Contributors: Mark Oyama

 Species: Canine   |   Classification: Miscellaneous

Introduction

  • Peripheral vascular disease encompasses disease of:
    • Arteries.
    • Arterioles.
    • Capillaries.
    • Venules.
    • Veins.
    • Lymphatics.
  • In veterinary medicine, diagnosis and treatment of vascular disease is challenging, due to:
    • Vague clinical signs.
    • Difficulty in diagnosing.
    • Confusion regarding terminology of diseases.
  • Vascular disease often classified according to:
    • Type of vessel affected (arterial vs venous vs lymphatic).
    • Presence or absence of vessel obstruction (occlusive vs non-occlusive).
    • Inflammatory component (-itis).
  • Main forms of peripheral vascular disease in small animals, excluding conditions caused by peripheral thromboembolism, are:
    • Atherosclerosis.
    • Arteriosclerosis.
    • Aneurysms.
    • Peripheral arteriovenous fistulae.
    • Vasculitis.
    • Polyarteritis nodosa.
    • Phlebitis.

Forms of peripheral vascular disease

Atherosclerosis

  • Atherosclerosis is the leading cause of heart disease in man, caused by deposition of lipid-containing plaque on endothelial surfaces of coronary and systemic arteries.
  • Development of extensive plaque material, release of vasoactive substances, thrombus formation and subsequent embolism within coronary vessels leads to occlusion and onset of ischemic myocardial damage.
  • Atherosclerosis rare in small animals and usually associated with canine hypothyroidism Hypothyroidism or diabetes mellitus Diabetes mellitus.
  • Miniature Schnauzers Schnauzer: miniature , Doberman Pinschers Dobermann , and Labrador Retrievers Retriever: Labrador may be overrepresented.
  • In addition to affecting arteries of the heart, plaques may also develop in carotid and renal arteries.
  • Clinical signs are usually related to embolization of plaques or associated thrombus and may include:
  • Electrocardiographic ECG: overview studies in patients with advanced atherosclerosis may reveal:
    • Low amplitude QRS complexes.
    • ST segment change.
    • Supraventricular or ventricular arrhythmias Heart: dysrhythmia.
  • Serum chemistry reveals:
    • Hyperlipidemia Hyperlipidemia.
    • Hypercholesterolemia.
    • Low T3 and T4 values.
  • Treatment consists of:
  • Most cases of atherosclerosis probably go undiagnosed until very late in course of disease when significant arterial damage has already occured.
  • Compared with human medicine, clinical significance of atherosclerosis in small animals is minimal.

Arteriosclerosis

  • Arteriosclerosis refers to age-related degeneration of arterial walls, resulting in loss of normal vessel elasticity.
  • In comparison with atherosclerosis, arteriosclerosis is relatively common in geriatric small animals.
  • Histological examination of affected vessels reveals proliferation and degeneration of normal connective tissue elements of vessel wall.
  • Most changes are noted as incidental findings during necropsy and have not resulted in clinical signs.
  • Severe cases of arteriosclerosis may result in occlusion of coronary arteries and myocardial infarction Myocardial infarct pathology.
    Cases are extremely rare.
  • Age-related arteriosclerosis may contribute to development of systemic hypertension Hypertension in older populations, but extent of association in small animals is not fully known.

Aneurysms

  • Arterial aneurysms are defined as a sac-like dilation of the vessel wall.
  • Uncommon in small animals and most detected as incidental findings at post-mortem.
  • True aneurysms caused by a weakening of the arterial wall and formation of a focal dilation of the vessel lumen.
  • Mild aneurysms are typically present in cases of:
  • More severe aneurysms caused by degenerative processes affecting connective tissue of vessels and may be subject to acute rupture and exsanguination.
  • Peripheral arterial aneurysms identified as warm compressible bulges under the skin.
  • Aneurysms associated with peripheral arteriovenous fistulae may be accompanied by a palpable thrill or continuous murmur.
  • Familial predisposition for aortic aneurysm in the dog reported.

