Cardiology: Common Diseases of Companion Animals

Anatomy of the Heart

Basic structure and function of the heart.

Initial Assessment

Questions for History Taking by Technicians:
- Activity level of the animal.
- Dietary changes.
- Presence of coughing.
- Current medications.
Physical Examination Aspects:
- Pulse palpation.
- Heart rate assessment.
- Cardiac auscultation.
- Examination of mucosal membranes for color changes.

Heart Failure

Definition:
- Heart failure occurs when the blood returning to the heart cannot be pumped out at a rate that meets the body's needs.
Potential Causes of Heart Failure:
- Myocardial Failure:
- Cardiomyopathy.
- Myocarditis.
- Taurine deficiency.
- Circulatory Failure:
- Hypovolemia.
- Anemia.
- Valvular dysfunction.
- Congenital shunts or defects.
Congestive Heart Failure (CHF):
- Characterized by fluid accumulation in the body due to heart failure.
Differences Between Right and Left-Sided Heart Failure:
- Right-sided tends to result in systemic fluid retention, while left-sided often leads to pulmonary congestion.

CardioMYOpathies

Canine Dilated Cardiomyopathy

**Description: **
- Acquired condition primarily seen in older male large and giant breeds.
- Characterized by dilation of all chambers of the heart, decreased cardiac output (CO), and increased afterload.
Etiology:
- Cause is unknown.
Clinical Signs:
- Weakness.
- Exercise intolerance.
- Syncope (fainting).
- Shock.
- Potential progression to atrial fibrillation.

Canine Hypertrophic Cardiomyopathy

Prevalence:
- Uncommon in dogs; most common in cats.
Pathophysiology:
- Left ventricular muscle hypertrophies leading to decreased filling capacity of the ventricle and potential blockage of blood outflow during systole.
Clinical Signs:
- Fatigue.
- Cough.
- Tachypnea (rapid breathing).
- Syncope.
- Possible presence of a heart murmur.
- Sudden death may occur.
Genetic Factors:
- Heritable condition.

Feline Dilated Cardiomyopathy

Association:
- Linked to taurine deficiency, now largely mitigated by supplementing taurine in commercial diets.
Demographics:
- Primarily affects older cats.
Clinical Signs:
- Dyspnea (difficulty breathing).
- Inactivity.
- Anorexia.
- Hypothermia.
Diagnosis:
- Via ultrasound, possible EKG.
Treatment Approaches:
- Supplementing with taurine and addressing other clinical signs.

Cat Handling Alerts

Caution:
- Extreme care is needed when handling dyspneic cats as they can experience fatal stress from restraint.

Feline Hypertrophic Cardiomyopathy

Demographics:
- More common in neutered male cats.
Pathophysiology:
- Abnormal myosin or calcium transport within muscle cells leading to hypertrophy.
Clinical Manifestations:
- Presence of a heart murmur or arrhythmia.
- Risk of thromboembolism.

Thromboembolism (Saddle Thrombus)

Symptoms:
- Acute onset with hind leg pain and paresis.
- Cold hind legs and absence of palpable pulses.
Treatment Options:
- Use of aspirin or heparin; however, most cases (95%) lead to humane euthanasia.

Congenital Heart Disease

Patent Ductus Arteriosus (PDA)

Definition:
- Failure of the ductus arteriosus to close after birth, leading to abnormal circulation.
Clinical Features:
- Machinery murmur best heard over the left pulmonary artery.
- More common in female dogs, especially certain breeds (e.g., chihuahua, collie, Maltese, etc.).
- Some puppies may be asymptomatic.

Atrial and Ventricular Septal Defects

Clinical Findings:
- Presence of a heart murmur.
- Signs of congestive heart failure may appear before 8 weeks of age.
- Heritable but not necessarily a requirement.

Pulmonic and Aortic Valve Stenosis

Mechanism:
- Narrowed outflow tract leading to decreased cardiac output during exercise.
Signs:
- Syncope.
- Exercise intolerance.
- Heart murmur.

