His bundle electrocardiography in digitalis-induced "atrioventricular junctional" Wenckebach periods with irregular H-H intervals

His bundle electrograms were recorded during catheter insertion for prophylactic demand pacing in two patients with accelerated or nonaccelerated "atrioventricular (A-V) junctional" rhythms associated with A-V junctional Wenckebach periods. This appears to be the first published report of so-called A-V junctional Wenckebach periods in which the characteristic irregularities of the H-H intervals were recorded. Patient 1 had an additional area of "complete" anterograde A-V nodal (A-H) block. In Patient 2 the rate of impulse formation was consistent with nonparoxysmal A-V junctional tachycardia. The His bundle recordings were obtained in patients with digitalis toxicity and should be interpreted in the context. The integration of clinical and intracardiac findings with extrapolations from microelectrode and pharmacolic studies and with deductions from the clinical electrocardiograms suggests that the conduction disturbances probably occurred within the A-V node itself (in its AN region). This hypothesis implies that automaticity also originated in the A-V node because the site of impulse formation must have been proximal to the site of the Wenckebach periods. However, conclusive proof of of these postulates will require further studies with refined techniques.

Electrophysiological effects of disopyramide in patients with bundle branch block

Electrophysiological studies were performed in 22 patients with intraventricular conduction delay before and after intravenous infusion of disopyramide (Norpace), 2 mg/kg. Mean control maximal sinus node recovery time (1039 +/- 187 msec), atrioventricular nodal conduction time (113 +/- 28 msec), and atrioventricular nodal effective refractory periods (349 +/- 67 msec) did not change significantly after administration of disopyramide (1073 +/- 284 msec, 112 +/- 31 msec, and 342 +/- 42 msec, respectively). Mean spontaneous cycle length (756 +/- 146 msec) decreased significantly 5 minutes after disopyramide (717 +/- 124 msec) (p less than 0.05), but not after 30 minutes (734 +/- 142 msec). A small but statistically significant (p less than 0.05) increase occurred after disopyramide in the mean atrial effective refractory period (259 +/- 51 to 280 +/- 53 msec), ventricular effective refractory period (253 +/- 23 to 275 +/- 33 msec), as well as the relative refractory period of the ventricular specialized conduction system (six patients) 433 +/- 78 to 479 +/- 62 msec). Although mean control infranodal conduction time (67 +/- 35 msec) increased 5 minutes after disopyramide (79 +/- 41 msec) (p less than 0.001) (18%), no spontaneous episodes of second-degree or third-degree atrioventricular block were observed. In six patients with premature ventricular depolarizations (greater than or equal to 1/min), the arrhythmia was totally abolished in four, markedly reduced in one, and remained unchanged in one. Disopyramide resulted in significant prolongation of infranodal conduction time as well as in atrial and ventricular refractoriness, but nevertheless appears to be safe in patients with bundle branch block.

[Electrophysiological effects of anti-arrhythmia agents in man. Attempt at classification]

The electrophysiological effects of anti-arrhythmic drugs in man may be classified in three groups: -- Group I: comprising drugs whose characteristic action is on the AV node (beta blockers, verapamil, digitalis) The nodal conduction time (A-H interval) and refractory periods are increased. -- Group II: comprising drugs acting on the His-Purkinje system, the AV nodal conduction staying unchanged. This group has two sub-groups. Sub-group A: these drugs delay the His-Prukinje conduction (increased H-V interval). Examples are quinidine, procainamide, disopyramide, ajmaline, chloro-acetyl-ajmaline. In addition these drugs usually increase the atrial refractory periods and those of accessory pathways. Sub-group B: the His-Purkinje conduction is unchanged but the refractory periods are modified: lengthened (bretylium tosylate) or shortened (diphenylhydantoin, lignocaine, mexiletine). -- Group III: which includes amiodarone and aprindine whose effects are mixed: on the one hand AV nodal depression, and on the other, alteration of the His-Purkinje conduction manifested by an increased H-V internal (aprindine) or refractory periods (amiodarone). These preparations also increase the refractory periods of accessory AV pathways and amiodarone increase the refractory periods of the atria. This type of classification could help towards a more rational clinical approach to the use of anti-arrhythmic drugs.

