Br.J.Pharmac. (1972), 45, 561-573. The effect of Ko 1173, a new anticonvulsant agent on experimental cardiac arrhythmias J. D. ALLEN, J. M. KOFI EKUE, R. G. SHANKS AND S. A. ZAIDI Department of Therapeutics and Pharmacology, The Queen's University, Department of Cardiology, Royal Victoria Hospital, Belfast, N. Ireland Summary 1. The effects of the intravenous injection of Ko 1173, a new anticonvulsant drug, phenytoin and procainamide were studied on three types of cardiac arrhythmia in dogs. 2. Ventricular ectopic beats produced by intravenous injection of adrenaline in anaesthetized dogs respired with halothane were abolished by Ko 1173, 06+01 mg/kg, phenytoin, 1 1+0±3 mg/kg and procainamide, 4-1+1±8 mg/kg. 3. Ventricular tachycardia was produced in anaesthetized dogs by the intra- venous injection of ouabain and the three drugs infused intravenously at 0-2 (mg/kg)/min until sinus rhythm returned. Ko 1173 was effective in 8 out of 9 dogs after a mean dose of 1 3+0 3 mg/kg; phenytoin in all 3 dogs after 2-7+0O6 mg/kg and procainamide in the 3 dogs tested after 16-6+1-3 mg/kg. 4. The intravenous injection of Ko 1173, 8-0 mg/kg, greatly reduced the number of ventricular ectopic beats occurring in conscious dogs 18-44 h after ligation of the anterior descending branch of the left coronary artery, with a resultant increase in the number of sinus beats. Phenytoin, 80 mg/kg, had a similar effect but procainamide was much less effective. 5. These results indicate that Ko 1173 is effective in abolishing experimental cardiac arrhythmias and suggest that its effects should be studied in patients. Introduction All drugs which are effective in the treatment of cardiac arrhythmias may cause serious side-effects when administered on a long-term basis. Hence procainamide has been shown to produce a syndrome like systemic lupus erythematosis (Ladd, 1962; McDevitt & Glasgow, 1967); the 8-adrenoceptor blocking drugs, propranolol and practolol, may produce cardiac failure or bradycardia (Stephen, 1966; Allen, Pantridge & Shanks, 1971), and phenytoin (also widely used as an anticonvulsant agent) may cause ataxia, nystagmus, tremor and diplopia as well as hyperplasia of the gums on long-term administration (Toman, 1965). There is, therefore, still a place for new effective antiarrhythmic drugs which will not have deleterious results when used over a prolonged period. Recently a new anticonvulsant agent, Ko 1173, has become available. The purpose of this study was to evaluate its action on experimental cardiac arrhyth- mias and to compare its actions with those of phenytoin and procainamide. The 562 J. D. Allen, I. M. Kofi Ekue, R. G. Shanks, and S. A. Zaidi structure of the three drugs is given in Fig. 1. Some of the results of the present experiments have been described to the British Pharmacological Society (Allen, Kofi Ekue, Shanks & Zaidi, 1970). Methods Observations were made in dogs anaesthetized by the subcutaneous injection of morphine sulphate, 05 mg/kg, followed one hour later by the intravenous injection of pentobarbitone, 20 mg/kg. A cuffed endotracheal tube was inserted and the dogs were respired with room air from a Starling Ideal pump at a rate of 18 strokes per minute and a stroke volume of 13 ml/kg body weight. Arterial pressure was measured through a metal cannula inserted in the left carotid artery and attached to a pressure transducer (Consolidated Electrodynamics Type 4-327-L 221). Arterial pressure and the electrocardiogram (Lead II) were recorded on a Devices recorder (Type M8 or M4) and displayed on a four-channel oscillo- scope (Airmec). Drugs were injected through a polythene catheter inserted in a foreleg vein. Ouabain arrhythmias Observations were made on 18 dogs prepared as described above. In 15 dogs the right vagus nerve was exposed in the neck and divided. Bipolar electrodes were applied to the distal end of the nerve which was stimulated for periods of 10 s with shocks of 1 ms duration at a frequency of 25 Hz and a voltage sufficient to produce maximal sinus slowing without loss of sinus dominance. This voltage was determined for each animal before the administration of any drug and was in the range of 2-10 volts. Ventricular tachycardia was produced by the intra- venous injection of ouabain, 40 ug/kg, followed after 30 min by 20 ug/kg and by CH3 0 >~CH2-CIHNIH~2~~~~~~~~~N~H~~a~4~~O~IC-NHCH,CH2N(CH2CH,)2 