Figure 4. Illustration of the ECG analysis via WPW24.com
application at the beginning of the ablation procedure. Left panel: the
fully preexcited QRS is obtained with fast atrial pacing. At steps 1-4
the information regarding QRS morphology is introduced into the
application. Step 1 : predominantly negative V1 nearly eliminates
the left sided access accessory pathways (AP), only small admixture of
left septal APs remains, the point of maximum is now at the most common
right-sided region i.e. right posteroseptal (RPS). Step 2 :
predominantly negative QRS in V2 now eliminates the possibility of left
sided APs and makes RPS AP relatively unlikely, shifting the point of
maximum probability to the parahisian region (PHIS) and adjoining right
anteroseptal (RAS) region, but many other right-sided locations are also
possible. Step 3 : equiphasic QRS in V3 lowers the chances of a
right free wall AP and shifts the focus to septal pathways as 50% of
possible APs are now at the PHIS or RAS regions. Step 4 :
predominantly positive aVF, intuitively, should eliminate posterior
pathways (RPS, RMS, RP i RPL), but it does more than that: it identifies
a rare QRS pattern that was seen only 3 times per 509 APs and in all
those three cases (from the exploratory cohort) the successful ablation
was in the PHIS region. In this fourth case analysed, (from the
validation cohort) the successful ablation (left panels) was also in the
PHIS region.