253 Feline Myocardial Diseases

Question 1

What is the definition of hypertrophic cardiomyopathy?

Answer 1

= phenotypically characterised by increased cardiac mass due to hypertrophied non-dilated LV in the absence of obvious cause of LV hypertrophy, such as pressure overload, or hormonal stimulation (hyperthyroid, or acomegaly)

Question 2

What population of cats most likely suffers from HCM?

Answer 2

• Males 70-79%
• DSH (65-70%)
• DLH (9-22%)
• Persians (3-12%)
• British shorthair, Chartreux, Himalayan, Maine cone, Sphinx, and rag doll. Burmese, siamese, oriental shorthairs, and abyssinians
• middle aged= 5-7 years

Question 3

What is the causative mutation for HCM in Maine Coone’s?

Answer 3

• Myosin Binding Protein C sarcomeric gene (MyBPC3-A31P) for inherited HCM, with autosomal dominant inheritance
• MyBPC3 shown to mutated in exon 3, with single base pair change (guanine o cytosine) causing alteration of protein structure owing to replacement of a conservative amino acid (alanine on 31st codon) by proline (P)

Question 4

What is the causative mutation for HCM in Ragdolls?

Answer 4

• a second substitution mutation MyBPC3 associated with HCM identified in the rag doll breed
• This MyBPC3 R820W mutation is characterised by a single base pair change (cytosine to thymine in codon 820), with secondary change of one aminos acid (arginine to tryptophan)

Question 5

What are the main pathophysiological consequences of HCM?

Answer 5

• Ventricular arrhythmias
• myocardial dysfunction
• dynamic LVOTO
• Diastolic dysfunction is major mechanisms for CHF. It results in progressively increased LA Pressure, with secondary LAE, and CHF (pulmonary oedema).
• Visceral pleural veins drain into LA inc acts, increase LA pressure can lead to pleural effusion due to decreased visceral pleural venous drainage.
• Regional/global systolic dysfunction may be resent.
• mitral valve systolic anterior motion

Question 6

What are the clinical signs of a cat with HCM?

Answer 6

• 33%-77% do not show clinical signs at time of diagnosis
• 70-80% of symptomatic cats show CHF (tachypnoea and dyspnea related to pulmonary oedema, +/or pleural effusion in 18-46% of HCM cats at presentation)
• Anorexia and lethargy can precede onset of CHF by 24-72 hrs
• ATE 4-17% of cats with HCM +/- CHF
• 1-6% syncope and weakness
• Open-mouth breathing & dyspnea despite absence of radiographic and echocardiographic signs of CHF reported in HCM
• Rarely coughing
• Rarely ascites due to RSCH

Question 7

What is a common finding on cardiac auscultation in a cat with HCM?

Answer 7

Most common is systolic heart murmur (64-89% of cats) heard over left apex or the cranial sternum, and respectively resulting from mitral regurgitation and lvOTO.
- Gallop rhythm and arrhythmias detected by 33% and 6-10% of HCM.

Question 8

What are the ECG findings of a cat with HCM?

Answer 8

• LVH =QRS amplitude >0.9mV
• LAE = P wave duration >0.04s, PR interval >0.09s
• left axis deviation suggestive of left anterior fascicular block in 11-33%
• Arrhythmias: VPCs, supraventricular premature completes, atrioventricular blocks or atrioventricular dissociation and atrial fibrilllation

Question 9

What is the prognosis of cats with HCM?

Answer 9

• Highly variable: some days, some years
• median survival time of 709 days with a wide range 2-4418 days
• Variables depend on presence of clinical signs, breed, genetic status, and imaging variables

Question 10

What is the definition of feline RCM?

Answer 10

= a myocardial disease characterised by left or biatrial enlargement and diastolic dysfunction associated with ventricular wall stiffness.
- ventricular compliance is impeded by endocardial, eubendocardial, or myocardial fibrosis or an infiltration condition.

Question 11

What is the aetiology of RCM?

Answer 11

Primary: idiopathic condition characterised by endocardial fibrosis with normal ventricular size and abnormal ventricular stiffness
Secondary: ventricular stiffness rising secondary to primary cardiac disease, such as end-stage HCM, DCM, myxomatosis or degenerative valve disease, myocardial failure, and myocardial infarction

Question 12

What is the pathophysiology of RCM?

