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.

Estudo multicêntrico comparativo de quatro diferentes tipos de sensores: atividade, acelerômetro, temperatura e período de pré-ejeçäo / Comparative study with different rate adaptive pacing systems

Recentemente diferentes princípios têm sido utilizado para estimular o coraçäo na tentativa de recuperar o débito cardíaco. Neste estudo multicêntrico, foram comparadas as respostas à estimulaçäo por 4 tipos de sensores, sendo 3 tipos de resposta de alça aberta (atividade física, acelerômetro e temperatura venosa central) implantados em 30 (SSIR-8 e DDDR-22), 9(SSIR-5 e DDDR-4) e 12 (SSIR) pacientes respectivamente. Um outro sensor do tipo alça fechada, sensível às variaçöes do sitema nervoso autôno, foi implantado em 57 pacientes, todos no modo DDDR. Os resultados obtidos durante a realizaçäo de atividade física diária, de teste ergométrico e de Holter de 24 horas foram comparados sendo possível observar uma maior fidelidade na curva de resposta de frequência frente a atividade física, nos pacientes submetidos à estimulaçäo de alça fechada

P wave recognition and atrial stimulation with fractally iridium coated VDD single pass leads.

UNLABELLED: The bottleneck of VDD systems is the reliable detection of the small atrial signals by a floating atrial electrode. Fractally iridium coated electrodes offer excellent sensing and pacing performance. In this study, the performance of such a floating atrial lead in P wave sensing and synchronous ventricular stimulation was examined. Atrial pacing was also used as a test of atrial wall contact. PATIENTS AND METHODS: A fractally iridium coated VDD lead was implanted in 18 patients. In 15 patients it was interfaced with a VDD pacemaker and in 3 patients with a DDD system depending on the P wave amplitude measured acutely (> or = 2 mV). Simultaneous recordings of the surface ECG and pacemaker telemetry were used to analyze P wave amplitudes and AV synchrony in different body positions, and during normal and deep breathing. Additionally, exercise tests based on daily life activities and 24-hour ECG monitoring were performed to test the pacemaker function. RESULTS: During implantation P wave amplitudes were 1.86 mV +/- 1.08 mV (range 0.5-4.9 mV) and during follow-up (6.6 +/- 5.6 weeks) 0.18-3.8 mV. Holter recordings revealed reliable P wave sensing at a sensitivity setting of 0.5 mV (95.5%). P wave sensing was further improved by a higher atrial sensitivity. AV synchronous pacing > or = 99.9% was achieved in all patients. In 7 patients the atrial electrode could be positioned close to the atrial wall enabling atrial stimulation thresholds at an average of 4.3 volts. CONCLUSION: This fractally iridium coated VVD lead allowed consistent and reliable P wave sensing at an atrial sensitivity as low as 0.5 mV in selected patients.

Transesophageal atrial pacing--stimulation and discomfort thresholds: the role of electrode configuration and pulse width.

A balloon catheter with six electrodes has been developed for transesophageal atrial stimulation of the human heart. Introduction is easy and its positioning is simple with the help of six unipolar atrial electrograms. In a group of 20 healthy volunteers, stimulation and discomfort thresholds (intolerable discomfort) were measured for three levels of pulse widths (12, 16, and 20 msec) and for five electrode configurations. Stimulation thresholds were below discomfort thresholds in each case. The stimulation threshold depended on pulse width and not on electrode configuration. The discomfort threshold, however, depended on the electrode configuration and not on the pulse width. A moderate but potentially important increase of the ratio between stimulation threshold and discomfort threshold could be achieved by combining a long pulse width (20 msec) and avoiding the largest distance between the active (cathode) and the passive (anode) electrode. Transesophageal atrial stimulation promises to be a practical noninvasive tool for the termination of regular supraventricular tachycardias, basal electrophysiological studies, and controlled acceleration of the heart rate in the study of myocardial ischemia.

Improved rate responsive algorithm in QT driven pacemakers--evaluation of initial response to exercise.

The QT pacemaker is a rate modulated pacemaker that uses the evoked QT interval as an indicator to determine its optimal pacing rate. Despite the generally favorable clinical results with this form of pacing, some flaws in the system have been reported, such as the frequently observed rather slow initial response of the pacing rate to physical exercise, and the phenomenon of oscillation of the heart rate. These problems can be attributed to the rate adaptive algorithm used in the current QT pacemaker. Recently, in a reexamination of the relationship between evoked QT interval and pacing rate, a curvilinear relationship between these parameters has been demonstrated. As a result, a new algorithm has been developed for the next generation of the QT pacemaker. Before this new algorithm was implemented in new implantable devices, it was evaluated in a multicenter clinical investigation, with emphasis on the initial response of the pacing rate to exercise. This study was carried out by means of special software in the programmer of the QT pacemaker. By employing real-time bidirectional telemetry, it was possible to submit the study population, consisting of 37 patients with implanted QT pacemakers of the current generation, to identical exercise tests. Comparing these exercise tests, it appears that a considerable gain in speed of response to exercise can be achieved by using the same sensor with a faster reacting, nonlinear rate adaptive algorithm.