[Antiviral effect of (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl) cytosine on adenovirus]

PURPOSE

Adenovirus is the most frequent causative virus of conjunctivitis in Japan. Recently (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl) cytosine (HPMPC) has been promoted as a new drug against adenoviral conjunctivitis. So we examined the antiviral activity of HPMPC against adenoviruses in vitro.

METHOD

The antiviral activity of HPMPC against adenovirus (Ad) type 3, type 4, type 19, and type 37 isolated from conjunctivial scrapings in Japan and the prototype of adenovirus type 5 was examined by plaque reduction assay using A 549 cells in vitro.

RESULTS

The 50% inhibitory dose (ID50) of HP-MPC was 3.50 (1.44-4.79) micrograms/ml for Ad type 3, 4.50 (4.17-4.92) micrograms/ml for Ad type 4, 2.11 (1.03-3.13) micrograms/ml for Ad type 5, 1.64 (1.40-2.02) micrograms/ml for Ad type 19, and 2.02 (1.17-2.73) micrograms/ml for type 37. The 50% cytotoxic dose of HPMPC for A 549 cells was 205 micrograms/ml by the deoxythimidine uptake inhibition test, and 537 micrograms/ml by the trypan blue exclusion inhibition test.

CONCLUSIONS

HPMPC proved to be highly effective in inhibiting replication of adenoviruses at lower concentrations than the cytotoxic level in vitro.

Effects of lidocaine and diltiazem on ventricular tachyarrhythmia and dispersion of conduction during severe myocardial ischemia in canine hearts

The purpose of this study was to investigate the effects of lidocaine and diltiazem on ventricular tachyarrhythmia and dispersion of conduction during severe myocardial ischemia in dogs. Myocardial ischemia was produced by a 10-min occlusion of the left anterior descending artery by the retrograde blood flow technique. Saline, lidocaine, and diltiazem were infused intravenously before and during occlusion in groups A (n = 16), B (n = 22) and C (n = 13), respectively. The incidence of ventricular tachycardia (VT) consisting of ten or more VPC was 19% in group A, 73% in group B and 31% in group C (A vs. B, P < 0.01), and that of ventricular fibrillation (VF) was 31%, 64%, and 15%, respectively (A vs. B, P < 0.05). The time of the onset of VT preceding VF was shorter in group B than in group A (207.9 +/- 13.9 vs. 353.2 +/- 70.7 sec, P < 0.05). The time taken to reach maximal dispersion of conduction delay in the epicardium was shorter in group B than in group A (192.1 +/- 11.9 vs. 337.5 +/- 38.2 sec, P < 0.01), and the dispersion of conduction delay in the intramyocardial layers was smaller in group B than in group A (229.9 +/- 24.5 vs. 360.0 +/- 35.6 sec, P < 0.01). The time taken to reach maximal dispersion of conduction delay in the endocardium was greater in group C than in group A (400.8 +/- 38.8 vs. 274.4 +/- 23.9 sec, P < 0.01). However, there were no significant differences among the three groups with regard to the maximal dispersion of conduction delay in the epicardium, in the endocardium, or intramyocardial layer. These results suggest that lidocaine increased ventricular tachyarrhythmia due to an acute increase in dispersion of conduction in the epicardium and intramural layer, and that diltiazem was not effective in preventing ventricular tachyarrhythmia and did not affect the dispersion of conduction in the epicardium or intramural layer despite improvement in the endocardium.

Effects of ischemic preconditioning on ventricular arrhythmias during ischemia and reperfusion using a retrograde blood flow model in dogs

