Electrophysiology and pharmacology of cardiac arrhythmias. IX. Cardiac electrophysiologic effects of beta adrenergic receptor stimulation and blockade. Part B

Association of Arrhythmia in Patients with Cervical Spondylosis: A Nationwide Population-Based Cohort Study

BACKGROUND

Sympathetic activity, including cervical ganglia, is involved in the development of cardiac arrhythmias.

OBJECTIVE

The present study investigated the association between cervical spondylosis and arrhythmia, which has never been reported before.

METHODS

Patients newly diagnosed with cervical spondylosis (CS) with an index date between 2000 and 2011 were identified from the National Health Insurance Research Database. We performed a 1:1 case-control matched analysis. Cases were matched to controls according to their estimated propensity scores, based on demographics and existing risk factors. Cox proportional hazard models were applied to assess the association between CS and arrhythmia.

RESULTS

The CS cohort comprised 22,236 patients (males, 42.6%; mean age, 54.4 years) and non-CS cohort comprised 22,236 matched controls. There were 1441 events of arrhythmia in CS cohort and 537 events of arrhythmia in non-CS cohort, which 252 and 127 events of atrial fibrillation in CS and non-CS cohort, 33 and 12 events of ventricular tachycardia in CS cohort and non-CS cohort, 78 and 35 events of supraventricular tachycardia in CS cohort and non-CS cohort. The CS cohort had an arrhythmia incidence of 11.1 per 1000 person-years and a higher risk [adjusted hazard ratio (aHR) = 3.10, 95% confidence interval (CI) = 2.80⁻3.42] of arrhythmia, 2.54-fold aHR of ventricular tachycardia (95% CI = 1.70⁻3.79), and 2.22-fold aHR of atrial fibrillation (95% CI = 1.79⁻2.76) compared with non-CS cohort.

CONCLUSIONS

Cervical spondylosis is associated with a higher risk of arrhythmia.

Compartmentalized regulations of ion channels in the heart

The rate and force of contraction of the heart are precisely controlled by compartmentalized regulation of cardiac ion channels which determine electrical activities. It is known that modulation of cardiac ion channels, which is caused by drug administration, sympathetic nervous system stimulation and gender difference, can increase risks of lethal arrhythmias in carriers of inherited disease mutations. These modulations are thought to also be involved in common cardiac arrhythmias. Because many signaling molecules are localized within single cells, an understanding of the molecular basis of compartmentalized regulation of cardiac channels is a key for understanding and treating the lethal arrhythmias. In this review, I will discuss molecular mechanisms of compartmentalized regulation of cardiac ion channels via drugs, cAMP and sex hormones.

Cardiac electrophysiologic effects of norepinephrine in human beings

BACKGROUND

The electrophysiologic effects of norepinephrine (NE) in human beings have not been previously described.

METHODS

The electrophysiologic effects of NE infused at a rate of 25 ng/kg/min were determined in 21 patients with a mean age of 41 +/- 11 years and without structural heart disease who underwent an electrophysiology procedure. In a subgroup of 10 patients electrophysiologic parameters were measured at baseline, after the infusion of NE, and after administration of beta-blockade while in continuous NE infusion.

RESULTS

The baseline NE plasma concentration of 298 +/- 153 pg/ml increased to 708 +/- 419 pg/ml after the infusion of NE. NE significantly increased the mean blood pressure, sinus cycle length, corrected sinus node recovery time, ventriculoatrial block cycle length, and the atrial and ventricular effective refractory periods. In a subset of 10 patients 0.2 mg/kg propranolol administered during continued infusion of NE resulted in a further increase in sinus cycle length, atrial-His interval, and ventricular refractoriness.

CONCLUSION

A physiologic elevation in the plasma NE concentration results in a depression of sinus node function and atrioventricular conduction and in prolongation of atrial and ventricular refractoriness. Some of NE's effects are partially offset by beta-adrenergic stimulation.