Effects of phenytoin on refractoriness and conduction in the human heart

Using His bundle electrograms and the atrial (A2) and ventricular extrastimulus (V2) techniques, anterograde and retrograde refractory period studies were performed (in 9 and 12 patients, respectively) before and 10 min after intravenous infusion of phenytoin (DPH; mean plasma level, 17.3 micrograms/ml). DPH had no effect on the duration of the QRS complex or the H-V interval of the sinus beats; it had variable but insignificant effects on the sinus rates and the atrial, A-V nodal, and ventricular muscle refractoriness. With the use of the A2 technique, the effective refractory period (ERP) of the His-Purkinje system (HPS) could not be determined in any patient; the relative refractory period (RRP) of the HPS could be determined in 2/9 patients and shortened in both patients after DPH. With the use of the V2 technique, retrograde functional refractory period (FRP) and RRP of the HPS could be determined in all 12 patients and the retrograde ERP of the HPS in 7/12; DPH significantly shortened all these parameters (p less than 0.001, less than 0.001, and less than 0.005, respectively). Functional refractory period of the ventriculo-atrial conduction system (VACS) could be determined in 11/12 patients during control studies (the remaining one patient had complete ventriculo-atrial block). DPH significantly shortened the FRP of the VACS in those (4) patients (Group I) in whom it was determined primarily by the HPS (p less than 0.025), and had variable but insignificant effects on FRP of the VACS in the other seven patients (Group II) in whom it was determined almost exclusively by the A-V node. DPH significantly decreased the retrograde HPS conduction times of the premature impulses (V2H2 intervals) for the same coupling (V1V2) intervals (p less than 0.001). It is concluded that, in the human heart, DPH exerts its most important effects on the HPS where it significantly decreases refractoriness and enhances conduction of the premature impulses. This study also demonstrates that the V2 technique is far superior to the A2 technique for evaluating the effects of drugs on refractoriness and conduction in the HPS.

Electrophysiologic properties of coffee in man

There is no information on the effects of coffee on the human conduction system. His bundle electrograms were obtained in 12 patients before and 20 minutes after the ingestion of coffee containing 150 mg caffeine. Antegrade and retrograde refractory periods were obtained with the extrastimulus method. The effective and functional refractory period of the atrioventricular node decreased after coffee ingestion. This improvement in conduction is probably mediated by a release of catecholamines.

Prolongation of cardiac conduction times by intravenous aprindine in man

The acute electrophysiologic effects of intravenous aprindine were evaluated in 48 patients to assess the effect on conduction times and refractoriness in patients with severe cardiac disease and arrhythmias. The patients had not responded to conventional antiarrhythmic medications or had been unable to tolerate effective doses of conventional medications because of side effects. Eleven patients had an abnormal H-V interval, 9 had prolonged QRS duration and 22 had evidence of severe left ventricular dysfunction. Aprindine prolonged conduction transiently in the atria, the atrioventricular (A-V) node, the His-Purkinje system and the ventricles. The refractory times of the atria, the A-V node and the ventricles increased insignificantly, both functionally and statistically. Atrioventricular block did not develop in any patient, and side effects were minor. Thus, aprindine can be safely administered intravenously (10 to 15 mg/min) to severely ill patients with arrhythmias that are refractory to other medications even in the presence of underlying conduction system and myocardial disease.

Intermittent atrioventricular block: procainamide administration as a provocative test

Twelve patients with clinical features suggesting possible intermittent high degree atrioventricular block were studied. All 12 patients had basic 1:1 atrioventricular conduction but nine had an electrocardiographic pattern of bifascicular distal conduction disease (right bundle branch block with left anterior or posterior hemiblock, or left bundle branch block). Intracardiac conduction was assessed by recording of the His bundle electrocardiogram and atrial pacing techniques, before and 20 minutes after intravenous administration of procainamide, in a dose of up to 10 mg/kg. Before procainamide administration, seven of the 12 patients had a prolonged H-V interval (greater than 55 ms). Procainamide administration lengthened the H-V interval in all 12 patients by 5--40 ms. In five patients, procainamide induced second or third degree AV block below the level of the bundle of His. It was concluded that the administration of procainamide may be a useful provocative test of distal conduction in patients with possible intermittent AV block.

[Electrophysiological study on mexiletine in man with reference to dose-response relation]

The electrophysiological properties of Mexiletine were investigated by endocavitary His Bundle recording and programmed electrical stimulation of the heart in 30 patients. Differing dosage (2, 2.7 and 3.4 mg/kg) were given intravenously in 3 groups of 10 patients. The effects on the length of the sinus cycle, conduction intervals and cardiac refractory periods were observed and the following results obtained : 1. Sinus rhythm increased at all dosages but this effect was much more pronounced with 3.4 mg/kg dosage (--12.8% +/- 2.81% : : % shortening of sinus cycle with respect to the basal cycle +/- SD, p less than 0.005); 2. Atrioventricular nodal conduction time (A-H interval) decreased, the effect being more marked with the larger dose regimes; 3.His-Pirkinje conduction time (H-V interval) unaltered except in 3 cases where it increased by 5 ms after injection of 2.7 mg/kg; 4. Relative refractory period of His-Parkinje system shortened, this effect also being more pronounced with the larger doses ( --3.75 +/- 0.25% :2.7 mg/kg, p less than 0,001; -- 7 +/- 1.46% 3.4 mg/kg, p less than 0.005). In conclusion, the changes observed in the His-Purkinje system after mexiletine were similar to those of Lignocaine and Diphenylhydantoin. The drug also appears to have a marked vagal inhibitory effect as shown by the acceleration of the sinus rhythm and reduced atrioventricular conduction times.

