Transition metal oxides with perovskite and spinel structures for electrochemical energy production applications

Transition metal oxide-based materials are an interesting alternative to substitute noble-metal based catalyst in energy conversion devices designed for oxygen reduction (ORR), oxygen evolution (OER) and hydrogen evolution reactions (HER). Perovskite (ABO₃) and spinel (AB₂O₄) oxides stand out against other structures due to the possibility of tailoring their chemical composition and, consequently, their properties. Particularly, the electrocatalytic performance of these materials depends on features such as chemical composition, crystal structure, nanostructure, cation substitution level, e_g orbital filling or oxygen vacancies. However, they suffer from low electrical conductivity and surface area, which affects the catalytic response. To mitigate these drawbacks, they have been combined with carbon materials (e.g. carbon black, carbon nanotubes, activated carbon, and graphene) that positively influence the overall catalytic activity. This review provides an overview on tunable perovskites (mainly lanthanum-based) and spinels featuring 3d metal cations such as Mn, Fe, Co, Ni and Cu on octahedral sites, which are known to be active for the electrochemical energy conversion.

Enzyme mediated synthesis of polypyrrole in the presence of chondroitin sulfate and redox mediators of natural origin

Polypyrrole (PPy) was synthesized by enzyme mediated oxidation of pyrrole using naturally occurring compounds as redox mediators. The catalytic mechanism is an enzymatic cascade reaction in which hydrogen peroxide is the oxidizer and soybean peroxidase, in the presence of acetosyringone, syringaldehyde or vanillin, acts as a natural catalysts. The effect of the initial reaction composition on the polymerization yield and electrical conductivity of PPy was analyzed. Morphology of the PPy particles was studied by scanning electron microscopy and transmission electron microscopy whereas the chemical structure was studied by X-ray photoelectron and Fourier transformed infrared spectroscopic techniques. The redox mediators increased the polymerization yield without a significant modification of the electronic structure of PPy. The highest conductivity of PPy was reached when chondroitin sulfate was used simultaneously as dopant and template during pyrrole polymerization. Electroactive properties of PPy obtained from natural precursors were successfully used in the amperometric quantification of uric acid concentrations. PPy increases the amperometric sensitivity of carbon nanotube screen-printed electrodes toward uric acid detection.

Design and synthesis of 6-anilinoindazoles as selective inhibitors of c-Jun N-terminal kinase-3

The structure-based design and synthesis of a new series of c-Jun N-terminal kinase-3 inhibitors with selectivity against JNK1 and p38alpha is reported. The novel series of substituted 6-anilinoindazoles were designed based on a combination of hits from high throughput screening and X-ray crystal structure information of the compounds crystallized into the JNK3 ATP binding active site.

[Isolated left ventricular muscular diverticulum in an adult. Value of non-invasive examinations]

The authors report a case of ventriculum in a 45 year old women investigated for chest pain. This was a congenital muscular left ventricular diverticulum confirmed by a complete imaging series including echocardiography, magnetic resonance imaging, angio-scintigraphy and conventional angiography. This diverticulum was unusual due to the fact that there was no associated congenital disease and that it was discovered in an adult. The authors review the literature and discuss the value of non-invasive imaging procedures.

[Palliative treatment of esophageal cancer with transendoscopic injection of alcohol]

BACKGROUND

Few patients who present with dysphagia from esophageal cancer are curable. The rates of surgical resecability are low and the reported 5-yr survival rates are < 10%. Nonsurgical, endoscopic palliation of obstructing gastrointestinal cancers has became popular with stents, Nd: YAG laser, BICAP tumor probe, self-expanding metallic stents. Because of limited availability and extraordinary cost of equipment, most gastrointestinal endoscopy units can't afford their acquisition. Endoscopic injections of ethanol are useful for palliation of malignant dysphagia.

AIMS

To examine if injections of ethanol are useful, in our patients, for palliation of malignant dysphagia.