We examined the effects of ischemic preconditioning on ventricular arrhythmias during ischemia and reperfusion from the electrophysiologic point of view by using the retrograde blood flow (RBF) model, which causes severe ischemia. A total of 51 anesthetized dogs were divided into 3 groups. Group 1 (10-min simple occlusion) consisted of 15 dogs; group 2 (10-min RBF) consisted of 20 dogs; and group 3 (10-min RBF with preconditioning) consisted of 16 dogs. Preconditioning consisted of 5 cycles of 2 min of ischemia (RBF) and 5 min of reperfusion. In the subepicardium, myocardial blood flow (MBF) in group 2 was significantly lower than in group 1 or group 3 [group 2 (4.7 +/- 2.3 ml/min per 100 g) vs group 1 (35.0 +/- 5.8) or group 3 (22.0 +/- 4.6); p < 0.01 and p < 0.05 respectively]. However, there were no differences in MBF in the subendocardium between the 3 groups. The incidence of conduction block in the subepicardium was significantly higher in group 2 than in group 1 or group 3 [group 2 (85%) vs group 1 (33%), p < 0.01; vs group 3 (38%), p < 0.01]. There were no differences in the incidence of conduction block in the subendocardium between the 3 groups. During 10-min ischemia, the incidences of ventricular fibrillation (VF) were 7% in group 1, 35% in group 2, and 6% in group 3 (group 2 vs group 1, p < 0.05; and group 2 vs group 3, p < 0.05). During 10-min reperfusion, the incidences of VF were 29% in group 1, 77% in group 2, and 33% in group 3 (group 2 vs group 1, p < 0.05; and group 2 vs group 3, p < 0.05). Ventricular arrhythmias were reduced during both 10-min ischemia and 10-min reperfusion as a result of the improvement in the conduction components by ischemic preconditioning which increased MBF in the subepicardium.

Effects of lidocaine and diltiazem on recovery of electrophysiologic activity during partial reperfusion following severe myocardial ischemia in canine hearts

The effects of lidocaine and diltiazem on recovery of electrophysiologic activity during partial reperfusion following severe myocardial ischemia were investigated in 28 dogs. The left anterior descending artery was ligated, and the distal end was connected to the carotid artery. Myocardial ischemia was induced by retrograde blood flow for 10 minutes, after which flow-limited reperfusion (30-60% of the coronary flow before ischemia) was performed. The dogs were divided according to the agent administered before ischemia into the following three groups: saline (group S, n = 11); lidocaine (group L, n = 8, 0.07 mg/kg/min by intravenous drip infusion following 2 mg/kg intravenous injection); and diltiazem (group D, n = 9, 0.02 mg/kg/min by intravenous drip infusion. There were no significant differences among the three groups in the incidence of ventricular tachyarrhythmia, which occurred as ventricular tachycardia (VT) or ventricular fibrillation (VF). In each group, the occurrence of VT was frequently preceded by delayed potential which was initiated after reperfusion, with depressed conduction in the epicardium, suggesting reentry (82%, 96%, and 87%, not significant). The determining factors for VT with degeneration into VF were long duration of VT in groups S and L (VT with degeneration into VF vs VT without, 1.2 +/- 0.2 seconds vs 0.6 +/- 0.1 seconds, P < .05, in group S and 11.6 +/- 2.5 seconds vs 2.2 +/- 0.4 seconds, P < .05, in group L), and decrease in average R-R interval during VT in groups L and D (195 +/- 8 ms vs 313 +/- 17 ms, P< .01, in group L and 201 +/- 11 ms vs 327 +/- 28 ms, P< 0.01, in group D). In addition, occurrence of epicardial electrophysiologic activity with reduced time from onset of the QRS complex in the surface electrocardiogram to the onset of the activity during VT preceded VF in group L (VT with degeneration into VF vs VT without, 130.0 +/- 15.1 ms vs 185.8 +/- 21.4 ms, P < .05), while that with prolongation of the time had this effect in group D (116.0 +/- 15.7 ms vs 69.0 +/- 10.7 ms, P < .05). It is concluded that, even when partial reperfusion is applied, neither lidocaine nor diltiazem suppresses VT because neither drug decreases delayed potential acting as a triggering factor or suppresses VF, since the alteration of the epicardial conductivity during VT can change the VT circuit to a smaller one.

[Rapid detection and identification of human adenovirus directly from conjunctival scrapings by polymerase chain reaction and restriction fragment length polymorphism analysis]

Polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis were combined for detection and identification of adenovirus (Ad), a common agent of conjunctivitis in Japan. Nested-PCR with two primer sets that hybridize to the conserved region for hexon protein of 14 prototypes of Ad serotype 1 to 8, 11, 14, 19, 37, 40, and 41, amplified 956 bps DNA fragment. The amplified fragments from 14 prototypes were completely differentiated with the combination of three restriction endonucleases, Eco T14I, Hae III, and Hin fI. We applied this new method to 70 conjunctival scrapings from patients with conjunctivitis, and compared the results with those of the combination of culture isolation and neutralization test. PCR was positive in 38 out of 70 samples (54.3%), whereas 33 of 70 samples (47.1%) were positive by cell culture. Compared with cell culture isolation, the PCR method had a sensitivity of 100% (33 of 33). Positive PCR samples were further classified into Ad 37 (44.7%), 3 (39.5%), 11 (7.9%), 8 (5.3%), and 4 (2.6%) by PCR-RFLP analysis. Of five samples that were PCR positive and cell culture negative, three samples were Ad 37 and two were Ad 8 by PCR-RFLP analysis. These differentiations of cell culture positive samples were identical to the results of the neutralization test. It took only about three days to detect and identify Ad by PCR-RFLP analysis, whereas it took at least two weeks by culture isolation and neutralization test. Our newly developed method of detecting and typing human Ad by PCR-RFLP analysis is more sensitive, accurate, and prompt than the conventional cell culture isolation and neutralization test.

Electrophysiologic changes before onset of ventricular tachyarrhythmias during partial reperfusion following severe myocardial ischemia in dogs

We examined the electrophysiologic changes before an onset of ventricular tachyarrhythmia during partial reperfusion following severe myocardial ischemia. The left anterior descending coronary artery was occluded and cannulated below the occluded portion in 26 dogs. To deplete collateral flow into the ischemic myocardium, retrograde blood flow was induced for 20 min. Then, in all dogs except 7 with ventricular fibrillation during retrograde blood flow, partial reperfusion through collateral flow into the ischemic myocardium was produced by stopping the retrograde flow. Within 2 min of partial reperfusion, sustained ventricular tachycardia (VT) occurred in 7 dogs (group A) and non-sustained VT degenerating ventricular fibrillation occurred in 11 dogs (group B) of the remaining 12 dogs. In 6 dogs of group A and 9 of group B, epicardial conduction block appeared 5.0 +/- 2.2 and 3.5 +/- 1.3 min after ischemia. This was followed by fractionated electrical activities 15.2 +/- 3.2 and 11.7 +/- 3.3 min after ischemia. In group A, the fractionation had a slight change in configuration and a small increase in amplitude before the onset of VT during reperfusion; in group B, new deflections with large amplitude emerged before it. There was a significant difference in the amplitude (0.38 +/- 0.2 vs 0.67 +/- 0.3 mV, p < 0.025) between the 2 groups, although there was no significant difference in the amplitude (0.33 +/- 0.2 vs 0.23 +/- 0.1 mV) of the fractionation just before reperfusion. Our results show that slight improvement in fractionation induces sustained VT, and new deflections induce non-sustained VT degenerating ventricular fibrillation, even during partial reperfusion.

Double atrial response to a single ventricular extrastimulus in a patient with Wolff-Parkinson-White syndrome

Electrophysiological examination in a 39-year-old male disclosed an accessory pathway between the right atrium and the right ventricle and AV nodal dual pathways. Atrial and ventricular extrastimuli induced paroxysmal supraventricular tachycardia (PSVT), which was shown to be AV reciprocating tachycardia. Double atrial response was noted during ventricular extrastimuli at V1V2 of 280 msec and V1V2 of 250 msec. The first atrial response is considered to have been transmitted in a retrograde fashion in the accessory pathway, and the second atrial response similarly in the slow pathway of the AV node.

Myocardial blood flow, alternans of ST segment elevation, conduction delay and ventricular arrhythmia during acute myocardial ischemia with and without retrograde blood flow in canine hearts

The technique of retrograde blood flow has been shown to decrease collateral flow into the ischemic myocardium, and to cause severe myocardial ischemia in dogs. Ischemia with retrograde blood flow in dogs is similar to ischemia in human hearts. Therefore, we examined the effect of retrograde blood flow on myocardial blood flow, ST segment elevation, alternans of ST segment elevation, conduction delay and ventricular arrhythmia in dogs. Sixty dogs were divided into two groups. In group A (N = 32), the left anterior descending coronary artery was occluded for 10 min. In group B (n = 28), ischemia was induced by the technique of retrograde blood flow for 10 min. During ischemia, the myocardial blood flow at the ischemic zone measured by a H2 gas clearance method was 11.2 +/- 1.6 in group A and 5.7 +/- 0.7 ml/min/100 g in group B (p less than 0.01). The maximal ST segment elevation was 13.6 +/- 1.9 in group A and 27.2 +/- 2.1 mV in group B (p less than 0.001); the maximal alternans of ST segment elevation was 5.3 +/- 1.1 in group A and 10.1 +/- 1.4 mV in group B (p less than 0.01); the maximal conduction delay was 51.6 +/- 8.4 in group A and 111.1 +/- 6.2 msec in group B (p less than 0.001); and the incidences of ventricular premature beats (greater than 5/min), ventricular tachycardia and fibrillation were 34%, 41% and 22% in group A, and 68%, 79% and 25% in group B (p less than 0.01, p less than 0.01 and not significant, respectively). It is concluded that ischemia with retrograde blood flow can be used to examine occlusive and reperfusion ventricular arrhythmia in dogs, because the incidences of ventricular premature beats and ventricular tachycardia were high, but that of ventricular fibrillation was not high despite the severe ischemia.

