as cisplatinum, which appreciably enhance urinary Mg loss. Correction of Mg-deficiency by parental and/or oral administration should lead to recovery. If the cause of the deficiency can be eliminated, once the deficit is repaired it may be acceptable to discontinue the supplement. However, the cause is often multifactorial, requiring further evaluation and treatment.

Therapeutic and toxic effects of digitalis: William Withering, 1785

William Withering's classic description of the effects of digitalis was published in 1785. Although he was largely unaware of the drug's cardiac effects, he successfully treated many patients with congestive heart failure. He also recorded many striking examples of digitalis toxicity. This review highlights Withering's experience with "the foxglove," and summarizes modern concepts of digitalis efficacy and toxicity.

Acute digitalis poisoning: the role of intravenous magnesium sulfate

Acute digitalis poisoning is a complex emergency with a reported mortality rate of 3% to 25%. In severe overdose, the sodium, potassium-adenosine triphosphatase system is severely inhibited, leading to cardiac dysrhythmias and an elevation of the serum potassium. Magnesium, a cofactor regulating this ion transport system, can successfully treat acute digitalis-induced rhythm disturbances and restore the transmembrane potassium gradient. This paper discusses the cellular mechanism involved in digitalis toxicity and reviews the literature concerning the use of magnesium in acute cardiac glycoside poisoning.

Pacemaker therapy

This article reviews the indications for pacemaker implantation and the techniques and devices currently in use. The management of patients who require permanent pacemakers and the potential complications involved are discussed. The article concludes with a brief synopsis of temporary pacing.

Reduced tolerance to digitalis-induced arrhythmias caused by coronary-flow alterations in isolated perfused heart of guinea pigs

The ligation of a main branch of coronary vein elevates the sensitivity of isolated, perfused (Langendorff) preparations of guinea-pig heart to arrhythmogenic actions of digoxin. Retrograde perfusion studies indicate that the presence of an area with a high extracellular K+ concentration, adjacent to an area with normal K+ concentration and exposed to the glycoside, predisposes the heart to digitalis-induced toxicity. This model may be useful in studying the mechanism by which acute myocardial infarction decreases the therapeutic index of cardiac glycosides.

Pharmacologic basis for developing rational drug regimens for elderly patients

Changes in responsiveness with age have been observed for autonomic drugs (agonists as well as antagonists, analgesics, anticonvulsants, bronchodilators, hypoglycemics, corticosteroids, and virtually every other group of drugs). As indicated earlier, however, this review is not meant to present an exhaustive treatment of the area, but rather to focus attention on the factors that contribute to alterations in sensitivity. As a secondary aim, the review serves to focus attention on the problem of adverse drug reactions, particularly those related to the practice of polypharmacy, which compounds the problem through drug interactions. As indicated in the introduction, adverse drug reactions (undesired or unwanted effects of drugs) occur more frequently in the older patient than in the young one. In the elderly, this relates to increased use of drugs, polypharmacy, diminution in the function of organs which play a role in drug distribution and elimination, and poor patient compliance. Drugs which most often result in adverse reactions in the elderly have been listed by Lamy (Table 1). It is of significance that this list includes many drugs that are obtainable over the counter without prescription, such as aspirin and antacids. Because of the widespread practice of polypharmacy in the elderly, there is an increased potential for drug interactions. Examples of drugs and the mechanisms whereby interactions occur, which are of particular significance in geriatric therapeutics, are provided in Table 3. Since monographs summarizing drug interactions have been available for a number of years, it is somewhat surprising that the magnitude of the problem is still so great. It appears clear that the more we understand about the basic changes that occur in the physiology, biochemistry, and structure of an organism as it ages, and the more we learn about basic pharmacologic principles, the better we can combine the knowledge toward the development of rational therapeutic drug regimens for the geriatric patient. For more detailed discussion, the reader is referred to Caird et al., Kayne, Vestal, Lamy, and Poe and Holloway. A summary of the major principles in prescribing drugs for the elderly, quoted from Riley, is provided in Table 2.

