Introduction.
Catheter ablation is an important curative therapy for arrhythmias and
sudden cardiac death caused by accessory pathways (AP). (1-3) An
important part of catheter ablation is precise electrocardiographic
localization of AP localization along the mitral and tricuspid annuli.
AP capable of orthodromic conduction influences QRS morphology by
preexciting the adjacent ventricular myocardium. The preexcited QRS
configuration depends on the localization of the AP and the degree of
preexcitation. Those observations form the foundation of all ECG based
methods for APs localization.
Precise electrocardiographical localization of AP remains an elusive
goal. Despite various complex algorithms that were developed over the
last three decades, accuracy is suboptimal - as demonstrated by several
independent validation studies. (4-9) Moreover, those detailed
algorithms are difficult to remember and follow which further limits
their practical application. The inherent limitation of all AP
algorithms stems from the fact that the AP regions used by the
algorithms are categorical, rather than along a spectrum. The same
applies to ECG features such as QRS polarity or delta wave polarity,
which do not follow binary categorization. Furthermore, uniform 12 ECG
lead placement cannot compensate for the variability in heart position
within the chest and oblique APs. Therefore, it is unrealistic to expect
that some combination of QRS morphologies in 12 ECG leads will precisely
identify a particular AP region in a 0 vs. 1 fashion.
We hypothesized that 12-lead ECG QRS morphology patterns point to a
region of possible AP locations, albeit with identification of the
anatomic sites with highest probability.