[Effect of the sympathetic nervous system activation on the antifibrillatory efficacy of various anti-arrhythmia agents]

Experiments with a 7-min occlusion followed by reperfusion of the left coronary artery in narcotized rats showed that antiarrhythmic drugs of various classes--ethacizin (class I), AL-275 (class III), and CM-345 (class V)--produce pronounced antifibrillatory and antiarrhythmic effects. AL-275 and CM-345, in contrast to ethacizin, retained their efficacy under the conditions of isoproterenol-induced stimulation of beta-adrenoceptors. This difference in behavior is probably explained by dissimilar effects of the antiarrhythmics on the ion channels of cardiomyocite membranes.

Simultaneous determination of moricizine and its sulphoxidation metabolites in biological fluids by high-performance liquid chromatography

A simultaneous assay for moricizine, its two sulphoxidation metabolites, moricizine sulphoxide and moricizine sulphone, using high-performance liquid chromatography (HPLC) is described. The drug and metabolites and clozapine (internal standard) in biological fluids were extracted using pentanesulphonic acid into diethyl ether. The ethereal extract was evaporated to dryness and the residue was redissolved in the mobile phase (methanol-water-triethylamine, 65:35:0.5, v/v). The analyses were performed on a microBondapak reversed-phase C18 column housed in a Waters Z-module, linked to a C18 pre-column, with a run-time of 12 min. The retention times were 2.7, 3.5, 6.2 and 9.7 min for moricizine sulphone, moricizine sulphoxide, moricizine and clozapine, respectively. The recovery of the compounds from plasma ranged from 89.9% for the sulphoxide to 98.1% for clozapine. The limits of detection of the assay for moricizine, moricizine sulphoxide and moricizine sulphone were 20, 10 and 5 ng/ml, respectively.

Combination ethacizin and ethmozin treatment of resistant ventricular ectopy: theoretical, experimental, and clinical study

Ethmozin (Moricizine HCl) and ethacizin are two class I antiarrhythmic drugs with different rate constants of interaction with the sodium channel. Computer simulation using the "guarded-receptor" model predicted that the combination of ethacizin and ethmozin should exert a greater decrease in excitability and conduction at short coupling intervals, but little effect at normal heart rates (HR). To test this prediction, we measured intraventricular conduction delay in canine hearts in vivo. In agreement with the model, the combination more potently prolonged the delay only at intervals < 600 ms as compared with ethacizin alone. Combination therapy was tested in 6 patients with idiopathic ventricular ectopic depolarizations (VEDs). Three patients were resistant to either ethmozin or ethacizin monotherapy, and three could not tolerate effective doses because of side effects. Quantitative continuous ECG monitoring showed that total VEDs in the resistant group decreased 0 and 17 +/- 13% for 400 and 800 mg/day ethmozin and 18 +/- 12 and 55 +/- 12% for 100 and 200 mg/day ethacizin, respectively. Combined therapy with ethmozin (400 mg/day) and ethacizin (100 mg/day) reduced the number of VEDs by 78 +/- 2% in these patients without side effects. In the "nonresistant" but intolerant group of patients, use of the combination allowed relief of symptomatic ectopy without side effects. A theoretical model correctly predicted an effective combination of class I antiarrhythmic drugs, one with "fast-off" and one with "slow-off" kinetics, which may provide a general rationale for choosing drug combinations.

[Pharmacokinetics of moracizine and moracizine sulfoxide in healthy volunteers]

The pharmacokinetics of moracizine (Mor) and moracizine sulfoxide (Mor-SO) determined by reversed phase HPLC was reported. The data in 6 volunteers after a single oral dose (600 mg) showed an one-compartment open model. The peak concentration in plasma (2.1 +/- 0.4 micrograms.ml-1) of Mor reached within 1-2 h. The Mor-SO concentration in plasma was much lower (0.19 +/- 0.06 micrograms.ml-1) than that of Mor, but its elimination T1/2 (2.3 +/- 1.0 h) was similar to that of Mor (1.5 +/- 1.0 h). The recoveries of Mor, Mor-SO, moracizine sulfone (Mor-SO2) in urine within 48 h were 0.07%, 0.25%, and 0.06% of the total dose, respectively. The Mor and Mor-SO concentration ranges in plasma for 9 arrhythmic patients after 2-wk therapeutic trial were 0.09 +/- 0.07 to 0.9 +/- 0.5 microgram.ml-1 and 0.040 +/- 0.023 to 0.15 +/- 0.06 micrograms.ml-1, respectively. These results suggested that cumulative doses would not result in accumulation of the drug and the anti-arrhythmic effect of Mor-SO might not be realized.

