Index-Beat Assessment of Left Ventricular Systolic and Diastolic Function during Atrial Fibrillation Using Myocardial Strain and Strain Rate

Abstract

Accurate assessment of left ventricular (LV) function in patients with atrial fibrillation (AF) remains difficult, mainly because of the beat-to-beat variability of many echocardiographic parameters. The aim of this study was to assess the hypothesis that LV function can be estimated from an index-beat echocardiographic assessment in patients with AF using myocardial strain and strain rate. A prospective study was conducted to assess 25 patients with AF (mean age, 66 ± 10 years). Peak systolic longitudinal strain (LS) and peak diastolic longitudinal strain rate (dSR) were measured using two different methods: (1) mean LS and dSR, the averages of instantaneous LS and dSR over 10 sec, and (2) index-beat LS and dSR, calculated when the ratio of the preceding (RR1) to the pre-preceding (RR2) interval was 1 (range, 0.96-1.04). These variables were compared with simultaneously measured LV pressure parameters using Millar catheters. There was a positive linear relationship between mean LS and index-beat LS at RR1/RR2 = 1 (r = 0.94, P < .001) and a positive linear relationship between mean dSR and index-beat dSR (r = 0.69, P < .001). Index-beat LS was correlated with the maximal positive derivative of LV pressure (peak +dP/dt) (r = -0.73, P < .001). Index-beat dSR was correlated with the time constant of isovolumic LV pressure decay (τ) (r = -0.63, P < .001). To investigate the independent predictors of τ, a stepwise multilinear regression analysis showed that index-beat dSR was the best predictor of τ. Index-beat parameters accurately reflect the mean values of parameters in patients with AF. These noninvasively obtained index-beat parameters are useful to assess surrogate LV function even in patients with AF.