Subaortic Stenosis

Affected Breeds:
- Commonly seen in large breeds.
Pathophysiology:
- Thickening of endocardial tissue below the aortic valve, obstructing outflow from the left ventricle.
Clinical Signs:
- Exercise intolerance.
- Syncope.
- Sudden death.

Tetralogy of Fallot*

Constituents:
- Pulmonic stenosis.
- Right ventricular hypertrophy.
- Subaortic ventricular septal defect.
- Overriding aorta.
Genetic Nature:
- It is a genetic disorder.
Risks:
- Animals with this condition can experience adverse reactions to sedatives, such as bradycardia that may not improve with oxygen supplementation.

Persistent Right Aortic Arch, Vascular Ring Anomalies

Anatomy Involved:
- Involves the left subclavian artery (retroesophageal), trachea, and esophagus.
Complications:
- Regurgitation of solid food, esophageal strictures, weight loss, aspiration pneumonia.

Acquired Valvular Diseases

Detailed anatomy of heart valves (mitral, tricuspid, aortic, and pulmonic).

Chronic Mitral Valve Insufficiency

Prevalence:
- The most common cardiovascular disorder in dogs.
Pathophysiology:
- Proliferation of fibroblastic tissue resulting in nodular thickening of the valve leaflets, leading to functional impairment.

Tricuspid Valve Insufficiency

Chemical Structure:
- Similar to mitral valve insufficiency but primarily presents as right-sided heart failure.

Cardiac Arrhythmias

Definition:
- Deviations from normal heart rate and rhythm, potentially originating from abnormal locations within the heart.

Alterations in Normal Rhythm

Possible Causes of Abnormal Impulse Formation:
- Hypoxia.
- Hypocalcemia & Hypercalcemia.
- Cardiomyopathy.
- Excess catecholamines.
- Reperfusion injury.

Recognition by Technicians

Key Symptoms to Monitor:
- Weakness, syncope, collapse, rapid irregular heart rate.

Types of Arrhythmias

Supraventricular Tachycardias

Heart Rate (HR) Range:
- 160 - 180 bpm.
P-QRS-T Complexes:
- Normal.
Specific Types:
- Atrial premature contractions (APCs) characterized by premature P waves without following QRS complexes.
- Atrial fibrillation lacks organized atrial contraction, often found in large breed dogs or those with enlarged hearts.

Ventricular Tachycardia

Potential Causes:
- Associated with cardiomyopathy, congestive heart failure, endocarditis, myocarditis, cardiac neoplasia, and electrolyte imbalances.
Clinical Signs:
- Weakness, syncope, collapse, and sudden death due to potential progress to ventricular fibrillation.
Diagnosis Strategies for Technicians.

Treatment Approaches

Ventricular Tachycardia:
- Goal: Decrease myocardial excitability.
- It's considered an emergency situation with a guarded prognosis.

Sinus Arrhythmia

Occurrence:
- Common in dogs, not in cats.
Sinus Bradycardia:
- Notably found in brachiocephalic breeds during intubation, which can be severe.

Heartworm Disease

General Facts:
- Dogs are infected more frequently than cats; larger dogs are more prone than small breeds; outdoor dogs are more affected than indoor ones; male dogs are more commonly infected than female dogs.
- Average age of affected dogs is between 3-8 years.
Lifecycle of Heartworm:
- Microfilariae are injected into a female mosquito, developing for 2-2.5 weeks.
- Migrates within the host’s skin for 100 days before reaching the pulmonary artery to mature.
- If both sexes are present, microfilaria production occurs.

Clinical Signs of Heartworm Disease

Most infected dogs are asymptomatic, but signs can include:
- Cough.
- Dyspnea (difficulty breathing).
- Exercise intolerance.
- Right-sided heart failure.

Treatment Guidelines

Resources:
- Heartworm toolkit app for current treatment guidelines, refer to American Heartworm Society website.
- Recommend year-round heartworm preventative (HWP).

Feline Heartworm Disease

Prevalence:
- Less common in cats compared to dogs.
Diagnosis Challenges:
- It is difficult to diagnose and treat.
Symptoms:
- Cough.
- Vomiting.
- Anorexia and weight loss.
- Lethargy.
- Right-sided heart failure.
- Risk of sudden death.