Adjuvant metoprolol improves efficacy of class I antiarrhythmic drugs in patients with inducible sustained monomorphic ventricular tachycardia

Inducible ventricular tachycardia frequently persists despite solitary class I antiarrhythmic drug therapy. To determine the effect of metoprolol as adjuvant therapy, 19 patients with clinical ventricular tachycardia with baseline inducible sustained monomorphic ventricular tachycardia and persistently inducible ventricular tachycardia despite class I drugs were evaluated. Eight of 19 patients (42%) became noninducible when metoprolol was added to class I drug therapy. Sixteen of 19 patients (84%) were harder to induce or noninducible on a regimen of adjuvant metoprolol therapy. In evaluating the clinical characteristics of the 19 patients, no significant differences were found between patients who were persistently inducible and those rendered noninducible. In evaluating the electrophysiologic characteristics, the group eventually rendered noninducible had a significantly shorter baseline induced cycle length (259 +/- 27 vs 305 +/- 53 msec). Combination class I drug and metoprolol therapy significantly lengthened the ventricular effective refractory period in both groups compared with baseline. The long-term follow-up was excellent in all patients remaining on metoprolol in the noninducible group. Therefore adjuvant metoprolol therapy creates a significant improvement in a number of patients with persistently inducible ventricular tachycardia despite class I drug therapy.

Persistent functional atrioventricular block in two patients with prolonged QT intervals: elucidation of the mechanism of block

This article describes two infants with prolonged QT interval and intermittent second-degree atrioventricular block. An asymptomatic 14-month-old child with persistent 2:1 atrioventricular conduction since birth underwent electrophysiology study including measurements with a contact monophasic action potential catheter. During 2:1 conduction, atrioventricular block occurred distal to the site of the His-bundle recording. Monophasic action potential duration was closely related to prior RR intervals. Single premature atrial or ventricular depolarizations during 1:1 conduction followed by a pause, lead to monophasic action potential prolongation and subsequent 2:1 atrioventricular conduction, which was perpetuated by the resulting long RR intervals. Paired premature ventricular contractions or short bursts of ventricular pacing elicited monophasic action potential shortening and subsequent 1:1 atrioventricular conduction that was perpetuated by the resulting short RR intervals. A second infant presented at birth with a prolonged QT interval, ventricular tachycardia, and episodes of second-degree atrioventricular block with persistent 2:1 atrioventricular conduction. The atrioventricular block was repeatedly elicited by single premature ventricular contractions and terminated by ventricular couplets. We conclude that the atrioventricular block in both patients is functional in nature and results from the interrelationships between ventricular rate, action potential duration, and His-Purkinje system refractoriness.

Antiarrhythmic efficacy of solitary beta-adrenergic blockade for patients with sustained ventricular tachyarrhythmias

To assess the efficacy and predictability of solitary beta-adrenergic blocker (BB) therapy for ventricular tachyarrhythmia (VT), 30 patients (16 men and 14 women) with a mean age of 55 years, who initially had sustained ventricular tachycardia (70%) or ventricular fibrillation (30%), were studied. Results of baseline arrhythmia tests showed VT on ECG monitoring in 57% of the patients, during exercise in 50%, induced by programmed stimulation in 69%, increasing to 86% during isoproterenol. BB therapy prevented inducible VT during programmed stimulation in 37% of the patients, prevented VT on ECG monitoring in 54%, and prevented VT during exercise in 83%. Long-term BB therapy was given to 24 of 30 patients, whereas six other patients with hemodynamically unstable VT during BB therapy received other long-term treatment. During a mean follow-up of 824 days, 6 of 24 patients had recurrent VT. BB therapy was discontinued in two patients because of side effects. Long-term success was predicted by left ventricular ejection fraction greater than 45%, absence of coronary disease, and age less than 60 years (all p less than 0.02). Neither suppression of arrhythmia during exercise testing, nor results of programmed stimulation or ECG monitoring were predictive of outcome. Thus beta-adrenergic blockers can be effective as solitary antiarrhythmic therapy in selected patients with VT.