Efficacy of low-dose propranolol in preventing postoperative supraventricular tachyarrhythmias: a prospective, randomized study

A prospective, randomized study was performed in 100 consecutive patients undergoing coronary artery bypass surgery to assess the efficacy of the early reinstitution of propranolol in reducing the incidence of postoperative supraventricular tachyarrhythmias (SVT). Patients were randomized to receive propranolol 10 mg every 6 hours enterally starting the morning after surgery (Group I, 50 patients) or to serve as controls (Group II, 50 patients). No patient was excluded because of poor ventricular function, need for urgent revascularization, or transient necessity for ionotropic support. Both groups had a comparable incidence of risk factors, previous infarction, unstable angina, and abnormal ventricular function. The extent of coronary disease, preoperative propranolol dose, and number of grafts performed were also similar. SVT occurred in 3/50 (6%) patients in Group I compared with 14/50 (28%) in Group II (p less than 0.01). There were no preoperative or intraoperative discriminators to predict the occurrence of SVT. In addition, perioperative infarction and the need for mechanical or pharmacologic circulatory support did not predispose to SVT. The data indicate that early administration of propranolol should be given to all patients after myocardial revascularization to decrease the incidence of these postoperative rhythm disturbances.

Acute and chronic digitalis toxicity: presentation and treatment

Although digitalis toxicity is commonly encountered, it can easily be mistaken because of its many manifestations. Recognition of toxicity depends on an awareness of the difference between an acute digitalis overdose and chronic digitalis toxicity. The gastrointestinal, central nervous, and cardiac conduction systems are most commonly involved. Ventricular ectopy and arrhythmias are common with chronic toxicity, while disturbances of sinus impulse formation, A-V blocks, and nodal arrhythmias are seen with both acute and chronic digitalis toxicity. Treatment is mainly supportive, except in acute poisoning, in which case attempts must be made to clear as much drug as possible from the gastrointestinal tract.

Acute, massive poisoning with digitoxin: report of seven cases and discussion of treatment

Severe digitoxin poisoning in seven patients is reported. Doses taken varied from 2 to 20 mg, and maximal plasma concentrations of digitoxin from 50 to 237 nmol/L. One patient died from ventricular fibrillation, and the course in another was considerably protracted due to severe complications. The course in all patients was more dependent on underlying heart disease than on the plasma digitoxin concentration. Based on our own experiences and survey of the literature the following treatment is proposed: Gastric aspiration and lavage followed by instillation of activated charcoal should even be performed many hours after drug intake. In order to interrupt the enterohepatic circulation of digitoxin, repeated doses of charcoal should be given. Charcoal is preferable to cholestyramine because of its better tolerability. Ventricular arrhythmias should not be treated unless they are serious, because most antiarrhythmic drugs may further impede the AV-conduction. Phenytoin is the drug of choice, because the AV-conduction is less affected or even improved, and because the metabolism of digitoxin is accelerated. Conduction disturbances with bradycardia are frequently seen and may occur suddenly. Prophylactic introduction of a transvenous pacing catheter is therefore recommended as a routine procedure.

