Estimulaçäo com adaptaçäo de freqüência controlada pelo sistema nervoso autônomo - uma avaliaçäo clínica / ANS controlled rate-adaptive pacing: a clinical evaluation

Para o tratamento da incompetência cronotrópica, marcapassos com adaptaçäo em freqüência baseados em diferentes sinais de sensores têm sido desenvolvidos, visando restaurar o mecanismo fisiológico em malha fechada e utilizando informaçäo fornecida pelo sistema nervoso autônomo (SNA). A medida da impedância cardíaca unipolar permite a monitorizaçäo do estado de contraçäo do coraçäo, diretamente relacionado ao tônus simpático. Marcapassos uni ou bicamerais com sistemas responsivos controlados pelo SNA foram implantados em 262 pacientes em vários centros clínicos. Protocolos de exercícios clíncos, monitorizaçäo por Holter, testes de estresse psicológico e estudos adicionais visando uma variaçäo intencional do tônus simpático confirmaram a resposta fisiológica em freqüência para os vários tipos de mudanças hemodinâmicas.

Estimulaçäo cardíaca atrioventricular sincrônica através de um eletrodo flutuante único (Modo VDD) / Synchronous atrioventricular stimulation of the heart with a single floating electrode (Mode VDD)

Um marcapasso bicameral que utiliza um eletrodo flutuante único para estimulaçäo no modo VDD foi implantado em 25 pacientes com distúrbios da conduçäo intra-cardíaca do tipo bloqueio atrioventricular total (21 pacientes) ou de 2o. grau (4 pacientes). Presumiu-se funçäo sinusial normal através do eletrocardiograma convencional e da história clínica. As etiologias dos distúrbios de conduçäo foram a miocardioesclerose (22 pacientes), cirúrgica (2 pacientes) ou a doença de Chagas (1 paciente). O eletro flutuante único SL 60 (Biotronik), dotado de dois sensores atriais situados a 13 cm da extremidade que contém o eletrodo ventricular unipolar, foi introduzido por via transvenosa. As medidas eletrofisiológicas (média +/_ erro padräo) no implante foram onda P de 2,87 +/_ 0,27 mV, QRS de 10,97 +/_ 0,92 mV e linmiar de estimulaçäo ventricular de 0,51 +/_ 0,04 V. O gerador de pulsos Dromos SL (Biotronik) foi mantido na programaçäo padräo. Após implante os pacientes realizaram teste ergométrico e/ou eletrcrdiograma ambulatorial de 24 horas. As complicaçöes registradas foram a perda da sensibilidade atrial em dois pacientes (8 por cento), requerendo reposicionamento do eletro, insuficiência cronotrópica ao exercício por bradicardia sinusal em um (4 por cento) e estimulaçäo de músculo peitoral ou inibiçäo temporária do gerador por miopotenciais em um (4 por cento), solucionada por reprogramaçäo. Em até 6 meses de seguimento, 24 pacientes (96 por cento) apresentam sincronismo atrioventricular adequado graçs estimulaçäo procuzida pelo marcapasso implantado. O implante de um marcapasso atrioventricular sequencial com eletrodo flutuante único é simples e a estimulaçäo VDD é efetiva em pacientes com bloqueios cardíaco e funçäo sinusal normal. Seu uso em pacientes chagásicos deve ser avaliado, pois miopotenciais cardíacos reduzidos podem comprometer a sensibilidade atrial.

Correlation between colposcopically directed biopsy and cervical loop excision.

Colposcopy is standard for diagnosis of cervical cancer precursors, but the development of diathermy loop electrodes for excision of the cervical transformation zone offers a technique for validation. Loop excision of the transformation zone was performed for 47 consecutive women with dysplasia in colposcopically directed biopsies using 20 x 8-mm electrodes. Specimens were marked for orientation and serially sectioned. All pathology material was reviewed. Although 28% of women had disappearance of dysplasia at the biopsy site, only 9% had no dysplasia in the transformation zone. Half of the women with CIN 1 on directed biopsy had high-grade lesions found in loop excision specimens. Significant discrepancies may be found between the results of colposcopically directed biopsy and loop excision.

Cardioversor-desfibrilador implantável. Nova opçäo terapêutica para as arritmias ventriculares malignas

As arritmias ventriculares malignas por definiçäo säo: taquicardia ventricular monomórfica sustentada (>30s); taquicardia ventricular polimórfica sustentada (sem desencadeantes agudos - IAM, hipóxia, distúrbios metabólicos, etc); sobreviventes de parada cardíaca por fibrilaçäo ventricular (sem desencadeantes agudos - IAM, hipóxia, distúrbios metabólicos, etc); taquicardia ventricular näo-sustentada (<30s - causando deswquilíbrio hemodinâmico). Estatísticas apontam que acometidas de morte súbita de igem cardíaca apenas nos Estados Unidos, a maior parte destes episódios causados por arritmias ventriculares malignas.

