Effect of rhythm regularization on left ventricular contractility in patients with atrial fibrillation

The diagnosis and management of atrial fibrillation in the horse

Atrial fibrillation is the most common performance-limiting arrhythmia in the horse. Detailed cardiovascular evaluation will help guide prognosis and treatment. Many affected horses have lone atrial fibrillation (no predisposing cardiac abnormalities). These horses have a good prognosis for return to performance if sinus rhythm can be restored. The main therapeutic option continues to be quinidine, which has been used for over 60 years. Transvenous electrical cardioversion has proven to be a successful alternative. Other therapeutic options are being explored, but are currently limited.

Relation Between RR Intervals and Early Diastolic Mitral Annular Velocities in Atrial Fibrillation

Background and Objectives

Irregular RR intervals in atrial fibrillation (AF) make beat-to-beat changes in left ventricular (LV) systolic performance. Early diastolic mitral annular velocity (E') is one of the well-established parameters for evaluating LV diastolic function. The relation between RR intervals and E's is unknown. The aim of this study was to observe the influence of continuous changes in RR interval on the parameter for diastolic function in AF.

Subjects and Methods

Echocardiography was performed in 117 patients with AF. E' was adjusted for the effect of pre-preceding RR interval (RR-2) using the logarithmic equation between RR-2 and E'. The logarithmic equation between adjusted E' and preceding RR interval (RR-1) was calculated.

Results

The slope in the relation between RR-1 and E' varied from -2.5 to 2.6. The slope was lower (more likely negative) in patients with higher ratio of early diastolic mitral flow velocity (E) to E' (r=-0.21, p=0.023), ischemic heart disease (IHD, r=0.21, p=0.026), and higher systolic blood pressure (r=-0.19, p=0.046). When patients were divided into these 3 groups on the basis of slope, the lowest slope group (<-0.55, n=39) was associated with higher E'/E (p=0.004) and IHD (p=0.018) compared with the highest slope group (>0.57, n=39). The slope with regards to the relationship between RR-2 and E' also varied from -3.4 to 3.1.

Conclusion

Changes in RR intervals had variable effects on E's according to clinical variables in AF.

Association of the parameters derived from the relation between RR intervals and left ventricle performance with a history of heart failure in patients with atrial fibrillation

Parameters derived from the relation between RR intervals and left ventricular (LV) performance in atrial fibrillation (AF) have been useful to evaluate systolic LV function. This study investigated the association of these parameters with a history of heart failure. Echocardiography was performed in 107 patients with AF. LV outflow peak ejection velocity (Vpe) was adjusted for the effect of pre-preceding RR interval (RR-2) using the logarithmic equation between RR-2 and Vpe. The logarithmic equation between adjusted Vpe and preceding RR interval (RR-1) was calculated in the co-ordinates with RR-1 from 0.6 to 1 second. From this equation, the ratio of slope to Vpe at RR-1 = 1 second (slope/Vpe-1) was obtained. When patients were divided into 2 groups according to a history of heart failure, old age, high slope/Vpe-1, mitral regurgitation, and left atrial enlargement independently predicted the occurrence of heart failure. Fractional shortening was not different between the 2 groups. In patients with normal LV size and without significant regurgitation (n = 69), old age and high slope/Vpe-1 independently predicted the occurrence of heart failure. Areas under the receiver operating characteristics curve of slope/Vpe-1 for identifying heart failure were 0.72 (p <0.000) and 0.74 (p <0.001) in all patients and in patients with normal LV size, respectively. In conclusion, the new parameter, slope/Vpe-1, was one of the most useful predictors for the occurrence of heart failure in AF and was superior to the classic hemodynamic parameters. This parameter might be determined not only by systolic function but also by diastolic function of the left ventricle.

New parameters for left ventricular function in atrial fibrillation: based on the relationship between RR interval and performance

This study was designed to obtain new parameters representing left ventricular (LV) function independent of irregular RR intervals in atrial fibrillation (AF). AF patients were divided into Normal (n=9) and LV Dysfunction (n=9) groups. The relations between LV outflow peak ejection velocity (Vpe) and preceding (RR-1) or prepreceding RR intervals (RR-2) were obtained using logarithmic equations, from which the squared correlation coefficient (r2), slope, Vpe at RR-1 or RR-2=1 sec (Vpe-1), and the ratio of slope to Vpe-1 (Slope/Vpe-1) were calculated. Among the parameters between RR-1 and Vpe, Slope/Vpe-1 was higher in LV Dysfunction group than in Normal group (p=0.05). When only coordinates with RR-1 from 0.6 to 1 sec were included, Slope/Vpe-1 (p=0.001) was higher in LV Dysfunction group than in Normal group. Among the parameters between RR-2 and Vpe, Slope/Vpe-1, slope, and r2 were different between the two groups. In multivariate analysis, Slope/Vpe-1 between RR-2 and Vpe was only independent parameter. However, Slope/Vpe-1 between RR-1 and Vpe in the coordinates with RR-1 from 0.6 to 1 sec had the highest discriminating power. New parameters derived from the relations between RR intervals and LV performance might be useful to evaluate LV function quantitatively in AF.

Frequency distribution, variance, and moving average of left ventricular rhythm and contractility during atrial fibrillation in dog

Mean levels of left ventricular rhythm and contractility averaged over arrhythmic beats would characterize the average cardiac performance during atrial fibrillation (AF). However, no consensus exists on the minimal number of beats for their reliable mean values. We analyzed their basic statistics to find out such a minimal beat number in canine hearts. We produced AF by electrically stimulating the atrium and measured left ventricular arrhythmic beat interval (RR) and peak isovolumic pressure (LVP). From these, we calculated instantaneous heart rate (HR = 60,000/RR), contractility (E(max) = LVP/isovolumic volume above unstressed volume), and beat interval ratio (RR1/RR2). We found that all their frequency distributions during AF were variably nonnormal with skewness and kurtosis. Their means +/- standard deviations alone cannot represent their nonnormal distributions. A 90% reduction of variances of E(max) and RR1/RR2 required a moving average of 15 and 24, respectively, arrhythmic beats on the average, whereas that of RR and HR required 60 beats on the average. These results indicate that a statistical characterization of arrhythmic cardiodynamic variables facilitates better understanding of cardiac performance during AF.

Interval-dependent potentiation of left ventricular contractility is preserved in patients with atrial fibrillation and depressed ejection fraction

Echocardiographic techniques were used to measure left ventricular isovolumic and ejection phase indexes of contractility in 54 patients with atrial fibrillation, and the relations between cycle lengths and contractility were compared in patients with normal and depressed ejection fractions. Data indicate that variations in contractility occur in a pattern that is consistent with postextrasystolic potentiation and that such interval-dependent potentiation is preserved in patients with atrial fibrillation and depressed ejection fraction.