Dilated Cardiomyopathy Quiz

Canine Myocardial Diseases

• The presentation is about canine myocardial diseases, specifically cardiomyopathies.
• A Cardiologist, Eduardo J Benjamin, DVM, MS presented the information on December 10, 2024.
• Objectives include describing causes, complications, physical exam findings, diagnostic tools, and management for dogs with myocardial disease.

Myocardial Disease

• Myocardial disease affects the heart muscle.
• It is not caused by valve, endocardial, or pericardial problems.
• Key characteristics include decreased contractility and arrhythmias.

Canine Cardiomyopathies

• Dilated Cardiomyopathy (DCM):

  • A primary form of DCM exists, DCM.
  • Secondary causes include nutritional imbalances (L-carnitine, taurine, certain "grain-free" and BEG diets), myocarditis, infiltrative diseases, tachycardia-induced cardiomyopathy, and drug-induced cardiomyopathy (e.g., doxorubicin).

• Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC):

  • ARVC is a type of canine cardiomyopathy.

• Hypertrophic Cardiomyopathy (HCM):

  • HCM is a common type of canine cardiomyopathy.

• Atrial Standstill/Atrial Cardiomyopathy:

  • A condition involving the atria of the heart.

Cardiovascular System Functions

• Blood pressure equals cardiac output (CO) multiplied by systemic vascular resistance (SVR).
• CO equals stroke volume (SV) multiplied by heart rate (HR).
• Stroke volume is determined by preload, afterload, and contractility.

Dilated Cardiomyopathy (Primary)

• Characterized by dilation and systolic dysfunction.
• Usually considered primary or idiopathic.
• Diagnosed via exclusion of other possible causes.
• Genetic mutations are present in some cases (i.e.Pdk4 and Titin in Dobermans).

Genetics of Dilated Cardiomyopathy

• In human cases, 30-50% are familial.
• Over 50 mutations have been identified in humans.
• In dogs, the prevalence is high in certain breeds such as Dobermans, Irish Wolfhounds, and some other large breeds.
• Several genetic mutations have been identified in dogs, including PDK4 ('DCM1') and Titin ('DCM 2).
• Several modes of inheritance have been identified within the breed (i.e. Irish Wolfhound, autosomal recessive).

Breeds Commonly Affected by DCM

• Large breed dogs, often males, in middle age are most affected.
• Breeds commonly affected include Doberman Pinschers, Boxers, Irish Wolfhounds, Great Danes, Portuguese Water Dogs, English Cocker Spaniels, and American Cocker Spaniels.

Incidence and Prevalence of MVD vs DCM

• A graph demonstrates the different incidences of mitral valve degeneration (MVD) and canine dilated cardiomyopathy (DCM) across different dog weights.

Pathogenesis of DCM

• Poor contraction (systolic dysfunction) leads to less volume ejected and decreased cardiac output.
• Compensatory mechanisms (Renin-Angiotensin-Aldosterone System - RAAS) increase preload to regulate blood pressure via water retention.

Decreased Stroke Volume in DCM

• Normal contractility is an EF% of approximately 70%.
• DCM shows decreased contractility EF of approximately 25%.

Renin-Angiotensin-Aldosterone System

• A hormonal system regulating blood pressure, primarily through water and salt balance. Detailed presentation on the components.

Advanced Dilated Cardiomyopathy

• Severe DCM can be identified by lower than typical ejection fraction.

Pathogenesis of DCM

• Neurohormonal activation (RAAS) causes sodium and water retention and increased preload.
• Cardiac remodeling, including eccentric hypertrophy and fibrosis, occurs.
• Abnormal systolic/diastolic function and arrhythmias are present.
• The above contributes to the progression of heart disease.

Clinical Consequences of DCM

• Congestive Heart Failure: Signs might include pulmonary edema.
• Arrhythmias: This may involve the presence of normal and abnormal patterns on an ECG.
• Weakness/Syncope: Reduced cardiac output leads to less oxygen to the brain.

