The inhibited pacemaker (VVI or AAI) has become the most popular in recent years because of its ability to combine a physiological advantage with economical current consumption in cases with spontaneous activity. One of its disadvantages is its sensitivity to external electromagnetic interference. Though today's pacemakers possess effective protection against most interference signals there may be instances in which patients are subjected to uncomfortable or even life-threatening situations. This is the case of "amplitude modulated" or "pulsed" fields with modulation frequencies in the physiological range. Fields of that sort have been found in the vicinity of a welder, an electric steel plant, and in medical practice where therapeutic currents were applied. Even touch-actuated switches may influence a demand pacemaker. However, these situations may be overcome by a device within the pacemaker for simple time analysis which can be carried out with few components. If electromagnetic fields of diathermy equipment are applied, today's pacemakers may react with intolerably high or low rates. They should, therefore, be avoided.
There is still a high incidence of dislodgement, threshold rises, and loss of sensing with permanent transvenous endocardial leads. Atrial leads are an even greater problem and require particularly reliable methods of fixation. In March, 1976 we reported our preliminary results from animal experiments using a new transvenous screw-in lead with introduction protection. This lead differs from other screw-in models as its spiral tip is retracted in the insulating tube during insertion. For fixation purposes a torque is applied to the proximal end of the conductor coil, which is loosely positioned within the tube, and this moves the helical electrode forward. One hundred and fifty endocardial electrodes have been implanted; 127 of them in the dilated ventricle and 23 in the atrium. The technique of introducing the lead into the vein (cephalic or jugular) was the same as that for conventional leads. It was easy to manage and quite uncomplicated. The fixation features in the atrium or the ventricle were sufficiently reliable to allow some patients to go home several hours post-implant. The total working time of the leads used has been 900 months; the overall complication rate is 2%.
Internference with cardiac pacemakers Sources of of interference, pacemaker behaviour counteractionsAus der Abteilung Innere Medizin I der RWTH Aachen und dem Helmholt z-Institut /ür Biomedizinische Technik an der RWTH Aachen Gegenüber früheren Mitteilungen, in denen von Störungen bei Demand-Schrittmachern durch Haushaltsmaschinen, Rasiergeräte und Autozündanlagen berichtet wurde, treten als Störursachen in neuerer Zeit das Elektrokautergerät, Fernsehsender, Mikrowellen in den Vordergrund. Daneben gibt es auch Berichte über intrakorporale Störungen durch Muskelzittern und sich berührende Elektroden. Das Verhalten von synchronisierbaren Schrittmachern gegenüber niederfrequenten Störungen wird weitgehend durch ihre Filtercharakteristik und ihre Signalerkennungseinheit bestimmt. Heutige Schrittmacher schalten bei kontinuierlicher Störung um auf eine festfrequente "Störfrequenz". Durch Störungen mit Rauschcharakter kann es allerdings immer noch zur Inhibierung kommen. Durch verbesserte Filtercharakteristik dürfte dieses Problem jedoch in Zukunft zu beherrschen sein. Der Arzt, der Elektrotherapie verordnet oder Elektrodiagnostik betreibt, sollte bei Schrittmacherträgern unbedingt eine Pulskontrolle durchführen. Die Möglichkeiten einer Störbeeinflussung sollten nicht dazu führen, den festfrequenten Schrittmacher bevorzugt zu implantieren. Vielmehr sollte bei den Patienten, bei denen eine Störung zu erwarten ist oder sich bereits gezeigt hat, vermehrt der Stand-by-Schrittmacher Anwendung finden. Brought to you by |
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