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Shortened left ventricular filling time in dilated cardiomyopathy: additional effects on heart rate variability?
M Mbaissouroum1, C O'Sullivan, S J Brecker
1Cardiac Department, Royal Brompton National Heart and Lung Hospital, London.
Insights
Reduced heart rate variability in dilated cardiomyopathy is linked to impaired left ventricular filling time, not cavity size. Functional mitral regurgitation may limit filling, influencing maximum heart rate and overall variability.
Area of Science:
- Cardiology
- Cardiac Electrophysiology
- Heart Failure Research
Background:
- Dilated cardiomyopathy is associated with reduced heart rate variability.
- The underlying mechanical factors contributing to this reduction are not fully understood.
Purpose of the Study:
- To investigate the mechanical influences, specifically left ventricular function, on heart rate variability in dilated cardiomyopathy patients.
Main Methods:
- Compared standard heart rate variability indices with echocardiographic Doppler measures of left ventricular function.
- Studied 20 patients with dilated cardiomyopathy and 15 healthy controls.
- Correlated heart rate variability with left ventricular cavity size, shortening fraction, isovolumic relaxation time, mitral regurgitation, and left ventricular filling time.
Main Results:
- Patients with dilated cardiomyopathy showed reduced overall mean RR interval and SD of five-minute mean RR intervals compared to controls.
- Heart rate variability measures did not correlate with left ventricular cavity size or shortening fraction.
- Both heart rate variability measures strongly correlated with left ventricular filling time, persisting even after correction for RR interval.
Conclusions:
- Functional mitral regurgitation in dilated cardiomyopathy may limit left ventricular filling time at higher heart rates.
- This limitation could be a mechanism setting maximum heart rate to optimize cardiac output.
- Impaired left ventricular filling time is a significant factor in the reduced heart rate variability observed in dilated cardiomyopathy.
Objective:
To assess possible mechanical influences underlying the reduced heart rate variability in patients with dilated cardiomyopathy.
Design:
Comparison of standard non-spectral indices of heart rate variability with echocardiographic Doppler measures of left ventricular function in patients and normal controls.
Patients:
20 patients with dilated cardiomyopathy and 15 normal subjects of similar ages were studied.
Methods:
Standard non-spectral indices of heart rate variability were measured over 24 hours. These were correlated with left ventricular cavity size, shortening fraction, and isovolumic relaxation time measured by M mode echocardiography, and the duration of functional mitral regurgitation and left ventricular filling time assessed by continuous wave Doppler.
Results:
Mean RR interval and estimates of short term variability (root mean square difference of successive RR intervals, proportion of adjacent RR intervals > 50 ms different, and SD indices) were not different from normal. The overall mean (SD) of the RR interval (65 (35)), and SD of five minute mean RR intervals (55 (30)), however, were reduced compared with normal values (115 (40) and 105 (45); p < 0.01 for both). Neither correlated with left ventricular cavity size or shortening fraction, but both were strongly related to left ventricular filling time (coefficient of variation, r = 0.82 and r = 0.81 respectively). Correlation persisted when the SD was corrected for RR interval (r = 0.69) although this correlation was not found in the controls. In individual patients, the difference between RR interval at the time of echo and minimum value during the 24 hours, a measure of ability to increase heart rate, also correlated closely with filling time (r = 0.92).
Conclusion:
As the duration of functional mitral regurgitation is effectively fixed, its presence can limit the time available for left ventricular filling in dilated cardiomyopathy when heart rate is high. This may become the mechanism by which maximum heart rate is set, becoming fixed to optimise cardiac output. This manifestation of dilated cardiomyopathy may be an important factor in reduction of heart rate variability in these patients.