Drugs and the heart. IV. Antiarrhythmic agents

Beneficial effects of carbon monoxide-releasing molecules on post-ischemic myocardial recovery

There is increasing evidence corroborating a protective role of carbon monoxide releasing molecules (CORMs) in injured tissues. Carbon monoxide (CO) carriers have been recently developed as a pharmacological tool to simulate the effect of heme oxygenase-1-derived CO. The effects of CORM-3, a water-soluble CO releaser, on the incidence of reperfusion-induced ventricular fibrillation (VF) and tachycardia (VT) were studied in isolated rat hearts. Hearts were treated with different doses of CORM-3 before the induction of 30 min global ischemia followed by 120 min reperfusion. We found that at concentrations of 25 microM and 50 microM of CORM-3 promoted a significant reduction in the incidence of VF and VT. Thus, the incidence of VF was reduced by 67% (p<0.05) and 92% (p<0.05) with 25 microM and 50 microM of CORM-3, respectively. The protective effect of CORM-3 on the incidence of VT followed the same pattern. The antiarrhythmic protection was associated with a marked attenuation in infarct size, significant decreases in cellular Na(+) and Ca(2+) gains and K(+) loss. Consequently, the recovery of post-ischemic function was significantly improved. In conclusion, CORM-3 exerts beneficial effects against ischemia/reperfusion-induced injury through its abilities to release CO which mediates a cardioprotective action by regulating tissue Na(+), K(+), and Ca(2+) levels.

Continuous infusion of drugs: a simple and rational system

Continuous infusion of potent, often short-acting drugs particularly affecting the cardiovascular system is becoming more common in the operating room and intensive care unit. Accuracy and, hence, safety are always important in drug therapy, and never more so than when using the potent vasoactive and cardioactive drugs, yet the multiplicity of methods for preparing these drugs for infusion creates a situation in which mistakes may easily occur. A series of decimally related dilutions for drug preparation is presented, which has been in use for the past 5 years in the cardiac intensive care units at this hospital. It is believed that this system is easy to understand and remember and it thereby simplifies the process. This system may enhance the accuracy of dosage and improve the safety for patients.

Long-term prognosis after resuscitation from primary ventricular fibrillation complicating acute transmural myocardial infarction in the north east of Scotland

The aim of this study is to determine the long-term prognosis of patients successfully resuscitated from primary ventricular fibrillation in the acute phase of transmural myocardial infarction and to identify predictors of mortality. Details of 75 consecutive patients between October 1971 and May 1981 were reviewed in October 1985. The cumulative survival rates at one year, two year, five year and 10 year were 84%, 77% 67% and 40.5% respectively with a median survival time of 8.7 years. Univariate and Cox survival analyses were used to determine predictors of mortality. Only the age of the patient at the time of infarction was found to be highly significant with a greatly increased mortality rate in the older age group (p less than 0.001). The sex, site of infarction (anterior or inferior) and time of entry in the study did not significantly influence long-term prognosis.

The cardiovascular effects of antidepressants

This monograph comprises a review of the cardiovascular effects of the various types of antidepressant drugs in clinical use. The frequency, severity and clinical importance of these effects are placed in perspective. Most antidepressants can cause changes in blood pressure. Both the tricyclic type (TCA) and the monoamine oxidase inhibitors (MAOIs) can produce postural hypotension which may be dose-limiting. In addition, the MAOIs may be associated with severe hypertension when amine-containing foods or medicines are ingested. It is unlikely that therapeutic doses of any available antidepressant drug could impair cardiac contractility. Typical TCAs can cause abnormalities of cardiac conduction and arrhythmias, but this affects less than 5% of patients, mostly to a clinically insignificant extent. Newer compounds such as lofepramine, mianserin, trazodone and viloxazine seem safer in this respect. Reports of an association between therapeutic use of TCAs and sudden death are far from convincing. Overdosage with the MAOIs, lithium and carbamazepine is dangerous but not common; overdose with a TCA is a major source of morbidity and mortality. Lofepramine, mianserin and trazodone are relatively safe in overdose. The use of various antidepressants in patients with hypertension, cardiac failure, angina pectoris, myocardial infarction, or cardiac arrhythmias is discussed and guidelines suggested for the selection and use of antidepressant medication.

