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J Sousa

Publications and source records attributed to J Sousa.

At least 19 recordsLinked to original sources
PubMed2000

A mathematical analysis of TCR serial triggering and down-regulation.

Despite the increasing knowledge on the pathways involved in TCR signal transduction and T cell activation, the molecular mechanism of TCR triggering by ligand, MHC-peptide complexes, is still elusive and controversial. The present paper addresses the controversy on the early events of TCR engagement and triggering. Mathematical modelling techniques are applied to experimental data to infer plausible molecular mechanisms of TCR triggering and down-regulation. A similar approach has been followed by Bachmann et al. (Eur. J. Immunol. 1998, 28: 2571 - 2579), who concluded that the TCR triggering requires the formation of MHC-TCR dimers or trimers. We report here the failure to generalize this conclusion to the data reported by Valitutti et al. (Nature 1995, 375: 148 - 151). We show that there are several kinetic features in these experimental curves of TCR down-regulation that cannot be explained by the simple model proposed by Bachmann et al. unless some phenomenological extensions are considered. These extensions are: (1) a ligand independent turnover of the TCR; (2) a transient accumulation of triggered TCR; (3) a high order of TCR triggering kinetics; and (4) two pools of membrane TCR in dynamic equilibrium.

Animals↗
PubMed1999

Symptomatic calcified subdural hematomas.

Two unique cases of chronic calcified subdural hematomas are reported in children as a long-term complication of a ventriculoperitoneal shunt. Both the patients had undergone shunt procedures in infancy for congenital hydrocephalus. In one patient, the cause of the hydrocephalus was aqueduct stenosis, while in the second patient, a lumbar meningomyelocele was associated with hydrocephalus. In both these patients, a ventriculoperitoneal shunt was done in infancy. In one of them, following the shunt surgery, a bilateral subdural collection was noticed which required burr hole evacuation. Both the patients remained asymptomatic for 9 years, when they presented to our center with acute raised intracranial pressure and contralateral hemiparesis. Both the patients had a relatively short history and had altered sensorium at admission. Surprisingly, in both the patients, the CT scan showed significant mass effect producing calcified subdural hematomas. The shunt systems were found to be working well at surgery. Craniotomy and excision of the calcified subdural hematomas was undertaken. Postoperatively, the patients showed satisfactory recovery, and at discharge the patients were doing well. At the follow-up at the outpatient clinic, the patients were asymptomatic.

Calcinosis↗
PubMed1998

[Thyrotoxicosis induced by amiodarone].

The Authors report a case of toxic multinodular goiter induced by longstanding administration of Amiodarone, in which the option was near total thyroidectomy for control of toxic symptoms without withdrawal of the antiarhuthmic drug. In this case, the post-operative period was complicated by compressive cervical hematoma, which was managed by performing an emergent tracheostomy.

Amiodarone↗
PubMed1998

[Thyrotoxicosis induced by amiodarone].

The Authors report a case of toxic multinodular goiter induced by longstanding administration of Amiodarone, in which the option was near total thyroidectomy for control of toxic symptoms without withdrawal of the antiarhuthmic drug. In this case, the post-operative period was complicated by compressive cervical hematoma, which was managed by performing an emergent tracheostomy.

Amiodarone↗
PubMed1998

[Treatment of malignant ventricular arrhythmia guided by electrophysiologic study].

The purpose of this study was to assess the results of the treatment of malignant ventricular tachyarrhythmias guided by electrophysiologic studies. Thirty patients with ventricular arrhythmias, aged 56.6 +/- 14.1 years, were submitted to EP testing. The clinical presentation of arrhythmia was sustained monomorphic ventricular tachycardia in 24 (80%), non-sustained ventricular tachycardia in three and another three were survivors of sudden cardiac death. Twenty five patients (83%) had evidence of structural heart disease and left ventricular ejection fraction was less than 40% in 16 (53%). Antiarrhythmic drugs were considered effective when sustained monomorphic ventricular tachycardia was noninducible or significantly slowed in serial EP testing. Sustained monomorphic VT was induced in 19 patients (63%) and an effective drug therapy was found in 13 (68%). In the other 11 patients sustained arrhythmias were not induced, although in six of them the study was done already under antiarrhythmic drugs, that were continued in the follow-up. In the six patients in which an effective drug regimen could not be found and in two sudden death survivors with primary ventricular fibrillation and negative EP testing, an Implantable Cardioverter-Defibrillator was implanted. After 17.8 +/- 10.5 months, there was recurrence of the arrhythmia in 4 (18%) of the 22 patients on antiarrhythmic drugs and half of the patients with ICDs received appropriate therapy from the device. Three patients (10%) died in the follow-up, of which only one due to sudden death. We conclude that selection of optimal antiarrhythmic treatment based on the results of EP testing, is associated with decreased episode recurrence and sudden death.

