5.2. Slow LACV as a marker of left atrial AF substrate
In this study, we found that a slow anterior LACV more accurately predicted AF recurrence than any other previously reported predictor, including AF type, left atrial size, and low-voltage-area existence. This excellent predictive value of a slow LACV might be explained as follows. First, conduction slowing is a direct measure of factors associated with arrhythmia with the reentrant mechanism, such as rotor during AF,12-14 and slow conduction zone during regular atrial tachycardia.15 Second, as described in the above paragraph, conduction slowing is a likely consequence of atrial fibrosis, which could also provoke shortening of the refractory period and triggered activity. Thus, a slow LACV possibly represents a variety of electrophysiological characteristics which in concert render the subject vulnerable to AF development. Third, this study measured LACV from the start to the end of the left atrial propagation wave front, which facilitates comprehensive assessment of left atrial arrhythmogenicity. Anterior LACV was slower than posterior LACV, irrespective of the presence of AF recurrence. A physiological slow anterior LACV would be partially attributable to conduction slowing of the anterior propagation wave perpendicularly crossing the septo-pulmonary bundle.16 In addition, LACV slowing on the anterior route more precisely predicted AF recurrence than that on the posterior route. Left atrial fibrosis would progress initially in the anterior-septal region before other regions, as reported in previous studies which showed that low-voltage areas most commonly existed in the anterior-septal region.8, 15 Several studies have assessed atrial conduction disturbance using P-wave duration obtained by surface signal-averaged electrocardiogram,5-7 and found that P-wave prolongation was associated with AF recurrence after PV. These results suggest that inter- and intra-atrial conduction disturbances represent an arrhythmogenic substrate of AF. Our present study using a recently available high-density mapping system confirms these previously reported findings.