Preclinical toxicology of pirmenol hydrochloride

Pirmenol hydrochloride, a novel pyridinemethanol derivative, is a long-acting class Ia antiarrhythmic agent. Preclinical toxicology data were obtained in rat, mouse, dog and rabbit. In acute toxicity studies by oral and intravenous routes, no pathologic changes were observed in surviving mice, rats and dogs. In repeated dose toxicity studies, no drug-related pathologic changes were evident; dryness of the oral mucosa in dogs and body weight gain reductions in rodents were the only significant clinical signs. In a chronic (52 week) toxicity study in rats, pirmenol given in the diet was tolerated clinically at doses up to 100 mg/kg/day. No drug-related aberrations in clinical laboratory parameters or ophthalmic or pathologic findings were evident. In a similar study in beagle dogs, pirmenol was tolerated clinically at a dosage up to 30 mg/kg/day. No significant changes in biochemical, hematologic, urinary or bone marrow determinations were found in either species. In reproductive toxicology studies in rats, pirmenol had no significant effect on litter size or embryonic viability. In rabbits pirmenol had no effect on average litter size, embryonic viability or fetal wastage. Given to male rats, pirmenol had no overt effects on fertility. Pirmenol failed to elicit deoxyribonucleic acid damage or induce cytogenetic alterations. Pirmenol appears to be without significant limiting toxicologic properties.

Poisoning by antidysrhythmic drugs

This article discusses the management of antidysrhythmic drug overdoses in children and adolescents.

Flecainide: a new antiarrhythmic drug

Flecainide acetate is a new class 1 c antiarrhythmic drug. It slows conduction in the working myocardium and the specialized conduction system and may depress sinus node activity in patients with pre-existing sinus node disease. Its hemodynamic effects are minimal. The drug is completely absorbed and shows a half-life of 7-22 hours. Elimination is mainly through the kidneys. Flecainide is highly effective in the treatment of ventricular arrhythmias, pre-excitation syndromes and AV reentry tachycardias. Side effects are mild and consist mostly of dizziness, visual disturbances, and nervousness. They rarely require discontinuation of therapy. Proarrhythmic effects have been reported. Caution is required in patients with congestive heart failure, AV block, and/or bundle-branch block or sinus node dysfunction.

Combination of procainamide and quinidine for better tolerance and additive effects for ventricular arrhythmias

The efficacy and tolerance of quinidine and procainamide used individually and in combination were studied in 19 patients with frequent ventricular premature complexes (VPCs). During single-drug treatment, the maximum tolerated dose of quinidine without extracardiac dose-related side effects was 1.6 +/- 0.21 g/day and that of procainamide was 4.1 +/- 1.05 g/day. During combination therapy with smaller doses (p less than 0.05) of quinidine (1.16 +/- 0.26 g/day) and procainamide (2.80 +/- 0.98 g/day), no patient had side effects. Before treatment, all patients had frequent (more than 60 per hour) VPCs and 17 had ventricular tachycardia on Holter monitoring. The frequency of VPCs was reduced to 22 +/- 19% with quinidine, 47 +/- 40% with procainamide and 9 +/- 11% with combination therapy (p less than 0.05, combination vs procainamide or quinidine alone). Individually, an effective regimen (more than 83% reduction of VPCs and abolition of ventricular tachycardia) was found in 5 patients (26%) receiving quinidine alone at maximal tolerated dose, in 4 (21%) receiving procainamide alone at maximal tolerated dose, and in 14 (74%) receiving combination therapy (p less than 0.01 vs quinidine or procainamide). Thus, the antiarrhythmic effects of quinidine and procainamide are additive. When quinidine or procainamide are additive. When quinidine or procainamide is ineffective because dose-related extracardiac side effects limit the maximal tolerated dose, combination therapy in smaller and tolerable doses avoids side effects and is more effective than either drug alone at the maximal tolerated dose.

