Relationship between beat to beat interval and left ventricular function in patients with atrial fibrillation
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1First Department of Internal Medicine, Nagoya University School of Medicine, Japan.
Insights
In atrial fibrillation, stroke volume and filling volume depend on preceding R-R intervals in patients with normal left ventricles. This relationship is lost in dilated cardiomyopathy due to impaired cardiac function.
Area of Science:
- Cardiology
- Echocardiography
- Cardiac Physiology
Background:
- Atrial fibrillation (AF) complicates understanding pulse rhythm and volume dynamics.
- Beat-to-beat measurement of filling volumes in AF has been challenging.
- Recent advancements enable detailed analysis of ventricular filling and outflow.
Purpose of the Study:
- To evaluate left ventricular outflow and inflow velocity in AF patients.
- To correlate these velocities with preceding R-R intervals.
- To elucidate the impact of R-R interval variations on stroke and filling volumes.
Main Methods:
- Pulsed Doppler echocardiography used to measure flow velocities.
- 12 patients with atrial fibrillation (10 idiopathic, 2 dilated cardiomyopathy) included.
- Stroke and filling volumes calculated from velocity integrals and annulus dimensions.
Main Results:
- In idiopathic AF, positive correlation between preceding R-R interval and stroke/filling volumes for R-R < 600ms.
- Volumes remained constant for R-R > 600ms (filling completion interval).
- In dilated cardiomyopathy, no significant correlation observed between R-R interval and volumes.
Conclusions:
- In normal left ventricles, stroke volume regulation in AF depends on preceding cycle length and filling, consistent with Starling's law.
- Dilated cardiomyopathy impairs this relationship due to reduced contractile reserve and altered diastolic function.
- Pulsed Doppler echocardiography is valuable for assessing AF-induced hemodynamic changes non-invasively.
Abstract:
In atrial fibrillation, the relation between the rhythm and volume of the pulse has long been of interest. However, changes in preload in this condition have not been fully addressed since beat to beat measurement of filling volume have been difficult until recently. In the present study, we evaluated left ventricular outflow and inflow velocity using pulsed Doppler echocardiography and correlated these results with the R-R interval in the individual patient. The study population consisted of 12 patients with atrial fibrillation, aged 36 to 69 years (mean 54 years). The etiology of atrial fibrillation was idiopathic in 10 and 2 patients had dilated cardiomyopathy. Stroke and filling volume were calculated as a pruduct of the flow velocity integral of left ventricular outflow and inflow velocity, and the cross-sectional area of aortic and mitral annulus, respectively. In 10 patients with idiopathic atrial fibrillation, significant positive correlations were observed between the preceding R-R interval and both the stroke volume and the filling volume of the preceding beat when the R-R interval was shorter than 600 msec. Stroke volume and filling volume of the preceding beat were almost constant, independent of the preceding R-R interval when the preceding R-R interval was longer than 600 msec, the interval necessary for the completion of the preceding rapid filling. In the same preceding R-R interval, a larger stroke volume was observed in a shorter pre-preceding R-R interval. In 2 patients with dilated cardiomyopathy no relationship could be observed between the preceding R-R interval and the filling volume of the preceding beat or the stroke volume. In patients with a normally functioning left ventricle (idiopathic atrial fibrillation), reduced cycle length and filling volume in the preceding cardiac cycle appear to be the underlying cause of the regulation of stroke volume, dependent on Starling's law. However, in patients with dilated cardiomyopathy no significant correlation was observed between the preceding R-R interval and both the filling volume of the preceding beat and the stroke volume. In these patients the left ventricle may have limited contractile reserve and altered diastolic re-coil forces possibly due to degenerative changes of myocardium. Pulsed Doppler echocardiography provides a non-invasive method of evaluating the instantaneous changes in left ventricular flow dynamics caused by atrial fibrillation and understanding its fundamental mechanism.