[Atherogenic properties of phenothiazine drugs manifesting in cultured cells of the human aortic intima]

The effects of phenothiazine drugs on the levels of cholesterol in smooth cells of the human aortic intima. Two antiarrhythmics (ethacizin and ethmozine) and two neuroleptics (trifluoperazine and chlorpromazine) were evaluated. The three agents ethacizin, trifluoperazine, and chlorpromazine given in concentrations of 10(-7) to 10(-5) M were ascertained to cause intracellular cholesterol accumulation, whereas ethmozine produced no effects on the intracellular levels of cholesterol. Ethacizin failed to cause cholesterol accumulation when the cells were incubated with ethacizin in the culture medium supplemented with lipid-deficient serum. Ethacizin in a concentration o 10(-5) M was shown to inhibit the synthesis of cholesterol esters and had no action on the intracellular synthesis of steroids.

[Comparative analysis of antiarrhythmic action and electrophysiological effects of a new benzodiazepine derivative gidazepam and ethacizin in arrhythmias of various genesis]

The antiarrhythmic and electrophysiological effects of the new benzodiazepine tranquilizer gidazepam versus ethacizin were examined in patients with cardiac arrhythmias. The antiarrhythmic effect of the agent was found during 24-day monitoring and simulated psychoemotional stress in 81% of patients with neurocirculatory dystonia and in 61% of patients with coronary heart disease. The antiarrhythmic effects developed with gidazepam-induced changes in electrophysiological properties of the cardiac conduction system. The preventive antiarrhythmic effect of gidazepam was demonstrated to be higher than that of ethacizin during stress in patients with arrhythmias of extra-ischemic genesis.

[Clinical effectiveness of cordarone in combination with other anti-arrhythmia agents in refractory atrial fibrillation and adverse effects of the drugs]

The study was undertaken to examine 105 patients with various circulatory diseases complicated by atrial fibrillation. Patients with refractory atrial fibrillation who had taken combined antiarrhythmic therapy were found to be more responsive to the combinations of cordarone + kinilentin (quinidine disulphate) and cordarone + ethacizin. The combinations of cordarone+digoxin and cordarone + finoptin were demonstrated to be less beneficial.

Effects of multiple doses of moricizine hydrochloride on its pharmacokinetics and hepatic microsomal enzymes in rats

We studied the influence of chronic moricizine hydrochloride (MRZ) treatment on the drug's pharmacokinetics and on drug metabolizing enzyme activities in rats. Separate groups of 8 rats (4 males and 4 females) were treated with 40 and 100 mg/kg oral MRZ once daily for 7 days and saline control for 7 days prior to the preparation of hepatic microsomal enzyme suspensions. Depending on the substrate, treatments with multiple oral MRZ increased or decreased hepatic microsomal enzyme activities. For the pharmacokinetic study, rats (4 males and 4 females) were treated with 40 mg/kg oral MRZ once daily for 7 days. A comparison of MRZ pharmacokinetics obtained on day 1 relative to day 7 revealed that both AUC0-t and AUC0-infinity increased about 7-fold in males and 2-fold in females. Cmax also increased about 5-fold from day 1 to day 7 in males. These increases in blood concentrations and AUC's are likely due to enzyme inhibition. Results obtained from female rats on days 1, 4 and 7 suggest that metabolic changes probably occur after the 4th day of dosing. Therefore, chronic MRZ treatment affected its pharmacokinetics and hepatic metabolizing enzyme activities in rats.

[Prospective course of therapy arresting attacks of atrial fibrillation in patients with preexcitation syndromes]

A comparative study of antiarrhythmic drugs was performed in 81 patients with atrial fibrillation attacks in the presence of preexcitation syndrome. The first intravenous administration of cordarone was effective in 84.06%, disopyramide--in 69%, ajmaline in 44.8, verapamil in 42.1, novocaine amide in 39.4 and ethacizin in 38.5% of the patients. The first oral administration of quinidine and kinilentin arrested 80.4% of arrhythmia attacks, disopyramide 66.7% propranolol and mexitil 37.5 and 33.3%, respectively. Prospective evolution of antiarrhythmic therapy manifested with decreased therapeutic efficacy of the drugs from 55.7 to 26.2% in the whole group during the period of 1-5 years.

Modulating intraventricular conduction through competition of two class 1 antiarrhythmic agents: experience with ethacizin and lidocaine in canine heart

The frequency-dependent effects on the intraventricular conduction through the dog heart in situ produced by two class 1 antiarrhythmic drugs, ethacizin and lidocaine, with different kinetic properties were investigated. Conduction delay was measured using stimulation of the His-bundle after pharmacologically induced atrioventricular (AV) block. Electrical events were derived from local epicardial bipolar electrograms at the base of the right ventricle. The stimulation program consisted of several 50-pulse trains with progressively shorter interstimulus intervals (ISI) separated by a l-s pause. Ethacizin (1.5 mg/kg) increased conduction delay by 30% at ISI of 1000 ms, and the effect was enhanced when ISI was shortened to 200 ms; l-s pauses did not significantly increase conduction velocity. Addition of lidocaine (12 mg/kg) strongly potentiated the ethacizin effect at ISI shorter than 300 ms without any noticeable increase in conduction delay at longer intervals. The major result was dramatic acceleration of conduction during the l-s pauses while both drugs were infused. With this combination, conduction delay after pause was shorter than with ethacizin alone, which is consistent with the competition of the drugs for the same binding site inside the sodium channel. Combination of two class 1 compounds in clinical practice may enhance their antiarrhythmic effects without adversely inhibiting normal impulse conduction in the heart. Computer-predicted data were in reasonable agreement with experimental results. The "guarded receptor" model, thus, can provide a simple method for predicting local anesthetic drug interactions in man.

Ethacizin blockade of calcium channels: a test of the guarded receptor hypothesis

The effect on calcium channels of the sodium channel antagonist, ethacizin, was studied in isolated frog ventricular cells using the whole cell voltage-clamp methodology. Ethacizin was found to block inward calcium current in a frequency-, voltage-, and concentration-dependent manner. The frequency-dependent blocking properties were modeled by considering the drug interaction with a voltage-dependent mixture of calcium channels harboring either an accessible or an inaccessible binding site. With repetitive stimulation, the pulse-to-pulse reduction in peak current is shown to be exponential, with a rate linearly related to the interstimulus interval and the drug concentration. Observed frequency- and concentration-dependent blocks were consistent with the predictions of the model, and mixture-specific rate constants were estimated from these data. The negligible shift in channel inactivation and the reduction of apparent binding and unbinding rates with more polarized membrane potentials imply the active moiety of ethacizin blocks open channels and is trapped within the channel at resting membrane potentials. The binding rate at 0 mV is similar to that observed in studies of interactions of other open channel blocking agents with voltage- and ligand-gated channels.

[Influence of ethacizin (the diethyl analog of ethmozine) on phase-dependent parasympathetic effects on the heart]

The influence of ethacizin (a diethylamine analog of ethmozine) (1.10(-7)-1.10(-6) g/ml) upon the phase-dependent chronotropic parasympathetic effects was studied on the perfused frog heart. The vagolytic influence of ethacizin (5.10(-7) and 1.10(-6) g/ml) was detected; the concentration of 1.10(-7) g/ml was found ineffective. The vagolytic effect consisted of a decreased maximum of phase-dependent effect, reduced latency and time required for the manifestation of the maximum increase. The period of inhibitory vagal stimulus effectiveness did not change significantly.

Ethacizin: a new efficacious Soviet antiarrhythmic drug of the phenothiazine group

Ethacizin, a new Soviet antiarrhythmic agent of the phenothiazine group, was tested on 82 patients with ventricular rhythm disturbances. Antiarrhythmic effects of the drug were assessed by means of ambulatory ECG monitoring. The investigation protocol included acute drug testing with 50 mg, 100 mg, and 150 mg, and short-term maintenance therapy with 150 to 300 mg/24 hours of ethacizin (mean 183 +/- 46 mg/24 hours) for 3 to 14 days (mean 7 +/- 3 days). Ethacizin reduced the total number of ventricular premature beats (VPBs) from 17,263/24 hours (on placebo) to 3458/24 hours (p less than 0.001) and suppressed couplets and ventricular tachycardia (VT) runs by 90% in 94% and 96% of patients, respectively. Maximum blood plasma concentration of ethacizin was observed in 110 to 120 minutes and accounted for 300 to 447 ng/ml (mean 354 +/- 77 ng/ml), with a minimum therapeutic drug plasma concentration ranging from 29 to 101 ng/ml (mean 73 +/- 27 ng/ml). There was a significant increase in PQ and QRS intervals with ethacizin. Ethacizin was well tolerated. Thus ethacizin had high antiarrhythmic efficacy in patients with VPBs and no significant side effects.