Reflection as a cause of mid-systolic deceleration of pulmonary flow wave in dogs with acute pulmonary hypertension: comparison of pulmonary artery constriction with pulmonary embolisation

STUDY OBJECTIVE

The aim was to examine whether mid-systolic deceleration of the pulmonary flow wave occurred in acute pulmonary hypertension due to pulmonary artery constriction and pulmonary embolisation, and if so whether it was related to reflection.

DESIGN

Various degrees of pulmonary hypertension were induced by both pulmonary artery constriction and pulmonary embolisation in dogs. During control periods and during pulmonary artery constriction and pulmonary embolisation, pulmonary flow and pulmonary artery pressure were recorded, and the forward and backward (reflected) flow waves were separated from the measured pulmonary flow wave by the method of Westerhof et al.

MATERIALS

20 adult mongrel dogs were used and 10 dogs qualified for analysis. The other 10 dogs, which died before both interventions were completed, were excluded.

MEASUREMENTS AND MAIN RESULTS

During pulmonary artery constriction, a distinct mid-systolic deceleration of the pulmonary flow wave was observed in five of the 10 dogs, while during pulmonary embolisation, no mid-systolic deceleration was found in these five dogs. The distinct deceleration of the pulmonary flow wave was related to a steep fall and early negative peak in the backward flow wave.

CONCLUSION

Mid-systolic deceleration of pulmonary flow wave is likely to be related to reflection.

Effect of pre-existing four hour coronary stenosis on ventricular arrhythmias during a subsequent 10 minute occlusion in dogs

STUDY OBJECTIVES

The aim was to assess the effect of pre-existing coronary stenosis on ventricular arrhythmia during subsequent acute coronary occlusion.

DESIGN

Dogs with a 4 h intact interval followed by a 10 min occlusion of left anterior descending coronary artery (group A) were compared for ventricular arrhythmias with dogs with a 4 h stenosis of the same artery followed by a 10 min occlusion (group B). Myocardial blood flow was measured in the ischaemic myocardium using the H2 gas clearance method to exclude dogs with good collateral flow (myocardial blood flow greater than 11.0 ml.min-1.100g-1).

EXPERIMENTAL ANIMALS

35 mongrel dogs of either sex, weight range 11-26 kg, were used in the experiments (group A, n = 17; group B, n = 18). After exclusion of dogs with good collateral circulation there were 11 dogs in group A (subgroup A1) and 12 dogs in group B (subgroup B1).

MEASUREMENTS AND MAIN RESULTS

The incidence of ventricular fibrillation was lower in group B (pre-existing stenosis) than in group A during the 10 min occlusion, though there was no difference in numbers of ventricular premature beats. Maximum ST segment elevation and maximum conduction delay were less in group B than in group A, but myocardial blood flow did not differ during the 10 min occlusion. In the subgroups the incidence of both types of ventricular arrhythmia was lower in subgroup B1 during the 10 min occlusion, while the maximum ST segment elevation and maximum conduction delay were less, and myocardial blood flow was greater.

CONCLUSIONS

Pre-existing 4 h coronary stenosis causes the development of collateral flow and reduces the incidence of ventricular arrhythmias during subsequent occlusion.