Differential sensitivity of sinus node, atrioventricular node, atrium, and ventricle to propranolol

The purpose of this study was to test the hypothesis that less propranolol was required to block stellate-induced shortening of atrial and ventricular effective refractory periods (ERPs) than was required to prevent stellate-induced shortening of the spontaneous sinus nodal cycle length and atrioventricular (AV) nodal conduction time. Studies were performed in open-chest, neurally decentralized dogs anesthetized with secobarbital. We determined the dose of propranolol (propranolol dose-response curves) required to block the effects of 1 Hz, 2 Hz, and 4 Hz bilateral ansae subclaviae stimulation on sinus nodal automaticity, AV nodal conduction, and atrial and ventricular ERPs. We found that propranolol at a dose of 0.5 mg/kg eliminated ansae subclaviae-induced shortening of atrial and ventricular ERPs, whereas sinus nodal cycle length and AV nodal conduction time still shortened. These data indicate a differential sensitivity of the sinus and AV nodes compared with atrial and ventricular myocardium to the beta-adrenergic receptor-blocking effects of propranolol in response to efferent sympathetic neural stimulation. Clinical implications are that it might be possible to treat sympathetically mediated ventricular arrhythmias with doses of propranolol that still preserve sinus and AV nodal responses.

Parasympathetic and sympathetic alterations of Mobitz type II heart block

This study examined the effects of changes in parasympathetic and sympathetic tone on the cycle length at which Mobitz type II second degree atrioventricular (AV) block occurred. Four patients who had electrocardiographic evidence of type II AV block and confirmation of block in the His-Purkinje system during electrophysiologic study were evaluated. These patients received intravenous atropine (1.0 to 2.4 mg), propranolol (0.15 mg/kg body weight) or isoproterenol (1 and 2 micrograms/min) alone or in combination. In two of three patients receiving propranolol, the atrial pacing cycle length at which 1:1 His-Purkinje conduction occurred was prolonged relative to control (from 360 to 470 ms and 440 to 590 ms, respectively). In contrast, atropine in the presence of beta-adrenergic blockade shortened the cycle length at which 1:1 His-Purkinje conduction occurred in three of four patients receiving the drug (470 to 390, 630 to 570 and 590 to 560 ms, respectively). Isoproterenol also improved His-Purkinje conduction in the one patient receiving this drug. No agent affected the duration of the HV interval during spontaneous sinus rhythm or right atrial pacing. Thus, drugs that alter autonomic tone influence abnormal His-Purkinje conduction minimally during sinus rhythm but, importantly, may modulate the atrial pacing cycle length at which type II AV block occurs.

Metoprolol in acute myocardial infarction reduces ventricular arrhythmias both in the early stage and after the acute event

Fifty three of the 5778 patients included in the MIAMI (Metoprolol in Acute Myocardial Infarction) trial were investigated with long-term ECG recordings in order to evaluate the effect of acute beta-blockade on premature ventricular complexes in and after acute myocardial infarction. Twenty five patients were given placebo and 28 metoprolol in a double-blind randomized fashion for 15 days. After this period the patients were put on open beta-blockade without breaking individual study codes. The mean number of premature ventricular complexes during the inclusion day (day 0) was the same in the two groups. The median numbers were also similar in the two groups: 190 and 154 in the placebo and metoprolol groups, respectively. Metoprolol significantly reduced the median number of premature ventricular complexes in the randomized period. The median numbers on days 1, 2 and 15 were 146, 101, 84 in the placebo group and 73, 59 and 10 in the metoprolol group, respectively (P less than 0.05). Also during the further follow-up, when investigated 1, 3 and 6 months after the infarction, the median number of premature ventricular complexes was lower in the metoprolol group (74, 257, 142 in the placebo group and 7, 5 and 11 in the metoprolol group, P less than 0.05). This indicates that metoprolol treatment in the acute phase of myocardial infarction reduces ventricular arrhythmias both in the early stage and also after the acute event.

Autonomic control of ventricular tachycardia: direct effects of beta-adrenergic blockade in 24 hour old canine myocardial infarction