The role of Holter monitoring in detecting digitalis-provoked arrhythmias

Certain arrhythmias detected on the electrocardiogram are considered to be reliable indicators of digitalis intoxication. We have evaluated the incidence of these arrhythmias on 24-hour electrocardiographic monitoring (Holter monitoring) in 69 consecutive patients who had serum levels of digoxin determined within 24 hours of the onset of continuous electrocardiographic monitoring. According to teh serum level of digoxin, the patients were divided into the following three groups: (1) group 1 had 0 to 1.0 ng/ml (31 patients); (2) group 2 had 1.1 to 2.0 ng/ml (27 patients); and group 3 had greater than or equal to 2.1 ng/ml (11 patients). The following arrhythmias were considered to reflect digitalis-provoked arrhythmias: (1) persistent sinus bradycardia or sinus pauses (or both); (2) atrioventricular block; (3) paroxysmal atrial tachycardia with block; (4) accelerated junction rhythm; (5) complex ventricular arrhythmias (multifocal ventricular premature beats, bigeminy and trigeminy, and pairs); and (6) ventricular tachycardia. There was no significant difference in the incidence of these six categories of arrhythmias among the three groups. In addition, there was no significant difference in the mean serum level of digoxin for patients with and without the arrhythmias within each category. Ten of the 69 patients had combinations of three of the so-called digitalis-provoked arrhythmias, with incidences among the three groups showing no significant differences. In conclusion, rhythms considered to be potentially due to digitalis intoxication are frequently observed in hospitalized patients undergoing 24-hour electrocardiographic monitoring, are frequently unrelated to the serum level of digoxin, and appear unlikely to reflect true digitalis intoxication in many of these patients.

Treatment of a case of lanatoside C intoxication with digoxin-specific F(ab')2 antibody fragments

In animal experiments arrhythmias induced by cardiac glycosides which prove fatal if untreated can be terminated by administration of glycoside-specific antibodies. Immunotherapy with digoxin-specific antibody fragments had hitherto only been employed on one occasion, namely in a person who had taken a massive overdose of digoxin with suicidal intent and who had failed to respond to symptomatic treatment. The present paper describes the use of F(ab')2 fragments of digoxin-specific antibodies in a female patient with lanatoside C intoxication to treat the associated life-threatening cardiac arrhythmia. The arrhythmia was rapidly terminated and normal sinus rhythm was restored. Treatment with the heterologous antibodies did not cause any side-effects.

Cardiotonic activity of amrinone--Win 40680 [5-amino-3,4'-bipyridine-6(1H)-one]

The cardiotonic activity of a new, noncatechol, nonglycoside agent, amrinone, was investigated in vitro and in anesthestized and unanesthetized dogs. Amrinone (3-100 microgram/ml) caused a dose-dependent increase in papillary muscle developed tension and df/dt without significant changes in duration of the contractile cycle or time-to-peak tension. Amrinone induced slight increases in right atrial rate with no changes in electrophysiological properties of the cat papillary muscle or dog Purkinje fibers. In anesthetized dogs, intravenous bolus injections of amrinone at doses ranging from 1 to 10 mg/kg caused increases in cardiac contractile force and left ventricular dp/dt max with relatively small changes in heart rate and blood pressure. No significant changes in lead II ECG were observed. In unanesthetized dogs, intravenous infusion of amrinone (10-100 microgram/kg per min) caused increases in left ventricular dp/dt max and only small changes in heart rate and blood pressure. Amrinone, tested orally in this model at doses of 2-10 mg/kg, produced a positive inotropic effect with a rapid onset and long duration of action. The inotropic response to amrinone was not blocked by propranolol, dibenzyline, chlorisondamine, atropine, metiamide, or reserpine. Amrinone's inotropic response was not associated with significant alterations in cardiac norepinephrine, phosphodiesterase, cyclic AMP, or Na+, K+-activated ATPase.

[Plasma concentrations of digoxin in patients under intensive care conditions and in patients undergoing anesthesia and operation (author' transl)]