PATIENTS, METHOD AND RESULTS

Six male patients with dysphagia caused by inoperable or unresecable esophageal cancer were treated by endoscopic injection of ethanol to induce tumor necrosis. Prior to treatment, patients had a mean dysphagia grade of 3.6. After treatment, an optimum dysphagia grade (mean 0.8) was achieved with a mean of 6 injections treatments. There were no complications associated with endoscopic injection of ethanol. Mean patient survival rate was 286 days (range: 36-973).

CONCLUSIONS

These results suggest that injections of ethanol to induce tumor necrosis have considerable potential for palliation of malignant dysphagia in patients with exophytic neoplasm.

[Extraction of foreign bodies in the esophagus. Experience in 215 cases]

OBJECTIVE

To analyze our experience in management of foreign bodies in esophagus.

BACKGROUND

At present, the flexible endoscope is usually the instrument of choice for foreign bodies of the esophagus. The rigid endoscope is less expensive, but the advantages of the flexible endoscope are numerous.

MATERIAL, METHODS

Management of 215 foreign bodies of esophagus are reported. The flexible endoscope was used to manage these foreign bodies. The patients comprised 151 children and 64 adults.

RESULTS

In children, coins were the commonest foreign bodies (119 cases), whereas in adults, the commonest cause was impacted meat (35 cases). Two hundred fourteen foreign bodies (99.5%) were successfully managed endoscopically. The surgery rate was 0.5%. There was no morbidity or mortality. In fifteen adults we diagnosed significant associated medical conditions: benign esophageal stricture in eleven, esophago-gastric junction carcinoma in one, two patients with esophageal motility disorders and remaining with Plummer-Vinson Syndrome.

CONCLUSIONS

The forward-viewing flexible endoscope has became the instrument of choice in diagnosis and management of esophageal foreign bodies.

[Management of difficult cases of biliary lithiasis]

To assess that insertion of a biliary endoprosthesis is a safe and effective treatment in patients with retained common bile duct stones (CBDS).

BACKGROUND

Before 1974, surgical exploration including cholecystectomy with choledochotomy was the only effective treatment for CBDS. However, morbi-mortality increases rapidly in the elderly and is over 10% in patients over 65, particularly if other serious medical conditions are present. Endoscopic sphincterectomy is now an established procedure, with a success rate of about 90%, complications are relatively rare, and mortality is about 1%. However, the size and number of the stones, the appearance of the terminal bile duct and presence of peripapillary diverticulum influence the outcome. At the present time technique of fragmenting the stones using intracorporeal electrohydraulic, extracorporeal shock waves or laser lithotripsy would be seen to be an attractive alternative approach. Endoprosthesis insertion is a safe, effective and cheap treatment in CBDS.

PATIENTS, METHODS AND RESULTS

40 patients with unextractable CBDS were studied and treated with endoscopic stenting. Four patients were lost for follow-up. The remaining patients comprised 29 females and 7 males, with a mean age of 67 years. Four patients underwent surgical treatment for post-sphincterotomy haemorrhage (1 patient), internal endoprosthesis migration (1 patient) and peripapillary diverticulum (2 patients). In 7 high-risk patients with large CBDS, recurrent obstructive jaundice was successfully treated by replacing the endoprosthesis. In 6 of them we added medical treatment with ursodeoxycholic acid and after 24 months follow-up, the stones disappeared. In 13 patients the endoprosthesis were inserted temporally, and in a second approach we removed the CBDS by mechanical lithotripsy. The remaining 12 patients were still alive without symptoms after a follow-up of 24 months.

CONCLUSIONS

On the basis of these findings we therefore concluded that endoscopic insertion of a biliary endoprosthesis is a safe and effective treatment for CBDS in patients in whom endoscopic sphincterotomy and attemps to remove the stones are not successful.

