tailieunhanh - Dual-chamber pacing: Special considerations

In Chapter 5, we discussed types of pacemakers and the hemodynamics of pacing, so now we can take a closer look at some of the features unique to dual-chamber pacing. Lower Rate Limit of DDD Pacemakers | This rhythm may occur in a DDD paced patient. The origin and propagation of this rhythm is demonstrated in Figure 6-4. In the first beat the patient has normal function, in this case atrial pacing and ventricular conduction with a normal QRS. This is followed by a PVC with retrograde P wave. This P wave falls within the PVARP of the previous beat. It also initiates a new PVARP. (Please note that we will be using the term refractory period in both its physiologic sense and its pacemaker sense. For people new to pacing and not routinely versed in electrophysiology, this is a very important teaching point.) Because the retrograde P wave occurred within the PVARP, the pacemaker does not respond to it as an atrial event. The next event shown in the figure is the appropriate atrial spike. Because the atrium is still physiologically refractory, there is no capture of the atrium and the baseline remains flat. This is then followed by a ventricular-paced beat, which initiates another retrograde P wave and the rhythm is thus propagated.