The electrocardiogram in the assessment of the effect of drugs on cardiac arrhythmias

The search for the ideal antiarrhythmic drug continues since none of the available agents offers optimum antiarrhythmic therapy. The continuing search coupled with the interest in the mechanisms of cardiac arrhythmias has led to the development of new techniques for the study of arrhythmias and antiarrhythmic drugs. In this article it is proposed to discuss the electrocardiographic methods used in the assessment of antiarrhythmic drugs. Firstly, to discuss the electrocardiogram in the assessment of the clinical electrophysiological properties of a drug and secondly, the electrocardiogram in the assessment of the value of the drug in the management of cardiac arrhythmias in man.

Effects of digitalis on ventricular myocardial and His-Purkinje refractoriness and reentry in man

The effects of digitalis on retrograde conduction and refractoriness of the His-Purkinje system, ventricular myocardium and reentry within the His-Purkinje system were studied in 17 patients using the ventricular extrastimulus (V2) technique. Studies were performed, before and 30 minutes after intravenous administration of ouabain, 0.01 mg/kg. After treatment with ouabain, there was a significant decrease in the functional refractory period (266 +/- 19 to 254 +/- 18 msec, P less than 0.001), relative refractory period (253 +/- 17 to 240 +/- 16 msec, P less than 0.001) and effective refractory period (242 +/- 23 to 231 +/- 24 msec, P less than 0.005) of the ventricular muscle. In contrast, there was no significant change in retrograde His-Purkinje conduction and refractoriness. The phenomenon of reentry within the His-Purkinje system characterized by the reentrant beat (V3) at critical retrograde conduction delays in the His-Purkinje system (V2-H2) within a narrow range of V1-V2 intervals was seen in 10 of 17 patients. Ouabain increased and shifted to the left the zone of reentry within the His-Purkinje system in 7 of 10 patients (36 +/- 23 to 55 +/- 23 msec, P less than 0.001) and decreased it by 10 to 30 msec in the remaining 3 patients. The critical V2-H2 (186 +/- 29 to 193 +/- 27 msec, difference not significant [NS]) and V1-V2 (299 +/- 30 to 294 +/- 36 msec, NS) intervals for reentry did not significantly change after ouabain. However, the minimal V1-V2 intervals (266 +/- 26 to 253 +/- 25 msec, P less than 0.025) decreased significantly, whereas the maximal V2-H2 intervals (266 +/- 40 to 239 +/- 37 msec, P less than 0.01) increased significantly. Thus, in the intact human heart, digitalis (1) significantly decreased all measures of ventricular myocardial refractoriness, (2) had no significant effect on retrograde conduction and refractoriness of the His-Purkinje system, and (3) widened the zone of reentry within the His-Purkinje system due to shortening of the functional refractory period of the ventricular muscle with attainment of longer V2-H2 delays.

Abolition and modification of reentry within the His-Purkinje system by procainamide in man

The effects of intravenous procainamide infusion of 10--14 mg/kg body weight (i.e., 750 mg) of procainamide (PA) on reentry within the His-Purkinje system (HPS) were studied in 13 patients using His bundle electrograms and ventricular extrastimulus method. PA abolished reentry in eight patients (group 1) and decreased the width of reentry zone in the remaining five (group 2). At comparable S1S2 intervals, the S2H2 intervals after PA were longer than control in all patients. In group 1 patients, after PA, reentry did not occur even at S2H2 intervals that were significantly longer than control critical S2H2 intervals. In two of eight patients in group 1, PA abolished reentry by converting unidirectional block into bidirectional block in the antegrade limb (right bundle) of the reentry circuit. In the remaining six patients reentry was abolished because of consistent retrograde block of S2 impulse at some point between the site of stimulation and the His bundle recording site. In group 2, reentry was initiated after PA at approximately the same S1S2 intervals as in control, but required significantly longer S2H2 intervals; in these patients the zone of reentry was shortened due to increase in effective refractory period of the ventricular muscle. PA significantly increased the functional refractory period of HPS and the effective refractory period of ventricular muscle. The results of this study differ from the previously reported effects of lower concentrations of PA which facilitated reentry within the same circuit. We conclude that the effects of PA on reentry are dose-related and can both facilitate and suppress reentry, depending on critical changes in conduction and refractoriness of the HPS.

