Pathology: Cardiovascular

Pathogenesis and Diagnosis of Cardiovascular Diseases

• Understanding cardiovascular disease pathogenesis is crucial for diagnosis and treatment.
• Key components include anatomy, blood flow, heart injury responses, lab changes, congenital deformity pathophysiology, and blood flow dynamics.

Importance of the Cardiovascular System

• Cardiovascular system functions continuously, pumping blood approximately every second.
• Minor dysfunction can lead to mortality; diseases account for high morbidity and mortality rates, particularly in Western populations.
• Cardiovascular diseases are less common in animals, mainly due to lower incidences of serum lipid abnormalities and hypertension.

Heart Structure and Function

• The heart consists of two sides: left (oxygenated blood from lungs) and right (deoxygenated blood from body), each further divided into atria and ventricles.
• Systemic circulation operates at higher pressure than pulmonary circulation due to extensive capillary beds.
• Four valves ensure unidirectional blood flow: aortic, left atrioventricular, pulmonary, and right atrioventricular.

Heart Histology

• The heart has three layers: endocardium (innermost), myocardium (muscle), and epicardium (outer).
• Coronary arteries supply myocardium, which consists of rich capillary networks; cardiac muscle relies heavily on oxidative metabolism.

Heart Response to Injury

• Damaged cardiac myocytes cannot regenerate; healing occurs through scar tissue, which reduces elasticity and contractility.
• Heart compensates via mechanisms like increased heart rate, myocyte hypertrophy, and blood volume redistribution.
• Congestive heart failure (CHF) occurs when compensatory mechanisms are inadequate, leading to marked dilation and cardiac decompensation.

Congestive Heart Failure (CHF)

• Two types of CHF: left-sided (most commonly due to left AV/aortic valve dysfunction) and right-sided (secondary to pulmonary issues).
• Left CHF leads to pulmonary edema from blood accumulation in pulmonary circulation, resulting in fluid leakage.
• Right CHF causes systemic blood pooling, often presenting as peritoneal (ascites) or pleural edema (hydrothorax), with liver congestion leading to 'Nutmeg' liver appearance.

Changes in Heart Size

• Physiologic hypertrophy occurs in athletes without causing pathology.
• Pathologic hypertrophy may arise from primary myocardial disorders or as a compensatory response to other diseases.

Laboratory Diagnosis of Heart Disease

• Creatine kinase (CK) and aspartate aminotransferase (AST) levels rise following cardiac myocyte necrosis, although typically insufficient for isolated heart disease detection.
• proBNP test aids in diagnosing heart disease; elevated levels suggest heart failure, particularly in dogs and cats.

Congenital Heart Disorders

• Commonly observed in young animals; congenital defects can be heritable and lead to turbulent blood flow.
• Notable congenital defects include patent ductus arteriosus, atrial septal defect, and ventricular septal defect, with characteristic hemodynamics.

Heart Valve Development Abnormalities

• Pulmonic and subaortic stenosis lead to increased intracardiac pressure and secondary hypertrophy.
• Congenital valvular malformations may affect valve patency and function.

Pericardial Disease

• Inflammation of the pericardium (pericarditis) is often due to bacterial infection, classified as purulent or fibrinous.
• Cardiac tamponade occurs when fluid accumulation in the pericardial sac restricts heart filling and reduces stroke volume.

General Considerations on Blood Flow

• Turbulent or slowed blood flow poses significant risks, including embolism or hemorrhage, which can lead to serious health implications.### Fibrinous Pericarditis and Related Conditions
• Large aggregates of fibrin can attach to pericardial surfaces, leading to the "bread-and-butter heart" appearance.
• Maturation and contraction of fibrin cause heart constriction, leading to inadequate filling and possible heart failure.
• Common infections causing fibrinous pericarditis include:
  • Haemophilus parasuis (pigs, Glasser’s disease)
  • Streptococcus sp. (horses)
  • Haemophilus somnus (cattle)
  • Feline infectious peritonitis can also cause fibrinous pericarditis.
• Vitamin E/Selenium deficiency in pigs leads to oxidative damage in myocardial blood vessels, causing blood leakage and mulberry heart disease.
• Hemopericardium refers to blood presence within the pericardial sac, common due to:
  • Right atrial hemangiosarcoma rupture in dogs.
  • Aorta rupture in pigs and horses.
  • Rare cases involve penetrating wounds.

Enterotoxemia

• Primarily affects sheep and is caused by Clostridium perfringens type D, leading to significant vascular damage and fibrin leakage.
• Diagnosis may be suggested by a large fibrin clot observed in the pericardium.

Endocardial Disease

Endocardial Mineralization

• Common in cattle due to chronic diseases like Johne’s disease.
• Localized mineralization occurs from blood reflux due to valvular insufficiency, identified as ‘jet lesions’ in canines.

Valvular Endocardiosis

• Common in older dogs, resulting from collagen degeneration, leading to congestive heart failure (CHF).
• Mostly affects the left atrioventricular (AV) valve, leading to potential regurgitation and heart murmurs.