Adult↗
PubMed1997

Failure of single- and multisite high-frequency atrial pacing to terminate atrial fibrillation.

This study determined the efficacy of single- and multisite atrial pacing for terminating episodes of atrial fibrillation induced in patients in the electrophysiology laboratory. One- to 5-second bursts of atrial pacing at a cycle length of 20 ms were not effective in terminating atrial fibrillation, when delivered either in the high right atrium or when delivered simultaneously at the high right atrium, midseptum, and coronary sinus.

Atrial Fibrillation↗
PubMed1997

[The implantable cardioverter-defibrillator: the Portuguese experience].

OBJECTIVE: The aim of this study was to review the Portuguese experience with implantable cardioverter-defibrillator therapy (ICD), in order to evaluate the increase in the number of ICD implanted, the main indications for this kind of therapy, the technical evolution of the procedure and the results of the follow-up of these patients during the last five years. PATIENT SELECTION: The study group consists of 58 patients, 53 male and 5 female, mean age 54 +/- 14 years with ICD implanted in our country since 1992. The ICDs were implanted in 4 Hospitals, namely, Santa Cruz Hospital with 36 patients, Santa Maria Hospital with 11, Santa Marta Hospital with 8 and Coimbra University Hospital with 3 patients. Twenty six patients were resuscitated from cardiac arrest and the other 32 had ventricular tachycardia (VT) not tolerated haemodynamically and refractory to therapy. The diagnosis was coronary artery disease in 31 patients, dilated cardiomyopathy in 8, valvular disease in 4, congenital cardiopathy in 3, right ventricular dysplasia in 2, congenital long QT syndrome in 1, hypertrophic cardiomyopathy in one. Seven patients had idiopathic ventricular fibrillation without structural heart disease and one patient had isolated right ventricular dilatation. METHODS: All patients underwent electrophysiological study before ICD implantation. In 2 patients epicardial leads were used and in the remaining 56 patients a transvenous approach was used. The device was implanted in an abdominal position in 36 patients and in a pectoral position in 22. Defibrillation and pacing thresholds were measured during the implantation procedure and whenever necessary. Patients were followed up on an outpatient basis with evaluation of the number of arrhythmic episodes, therapy efficacy with reprogramming of the device when required. RESULTS: The number of implantations has increased, from 4 devices implanted in 1992, to 32 in 1996. The implantation was successful and without mortality or complications in all patients. Defibrillation threshold was 16 +/- 3 J, with an electrode impedance of 48 +/- 9 Ohms. During a mean follow-up time of 18 +/- 15 months (1 to 56) 5 patients died, one of sudden death and 4 of non cardiac deaths, 15 patients were re-admitted to hospital and in 8 patients the device was replaced due to exhaustion. In this period, 37 patients (64%) had arrhythmic episodes detected by the device, 32 patients (55%) had shocks and 9 (16%) were treated with anti-tachycardia pacing. Inappropriate shocks were observed in 10 patients (17%). The ICD were reprogrammed in 11 patients. CONCLUSIONS: Portuguese experience with IC implantation is increasing and has shown to be a safe procedure with no operative mortality or morbidity. The incidence of appropriate shocks was high with a good efficacy in sudden death reduction.

Adult↗
PubMed1997

[A comparison of unipolar versus bipolar mapping in the ablation of left-sided accessory atrioventricular conduction pathways].

PURPOSE: To compare the utility of unipolar versus bipolar mapping to guide radiofrequency catheter ablation of manifest left-sided accessory pathways. SETTING: University Hospital PATIENTS AND INTERVENTIONS: We studied twelve patients with a mean age of 42 +/- 13 years, submitted to a successful left-sided accessory pathway ablation. Detailed mapping was performed with the ablation catheter, recording simultaneous unipolar (distal electrode) and bipolar electrograms, in sinus rhythm. Twenty-three recordings were analyzed, including twelve successful, and eleven unsuccessful sites. The following measurements were analyzed: atrial and ventricular amplitude; interval between atrial and ventricular electrogram onset; interval between onset of ventricular electrogram and delta wave; interval between ventricular electrogram activation and delta wave and; unipolar morphology, classified as P-rS, P-QS or PQS. MAIN RESULTS: Accessory pathway ablation required a mean of 6.3 +/- 7.9 (median of 2) energy applications. Analysis of the electrogram revealed that ventricular activation was significantly earlier in successful versus unsuccessful sites. Unipolar morphology was also different according to the ablation result: among unsuccessful applications the P-rS configuration occurred in one, and the P-QS in ten cases, while in successful sites, seven had P-QS, and five had PQS morphology. CONCLUSIONS: Unipolar recordings are useful to guide radiofrequency catheter ablation of manifest left-sided accessory pathways and should be used in association with bipolar electrograms.