Ventricular fibrillation during partial reperfusion following severe myocardial ischemia in the canine model

The authors examined whether partial reperfusion protects against reperfusion ventricular fibrillation (VF) following severe acute myocardial ischemia. Fifty-seven dogs were divided into two groups. In group A (n = 21), the left anterior descending coronary artery was occluded for 10 minutes, followed by full reperfusion. In the remaining 36 dogs (group B), myocardial ischemia was induced by retrograde blood flow (RBF) for 10 minutes. Thereafter, these dogs were divided into three subgroups: in group B1 (n = 10), full reperfusion was made by a carotid-left anterior descending coronary artery bypass; in group B2 (n = 13), partial reperfusion was achieved by collateral flow into the ischemic zone due to stopping RBF; in group B3 (n = 13), RBF was continued for an additional 5 minutes. During 10 minute ischemia, the myocardial blood flow at the ischemic zone measured by the H2 gas-clearance method was 12.3 +/- 2.0 ml/min/100 g in A, 3.4 +/- 0.9 ml/min/100 g in B1, 4.7 +/- 0.6 ml/min/100 g in B2, and 4.7 +/- 0.6 ml/min/100 g in B3 (A vs B1, p less than 0.02; A vs B2 and B3, p less than 0.01). Maximal ST-segment elevation was 11.4 +/- 1.8 mV in A, 28.2 +/- 2.7 mV in B1, 25.1 +/- 3.0 mV in B2, and 27.0 +/- 1.9 mV in B3 (A vs B1, B2, and B3, p less than 0.001). Maximal conduction delay was 48.6 +/- 9.4 ms in A, 106.4 +/- 5.2 ms in B1, 101.6 +/- 9.9 ms in B2, and 91.2 +/- 5.1 ms in B3 (A vs B1, B2, and B3, p less than 0.001). The incidence of reperfusion VF was 14% (3/21) in A, 80% (8/10) in B1, and 69% (9/13) in B2 (A vs B1, p less than 0.001; A vs B2, p less than 0.005). In group B3, VF occurred in only 1 of 13 dogs for the additional 5 minutes. It is concluded that reperfusion VF occurred frequently when ischemia was severe even though the duration of ischemia was short (B1), and that reperfusion VF was not prevented by partial reperfusion when the ischemia was severe (B2).

Relationship of alternans of monophasic action potential and conduction delay inside the ischemic border zone to serious ventricular arrhythmia during acute myocardial ischemia in dogs

We studied the relationship of conduction delay and monophasic action potential (MAP) at an ischemic border zone to serious ventricular arrhythmia (VA). Measurements were made in 36 adult mongrel dogs 15 minutes after occlusion of the left anterior descending coronary artery. We recorded MAPs and bipolar electrograms simultaneously inside and outside the ischemic border zone in the dog hearts. Of the 36 dogs, 24 that had favorable MAP recordings were chosen and were divided into two groups according to an occurrence of VA. In group A (n = 12), an onset time of VA was 5.1 +/- 0.8 minutes after ischemia, while in group B (n = 12) VA did not occur during ischemia. The conduction delay at the ischemic border zone was significantly greater from 3 minutes after ischemia in group A than in group B. MAP alternans, defined as the difference in duration of two consecutive MAPs inside the ischemic border, was marked in group A but mild in group B. Duration of a small MAP of alternans was markedly shorter than that of a corresponding MAP outside the ischemic border in both groups, but was followed by VA in group A. Duration of a large MAP was markedly prolonged compared with that of a corresponding MAP outside the ischemic border in seven dogs of group A and in only one dog of group B (p less than 0.01), and was followed by VA in seven dogs of group A. Our results suggest that the mechanism of VA is due not only to reentry but also to an injury current flowing from ischemic to nonischemic tissues, because VA was preceded by conduction delay and by a difference in MAP durations when comparing regions inside and outside the ischemic border.

[A case of intermittent ventricular pre-excitation syndrome with a Mahaim fiber]

A 61 year-old woman with intermittent ventricular pre-excitation syndrome using a Mahaim fiber was reported. The electrocardiogram showed QRS-complex with small delta wave (100 msec in QRS width) or without small delta wave (80 msec in QRS width). On electrophysiological study, during sinus rhythm, A-H interval was 100 msec. H-V intervals were 25 msec in QRS-complex with small delta wave and 45 msec in QRS-complex without small delta wave. From these findings, it was considered that the small delta wave was produced by a Mahaim fiber.

