What is the clinical evidence from this study?

Study design: Other. Population: Mild mitral regurgitation (n=6). Intervention: Experimental induction of mild mitral regurgitation vs. Baseline (before induction). Primary outcome: High-frequency (HF) power between 6 AM and noon (ms^2) (p=0.01).

February 1, 2003Open Access

Spectral analysis of heart rate variability in dogs with mild mitral regurgitation

YFYoko FujiiAzabu University YWYoshito WakaoAzabu University

Key Result

Experimental induction of mild mitral regurgitation in dogs significantly decreased high-frequency power and increased the low-to-high frequency ratio, indicating compensatory autonomic modulation.

Structured PICO

Does experimentally induced mild mitral regurgitation alter autonomic function as measured by heart rate variability in dogs?

Population

6 healthy adult Beagles aged 1 to 5 years underwent experimental induction of mild mitral regurgitation to assess autonomic function via 24-hour ambulatory ECG.

Intervention

Experimental induction of mild mitral regurgitation via transection of chordae tendineae.

Comparator

Baseline measurements before induction of mitral regurgitation.

Outcome

Heart rate variability (HRV) analyzed in frequency domains (LF power, HF power, LF/HF ratio) using 24-hour ambulatory ECG.surrogate

Compensatory autonomic modulation, characterized by decreased vagal tone and an increased index of sympathetic tone, occurs in dogs with mild, asymptomatic mitral regurgitation.

Main Result

Absolute Event Rate: 4246% vs 7615%

p-value: p=0.01

Limitations

Other factors influence the HF component as well as parasympathetic activity, such as breathing-related changes in atrial transmural pressure or the cardiac axis.
Respiratory rate could not be controlled to diminish artifacts.
An increase in the ratio of LF to HF could be caused by a decrease of HF and may not be caused by an increase in sympathetic tone.
Other measures of sympathetic activity, such as circulating catecholamines, may be needed for a more accurate evaluation.

Abstract

OBJECTIVE: To assess autonomic function in dogs with mild mitral regurgitation (MR) that did not have clinical signs of the condition. ANIMALS: 6 healthy adult Beagles. PROCEDURE: Mild MR was experimentally induced. A 24-hour ambulatory ECG was recorded before and after induction of MR. Heart rate variability was analyzed in frequency domains by use of the ambulatory ECG. Low-frequency (LF) and high-frequency (HF) power were calculated by integrating over their frequency intervals, and the ratio of LF to HF was also calculated. Measurements of frequency domains were analyzed for 4 time periods (midnight to 6 AM, 6 AM to noon, noon to 6 PM, and 6 PM to midnight). RESULTS: Dogs with experimentally induced MR were classified as International Small Animal Cardiac Health Council class Ia. The HF power of dogs with MR was significantly decreased between 6 AM and noon. The ratio of LF to HF in dogs with MR was significantly increased for the periods between midnight and 6 AM, 6 AM and noon, and noon and 6 PM. CONCLUSIONS AND CLINICAL RELEVANCE: Compensatory response through autonomic modulation was observed in dogs with mild MR that did not have abnormalities, except for cardiac murmur, during clinical examination. This result suggests that treatment during the early stages of mild MR may be beneficial. Additional studies are necessary to determine whether such treatment will delay the onset of congestive heart failure and prolong survival in dogs affected with mild MR.

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