Antiarrhythmic effects of a novel class III drug, KCB-328, on canine ventricular arrhythmia models

KCB-328 is a newly synthesized class III drug. To determine whether this drug has antiarrhythmic or proarrhythmic effects, we used canine ventricular arrhythmia models induced by coronary ligation and reperfusion, programmed electrical stimulation (PES), two-stage coronary ligation, digitalis, or epinephrine. KCB-328, in an intravenous infusion of 0.5 mg/kg/30 min, prolonged the QTc interval only 11%, but had antiarrhythmic effects on the reentry arrhythmias induced by PES (12 of 12 dogs with old myocardial infarction; p < 0.05). KCB-328, in an infusion of 1 mg/kg/h, suppressed the occurrence of fatal ventricular fibrillation (VF) induced by coronary ligation and reperfusion under either halothane anesthesia (p < 0.05) or pentobarbital anesthesia (p < 0.05). Under the halothane anesthesia, KCB-328 alone showed proarrhythmic effects [i.e., induction of ventricular premature contractions (VPCs)], but it did not induce a more severe effect such as torsades de pointes-type ventricular tachycardia (VT). In addition, KCB-328 had weak antiarrhythmic effects on the automaticity arrhythmias induced by 24-h coronary ligation but was effective neither on 48-h coronary ligation arrhythmias nor on the digitalis- and epinephrine-induced arrhythmias. Our results indicate that KCB-328 has powerful antiarrhythmic effects with fewer proarrhythmic potencies.

Long-term survival effect of metoprolol in dilated cardiomyopathy. The SPIC (Italian Multicentre Cardiomyopathy Study) Group

OBJECTIVE

To evaluate the additive effect of metoprolol treatment on long-term incidence of fatal and non-fatal cardiac events in idiopathic dilated cardiomyopathy.

DESIGN

586 patients with idiopathic dilated cardiomyopathy were prospectively enrolled in a multicentre registry and followed up for a mean (SD) of 52 (32) months. Metoprolol, carefully titrated to the maximum tolerated dose, was added to conventional heart failure treatment in 175 patients.

RESULTS

Survival and transplant-free survival at seven years were significantly higher in the 175 metoprolol treated patients than in the remaining 411 on standard treatment (81% v 60%, p < 0.001, and 69% v 49%, p < 0.001, respectively). By multivariate analysis, metoprolol independently predicted survival and transplant-free survival (relative risk reduction values for all cause mortality and combined mortality or transplantation 51% (95% confidence interval 21% to 69%), p = 0.002, and 34% (5% to 53%), p = 0.01, respectively). New York Heart Association class, left ventricular end diastolic diameter, and pulmonary wedge pressure were also predictive. Seven year survival (80% v 62%, p = 0.004) and transplant-free survival (68% v 51%, p = 0.005) were significantly higher in 127 metoprolol treated cases than in 127 controls selected from the entire control cohort and appropriately matched. Metoprolol was associated with a 30% reduction in all cause mortality (7% to 48%, p = 0.015) and a 26% reduction in mortality or transplantation (7% to 41%, p = 0.009).

CONCLUSIONS

The addition of metoprolol to standard heart failure treatment, including angiotensin converting enzyme inhibitors, was effective in the long-term, reducing both all cause mortality and transplantation in patients with idiopathic dilated cardiomyopathy.

[Pheochromocytoma and cardiac insufficiency]

Catecholamine-induced cardiomyopathy is a rare complication of pheochromocytoma. We present a case of pheochromocytoma that developed preoperative heart failure. Left ventricular dilation and severe hypokinesia were demonstrated by echocardiography. Heart failure was successfully treated with digitalis, diuretics and captopril. There were no surgical complications and the follow up showed and improvement on the systolic function evaluated by echocardiography and isotope ventriculography, 3 and 6 months after surgery. We review the pathophysiology and evolution of catecholamine induced cardiomyopathy. Preload reserve can be one of the adaptive mechanisms of the ventricle in catecholamine-induced cardiomyopathy. Conventional therapy of hypertension and heart failure can be effective to correct the symptoms of cardiac dysfunction.

Cardiac hypertrophy determines digitalis action on intracellular Ca2+ in human myocardium

Ventricular hypertrophy alters transporters associated with digitalis action, but the outcome of digitalis treatment on intracellular cations in the hypertrophied human myocardium remains unknown. Using double-barreled Ca2+-selective microelectrodes, we simultaneously measured Ca2+ activity and membrane potential in myocardial samples from patients without and with ventricular hypertrophy, prior to and following exposure to strophanthidin, a prototype digitalis. We found that ventricular hypertrophy is associated with greater strophanthidin-induced increase in diastolic Ca2+ levels compared to that observed in the absence of hypertrophy. Furthermore, in hypertrophied myocardium the magnitude of the increase in Ca2+ induced by strophanthidin was inversely related to increase in myocardial mass. Thus, the extent of ventricular hypertrophy determines digitalis action on intracellular Ca2+ within the human myocardium.

