Variability in the manifestation of pre-excited atrial fibrillation: Its quantification, theoretical origin, and diagnostic potential

Abstract

Background: Irregular broad complex tachycardia (BCT) may be due to atrial fibrillation (AF) occurring in the presence of ventricular pre-excitation (pre-excited AF) or bundle branch block (BBB-AF). While irregularity is a defining characteristic of AF, it is a common subjective impression that greater variability in manifestation exists for pre-excited AF than BBB-AF. This difference can potentially be exploited for distinguishing the two conditions if some means can be found to quantify it. Methods: For each of 75 ECGs showing irregular BCT (41 pre-excited AF and 34 BBB-AF), a random sample of 10 distinct QRS complexes were selected for quantitative measurement of variability in manifestation, which included the standard deviation (SD) of the width, the SD of the axis, and the coefficient of variation (CV) of the amplitude of the QRS complex. Results: Pre-excited AF showed statistically significantly greater values than BBB-AF with respect to these measures, and receiver-operating characteristic curves showed that these differences could be useful for their discrimination. For the SD of QRS width, a cut-off value of 8 ms appeared optimal (sensitivity 1.00 and specificity 0.79). For the SD of QRS axis, a cut-off value of 2.5 degrees appeared optimal (sensitivity 0.84 and specificity 0.56). For the CV of QRS amplitude, a cut-off value of 0.10 appeared optimal (sensitivity 0.82 and specificity 0.76). Conclusions: Pre-excited AF demonstrated greater variability than BBB-AF in manifestation. The measures of variability developed can potentially be useful for diagnosing irregular BCT in practice, especially in the context of automated computer-aided diagnosis.