The purpose of this study was to determine whether alpha- or beta-adrenergic influences directly modulate the rate of spontaneous ventricular tachycardia occurring 24 hours after left anterior descending coronary artery occlusion. Chloralose-anesthetized, open chest dogs (n = 41) with ventricular tachycardia were studied. The left anterior descending artery was cannulated distally. Neither intracoronary saline solution nor phenylephrine (0.3 to 12 micrograms) changed the rate of ventricular tachycardia; however, isoproterenol (0.01 to 10 micrograms) produced dose-dependent increases in the rate. In six dogs, metoprolol, 5 mg given intravenously, slowed ventricular tachycardia from 174 +/- 10 (mean +/- SE) to 140 +/- 17 beats/min (p less than 0.05). This was accompanied by decreases in mean arterial pressure from 106 +/- 7 to 95 +/- 8 mm Hg, cardiac output from 2.6 +/- 0.3 to 1.6 +/- 0.3 liters/min and prolongation of atrioventricular conduction from 134 +/- 10 to 189 +/- 29 ms (all p less than 0.05) during atrial pacing at a cycle length of 300 ms. In 10 dogs, metoprolol (0.5 mg) given intracoronary, a dose that shifted the isoproterenol dose-response curve to the right, slowed ventricular tachycardia from 174 +/- 7.2 to 140 +/- 9.7 beats/min (p less than 0.05) without hemodynamic changes. Additional metoprolol (4.5 mg) given intravenously produced hemodynamic alterations, but ventricular tachycardia did not slow further. Therefore, beta- but not alpha-adrenergic influences control the rate of ventricular tachycardia occurring 24 hours after left anterior descending coronary artery occlusion. Furthermore, beta-adrenergic blockade slows ventricular tachycardia solely by a direct electrophysiologic effect on the tachycardia foci and not indirectly as a result of hemodynamic effects.

Electrophysiology of esmolol

The electrophysiologic characteristics of esmolol were studied in 14 patients. Ten men and 4 women, mean age 57 years, were electrophysiologically evaluated at baseline, and also at 4 to 8 minutes after the administration of a maintenance infusion of esmolol. Plasma samples for esmolol blood levels were drawn at 10 minutes of the maintenance infusion, at the end of the maintenance infusion and 30 minutes after the maintenance infusion was discontinued. Results of this study showed that esmolol has typical beta-blocker electrophysiologic effects. Its major action was on sinus node function; it prolonged this basic sinus cycle length but had no significant effect on intrinsic automaticity as reflected by the corrected sinus node recovery time and sinoatrial conduction. Direct effects on atrioventricular (AV) nodal function were reflected by effects on AV nodal conduction and refractoriness. There was no direct effect on atrial function and, as expected, no effect on His-Purkinje or ventricular function. The intensity of esmolol's electrophysiologic effects on sinus node function, AV nodal conduction and AH interval is comparable to those of other beta blockers.

Reduction of ventricular arrhythmias by atenolol

The effects of atenolol on ventricular arrhythmias were evaluated in 25 men with significant ventricular ectopy. The patients received 2 weeks each of placebo, 50, 100, and 200 mg of oral atenolol. Efficacy was determined by weekly 24-hour Holter monitors. In 20 patients who completed the protocol, the frequency of total ventricular ectopic beats, ectopic couplets, and ventricular tachycardia was significantly decreased after treatment. The complexity of ventricular ectopy was also decreased as measured by the Lown grade and the proportion of hours in which multiform ectopic beats were present. A therapeutic response, defined as the minimum percentage reduction in ventricular arrhythmias to demonstrate an effect due to atenolol rather than spontaneous variation, was achieved in up to 70% of patients for total number of ectopic beats, 75% for ectopic couplets, and 73% for ventricular tachycardia beats. The results show that oral atenolol is an effective agent for the treatment for ventricular arrhythmias.

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.

Mechanism of antiarrhythmic action of beta-blocking agents

We investigated the antiarrhythmic effect of beta-blocking agents. Using 35 anesthetized dogs, the chest was opened and the left anterior descending coronary artery (LAD) was ligated for 30 min and the ventricular multiple response threshold (VMRT) was observed in the time course. The dogs were divided into five groups premedicated intravenously ten min before LAD ligation with either isotonic saline (the control group), D,L-propranolol (0.5 mg/kg), D-propranolol (0.5 mg/kg), D,L-pindolol (0.1 mg/kg), or D,L-acebutolol (2.5 mg/kg). Thirty min after ligation, myocardial mitochondria were prepared from the ischemic and the non-ischemic areas, and then the content of mitochondrial long-chain acyl-CoA and Ca++-binding activity were measured. The value of VMRT 1.59 +/- 0.21 mA before ligation decreased to 0.99 +/- 0.13 mA 30 min after ligation. Content of acyl-CoA in mitochondria from the ischemic area increased significantly compared to those from the non-ischemic area. Mitochondrial Ca++-binding activity in the ischemic area decreased significantly compared to that in the non-ischemic area. Each administration of three beta-blocking agents prevented the decreases in VMRT and Ca++-binding activity and excessive accumulation of acyl-CoA; D-propranolol had no effect. These results suggest that the antiarrhythmic action of beta-blocking agents is based, at least in part, on the protection from decrease in Ca++-binding activity due to mitochondrial dysfunction induced by the excessive accumulation of long-chain acyl-CoA in mitochondria.