Atrial Thrombosis

• Thrombi usually develop in the atrium due to turbulent blood flow and can be caused by cardiomyopathy.
• Sudden death can occur from large atrial thrombi impairing heart function, with smaller emboli causing distal infarctions.

Endocarditis

• Frequently bacterial, causing valvular lesions, particularly on the valves, resulting in nodular vegetations that impair valve function.
• Inflammation can lead to septic emboli, with left AV or aortic valve infections leading to heart or kidney infarctions.

Myocardial Disease

• Myocardial necrosis can result from toxic substances or nutritional deficiencies (e.g., Vitamin E/Selenium).
• Notable cardiotoxins include ionophores and doxorubicin.
• Necrosis often presents with fibrin-containing pericardial fluid.
• Long-standing lesions can develop marked chalky appearances, especially in papillary muscles.

Cardiomyopathy

• Degenerative conditions of the heart impacting function and blood flow, potentially leading to sudden death or CHF.
• Feline Hypertrophic Cardiomyopathy (HCM) is prevalent in male cats around 4 years of age, often diagnosed post-mortem.
• Canine HCM is less common, typically presenting in large breeds.
• Dilated Cardiomyopathy (DCM) frequently occurs in large-breed dogs and is associated with congestive heart failure.

Neoplastic Diseases of the Heart

• Neoplasms within the heart include hemangiosarcomas, typically in the right atrium, leading to hemopericardium and poor prognosis.
• Bovine leukemia virus commonly causes lymphoma within the heart of cattle, resulting in CHF due to myocardial infiltration.

Vascular System Overview

• Comprises arteries, veins, and lymphatics with three layers: intima, media, and adventitia.
• Endothelial cells prevent clotting, and damage to these cells can trigger clot formation.

Arterial Disease

Aneurysms and Ruptures

• An aneurysm is an arterial wall outpouching, resulting from compromised wall strength.
• Copper deficiency in pigs can lead to aortic aneurysms.
• Symptoms of aneurysms are often sudden and fatal, with clinical signs of compression being rare.
• Atherosclerosis is the leading cause of aortic aneurysms in humans, while syphilis was historically significant.### Arterial Rupture
• Commonly occurs due to trauma; spontaneous rupture observed in horses and pigs during exercise.
• Proximal aorta rupture within the pericardial sac is most frequent, leading to rapid death often from cardiac tamponade.
• Inflamed or neoplastic regions surrounding arteries can also cause rupture.
• Guttural pouch mycosis in horses can lead to internal carotid artery rupture and sudden death.

Thrombosis and Embolism

• Thrombosis is the formation of an intravascular blood clot influenced by endothelial damage, turbulent blood flow, and hypercoagulable states.
• In animals, thrombi often form due to altered blood flow from heart shape changes, valvular damage, or congestive heart failure.
• Thrombi commonly develop in the atria; emboli can cause myocardial infarction or renal infarction.
• Affected cats may experience "saddle embolus," leading to hindlimb infarction and acute paresis.

Arterial Degeneration and Necrosis

• Atherosclerosis, fat deposition in arterial intima, primarily affects hypothyroid dogs and some other species but doesn't cause clinical signs.
• Arterial calcification commonly appears in debilitated cattle, leading to characteristic aorta changes seen as non-collapsible pipes.
• Fibrinoid necrosis primarily affects pigs and chickens due to vitamin E/selenium deficiency, causing hemorrhage and edema.

Arteritis

• Arteritis arises from endothelial cell damage, notably from septicemia.
• Erysipelothrix infection in pigs leads to septicemia and skin lesions known as "diamond skin disease."
• Feline Infectious Peritonitis (FIP) is caused by a mutated coronavirus, leading to endothelial damage, vasculitis, and variable organ system involvement, mainly liver and kidneys.

Malignant Catarrhal Fever (MCF)

• Caused by ovine herpesvirus-2, it induces vasculitis in susceptible cattle, presenting with corneal edema and gastrointestinal signs.
• Infection often occurs without sheep contact and has variable manifestations, including behavioral changes.

Parasites Causing Vascular Disease

• Strongylus vulgaris in horses leads to arteritis and any resultant embolism.
• Dirofilaria immitis (heartworm) is a common cause of arteritis in cats and dogs.

Lymphatic Disease

• Congenital abnormalities causing lymphatic malformations are rare but lead to swollen limbs.
• Intestinal lymphangitis, particularly Johne’s disease, showcases bacterial lymphatic inflammation.

Hematoma and Neoplastic Lesions

• Hematomas result from trauma, encapsulated by fibrous tissue, and can mimic tumors.
• Hemangioma occurs predominantly on the skin, while hemangiosarcoma, a highly malignant tumor, is common in older dogs, especially in the spleen and right atrium.

Clinical Considerations

• Early detection of embolic events is crucial for prompt intervention in affected animals.
• Diagnosis of FIP can be difficult, especially in the dry form, often requiring histological confirmation.