[Rate-responsive cardiac pacing].

The term "synchronous pacemaker (SPM)" is used to describe all pacemakers of which the frequency can be accelerated by means of a sensor other than the sinus node. The most commonly used system is the detection of changes in physical activity by means of a quartz crystal included in the casing. Changes in respiratory volume, the respiratory rate, the QT interval or central temperature have been less successfully used. Single and double-chamber (DC) synchronous pacemakers exist. Ventricular single-chamber synchronous pacemakers (VVIR) are primarily intended for active patients in a state of chronic atrial fibrillation or, secondarily, in cases in which the insertion of an atrial electrode raises difficulties. The single-chamber atrial synchronous pacemaker (AAIR), or preferably the double-chamber equivalent (DDDR) is intended for the correction of chronotropic failure, whether this is primary or induced by bradycardiac antiarrhythmic medication. AVB should be treated by double-chamber simulation designed to pick up P waves. The value of the synchronous pacemaker in these patients is that it makes it possible to partially offset the loss of atrial systole in cases of ventricular fibrillation by a synchronous pacemaker (pacemaker programmed to shift from DDD to VVIR). The setting of the SPM is fairly complex and calls for exercise tests. Iatrogenic acceleration is not unusual and must be identified by long-term recordings. All these pacemakers will here include a "synchronous" option, which may be of variable efficacy. It is up to the clinician to use them appropriately, and not automatically, remembering that the best sensor is the sinus node and that synchronous pacemakers are only second best.