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Diseases

Cardiac & Respiratory Diseases

Diagnosis and Treatment of Common Cardiac and Respiratory Diseases

Heart Failure

Cardiac disease (11% of dogs, 15% of cats)

Causes:

Pressure overload (concentric hypertrophy)

Narrowing of outflow tract (pulmonic stenosis, aortic stenosis)

Hypertension (systemic, pulmonary)

Volume overload (eccentric hypertrophy)

Valvular insufficiency (mitral, tricuspid, aortic)

Shunts (PDA)

Chronic anemia

Systolic (pump) failure (affects contractility)

Myocardial disease (dilated, arrhythmogenic, hypertrophic cardiomyopathies)

Diastolic failure (affects preload)

Pericardial effusion

Hypertrophic cardiomyopathy

Arrhythmias (affects heart rate)

CO = HR x SV

Congestive Heart Failure

Neural regulation:

↓ CO → ↓ arterial BP (arterial underfilling)

To stabilize BP + perfusion: ↑ sympathetic + ↓ parasympathetic activity

Sympathetic effects:

↑ HR, ↑ contractility, vasoconstriction (weak peripheral pulses, pale MM), stimulates RAAS, vasopressin (ADH)

Renin-Anigiotensin-Aldosterone System (RAAS):

↑ circulating fluid volume (reabsorbs more Na + water)

Preload, cardiac output, excessive fluid retention (edema, effusion)

↑ systemic vascular resistance

Improves BP, excessive vascular resistance, weak peripheral pulses, pale MM

Replaces myocardium with fibrotic tissue

Neurohormonal effects:

Myocardial stretch releases counter-regulatory hormones (ANP, BNP) → vasodilation, natriuresis, diuresis BUT is outweighed by RAAS + sympathetic system

Heart Failure Classification:

A: high risk of developing heart disease

B: heart disease, NO clinical signs

B1: no chamber enlargement

B2: enlarged left atrium/ventricle

C: past or current signs of heart failure (even if stable on medication)

D: end-stage disease (refractory to standard therapy)

Clinical Signs:

Weakness, exercise intolerance, syncope, inappetence

Sympathetic tone → tachycardia

RAAS (Na/water retention) → edema (respiration >35-40 brpm, cough), effusion (distended veins, ascites, pleural effusion, “weight gain”)

Peripheral vasoconstriction → pale MM, weak peripheral pulses

Heart Murmur:

Timing (systolic, diastolic, continuous)

Punctum maximum (apex, base, left, right)

Grade (1-6) *anemia, flow murmur (physiologic in <6 mo) or athletic dogs should always have low grade murmur*

Thoracic Radiographs:

Size of heart: VHS (8.5-10.5), left atrial size, tracheal deviation, sternal contact (see radiograph notes)

Bloodwork:

RAAS, vasopressin → ↓ Na, K, Cl (water reabsorption dilutes Na)

↓ perfusion → ↑ urea, creatinine (pre-renal azotemia)

↑ ALT (back up in systemic circulation, NOT liver disease)

Anemia? Inflammation?

Therapy:

Modify preload

Diuretics: Furosemide (↓ fluid volume) helps lungs remove fluid via kidneys

Venodilators: ACE inhibitors (↓ venous tone) reduces volume back to heart

Modify cardiac function

Inotropes: Pimobendan (↑ contractility) improves sensitivity to calcium that is there

Modify afterload:

Arteriodilators: ACE inhibitors (↓ arterial tone/vasoconstriction) reduces pressure that heart has to work against

Dilated Cardiomyopathy (DCM)

Etiology:

Primary (#1) vs. acquired (#2)

GENETIC (Dobermans, large/giant breeds)

Nutritional (taurine deficiency, Cocker Spaniel, Golden Retriever, cats, grain-free diet?)

Tachycardia-induced

Toxicity (doxorubicin)

Infection (Chagas dz [Trypanosoma cruzi], parvovirus)

IDIOPATHIC

Stages:

Stage A: normal heart, no clinical signs but predisposed (all Dobermans)

Stage B (pre-clinical): abnormal heart, no clinical signs ie. no CHF (lasts 2-4 years in Doberman)

Stage C: abnormal heart, with clinical signs ie. CHF

Stage D: abnormal heart, with clinical signs ie. CHF and refractory to medication; sudden death by ventricular fibrillation (not atrial); euthanasia (lasts 4-6 months in Doberman)

ECG:

ATRIAL FIBRILLATION: absence of P waves, irregular irregular rhythm +/- f waves, typically narrow QRS complexes (supraventricular)

Consequences: no atrial filling, tachycardia, wide HR fluctuations → worsening of CHF

Thoracic Radiographs:

Large left atrium and ventricle

+/- Pulmonary venous distension

+/- Diffuse broncho-interstitial pulmonary pattern (worse caudodorsally)

Blood Pressure:

Low (weak peripheral pulses)

Treatment:

Pimobendan +/- ACEi, furosemide

Calcium channel blocker (treat HR only if pathologic tachyarrhythmia)

Taurine supplement, nutrition/diet

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

Etiology:

Progressive fibrofatty replacement of right +/- left ventricular myocardium

Any age (6-10 years)

Subtypes:

Asymptomatic: incidental detection of arrhythmia

Exercise intolerance or syncope: associated with ventricular arrhythmia

Systolic dysfunction + CHF: rare (10%)

*majority show ONLY arrhythmia with NORMAL echocardiogram

Holter (24 hour ECG):

VENTRICULAR ARRHYTHMIA

Rule out other causes: other cardiac dz, electrolyte abnormalities, neoplasia, etc.

Treatment:

When? If (1) symptomatic due to ventricular arrhythmia or (2) asymptomatic but arrhythmia severe in frequency/complexity

Sotalol: K channel blocker + beta blocker

Mexiletine: oral Na channel blocker (similar to lidocaine)

Goal: reduce frequency/complexity of arrhythmias, reduce symptoms but NO treatment proven to prevent sudden death (unpredictable)

Degenerative Valve Disease

Etiology:

Progressive fibrofatty replacement of right +/- left ventricular myocardium

Any age (6-10 years)

Subtypes:

Asymptomatic: incidental detection of arrhythmia

Exercise intolerance or syncope: associated with ventricular arrhythmia

Systolic dysfunction + CHF: rare (10%)

*majority show ONLY arrhythmia with NORMAL echocardiogram

Holter (24 hour ECG):

VENTRICULAR ARRHYTHMIA

Rule out other causes: other cardiac dz, electrolyte abnormalities, neoplasia, etc.

Treatment:

When? If (1) symptomatic due to ventricular arrhythmia or (2) asymptomatic but arrhythmia severe in frequency/complexity

Sotalol: K channel blocker + beta blocker

Mexiletine: oral Na channel blocker (similar to lidocaine)

Goal: reduce frequency/complexity of arrhythmias, reduce symptoms but NO treatment proven to prevent sudden death (unpredictable)

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