Effects of heart rate and diltiazem hydrochloride on alternans of ST segment elevation and ventricular arrhythmia during acute myocardial ischaemia in dogs

Although the incidence of ventricular arrhythmias following myocardial ischaemia lessens as ischaemia improves, it is not clear whether this is correlated with a reduction in the degree of ST segment elevation. To explore this further we examined the effects of change in heart rate and the administration of the calcium antagonist diltiazem, 0.02 mg.kg-1.min-1, on ST segment elevation and the alternans of ST segment elevation (STA) and on serious ventricular arrhythmia induced by 10 min occlusion of the left anterior descending coronary artery in 86 mongrel dogs. The dogs were divided into three groups: 26 dogs paced at a rate of 180 beats.min-1 (group A); 44 dogs paced at a rate of 120 beats.min-1 (group B); and 16 dogs paced at a rate of 180 beats.min-1 and given diltiazem intravenously from 25 min before the coronary occlusion (group C). The degree of ST segment elevation and STA within 3 min of ischaemia was significantly lower in group B than in group A. There was no marked difference in the degree of ST segment elevation between groups A and C, but the STA was lower in group C than in group A. Incidence of ventricular tachycardia and ventricular fibrillation was significantly lower in groups B and C than in group A, and the timing of their first appearance was 4.5 (SEM 0.6), 4.2(0.9) and 3.0(0.4) min, respectively. We suggest that the reduction in serious ventricular arrhythmias associated with the decrease in heart rate was caused by the improvement of STA secondary to the improvement of ST segment elevation.(ABSTRACT TRUNCATED AT 250 WORDS)

A case of left atrial automatic tachycardia successfully treated with aprindine

Electrocardiogram in a 15-year-old girl showed persistent supraventricular tachycardia at rates of 130 to 140 bpm. Electrophysiological study confirmed left atrial automatic tachycardia, which was transferred to sinus rhythm by intravenous infusion of aprindine (100 mg/10 min). Therefore, aprindine (60 mg/day) was administered orally, and neither recurrence of left atrial automatic tachycardia nor side effects were observed during subsequent follow-up period of 16 months.

Electrophysiological actions of mexiletine (Kö1173) on canine Purkinje fibres and ventricular muscle

1 The effects of mexiletine (Kö1173) were investigated in canine isolated cardiac Purkinje fibres and ventricular muscle with microelectrodes. Some Purkinje fibres were depolarized by mechanical stretch to induce spontaneous activity with slow upstroke velocity. The preparations were stimulated at rates of 1, 2, 3 and 4 Hz. The drug concentrations tested were 0.4, 2 and 10 mug/ml in Tyrode solution (KCl = 5.4 mM).2 The ;therapeutic' drug concentration (2 mug/ml) shortened action potential duration and effective refractory period of Purkinje fibres, the effect being pronounced at lower stimulation rates. In ventricular fibres, action potential duration changes were not consistent while the effective refractory period was prolonged.3 In depolarized Purkinje fibres showing automatic activity, the drug (0.4 or 2 mug/ml) depressed phase 4 depolarization and reduced the firing rate without changing maximum diastolic potential. However, when depolarized Purkinje fibres were electrically driven at a constant rate, the maximum diastolic potential became more negative with a concomitant decrease of pacemaker slope and increase of maximum rate of rise (V(max)) of action potentials.4 Moderate (2 mug/ml) to high (10 mug/ml) concentrations of the drug depressed V(max) in Purkinje fibres stimulated at 2 Hz by 12 and 42% respectively and depressed ;membrane responsiveness'. The decrease in V(max) depended upon the stimulation rate, being minimum at the lowest (1 Hz) and maximum at the highest (4 Hz) stimulation rate.5 The drug (2 mug/ml) improved V(max) of the earliest propagated premature action potentials by shifting the takeoff potential to more negative levels in both Purkinje and ventricular fibres.6 Membrane conductance in fibres mounted in a single sucrose gap chamber was increased by the drug (2 mug/ml) in both fibre types in normal and in Na(+)-deficient solutions. This increase was attributed to an increase in membrane K(+) permeability produced by the drug.7 All these effects are similar to those of lignocaine, diphenylhydantoin or aprindine, and can explain the antiarrhythmic action of mexiletine.