Pharmacokinetic behavior of digoxin or beta-acetyldigoxin was examined in 66 patients (27 patiets under intensive care conditions, partially with controlled breathing, 22 patients undergoing extirpation of the uterus and 17 patients treated with radium or chemotherapeutics; 19 males and 47 females) by determining plasma concentrations of digoxin (PDC). After intravenous and oral application with a maintenance dose of 0.20--0.50 mg/day blood was taken daily during a 2 to 3 week period, resulting in 510 determinations. 24 hours after the first application of 0.50 mg digoxin i.v. the mean values of PDC amounted to 0.62 +/- 0.08 ng/ml. After 0.40 or 0.25 mg digoxin per day i.v. therapeutical concentrations could be observed at the third vs fifth day. An equilibrium of PDC was reached on the 6th day after starting digitalization using maintenance doses. Intravenous application of 0.25, 0.40 or 0.50 mg digoxin per day resulted in a mean steady state of 0.68 +/- 0.37, 0.86 +/- 0.33 or 1.27 +/- 0.49 ng/ml PDC, respectively. The results were significantly different (p less than 0.01--0.001). Serial measurements indicated a great variation of PDC. In patients without renal failure the intraindividual variation of the plasma concentrations was maximal 37.4% referring to the mean steady state, interindividual 37.1% and the evaluation of the inter- and intraindividual differences amounted to 54.1%. After oral administration of digoxin (maintenance dose: 0.50 mg/day) or beta-acetyldigoxin (maintenance doses: 0.20--0.40 mg/day) differences in PDC of 38.3% and 29.7% were obtained. Body weight, age and serum creatinine concentration were partly responsible for the variance of PDC. Multiple linear regression between stead state PDC and dose, age, body weight and serum creatinine concentration revealed 62.1% of the variance of the PDC after intravenous administration of digoxin. After oral administration of beta-acetyldigoxin 39.9% were obtained. Thus, 40% of the variance were caused by differences in distribution and elimination of digoxin after i.v. application. After oral application additional 20% of the variance could be attributed to resorption and possible disturbances.

Massive digoxin ingestion. Report of a case and review of currently available therapies

Recent reports of treatment of massive digoxin overdosage have emphasized the success of medical therapy. This report describes a fatal outcome to this problem despite aggressive medical management, including pervenous cardiac pacing and draws attention to deficiencies in current treatment of a serious problem.

The relationship between Na+, K+-ATPase inhibition and cardiac glycoside-induced arrhythmia in dogs

In order to determine if there is a relationship between Na+, K+-ATPase inhibition and cardiac glycoside-induced arrhythmia, the time course of the onset and offset of the arrhythmia induced by the semi-synthetic glycoside, actodigin, and the enzyme activity during arrhythmia and following reversion to normal sinus rhythm was studied in the intact, anethetized dog. An infusion of actodigin(AY22,241) at the rate of 0.1 micronmol/kg/min for 30 min induced a severe and persistent arrhythmia within 13.1 +/- 192 min of 9 dogs. Upon termination of the actodigin infusion, the arrhythmia spontaneously converted to sinus rhythm within 17.5 +/- 2.3 min. Left ventricular tissue was taken from dogs sacrificed at the peak of the actodigin-induced arrhythmic periods or from the dogs that were allowed to recover from the actodigin-induced arrhythmia. These samples were homogenized and the membrane-containing fraction was passed through a Millipore filter. The membrane fraction trapped in the filter was then assayed for Na+ + K+ stimulated, Mg2+ dependent ATPase acctivity. The results showed that, in comparison to the time matched control dogs, the cardiac microsomes prepared from the arrhythmic dogs had a markedly reduced Na+, K+-ATPase activity. On the other hand, actodigin-treated dogs that were allowed to recover from the arrhythmic episode had Na+, K+-ATPase activity that was not significantly different from the control values. The amount of 3H-actodigin bound by the cardiac muscle microsomal fraction was also investigated. The microsomes from left ventricle were isolated with a slight modification of the method of Dutta et al. (1968). The microsomal binding of 3H-actodigin was maximum at 30 min (26.6 mol/mg protein) when the sample was prepared from the dogs at the peak of the arrhythmic effect. However, the binding was significantly reduced (11.5pmol/mg protein) in the microsomal fraction from hearts that had returned to sinus rhythm. These data provide direct evidence that inhibition of Na+, K+-ATPase and cardiac glycosideinduced arrhythmia may have some cause and effect relationship.

Ventricular arrhythmias and hypokalaemia

Two cases of life-threatening ventricular arrhythmia (torsade de pointes) due to chronic mild hypokalaemia, caused by hyperaldosteronism and familial periodic paralysis are described. Correction of the hypokalaemia, supplemented by mexiletine, controlled the arrhythmias.

