In horses, persistent depression of left atrial (LA) mechanical function is a prognostic indicator of recurrence of atrial fibrillation (AF) after cardioversion. The objective of this prospective study was to characterize LA mechanical function in Warmblood horses after successful transvenous electrical cardioversion (TVEC) of AF using standard two-dimensional echocardiography (2DE) and 2D speckle tracking (2DST) analyses. 2DST was recently described to be a feasible method to quantify LA function in healthy horses. We aimed to provide proof of concept for use of 2DST to detect compromised LA booster pump function in horses.
Warmblood horses with atrial fibrillation, successful TVEC and continued normal sinus rhythm for at least one month thereafter were included in this study. Echocardiography was performed 24h, 72h and 1mt after TVEC. Maximum LA area (LAAmax) and LA diameter (LADmax) as well as active and passive LA fractional area change (FAC) were measured using 2DE on a right-parasternal 4-chamber view focusing on the left atrium. LA dimensions were measured at end-systole and allometrically scaled to a body weight of 500 kg. Global longitudinal peak strain (SL) and strain rate (SRL) during active booster pump function were measured on the same recordings using 2DST analyses. Measurements were judged in relation to previously established reference intervals. Friedman one-way ANOVA with Dunn’s multiple comparison test was performed to detect differences between timepoints. Linear regression analysis was performed to describe associations of SL and SRL with conventional 2DE measurements of LA size and function, considering for repeated measurements within horses. P < 0.05 was considered significant.
Thirteen Warmblood horses fulfilled the inclusion criteria. Measurement of all indices at all 3 timepoints was feasible in 6/13 horses, whereas severe LA enlargement prevented measurement in 7 horses. LA contractile dysfunction 24h after TVEC was detected in 5/6 horses based on active LA FAC and global SL. Active LA FAC did not change over time (p = 0.14) and remained below reference limits in 5/6 horses. Global SL significantly increased from 24h to 1mt after TVEC (p = 0.028); at that time, SL of all 6 horses was within (but at the lower range) of the reference interval. SRL was below the reference interval in 2/6 horses 24h after TVEC and within reference limits in all 6 horses 1mt after TVEC (p = 0.30). Strain and strain rate were significantly associated with active FAC (p2adj=0.76 and p2adj=0.77), passive FAC (p=0.016, R2adj=0.55 and p=0.016, R2adj=0.55), LAAmax (p2adj=0.85 and p2adj=0.88), and LADmax (p2adj=0.83 and p2adj=0.85), with lower SL and SRL in larger atria.
This study shows that 2DST is useful to detect compromised LA contractile function in horses after conversion of AF to NSR using TVEC. Strain and strain rate are negatively related to LA enlargement. The clinical value of 2DST to predict the risk of recurrence of atrial fibrillation will have to be established in future studies.
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