Diseases of the Cardiovascular System: Ch. 1

Introduction to Animal Cardiovascular System

• The cardiovascular system transports nutrients, gases (oxygen, carbon dioxide), hormones, and waste products throughout the body

• It consists of the heart, blood, and the blood vessels

  • Veins: go towards the heart

  • Arteries: go away from the heart

• Essential for maintaining homeostasis in the body

Key Components of the Cardiovascular System

• Heart: a muscular organ that pumps blood

• Blood Vessels: arteries, veins, and capillaries

• Blood: plasma, red blood cells, white blood cells, platelets

The Heart’s Structure

• Atria: upper chambers that receive blood

• Ventricles: lower chambers that pump blood

• Valves: prevent backflow (e.g. mitral, tricuspid, aortic, pulmonary)

• Layers of the heart: epicardium, myocardium, endocardium

The Heart

• Base of the heart at rounded cranial end

• Apex of hear at more pointed caudal end

• Located in middle of the thoracic cavity

  • In the space between the 2 lungs= mediastinum

• Apex shifter to left

• Sits more ventrally

• Pericardium= fibrous sac containing the heart

  • Pericardial sac

    • Visceral layer

    • Parietal layer

• Pericardial space is filled with pericardial fluid

The Blood Flow Through the Heart: Pathway

• Blood flows from the body into the right atrium, passes through the right ventricle, and is pumped to the lungs via the pulmonary artery.

• Oxygenated blood returns from the lungs to the left atrium, moves to the left ventricle, and is pumped to the rest of the body via the aorta.

• Heart Failure: this occurs when the blood is returning to the heart can’t be pumped out at a rate matching the body’s need

  • Many causes

  • Complicated

  • Pump failure versus circulation failure

Common Cardiovascular Diseases

• Hypertension: High blood pressure can lead to heart failure or stroke.

• Atherosclerosis: Build-up of fatty plaques in arteries.

• Congestive Heart Failure: When the heart is unable to pump blood efficiently.

• Arrhythmias: Abnormal heart rhythms.

Common Types of Cardiomyopathies in Dogs Include:

• Dilated Cardiomyopathy (DCM) Dogs:

  • Most common in older male large and giant dog breeds like Scottish Deerhound, Irish Wolfhound, Doberman Pinschers, Boxers, and Great Danes.

  • The heart becomes enlarged (dilated) and weak, leading to poor blood circulation and heart failure.

  • Decrease cardiac output and increase in cardiac afterload

  • Nutritional cause/component (grain free diets)

  • Rapid irregular HB followed by death

• Hypertrophic Cardiomyopathy (HCM) Feline:

  • Rare in dogs

  • Left ventricular hypertrophy

  • Breed pred: Main Coon, Ragdoll breeds

  • Left ventricular very thickened. Mitral regurg followed by emboli

  • Grade 2-3 murmur (6 in the end stages)

  • Arrythmias

  • ‘Valentine’ shaped heart

  • Saddle Thrombi: hind limb Paralysis. Very painful

Congenital Heart Disease: heart defects that are present at birth

• Patent Ductus Arteriosus (PDA): A persistent vessel that should close after birth remains open, affecting blood flow. (Murmur)

• Ventricular Septal Defect (VSD): A hole in the heart's wall separating the ventricles. (soft murmur)

• Pulmonic Stenosis: Narrowing of the pulmonary valve, affecting blood flow to the lungs. (syncope)

• Aortic Stenosis: Narrowing of the aortic valve, affecting blood flow to the body.

• Tetralogy of Fallot: Genetic defect of the heart. Keeshond breeds, English bulldogs

• Clinical Signs of Congenital Heart Disease. Signs in Puppies and Kittens:

  • Murmurs (most common sign)

  • Poor growth or failure to thrive

  • Coughing, labored breathing

  • Exercise intolerance

  • Signs in Adult Small Animals: Heart failure signs (fluid retention, lethargy)Cyanosis (blue gums or tongue), fainting.

Diagnose & Treatment

• Diagnosis of Congenital Heart Disease:

  • Physical Examination: Auscultation (listening for murmurs or abnormal heart sounds)

  • Detection of cyanosis or irregular heart rhythms

  • Diagnostic Tests: 

  • Echocardiography (Ultrasound): The gold standard for visualizing heart structure and function.

  • X-rays (Chest Radiographs): To assess heart size and pulmonary congestion.

  • Electrocardiogram (ECG): To check for arrhythmias.

  • Blood Tests: To assess heart-related biomarkers.

• Treatment options:

  • Medical Management:

    • Diuretics: For fluid retention.

    • Vasodilators: To reduce blood pressure.

    • Beta-Blockers: To reduce heart rate in certain conditions.

  • Surgical Intervention:

    • Surgery may be required for severe cases, such as PDA ligation or correction of VSD.

  • Prognosis: Varies with the type of defect; some animals can live with mild conditions, while others require immediate intervention.

Cardiac Arrythmias

• Tachyarrhythmias (Fast Heart Rhythms)

  • Supraventricular Tachycardia (SVT)

  • Ventricular Tachycardia (V-tac)

  • Fibrillation (Atrial or Ventricular)

• Bradyarrhythmia (Slow Heart Rhythms)

  • Sinus Bradycardia

  • Atrioventricular (AV) Block

  • Sick Sinus Syndrome

Cardiac Conduction System

• The process starts with the SA node which generates an electrical impulse

• This impulse spreads through the atria, causing them to contract and push blood into the ventricles

• The electrical impulse then travels to the AV node, where it is delayed to allow the atria to empty

• After the delay, the impulse travels down the ‘Bundle of His’ through the bundle branches, which then further branch into the Purkinje fibers, a network of specialized cells that conduct electrical signals rapidly throughout the ventricles. 

• The electrical impulse, conducted by the Purkinje fibers, causes the ventricles to contract, pumping blood out of the heart and into the aorta and pulmonary artery.