Effect of alpha-adrenergic receptor stimulation on ventricular electrical properties in the normal canine heart

We examined the effects of alpha-adrenergic stimulation on ventricular excitability, refractoriness, and vulnerability to fibrillation. Methoxamine or phenylephrine was infused in five dogs each before and after aortic arch and carotid sinus baroreceptor denervation, in doses which increased mean arterial blood pressure by 20 to 30 mm Hg. Methoxamine or phenylephrine caused an increase in the ventricular fibrillation threshold (VFT) (from 27% to 41%) and in the repetitive extrasystole threshold (RET) (from 28% to 39%). This effect was abolished by baroreceptor denervation. Neither drug altered mid-diastolic threshold or effective refractory period duration either before or after denervation. We conclude that alpha-receptor activation exerts no direct effect on ventricular excitability or refractoriness in the normal intact heart.

The antiarrhythmic effects of controlled release disopyramide phosphate and long acting propranolol in patients with ventricular arrhythmias

The antiarrhythmic effect of slow-release disopyramide phosphate (DR) 300 mg twice daily and of long-acting propranolol (PR) 1 X 160 mg daily was compared in a randomized cross-over study in patients with premature ventricular beats (PVB). 12 patients with PVB (Lown Classes II-V) were given: placebo I for 3 days, DR or PR for 7 days, placebo II for 5 days and PR or DR for 7 days. During each study phase Holter-ECG recordings were taken over a period of 24 h. With DR 6 patients showed a positive qualitative effect, improving by at least one Lown class, whereas only 2 patients did so with PR. With DR reduction of PVB greater than 80% occurred in 7 patients, and with PR in 2 patients. In all patients with any reduction in PVB, the median decrease was 85% with DR and 59% with PR. The overall results suggest that the antiarrhythmic effect of disopyramide phosphate in the slow-release preparation is at least satisfactory and comparable to that of disopyramide phosphate in the standard capsule formulation given in the usual and more complicated regime of four divided doses. The antiarrhythmic effect of PR in the recommended dose as given was not convincing.

Pharmacologic treatment of cardiac arrhythmias: 25 years of progress

This review of practical and theoretical advances in antiarrhythmic drug therapy consists of four parts. Part 1, on clinical applications, compares the approaches to treatment 25 years ago with those of today, examines the current status of antiarrhythmic drugs used 25 years ago, reports on drugs approved for clinical use during the past 25 years, reviews new experimental drugs and suggests an approach to classification of antiarrhythmic drugs. Part 2 summarizes the contributions of cellular electrophysiology to the understanding of drug action, with emphasis on the drug-induced block of the voltage- and time-dependent properties of the rapid sodium channel. The subsequent section contains a brief discussion of the impact made by the new knowledge and the new diagnostic technology on the contemporary practices. The main conclusions are 1) that the more rational approach to treatment has benefited proportionately more patients with supraventricular than with ventricular arrhythmias, and 2) that new advances have made it possible to design successful treatments for certain patients with problems that could not be resolved in the past.

Digoxin and propranolol in the prophylaxis of supraventricular tachydysrhythmias after coronary artery bypass surgery

Supraventricular tachydysrhythmia is a bothersome and potentially harmful occurrence after coronary artery bypass graft operation (CABG). Use of digoxin prophylaxis preoperatively has yielded conflicting results in lowering the incidence of supraventricular tachydysrhythmia. In this study, three groups of patients were formed. Group 1 served as the control; no prophylactic medication was given. Group 2 was given digoxin prophylaxis beginning immediately after operation. Group 3 received digoxin postoperatively as did Group 2, plus orally administered propranolol beginning on postoperative day 2. No difference in the incidence of supraventricular tachydysrhythmia was found between Groups 1 and 2 (28.2% versus 28.9%). However, the incidence in Group 3 was 2.2%, and this represented a statistically significant difference (p less than 0.005) compared with either Group or 2. The combined use of digoxin and propranolol postoperatively significantly reduced the incidence of supraventricular tachydysrhythmia after CABG.