Effect of lidocaine on conduction in the ischemic His-Purkinje system of dogs

The effect of lidocaine on His-Purkinje conduction in dogs with ischemic damage to the His bundle was compared with the effect of lidocaine in normal dogs. The anterior septal artery was ligated in 14 dogs, and 30 minutes later atrial pacing was performed to increase residual ischemic damage. Four to 6 days later, His bundle recordings were obtained during sinus rhythm and atrial pacing before and after the administration of lidocaine in a dose of 2 mg/kg and a total dose of 4 mg/kg. His bundle recordings were also obtained in nine control animals beofre and after the administration of lidocaine. Lidocaine significantly increased the H-V time in the animals with ischemic damage during sinus rhythm and at all packing rates. It also resulted in advanced His-Purkinje conduction defects including His bundle block and right bundle branch block in these animals. In contrast, the effect of lidocaine in the normal animals was negligible. It is concluded that lidocaine significantly depresses His-Purkinje conduction in the setting of preexisting ischemic damage. These results suggest that lidocaine may be used as a diagnostic tool to unmask latent His-Purkinje conduction defects due to ischemia.

The effect of phentolamine on intra-Hisian conduction

A His bundle electrogram was obtained in a 70 year old male with syncopal episodes. A split bundle of His deflection was recorded. After the intravenous administration of phentolamine, a marked shortening of the H-H' interval was observed. This signifies an improvement in conduction at the bundle of His level.

Contrast media in coronary arteriography: a review

Much knowledge of coronary artery disease and much of the progress in surgical treatment of coronary artery disease has been directly dependent upon the safety with which coronary arteriography has been performed. This safety depends upon the ease of placing the contrast media in the arteries and on the toxicity of the contrast medium itself. This review deals with contrast media toxicity in coronary arteriography, as distinct from toxicity in angiocardiography and other angiography.

The effect of digitalis on refractoriness of the intact canine His-Purkinje system

The effect of therapeutic doses of digitalis on functional (F), relative (R) and effective (E) refractory periods (RP) of the His-Purkinje system (HPS) was studied in 12 open-chested, innervated adult mongrel dogs (10-20 kg) during control and 15, 30 and 45-60 min after 0.016 mg/kg of intravenous ouabain. To determine the stability of the preparation and to assess time-dependent changes in His-Purkinje refractoriness, another six dogs (Group II) had similar studies, but without drug administration. In all dogs, the His bundle was paced by using the plunge wire technique at a predetermined cycle length (CL) and a premature stimulus (S2) to the His bundle was introduced at decreasing S1 S2 intervals. Following ouabain, in Group I dogs, at the longest Cls tested (458 +/- 125 msec; +/- SD) there was significant increase in the FRP (+4.34%; P less than 0.05), RRP (S2 V2 (+6.57%, P less than 0.05), RRP (Ab) (+6%, P less than 0.05) and ERP (52%, P less than 0.05) of the HPS. These significant changes were generally observed 30 minutes after drug administration. Changes in RPs were of greater magnitude at longer CLs (greater than 400 msec), but insignificant at shorter CLs (less than 400 msec). The H-V interval during sinus rhythm and the S1 V1 interval during His bundle pacing at all CLs did not change after ouabain. In Group II dogs there were no significant change in His-Purkinje refractoriness over 60 minutes. These findings suggest that therapeutic doses of digitalis 1) tend to increase refractoriness within the HPS to a very small degree, 2) have no appreciable effect on His-Purkinje conduction, and 3) affect CL-dependent changes in refractoriness. The His bundle extrastimulus method is useful in studying the HPS in the intact heart.

[Action of the calciumantagonistic compound gallopamile on sinus node, atrioventricular and intraventricular conduction (author's transl)]

The influence of the calciumantagonistic agent Gallopamile (D 600) on cardiac conduction and sinus node function was studied by using His bundle recordings and atrial stimulation in 13 patients with normal sinus rhythm. Intravenous administration of a single dose of 4 mg produced a significant increase in the atrioventricular conduction time by 30 %. On atrial stimulation second degree a-v block occurred at lower stimulation rates in all patients after Gallopamile. The impulse propagation in atrial tissue and within the His-Purkinje system was not affected, even in patients with diseased conduction system. There was an impairment in sinus node automaticity, the sinus node recovery time was increased by 58 % of the control value.