Cardiac NaK ATPase activity during positive inotropic and toxic actions of ouabain

In order to define pharmacological actions of ouabain in the dog heart, ouabain uptake and subcellular distribution and its effect on NaK ATPase (MG2+ dependent, Na+-K+-activated adenosinetriphosphate phosphohydrolase, E.C. 3.6.1.3), have been investigated in 21 open-chest dogs. A continuous infusion of ouabain (0.036 mug/kg/min) after a loading dose (20 mug/kg) produced a relatively constant plasma concentration of approximately 10(-8) M (6 ng/ml) ouabain, which induced a sustained positive inotropic response for the 300 min experimental period. In these hearts much greater binding of ouabain was noted in the NaK ATPase and microsomal fractions than in other myocardial fractions. No statistically significant inhibition of NaK ATPase activity was noted. Doubling the loading and infusion doses of ouabain raised the plasma level of ouabain to approximately 3 X 10(-8) M and produced various types of arrhythmia within an hour, which persisted for the rest of the 5 h experimental period. Under this experimental protocol there was a significant inhibition of NaK ATPase activity and increased binding of ouabain to this enzyme. This study does not support the hypothesis that there is a causal relationship between inotropic response to ouabain and NaK ATPase inhibition. It was concluded that NaK ATPase inhibition might be causally related to the development of ouabain toxicity.

A study of serum and myocardial digitoxin concentrations in man during cardiac arrest

In 22 digitalized (of a total of 39) patients studied at random by radioimmunoassay during cardiac arrest, the mean serum digoxin concentration was 2.6 (+/- 1.86, range 0.6-8.2) ng/ml, significantly higher (P less than 0.001) than the "eudigitalized" concentration (1.3 +/- 0.52, range 0.5-2.3 ng/ml) determined under carefully standardized conditions in a non-toxic population. Half of the arrest patients had serum digoxin levels in the toxic range (2.4 ng/ml or above), mainly due to significant renal failure (mean serum creatinine concentration 2.9 +/- 2.66 v. 1 +/- 0.26 mg/dl for non-toxic subjects, P less than 0.001), partly due to a higher mean daily digoxin dose (0.40 v 0.31 mg/day, P less than 0.05) and frequently associated with potent diuretic therapy (73 v 54%). A smaller fraction of digitalized patients survived, both short- (27%) and long-term (14%), than did non-digitalized subjects (35% and 26%, respectively). The mean myocardial digoxin concentration was 150 (+/- 63.3, range 52-252) ng/g with an average myocardial/serum ratio of 62.5 (range 38-91). There were significant positive correlations between the serum digoxin and left-ventricular myocardial digoxin concentration (r=0.8107, P less than 0.01) or serum creatinine concentration (r=0.4637, P less than 0.001).

The effect of hydrochlorothiazide and amiloride administered together on muscle electrolytes in normal subjects

Hydrochlorothiazide, 150 mg daily, and amiloride, 15 mg daily, have been administered together to 10 normal subjects during one week. Muscle biopsies were performed before and after the period of administration of the diuretics and the material was analysed for water and electrolytes. The body weight decreased by 1.9 kg. The serum sodium, chloride and potassium concentrations decreased significantly and standard bicarbonate and blood pH increased. In muscle tissue, extracellular water, chloride and sodium contents and intracellular sodium concentration decreased but the muscle potassium content, the intracellular potassium concentration and the muscle magnesium content were unchanged. A comparison with the results of an earlier study, in which hydrochlorothiazide was given without amiloride, showed that the intracellular potassium depletion and the increase in intracellular sodium concentration, observed with the benzothiazide diuretic, could be fully prevented by simultaneous administration of amiloride. The degree of hypokalemia and alkalosis was also smaller with hydrochlorothiazide + amiloride than with hydrochlorothiazide alone.