CH3 CH3 K6 1173 Procainamide H I N CH ,/ \\ C,gH5 |l -C NCH Phenytoin FIG. 1. Chemical structure of Ko 1173, procainamide and phenytoin. A new anti-arrhythmic drug 563 10 ,ig/kg every 15 min until ventricular tachycardia was produced. Stimulation of the vagus nerve, with the previously established voltage, had no effect on the ventricular tachycardia; this indicated complete loss of sinus dominance. When the arrhythmia had been established for 10 min the test compound was infused intravenously from a motor driven syringe at the rate of 0-2 or 1F0 mg/kg per minute. The infusion of each drug was continued until the return of sinus rhythm which slowed, without the occurrence of any ectopic beats, on vagal stimulation with the previously determined voltage. After this end-point had been achieved, insulin (80-160 u) was given intravenously to induce ventricular tachycardia, the appearance of which indicated the continued presence in the heart of toxic doses of ouabain. In 3 dogs the vagus nerve was not divided and was not stimulated. Ventricular tachycardia was produced by ouabain, as described above, and the test compound infused until the return of sinus rhythm which was taken as the end-point after which insulin was given to induce ventricular tachycardia. Hakothane-adrenaline arrhythmias Observations were made on 13 dogs. After preparation, the dogs were artifi- cially respired with room air and 1% halothane. Fifteen minutes later adrenaline, 0-2 fig/kg, was injected intravenously. The dose of adrenaline was then progres- sively increased from 0-4 ,ug/kg, in 0-4 ,ug/kg increments, with an interval of 7-10 min between each dose, until ventricular tachycardia or multifocal ventricu- lar ectopic beats had been produced. In some dogs adrenaline produced ventricu- lar fibrillation which was corrected by external direct current countershock deli- vered from an American Optical Defibrillator (Model 10645). After such defibril- lation, halothane was discontinued for 10 min and the adrenaline challenge was not repeated until 20 min later but with a dose less than that which had produced fibrillation. After the dose of adrenaline which produced an arrhythmia had been established, the test compound was injected intravenously. Five minutes later the adrenaline challenge, using the same dose, was repeated. Increasing doses of the test compound were given to determine the minimum dose that prevented the adrenaline challenge from producing any ectopic beats. Arrhythmias after coronary artery ligation Dogs were anaesthetized by the intravenous injection of methohexitone, 10 mg/ kg, and respired through a cuffed endotracheal tube with room air and halothane (0-5-1-5%). The heart was exposed through an incision in the fourth or fifth left intercostal space. The left anterior descending coronary artery was dissected free 2 cm below the tip of the left atrial appendage and was ligated at this level in two stages as described by Harris (1950). Two ligatures were placed round the artery and a 21 gauge needle. The first ligature was tied around the artery and the needle which was then removed. Thirty minutes later the second ligature was tied tightly around the artery. The chest was closed in layers 30 min after the second ligature had been tied and the dog was allowed to recover. Further ob- servations were made 18 to 44 h after ligation of the coronary artery when the dogs were conscious. Lead 2 of the electrocardiogram was continually recorded on a direct writing instrument (M2 or M4, Devices Ltd.) for 5 to 30 min before the administration of Ko 1173, phenytoin or procainamide and during their ad- ministration. A series of increasing doses of each drug was given at 5 mmn 564 J. D. Allen, J. M. Kofi Ekue, R. G. Shanks, and S. A. Zaidi intervals. The ventricular rate was obtained from the electrocardiogram by count- ing the total number of sinus beats and ectopic beats during each successive 5 min period. Post-mortem examination in all dogs showed the presence of an acute myocardial infarction. Drugs Ouabain (May & Baker); (-)-adrenaline bitartrate (C. Zimmerman & Co.); Ko 1173 (Boehringer Ingelheim); phenytoin (Parke Davis) and procainamide (Squibb). Drugs were dissolved in 09% NaCl solution at the required concentra- tion; doses are expressed in terms of the salt. Halothane ('Fluothane', I.C.I.) was administered