Effects on transmembrane action potential, slow inward current and force of contraction in ventricular cardiac muscle of BRL 31660, a new antiarrhythmic drug with class I and class IV activity

The effects of 1-30 mumol l-1 BRL 31660 on transmembrane action potential and force of contraction were investigated in guinea-pig electrically driven papillary muscles. Lidocaine was studied for comparison. BRL 31660 depressed Vmax of the action potential without changing the resting potential, decreased the force of contraction and decreased the action potential duration. Similar effects were obtained with lidocaine. BRL 31660 inhibited the recovery of Vmax from inactivation, the time constant of which was estimated to be about 1,100 ms in the presence of 10 mumol l-1 BRL 31660. The depressive effect on Vmax was particularly pronounced at low (less negative) membrane potentials. BRL 31660 can thus be classified as a class I antiarrhythmic agent of the lidocaine type. Additional voltage-clamp experiments in cow ventricular trabeculae provided evidence that BRL 31660 also depressed the slow inward current at concentrations similar to those producing the effects on the transmembrane action potential. BRL 31660 thus exerted an additional class IV action. This effect was not shared by lidocaine. It is concluded that BRL 31660 is a new antiarrhythmic agent which depresses both the fast and slow inward current at similar concentrations. The dual effects of BRL 31660 conceivably contribute to its antiarrhythmic activity, but the clinical relevance of these results remains to be elucidated.

Effects of oral prajmaline bitartrate on exercise test responses in patients with coronary artery disease

The safety, tolerability and haemodynamic effects of oral prajmaline bitartrate were assessed in a double-blind, randomized, placebo-controlled, crossover trial in 21 patients with stable angina pectoris and coronary artery disease. No serious side-effects occurred. Prajmaline bitartrate produced no statistically significant changes in resting heart rate or systolic blood pressure or in work capacity on the treadmill, or in heart rate or systolic blood pressure at maximum exercise compared to placebo values. No new arrhythmias or conduction abnormalities were produced in any patient. We conclude that oral prajmaline bitartrate is well tolerated and can be given safely to patients with coronary artery disease without producing deleterious haemodynamic effects or changes in exercise capacity.

Determinants of survival in patients with ventricular tachyarrhythmias

We analyzed data from 239 patients with sustained ventricular tachycardia or ventricular fibrillation to determine prognosis, predictors of survival, and the prognostic value of inducing arrhythmia and assessing therapy at the time of electrophysiologic study. Therapy predicted to be effective on the basis of electrophysiologic study was administered over a sustained period. There were 71 cardiac deaths, including 44 sudden deaths, during a mean (+/- S.D.) follow-up period of 14.8 +/- 13.9 months (range, one day to 67 months). At one, two, and three years, the actuarial incidence of sudden death was 17 +/- 3, 25 +/- 4, and 34 +/- 6 per cent, and that of cardiac death was 28 +/- 3, 37 +/- 4, and 50 +/- 6 per cent. Multivariate regression analyses demonstrated that the two strongest predictors of both sudden death and cardiac death were a higher New York Heart Association functional class (P less than 0.0001 for sudden death and P less than 0.0001 for cardiac death) and the failure of any therapy to be identified as potentially effective on the basis of electrophysiologic study (P = 0.0019 and P = 0.0003). The majority of deaths in patients with ventricular tachyarrhythmias were sudden, but the severity of heart failure was the strongest independent predictor of mortality. Response to therapy during electrophysiologic study was also an independent predictor of survival.

Biotransformation of cibenzoline to 2-(2,2-diphenylcyclopropyl)-1H-imidazole

A microsomal metabolite of cibenzoline, 4,5-dihydro-2-(2,2-diphenylcyclopropyl)-1H-imidazole butanedioate, was identified by n.m.r. as the 4,5-dehydro analogue, 2-(2,2-diphenylcyclopropyl)-1H-imidazole. Three dogs dosed orally with 13.8 mg/kg 14C-cibenzoline base excreted 1.8-3.5% of the dose as this metabolite in the urine. Mean plasma concentrations of cibenzoline reached a peak of 1.5 micrograms/ml at 2 h while mean concentrations of the metabolite of 0.4-0.5 micrograms/ml were found between 2 and 7 h. The metabolite was synthesized and found to decrease the frequency of ventricular premature depolarizations in conscious dogs having a two-stage occlusion of the left anterior descending coronary artery performed 48 h before. It did not inhibit ventricular arrhythmia in rats induced by i.v. infusion of aconitine. Thus, in contrast to cibenzoline, the metabolite does not appear to be a true antiarrhythmic agent.