Adult↗
PubMed1995

[The catheter ablation of atrioventricular nodal reentry tachycardia: the results of a mixed electrophysiological/anatomical technic].

OBJECTIVE: To describe the results of radiofrequency catheter ablation of atrioventricular nodal reentrant tachycardia (AVNRT) by using a mixed electrophysiologic/anatomic mapping technique. DESIGN: Consecutive patients with AVNRT, submitted to AV node modification between November 1992 and March 1995. SETTING: Cardiology Department at an University Hospital. INTERVENTIONS: Twenty consecutive patients with AVNRT were submitted to AV node modification. The ablation technique included two sequential steps. Initially, a detailed electrophysiologic mapping was performed with the ablation catheter, positioned near the coronary sinus ostium, looking for a specific recording: fractionated atrial electrogram, suggestive "slow pathway" potential and a ratio of atrial: ventricular electrogram amplitude > 1. In case of failure, after 5 applications of radiofrequency energy, an anatomic technique was used. The fluoroscopic image, in left anterior oblique projection, was used to guide catheter progression, and the radiofrequency energy applied sequentially in the posterior (P), followed by medium (M) and anterior (A) septal areas if needed. Radiofrequency energy was applied a power of 16-36 watts for 30-60 sec. If a His bundle deflection > 0.0025 mV was recorded, energy was not applied. MEASUREMENTS AND RESULTS: Suppression of a AVNRT was initially obtained in 19 patients (95%). A mean of 8.3 +/- 6.1 energy application were required. Mean during of the entire procedure was 142 +/- 45 min and the fluoroscopy duration was 22 +/- 12 min. There were no complications. The location of successful ablation areas was: P in 15 patients, M in three and A in one. After a mean follow up of 10 +/- 6 months, two patients had recurrence of AVNRT. A second procedure was successful in the initially failed patient and in these two recurrences. CONCLUSIONS: A mixed electrophysiologic/anatomic mapping technique to perform radiofrequency catheter ablation of AVNRT was associated with high efficacy and no complications.

Adult↗
PubMed1994

[Atrioventricular junction ablation: therapy of refractory atrial tachyarrhythmia].

OBJECTIVES: To assess the safety and efficacy of radiofrequency atrio-ventricular junctional ablation. DESIGN: Consecutive group of patients with refractory atrial tachyarrhythmias in whom catheter ablation of the atrio-ventricular junction was performed. SETTING: Cardiology Department at University Hospital. INTERVENTIONS: Atrio-ventricular junctional ablation was performed in 13 patients with a mean age of 53 +/- 13 years. Among six patients there was no evidence of organic heart disease, two had operated congenital heart disease, two had hypertensive heart disease, one had rheumatic heart disease with a prosthetic valve and the other had ischemic heart disease. The indication for ablation was drug-refractory atrial tachyarrhythmia in all patients: atrial fibrillation with uncontrolled rate in eight patients, atrial flutter in three, atrial tachycardia in one and inappropriate sinus tachycardia in one. An average of 3.7 +/- 0.9 anti-arrhythmia drugs was previously ineffective or associated with significant side-effects. Radiofrequency energy was applied between the distal pole of the ablation catheter and an indifferent cutaneous electrode with intensity of 40-65 volts for 30-60 secs. The ablation was initially performed utilizing the classical technique with the ablation catheter across the tricuspid valve. In the case of failure, an alternative method was used, with the ablation catheter positioned in the left ventricular septum. After the procedure a VVI-R permanent pacemaker was inserted in all patients. MEASUREMENTS AND RESULTS: Atrio-ventricular junctional ablation was successful in all patients after an average of 4.4 +/- 3.7 radiofrequency applications. The classical technique was successful in 11 patients (85%). The average amplitude of the His bundle electrogram recorded in the successful sites was not significantly different from the average maximum amplitude at unsuccessful sites (0.1 +/- 0.05 mV vs. 0.17 +/- 0.12 mV). There were no complications related to the procedures. During a mean follow-up of 7 +/- 4 months there was functional and symptomatic improvement in all patients. The only significant complication was an episode of sustained ventricular tachycardia that occurred three months after the ablation in a patient with Tetralogy of Fallot. CONCLUSIONS: In patients with refractory atrial tachyarrhythmias, atrio-ventricular junctional ablation is a safe and effective therapeutic option. The alternative technique should be reserved for cases of unsuccessful ablation with the classic method. Due to its potential significant side-effects, this therapy should be a last alternative option.

