SA Cardiology

5 Phenotypes of Cardiomyopathies

Hypertrophic (HCM)
Restrictive (RCM)
Dilated (DCM)
Arrhythmogenic right ventricular (ARVCM)
Non-specific/unclassified

Pathophysiology of primary HCM

Concentric hypertrophy of LV = poor relaxation = diastolic failure
Diastolic failure = LA enlargement = L CHF
Diastolic failure = distal aortic thrombus (ATE)

In which cats is primary HCM seen most commonly

Domestic shorthairs
Earlier and more severe in males

Pathophysiology of primary RCM

Impaired diastolic function due to LV fibrosis

Echocardiographic features of RCM

Severe atrial dilation
Normal wall thickness and LV diameter
Effusions

Pathophysiology of primary DCM

Dilated and poorly contracting LV

Features of arrhythmogenic RV cardiomyopathy

RA and RV enlargement
RV wall thinning and aneurysmal bulges
Variety of arrhythmias
Leads to R CHF and thromboembolism

What is used to differentiate the different causes of heart murmurs

Echocardiography (as history, clinical exam and ECG are similar)

Echocardiographic features of HCM

Increased LV wall thickness

Echocardiographic features of DCM

Poor systolic function
Dilated LV (and possibly dilated RV)
Wall thickness normal or decreased

Echocardiographic features of ARVCM

Marked RV and RA dilation

Risk stratification for CHF

A = predisposed
B1 = low risk = normal/mild atrial enlargement
B2 = higher risk = moderate/severe atrial enlargement
C = current/previous CHF/ATE
D = refractory CHF

Biomarker used to differentiate cardiac and respiratory disease

NT-proBNP

Blood tests used when investigating murmurs

Renal function
Thyroid function
Taurine levels
Biomarkers (e.g. NT-proBPN)
Genetic tests (e.g. myosin binding protein mutations)

Treatment to improve diastolic function

Negative inotropes/chronotropes (Ca2+ channel blockers, Beta blockers)
Decreased myocardial fibrosis (ACE inhibitors, spironolactone)

Treatment to improve systolic function

Increase contractility, HR, and myocardial relaxation (Bigoxin - toxic in cats)
Positive inotrope and vasodilator (Pimobendan)

Acute management of thromboembolism

Cage rest
Warmth
Analgesia (opioids)
Heparin (low molecular weight)
Physiotherapy
Low dose i/v fluids
Vasodilation (ACP)

Prevention of thromboembolism

Clopidogrel (/Aspirin)
Heparin (low molecular weight)
Rivaroxaban (Factor Xa inhibitor)

Most common cause of CHF in dogs

Degenerative/Myxomatous Mitral Valve Disease

Breed association of degenerative/myxomatous mitral valve disease

Cavalier King Charles Spaniel

Pathophysiology of degenerative/myxomatous mitral valve disease

Mitral valve leakage =\> LV concentric hypertrophy =\> LV volume overload =\> decreased cardiac output =\> stimulation of RAAS =\> left-sided CHF

History for degenerative/myxomatous mitral valve disease

Many are asymptomatic
Signs of left-sided cardiomegaly (esp. cough)
Signs of left-sided CHF (tachypnoea, cough, exercise intolerance)
+/- signs of right-sided CHF

Clinical findings associated with degenerative/myxomatous mitral valve disease

Systolic murmur over mitral valve (grade related to severity)
In early stages - good pulse quality and myocardial function
In later stages - dyspnoea, ascites, arrhythmia

Further findings associated with degenerative/myxomatous mitral valve disease

Radiography - cardiomegaly (+/- pulmonary oedema, venous congestion)
ECG - arrhythmias, chamber enlargement
Echocardiography - Prolapse of valve leaflets into LA, thickened leaflets, LV/LA remodelling
Biomarkers - NT-proBNP

Treatment for degenerative/myxomatous mitral valve disease

Slowly progressive so treatment depends on stage and owner engagement/monitoring is very important
Prognosis guarded once CHF develops

On which side of the heart does bacterial endocarditis more commonly affect

Left in SA and horses
Right in cattle

Predisoposing factor for bacterial endocarditis

Aortic stenosis

Signs of bacterial endocarditis

Pyrexia
Joint pain/stiffness - shifting lameness
New left-sided heart murmur

Main diagnostic techniques for bacterial endocarditis

Blood culture
Echocardiography

Treatment and prognosis of bacterial endocarditis

I/V antibiotics (based on blood culture)
Guarded prognosis

Why are prophylactic antibiotics given to dogs with moderate/severe aortic stenosis when undergoing a dental procedure