How do Arrhythmias Decrease Cardiac Output?

• Heart filling during diastole is reduced with the presence of severe tachycardia
• Preload is decreased as diastolic time becomes shorter, resulting in lower stroke volume (SV) and cardiac output (CO).

Dilated Cardiomyopathy Efficiency

• Insufficient cardiac output and reduced cardiac efficiency result primarily from decreased preload.

Tachyarrhythmias and Cardiac Output

• Tachyarrhythmias result in decreased cardiac output due to decreased preload.

Clinical Course of DCM

• Three phases, including genetic predisposition (Stage A), preclinical (occult) phase (Stage B), and clinical (overt) phase (Stage C).

"Occult" DCM

• "Occult" DCM has no noticeable clinical signs initially.

History and Clinical Signs of DCM

• There may be no clinical signs in the occult phase.
• Respiratory signs like coughing, rapid breathing and abdominal distension can occur.
• Exercise intolerance, weakness, and weight loss can be evident.

Physical Exam Findings for DCM

• Soft systolic murmurs might be heard at the left apex, without the presence of a murmur not ruling out DCM.
• Gallop sounds (S3) can be heard.
• Weak peripheral pulses or pulse deficits may be observed.
• Jugular venous distention or pulsation is common.

Physical Exam for CHF

• Pale/cyanotic mucous membranes
• Pulmonary crackles, indicative of fluid accumulation in the lungs.
• Tachypnea or dyspnea (rapid/labored breathing).
• Tachycardia (rapid heart rate).
• Hypothermia (low body temperature).
• Presence of a fluid wave.

Diagnosis - Echocardiogram

• Fractional shortening can be calculated from echocardiogram data (LVIDs and LVIDs).
• LV end-diastolic volume and LV end-systolic volume are used to determine ejection fraction.
• The ratio of left atrium to aorta (LA:Ao) is measured.

Diagnosis - Electrocardiogram

• 300 or more ventricular premature complexes (VPCs) in a 24-hour Holter monitor are used to aid in diagnosis.

Diagnosis - Thoracic Radiographs

• Normal cardiac silhouette does not necessarily rule out systolic dysfunction.

Diagnosis - Biomarkers

• NT-proBNP can be elevated with cardiac enlargement.
• Cardiac Troponin I is elevated with myocardial cellular damage.

Genetic Testing

• Genetic testing is not preferred for screening, but can be useful when considering breeding pairs.
• Absence/presence of mutations does not ensure a patient will/will not develop DCM.
• Incomplete genetic penetrance exists.

Absence of Left Apical Murmur and DCM

• Absence of a left apical murmur does not rule out DCM.

Diagnostic Tests for Dilated Cardiomyopathy (DCM)

• Echocardiography
• ECG/Holter Monitor
• Thoracic Radiographs
• Biomarkers (NT-proBNP, Cardiac Troponin I)
• Genetic testing

Screening for DCM

• Goal: Identify disease early in the occult phase.

Pimobendan Randomized Occult DCM Trial

• The study, called PROTECT, looks further into pimobendan for slowing or delaying progression of the disease.

Ace Inhibitors During Preclinical DCM

• Benazepril given to dogs may delay onset of CHF and/or sudden cardiac death.

Treatment for Dogs with Overt DCM

• The presentation includes treatments for overt DCM
• Inotropic Support (Pimobendan, Dobutamine, Digoxin).
• Afterload Reduction (Pimobendan, ACE inhibitors, Amlodipine).
• Ventricular Arrhythmia Control (Lidocaine/Mexiletine, Sotalol, Amiodarone).
• Supraventricular Arrhythmias (Diltiazem, Digoxin, Amiodarone).
• Preload Reduction (Furosemide.
• Low-sodium diet.

Treatment for Dogs with Ventricular Arrhythmias

• Class I drugs (e.g., Lidocaine, Mexiletine, Procainamide).
• Class III drugs (e.g., Sotalol, Amiodarone).

