Dilated Cardiomyopathy-3 (1)

Presenter: Sarah M. Cavanaugh, DVM, MS, DACVIM (Cardiology)Contact: SCavanaugh@rossvet.edu.knLocation: Academic Hub, 3rd Floor

Identify the key canine breeds that are genetically predisposed to familial DCM.
Describe the functional impairments and structural changes that occur in the heart due to DCM.
Explain the underlying pathophysiology that leads to the development and progression of DCM.
List and discuss potential physical examination findings that may be present in dogs diagnosed with DCM.
Emphasize the importance of arrhythmia screening procedures, especially in Doberman Pinschers, and list the most common types of arrhythmias observed.
Summarize the primary echocardiographic findings that are definitive for diagnosing DCM.
Identify and classify the drugs utilized for treating both the occult and overt stages of DCM.
Discuss prognostic outcomes for dogs with occult DCM and their likelihood of developing heart failure (HF).

Prevalence: DCM is recognized as the second most common acquired heart disease among dogs, with significant morbidity associated with the condition.
Breed Predisposition: Primarily affects large and giant dog breeds, with the highest prevalence seen in Doberman Pinschers, where up to 50% may be affected in certain populations, showing geographical variation. Other breeds such as Great Danes, Irish Wolfhounds, and Newfoundlands are also at risk, along with exceptions like Cocker Spaniels and Toy Manchester Terriers.
Mechanism: DCM is characterized by ventricular systolic dysfunction, primarily indicated by decreased contractility; dilation of the cardiac chambers is a secondary effect of this dysfunction.

Genetic Factors in Doberman Pinschers: Key mutations linked to familial DCM include:
- Pyruvate Dehydrogenase Kinase 4 (PDK4).
- NCSU DCM 2 (missense mutation in the titin gene, TTN).
Familial DCM has also been documented in breeds such as the Great Dane, Irish Wolfhound, Newfoundland, Portuguese Water Dog, and Toy Manchester Terrier. In many cases, the etiology remains idiopathic.
Gross Findings: Left ventricular (LV) and left atrial (LA) dilation are hallmark signs, with possible involvement on the right side of the heart.
Histopathology: The condition is marked by significant myocyte abnormalities, including attenuated wavy myofibers, necrosis, and fibrosis.

Contractility and Hemodynamics: The decreased contractility associated with DCM leads to:
- Reduced stroke volume and cardiac output.
- Activation of the Renin-Angiotensin-Aldosterone System (RAAS), which increases blood volume and consequently, preload.
- Development of volume overload, reflected by increased end-systolic and end-diastolic volumes. This can provoke myocardial hypertrophy as a compensatory mechanism.
Disease Progression: As the volume overload progresses, compensatory mechanisms may fail, potentially leading to congestive heart failure (CHF). Atrial dilation and functional mitral/tricuspid regurgitation can develop, while arrhythmias such as atrial fibrillation and ventricular arrhythmias can decrease cardiac output due to loss of tachycardia and AV synchrony.

Age of Onset: DCM typically manifests in adults aged 4-9 years; however, juvenile forms do exist in certain breeds.
Breed Characteristics: Affects predominantly large and giant breeds, with some breeds exhibiting higher susceptibility.
Gender: Certain breeds, like the Great Dane, show a male prevalence.
Disease Severity: Severity generally increases with the dog's age.

Stages: DCM progresses through:
- Occult Stage: Asymptomatic with potential for later development of symptoms.
- Overt Stage: Symptomatic with clinical signs becoming evident.
Signs of Progression: Initially may present with mild exercise intolerance or weight loss; advanced stages reveal significant heart failure symptoms—exercise intolerance, tachypnea, coughing, dyspnea, syncope, abdominal distension, and lethargy. High incidences of sudden death are reported, especially in Dobermans (~30% in occult phase, ~50% in overt HF).

Key Findings:
- Low-grade left apical systolic murmur may be detected.
- Other potential findings include S3 gallop, decreased intensity of heart sounds, and arrhythmias like premature beats.
- Presence of CHF is indicated by tachycardia, tachypnea, dyspnea, abnormal lung sounds, jugular venous distension, hepatomegaly, ascites, and in low-output HF, signs such as depressed mentation, weakness, tachycardia, and hypothermia.

Echocardiography: The preferred diagnostic modality focuses on evaluating LV dimensions during diastole and systole and assessing systolic dysfunction.

Electrocardiogram (ECG): Critical for identifying ventricular premature complexes (VPCs) and other arrhythmias. Atrial fibrillation may be characterized by an irregularly irregular rhythm with absent P waves.
Holter Monitoring: Continuous 24-hour ECG monitoring is particularly important for Dobermans to detect arrhythmias.
Blood Pressure Measurement: Important for evaluating overall hemodynamic status; supplemental imaging with thoracic radiographs is vital for diagnosing left-sided CHF.
Genetic Testing: Recommended in Dobermans for identifying mutations associated with DCM.
Taurine Levels: Important in assessing diet-related implications in DCM dogs, alongside thyroid testing and NT-proBNP as adjunctive tests, noting its poor sensitivity for mild disease.

General Overview: While there is no curative treatment available for DCM, medications can delay disease progression. Current research focuses on alternative therapies like stem cell therapy.
Occult Stage Treatment: Medications such as Benazepril and pimobendan can delay the onset of CHF, while beta-blocker therapy should be considered pending further studies.
Overt Heart Failure Treatment: May involve acute management with Furosemide, pimobendan, and oxygen therapy, alongside chronic management strategies incorporating ACE inhibitors and spironolactone. Specific treatment for arrhythmias includes interventions for atrial fibrillation and utilization of medications like mexiletine or sotalol for ventricular arrhythmias.

Occult Stage: Generally, prognosis is fair to guarded, with most dogs progressing to HF within 4-5 years and sudden death being a potential risk.
Overt Stage: The long-term prognosis is poor, with an average survival time of 6-12 months owing to the elevated risk of sudden death.

These can be categorized into various types including:
- Tachycardia-induced, Nutritional (for example, taurine deficiency), Doxorubicin-induced, Inflammatory/infectious, and Hypothyroidism.
Generally, the prognosis is favorable if the underlying causes are identified and treated, except for cases related to doxorubicin toxicity.

Recent links have shown DCM-like diseases may be associated with non-traditional diets, prompting investigation by the FDA into these correlations. Ongoing research aims to better understand dietary implications regarding heart diseases, highlighting the importance of client communication regarding nutritional science from reputable sources.

DCM is significantly less common in felines, accounting for only 5-10% of feline cardiomyopathy cases, historically linked to taurine deficiency. Symptoms typically appear in the context of heart failure or arterial thromboembolism (ATE). Diagnosis follows similar echocardiographic standards as in canines, with comparable treatment and prognosis strategies, including potential antiplatelet therapy.