Lesson 18, Topic 4
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  1. Signalment:

    – Dogs are at least 6 months of age; usually middle aged
    – Males and large breed dogs are more often infected than are females and small dogs
  2. History:
  1. Asymptomatic cases:
    – positive on yearly testing
  2. Symptomatic cases:
    – having frequented a heartworm endemic area (south eastern US)
    – weight loss, anorexia
    – chronic non-productive cough
    – labored respiration, exertional dyspnea
    – exercise intolerance, syncope
    – if heart failure present, may note abdominal distention
  3. Physical Examination:
    Most cases examined annually as a screen for heartworm infection show no clinical signs
    • Mild HWD:
      • cough on tracheal manipulation
    • Moderate HWD:
      • increased rate and depth of respiration
      • normal lung sounds or fine crackles on pulmonary auscultation
      • mild weight loss, partial anorexia
    • Severe HWD:
      • signs of right heart failure (elevated right atrial preload) – jugular distention or pulsation, ascites
      • increased rate and depth of respiration
      • fine crackles on pulmonary auscultation
      • split second heart sound on cardiac auscultation
      • emaciation, anorexia
      • distended abdomen
Dirofilaria immitisAcanthocheilonema reconditum
Head end taperedHead end parallel-sided
Tail mostly straightHail button hooked (not often seen)
Body mostly straightBody mostly curved
Length 270-325 uLength 240-290 u
Width 6.7-7.3uWidth 3.4-6.4 u
  1. Radiology: May see:
    • Right ventricular enlargement
    • Main pulmonary artery enlargement
    • Dilation of peripheral pulmonary arteries
    • Tortuous pulmonary arteries
    • Pruned or truncated pulmonary arteries
    • The right caudal pulmonary artery is most affected; artery width > width of 9th rib where they cross
    • Evidence of pulmonary parenchymal disease
    • Radiographic changes occur early in the course of the heartworm disease
    • In severe cases see signs of right heart failure including pleural effusion, hepatomegaly, splenomegaly, or ascites
    • Pulmonary consolidation in severe cases
  2. Electrocardiography:
    • Signs of right ventricular enlargement only occur in the moderate to severe cases. These include:
      • S wave in leads I and II and III
      • MEA shifted to the right;
      • Deep S wave in V3 (S>0.7 mv or S>R)
  3. Blood work:
    • Hematology
      • Eosinophilia
      • Basophilia
    • Chemistry
      • Hyperproteinemia
      • Nephrotic syndrome (hypoalbuminemia, hypercholesterolemia, with proteinuria)
  4. Echocardiography:
    • Limited application for detection of worms. Worms may be visible in the main pulmonary artery or right branch, however most often worms are primarily in distal pulmonary arteries therefore not visible by ultrasound. Echo is useful, however, to detect secondary cardiac changes and pulmonary artery hypertension.
    • In severe disease, worms may be detected in the right ventricle or right atrium and caudal vena cava (caval syndrome).