To prevent the development of bacterial endocarditis

Causes of secondary dilated cardiomyopathy

Toxic (e.g. Doxorubicin)
Chronic tachycardia
Dietary (taurine deficiency, carnitine deficiency, association with grain-free diets)
Hypothyroidism

Pathophysiology of dilated cardiomyopathy

Systolic failure = decreased CO = RAAS stimulation = fluid retention = L CHF (+/- R CHF)
Systolic failure and RAAS activation = LV dilation = ventricular arrhythmias

Signs of dilated cardiomyopathy in dogs

Exercise intolerance
Signs of L CHF (+/- R CHF)
Syncope
Pallor, Poor CRT, weak pulses
Tachycardia
Arrhythmias and gallop sounds
Low grade systolic murmur
Can be asymptomatic (occult disease)

Diagnostic findings of dilated cardiomyopathy in dogs

Radiology - LA/LV enlargement, CHF
ECG - various arrhythmias (esp. atrial fibrillation and ventricular arrhythmias)
Echo. - Enlarged LA/LV and poor contractility

Treatment and prognosis for dilated cardiomyopathy in dogs

Improve systolic function (Digoxin/Pimobendan)
Decrease preload (diuretics) and afterload (ACE inhbitors)
Treat arrhythmias
Decrease further remodelling
Prognosis depends on breed (6-18 mth if CHF)

Dog breeds associated with Arrhythmogenic Right Ventricular Cardiomyopathy

Boxers and Bulldogs

Signs of arrhythmogenic right ventricular cardiomyopathy

Syncope
Signs of CHF (ascities, pulmonary oedema)
Can see cardiogenic shock due to rapid ventricular tachycardia
Histo = lysis and fibrofatty change in RV

Treatment of arrhythmogenic ventricular cardiomyopathy

Support systolic function (Pimobendan)
Decrease remodelling (ACE inhibitors)
Treat symptomatically

What causes secondary HCM in dogs

Systemic hypertension

SIgns of myocarditis

Not specific signs - pyrexia, arrhythmias
May see poor systolic function, secondary dilation, and low grade murmur
Don't often see CHF

Common causes of myocarditis

Toxoplasmosis
Neospora
Parvoviruses
Erhlichia
Barrelia (Lyme's disease)
Neoplasia

Diagnosis of myocarditis

High serum troponin I
Myocardial biopsy

Treatment and prognosis of myocarditis

Treat cause and any arrhythmias
Prognosis = guarded

Which lead is usually used for rhythm analysis on ECG

Lead II

3 uses of ECG

Diagnosis of arrhythmias
Provide information on chamber enlargement
Provide information of electrolyte disturbances (esp.K+)

Wandering pacemaker (ECG finding)

Varying height of P waves on ECG
Associated with high vagal tone

Atrial standstill (ECG finding)

Lack of P waves
Indicates problem with K+

Ventricular ectopics (ECG finding)

Beats which do not originate from the SA node
LV ectopics = predominantly -ve QRS complex
RV ectopics = predominantly +ve QRS complex
Often seen as premature of escape beats

ECG finding: wide, notched P waves

LA enlargement

ECG finding: Tall P waves

RA enlargement

ECG finding: Tall R waves

LV enlargement (also often see larger T waves)

ECG finding: negative R wave

RV enlargement (AKA right axis deviation)

ECG finding: small normal QRS complexes

Pleural effusion
Obeisity

ECG finding: small QRS complexes with varying heights (electricalalternans)

Pericardial effusion

ECG finding: Prolonged Q-T interval

Hypocalcaemia
Hypokalaemia
Hypothermia
Drugs

ECG finding: Shortened Q-T interval

Hypercalcaemia
Hyperkalaemia
Drugs

ECG finding: S-T depression

Myocardial hypoxaemia

ECG finding: S-T coving (not horizontal line)

LV enlargement

When should an arrhythmia be treated

When they're causing signs (e.g. syncope)
If they're potentially life-threatening (e.g. ventricular tachycardia)
If there's no immediately treatable underlying cause

