Secondary causes of myocardial disease

Question 1

Give some examples of secondary causes of myocardial disease

Answer 1

• Taurine deficiency
• Thyrotoxicosis
• Acromegaly
• Infiltrative disease (e.g., lymphoma)
• Inflammatory/infectious conditions (e.g., FIP)
• Protozoal or bacterial myocarditis
• Drugs (e.g., anthracyclines)
• Hypertrophic feline muscular dystrophy
• Trauma
• Cronic severe anemia
• chronic tachyarrhythmias (e.g., atrial fibrillation)

Question 2

What are the effects of thyrotoxicosis on the heart

Answer 2

Excess circulating thyroid hormones tend to affect the cardiovascular system in five main ways:
- myocardial hypertrophy (usually without systolic anterior motion of the mitral valve
- increased function of myocytes (i.e., increased contraction and relaxation)
- venoconstriction (increasing venous return to the heart)
- vasodilation and increased circulating blood volume
- increased heart rate and rhythm (i.e., enhanced response to sympathetic stimulation)

Question 3

Explain why despite systemic vasodilation, hyperthyroid cats maintains normal blood pressure or get elevated BP

Answer 3

Carddiac output is increased in many ways:
- increased preload via vasoconstriction
- increased circulating blood volume (secondary to activation of the RAAS which increases plasma volume)
- increased EPO synthesis which increases circulating RBC mass
- a faster and stronger myocardium due to up-regulation of beta-adrenergic receptors in the heart

As a conclusion, the heart pump more blood in a faster and stronger way