Effect of Different Surface Modifications on the Adhesion of Vulcanized Styrene-Butadiene Rubber

From the above results, the following conclusions may be drawn: 1. A water ultrasonic procedure for cleaning SBR surfaces has been proposed. The peel strengths attained with polyurethane adhesives are not great and increase with the amount and especially with the viscosity of the adhesive. 2. Surface roughening improves the adhesion between SBR and PUA. There are no important changes in peel strength with the amount and viscosity of the PUA. Zinc stearate removal could be responsible for the increase in peel strength. 3. Chlorination of SBR surface increases the peel strength with regard to ultrasonic-cleaned rubber, especially when both SBR test strip pieces are halogenated. This increase depends on the solvent and percentage of TIC, as well as the amount and viscosity of the adhesive. However, the type of solvent for TIC does not induce physical differences in the SBR surface, the variations being explained in terms of the extent of the chlorine reaction with double carbon bonds of butadiene; in fact, IR spectra show some bands due to the C-C1 groups and also for carboxylic groups. On the other hand, SBR chlorination creates cracks in the surface which are larger when the amount of TIC increases. Furthermore, peel strength, contact angle, and surface analysis measurements correspond well. 4. There is a degradation of the PUA during the time when chlorine reacts with the SBR surface. This reaction is favored by large TIC amounts when MEK is the solvent, and there are low adhesive viscosities. 5. The variation of the adhesion strength with the percentage of TIC depends more on the kind of solvent employed to disperse the halogen-precursor than on the chemical nature of the polyurethane adhesive, probably due to a chemical reaction between them which leads to different chlorinated products.

Ischaemia of the insular cortex increases the vagal contribution to the baroreceptor reflex in the rat

Neurones in the insular cortex have been shown to innervate medullary autonomic nuclei. Occlusion of the stem of the left proximal middle cerebral artery in rats caused a lesion in the insular and adjacent lateral frontoparietal cortices. Nine and 10 days after lesioning or sham operation, we examined the relationship between mean blood pressure and the heart rate in conscious rats, using the steady-state method. Individual contributions to blood pressure from the cardiac vagus and sympathetic nerves were determined after the administration of atenolol and methylatropine, respectively. Lesioning the insular cortex did not affect mean blood pressure or the heart rate. However, the lesion selectively enhanced the reflex vagal bradycardia that occurred when blood pressure was artificially elevated. There was no effect on the sympathetic heart rate range. These observations suggest that the unilateral cortical lesion chronically affected the baroreceptor control of the heart rate through mechanisms affecting the vagus.

Effects of middle cerebral artery occlusion on baroreceptor reflex control of heart rate in the rat

Neurons in the insular cortex have recently been shown to innervate medullary autonomic nuclei such as the nucleus tractus solitarii (NTS). The present study examines the effect of lesioning the insular cortex on baroreceptor-heart rate reflex in conscious rats. We did this by occluding the stem of the left proximal middle cerebral artery which causes a lesion of the insular and adjacent lateral frontoparietal cortices. Nine and 10 days after lesioning or sham operation, reflex heart rate responses were recorded following i.v. doses of the pressor agent phenylephrine and the depressor agent sodium nitroprusside. Baroreceptor reflex parameters were determined by computerized sigmoidal curve-fitting. The overall contribution of the sympathetic and the cardiac vagus were assessed by using peripherally acting muscarinic and beta-adrenoceptor antagonists, respectively. Lesioned rats were compared to sham-operated rats. Lesioning the insular cortex did not affect mean blood pressure and heart rate. However, the lesion selectively enhanced reflex vagal bradycardia that occurred when mean blood pressure was artificially elevated. A greater vagal bradycardia with no change in the upper plateau indicated that ischemia was acting entirely on the baroreflex-dependent vagal cardiac motoneurons. There was no effect on the sympathetic heart rate range but the normalized gain of the sympathetic component was increased in those lesioned rats. These observations suggest that the unilateral cortical lesion chronically affected the baroreceptor control of heart rate through mechanisms differentially affecting the vagus and the cardiac sympathetic nerves.

