F-wave sway in paroxysmal and chronic atrial fibrillation

Vectorcardiography (VCG) can evaluate the vector loops of electrocardiographic waves, being a time-spatial representation of the heart vector into the three orthonormal leads. During atrial fibrillation (AF), F waves reflect the disorganized depolarization of the atria, replacing the organized P wave. Usually, paroxysmal AF (PAF) spontaneously terminates, differently from chronic AF (CAF), possibly due to the still-preserved main direction of the P-wave vector loop. To investigate this hypothesis, this study aims to evaluate the similarities between the P-wave vector loop and F-wave vector sway in subjects affected by PAF and CAF. Overall, 10-s VCG were acquired from 10 healthy (HEA) subjects showing normal sinus rhythm, 10 subjects affected by PAF (one during normal sinus rhythm and one during AF), and 10 subjects affected by CAF. P waves were extracted using ECGdeli software, while F waves were extracted after QRST cancellation. Ellipse axes and eccentricities were calculated as the root mean square of VCG components and the ratio between axes, respectively. Overall, 84 beats of HEA, 205 beats of PAF (89 beats during normal sinus rhythm and 116 during fibrillation), and 103 beats of CAF were analyzed. Distributions of axes and eccentricities of PAF are not statistically different (P-value>0.05) than normal sinus rhythm but features related to the Z axis of CAF were statistically lower than PAF (P-value〈10^-3). F-wave vector sway in PAF resembles the P-wave vector loop, suggesting the maintenance of the atrial depolarization main direction in subjects with self-terminating AF. Moreover, the F-wave vector sway is more manifest in PAF than in CAF.