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Unipolar electrogram morphology 

Unipolar electrogram morphology
Unipolar electrogram morphology

Hein Heidbuchel

, Mattias Duytschaever

, and Haran Burri

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Introduction to the case

The configuration of the unipolar electrogram (Figure 9.1) provides information about the movement of the activation front at the recording site. At the site where activation arises, the unipolar electrogram only has a negative deflection. If the activation front is passing the recording site, the unipolar electrogram is biphasic, whereas the configuration is only positive at a site where activation comes to an end.

Figure 9.1 Configuration of the unipolar electrogram

Figure 9.1
Configuration of the unipolar electrogram


Which configuration of the unipolar electrograms shown in the figure occurs at the ‘origin’ (exit site) of an infarct-related re-entrant tachycardia?

  1. A A negative deflection only

  2. B A biphasic deflection

  3. C A biphasic deflection with a small initial negative component

  4. D A positive deflection only


A A negative deflection only


Unipolar electrogram morphology

In the unipolar electrogram, a positive deflection is generated by the approaching wavefront, whereas the receding wavefront produces a negative deflection.1 Infarct-related tachycardias are usually based on re-entry where the re-entrant circuit consists of small surviving myocardial bundles in the infarcted zone and remaining healthy myocardium (Figure 9.2). Because at all recording sites along a re-entrant circuit the wavefront is passing, a biphasic deflection would be expected to occur at all sites. The site where activation in the surviving bundle within the infarction leaves the infarcted zone and activates the remaining healthy myocardium is the exit site. Because the diameter of the myocardial bundle is usually very small, the positive deflection of the approaching wavefront is virtually missing (the few myocardial cells in the bundle generate hardly any current). Only the large receding wavefront in the adjacent healthy myocardium generates a large negative deflection.24

Figure 9.2 Depiction of re-entrant circuit within the myocardial scar

Figure 9.2
Depiction of re-entrant circuit within the myocardial scar


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    3. Spach MS, Barr RC, Johnson EA, Kootsey JM. Cardiac extracellular potentials: analysis of complex wave forms about the Purkinje networks in dogs. Circ Res 1973; 33: 465–73.Find this resource:

    4. Stevenson WG, Soejima K. Recording techniques for clinical electrophysiology. J Cardiovasc Electrophysiol 2005; 16: 1017–22.Find this resource: