The follow-up measurements of the capture threshold are scheduled when no other pending features have a higher priority, starting with a device interrogation to determine whether some programmed settings might interfere with its search. Over time, these measurements are used to construct a curve of its trend. When verifying the capture threshold, the pulse generator prepares for a search, carries out the search and measures the threshold. at 1 a.m.), the pulse generator measures the capture threshold to determine the lowest pulse amplitude, combined with the shortest duration, which consistently captures the myocardium. This function presumes that the device is able to recognize the efficacy versus inefficacy of a given pulse output amplitude.Īt programmable time intervals (e.g. While these values can be manually programmed, the “Capture Management” function can be applied to manage the pacing outputs in the atrium and ventricle. Multiple causes including oversensing, wire fracture, lead displacement, or interference.įailure to capture occurs when paced stimulus does not result in myocardial depolarisation.The strength of the pacing pulses in each cavity hinges on their individually programmed amplitude and duration. 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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