Adult↗
PubMed1993

[The diagnosis and ablation of accessory atrioventricular pathways in the initial electrophysiological exam: a new therapeutic modality in pre-excitation syndromes].

OBJECTIVE: To describe the experience and results in the diagnosis and catheter ablation of atrioventricular accessory (AP) pathways during the initial electrophysiologic study. DESIGN: We performed catheter ablation at the time of an initial electrophysiologic study in 22 consecutive patients (12 W and 10 M, mean age 42 +/- 15) with Wolff-Parkinson-White syndrome or supraventricular tachycardia. SETTING: Cardiology Department at University Hospital. INTERVENTIONS: The precise AP mapping was performed with the ablation catheter (4 mm distal electrode and deflectable tip) according to the earlier ventricular activation during sinus rhythm or the earlier atrial activation during ventricular pacing or orthodromic reentrant tachycardia. For left-sided pathways the ablation catheter was positioned on the mitral annulus retrogradely across the aortic valve, while for right-sided pathways it was positioned on the tricuspid annulus or near the coronary sinus os. Radiofrequency energy was applied for 20-60 segs with 55-65 Volts. MEASUREMENTS AND RESULTS: Seventeen AP were manifest and five were concealed. AP were left lateral in 11 patients (50%), left posterior in 5, and right postero-septal, right posterior or antero-septal in 2 patients each. The ablation was initially successful in 18/22 (82%), with 9 +/- 8 radiofrequency applications. Mean duration of the entire procedure was 145 +/- 59 min and the fluoroscopy duration was 39 +/- min. There were no major complications. During 2-9 months of follow-up AP conduction returned in two patients. CONCLUSIONS: Radiofrequency catheter ablation of AP is effective and safe and can be performed at the time of an initial electrophysiologic test, avoiding the need for long-term antiarrhythmic drug therapy or surgical ablation.

Adolescent↗
PubMed1992

Conversion of typical to "atypical" atrioventricular nodal reentrant tachycardia after radiofrequency catheter modification of the atrioventricular junction.

Typical atrioventricular (AV) nodal reentry tachycardia (AVNRT) is characterized by anterograde activation over a slowly conducting pathway and by retrograde activation through a rapidly conducting pathway. Preliminary reports suggest that radiofrequency catheter modification can eliminate typical AVNRT while preserving anterograde conduction. Radiofrequency catheter modification was used to treat 88 patients with typical AVNRT. After baseline electrophysiologic evaluation, the ablation catheter was positioned proximal and superior to the site of maximal His deflection. Radiofrequency energy was applied until there was significant attenuation of retrograde conduction, and elimination of AVNRT inducibility. Eighty-one patients were successfully treated and form the basis of this report. A new paroxysmal supraventricular tachycardia with RP greater than PR interval was induced at electrophysiologic testing after successful ablation in 9 patients (11%). Mean atrial-His activation time was 140 +/- 31 ms, and the ventriculoatrial activation time was 170 +/- 46 ms. This arrhythmia was induced only with ventricular pacing during isoproterenol infusion and appeared to be mediated by AV nodal reentry. New retrograde dual AV nodal physiology after modification was more frequent in patients with atypical tachycardia than in those without (4 of 9 vs 2 of 72; p less than 0.0001). Although none of the patients were treated, only 1 of 9 had an episode of spontaneous atypical tachycardia during a mean follow-up of 12 months. Results of this study confirm that typical AVNRT can be rendered noninducible without the complete destruction of reentrant pathways. Because induction of "atypical" AVNRT was not predictive of spontaneous arrhythmia recurrence, it should not be an indication for additional ablation sessions or long-term drug therapy.

Adult↗
PubMed1992

Effect of epinephrine on the efficacy of the internal cardioverter-defibrillator.