Human Electropharmacology of Tocainide, a lidocaine congener

The electropharmacology of tocainide, an orally active congener of lidocaine, was evaluated in 10 patients with coronary artery disease. Electrophysiologic measurements including sinus nodal recovery time, sinoatrial conduction time, intraatrial conduction time, atrial, atrioventricular (A-V) nodal and ventricular refractory periods and intraventricular conduction time were obtained before and after intravenous infusion of tocainide. At blood levels shown to be effective against ventricular arrhythmias, tocainide produced no statistically significant changes in the electrophysiologic measurements, although occasional marked individual effects were observed. No side effects were observed during these studies. No adverse effects on A-V conduction were observed in patients with an intraventricular conduction disturbance or a prolonged control H-V interval. Thus, plasma tocainide concentrations effective in the therapy of ventricular arrhythmias exert no adverse effects on cardiac electrophysiologic properties in patients with coronary artery disease.

Electrophysiological effects of edrophonium in the innervated and the transplanted denervated human heart

In order to determine the mechanism of action of edrophonium on the cardiac conduction system, we used His bundle recording and pacing techniques to examine the electrophysiological effect of edrophonium in 6 patients undergoing diagnostic evaluation for coronary artery disease and in 9 cardiac transplant recipients who were free of acute graft rejection. After control measures were made of sinus cycle length, conduction intervals, and conduction system refractory periods, edrophonium was administered by constant intravenous infusion, and all electrophysiological measurements were repeated. In the normally innervated patients, edrophonium significantly increased sinus cycle length from 778 +/- 21 ms to 883 +/- 36 ms (P less than 0.01), AH interval from 88 +/- 11 ms to 100 +/- 12 ms (P less than 0.01), and AV nodal functional refractory period from 351 +/- 44 ms to 391 +/- 36 ms (P less than 0.05). In the patients with transplanted hearts, edrophonium had no electrophysiological effect other than increasing the cycle length of the remnant recipient atrium from 722 +/- 21 ms to 798 +/- 31 ms (P less than 0.01). We conclude that the electrophysiological effects of edrophonium in man are mediated primarily through autonomic innervation of the heart.

Serum levels and electrophysiological effects of N-acetlyprocainamide as compared with procainamide in the dog heart in situ

The electrophysiological effects of procainamide and its major metabolite N-acetylprocainamide were tested and compared on the heart of the anaesthetized dog by means of His bundle electrography and programmed electrical stimulation. Both drugs exerted a negative chromotropic effect. They also increased intra-atrial and intraventricular conduction times; procainamide was, however, the more potent of the two drugs. In contrast to procainamide, N-caetylprocainamide did not increase His-Purkinje and atrioventricular nodal conduction times, and at the lowest dose employed, atrioventricular nodal conduction times were decreased during atrial pacing. Both drugs increased the functional and effective refractory period of the right atrium and ventricle. N-acetylprocainamide increased the functional refractory period of the atrioventricular node, but to a lesser extent than procainamide.

[Automatic activity of the pacemaker cells of the atrioventricular valves under the action of parasympathetic and sympathetic mediators]

Effects of neorpinephrine, epinephrine, and acetylcholine 4.5.10(-7) M--2.9.10(-6)M on the automatic activity of the pace-maker cells of the rabbit atrioventricular valves were studied. The sympathetic mediators accelerated spontaneous beating by increasing the rate of slow diastolic depolarization or by the inducing additional subthreshold potentials converted in action potentials. Acetylcholine (1.1.10(-6)M) reduced the rate of the spontaneous beating and in concentrations 2.7.10(-6)M eliminated automatic activity either by suppression of AP when subthreshold potentials gradually disappeared or by gradual decrement of AP rate and amplitude. Simultaneous application of equal doses of acetylcholine and sympathetic mediators revealed a predominant effect of acetylcholine as well as intensification of the acetylcholine effect under the influence of sympathetic mediators. Sympathetic-parasympathetic interactions can be explained by their influence on permeability of membrane of the pace-maker cells through the slow Na-Ca channel.

Cadmium feeding: apparent depression of atrioventricular-his-Purkinje conduction system

Male rats were exposed to 0, 10 and 130 p.p.m. cadmium administered in 0.5% saline drinking water for 71 days. Biweekly records of ECGs, Hct, body weight and blood levels of cadmium were made. Rats exposed to 130 p.p.m. cadmium showed slower growth rates and declining Hct indicative of acute cadmium poisoning. At the end of the experimental period, carotid artery blood pressures and whole heart cadmium levels were determined. Although no significant blood pressure changes were observed in the experimental groups, the cadmium content of the hearts of the higher dose group was significantly higher than in the hearts of the lower dose group. The PR interval of the ECG was lengthened progressively and to the same extent in both experimental groups with continued cadmium feeding. These experiments offer evidence that the accumulation of even moderate amounts of cadmium will be manifested in marked changes in cardiac conduction without overt signs of cadmium poisoning.

