Myocardial disease

• Primary myocardial diseases

  Dilated cardiomyopathy (DCM)

  Arrhythmic right ventricular cardiomyopathy (ARVC)

  Hypertrophic cardiomyopathy (common in cats)

  Restrictive cardiomyopathy (common in cats)
• Secondary cardiomyopathy diseases

  Infective myocarditis

  Deficiency diseases

  Toxic causes
• What is Dilated Cardiomyopathy?

  Most common form in the dog, rare in the cat.

  Characterised by impaired myocardial contractility with dilation of the left ventricle (+/- right ventricle).

  Tachycardias are common - supraventricular and/or ventricular.

  DCM is an end stage of many cardiac disease, primary DCM is a diagnosis of exclusion.
• DCM Pathophysiology

  Eccentric hypertrophy of the left ventricle.

  Systolic failure (forward failure) - not contracting enough.

  Diastolic failure (backward failure) - every time the ventricle tries to fill, and contract out is not pushing out all of the blood, the blood stares to back up in the system and you get congestion.

  Left atrial dilation and increased left atrial pressure.

  Right side can also be affected.
• Signalment of DCM

  Breed predisposition - genetic basis

  Doberman, Newfoundland, Irish wolfhounds, St Bernards, Labradors, Great Dane, Cocker spaniels, Boxers.

  Boxes autosomal dominance inheritance pattern.

  But different breeds have very different prognosis for the same disease.

  Usually middle aged dogs, usually dogs above 12kg, males tend to be more severely affected but no gender predilection.
• How does DCM cause disease

  Loss of systolic function results in low cardiac output (loss of contraction).

  Low cardiac output results in forward failure.

  Sympathetic hormonal and renal compensaoty mechanism activated, maintain cardiac output by increasing HR, peripheral vasoconstriction and volume expansion.

  The ventricle fails to empty resulting in increased ventricular pressure.

  This results in compromised coronary perfusion, worsening myocardial function further and resulting in arrhytmias.
• How do DCM patients present?

  If they present as symptomatic - usually present in CHF, weight loss, sudden death, soft murmur, atrial fibrillation, lethargy, exercise intolerance, dyspnoea (signs of left sided heart failure).

  Can be non-asymptomatic (occult phase) - can be prolonged, screening programmes of specific breeds to identify this phase (24 hour holter monitors, echo).
• Clinical examination of DCM

  Varies depending on the degree of myocardial dysfunction;

  Tachycardia +/- arrhythmias

  Variable pulses +/- pulse deficits

  Signs of LCHF +/- RCHF

  Gallop sounds (if in sinus rhythm)

  Soft mitral/ tricuspid regurgitation murmurs.

  If they have forward failure (often bad news)

  Pale mucous membranes

  Sluggish CRT

  Cool extremities
• DCM echo cardiography findings

  Large, round, poorly contractile left ventricle.

  Poor systolic function (poor contractility)

  Dilated, round left atrium.

  +/- mitral regurgitation small/moderate due to dilation.

  +/- right sided changes.
• Electrocardiography for DCM

  Finding are ver variable - range from normal to wide/ tall complexes

  Many DCM dogs have ventricular arrhythmias

  Treat heart failure first unless the arrhythmias are heamodynamically unstable.
• Arrhythmogenic right ventricular cardiomyopathy (ARVC)

  This is rhythm disturbance cased by the cardiac muscle in the right ventricle.

  Myofibre atrophy, fibrosis and fatty infiltration.

  3 stages of the disease:

  1. Asymptomatic with ventricular arrhythmias
  2. Symptomatic - normal heart size and left ventricular function but dogs are syncopal/ weak from ventricular arrhythmias.
  3. CHF - poor myocardial function, CHF and ventricular arrhythmias.
• Clinical signs of ARVC

  Can appear any age, tends to be 8 years or older.

  Ventricular arrhythmias

  Supra-ventricular arrhythmias

  >500 VPCs/24hrs

  Syncope

  Sudden death
• Diagnosis and treatment of ARVC

  Monitor with a 24 hour halter monitor. May need furhter physiological monitoring. Treat any heart failure and also treat with anti-arrhythmic medication (soltalol)
• Secondary myocardial diseases

  Myocarditis - infectious/ non-infectious

  Doxorubicin - acute and chronic cardio toxicity.

  Metabolic/ nutritional deficiencies

  L cartinine deficiency

  Taurine deficiency

  Ischaemic heart disease (clot that has landed in the heart muscle)

  Tachycardia induce cardiomyopathy.
• Hypertrophic cardiomyopathy

  Occurs in cats. Inappropriate myocardial hypertrophy of a non-dilated left ventricle, occurring in the absence of an indentifiable stimulus .

  Diagnosis of exclusion - need to make sure no other cause.

  Other things that can result in concentric hypertrophy (thick walls at expense of lumen).

  Aortic stenosis - ventricle struggle to inject blood)

  Systemic hypertension

  primary, diabetes mellitus, cushings

  metabolic disorders capable of inducing hypertrophy

  renal disease and associated hypertension.
• Two clinical forms of hypertrophic cardiomyopathy

  Obstructive cardiomyopathy;

  Great majority of dogs, 42% of cats.

  Ventricular walls become so thick leading to systolic anterior motion of the mitral valve - dynamic left ventricular outflow tract obstruction.

  Non-obstructive
• What is SAMming?

  Systolic Anterior Motion of the Mitral valve in obstructive hypertrophic Cardiomyopathy.

  1. Papillary muscle displaced towards the septum.
  2. Mitral valve mal-alignment
  3. Narrowed LVOT (Venturi effect).

  
• Patient signalment of HCM

  3 genetic mutations now discovered - 2 in Maine Coons and 1 in Ragdolls, rare in dogs.

  Excessive left ventricular wall/ septum hypertrophy without dilation - the left ventricular wall is very thick, can’t fit enough blood in there, so when the heart pumps you get forward and backward failure.

  Extent and distribution of LVH is variable.

  Left atrial enlargement varies depending on the severity of diastolic dysfunction.
• What is restricitive cardiomyopathy?

  Unknown aetiology probably multifactorial as there is a range of pathological findings. Could be end stage disease.

  2 forms of disease;

  Endomyocardial

  Myocardial

  Extensive Endocardial, subendocardial or myocardial fibrosis.

  Atrial enlargement (usually very large), due to poor ventricular filling and regurgitation.

  Mild left ventricle hypertrophy can happen.

  Diastolic failure (poor filling) leads to backwards failure.
• How does Restrictive cardiomyopathy present?

  Very variable, often present in heart failure. Can range form an asymptomatic cat with a small murmur to a recumbent, cold dyspnoeic cat via congestive heart failure. Often have an increased RR at rest. Stress can lead to severe dyspnoea.
• What are Gallop sounds?

  Happens because of turbulent blood.

  
• Feline dilated cardiomyopathy

  Very rare in cats. Taurine deficiency was a major cause prior to the 80s as it was not in cat food as we didn't know that they needed it in their diet. DCM is often an end stage of another myocardial abnormality - toxic drug induced, CM or infection.