Electrocardiographic and electrophysiologic differentiation between atriofascicular, long atrioventricular, and short atrioventricular decrementally conducting accessory pathways

Aims: We aimed to examine the electrocardiographic and electrophysiologic characteristics of anterograde-conducting decremental accessory pathways (DAP) and to identify surrogate criteria to distinguish short atrioventricular (SAV) DAP from atriofascicular (AF) AP and long atrioventricular (LAV) DAP. Methods and results: We identified all patients with DAPs and analysed electrocardiographic and electrophysiologic characteristics. Distal insertion sites were examined using existing criteria, including V-H interval, ventricular activation at the right ventricular apex, and around tricuspid annulus during antidromic atrioventricular re-entrant tachycardia (A-AVRT) or complete pre-excitation and evaluated the AV node-like properties according to the response to adenosine and radiofrequency ablation. Out of 45 patients with DAPs, 28 (62.2%) had SAV-DAP (13 with definite AF-AP, 2 with definite LAV-DAP, 2 indeterminate). In all, 50% of SAV-DAPs and 53.3% of AF-AP/LAV-DAPs had 'rS' pattern in lead III. Longer QRS duration (159.9 ± 17.4 ms vs. 139.2 ± 14.3 ms, P < 0.0001) during full pre-excitation or A-AVRT differentiated SAV-DAP from AF-AP. The QRS-V(His) interval was longer for those with SAV-DAP compared vs. AF-AP/LAV-DAP (45.3 ± 2.4 ms vs. 22.9 ± 2.5 ms, P < 0.0001) and a cut-off value of 33.0 ms differentiated the two (sensitivity 81.3%, specificity 87.5%). Conclusion: The majority of the SAV-DAPs are located at the TA free wall. An 'rS' pattern in lead III is frequently seen in SAV-DAP as well as AF-AP/LAV-DAPs. Measuring the QRS-V(His) interval would be helpful to distinguish SAV-DAP from AF-AP/LAV-DAP.