beta-Receptor blockade and neurolept anaesthesia. Withdrawal vs continuation of long-term therapy in gall-bladder and carotid artery surgery

Forty-eight chronically (greater than 3 months) beta-receptor-blocked patients with ischaemic heart disease and/or hypertension were studied on 49 occasions after random distribution to a 4-day, gradual preoperative withdrawal (n = 26) or a continuation (n = 23) of beta-receptor blockers. The patients were scheduled for either a cholecystectomy (n = 28) or a carotid thrombendarterectomy (n = 21) under neurolept anaesthesia. Three patients were excluded from the randomized part of the study due to complications (tachycardia, hypertension, severe angina) after therapy withdrawal. In subgroups, central haemodynamics (beta-receptor blockers withdrawn n = 6, continued n = 8) and creatinine-kinase B (beta-receptor blockers withdrawn n = 9, continued n = 11) were studied. Withdrawal of beta-receptor blockers was associated with high heart rates, supraventricular tachyarrhythmias and a hyperkinetic circulation during pain stimuli. Significantly more postoperative ECG changes (P less than 0.02) indicative of myocardial ischaemia were found than in beta-receptor blocked patients. These patients had low heart rates but also pronounced increases in pulmonary capillary wedge pressures, which in single patients could be associated with myocardial damage. These results imply that beta-receptor blockers should be continued before surgery and that a concomitant vasodilatatory therapy is likely to avoid the drawbacks of an increased cardiac afterload.

Bupivacaine for intercostal nerve blockade in patients on long-term beta-receptor blocking therapy

Possible cardiovascular side effects of a local anaesthetic in patients on long-term beta-receptor blocking therapy were studied in 26 patients given postoperative intercostal nerve blockades (ICB) with 18-28 ml of plain bupivacaine 0.5% (1.30-1.82 mg kg-1). The patients had a history of hypertension and/or ischaemic heart disease and were scheduled for gall bladder surgery. Thirteen patients were randomized to a gradual preoperative withdrawal of the beta-receptor blockers and the other 13 continued the beta-receptor blockade until surgery. Cardiovascular changes were measured noninvasively and 11 patients were also monitored with pulmonary artery catheters. Blood pressure and heart rate (HR) were stable in all patients although those in whom the beta-receptor blockade was withdrawn had the highest HR and most frequent arrhythmias both before and after ICB. The ICB was associated with a decrease in the overall postoperative arrhythmia incidence, but seemed most efficient (P less than 0.02) concerning the ventricular arrhythmias in the beta-receptor-blocked patients (even including idionodal rhythm). The bupivacaine blood levels did not modify other cardiovascular changes except in one beta-receptor-blocked patient with cardiac failure in whom signs of a slight transient cardiodepression were observed. It is concluded that bupivacaine does not negatively affect cardiovascular stability in long-term beta-receptor-blocked patients. In the presence of cardiac failure, however, an additive cardiodepression may be elicited.

Intravenous amiodarone in ventricular fibrillation

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A new histochemical method to assess and evaluate potential bone marrow damage from therapeutic substances

A new model is presented for assessing and evaluating the influence of bone-marrow-damaging substances in mice. Qualitative and quantitative results of histological, histochemical and enzyme histochemical studies facilitate the assessment of bone marrow damage in terms of extent and intensity. Bone marrow taken from the right femur of treated animals was embedded in renal tissue of controls for subsequent work-up in different techniques. From each of the experimental groups specimens from 10 animals were frozen in liquid nitrogen, specimens from another 10 animals were fixed in buffered formalin. Assessment and evaluation of changes was performed after the required histologic and histochemical staining (nucleic acid). Results were correlated with the cytology of bone marrow smears sampled from the left femur of each respective animal. Damage was visualized, in smear cytology or in histologic and histochemical preparations, and quantified by microphotometry and special staining for cytochrome oxidase activity.