3D maps are models. EGMs are Truth.

Answer:

 

• Whilst the map appears promising for focal AT origin, the EGM appears less promising. The high frequency component appears to occur within the P wave.

 

• Inspection of the unipolar EGM (not shown) also shows an rS complex, which is not consistent with a focal origin of tachycardia.

Key point 1:

Always verify the EGM morphology at the earliest site using fundamental EP principles.

• 3D maps can be misannotated or mis-represented. But EGMs don’t “usually” lie.

 

 

Key point 2:

In a focal arrhythmia, if the earliest site lacks favourable EGM features (pre‑P wave, unipolar QS), suspect a far‑field source from another chamber. In this case, the PAC arose from the LA and conducted across an LA–RA muscular connection.

Take a close look at the EGM. There is likely two components, one far field early LA, and one near field (higher frequency) RA component which is “late”. Hard to prove, but I think it’s likely.

In this case, the earliest RA site lay adjacent to the LA, but the EGM lacked features predictive of successful ablation. Delivering thermal energy here carried a potential risk of phrenic nerve injury.

 

The Final Map

• Earliest LA activation displays a discrete local EGM preceding P wave onset.

 

• Unipolar QS morphology observable. Ablation at this location successfully terminated tachycardia.

 

 

 

Key Concept 3: “Blush” means “Please look away”

• Broad, diffuse zones of equally early focal activation on a 3D map (a wide area of “red” or “white”) — are often referred to as a blush by mapping specialists using 3D systems that code early activation in red (CARTO, RHYTHMIA, AFFERA).

 

• When mapping in the RA, this diffusely early area is rarely the site of tachycardia origin, and usually indicates that the focal origin is elsewhere such in the LA or Aortic root.

 

• Inspection of the earliest EGM morphology and timing in a region of blush usually demonstrates a “late” EGM (after P wave onset) and an absence of a unipolar QS morphology.

 

Example Map (different case):

• In the map below, a broad region of equally early activation was found on the RA septum in the Parahisian region.

 

• Mapping & ablation in the NCC within the Aortic root demonstrates an early EGM with a QS unipolar morphology and successfully terminated tachycardia.

 

My two cents:

• 3D mapping is wonderful tool for many reasons, but it only offers another perspective, not an objective truth.

 

• Always verify the early site of the 3D map with a careful analysis of the EGM timing and morphology.
  • Is it early?
  • Is it high frequency (local)?
  • Is there a unipolar QS?
  • Is there fractionation (admittedly not always relevant).

 

The EGM’s are the only source of truth.

Thanks for tuning in :)
Cheers
Mitch & CPiP Team

Interpreting activation maps alongside electrograms is taught in more depth in the Mapping in 3D program of EP in Practice.