[Possibility of the pharmacologic treatment of post-ischemic myocardial damage]

The influence of ethacizin and nonachlazin on the size of myocardial necrosis, caused by 1.5-hour partial occlusion of the coronary artery was studied in conscious rabbits. The drugs were administered for 3 days, after the blood supply in the ischemic zones had been recovered. Ethacizin had a more pronounced effect, as compared to nonachlazin. The data obtained suggest that in the case of isochemic heart disease pharmacotherapy can be used not only for the prevention and arrest of anginal attacks, but also for the treatment of postischemic cardiac lesions.

[Clinical pharmacokinetics and hemodynamics of ethacizin in the acute period of myocardial infarct]

Clinical pharmacokinetics of ethacizine and its effect on parameters of the central and peripheral hemodynamics in the acute period of myocardial infarction were studied. The appearance of an additional maximum or "concentration plateau" on the concentration-time curve following a single intravenous injection of the drug was noted in most cases. To describe experimental data, a three-compartment model with lag time was proposed. The pharmacokinetic parameters obtained indicate that ethacizine is characterized by a less value of clearance and greater period of half-elimination as compared to ethmozine. Ethacizine was shown to exert no considerable effect on hemodynamics that makes it possible to recommend its use in acute myocardial infarction when cardiac rhythm disorders occur.

[Action of ethacizin on normal and anomalous forms of Purkinje fiber automaticity in the dog]

The effect of a new anti-arrhythmic drug etacysin was studied in various forms of dog Purkinje's fibres automativity: normal and abnormal arising at a late stage of experimental myocardial infarction (24 hrs after coronary artery ligation) and induced by ions Ba2+. An average 57% decrease in the frequency of automaticity of normal Purkinje's fibres due to steepening the slope of slow diastolic depolarization and almost complete depression of an abnormal one was observed for the drug concentrations 5 X 10(-7) and 10(-6) g/ml. Reduced automaticity was also related to decreased slow diastolic depolarization. Maximal values of diastolic potential were found unchanged.

[Electrophysiological action of ethacizin in acute myocardial ischemia in dogs]

The effects of ethacizin on delayed activation of the ischemic myocardium by acute left anterior descending coronary artery occlusion were studied in dogs. Ethacizin, administered intravenously at a dose of 0.5 or 1 mg/kg depressed the conduction of excitation in the ischemic myocardium and significantly increased the incidence of ventricular fibrillation. Electrophysiological effects of ethacizin in acute myocardial ischemia, as well as its antiarrhythmic activity at the advanced stages of experimental myocardial infarction might be related to an intensive influence of ethacizin on fast inward sodium current in the myocardial fibers.

A patch clamp study of the action of ethacyzine on the rapid inward sodium current in single rat heart muscle cells

The effect of ethacyzine (a diethylamine analogue of ethmozine) on the rapid inward sodium current (INa) was studied in single rat ventricular muscle cells by a patch clamp technique. Extracellular application of 3 microM ethacyzine depressed the INa in a use-dependent fashion. Rest recovery from the use-dependent block by ethacyzine followed an exponential time course with a time constant of about 215 +/- 40 s (n = 4, mean +/- S.E.).

[Effectiveness of ethacizin in ventricular arrhythmias refractory to prior anti-arrhythmia drug therapy]

Using Holter ECG monitoring, the efficiency of the new drug ethacizin was assessed on an individual basis in 48 patients with ventricular arrhythmias refractory to past treatments (group 1) and in 46 patients who responded to at least one of the available antiarrhythmic drugs (group 2). Ethacizin proved effective in 63% of first-group patients and in all second-group patients, with an overall response rate of 81%. The efficiency of ethacizin, ethmozin, and disopyramide was 100, 73 and 69%, respectively, in the same patients. It is suggested that separate assessments of new antiarrhythmic drugs are preferable in patients with treatment-resistant ventricular arrhythmias and those responding to at least one of the drugs available.

