Influence of detomidine on atrial fibrillation cycle length measured by intracardiac electrogram recording and by colour tissue Doppler imaging in horses

Reasons for performing study: Shortening of atrial fibrillation cycle length (AFCL) is a marker of atrial electrical remodeling due to atrial fibrillation (AF). Objectives: To investigate the effect of detomidine administration on AFCL measured invasively from an intra-atrial electrogram (AFCLEGM) and non-invasively by tissue Doppler imaging (AFCLTDI). We hypothesized that detomidine would have no effect on AFCL but would improve the ease of TDI measurements and facilitate non-invasive AFCL determination. Study design: Prospective study. Methods: Measurements were performed before and after intravenous administration of 7.5 µg/kg detomidine in 33 episodes of AF in 32 horses (582±64 kg, 10±3 years) referred for electrical cardioversion. AFCLEGM was measured from a right atrial intra-cardiac electrogram. AFCLTDI was measured from atrial color tissue velocity curves in five atrial wall regions. Mean AFCLEGM and AFCLTDI without and with sedation were compared using a repeated measures linear mixed model with Bonferroni correction for multiple comparisons and calculation of the Bland-Altman mean bias and limits of agreement between AFCLEGM and AFCLTDI. Results: The mean AFCL was significantly increased after sedation, however, this increase was very small (mean difference +4 ms). For AFCLTDI measurements, sedation significantly improved the quality of the atrial myocardial velocity curves and the number of AF cycles that could be measured per cardiac cycle. The Bland-Altman bias between AFCLEGM without sedation and AFCLTDI with sedation ranged from –18 ms to +15 ms depending on wall region. Bland-Altman limits of agreement were similar between AFCLEGM without sedation and AFCLTDI without and with sedation. Therefore, non-invasive AFCLTDI measurements with sedation can be used to estimate the atrial fibrillatory rate. Conclusions: Sedation facilitates non-invasive AFCL measurements but causes a slight increase in AFCL. Non-invasive AFCL measurements can be used as an indicator of atrial electrical remodeling, to study AF pathophysiology and to investigate the effect of anti-arrhythmic drugs