双腔起搏器时间间期教学课件.ppt

* Dual-chamber pacing requires attention to these parameters: Lower rate AV and V-A intervals Upper rates Refractory periods Blanking periods * In order to provide optimal hemodynamic benefit to the patient, dual-chamber pacemakers strive to mimic the normal heart rhythm. In dual-chamber pacemakers, the lower rate is the rate at which the pacemaker will pace the atrium in the absence of intrinsic atrial activity. Similar to single-chamber timing, the lower rate can be converted to a lower rate interval (A-A interval), or the longest period of time allowed between atrial events. * This upper rate is defined as the upper activity rate, also known as the upper sensor rate or maximum sensor rate. Before mode switching was available, pacemakers utilized a separate activity/sensor rate and upper tracking rate to limit the rate to which the patient could track (e.g., in the presence of SVTs), but allow the patient to pace to higher rates if they were exercising. * The Post-Ventricular Atrial Refractory Period (PVARP) is the period of time after a ventricular pace or sense when the atrial channel is in refractory. In other words, atrial senses outside of blanking that occur during this period are seen (and marked 揂R) on the marker channel), but do not initiate an AV interval. The purpose of PVARP is to avoid allowing retrograde P waves, far-field R waves, or premature atrial contractions to start an AV interval which would cause the pacemaker to pace in the ventricle at a high rate. The refractory period after a ventricular event (paced or sensed) is designed to avoid restarting of the V-A interval due to a T wave. Ventricular sensed events occurring in the noise sampling portion of the ventricular refractory period are seen (and marked 揤R?on the marker channel) but will not restart the V-A interval. The atrial channel is refractory following a paced or sensed event during the AV interval. This allows atrial senses occurring in the AV interval to be seen but not resta