The chronotropic effect of adenosine and ATP in dogs. The antagonism by theophylline

We analyzed the action of adenosine and adenosine triphosphate (ATP) on the chronotropism of the dog heart in situ. The compounds were administered either intravenously (i.v.) after bivagotomy and propranolol treatment, or intracoronary (i.c.) in the sinus node blood supply. Under these conditions the intervention of reflex reactions was eliminated, and a constant and dose-dependent negative chronotropic effect was obtained. From the dose-response curves the relative potencies of ATP and adenosine were calculated, and found to be similar for both routes of administration (potency ratio 0.77 (0.72-0.82) by i.v. administration, and 0.52 (0.36-0.78) by intracoronary administration). The effect was also mimicked by 2-chloroadenosine, (a long acting P1 agonist), and by 5'-adenylyl (beta, gamma-imido) diphosphonate, a non-hydrolysable ATP analog. The chronotropic effect of ATP and adenosine were not prevented by 1 mg/kg atropine intravenous. Theophylline, at 3 mg/kg i.v., shifted the dose-response curves of i.v. ATP and adenosine to the right, suggesting a competitive antagonism. At a dose of 6 mg/kg theophylline, the effects of i.c. adenosine were competitively blocked. Theophylline also antagonized, in a competitive manner, the hypotensive effect of the i.v. administration of both compounds. Our results suggest that the chronotropic effect of purine compounds in anaesthetized animals could be brought about by a specific purinergic theophylline-sensitive mechanism and not by direct vagal activation.

Calcium blocking properties of piprofurol

Piprofurol is a benzofuran chalcon derivative. It was studied under various experimental conditions which allow the recognition of calcium antagonistic activity. Piprofurol inhibited in a concentration-dependent manner the calcium-induced contractions in isolated potassium depolarized preparations of rat aorta (pA2: 9.29) and relaxed the K+-induced contraction of the dog coronary artery and the rabbit basilar artery (IC's 50: 2 10(-8) M; 3 10(-9) M). Piprofurol also inhibited noradrenaline-induced vascular smooth muscle contractions but the antagonism was clearly noncompetitive and the contractions induced were altered by concentrations two orders of magnitude higher than the concentration inhibiting calcium-induced contractions. Calcium antagonism was demonstrated in cardiac muscle: calcium mediated slowly rising action potentials were evoked in partially depolarized guinea-pig papillary muscle by electrical stimulation in the presence of isoprenaline. Piprofurol decreased the rate of rise of these slow action potentials. The inhibitory effect was reversed by an elevation of the calcium concentration in the bath fluid. Piprofurol exerts a negative inotropic effect (IC50: 5 10(-6) M) on guinea-pig papillary muscle. The ratio IC50 inotropic action/IC50 relaxant activity was 230, i.e. higher than that obtained with verapamil or diltiazem, and near that observed for cinnarizine. The pharmacological profile from in vivo dog experiments is in agreement with its in vitro properties: coronary sinus blood flow was increased and heart rate decreased. These effects suggested a potentially anti-ischaemic activity. This is confirmed in anaesthetized dogs, where piprofurol reduced the epicardial ST-segment elevation following coronary artery occlusion, and in isolated heart preparations, where it decreased the leakage of LDH during periods of anoxia and reoxygenation.

Effects of carocainide (770207) on canine cardiac automaticity

The benzofuran derivative carocainide is a new class I antiarrhythmic drug which has been shown to prevent and stop experimental ventricular arrhythmias. The effects of this drug on different types of cardiac automaticity were investigated by experimental models using "in situ" dogs' hearts. Complete A-V block was produced by local formaldehyde injection into the A-V junction. Carocainide at doses of 2.5, 5 and 7.5 mg/kg body weight i.v. produced the following effects: a significant and dose-related slowing of the idioventricular rate; a non-significant change of the sinus rate at 2.5 and 5 mg/kg b.w.; and a significant decrease of the total number of triggered ventricular beats induced by ventricular pacing during slow norepinephrine infusion. Our results suggest that carocainide could be a safe and effective drug for the treatment of ventricular arrhythmias.