Peripheral Arteriovenous Fistulas

  • Arteriovenous (AV) fistulas Heart: peripheral arteriovenous fistula are abnormal connections between artery and vein that bypass the capillary bed.
  • AV fistulas in small animals are usually classified based on their congenital or acquired etiology:
    • Congenital AV fistulas usually small and of incidental importance.
    • Acquired AV fistulas localized and, if large, may be clinically significant.
  • AV fistulas allow blood to bypass the high-resistance arteriole and capillary system and offer a low-resistance alternative route for arterial blood flow.
  • Large AV fistulas may produce:
    • Systemic arterial hypotension.
    • Venous hypertension.
    • Increased venous return to the heart.
  • Low resistance of systemic circulation creates an environment of:
    • High-cardiac output.
    • Volume expansions.
    • Development of high-output heart failure.
  • Elevated venous pressure causes:
    • Localized edema (often seen as peripheral pitting edema).
    • Poor arterial circulation.
    • Ischemia.
  • AV fistula may be detectable under skin as area of localized swelling.
  • Continuous murmur is often auscultated over the fistula.
  • In some cases, murmur may be accompanied by a palpable thrill.
  • Compression of fistula can acutely increase systemic arterial blood pressure and result in reflex bradycardia.
  • Most acquired AV fistulas are result of blunt or penetrating trauma but also reports of fistula formation due to:
    • Cervical tumors.
    • Surgery.
    • Venipuncture.
    • Extravasation of irritating substances ie thiobarbiturates.
  • Definitive diagnosis of AV fistulas best accomplished by angiography. The artery proximal to suspected fistula site is catheterized and a small amount of radiographic contrast material injected during fluoroscopic examination. technique allows assessment of :
    • Fistula size.
    • Location.
    • Anatomy.
  • Surgical correction involves ligation of arterial branches that feed into, and venous branches that feed out of, fistula, and is guided by angiographic results.
  • Vascular ultrasonography Ultrasonography: cardiac can also be used to identify AV fistulas.
  • In cases of fistulas with extensive limb involvement, amputation may be the only remedy.

Vasculitis

  • Vasculitis (inflammation of vessels Cutaneous vasculitis ) is a non-specific condition that occurs in response to a variety of systemic diseases.
  • Vasculitis may occur secondary to vascular damage that disrupts endothelial surface and activates:
    • Complement.
    • Kinin.
    • Plasmin systems.
  • Systems induce an inflammatory response that can further damage integrity of vessel wall and increase vessel permeability.
  • Leukocytes and activated platelets are attracted to damaged area and contribute to inflammation and vessel damage.
  • Hemorrhage or edema into surrounding tissue can develop.
  • In cases of chronic vessel injury, a localized granulomatous reaction can occur.
  • Vasculitis can also be caused by extension of extra-vascular disease into the vessels eg local tissue damage or infection can extend into vessels and mediate an inflammatory response.
  • Systemic disease such as the tick-borne infections can also trigger development of diffuse systemic vasculitis.
  • Drug reactions or autoimmune disease may also be predisposing factors.
  • Treatment mainly aimed at treating underlying cause.

Polyarteritis nodosa 

  • Polyarteritis nodosa Polyarteritis nodosa is inflammatory disease of small arteries that results in:
    • Vessel necrosis.
    • Thrombosis.
    • Degeneration.
  • In man, polyarteritis nodosa thought to be caused by autoimmune response against connective tissue. Inflammation of the small vessels results in sc purpural lesions, common in man (hence origin of disease name), but rare in small animals.
  • Clinical signs in animals may be systemic:
    • Fever
    • Weakness.
  • Or localized:
    • Petechia.
    • Ecchymosis.
    • Skin ulcers.
    • Lameness.
    • Joint and limb pain.
  • Commonly affects arteries of:
    • Skin
    • Heart.
    • Kidneys
    • GI tract.
    • Connective tissue.
  • Diagnosis made via skin biopsy and histological findings of:
    • Intimal proliferation.
    • Vasculitis.
    • Vessel wall degeneration.
  • Prognosis is poor.
  • Treatment consists of anti-inflammatory and immune-suppressive medications ie corticosteroids Therapeutics: glucocorticoids or cyclophosphamide Cyclophosphamide.

Phlebitis

  • Phlebitis (inflammation of the veins) can result from:
    • Trauma
    • Extension of local disease.
    • Iatrogenic causes.
  • Many cases of phlebitis are caused by placement and subsequent infection of a peripheral venous catheter Central venous catheter placement.
  • Venous injection of irritating substances ie thiobarbiturates or caparsolate can also induce inflammatory response.
  • Local thrombosis and vessel occlusion may result.
  • Clinical signs include:
    • Pain.
    • Redness.
    • Swelling over vessel area.
  • Most cases are self-limiting; however, occlusion of large veins may result in formation of peripheral edema
  • In cases of vasculitis due to localized infection, immunocompromised patients may be at risk for development of sepsis Shock: septic or bacterial endocarditis Endocarditis: bacterial.