![]() It varies with the manufacturer several manufacturers set a constant magnet rate well above the expected spontaneous rate (e.g., 100 beats per minute) in order to allow myocardial depolarization (pacing) to be confirmed ( Fig. The magnet rate (designated AOO, VOO, or DOO, as sensing, and therefore response to a sensed signal, do not occur thus, the letter “O”-an asynchronous mode) is that nonprogrammable rate that occurs when a magnet is placed over the pulse generator. Whereas these rates are often programmed to be the same, the sensor-based rate can be programmed to exceed the tracking rate in response to exercise, thereby avoiding rapid ventricular paced rates triggered by supraventricular tachycardias. The maximum tracking rate is that rate at which ventricular pacing will be triggered by native P waves in a 1:1 relationship (atrial based) the maximum sensor-based rate is the highest programmed rate dictated by sensor input to the pulse generator. The upper rate limit, which is either atrial (native P wave) based or sensor based, is the programmed maximum pacing rate that can occur. In devices programmed to rate responsiveness, the base rate is the lowest programmed rate at rest. The base rate (lower rate limit, standby rate) of a pacing system is that programmed rate at which pacing will occur if there is no spontaneous cardiac depolarization. This represents a dual-chamber pacemaker with ventricular pacing in response to atrial sensing (P-synchronous pacing). Multiple causes including oversensing, wire fracture, lead displacement, or interference.įailure to capture occurs when paced stimulus does not result in myocardial depolarisation.This 12-lead ECG tracing with rhythm strips shows a ventricular paced rhythm, but each ventricular paced beat is preceded by a sinus P wave (sinus rate of 55 bpm). Results in decreased or absent pacemaker function. Output failure occurs when a paced stimulus is not generated in a situation where expected. Reduced pacemaker output / output failure may be seen on ECG monitoring if the patient stimulates their rectus or pectoral muscles (due to oversensing of muscle activity). These inappropriate signals may be large P or T waves, skeletal muscle activity or lead contact problems.Ībnormal signals may not be evident on ECG. Oversensing occurs when electrical signal are inappropriately recognised as native cardiac activity and pacing is inhibited. Undersensing occurs when the pacemaker fails to sense native cardiac activity.Ĭauses include increased stimulation threshold at electrode site (exit block), poor lead contact, new bundle branch block or programming problems.ĮCG findings may be minimal, although presence of pacing spikes within QRS complexes is suggestive of undersensing. Pacemaker malfunction can occur for a wide variety of reasons, ranging from equipment failure to changes in underlying native rhythm.ĭiagnosis of pacemaker malfunction is challenging and often associated with non-specific clinical symptoms while ECG changes can be subtle or absent. Underlying rhythm left on its own, with a long pause followed by a ventricular escape beat. The ekg strip below shows the first two spikes pacing, then the pacemaker fails to pace. Its absence will result in the underlying rhythm running (if any). It may be the pacemaker battery, the leads or it could be an over sensing problem. ![]() In general, you will have no pacing spikes where they need to be. It could be an intermittent problem or failure altogether. There is no particular rhythm to define this. Somehow, the electrodes have no current flowing through them. Spikes are sensing correctly and pace the ventricles.įailure to output (failure to pace) simply means there is no output signal being generated from the pacemaker. (undersensing) shows the first two spikes fire out of place. ![]() Sensing issues are identified when there are pacemaker spikes showing up where they do not belong. Which occurs when a foreign signal (non-cardiac) such as a muscle twitch, are mistaken for real cardiac activity. Sensing problems include “undersensing” where the pacemaker fails to sense the native cardiac rhythm. In most cases, sensing problems are less threatening and can be corrected by performing a pacemaker interrogation. The example below shows the first two ventricular paced beats capture, then the next This is identified by having pacing spikes present with no resulting QRS, (capture). Failure to capture is when the pacemaker signal fires but there is no response.
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