[Electrophysiological classification of newer antiarrhythmic drugs (author's transl)]

Newer antiarrhythmic drugs are tentatively classified on the basis of their influence on the transmembrane action potential, the fast sodium inward current and its kinetics, and the slow inward current which is primarily carried by calcium ions. Disopyramide is probably a quinidine-like antiarrhythmic drug, while the effects of aprindine, lorcainide, and tocainide resemble those of lidocaine. Mexiletine and propafenon cannot be classified definitely on the basis of the hitherto available electrophysiological data. Besides their effects on the fast inward current these substances may have additional calcium antagonistic properties.

Clinical electrophysiologic effects of encainide, a newly developed antiarrhythmic agent

Encainide is a newly developed antiarrhythmic agent. With the use of intracardiac electrophysiologic techniques, its effects on the cardiac conduction system were examined in 10 patients with coronary artery disease. Five patients received 0.6 and five received 0.9 mg/kg body weight of encainide intravenously over 15 minutes. Plasma concentration, heart rate, blood pressure and conduction intervals (A-H, H-V, QRS and Q-T) were measured before, during and after encainide infusion. In addition, sinus nodal recovery time, Wenckebach cycle length, and atrial, atrioventricular (A-V) nodal and right ventricular refractory periods were measured before and after encainide infusion. The average peak plasma concentration was 0.49 +/- 0.35 microgram/ml (mean +/- standard error of the mean). Encainide significantly prologned H-V and QRS intervals in all patients by an average of 31 +/- 7 and 18 +/- 9 percent (standard deviation) (P less than 0.001), respectively. A minimal increase in the Q-T interval was also observed after encainide infusion (2 +/- 9 percent, P less than 0.01), but no significant changes were noted in heart rate, blood pressure, A-H interval, corrected sinus noal recovery time, Wenckebach cycle length or refractory periods of the atrium, A-V node or right ventricle. It is concluded that encainide significantly prolongs conduction in the His-Purkinje system without affecting conduction or refractoriness of other parts of the cardiac conduction system in man.

Canine electrophysiology of encainide, a new antiarrhythmic drug

Encainide, a new benzanilide derivative with high potency and a good therapeutic/toxic ratio, was evaluated with the use of standard His bundle recording techniques to determine its effects on the cardiac conduction system in closed chest animals. Twenty mongrel dogs weighing 18 to 29 kg were anesthetized with 4 percent chloralose and classified into groups: group 1, a control group and groups 2, 3, and 4, which were given 0.3, 0.9 and 2.7 mg/kg body weight, respectively, of encainide in an intravenous infusion over a 15 minute period. Plasma concentration, blood pressure, surface electrocardiogram and atrial and His bundle electrograms were recorded before, during and after drug infusion for a total of 120 minutes. Heart rate, A-H and H-V intervals, the QRS complex and Q-Tc interval were measured every 5 minutes during sinus rhythm and with constant atrial pacing. In addition, sinus nodal recovery time and atrial, atrioventricular (A-V) nodal and left ventricular refractory periods were measured before and immediately after infusion and every 30 minutes for 2 hours. Peak plasma concentration averaged 450 ng/ml in group 2, 1,300 ng/ml in group 3 and 4,000 ng/ml in group 4. Blood pressure was not altered at any dose level throughout the study. The QRS complex and H-V interval were significantly prolonged (P less than 0.005) at doses of 0.9 mg/kg and greater. These effects correlated well with plasma concentration. There was no significant change in heart rate, corrected sinus nodal recovery time, A-H interval, Q-Tc interval atrial, A-V nodal or left ventricular refractory period. It is concluded that, unlike other antiarrhythmic agents, encainide prolongs His-Purkinje system conduction without significantly affecting conduction or refractoriness of other parts of the cardiac conduction system in animals.

