Hypertrophic Cardio Myopathy (HCM)

Hypertrophic Cardio Myopathy (HCM)

Hypertrophic Cardio Myopathy (HCM) is rare in dogs and common in cats. It called Feline hypertrophic cardiomyopathy in cats and Canine hypertrophic cardiomyopathy in dogs.

Hypertrophic Cardio Myopathy (HCM) in Dog and Cats
Fig.: Hypertrophic Cardio Myopathy (HCM) in Dog and Cats

Canine Hypertrophic Cardiomyopathy

In canine hypertrophic cardiomyopathy, the left ventricular muscle hypertrophies or thickens, decreasing the filling capacity of the ventricle and often blocking the outflow of blood during systole.

Etiology

  • The cause appears to be heritable.
  • The disease may run in families of certain breeds like German Shepherd, Rottweiler, Dalmatian, Cocker Spaniel, Boston Terrier, Shih Tzu.

Pathophysiology

The left ventricular muscle hypertrophies or thickens, decreasing the filling capacity of the ventricle and often blocking the outflow of blood during systole.

Clinical Signs

  • Fatigue
  • Cough
  • Tachypnea
  • Syncope
  • Presence or absence of cardiac murmurs
  • Sudden death
  • Some animals may be asymptomatic
  • Sudden death and CHF may occur in dogs with HCM.

Diagnosis

  • Based on clinical signs and history.
  • Echocardiography indicates concentric thickening and hypertrophy of the left ventricle.

Treatment

  • Mexiletine to decrease the VPCs.
  • Pimobendan, ACE inhibitors, if ventricular dilation is present.
  • Owners should be warned that sudden death of these dogs can occur usually with exercise or excitement.

Feline Hypertrophic Cardiomyopathy

HCM in cats is similar to the disease in dogs. This disease is the most common cardiomyopathy seen in cats. From all the feline cardiac cases, up to 35% involve feline hypertrophic cardio myopathy. Neutered male cats between 1 and 16 years of age have been found to be most at risk.

Etiology

  • The cause of the disease may be related to abnormal myocardial myosin or calcium transport within the myocardial cells.
  • This disease is more common in Main Coon and Ragdoll breeds.

Pathophysiology

Left ventricular hypertrophy being the predominant pathology. The left ventricle becomes thickened and stiff. Mitral regurgitation and aortic embolization occur frequently.

As the atria dilate, the endothelium lining the chambers is damaged, resulting in the release of clotting enzymes, which can result in clot formation. The cats that form thrombi also show evidence of hypercoagulability of their platelets.

Thromboembolism occurs in about 16% to 18% of feline HCM cases. Although the thrombus can lodge in any artery, it appears that the trifurcation of the aorta is a frequent spot resulting in a decrease in circulation to both rear legs.

Clinical Signs

  • A soft, systolic murmur (grade 2–3 or 6)
  • Gallop rhythms or other arrhythmia
  • Acute onset of heart failure or systemic thromboembolism

Diagnosis

  • Based on history and clinical signs
  • X-ray may show a normal-size heart or mild left atrial enlargement (valentine heart shape in the dorsoventral view)
  • In ECG: increased P-wave duration, increased QRS width, sinus tachycardia
  • Echocardiography reveal increased left ventricular wall thickness and a dilated left atrium
  • Biomarkers like BNP, pro-BNP, and CTn1 will be increased
  • Magnetic resonance imaging (MRI) is a most accurate method of diagnosis

Treatment

  • ACE inhibitors
  • Propranolol, Atenolol like β-blocker are used to decrease myocardial oxygen demand, decrease sinus heart rate
  • Diltiazem (calcium channel blocker) to inhibits cardiac and vascular smooth muscle contractility; reduces blood pressure and cardiac after load
  • Low dose heparin or low-dose aspirin
  • Frusemide for diuresis
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