[Bradycardiac atrial fibrillation after consuming herbal tea]

HISTORY AND CLINICAL FINDINGS

One day after drinking what she thought to be a tea made from borage leaves a 72-year-old woman developed nausea, vomiting and diarrhoea, later also flickering in her eyes and palpitations. She was in a good general state with a blood pressure of 120/75 mm Hg and an irregular heart rate of 52/min. Physical examination was otherwise unremarkable. She had not been on any medication.

INVESTIGATIONS

The usual laboratory tests were normal. The electrocardiogram showed atrial fibrillation with a slow ventricular rate with pauses of up to 1.5s. intermittently type I and II 2 degrees AV block, and depressed concave ST segments. The level of digoxin was 3.93 ng/ml, that of digitoxin 133.5 ng/ml.

TREATMENT AND COURSE

The patient's symptoms quickly improved under symptomatic treatment. Further questioning suggested that she had probably mistaken foxglove leaves for those of borage when picking them to make a brew.

CONCLUSION

If cardiac arrhythmias have occurred after intake of self-picked herbal leaves one should consider digitalis intoxication resulting from misidentification.

Inotropic agents in the treatment of heart failure: despair or hope?

Depression of myocardial contractility plays an important role in the development of heart failure; therefore, intensive interest and passion have been generated to develop cardiotonic agents to improve the contractile function of the failing heart. Inotropic agents that increase cyclic AMP, either by increasing its synthesis or reducing its degradation, exert dramatic short-term hemodynamic benefits, but these acute effects cannot be extrapolated into long-term improvement of the clinical outcome in patients with advanced heart failure. Administration of these agents to an energy-starved failing heart would be expected to increase myocardial energy use and could accelerate disease progression. The role of digitalis in the management of heart failure has been controversial, but ironically the drug has now been proved to favorably affect the neurohormonal disorders and its reevaluation is now being intensively investigated. More recently, attention has been focused on other inotropic agents that have a complex and diversified mechanism. Recent clinical studies have demonstrated that they are potentially useful in the long-term treatment of heart failure patients. These agents have some phosphodiesterase-inhibitory action but also possess additional effects, including acting as cytokine inhibitors, immunomodulators, or calcium sensitizers. However, their therapeutic ratio is narrow and further studies are warranted to establish their optimal doses and their eventual status in the treatment of heart failure.

Antiarrhythmic effects of an aconitine-like compound, TJN-505, on canine arrhythmia models

We examined the effects of an aconitine-like compound, TJN-505 (1alpha-16beta-dimethoxy-20-ethyl-14alpha-(4-methox ybenzoyloxy)-aconitan-8,13-diol hydrochloride), on canine arrhythmias provoked by digitalis, two-stage coronary ligation, adrenaline, programmed electrical stimulation, or aconitine. TJN-505 (2-2.5 mg/kg i.v.) suppressed digitalis-, two-stage coronary ligation- and adrenaline-induced ventricular arrhythmias. The antiarrhythmic plasma concentrations (IC50) of TJN-505 for these arrhythmia models were 1.26, 0.94 and 1.31 microg/ml, respectively. TJN-505 (2 mg/kg i.v. followed by the infusion of 0.1 mg/kg per min) prolonged PR, QRS, QTc and JTc intervals and the ventricular effective refractory period and reduced the incidence of programmed electrical stimulation-induced arrhythmias in dogs with 7-day-old myocardial infarction (P < 0.05). TJN-505 (2 mg/kg i.v.) also suppressed the aconitine-induced atrial arrhythmias. In conclusion, TJN-505 suppressed various canine ventricular and atrial arrhythmias and seems to act as a blocker of multiple channels.

Skeletal muscle changes in patients with chronic heart failure before and after treatment with enalapril

To evaluate if enalapril treatment can influence skeletal muscle metabolism and histology we investigated 26 patients with congestive heart failure and 20 normal subjects. The patients were treated with enalapril for 3 months in addition to diuretics and digitalis. Biopsies from the lateral vastus muscle were taken before and after treatment. Citrate synthetase, 3-hydroxyacyl-CoA dehydrogenase and phosphorylase activities were significantly decreased in the patients compared with controls. The number of capillaries per fibre and the number of capillaries surrounding each fibre were significantly decreased among patients. After 3 months of enalapril treatment functional class improved significantly. The lactate dehydrogenase activity increased whereas the oxidative enzymes did not change significantly. The type I, II and II A fibre areas increased significantly after enalapril treatment. We conclude that patients with chronic heart failure have decreased activity of oxidative enzymes and of phosphorylase in skeletal muscle. They also have decreased capillarization in skeletal muscle. These changes were not influenced by enalapril treatment. The increase in muscle fibre area seen after enalapril treatment could be due to increased physical activity. The cause of increased muscle lactate dehydrogenase activity after enalapril treatment needs further investigation.