Heart Rate Variability in Cavalier King Charles Spaniels with Different Degree of Myxomatous Mitral Valve Disease

Rasmussen, C.E. 1, Falk, T. 1, Zois, N.E. 1, Moesgaard, S.G. 1, Häggström, J. 2, Pedersen, H.D. 3 and Olsen, L.H1.

1Department of Basic Animal and Veterinary Sciences, Faculty of Life Sciences, University of Copenhagen, Frederiksberg, Denmark, 2Department of Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden; and 3Novo Nordic A/S, Maaloev, Denmark.

Introduction: Modulation of heart rate by the autonomic nervous system can indirectly be measured by heart rate variability (HRV). Reduced HRV is seen in dogs with heart failure secondary to myxomatous mitral valve disease (MMVD). However, HRV is suggested to increase with disease progression in dogs with early stages of MMVD. Comparable results are found in people with primary mitral valve prolapse, a disease resembling canine MMVD.

Aim: To associate progression of MMVD in dogs with time and frequency domain HRV, analysed from 24-hour electrocardiography.

Materials and Methods: Eighty-one Cavalier King Charles Spaniels (CKCS) were examined by echocardiography and 24-hour electrocardiography. CKCS were divided into 4 groups: 1) no or minimal mitral regurgitation (MR) (MR jet=15% of the left atrial area) and no murmur, 2) mild MR (20%<jet=50%), 3) moderate to severe MR (jet>50%) and no clinical signs of heart failure, 4) left atrium to aortic root ratio >1.5, clinical signs of heart failure and furosemide responsiveness.

Results: Ten out of 13 HRV variables decreased with increasing MMVD severity. In group 1, 10 HRV variables were increased compared to group 3 and 4 (P<0.05) and 2 HRV variables were increased compared to group 2 (P<0.04). Eight and 10 HRV variables were increased in group 2 compared to group 3 (P<0.01) and group 4 (P<0.001), respectively. Group 1 and 2 were younger than group 3 and 4 (P<0.0001). Only 2 HRV variables were influenced by age.

Discussion and conclusion: Most HRV variables decreased with progression of MMVD in dogs; even prior to the development of overt congestive heart failure.