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.