Summary/Staging of DCM

• The presentation outlines several stages for diagnosing and treating DCM in dogs (A, B1, B2, C, and D).

Prognosis of DCM (Stage C)

• Typical survival time is <1 year (usually 6 months).
• Negative predictors for survival include ascites, atrial fibrillation and significantly decreased left ventricular function.

Monitoring for Recurrent CHF

• Home monitoring of resting respiratory rate is an excellent way to proactively detect recurrent heart failure. Frequency should be daily.

Secondary Causes of Systolic Dysfunction

• Volume or pressure overload.
• Metabolic issues such as tachycardia.
• Nutritional deficiencies.
• Toxic exposure/ingestion.
• Infiltrative diseases like myocarditis.
• Ischemic heart disease.

Nutritional Cardiomyopathy

• 2018 increase in reported DCM cases from non-traditional diets ("BEG" diets).
• Some specific common ingredients implicated are boutique/exotic proteins or carbohydrates, grain-free diets and several types of home-prepared diets.
• Potential causes include deficiencies and altered bioavailability of nutrients or inadvertent inclusion of toxins (pesticides, mycotoxins, additives).

Diagnosis - Nutritional Cardiomyopathy

• Echocardiogram, Diet History, Taurine levels (plasma & whole blood), and response to therapy/diet changes.

Treatment for Diet-Associated DCM

• Treat DCM similar to primary DCM, including diet changes (switch to standard diet if allergy free).
• Check taurine levels in suspected patients.
• Report to FDA any suspected cases.

Outcome of DCM

• Reverse remodeling of the heart is possible in diet-associated cases.

Taurine - Amino Acid

• Critical amino acid for cardiovascular and retinal function.

L-Carnitine

• Important in transporting fatty acids into mitochondria.

Myocarditis

• Myocarditis is diagnosed with myocardial necrosis and inflammation.
• Due to physical trauma or infections (e.g., various viruses, protozoa, bacteria, fungi).

Chagas Disease Myocarditis

• Low but increasing prevalence in dogs, often originating in Texas.
• Rapid RV (right ventricle) infection/damage.
• Common signs are sudden death, bradycardia, or tachycardia; severe acute CHF.
• Chronic stage is characterized by gradual progression of heart dysfunction, which is similar to idiopathic DCM.

Diagnosis of Chagas Disease Myocarditis

• Antibody titers (IFA) may be positive.
• Examination for trypomastigotes and amastigotes in tissue or blood.

Tachycardia-Induced Cardiomyopathy

• Sustained rapid heart rate.
• Potentially reversible cardiac dysfunction.
• Ablation may be a useful treatment option.

Metabolic Hypothyroidism

• Reduced adrenergic receptor number and Na+/K+ ATPase activity, among other potential factors.

Drug-Related Cardiomyopathy - Doxorubicin

• Doxorubicin is a primary cause and often dose-dependent.
• Cardiotoxicity can be severe.
• No specific therapy exists.

Hypertrophic Cardiomyopathy

• Differential diagnosis to rule out concentric hypertrophy.
• Shi Tzu and Terrier breeds are largely affected (though generally subclinical).
• A significant proportion progress to congestive heart failure (CHF), and a portion die suddenly.
• Survival time of approximately 8-14 months after diagnosis.

Atrial Myopathy/Persistent Atrial Standstill

• Specific breeds (English Springer Spaniels and Labrador Retrievers).
• Characterized by damage to atrial myocardium.
• This can lead to persistent atrial standstill, bradycardia, and other related clinical signs.
• Pacemaker implant is sometimes a suitable treatment option.

Which Diagnostic Test is Best for ARVC?

• A Holter monitor is suggested as the best clinical diagnostic tool in ARVC cases.

A Normal Echocardiogram and ARVC

• A normal echocardiogram does not completely rule out ARVC.

Contact Information

• Email address for questions: [email protected]