[Effect of ethacizin (diethylamine analog of ethmozine) on the efferent activity of the sympathetic and parasympathetic nerves of the heart]

This study examined the effects of the diethylamino analogue of ethmozin (ethacizin) (1 mg/kg, i.v.) on the spontaneous and reflex elicited efferent activity in thoracic cardiac sympathetic and parasympathetic nerves. Nitroglycerin and phenylephrine (4 and 8 micrograms/kg, i.v.) were administered to 15 anesthetized mongrel dogs while monitoring blood pressure and heart rate. In each dog, two cardiac nerves were isolated and efferent neurograms were simultaneously recorded and analyzed by microprocessor. Ethacizin significantly attenuated the spontaneous sympathetic efferent activity in both left and right, preganglionic (n-8) and postganglionic (n-14) sympathetic nerves to the heart. In contrast, reflex changes in sympathetic activity elicited by baroreceptor challenges, were not affected by ethacizin. Also, ethacizin did not significantly affect either spontaneous or baroreceptor reflex-induced parasympathetic efferent activities in 8 preganglionic nerves. Thus, this new phenothiazine derivative may exert part of its antiarrhythmic action through a reduction of the spontaneous sympathetic tonic discharges to the heart. The fact that ethacizin did neither reduce the reflex-induced changes in sympathetic or parasympathetic activities nor influence the tonic vagal discharges further suggests that the compound is not likely to interfere with reflexly mediated cardiovascular adaptive changes.

[Correlation between the anti-arrhythmia effect of ethacizin and pharmacokinetic parameters in a model of rhythm adoption by the heart]

Pharmacokinetics and pharmacodynamics of ethacizin were studied in a model of rhythm adoption by the heart, with the drug administered intravenously to anesthetized cats. A relation was demonstrated between blood ethacizin pattern and the drug's biphasic effect on the adoption of stimulation-imposed pace by the heart and ventricular fibrillation threshold. The estimated correlation coefficients, reflecting the relationship between the development of ethacizin anti-arrhythmic and antifibrillation effects and variation of its plasma levels between 10 and 120 min after the administration, were rather high (-0.85 and +0.93, respectively). Ethacizin shows anti-arrhythmic and antifibrillation activity when its plasma levels are between 2400 and 200 ng/ml.

[Mechanism of action and the effectiveness of ethacizin in patients with paroxysmal atrioventricular nodal reciprocal tachycardia]

An electrophysiologic study of ethacizin's mechanisms of action was carried out in patients with paroxysmal atrioventricular nodal tachycardia. Tachycardia was controlled by 0.5 mg/kg ethacizin in all patients. No patients demonstrated induced tachycardia in the presence of the drug, and 55% developed a complete retrograde atrioventricular block. The assessment of the preventive effect of oral ethacizin administration showed that paroxysms of tachycardia could not be provoked by esophageal electrostimulation of the heart in 87% of the patients. In the same patients, stable antiarrhythmic effect was maintained by long-term treatment with this drug. The suppression of retrograde stimulus conduction along the quick path of the atrioventricular node is assumed to be the principal electrophysiological mechanism of ethacizin action. Ethacizin can be used to control or prevent paroxysms of atrioventricular nodal tachycardia.

Effects of the diethylamino analog of ethmozin (ethacizin) upon sympathetic and parasympathetic efferent activity to the canine heart

This study examined the effects of the diethylamino analog of ethmozin (ethacizin) (1 mg/kg i.v.) on the spontaneous and reflexly elicited efferent activity in thoracic cardiac sympathetic and parasympathetic nerves. Nitroglycerin and phenylephrine (4 and 8 micrograms/kg i.v.) were administered to 15 anesthetized mongrel dogs while monitoring blood pressure and heart rate. In each dog two cardiac nerves were isolated and efferent neurograms were recorded simultaneously and analyzed by microprocessor. Ethacizin significantly attenuated the spontaneous sympathetic efferent activity in both left and right, preganglionic (n = 8) and postganglionic (n = 14) sympathetic nerves to the heart. In contrast, reflex changes in sympathetic activity elicited by baroreceptor challenges were not affected by ethacizin. Also, ethacizin did not significantly affect either spontaneous or baroreceptor reflex-induced parasympathetic efferent activities in eight preganglionic nerves. Thus, this new phenothiazine derivative may exert part of its antiarrhythmic action through a reduction of the spontaneous sympathetic tonic discharges to the heart. The fact that ethacizin reduced neither the reflex-induced changes in sympathetic or parasympathetic activities nor influenced the tonic vagal discharges further suggests that the compound is not likely to interfere with reflexly mediated cardiovascular adaptive changes.