Electrophysiological effects of carocainide (770207) on the dog heart

The electrophysiological effects of carocainide (770207) were assessed in "in vivo" and "in vitro" experiments on dogs' hearts. Intravenous administration of 5 mg/kg body weight of carocainide significantly lengthened the following: A-H interval, the shortest atrial pacing cycle length maintaining 1:1 atrioventricular (A-V) nodal conduction, H-V interval, left bundle-ventricle (LB-V) interval, the shortest His bundle pacing cycle length maintaining 1:1 His-Purkinje conduction, QRS duration, right atrial and right ventricular effective refractory periods. In Purkinje fiber-papillary muscle junction preparations driven at a constant cycle length of 1000 msec, perfusion of carocainide at the concentration of 1.25 10(-5) M and 2.5 10(-5) M, increased conduction time between Purkinje and muscle fibers and decreased the rate of depolarization of Purkinje fibers and papillary muscle. These results suggest that carocainide depresses conduction and lengthens refractory periods at atrial and ventricular levels and provide an explanation for the positive effect of this compound against experimental cardiac arrhythmias.

Effects of MD770207 (carocainide) on experimental ventricular arrhythmias

Administered by intravenous or oral route, carocainide, MD770207, abolished experimental ventricular arrhythmias in anaesthetized and conscious dogs. Slow rate intravenous infusion (0.5 mg/kg/min) studies in conscious coronary ligated dogs demonstrated a good arrhythmia conversion as well as a wide margin of safety; mean conversion to 95% of normal sinus rhythm was achieved at 10.5 +/- 2.1 mg/kg while first signs of reversible neuro and cardio-toxicity occurred at 37.8 +/- 8 mg/kg. The reference agents disopyramide and lidocaine showed less favourable safety margin. Carocainide reduced epicardial ST-segment elevation produced by short coronary artery occlusion and prevented the occurrence of ventricular fibrillation resulting from reperfusion after acute coronary artery ligation. At antiarrhythmic dose levels there were no undesirable effects noted on cardiovascular function. Given intravenously the compound increased the ventricular fibrillation threshold in spontaneously hypertensive rats.

Reflex mechanisms responsible for early spontaneous termination of paroxysmal supraventricular tachycardia

The incidence and possible mechanism of early spontaneous termination of paroxysmal supraventricular tachycardia was studied in 20 consecutive patients. Episodes of induced tachycardia that terminated spontaneously within the 1st minute after initiation were included. Tachycardias ending spontaneously were associated with a reproducible course of hypotension at the onset followed by blood pressure recovery above control levels and termination. Spontaneous termination of tachycardias occurred within the A-V node 18 to 45 seconds (mean +/- standard error of the mean 27.9 +/- 5.3) after their onset. In the supine position (0 degrees) 9 (45 percent) of 20 patients showed spontaneous termination in 36 (16 percent) of 219 episodes of tachycardia. In the head-dependent position (-20 degrees) only 1 (8 percent) of 13 patients manifested spontaneous termination in 2 (4 percent) of 54 episodes. In the head up position (+60 degrees) only 1 (6 percent) of 18 patients exhibited termination in 2 (2 percent) of 102 episodes. After partial cholinergic blockade with intravenous hyoscine butylbromide, 20 mg, or atropine, 0.6 mg, none of five patients showed spontaneous termination in 25 episodes. After beta adrenergic blockade with 10 mg of propranolol intravenously, none of 16 patients showed spontaneous termination in 87 episodes of tachycardia. We conclude that the initial hypotension during tachycardia evokes a sympathetic response that increases blood pressure and this increase in turn causes a rise in vagal tone that breaks the tachycardia.

Continuous on-line beat-to-beat analysis of AV conduction time

A simple analog circuit is described which is capable of measuring on a beat-to-beat basis P-R, R-P, P-P, and R-R intervals during sinus rhythm and paroxysmal supraventricular tachycardia. In addition the circuit will emit a pulse when the consecutively alternating P and R wave sequence is interrupted thereby signalling a trigger problem or a change in rhythm. The operation of the device requires proper P and R wave sensing and provides outputs which are linear over a range of rates which are applicable to the human heart.