by means of a Blease Universal anaesthetic vaporizer. Results Ouabain arrhythmias Observations were made in 18 dogs in which the intravenous administration of ouabain produced ventricular tachycardia. The mean dose of ouabain which pro- duced this arrhythmia in each group of animals is given in Table 1. Ko 1173, phenytoin and procainamide were administered by constant intravenous infusion after establishment of the ventricular tachycardia in each dog. Effect of Ko 1173 The effects of the intravenous infusion of Ko 1173 were studied in 2 groups of dogs consisting of 6 and 3 animals. The results of part of one experiment from the first group are shown in Figure 2. Stimulation of the distal end of the right vagus nerve before the administration of ouabain produced slowing of sinus rate without any ectopic beats (A). After the administration of ouabain, 40 ug/kg, followed by 20 ,ug/kg, a ventricular tachycardia developed; this rhythm was unaltered by vagal stimulation (B). The constant intravenous infusion of Ko 1173 at 0-2 (mg/kg)/min was then started. Sinus rhythm returned after the infusion of 0-6 mg/kg Ko 1173, but ectopic beats occurred during vagal stimulation (C). After infusion of 1-5 mg/kg, ectopic beats did not occur on vagal stimulation (D). The TABLE 1. EffectsofKo1173,phenytoinandprocainamideonouabain-inducedarrhythmias. Ventricular sachycardia wasproducedbyintravenousadministrationofouabain. Afterarrhythmiahadbeenpresent for 10min,KIo 1173,phenytoin, orprocainamide wasinfused Meandoseofantiarrhythmic drug(mg/kg±s.E.M.) required Toprevent Meandoseof Rateof ectopic beats ouabain infusion Torestore onstimulation Drug No. ofdogs mg/kg±s.E.M. (mg/kg)/min sinusrhythm ofvagusnerve Ko 1173 a 5 77-0+ 6.9 0-2 1-3±0-6 3-9+1-8 (4 dogs) b 3 700+ 5-8 0-2 1.3±008 Phenytoin a 3 66.6± 3.3 0-2 2-7±0-6 13-4 (I dog) Procainamide a 3 63-3+ 3.3 0-2 16-6±1-3 22-2 (2dogs) a 3 63'3±12.1 1.0 2-5 90 (I dog) (1 dog) a-Vagalstimulation performed. b-Novagalstimulation. A new anti-arrhythmic drug 565 continued presence of toxic amounts of ouabain in the heart was shown by the appearance of a ventricular tachycardia following the intravenous injection of insulin 120 units (E). Similar results were obtained in a total of 4 dogs and are shown in Table 1 which gives the mean doses of Ko 1173 for reversion to sinus rhythm and for complete suppression of ectopic pacemaker activity. In the fifth dog, Ko 1173 restored sinus rhythm but ectopic beats occurred on vagal stimula- tion and after the administration of 2 mg/kg (i.e. 10 min of infusion) spontaneous ventricular ectopic beats recurred and within 20 min, despite the infusion of Ko 1173, ventricular fibrillation developed. In the sixth dog in this group ventri- cular fibrillation occurred five minutes after the start of the infusion of Ko 1173, before any change in the ventricular tachycardia had occurred. The results from this dog are not included in Table 1. In the second group of dogs the end-point was taken as the return of sinus rhythm as vagal stimulation was not carried out. The mean dose of Ko 1173 which restored sinus rhythm in this group was 1P3+0-3 mg/kg. Control Ouabain 60 gg/kg Arterial 300 A B pressure 200 mmHg 100l OJ 4W4L-L Lead2 j KO 11730.6mg/kg KO 1173 1-5 mg/lkg Arterial 300 D pressure 200 ~ 100j mmHg Lead ULtLr. _IJ I L-I 2 I sec Insulin 120i.u. Arterial pressure 200I mmHg 1000j Lead2 FIG. 2. The effect of Ko 1173 on ventricular tachycardia produced by ouabain in an anaesthetized dog. Records -of arterial pressure and the electrocardiogram (Lead 2) are shown. Thie peripheral end of the right vagus nerve was stimnulated during the period indicated by the solid bar. A, Control: B, after intravenous injection of ouabain (60 jag/kg); C, D, after the intravenous infusion of Ko 1173 at 0-2 (mg/kg)/min for 3 min, and 7-5 min respectively; E, after the intravenous injection of insulin, 120 units. 