Abstract:
Mitral valve disease (MVD) progression is associated with autonomic nervous system (ANS) imbalance. This
study hypothesized that sympathetic and parasympathetic tones would be altered with MVD progression. ANS
activity was assessed among different MVD classes in untreated dogs. This cross-sectional retrospective study
included 29 healthy control dogs and 71 dogs with MVD divided according to American College of Internal
Medicine (ACVIM) guidelines. Heart rate variability (HRV) analyses utilised time and frequency domains and
were derived from 5 min, six-lead electrocardiogram recordings of sinus rhythm or respiratory sinus arrhythmia.
While all time domain-related HRV parameters decreased with disease severity, only dogs in stage C exhibited
significantly lower values (P < 0.05). High frequency (HF) band values decreased more than low frequency (LF)
band values as disease severity increased (P < 0.05). The LF/HF ratio also progressively increased with MVD
severity. A negative correlation was observed between HRV parameters and La/Ao ratio when the entire MVD
case population was pooled (P < 0.05). Both sympathetic and parasympathetic tones were altered in dogs with
MVD before clinical signs were observed and prior to the development of cardiomegaly. This is the first HRV
study in untreated dogs with MVD. Investigating ANS imbalances preceding subclinical left-sided cardiomegaly
in dogs with MVD should be considered in future age-matched, longitudinal studies to determine the potential
benefits of early vagal tone augmentation in high-risk canine patients.