Module 1
Topic 1
Lesson 2

Electrical zigzags from heart cables – understanding signals from the intracardiac electrodes

Micaela Ebert
Consultant Electrophysiologist

What will you learn?

  • basic idea on how and where to place the diagnostic catheters for your standard 4-wire EP study
  • how to interpret the electrocardiograms recorded from distinct locations in the heart
  • how to arrange the signals in your recordings system in order to be able to extract the optimal amount of information from your recordings

About this scenario

  • An EGM is a recording of intracardiac potentials by bipolar electrodes = local depolarization of the structures near the recording electrodes. Distinct EGMs patterns can be recorded dependent on the proximity to the respective structure.
  • Typical EP recordings include also surface ECG (I, aVF, V1, and V6).  The labels are displayed along the left side of the margin in the EP recording system.
  • Electrode catheters are always inserted via Seldinger technique under local anesthesia. Usually femoral venous access but occasionally subclavian or jugular access can be useful (i.e. in the case of difficult CS cannulation).
  • Diagnostic electrode catheters are usually 4-6F. At least 2 electrode pairs are preferred to allow simultaneous pacing (via the distal pair, in contact with the endocardium) and recording (via the proximal pair) or recording at more than one location.
  • Different interelectrode spacing is available: (1) Small electrode spacing (1-2mm) provides signals over a very localized area; (2) 5-10 mm larger electrode separation allows recording of greater proportion of the chamber; (3) CS deflectable (2-8-2 mm), His (2mm), RVA (5mm).
  • Standard diagnostic EP study for the investigation of SVT uses 3-4 catheter electrodes: The right ventricle (RVA) records the ventricular apex; High right atrium (HRA) records the right atrial wall; Coronary sinus (CS) along the mitral annulus, records left atrial and ventricular activation; His bundle (HBE or His.d) records EGMs in the region of the atrioventricular node