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Biomedical subjects

F Huerta

Publications and source records attributed to F Huerta.

At least 19 recordsLinked to original sources
PubMed1997

[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.

Angiocardiography↗
PubMed1989

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.

Animals↗
PubMed1989

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.

Animals↗
PubMed1985

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.

Action Potentials↗
PubMed1984

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.

Animals↗
PubMed1984

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.

Animals↗
PubMed1983

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.

Administration, Oral↗
PubMed1982

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.

Adrenergic beta-Antagonists↗
PubMed1981

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.

Atrioventricular Node↗
PubMed1980

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.

Adolescent↗
PubMed1976

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.

Adult↗
PubMed1976

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.

Adult↗
PubMed1976

[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.

Action Potentials↗
PubMed1976

[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.

Action Potentials↗