Canine Cardiomyopathy

Question 1

describe canine cardiomyopathy

Answer 1

1. primary disorder of cardiac muscle
   -dilated cardiomyopathy
   -arrhythmogenic right ventricular cardiomyopathy (ARVC)
2. secondary disorder of the cardiac muscle (if find, get excited bc can reverse remodel the heart!)
   -nutritional deficiency
   -infectious/myocarditis
   -drug-induced, toxin
   -tachycardia induced

ddx:
-myocardial failure due to chronic insult from other primary disease (end-stage volume-loading valvular disease)
-congenital left to right shunt

Question 2

describe dilated cardiomyopathy pathology

Answer 2

1. four chamber enlargement; left side worse than right
2. walls thin to normal, valves normal
3. myocardial fibrosis

Question 3

describe DCM pathogenesis

Answer 3

1. systolic dysfunction causes decreased stroke volume
2. hypotension and activation of SNS and RAAS
3. secondary (functional) valvular regurgitation due to annular stretch
4. cardiac chamber dilation: profound left atrial and ventricular dilation
5. increased atrial pressure results in pulmonary edema (or ascites if right side involvement; can also see pleural or pericardial effusion)
6. arrhythmias can be due to atrial stretch or ventricular ischemia
   -atrial fibrillation, ventricular tachycardia

Question 4

describe DCM pathophysiology

Answer 4

systolic dysfunction and increased left atrial pressure results in pulmonary edema/left CHF

Question 5

describe clinical findings of DCM

Answer 5

1. compensated:
   -murmur, systolic apical (L or R)
   -gallop (S3 due to ventricular dilation)
   -weak femoral pulses
   -arrhythmias with pulse deficits
2. decompensated:
   -left CHF: tachypnea, cough, tachycardia, crackles (edema)

-right CHF: ascites, distended jugular veins, muffled heart sounds, tachycardia

Question 6

how differentiate between degenerative valves and DCM on physical exam?

Answer 6

breed/signalment is a good clue
-10 y/o cavalier likely degen

murmur: might not help much
-degen: left apical systolic
-DCM: same

femoral pulses!!!
-degen: normal
-DCM: weak

both tachycardic, tachypneic, coughing

Question 7

describe radiographic findings of DCM

Answer 7

1. generalized cardiomegaly
2. prominent left atrial enlargement
3. left ventricular enlargement
4. L CHF:
   -distended pulmonary veins
   -interstitial or alveolar infiltrates
5. R CHF:
   -distended caudal vena cava
   -pleural effusion
   -ascites

Question 8

describe ECG of DCM

Answer 8

1. tall R waves: left ventricular enlargement
2. tall (P pulmonale) or wide (P mitrale) P waves: right or left atrial enlargement
3. atrial fibrillation is common!
4. ventricular arrhythmias: VPCs or VT
   -sudden cardiac death
5. tachycardia may contribute to CHF

Question 9

describe breed disposition of DCM

Answer 9

more commonly diagnosed in large dogs!

-doberman pinscher
-great dane
-irish wolfhound
-american cocker spaniel
-boxer
-juvenile portuguese water dog

Question 10

describe echocardiography of DCM

Answer 10

1. chamber dilation
   -LA enlargement
   -LV eccentric hypertrophy- due to volume overload
   -left atrial dimension: LA:Ao >1.6 (FYI)
2. systolic dysfunction
   -systolic mitral regurgitation
   -mitral regurgitation is functional
   -typically central jet
   -measure fractional shortening: decreased = FS <25% (FYI)

Question 11

how to differentiate degenerative valves versus DCM on echo?