Cardiac electrophysiologic action of carteolol hydrochloride (OPC-1085), a new beta-adrenergic blocking agent

Cardiac electrophysiologic action of a new beta-adrenergic blocking agent carteolol hydrochloride, or OPC-1085, was studied in either isolated, perfused rabbit hearts or in atrial, ventricular or Purkinje fibers of dogs and rabbits superfused in the tissue bath. Transmembrane potentials were recorded with intracellular microelectrodes and atrioventricular conduction was studied by recording a His bundle electrogram. OPC-1085 at a concentration of 0.1 mg/L shortened the sinus node recovery time, while propranolol at a comparable concentration prolonged it. Isoproterenol-enhanced canine Purkinje automaticity was more markedly depressed by OPC-1085 than by propranolol. In rabbit atrial and ventricular muscle, OPC-1085 up to the concentration of 2 mg/L did not alter the action potential characteristics but tended to shorten the conduction time. At 20 mg/L, OPC-1085 significantly decreased the maximal rate of depolarization and maximal following frequency, and prolonged the action potential duration and conduction time in non-reserpinized as well as reserpinized preparations. On atrioventricular conduction, 0.1 mg/l to 5mg/L of this drug prolonged the St-A and H-V intervals but tended to shorten the A-H interval. All these intervals were prolonged at 20 mg/L. The action potential duration of canine Purkinje-ventricular block developed at higher frequencies of stimulation. In view of the clinical dosage levels, it is sugg ested that the antiarrhythmic effects of OPC-1085 depend predominantly on its beta blocking action. At higher concentrations, OPC-1085 may exert some beta stimulating action, whereas still higher and possibly toxic concentrations could depress conduction through a direct membrane effect.

Metoprolol--a new cardioselective beta-adrenoceptor blocking agent for treatment of tachyarrhythmias

The antiarrhythmic effect of the cardioselective beta-adrenoceptor blocking agent metoprolol, given intravenously, was studied in 44 patients with various tachyarrhythmias, including patients with congestive heart failure and signs of digitalis intoxication. All patients with atrial tachycardia (12 cases) reverted to normal sinus rhythm. In 3 out of 18 patients with atrial fibrillation, sinus rhythm was restored, and in the others there was a significant reduction in ventricular rate. In 6 of 10 patients with ventricular ectopic beats, and 1 of 2 patients with ventricular tachycardia, the ectopic rhythm was abolished. The drug was well tolerated, without any significant changes in blood pressure, even by patients with signs of digitalis intoxication and varying degrees of pulmonary or peripheral circulatory congestion. Metoprolol is of clinical value for treatment of tachyarrhythmias, especially those of supraventricular origin.

Clinical efficacy of amiodarone as an antiarrhythmic agent

Amiodarone, administered orally in doses of 200 to 600 mg/day, was remarkably effective in the treatment and prevention of a wide variety of atrial and ventricular arrhythmias. Total suppression and control was provided in 98 (92.4 percent) of 106 patients with supraventricular arrhythmias and in 119 (82 percent) of 145 patients with ventricular arrhythmias. The rates of total control of the arrhythmia were: 96.6 percent in 30 patients with recurrent atrial flutter or fibrillation, 96.6 percent in 59 patients with repetitive supraventricular tachycardia, 100 percent in 27 patients with Wolff-Parkinson-White syndrome and 77.2 percent in 44 patients with recurrent ventricular tachycardia unsuccessfully treated with other drugs. Excellent results were obtained in 6 to 8 patients with repetitive ventricular tachycardia and ventricular fibrillation related to postinfarction ventricular aneurysm and in 12 of 14 patients with ventricular extrasystoles and ventricular tachycardia related to Chagasic myocarditis. Amiodarone proved safe in patients with severe congestive heart failure and severe myocardial damage. Its clinical efficacy was related to its electrophysiologic properties and to two unique properties: its wide safety margin and its cumulative effect. The latter liberates patients from a rigid hourly schedule and provides for continuous antiarrhythmic control, days and even weeks after treatment is discontinued.

Present state of alpha and beta adrenergic drugs. II. The adrenergic blocking agents

There are selective blocking agents (antagonists) for alpha receptors and beta receptors. These blocking agents prevent the response to injected agonists and neurogenically released norepinephrine. The principal cardiovascular response to alpha blockade is postural hypotension with reflexly induced cardiac stimulation. If neurogenic vasoconstriction is present, this will be removed. The principal cardiovascular response to beta blockade is bradycardia. If fast arrhythmias are present, these will be slowed. Beta blockade tends to increase peripheral resistance. Unless circulation is previously impaired this vasoconstrictive effect is insignificant.