[Initial results of clinical research on a tabletted form of ethacizin (the diethylamino analog of ethmozine) in ventricular arrhythmias]

The clinical effectiveness, pharmacodynamics and some pharmacokinetic aspects of a new antiarrhythmic drug ethacyzin (a diethylamine analogue of ethmozin) were studied, using diurnal electrocardiographic monitoring and exercise testing, in 50 patients with frequent and chronic ventricular heart rhythm disorders. The drug had positive antiarrhythmic effect in 87-90% of patients treated with single 100-150 mg oral doses and courses of 150-300 mg daily (the mean dose being 200 +/- 50 mg). With a single oral dose of 100 mg ethacyzin, the onset, peak and overall duration of its therapeutic effect were noted at 0.5-1, 1.5-2 and 6-8 hours, respectively. The minimal therapeutic plasma ethacyzine concentration was 40-70 ng/ml. Both in acute testing and during treatment courses, the drug significantly expanded the P wave, the P-Q interval and the QRS complex of the electrocardiogram, without affecting heart rate or Q-T duration, the magnitude of the resulting change in the said parameters depending on the dose administered and the antiarrhythmic effect of ethacyzin.

[Comparative study of the effect of ethacizin and lidocaine on the blood supply and function of the intact and ischemic myocardium]

It has been shown in experiments on cats anesthesized with nembutal that lidocaine (1.0 and 2.0 mg/kg) and etacizine (0.5 and 1.0 mg/kg) decrease heart work and create in the heart muscle a definite oxygen reserve, without exerting any inhibitory effect on myocardial contractile function. The drugs improve the function of the focus of myocardial ischemia, with the effect of etacizine being more lasting.

[Ethacizin: pharmacologic properties and prospects for clinical application]

The study of the regularities between the chemical structure and pharmacologic action of phenathiazine dialkylaminoacyl derivatives led to the identification and investigation of a new drug called ethacizine-phenothiazin-2-carbethoxyamino-10 (beta-diethylamino-propionyl) hydrochloride. Ethacizine exceeds its structural analogue ethmozin by two times in terms of intensity and by 4-5 times in terms of the duration of antiarrhythmic effect. Ethacizine has marked antianginal properties. It shows a prolonged inhibitory effect on the average elevation of the ST interval at multiple leads of the epicardial electrogram during coronary occlusion, increases the threshold of myocardial ischemia development, and reduces the size of experimental infarction. The combination of potent antiarrhythmic activity, already confirmed by clinical observations, with antianginal properties and a capacity to limit the size of infarction makes in possible to consider ethacizine a promising means for treating coronary heart disease.

[Pharmacokinetics of the new Soviet anti-arrhythmia preparation etacizin]

Ten patients without marked abnormalities on the part of the liver and kidneys were examined for the pharmacokinetics of a new Soviet antiarrhythmic drug etacizin. The drug was injected intravenously at a rate of 0.5-0.8 mg/kg bw. The blood required for determining drug concentrations was taken 1, 2, 3 and 4 hours after drug jet injection. It was demonstrated that the drug half-life was on the average 164 +/- 24.7 min, exceeding 2 times the half-life of etmozine, a drug of the same series applied to the treatment of some forms of heart rhythm abnormalities.

[A new Soviet drug, ethacizine, in the treatment of ventricular rhythm disorders]

The intravenous form of the Soviet anti-arrhythmic pharmaceutical ethacizine has been studied clinically. The pharmaceutical was administered to 30 patients with ventricular rhythm disorders during 3 to 15 minutes, at an average dose of 0.63 mg per 1 kg body weight, under the Holter monitor control. On the average the effect became apparent 6.5 min, after the injection and lasted on the average 149 +/- 15 min. Etacizine was effective in 77% of cases. It was established that there was no pronounced negative effect on the heart rate and the arterial pressure. Uzineg the tetrapolar rheography method it was shown that there was no pronounced negative effect on the central hemodynamics. The observation was made that etacizine induced a moderate decrease of the conductivity in atria AV-system and ventricles. Etacisin could be successfully used for rapid suppression of the ventricle rhythm disorders in various forms of coronary disease of the heart.