Electrophysiologic evaluation of intravenous verapamil in man

The acute electrophysiological effects of intravenous verapamil (0.15 mg/kg body weight) were studied in 21 subjects with estimated normal impulse formation and conduction. Significant effects were sinus cycle shortening, depression of intranodal conduction and prolongation of AV node refractory periods. Sinus node recovery time, sinoatrial conduction time, atrial refractory periods, infranodal conduction, His--Purkinje system, and bundle branch refractory periods were unchanged. The clinical implications of these properties are discussed.

The effect of mexiletine on the electrophysical properties of the intact human heart

The effect of an intravenous dose of mexiletine, a new anti-arrhythmic agent, on the electrophysiological properties of the intact human heart was studied in ten subjects with no evidence of cardiovascular disease. Mexiletine produced no significant changes in the sinus node recovery time, the corrected sinus node recovery time or in the atrial, atrio-ventricular and ventricular effective refractory periods. In addition mexiletine had no significant effect on proximal atrioventricular conduction. The drug did, however, prolong atrio-ventricular conduction distal to the bundle of His in all ten subjects by an average of 6 msec. This change was statistically significant (P less than 0.01). The drug is recommended to be used with caution in patients with conduction disturbances.

[Action of chloro-acetyl-ajmaline on the electrical properties of the human heart]

The electrophysiological changes caused by the intra-atrial injection of 1.5 mg/kg of chloro-acetyl-ajmaline were studied in 23 patients by recording the His potential and by the stimulustest method. The length of the basal cycle being kept constant by atrial stimulation, measurements were made before and after the injection, on the one hand of the -VA node conduction time (A-H interval) and the infra-His conduction time (H-V interval) and on the other of the refractory periods of the right auricle, A-V node, and the His-Purkinje system. The effective refarctory period of the right ventricle was determined under pace-making of the ventricle. Finally, the variability of the sinus rate was measured. The results were as follows: 1. The sinus cycle was significantly shortened after administration of the drug (p 0.001); 2. The conduction time and refractory periods of the A-V node were not influenced by this substance; 3. The H-V interval was increased in 20 patients by an average of 11 ms (p less than 0.001). The relative refractory period of the His-Purkinje system was reduced in 4 cases out of 7 by 21 ms (p less than 0.05); the effective refractory period in one case showed a reduction of more than 45 ms. These findings will serve as a base line for assessing the anti-arrhythmic action of chloro-acetyl-ajmaline.

[Dromotropic effects of drug combinations. Initial results bearing on a combination of deslanoside and ajmaline]

The electrophysiological effects of the cardiotropic drugs have been studied in man by the agency of endocavitary electrocardiography. The effects of drug combinations, which are often prescribed therapeutically, have been studied less often. The authors report the results of a preliminary study of the combination of deslanoside with ajmaline in 26 patients; its effects were compared with those using each drug separately. This combination seems to have true dromotropic effects; although deslanoside alone, in the doses used, does not modify conduction below the bundle of His, it can still act synergistically with ajmaline at this level. A detailed study of the pharmacological effects as a function of the original status of conduction shows that at the level above the bundle His, the dromotropic action is quantitively less on healthy conducting tissue than on abnormal tissue. The effects of ajmaline on the conduction times below the bundle seem to be similar whether or not there is any conduction defect under basal conditions. The difficulties in obtaining and interpreting such measurements in man are discussed in the hope of arriving at a general protocol for studying drug combinations.

Comparison of the antiarrhythmic activity of quinidine and quinine

A comparison was made between the effects of quinidine and quinine on experimental arrhythmias and on cardiac electrophysiologic parameters. Both drugs raised ventricular fibrillation thresholds, reversed aconitine-induced atrial fibrillation, decreased ouabain-induced abnormal ventricular beats, and increased atrial refractory periods and His-Purkinje conduction time. In contrast, only quinidine antagonized acetylcholine-induced atrial fibrillation. In addition, quinidine increased ventricular fibrillation thresholds and atrial refractory periods for a longer time period than quinine. These observations are discussed in terms of choosing an appropriate model for testing new compounds with suspected quinidine-like activity.