Automaticity and time-dependent conduction disturbance produced in canine ventricular myocardium. New aspects for initiation of ventricular arrhythmias

1) In isolated canine ventricular myocardium, automaticity could be induced by a passage of small depolarizing DC-currents. The mechanism was attributed to inflowing Ca++ and Na+ currents and time-dependent deactivation of outward K+ current under a condition of high membrane resistance due to an anomalous rectification. Significance of the automaticity was discussed in relation to the ventricular arrhythmias encountered in very early stage of myocardial infarction. 2) In in situ canine hearts, chloropromazine induced time (preceding cycle length)-dependent decrease in conduction velocity within the ventricle. Thus QRS-duration of non-premature beats was lenghtened at rapid pacing rates while QRS-duration of atrial premature beats was lengthened also at short coupling intervals in the drug-treated dogs. These slow conductions were not due to reduced take-off potential of action potentials bue due to drug-induced slow recovery of rapid Na+ system. The phenomenon may be responsible for reported QRS-prolongation and fatal ventricular arrhythmias encountered in the patients receiving phenothiazines.

The prolongation of QRS-duration resulting from delayed recovery of ventricular excitability. A new mechanism for intraventricular conduction disturbance. A preliminary note

Chlorpromazine (1, 5, and 20 mg/Kg) was injected intravenously to anesthetized and open-chest dogs under artificial respiration. Using right atrial pacing, the heart rate was increased stepwise from intrinsic sinus rate to higher rate where the A-V block first developed. ECG (II) was recorded simultaneously with arterial blood pressure, ventricular monophasic action potentials and left atrial electrogram. In the control, QRS-duration was constant (46.9 +/- 0.8 msec) irrespective of heart rate. After the drug injection, however, the duration increased significantly with increasing heart rate, the effect depending on the injected dosage (r==0.283, P less than 0.1 in 1 mg/Kg; r==0.406, P less than 0.01 in t mg/Kg; r==0.631, P less than 0.001 in 20 mg/Kg). During the drug action, QRS-duration of atrial premature beats was also longer than that of sinus beats, and the lengthening increased with shortening of preceding cycle length. The observed QRS-prolongations were due to neither incomplete ventricular repolarization nor bundle branch block. The mechanism of prolongation was attributed to delayed or time-dependent recovery of ventricular excitability, i.e., slowed removal of inactivation in rapid sodium system in the ventricular muscle fibers.

Electrically induced automaticity in canine ventricular myocardium

Repetitive spontaneous action potentials (SAP) could be induced in canine ventricular and atrial muscle, although this inhibitory action was antagonized by the pretreatment with voltage range between about -60 mV and 0 mV. The SAP seemed dependent on both slow inward Ca2+ and Na+ currents and was suppressed by verapamil, Mn2+, and diltiazem, but not by tetrodotoxin. The increase of extracellular potassium concentration also suppressed the SAP. Acetylcholine could not block the SAP in ventricular muscle, but inhibited that in atrial muscle, although this inhibitory action was antagonized by the pretreatment with atropine. The automatic activity was attributed to slow inward Ca2+ and Na+ currents modified by decreasing time-dependent K+ outward current and K+ anomalous rectification.

Spontaneous electrical activity induced by depolarizing currents in canine ventricular myocardium. A preliminary note

Spontaneous action potential (AP) discharge could be induced by an application of long (5-10 sec) depolarizing currents in 68% of canine ventricular myocardium tested in the voltage range between about -65 and -10 mV. The constant currents of various intensities were applied across a sucrose gap, and intracellular potentials were recorded with a microelectrode. The firing rate of the AP's was voltage-dependent and ranged between 0.7 and 2.5 Hz. The AP was dependent on both [Ca++]0 and [Na+]0. Increase of [Na+]0. Increase of [Na+]0 from 37 to 149 mM increased the firing rate, maximum rate of rise, and overshoot of the AP's while increase of [Ca++]0 from 0.45 mM to 1.8 and 7.2 mM increased the firing rate and maximum rate of rise, but did not change the amplitude of overshoot. AP discharges were not blocked by tetrodotoxin (10(-5) Gm/ml), but were effectively blocked by verapamil (6 X 10(-6) Gm/ml). Adrenaline (5 X 10(-6) Gm/ml) initiated AP's in otherwise quiescent preparations. The results suggest that spontaneous AP's may be produced by inflowing of slow Na+ and Ca++ currents modified by underlying change of K+-permeability. Possible clinical significance of this phenomenon is discussed in relation to ventricular arrhythmia.