PV entrance conduction or Far Field potentials?

Answer: Far field SVC signals: they occur <30ms from P wave onset during sinus rhythm when the catheter is located in the RSPV.

 

Clinical Context:

• The SVC & RSPV are adjacent structures. SVC potentials can be recorded from the RSPV in >38% of patients. Below is an example of the “PRE-Ablation” EGM recording within the RSPV from the Farawave.

 

 Important “technology” consideration when assessing for far field potentials

• • The Farawave catheter has widely spaced bipolar recordings – this predisposes it to picking up far field EGMs from adjacent anatomical structures. Many ablation catheters, such as the STSF are also predisposed to this, due to the large distal electrode tip size (3.5mm)

   

  • Smaller bipoles & electrode sizes (such as on the Intellemap Orion or Octaray Catheter) are less prone to detecting far field EGM because their electrodes are <0.5mm in size & bipolar spacing 2-3mm.

 

 

Consequences of mistaking far-field for near-field potentials?

• If mistaken for persistent RSPV conduction, this can lead to unnecessary ablation. This is especially important with thermal ablation, where additional ablation increases the risk of phrenic nerve injury, stroke, tamponade, and PV stenosis.

 

• Additional PFA creates additional haemolysis risk which may result in an acute kidney injury.

 

 

Key distinguishing features of SVC vs RSPV potential

 

Anatomical explanations

• Anterior RSPV is immediately posterior to the SVC. Any anteriorly placed electrode in the RSPV can often pick up SVC far‑field signals.

 

• In sinus rhythm, true SVC potentials occur almost immediately after sinus node activation at P‑wave onset.

 

• True RSPV potentials occur later because conduction must:
  • Travel from the sinus node → LA (via Bachman’s bundle and interatrial septum)
  • Then into the RSPV, after most of the atrial myocardium has depolarised.

 

 

 

My Two cents:

• To distinguish RSPV vs SVC potentials following ablation, record in sinus rhythm and measure EGM–P‑wave onset.

 

• <30ms from P onset → almost certainly SVC far‑field.

 

• >40ms from P onset → possible true PV conduction.

 

• (Also: Cross‑check distribution — true PV signals should appear across multiple electrodes, not just anteriorly – but this is not always the case, because of discontinuous muscular sleeves of the Pulmonary veins, and also accounting for segmental ablation of the PV sleeves, especially with “one-shot” PFA technologies).

 

Thanks for tuning in :)
Cheers
Mitch & CPiP Team

 

 

References:

1. (image below). Shah D, Burri H, Sunthorn H, Gentil-Baron P. Identifying far-field superior vena cava potentials within the right superior pulmonary vein. Heart Rhythm. 2006 Aug;3(8):898-902.

1. Gu W, Liu W, Li J, Shen J, Pan J, Wu B, Shi H, Luo X, Xiong N. Anatomy-based characteristics of far-field SVC electrograms in right superior pulmonary veins after isolation. Scand Cardiovasc J. 2022 Dec;56(1):224-230.