Halothane effects on conductivity of the AV node and His-Purkinje system in the dog

His-bundle electrocardiography was used to evaluate the effect of halothane on AV nodal and His-Purkinje system conduction times in the spontaneously beating dog heart. During artrial pacing at basic heart rates of 120 or 200 beats per minute (bpm), an extrastimulus (cycle length longer or shorter than that of the basic rate) was delivered to test the effect of halothane on several parameters of AV nodal conductivity. Included were the functional refractory period, basal conduction time, and fatigue effect (prolongation of basal conduction time as heart rate was increased from 120 to 200 bpm). Increasing MAC level of halothane (1.25 to 2.75 MAC) prolonged both AV node and His-Purkinje conduction times, yet had little effect on the parameters of nodal conductivity tested for. These effects of halothane could be potentially dangerous in the clinical setting for patients with defective AV conduction. In addition, changes in conduction may be in part responsible for arrhythmias seen during halothane anesthesia.

Clinical evaluation of the enhancement of vagal tone in acute myocardial infarction by edrophonium hydrochloride: effects on ventricular arrhythmias, His bundle electrography, and left ventricular function

Enhanced electrical stability of acutely ischemic myocardium with vagal stimulation and acetylcholinesterase inhibition has been demonstrated experimentally. To extend these findings clinically, within 24 hours of acute myocardial infarction, 11 patients underwent continuous 10 hour Holter monitoring: 2.5 hour control before and after 5 hour constant edrophonium infusion (0.25 to 2.00 mg./minute). Continuous infusion of the agent lowered heart rate 92 to 78 b.p.m. (p less than 0.01). Although mean total ventricular extrasystoles (PVC's) per 5 hours per patient (131) and PVC's per 1,000 beats (4.7) were unchanged (p greater than 0.05), potentially lethal tachyarrhythmias (malignant PVC's: multifocal, R on T, paried, greater than 5 per minute or ventricular tachycardia) were terminated in six of 10 patients by edrophonium. However, serious ventricular arrhythmias continued in three patients and appeared in four despite the agent. Ventricular fibrillation did not occur during the 10 hour period of study. In addition, the patients were evaluated hemodynamically and by His bundle electrograms before and after a 10 mg. bolus of edrophonium prior to the 10 hour constant infusion: heart rate declined (88 to 72 b.p.m., p less than 0.01), while mean arterial pressure (98 mm. Hg), left ventricular filling pressure (14 mm. Hg), cardiac index (2.4 L. per minute per square meter), and stroke work index (36 Gm.m./M.2) were unchanged (p greater than 0.05). The edrophonium bolus prolonged the A-H interval (117 to 135 msec., p less than 0.01) while the H-Q interval was unaltered (48 msec; p greater than 0.05). It is concluded that increased vagal tone with edrophonium did not reduce the over-all presence of premature ventricular contractions in the entire study group; however, the malignant nature of PVCs and ventricular tachycardia appeared to be lessened by the parasympathomimetic agent in certain patients. In addition, no adverse hemodynamic or intraventricular conduction effects were produced by edrophonium administration.

[Pharmacologic complications of the unequal reactivity of constituent elements of the myocardium to the parasympathetic system]

Pharmacological consequences of the unequal reactivity of the myocardial different parts to parasympathic system. The effects of acetylcholine on the various levels of cardiac automatism are studied on open chest dogs with extracorporeal circulation. This drug depresses the sinus node, and more specially the atrio-ventricular node (AV node), but does not alter the His bundle and the Purkinje fibers activity. The sensitivity of the intra-cardiac conduction to acetylcholine also depends upon the considered level of conduction: measured with a bipolar electrode situated upon the His bundle, this one is lowered electively in the atrio-ventricular part. So, the A, V. node can be considered as the elective place of action of acetylcholine on the double point of view of automatism and conduction. Drugs modifying the vagal tonus see their action altered, either in a plus way (antiarrhythmic agents), either in a minus way (cardiac glycosides, halogenated hydrocarbons).

A study of the verapamil-induced changes in conductivity and refractoriness and monophasic action potentials of the dog heart in situ

In the dog heart in situ, verapamil 0.30 mg/kg injected intravenously did not impair intraatrial, His--Purkinje and intraventricular conduction. The monophasic action potential (MAP) derived from the right atrium and ventricle was not altered by the drug. The functional refractory period (FRP) and the effective refractory period (ERP) of the atrium was not changed by verapamil. However, the drug caused a small but statistically significant decrease in the ratio between 50 and 90% repolarization, respectively, and the ERP of the right atrium, i.e. the ERP of the atrium increased in relation to the MAP duration. Verapamil used a marked reduction of the conduction velocity within and a pronounced increase of the AV nodal FRP and ERP. These changes were reversed by a rapid injection of calcium gluconate 40 mg/kg. The sinus node automaticity was not influenced by verapamil.