Vagal techniques for termination of paroxysmal supraventricular tachycardia

Maneuvers that reflexly increase vagal tone were deployed to terminate the tachycardia in 68 consecutive patients with paroxysmal supraventricular tachycardia. The order and success rate of the protocol was as follows: 57 episodes were terminated with carotid sinus pressure alone or after pretreatment with edrophonium, 5 were terminated with the Valsalva maneuvers and 6 were terminated with phenylephrine. Potency testing showed that phenylephrine evoked the greatest increase in vagal tone. All cases demonstrated slowing of tachycardia ranging from 40 to 220 ms +/- standard error of the mean (mean 79.0 +/- 3.8 ms) followed by abrupt termination. Pauses after termination ranged from 900 to 3,300 ms (mean 1,683.8 +/- 66.6) with 54 patients showing pauses of 2,000 ms or less. Termination was highly reproducible showing an overall success of 148 (92 percent) of 160 trials among 22 selected cases. The extent of increased vagal tone needed to terminate paroxysmal supraventricular tachycardia was raised by augmented sympathetic tone (infusion of isoproterenol) and decreased by reduced sympathetic tone (pretreatment with propranolol). Thus, paroxysmal supraventricular tachycardia can be rapidly, safety and consistently terminated by maneuvers that reflexly increase vagal tone.

[Electrophysiologic basis of the anti-arrhythmic action of amiodarone in man]

The aim of this study was to analyse the effect of an intra-atrial injection of 5 mg/kg of amiodarone on the heart rate, the A-V conducting pathways, and the right atrium and ventricle of 23 patients. By recording the potentials in the bundle of His, it was possible to measure the nodal A-V conduction time (A-H interval) and the conduction time below the bundle of His (H-V interval) during atrial pacemaking. The refractory periods were calculated by the stimulus-test method. The results were subjected to statistical analysis using Student's test. They may be summarised as follows: - slowing of the sinus rhythm; - depressed conduction in the A-V node, but without any effect on the speed of conduction infranodally; - an increase in the atrial effective refractory period; - persistant lengthening of both the effective and the functional refractory periods of the A-V node; - an increase in the relative refractory period in the His-Purkinje system, and in the effective refractory period of the ventricle. These findings throw light on the mechanism of the anti-arrhythmic action of amiodarone in man.

[Electrophysiologic effects of amiodarone in Wolf-Parkinson-White syndrome]

Eight patients with WPW syndrome were catheterised and, during the course of this investigation, the electrophysiological effects of amiodarone were assessed. By registering the potentials of the bundle of His and by using the stimulus-test technique, we were able to measure the refractory periods of the atrium and of the normal and accessory conducting pathways both before and during the first 40 minutes after an intra-atrial injection of 5 mg/kg of amiodarone chlorhydrate. The action of the conduction time was also studied. In the five cases in which we were able to measure it, the effective refractory period of the abnormal pathway increased, which led in two instances to the temporary suppression of all pre-excitation. At the same time, it was repeatedly found that the refractory periods of the A-V node were increased: the effective refractory period in 3/3 cases, and the functional refractory period in 2/2 cases. The effective refractory period of the right atrium was increased in 5 cases, and did not change in the others. The intranodal conduction time (A-H- interval) was always increased after amiodarone. Finally, in three patients runs of reciprocal tachycardia could be initiated by premature atrial stimulation. In one case, this was no longer possible after amiodarone. In the other two cases, although the attacks could still be brought on, they were slower because of the lengthening of the A-H interval. These findings explain why amiodarone is effective in controlling the tachycardia of WPW syndrome.

Retrograde conduction in complete atrioventricular block Study using His bundle recordings

Using His bundle recordings and ventricular stimulation retrograde conduction was studied in 57 cases of complete AV block. VA conduction was observed in 13 patients. Of the 13, 12 had AV block distal to H, and during cardiac pacing 5 of them showed a retrograde His bundle potential. In all cases the AV node-His pathway was implicated in the transmission of the retrograde impulse. There was no retrograde atrial response in the remaining patients. VA block usually occurred at the same level as AV block. Nevertheless, two cases of AV block distal to H were associated with concealed retrograde conduction which stopped within the AV node.

