Failure to Sense vs. ArtifactFailure to Sense vs. ArtifactThe 12 lead EKG shows sinus rhythm with a left anterior hemi-block and a poor R wave progression compatible with a previous anterior myocardial infarction. The patient had recurrent ventricular fibrillation for which he was implanted with an implantable defibrillator.
The two spikes seen before the 6th and after the 7th QRS are suggestive of failure of sense on the part of the pacing section. As the spikes land in the QRS and the ST segment is it not possible to see if they capture the ventricle. (this would confirm that these are pacemaker spikes)
Another possibility is that the spikes are artifacts from another source that were recorded at the time of the EKG. This is the probable explanation as the rate of the spikes is about 60/min (about 5 large squares) and the device was set at 50/min. Further the interval between 5th QRS and the first spike of four large squares is shorter than the apparent pacing interval.
This can be checked in the pacemaker clinic by viewing the EKG and marker channel on the programmer display. Lack of sensing can be a serious problem as this may represent a lead failure which could make the device insensitive to a recurrent episode of VF.
The spikes are probably artifacts and not failure to sense.