Electrophysiological effects of mexiletine in man

The electrophysiological effects of intravenous mexiletine in a dose of 200 to 250 mg given over 5 minutes, followed by continuous infusion of 60 to 90 mg per hour, were studied in 5 patients with normal conduction and in 20 patients with a variety of disturbances of impulse formation and conduction, by means of His bundle electrography, atrial pacing, and the extrastimulus method. In all but 2 patients the plasma level was above the lower therapeutic limit. Mexiletine had no consistent effects on sinus frequency and atrial refractoriness. The sinoatrial recovery time changed inconsistently in both directions; however, of the 5 patients in whom an increase was evident, 3 had sinus node dysfunction. In most patients mexiletine increased the AV nodal conduction time at paced atrial rates and shifted the Wenckebach point to a lower atrial rate. The effective refractory period of the AV node was not consistently influenced, while the functional refractory period increased in 12 out of 14 patients. The HV intervals increased by a mean of 11 ms in 8 patients and were unchanged in 17. Both the relative and effective refractory period of the His-Purkinje system increased after mexiletine. Non-cardiac side effects occurred in 7 out of 25 patients, and cardiac side effects, including one serious, in 2. The results indicate that mexiletine shares some electrophysiological properties with procainamide and quinidine, when given to patients with conduction defects, and that the drug should not be used in patients with pre-existing impairment of impulse formation or conduction. It has additional effects on AV nodal conduction which may be of value in the treatment of re-entrant tachycardias involving the AV node.

Intra-His bundle blocks (102 cases)

Some intra-His bundle (intra-HB) blocks escape the routine exploration of the His bundle and are confused with supra- or infrahisian blocks. We believe that a more accurate exploration (recording of His bundle activity successively at the proximal end and the distal end of the His bundle, dynamic tests and drug injection) is needed to detect some concealed cases, mostly paroxysmal intra-HB blocks. In this series of 102 cases of intra-HB blocks, 20% had no criteria of AV block on the surface electrocardiogram, and only 4% had an intact conduction pattern (normal PR interval and normal QRS complexes.) A first degree intra-HB block was found in 35% (15 cases with a normal PR interval), a second degree intra-HB block in 23% and a thired degree intra-HB block in 42% of the cases (unidirectional in 4 cases). Of the 43% having an isolated intra-HB block, most were elderly women with a chronic third degree AV block.

[Comparative study, in the anesthetized dog, of the dromotropic effects of N-propyl ajmaline bitartrate, ajmaline hydrochloride and ajmaline monochloroacetate, by recording of His electrogram]

A-V and intraventricular conduction disturbances induced by 3 different salts of ajmaline: N-propyl ajmaline bitartrate (NPAB), hydrochloride (CHA) and mono chloro-acetate (MCAA), were studied by recording endocavitary His bundle activity in pentobarbital anesthetized dogs. Cumulative dose-response curves were obtained with 3 doses of each compound. The results demonstrate that: a) NPAB exerts a significant depressor effect (9 to 10 times more potent than CHA) on the following three conduction times: auriculo-Hisian, His-Pinkinje and Purkinje-ventricular; b) on His-Purkinje and intra ventricular conduction, MCAA exerts a weaker depressor effect than that of Nab. The lack of parallelism of dose-response curves prevents further comparative quantification; c) on atrio-hisian conduction, MCAA presents a delayed dose-related depressor effect suggesting the presence of an active metabolite. It is concluded that among ajmaline derivatives studied, Nab appears to be the most depressor on A-V and intraventricular conduction in the pentobarbital anesthetized dog.

His bundle recordings: their contribution to the understanding of human electrophysiology

His bundle electrocardiography has increased our understanding of the electrophysiology of the conducting system and has confirmed a number concepts which evolved from analysis of surface electrocardiograms. Electrophysiologic evaluation of conduction disease in the cardiac catheterization laboratory has become an accepted diagnostic procedure in determining the site of atrioventricular and ventriculo-atrial block as well as in the evaluation of patients with pre-excitation resulting from conduction through Kent and James bundles. Recent reports suggest that His bundle electrograms may prove to be of clinical and therapeutic significance in determining the site of re-entry in patients with PSVT as well as in determining the short-term prognosis of patients with acute myocardial infarction complicated by incomplete bundle branch block. As our knowledge and understanding of the basic mechanisms, specific therapy, and prognosis of cardiac arrhythmias are expanded, the data derived from His bundle electrocardiography will become more useful in the clinical practice of cardiology.