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ED 4 | ED 5 | ED 6 | ED 7 | ED 8 ED 9 |
Edition 9 (Nov / Dec 2007)
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Patient was admitted for a non cardiac surgical procedure and reported occasional palpitations. A pacemaker check was requested as a result of this ECG. Patient has a dual chamber pacemaker (implanted 18thms ago). Last pacemaker check 6 months ago was normal. What’s the problem? The ECG shows a nodal tachycardia with what appears to be just a singular pacing spike occurring in the T wave every second complex. When the pacemaker is interrogated EGRAM 1 clearly shows DDD pacing occurring, albeit incorrectly. The atrial pacing spike is occurring within the R wave and its pacing polarity is bipolar, meaning that the pacing spike is small and therefore impossible to see on the surface ECG. Although its not clear from the surface ECG that it is the ventricular pacing spike that is seen, it is more easily visualised due to the pacing polarity being unipolar. |
 EGRAM1 |
As this is a nodal tachycardia the intrinsic atrial signal is within the pacemakers atrial blanking period and the pacemaker does not see it. The pacemaker will then assume there is no intrinsic atrial signal and try to pace the atrium which is annotated by an atrial pace marker (AP), and as atrial depolarisation has occurred (because of the nodal tachycardia) this will have no effect. After the atrial pacing marker (AP) an intrinsic ventricular signal occurs and is annotated by a ventricular sense marker (VS). As the ventricular sense (VS) has happened so soon after the atrial pace (AP) the pacemaker assumes the ventricular sense is an over sense and a ventricular safety pace occurs, as ventricular depolarisation has already occurred the pacing spike falls into the T wave and has no effect (although it is not desirable to have pacing occurring during the T wave!). The ventricular safety pace does have a marker but it is not annotated. The next ventricular event is only annotated by a ventricular sense (VS) as the pacemaker has not timed out for atrial pacing and the pacemaker assumes the ventricular sense (VS) is a ventricular ectopic. |
 EGRAM2 |
EGRAM 2 shows the attempt to terminate the tachycardia by pacing faster than the tachycardia rate. Unfortunately after the burst of faster pacing the tachycardia remains. Several attempts of increasingly faster pacing were made to terminate the tachycardia (not shown) but tachycardia only resolved after the addition of a Beta Blocker |
Submitted by Mr Stuart Allen, Consulting Editor. |
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