Why is careful monitoring of patients on anti-arrhythmic drugs important

Anti-arrhythmic drugs can also be pro-arrhythmic

Sinus arrhythmia

HR varies with respiration
Normal in dog but not cat

5 types of bradyarrhythmias

Sinus arrest
Sick sinous syndrome
Sinus bradycardia
Atrial standstill
AV blocks

Sinus arrest

SA node doesn't always fire (but still does at least intermittently)
Often see ectopic escape beats (rescue beats)

Causes of sinus arrest

Medications: beta blockers, Ca2+ channel blockers, digoxin
Disease: high vagal tone, atrial disease, hypothyroidism

Sick sinous syndrome

Lots of issues seen which are associated with the SA node
Hereditary, idiopathic

Treatment for sick sinous syndrome

Pacemaker
Sympathomimetics
Parasympatholytics

Sinus bradycardia

Normal rhythm but very slow

Causes of sinus bradycardia

medications: sedatives
disease: hypothyroidism, increased ICP, dysautonomia\`

Atrial standstill

No P waves
Persistent or temporary

Causes of temporary atrial standstill

Acute renal failure
Hyperadrenocorticism
Hyperkalaemia

1st Degree AV Block

Increased PQ interval
Can be normal if very fit

Causes of 1st Degree AV Block

Sedatives
High vagal tone
AV node fibrosis

2nd degree AV block

Dropped beats (P wave but no QRS)
Mobitz type I = progressive lengthening of PQ until dropped beat occurs
Mobitz type II = pattern of dropped beats. Indicates AV node disease.

3rd degree AV block

No relationship between P and QRS waves
All QRS beats are escape beats
Indicates AV node disease

Types of tachyarrhythmias

Sinus tachyarrhythmia
Supraventricular premature beats
Atrial fibrillation
Supraventricular/Atrial tachycardia
Ventricular premature complexes
Ventricular tachycardia
Ventricular escape beats

Sinus tachyarrhythmia

Normal rhythm but very fast
Normal if nervous/excited

Supraventricular premature beats

No P waves (but QRS looks normal)
Due to atrial dilation, infiltration or fibrosis

Atrial fibrillation

Very jagged rhythm
Life-threatening
Due to atrial dilation, infiltration or fibrosis

Ventricular premature beats

Wide QRS complexes

Causes of ventricular premature beats

Ventricular dilation, inflammation, infiltration, or fibrosis
Anaemia
Sepsis
Splenic masses
Pyometra
Hypokalaemia

Ventricular tachycardia

Runs of ectopics
Emergency situation

Ventricular escape beats

Follow a pause (the cause of the pause is the real problem)

What test can be used to determine whether an arrhythmia is vagal in origin

Atropine response test

3 general classifications of murmurs

Pathological (cardiac)
Physiological (functional)
Innocent (flow)

Innocent murmurs

Grade 1-2
Systolic
Disappear by 16-20 weeks

3 most common congenital defects in puppies

Aortic stenosis
Patent ductus arteriosus
Pulmonary stenosis

3 most common congenital defects in kittens

Ventricular septal defect
Mitral valve displacement
Tricuspid valve displacement

Breed associations of aortic stenosis

Newfoundlands, Boxers, Rottweilers, Golden Retrievers, German Shepherds

Breed association of PDA

Poodle, Collies, Spaniels, CKCS

Breed association of tetralogy of fallot

Keeshound

Breed association of pulmonary stenosis

Beagle, Boxers, Westies, Bulldogs, Cocker Spaniels

Breed association of persistent R aortic arch

German Shepherd

Congenital heart conditions resulting in murmur at left heart base

PDA
Aortic stenosis
Pulmonary stenosis
Innocent murmur

Congenital heart condition resulting in murmur at left heart apex

mitral valve displasia

Congenital heart condition resulting in murmur on the right hand side

Tricuspid valve displasia
Ventral septal defect
Tetralogy of fallot

Pathophysiology of aortic stenosis

Narrowed valve = decreased CO = forward failure = exercise intolerance/collapse

Narrowed valve = pressure overload of LV = LV concentric hypertrophy = arrhythmias/syncope/sudden death/CHF

Aortic stenosis: history and clinical signs

Harsh systolic murmur at left heart base
May be asymptomatic
Exercise intolerance/syncope
L CHF signs
Weak pulses

Aortic stenosis: diagnosis

Echocardiography - aortic valve dysplasia/ stenosis/turbulence, LV concentric hyperplasia

Aortic stenosis: treatment and prognosis

Mild cases: no treatment, good prognosis
Severe cases: beta blockers, guarded prognosis