To evaluate the effect of sympathetic activation on the efficacy of the implantable cardioverter-defibrillator (ICD) in converting ventricular tachycardia (VT) or ventricular fibrillation (VF), 32 patients who received an ICD because of life-threatening VT/VF underwent 1 week postimplant ICD testing both before and after infusion of 25 (16 patients) or 50 (16 patients) ng/kg/min of epinephrine for greater than or equal to 12 minutes. These infusion rates are known to result in plasma epinephrine concentrations comparable to mild-moderate stress. The patients' mean age was 63 +/- 10 years; 26 had coronary artery disease, 2 had dilated cardiomyopathy and 4 had no evidence of structural heart disease. VT and VF were induced in 16 patients each by programmed stimulation or alternating current. Among the 16 patients with VT, the first ICD discharge (26 to 30 J) was effective in 15 patients in the baseline state and in all 16 patients during epinephrine infusion. Among patients with VF, the first ICD discharge (26 to 30 J) terminated VF in all patients in the baseline state, compared with 12 of 16 patients during epinephrine infusion (p less than 0.05). In 4 patients, VF was terminated during epinephrine infusion only by the second or third ICD discharge (30 J). In conclusion, physiologic increases in the plasma epinephrine concentration may increase the number and energy of shocks needed to terminate VF.

Aged↗
PubMed1992

Reversal of antiarrhythmic drug effects by epinephrine: quinidine versus amiodarone.

Although previous studies have demonstrated that the electrophysiologic effects of many antiarrhythmic agents can be reversed by catecholamines, the susceptibility of amiodarone to such reversal is unknown. The objective of this study was to compare the relative degree of reversal of the electrophysiologic effects of quinidine and amiodarone by epinephrine infusions that result in plasma epinephrine levels similar to those achieved during various physiologic stresses. Twenty-nine patients who had inducible sustained monomorphic ventricular tachycardia and underwent electropharmacologic testing with quinidine and amiodarone were enrolled in the study. The variables measured before and during an epinephrine infusion (25 or 50 ng/kg per min) included the sinus cycle length, mean arterial pressure, QT interval and effective refractory period at drive train cycle lengths of 600 and 400 ms. The effective refractory period measured at a drive train cycle length of 600 ms shortened less during amiodarone therapy (2 +/- 2%) than during quinidine therapy (6 +/- 4%) or than in the baseline state (6 +/- 4%; p less than 0.01). Similar results were obtained during evaluation of the effective refractory period at a cycle length of 400 ms. Epinephrine infusion, at both 25 and 50 ng/kg per min, completely reversed the effects of quinidine and partially reversed the effects of amiodarone on the effective refractory period. The effects of epinephrine on the sinus cycle length and QT interval were similar in the baseline state and in conjunction with quinidine and amiodarone. Twenty-four patients underwent programmed ventricular stimulation during amiodarone therapy alone and in conjunction with either a 25- or a 50-ng/kg per min infusion of epinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiodarone↗
PubMed1992

Recurrence of conduction in accessory atrioventricular connections after initially successful radiofrequency catheter ablation.

The purpose of this study was to characterize the incidence and clinical features of accessory pathway recurrence after initially successful radiofrequency catheter ablation and to identify variables correlated with recurrence. Radiofrequency ablation was performed with a 7F deflectable tip catheter with a large (4 mm in length) distal electrode. Left-sided accessory pathways were approached through the left ventricle and right-sided pathways by way of the right atrium. Patients were included in the study if 1) they had an initially successful procedure, defined as the absence of accessory pathway conduction immediately after ablation, and 2) had undergone a 3-month follow-up electrophysiologic test or had documented recurrence of accessory pathway conduction. Accessory pathway conduction recurred after initially successful ablation in 16 (12%) of 130 patients. Almost half (7 of 16) of these recurrences were in the 1st 12 h after ablation, and the last occurred after 106 days. Return of delta waves on the electrocardiogram (ECG) or spontaneous paroxysmal supraventricular tachycardia was the initial indication of recurrence in 15 of the 16 patients. Two patients with manifest accessory pathways exhibited recurrence with exclusively concealed accessory pathway conduction. Accessory pathways ablated from the tricuspid anulus (right free wall or septal accessory pathways) had a much higher recurrence rate (24%) than did those on the mitral anulus (6%). Fourteen of 15 patients have had successful repeat accessory pathway ablation after the initial recurrence. After a mean follow-up period of 4 +/- 3 months, there have been no repeat recurrences of any of these accessory pathways. It is concluded that accessory pathway recurrence is infrequent after successful radiofrequency catheter ablation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