566 J. D. Allen, J. M. Kofi Ekue, R. G. Shanks, and S. A. Zaidi EfFect of phenytorn The effects of phenytoin were studied in 3 dogs in which the drug was infused at the rate of 0f2 (mg/kg)/min. Sinus rhythm developed in all 3 dogs after the administration of a mean dose of 2-7+0-6 mg/kg; slowing of this rhythm on vagal stimulation without the appearance of ectopic beats occurred in one out of the 3 dogs (Table 1). EJffect of procainamide The effects of the infusion of procainamide on the ouabain-induced ventricular tachycardia were studied in 6 dogs. In 3 dogs, in which the rate of infusion was 0-2 (mg/kg)/min, sinus rhythm was restored after a mean dose of 166+1-3 mg/kg (Table 1). Absence of ectopic beats on vagal stimulation occurred in 2 of these 3 dogs after a mean dose of 22-2 mg/kg had been infused. In another 3 dogs pro- cainamide was given at a rate of 10 (mg/kg)/min. In one dog the ventricular tachycardia was abolished after infusion of 2-5 mg/kg and after 90 mg/kg ven- tricular ectopic beats did not occur on vagal stimulation (Table 1). In the second of these dogs the ventricular tachycardia was still present after administration of procainamide, 30 mg/kg, after which the infusion was stopped. In the third dog the ventricular tachycardia was converted to a nodal tachycardia after the infusion of 60 mg/kg of procainamide. Control KO 1173 KO 1173 0 I mg/kg 0-25 mg/kg 3001 Arterial. pressure 1001N N\NP\NNJNj'-. nmmHg 100 Lead 2 LLL ILAL LL LLL.U Adrenaline 3-2 pg/kg Arterial 300- 1200-' pressure mmHg tJ244 LLUL,LL Lead 2 J I s FIG. 3. The effect of the intravenous injection of Ko 1173 on the ventricular arrhythmia produced by the intravenous injection of adrenaline in an anaesthetized dog respired with 1% halothane. Records of arterial pressure and the electrocardiogram (Lead 2) are shown. The upper pair of records were obtained before and the lower pair after the intravenous injection of adrenaline 3-2 ,ug/kg. The responses to the administration of adrenaline before (control) and after 0-1 and 025 mg/kg Ko 1173 are shown. A new anti-arrhythmic drug 567 Halothane-adrenaline arrhythmias Egect of Ko 1173 Five dogs were given Ko 1173 following determination of the dose of adrenaline required to produce a ventricular arrhythmia. Increasing doses of Ko 1173, 01, 025, 05 and 1 0 mg/kg were given by intravenous injection at 15 min intervals until the adrenaline arrhythmia was prevented. The adrenaline challenge was given 5 min after the intravenous administration of each dose of Ko 1173. Portions of the records from one experiment are shown in Fig. 3. During the control period, the intravenous injection of adrenaline, 3-2 ,ug/kg, produced a burst of ventricular ectopic beats followed by a return to sinus rhythm. The administration of adrenaline after Ko 1173, 0 1 mg/kg, produced fewer ectopic beats and after Ko 1173, 0-25 mg/kg, adrenaline produced no ectopic beats. Similar results were obtained in the other 4 dogs but higher doses of Ko 1173 were required to prevent the arrhythmias. The mean dose of Ko 1173 that abolished the adrenaline arrhythmias in the 5 dogs was 0-6+0.1 mg/kg. Effect of phenytoin The effects of increasing doses of phenytoin, 01, 025, 0-5, 1.0 and 2-0 mg/kg were studied in 4 dogs. The adrenaline-induced arrhythmia was abolished in all 4 dogs, after the administration of a mean dose of phenytoin of 1.1+03 mg/kg. Effect of procainamide Procainamide abolished the adrenaline-induced arrhythmia in the 4 dogs in which observations were made. The mean effective dose of procainamide in the 4 dogs was 41+1-8 mg/kg. Coronary artery ligation arrhythmias Observations were made in 12 dogs 18-44 h after two-stage ligation of the anterior descending branch of the left coronary artery. All dogs had a severe ventricular arrhythmia consisting of multifocal ventricular tachycardia interspersed with normal sinus beats. After the initial period of observation the electrocardio- gram was recorded continuously in 4 dogs for 30 min before the administration of any drug; this period of observation in these dogs was used as a control. The results in these 4 dogs showed that the total ventricular rate and the number of sinus beats in each 5 min period during this 30 min period of observation varied slightly (Table 2). The values for each of these 5 min periods were similar to those observed during the 5 min control period in the three groups of dogs which received Ko 1173, phenytoin and procainamide. Effect of Ko 1173 The effects of the intravenous injection of a series of doses of Ko 1173 (0-5, 1-0, 2-0, 4-0 and 8-0 mg/kg) given at 5 min intervals on the arrhythmias which occur spontaneously 18-44 h after coronary artery ligation were studied in 5 conscious dogs. Some of the results of one experiment are shown in Fig. 4. The predominant rhythm during the 5 min control period, before