Short-term heart rate variability in healthy dogs and dogs in various stages of degenerative mitral valve disease evaluated before pharmacotherapy.

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.