myocardial disease

• There are different manifestations of myocardial disease which vary in severity…

  • No clinical signs
  • Poor performance
  • Due to AF or VPD's (ventricular premature depolarisation)
  • Collapse
  • Due to multiple VPD's and VT (ventricular tachycardia)
  • Death (Rare)
  • Due to VT progressing into VF (ventricular fibrillation)
• endocardial disease causes valvular regurgitation and jet lesions

  • These cases manifest as cardiac murmurs
• myocardial disease causes disruption to action potential propagation and abnormalities in contraction. This can cause collapse/sudden death.

  • These cases manifest as cardiac dysrhythmias
• Conditions that might lead to myocardial dysfunction include…

  • Electrolyte abnormalities
  • Increased myocardial muscle mass
  • Increased chamber size which occurs the cardiomyopathy
  • Myocarditis
• Clinical pathology can be used to evaluate the LA myocardium for the sensitivity and specificity of these tests are questionable and therefore have limited use. However, it includes

  • Proteins
  • These are large molecules so are released when the cell membrane is disrupted e.g., Cardiac troponin I
  • Enzymes
  • These are small molecules so are released by cell membrane dysfunction (i.e. less severe)
  • Creatine kinase (myocardial isoenzyme)
  • Marker of skeletal muscle damage
  • [hydroxybutyrate dehydrogenase]
• myocarditis = inflammation of the myocardium
• inflammation of the myocardium can be caused by…

  • Bacteria
  • Staph aureus
  • Strep equi
  • Clostridium chauvoei
  • Mycobacterium spp.
  • Secondary to sepsis, pericarditis, endocarditis
  • Borrelia burgdorferi (Lyme disease)
  • Viral
  •  e.g., FMD - foot and mouth disease, EIA - equine infectious anaemia, EVA - equine viral arteritis, EIV - equine influenza virus, AHS - African horse sickness
  • Parasitic e.g., large strongyles, Toxoplasma, Sarcocystis
  • (Thromboembolic –due to any of the above infectious agents)
• Myocardial evaluation involves…

  • Echocardiography (Long and short axis)
  • To assess myocardial appearance and some insight into function
  • Fractional shortening at rest and following exercise
  • To evaluate myocardial function and the hearts ability to contract
  • This is the difference in size of the heart from diastole to systole, it should be between 35-45
  • (Advanced echo techniques - a research tool)
  • Dobutamine-atropine stress echocardiography
  • Myocardial biopsies
• Dobutamine-atropine stress echocardiography can evaluate the heart at increasing heart rates allowing us to see if function is maintained at these different rates.

  • This can help predict the heart's function at exercise.
• Myocardial biopsies can now be done standing and are ultrasound guided. To perform, the biopsy instrument is inserted into the heart via the jugular vein.