Feline myocardial dx

What are the primary myocardial diseases in cats?

Can get most cardiomyopathies

• HCM (main one)

  • With or without LV obstruction

• Restrictive cardiomyopathy

• Non-specific cardiomyopathy

• DCM

• Arrythmogenic right ventricular cardiomyopathy

What are the 2° myocardial dx that can cause cardiomyopathy in cats?

• Hypertensive cardiomyopathy

• Hyperthyroid cardiomyopathy

• Cardiomyopathy associated with acromegaly, azotaemia, diabetes etc.

• Transient myocardial thickening (young cats, following stressful incident, reversible)

What can feline systemic hypertension lead to?

• 2° cardiomyopathy

  • Often can identify heart murmurs

• Ocular/ CNS complications (vital to recognise before this)

What do you need to screen for when a cat has systemic hypertension?

Screen for underlying systemic dx —> haematology, biochem, TT4 etc.

Explain the pathological processes that come with HCM

• Marked concentric hypertrophy of LV

• Diastolic dysfunction

  • Can pump but cant fill

What would be the gold standard diagnosis for HCM?

Histopath to rule out other potential causes of concentric hypertrophy

• Fibromyocyte disarray

• Fibrosis

What potential causes do you need to rule out to diagnose HCM?

• Aortic stenosis

• Systemic hypertension

• Hyperthyroidism

• CRF

• Acromegaly (± diabetes mellitus)

• Transient myocardial thickening

(All cause concentric left ventricular hypetrophy)

What causes true HCM?

Genetic:

• Can genetic test Maine coons & ragdolls —> mutations detected in genes encoding myosin binding protein C

How does preclinical HCM present?

• Asymptomatic heart murmur most common

• Sometimes arrythmias/ diastolic gallops (S3 & S4)

• Incr. NT-proBNP and/or Troponin I in blood sample (cardiac biomarkers)

What NT-pro-BNP value is normal?

<100 pmol/L

How does clinical HCM present?

• Dyspnoea/ tachypnoea because of CHF → pulmonary oedema +/or pleural effusion

• Feline arterial thrombo embolism (FATE)

• Syncope

• Period of open mouth panting

• Sudden death

How does FATE present?

• Non pigmented nail beds

• Loss of function of back legs (can also be front legs)

• Very painful

• Saddle thrombus seen in distal aorta PM

How does pulmonary oedema present on echo?

B lines

How does HCM present on echo?

Thick walls but normal sized L atrium which then progresses to incr. sized L atrum

How is feline HCM classified?

What is this lung pattern showing?

Alveolar pattern in caudodorsal lung field

Trachea no longer parallel to sternum = cardiogenic pulmonary oedema

How may a HCM heart present on a radiograph?

'Valentine' heart on DV view

• Atrial enlargement —> L & R atrium

• Pointed apex

• Enlarged cardiac silhouette

How may ECGs be useful in the diagnosis of HCM?

• Confirm presence of arrhythmias

• Intraventricular conduction disturbancces

• Tall R waves because of LV enlargement (0.9mV)

(Not always useful)

What does this ECG show?

Atrial fibrillation —> large R-R interval, no discernable P waves

What are the sources of murmurs in HCM?

• Septal bulge resulting in LV outflow tract obstruction

  

• Systolic anterior motion of MV → mitral regurgitation due to mitral valve being open in systole when it shouldn’t be

  

• Two jets

• Systolic anterior motion (SAM) of the septal mitral valve leaflet leading to dynamic left ventricular outflow tract obstruction (DLVOTO)

What does LVOT look like on echo?

Scimitar shape

What causes an audible S3?

Rapid deceleration of blood in LV

What causes an audible S4?

LV filling associated with atrial contraction

How do you treat HCM & CHF?

If CHF:

• Diuretics (Furosemide)

  • IV —> better as venodilatory effect —> if can be administered w/o stress if severe dyspnoea

  • IM if cannot be given IV

• Clopidogrel; aspirin —> to prevent thromboembolism

Depending on owner compliance can add:

• Venodilator (for life-threatening pulmonary oedema)

• ACE inhibitor (Benazepril licensed for CKD)

• Ang II blocker (Telmisartan)

Do you treat an asymptomatic HCM cat?

• Not much evidence for outcome but could use beta blockers because can reduce severity of LVOT obstruction/systolic anterior motion

  • indirectly improve diastolic function

  • DO NOT use beta blockers in cat with uncontrolled CHF —> will slow heart rate —> need symp drive to survive

• Maybe ACE inhibitors

• Maybe dilitazem —> positive lusitrope, improves diastolic function (no longer available)

What are some predisposing factors that contribute to cats being more likely to have HCM?

• Large, overweight males

• Increased insulin, glucose & IGF-1

  • Low carb, high protein diet over 12months can reduce progression of preclin HCM

Which drug may prevent significant increase in hypertrophy over 6 months?

Rapamycin

What is an important cause of DCM in cats?

Taurine def

• Reversible with taurine supplementation

DCM rare in cats because taurine present in most modern cat diets

What are the gross features of DCM

• Thin wall

• Insufficient contracting ability of ventricles

What can you use for DCM treatment?

• Supportive with warmth, O2, pleural effusion drainage

• Furosemide

• ACE inhibitors

• Pimobendan (+ve ionotrope) —> not in murmurs because worsen obstructions

• Taurine supplementation

What are the two forms of restrictive cardiomyopathy?

• Myocardial form

• Endomyocardial form

What is restrictive cardiomyopathy characterised by?

• Normal dimension and systolic function but reduced diastolic function

• Presents with LA enlargement

How do the forms of RCM differ on echo?

• Both cause severe heart m. stiffness & dyastolic dysfunction due to stretching & enlargement of LA

• Endomyocardial form = bridging scars formed

What is a non-specific-CM?

Features of more than one cardiomyopathy, describe the abnormalities

What is arrythmogenic RV cardiomyopathy?

• Fatty replacement of the myocardium, initially around RVOT

• Dilation of R heart usually

How do cats with arrythmogenic RV cardiomyopathy present?

• R-CHF so ascites

• Maybe arrythmias/ conduction disturbances

• Some 3rd degree AV block

  

Summarise your treatment plan for CHF in cats, whatever the form of cardiomyopathy?

• Furosemide

• ± Pimobendan (unless murmur)

• ACE inhibitor

• ± Spirinolactone

How do you stabilise a dyspnoeic cat with CHF?

• Oxygen therapy w/o additional stress

• Reduce anxiety (butorphanol)

• Calm, gentle handling & environ

• Delay investigations until more stable

• Nitroglycerin topically or GTN patches

• IV (or IM if stressed) furosemide

What samples can you use to run a NT pro-BNP SNAP test?

Blood / pleural effusion (drain)

• Can use in very dyspnoeic patient to identify cardiac cause / exclude it

What is recommended for specific breeds that are prone to HCM?

• Pedigree breeding cats screened annually by echo —> main diag but expensive, time-consuming, requires training

• NT pro-BNP quantitative assay (SNAP test)

  • immediate so useful in dyspnoeic petients

  • not usueful to screen healthy cats as needs values of > 150-200pmol/L to show “abnormal” on SNAP test

Summary of treatments for cardiomyopathy stages