administration of Ko 1173, was ventricular tachycardia with ventricular ectopic beats; nodal beats and sinus beats occurred irregularly at infrequent intervals. There was little change 568 J. 1). Allen, J. M. Kofi Ekue, R. G. Shanks, an(d S. A. Zaidi in the numberi- of ectopic or sinus beats following the adminiistration of Ko 1173, 0 5 and 1 0 mg/kg, but a slight increase in the number of sinus beats occurred after 20 mg/kg. After the administration of 4 0 mg/kg there was a slight fall in total ventricular rate and a marked reduction in the number of ectopic beats so that sinus rhythm became the predominant rhythm. After 8 0 mg/kg there was a further increase in the number of sinus beats with almost complete suppression of the ectopic foci, so that long runs of sinlus rhythm without any ectopic beats occurred. This effect of the drug was still presenit 30 Inin after adminiistration. The results obtailned in the 4 other dogs which were giveni Kb 1173 are shown in Figure 5. The total venitricular rate was reducecl by the drug in 3 dogs. The ventricular ectopic beats were rcduced in ali 4 dogs by 4 mg/kg and almost com- pletely abolished by 8 0 mg/kg. This effect lasted till the end of each experi- ment which was 10-30 min after the last dose of Kb 1173. Following the administrationi of 80 mgu/kg of Kb 1173, all dogs had transienit tonlic convulsions which lasted for a few seconds. The meani results from these 5 dogs are giveni in Table 2. ffeci of phelnvtoin Observations were made in 4 dogs which were given phenytoin (0 5, 1-0, 20, 40 anld 80 mg/kg) by intravenious inijectioni at 5 miii intervals after an initial control period of at least 5 minutes. The meani results are shown in Table 2. Phenytoini had no effect on total ventricular rate. Adnministration of 05 mg/kg Control KO 1173 4-0 mg/kg KO 1173 8-0 mg/kg sec 1 ~ ~ ~~ ~~~~~~~~~~~~~~~~~~_'I7 Heat rate KO 1173 (mg/kg) beats/min. 0-5 10 2-0 4-0 8-0 000 20 30 40 50 60 70 80 M1inutes FIG. 4. The effect of Ko 1173 on the ectopic beats occurring in a conscious dog 22 hours after coronary artery ligation. Top half of the record shows samples of the electrocardio- gram (lead II) obtained during the control period and after the intravenous injection of Ko 1173. 40 and 8-0 mg/kg. The histogram indicates the ventricular rate (clear columns) and numnber of sinus beats (black columns) for each minute. The point of administration of each dose of Ko 11l73 is shown. A new anti-arrhythmic drug 569 increased the number of sinus beats. Further increases in the number of sinus beats occurred after 2-0, 40 and 80 mg/kg. After the largest dose of phenytoin the dominant rhythm was sinus rhythm interspersed with a few ectopic beats. The dogs became transiently breathless and restless following both 4-0 and 8-0 mg/kg of phenytoin. The effect of phenytoin was similar to that of Ko 1173. The reductions pro- duced in the number of ectopic beats by 40 mg/kg of Ko 1173 and of phenytoin were 61-3% and 62-2% respectively and after 8-0 mg/kg of the two drugs, 89d1% and 85-7% respectively. Effect of procainamide The effect of the intravenous injection at 5 min intervals of procainamide (0-5, 1V0, 2-0, 4-0, 8-0, 16-0 and 32-0 mg/kg) was observed in 3 dogs. The effect of procainamide was different in the 3 dogs. In one dog there was complete abolition of the ectopic beats after 32-0 mg/kg. In the second dog, procainamide had no effect on the number of ectopic beats. In the third dog, procainamide reduced the number of ectopic beats but did not abolish them. The mean results from the 3 dogs are given in Table 2. Procainamide reduced the total ventricular rate to a small extent. Beats per 5 min 800 _ 1000 800- 600 i 400- 400, 200- 200- 0 L_0- 600++ 400- ~~~~~~~200 200 0 0-S51 2 4 8 0 KO 1173 (mg/kg) FIG. 5. Observations in 4 conscious dogs with multifocal ventricular tachycardia 18-44 h after ligation of the anterior descending branch of the left coronary artery. Each histogram refers to a separate dog and indicates the ventricular rate (clear columns) and number of sinus beats (black columns) for 5 min periods. After a control period of 30 min in 3 dogs and 20 min in the fourth dog, a series of doses of Ko 1173 were given at 5 min intervals as indicated. ~~ N u: c>\ b \0m N 570 J. D. Allen, J. M. Kofi Ekue, R. G. Shanks, and S. A. 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