Vascular function in dogs with myxomatous mitral valve disease

Abstract

Myxomatous mitral valve disease (MMVD) is the commonest heart disease in dogs. Vascular dysfunction contributes to human heart disease but has not been assessed in pet dogs by myography.

We hypothesised that vascular dysfunction contributes to progression of MMVD and can be quantified with myography.

Isomeric myography was performed on femoral, mesenteric, renal, and pulmonary arteries from pet dogs euthanised for welfare reasons. Testicular arteries were collected from dogs undergoing routine castration as a control group. Histopathology analysis was made for confirmation of arterial tissue. MMVD was graded 1-4 (Whitney classification). Arteries were stretched to an internal circumference (IC1) that generated maximal tension (mmHg) to high potassium concentrations (normalisation). The ratio of IC1:IC100mmHg (normalisation factor) was calculated for every artery. Vasoconstriction to phenylephrine, and vasodilation to acetylcholine (endothelial dependent) and sodium nitroprusside (endothelial independent) were assessed by cumulative response curves. Concentrations of agents that gave 50% maximal response (EC50/IC50) were calculated. Response to high potassium physiological salt solution (KPSS) was calculated as variation in percentage between minimum and maximum response and results for tissue from the same dog but on different days were compared.

Histopathology confirmed all the samples processed were arteries. Normalisation factors were determined for renal, femoral and mesenteric artery. Impaired endothelial dependent vasorelaxation was identified in all dogs with MMVD graded 3 and 4 and in some arteries of dogs with MMVD graded 1 and 2.

Pulmonary and testicular arteries failed to show response on myograph. No significant difference was identified in KPSS response in the same dog over seven days.

Isomeric myography is feasible in pet dogs and can be used to investigate vascular dysfunction. Impaired endothelial-dependent relaxation was identified more frequently in dogs with higher MMVD grade. Further investigation is required to establish the relationship between MMVD and vascular dysfunction.