[Study of the electrophysiological properties of bretylium tosylate in man]

The electrophysiological changes induced by bretylium tosylate have been studied in 22 patients during the 45 minutes following the intra-atrial injection of the drug at the dose of 5 mg/kg. The potential in the bundle of His was measured, and the stimulus-test method used to determine the refractory period. The results were subjected to Student's test. The sinus rate increased after bretylium. The A-V nodal conduction time (A-H interval) and infra hisian conduction time (HV interval), evaluated at the same imposed frequency, were not affected. The functional refractory period of the A-Vnode was decreased. The relative refractory period of the His-Purkinje system was increased. Finally, the right auricle showed an increase in its effective refractory period, while that of the ventricle remained unchanged. This study suggests that the electrophysiological effects of bretylium are due both to direct action at the cellular level and to sympathetic activity.

Reciprocal rhythm in patients with normal electrocardiogram: Evidence for dual conduction pathways

The present study refers to six patients in whom an A-V reciprocal rhythm could be documented; in four cases it took the form of sustained tachycardia. None of the patients showed any ECG feature of ventricular pre-excitation (PR interval of more than 0.12 sec. and normal QRS configuration). The extrastimulus method showed, at first, that the A-V conduction time of the premature beat varied only slightly with the decrease of the coupling interval. From a critical A1A2 interval there was a sudden lengthening of A2H2 preceding the occurrence of re-entrant beats. The curve of H1H2 responses reflected these changes, showing two distinct parts. The second part following the slowing of the impulse included the initiation zone of atrial echoes and of reciprocating tachycardia. These results suggest the existence of two A-V pathways, one fast and the other slow. The point at which the break between the two parts of the curve occurred might be related to the effective refractory period of the fast pathway. In the same way, when atrial pacing reached a critical rate, it induced an abrupt increase of AH in five cases. In the sixth patient, A-V conduction time remained unchanged up to 170 per minute. Ventriculoatrial conduction was always observed, the delay of which did not lengthen with the rate. In one case tachycardia could be induced by a premature ventricular beat without lengthening of the V-A time. It is concluded that in spite of a normal PR interval, the presence of dual A-V pathways may be implied in the genesis of reciprocal rhythm.

[Ventricular tachycardia due to premature supra-ventricular beats with a normal QRS complex. Analysis of a case]

Report of attacks of ventricular tachycardia in a 39 year-old man, free from heart disease. Cardiac pacing showed that the tachycardia could be induced by premature supraventricular beats normally propagated to the ventricles, and by atrial acceleration. The same part played by the cardiac rate on triggering of attacks was demonstrated during ventricular pacing. Besides, the possibility to interrupt the tachycardia by one electrically induced ventricular beat, supports the hypothesis of a re-entry machanism. The QRS configuration during the arrythmia suggested a propagation of excitation starting from the posterior-inferior area of the left ventricle. However, the absence of anomalies of the supraventricular beats initiating the tachycardia excluded a circus movement resulting from a unidirectional block on the left anterior hemibranch. More probably there existed an area of micro-reentry, stimulating the left ventricle from the posterior branches of the His-Purkinje system.

[Electrophysiological study of 2 cases of ventricular pre-excitation compatible with the presence of Mahaim's fibers]

Report of two cases of ventricular pre-excitation in which the presence of Mahaim's fibres was suggested by the electro-physiological studies. In both cases, the short-circuit of the His bundle was responsible for the abnormally short HV interval. In a patient, atrial acceleration induced an increase of rh at first, related to an A-V delay without HV variation. For a cycle of 360 ms, HV lengthened suddenly from 15 to 40 ms while QRS changed configuration, which is in favour of a functional exclusion of an accessory pathway. Combination with the pre-excitation of a left bundle-branch block complicated, in this case, the problems of identification. The other case responded also to cardiac pacing by an increase of the A-V delay due mainly to intra-nodal conduction slowing. In the same time HV increases from 20 to 30 ms (for a cycle change from 480 to 315 ms) and the delta wave decreased progressively. For a higher rate there was a 2:1 A-V block proximal to H. The extrastimulus method produced initially the same results. On the contrary, when the coupling-interval decreased to 290 ms, HV increased suddenly from 25 to 45 ms, with disappearance of the pre-excitation pattern. At a still shorter interval, HV shortened again (25 ms) in parallel with a marked lengthening of the A-V nodal conduction times, thus revealing a "gap" phenomenon of the accessory pathway.