- fibrous thickening of the intima or media of the aorta
- hyaline or amyloid thickening of the media of blood vessels
- calcification of the aortic intima
- calcification of the media in peripheral vessels
- muscular hypertrophy of small and medium-sized arterioles
- arteriocapillary fibrosis
- increased capillary fragility
- increased capillary permeability
- atherosclerosis - rare compared with man.
Arteriosclerosis of intramural coronary arteries has been reported to occur in 77.6%
of geriatric dogs over 12 years of age (Valtonen 1972), 60% of dogs over 14 years
of age (Detweiler et al. 1968) and 50% of dogs aged 13 years or older (Jonsson
1972). A direct association was found between the presence of arteriosclerosis and
microscopic intramural myocardial infarcts (MIMIs).
These structural changes cause a loss of elasticity of vascular walls and / or luminal
narrowing, and contribute to increased peripheral resistance which, combined with
reduced sensitivity to the vasodilator effect of b-adrenergic stimulation (see below),
probably contributes to the increased aortic impedance and left ventricular afterload
seen in geriatric patients.
Vessels supplying various organs throughout the body may be affected, notably the
kidney and brain, resulting in impaired vascular supply, and ultimately impaired
Atherosclerosis leading to myocardial infarction while common in humans is rare in
dogs and cats. Obesity and thyroid atrophy or frank hypothyroidism are associated
with the development of atherosclerosis in geriatric dogs. Experimentally, atherosclerosis
can only be caused in hypothyroid dogs on high fat diets. Miniature schnauzers with
hyperlipidaemia may be predisposed to develop atherosclerosis.