[Effect of a diethylamino analog of ethmozine on the force of contraction and action potential of the guinea pig myocardium]

Ethacizine applied in the concentration range between 1 X 10(-7) and 1 X 10(-5) g/ml decreased the rate of action potential growth (Vmax) of the mammal myocardium. Inhibition of the Vmax was accompanied by the diminution of the force of contraction which involved two phases. Ethacizine also decreased the overshoot of slow response action potential with the time constant similar to that in the first rapid phase of force reduction. It is assumed that the first rapid phase occurred due to the blockade of the slow calcium channels, while the second slow phase resulted from the inhibition of Na--Ca exchange because of the decrease of intracellular Na+ concentration after the blockade of the fast sodium channels by ethacizine.

[Effect of diethylamine analog of ethmozine on parameters of fast sodium current in normal and depolarized myocardial fibers]

The effect of a diethylamine analog of ethmozine (DAAE) on fast sodium current of normal and depolarized frog atrial trabeculae was studied by means of the double sucrose gap technique. The depolarization of the fibers was produced both by increasing extracellular potassium concentration up to 8 +/- 9 mM and by current passing. The resting potential of normal fibers was within the range of 75-80 mV, and the depolarized one was within 65 +/- 60 mV. DAAE (8 X 10(-7) g/ml) reduced sodium conductivity, slowed inactivation and reactivation of fast sodium current and shifted the steady-state activation curve (h infinity) to a more negative potential, but the steady-state activation curve (m infinity) to a more positive potential. All these effects were expressed more considerably in the depolarized fibers. The depressing ability of DAAE is assumed to be due to high concentration of the drug in the membrane owing to its high solubility in lipids. The slowing of sodium reactivation and inactivation shows the existence of a receptor for DAAE linked with a h-gate. Prolonged antiarrhythmic action is accounted for by a very slow recovery of sodium current after the drug superfusion. A stronger effect of DAAE on sodium current in the depolarized fibers is likely to point to its selective action on ischemic tissue.

[Effect of diethylamine analog of ethmozine on parameters of sodium current in isolated rat cardiomyocytes]

Voltage clamp experiments were made on ezymically isolated and internally perfused rat cardiac cells. The effect of a diethylamine analog of ethmozine (DAAE) on sodium current (INa) was tested when the drug was applied inside or outside the cell. It was found that the effect of DAAE (8 X 10(-6) g/ml) on INa was asymmetrical: after DAAE addition outside the cell, the amplitude of INa was effectively suppressed. Thus, 5 minutes after DAAE action the maximal value of INa in a voltage-current relationship was 20% of the control value without significant changes in the kinetics of INa. When the DAAE was added inside the cell preferentially, the inactivation time constant was increased without significant changes in the amplitude of the maximal INa. The same results were obtained with pronase (1 mg/ml) added inside the cell. It was supposed that as compared to ethmozine, the DAAE possesses a supplementary binding site on the cardiac cell membrane possibly linked to the structures responsible for inactivation processes.

[Effect of the diethylamine analog of etmozin and cesium chloride on the idioventricular rhythm in dogs in the late stages of experimental myocardial infarct]

Atrioventricular block was produced by infusion of 0.1-0.2 ml of 40% formaline into the A-V node or the bundle of His. Effect of diethylamine analog of etmozin (1 mg/kg) and cesium chloride (20 mg/kg) on the idioventricular rate was studied in control and experimental dogs 24 hours after the occlusion of the coronary artery. It was shown that cesium ions inhibit the idioventricular rate in the normal canine heart (from 49.9 +/- 3.8 to 6.9 +/- 4.5/min; p less than 0.001, n = 7) and have no influence on the ectopic ventricular rate in the late stage of myocardial infarction. On the contrary, diethylamine analog of etmozin has no significant effect on normal ventricular automatism and considerably reduces the ectopic ventricular rate (from 111.5 +/- 7.2 to 23 +/- 15.6/min; p less than 0.001, n = 8). The evidence points to the difference between the ionic mechanisms determining the normal specialized conduction system automatism and the ionic mechanisms which are responsible for the enhanced automatism in the late stage of experimental myocardial infarction.