Answer 11

both have mitral regurgitation!
-due to different pathologies though

function:
-degen valve: can have hyperkinetic systolic function (normal to increased unless endstage)
-DCM: heart is barely pumping, function hella low

Question 12

describe acute therapy for CHF (5)

Answer 12

1. oxygen
2. IV furosemide: decrease preload
3. pimobendan (PO), dobutamine (IV): increase contractility
4. +/- sedation: butorphenol
5. +/- afterload reducer: nitroprusside
   -very potent arterial vasodilator!! close BP monitoring

Question 13

describe chronic therapy for CHF

Answer 13

1. furosemide: loop diuretic
2. enalapril or benazepril: ACE-inhibitor
   -do NOT give in acute setting!
   -will drop GFR, can cause AKI in acute setting, so save for chronic when kidney values are better and are eating okay
3. pimobendan: inodilator
4. spironolactone: aldosterone antagonist

Question 14

describe follow up from an acute presentation of DCM

Answer 14

1. recheck in 5-7 days
2. thoracic rads, renal panel, blood pressure, +/- ECG

Question 15

what additional diagnostics could be considered for DCM?

Answer 15

1. 24 hour ambulatory ECG (Holter)
2. ambulatory event monitor
3. serum biochem, PCV/TS or CBC, +/- UA

Question 16

describe antiarrhythmic therapy for ventricular tachycardia

Answer 16

1. lidocaine: first choice in dog
   -IV bolus (2 mg/kg for dog), effects are short lived
   -follow with a CRI (50-75mcg/kg/min for dog)
2. check serum electrolytes

V-tach is a lethal arrhythmia!! when you see it, TREAT IT
-treat first!!!! will kill patient first!!!!!!!!!

3. lidocaine toxicity:
   -do NOT exceed 8mg/kg IV over 30 min!
   -toxicities: GI, tremors, seizures
4. other acute options if lidocaine unsuccessful:
   -procainamide IV
   -magnesium sulfate or magnesium chloride
   -esmolol
   -amiodarone: large side effect profile

Question 17

describe chronic treatment for ventricular tachycardia

Answer 17

1. sotalol: potassium channel blocker and beta blocker
   -CAUTION if heart failure or systolic dysfunction
2. mexiletine: sodium channel block
   -can use in combo with sotalol
3. amiodarone: potassium channel blocker
   -lots of side effects!!

Question 18

describe therapy for atrial fibrillation

Answer 18

1. A-fib is rarely reversible due to damaged myocardium!
2. goal: slow transmission of atrial impulses to the ventricle and thereby bring ventricular contraction rate to within reasonable range
   -this involves giving meds that cause controlled AV block
   -HEART RATE control
3. medications:
   -diltiazem (calcium channel blocker) +/- digoxin (ACE inhibitor) (can use together as combo therapy)
   -beta blocker: many patients in CHF have trash function, so negative inotropy may not be good for them

Question 19

what is the therapy for right CHF

Answer 19

abdominocentesis! tap that tummy!!

Question 20

describe DCM in dobermans

Answer 20

1. breed screening for occult disease
2. common in younger dogs: 3-4 years old
3. 24 hour holter testing:
4. echocardiogram
5. genetic testing:
   -mutation of pyruvate dehydrogenase 4 (PDK4)

Question 21

describe DCM in American cocker spaniels

Answer 21

1. may be associated with taurine deficiency
2. DCM may cause CHF in this breed
3. measure whole blood taurine, if low can treat with taurine and can reverse remodel the heart

Question 22

describe diet associated DCM

Answer 22

1. nutritionally based cardiomyopathy occurs in some dogs
2. clinical and echo improvement in some after diet change
3. role of taurine supplementation despite normal blood concentration unknown right now

Question 23

describe arrhythmogenic right ventricular cardiomyopathy (ARVC)

Answer 23

1. boxer cardiomyopathy:
   -primary disease of heart muscle
   -causes arrhythmias, syncope, sudden cardiac death
2. inherited disease, adult onset (6 years of age)
3. 3 forms:
   -asymptomatic ventricular arrhythmias: noted during PE; monitor for progression

-symptomatic ventricular arrhythmias: syncope, first sign might be sudden death

-ventricular arrhythmias with congestive heart failure

Question 24

describe pathology of ARVC

Answer 24

1. fibrofatty replacement and loss of normal myocardial tissue
2. close resemblance of pathological features of ARVC in humans

Question 25

describe echocardiography of ARVC

Answer 25

1. echo may be normal!
2. 24 hour holter monitor
   dx if 2/3 of: (FYI)

• at least or more than 100 VPCs in 24 hr
  -presence of couplets (VPC)
  -R on T phenomenon