Answer 12

• unclear.
• The left +/- right atrium become hypertrophied and dilated. Sometimes LV can be affected.
• Left atrial pressure increases as a result of restricted diastolic filling -> lead to increased pulmonary venous pressure and ultimately pulmonary oedema.
• Atrial dilation may lead to ventricular flow resistance that can manifest as chronic pulmonary hypertension, right heart enlargement, +/- elevated central venous pressure. The dilation can lead to blood flow stasis that predisposes cat to atrial thrombi

= as a result, pulmonary oedema, pleural effusion, and hepatic congestion are common.

Question 13

What abnormalities are found in cats with RCM?

Answer 13

• predominately CHF
• dyspnea (76%) (due to pleural effusion, and pulmonary oedema)
• non-specific: lethargy, weakness, hypothermia, anorexia, ascites, and paresis/paralysis related ATE
• Heart murmur: left apical systolic (in 90%) and gallop

Question 14

What ECG findings are predominant for cats with RCM?

Answer 14

• VPCs, and supraventricular tachycardia

- Less commonly AFib

Question 15

What is the prognosis for cats with RCM?

Answer 15

• poor prognosis

- MST= 132 days - 273 days

Question 16

What is dilated cardiomyopathy? What is it’s prevalence?

Answer 16

= dilated LV with systolic dysfunction. There is decreased contractility, with secondary compensatory ventricular dilation.

• was the second most common feline heart disease, but is now rare
• most cases related to taurine deficiency, and reversible and preventable with oral supplementation of taurine.

Question 17

What is the aetiology of DCM?

Answer 17

• Primary (idiopathic, genetic, inflammatory) or secondary
• Can arise secondary to tachycardia’s, toxicosis, muscular dystrophy, infection, metabolic conditions, and nutritional deficiencies (taurine).

Question 18

What is the pathophysiology of DCM?

Answer 18

• The primary change is ventricular eccentric hypertrophy from volume overload, and predominantly LV enlargement and dilation. This is in response to systolic, contractile failure.
• As stroke volume decreases, the body responds by retaining fluid and increasing preload. -> The heart tries to compensate by increasing ventricular volume to restore stroke volume. As myocardial failure worsens, hypertrophy progresses.
• When hypertrophy limits are reached, further increases in preload result in congestive heart failure (CHF).
• True dilation eventually occurs, with loss of myofibers, thinning of ventricular walls, and replacement of muscle by fibrous or fatty tissue. The atrioventricular annulus is also enlarges, subsequent CHF,and increased ATE>

Question 19

What is the typical epidemiology of cats with DCM?

Answer 19

• ## both high proportion of females and a high proportion of males in seperate studies. Both studies demonstrate age of 9-10 years.

Question 20

What are the typical ECG findings of cats wth DCM?

Answer 20

• non specific morphological alterations from cardiac chamber enlargement are commonly found.
• Various arrhythmias are diagnosed, predominantly VPCs and supraventricular tachycardia. A-fib is less common.

Question 21

What is the clinical course and prognosis of cats with DCM?

Answer 21

• short survival time
• MST of 11days in 1 study.
• most cases death resulted from euthanasia due to refractory CHF or ATE.

Question 22

How prevalent is ARVC in cats? What is the aetiology ARVC?

Answer 22

• <5% of myocardial diseases.

- no identified genetic transmission and no identified cause

Question 23

What is the epidemiology of ARVC in cats?

Answer 23

• most are middle aged, but age range is 1-20 years.
• ## no breed or sex predisposition.

Question 24

What is the clinical presentation of cats with ARVC?

Answer 24

• Most cats show right sided congestive heart failure
• Syncope related to ventricular tachyarrhythmia is less common
• Soft right apical systolic heart murmur consistent wit tricuspid regurgitation is detected in most ARVC cats.
• Arrhythmia may be detected.
• nonspecific general signs (e.g. lethargy, anorexia) also reported in cats, even those without evidence of CHF.

Question 25

What are the ECG findings of ARVC in cats?

Answer 25

• large variety: including VPCs of RV and LV origin, atrial fibrillation, supraventricular tachycardia, right bundle branch block, and first and third degree AV blocks.

Question 26

What is the clinical course and prognosis for cats with ARVC?

Answer 26

• most remain asymptomatic, but the prognosis of overt ARVC is usually poor.
• Most cats with ARVC related CHF die of cardiac causes, several days or weeks after initial diagnosis.