ANS controlled closed loop cardiac pacing - a multicenter study

A pacemaker system has been developed that in controlled by the autonomic nervous system (ANS). It measures the intracardiac impedance and derives a measure for the sympathetic drive from specific characteristics of the impedance curves. The pacing rate is adapted to this measure and thus is put under closed loop control of the ANS. In this paper the validity of the sensor principle and calculation of pacing rate were investigated. The formation of a closed-loop pacing rate regulation was demonstrad. Furthermore the entire system was validated in a clinical stting evaluating rate adaptive performance and benefit for the patient.

[Adequacy of of pacemakers responsive to the volume-minute ventilation rate in heart transplantation patients]. / Adequação de marcapasso com resposta de freqüência por volume-minuto respiratório em pacientes submetidos a transplante cardíaco.

PURPOSE: To evaluate in the late post-operative period (PO) the chronotropic response to exercise of patients submitted to orthotopic cardiac transplantation (CT) and the implant of a cardiac pacemaker (PM). METHODS: A rate response ventricular PM (VVI+R) which uses minute ventilation (MV) as a sensor was implanted in five patients in the early PO of CT due to chronotropic incompetence. The patients were 31 to 64 years old and the indication to implant of PM was low ventricular escape rhythm following atrial taquicardia/bradycardia (one case) or sinus bradycardia (4 cases). The study was performed by means of paired exercise tests using Naughton protocol in order to compare the heart rate in VVI (prefixed heart rate) and VVIR+MV (rate response) mode. The duration of the exercise was compared between the two modes of stimulation. RESULTS: In VVI mode the heart rate was significantly lower than in VVIR+MV mode for comparable periods of exercise (101 +/- 12 ppm vs 132 +/- 4 ppm; p < 0.05); in VVIR+MV mode the patients had a prolonged time of exercise as compared to VVI mode (15 +/- 7 min vs 12 +/- 7 min; NS). CONCLUSION: The MV rate response PM provided patients with satisfactory heart during exercise and may be an adequate option to patients submitted to CT who present chronotropic incompetence.

[Use of implantable pacemaker in the treatment of paroxysmal supraventricular tachycardia refractory to pharmacologic therapy]. / Uso de marcapasso implantável no tratamento da taquicardia supraventricular paroxística refratária à terapêutica farmacológica.

PURPOSE: To evaluate the results with the use of an automatic antitachycardia pacemaker in patients with refractory paroxysmal supraventricular tachycardia. PATIENTS AND METHODS: Nine patients aged 32 to 63 years with symptoms from 2 to more than 40 years and prophylactic treatment with several antiarrhythmic drugs that had failed to control tachycardia. The frequency of attacks in the year before the implant was from 1 per month to 3 daily and 4 of patients required direct counter current cardioversion at least once. The electrophysiologic studies demonstrated atrioventricular (AV) nodal reentry in 6 and AV reentry utilizing an accessory AV connection in 4 patients (in one patient both mechanisms were present). The patients have been followed from 2 to 18 months. RESULTS: All patients experienced new episodes of the arrhythmia that were successfully terminated by the pacemaker. Two patients presented episodes of tachycardia not terminated by the pacemaker. These events were successfully treated by reprogramming the unit. The drug treatment was discontinued in 7 patients. CONCLUSION: The antitachycardia pacemaker proved to be an effective therapeutic tool in reentrant supraventricular tachycardia refractory to pharmacologic therapy.

An unusual receptor mediates adenosine-induced SA nodal bradycardia in dogs.

To characterize the receptor mediating the negative chronotropic effect of adenosine in dogs, experiments were performed on conscious dogs with chronically implanted cardiovascular instrumentation. Autonomic blockade was used to eliminate any reflex influences on heart rate. Intravenous bolus injections of various adenosine analogues caused dose-dependent, aminophylline-blockable reductions in heart rate with a potency order of 5'-(N-ethylcarboxyamido)-adenosine (NECA)-78:2-chloroadenosine-17:adenosine-1. Dipyridamole enhanced the potency of adenosine to equal that of 2-chloroadenosine. Moderately selective A1-receptor agonists N6-(L-2-phenylisopropyl)-adenosine (R-PIA) and N6-cyclohexyladenosine and an A2-selective agonist 2-phenylaminoadenosine (200 nmol/kg) had no negative chronotropic effect in the conscious dog. Adenosine and its analogues, including R-PIA, caused coronary vasodilatation at smaller doses than were required to slow the heart rate. The selective A1-adenosine receptor blocker xanthine amine congener (XAC) antagonized the negative chronotropic action of adenosine but did so nonselectively, as the coronary vasodilative and negative chronotropic actions of adenosine were antagonized equally well. The spontaneous contraction rate of isolated perfused dog right atrial preparations, which included the sinoatrial node, was reduced by intrasinoatrial node artery infusions of adenosine analogues with a potency ratio of NECA-100:adenosine-15:N6-cyclopentyladenosine-2.3:R-PIA-1. We conclude that the adenosine receptor mediating the negative chronotropic action of adenosine in the dog does not display the pharmacological characteristics of either typical A1- or A2-adenosine receptors. Instead, either a novel adenosine receptor or an A1-receptor with unusual agonist and antagonist binding properties appears to exist in the dog's sinoatrial node.