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In cats, most infections are asymptomatic. However, sudden death can occasionally occur. This may be preceded by an acute respiratory crisis, thought to be due to parasitic thromboembolism and obstruction of a major pulmonary artery<sup>1, 2</sup>. When clinical signs are less acute, they are vague and may include anorexia, weight loss and letheargy. Intermittent coughing and dyspnoea can appear similar to feline asthma. Syncope may also occur, and cats may vomit. The cause of this vomiting is undetermined<sup>3</sup>.
 
In cats, most infections are asymptomatic. However, sudden death can occasionally occur. This may be preceded by an acute respiratory crisis, thought to be due to parasitic thromboembolism and obstruction of a major pulmonary artery<sup>1, 2</sup>. When clinical signs are less acute, they are vague and may include anorexia, weight loss and letheargy. Intermittent coughing and dyspnoea can appear similar to feline asthma. Syncope may also occur, and cats may vomit. The cause of this vomiting is undetermined<sup>3</sup>.
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===Diagnostic Imaging===
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===Radiography===
 
   
In dogs, thoracic radiography provides good information on disease severity and is useful for screening dogs showing clinical signs compatible with ''D. immitis'' infection<sup>1</sup>. However, thoracic radiograph do not neccessarily reflect the current worm burden: radiographic signs of advanced disease can persist long after an infection has run its course<sup>4</sup>. Conversely, dogs with high burdens may be inactive and thus show few clinical signs or radiographic changes. Radiographic signs are mild-to-moderate in class II disease, but become more obvious in class III infections. The main pulmonary artery is enlarged,sup>1, 4</sup>, and the caudal lobar vessels appear tortuous<sup>1</sup> Ill-defined, fluffy infiltrates are apparent, and often surroung in the caudal lobar vessels. Right-sided cardiomegaly may be appreciated, and pleural and peritoneal effusions can be noted if right-sided congestive heart failure occurs<sup>4</sup>.
 
In dogs, thoracic radiography provides good information on disease severity and is useful for screening dogs showing clinical signs compatible with ''D. immitis'' infection<sup>1</sup>. However, thoracic radiograph do not neccessarily reflect the current worm burden: radiographic signs of advanced disease can persist long after an infection has run its course<sup>4</sup>. Conversely, dogs with high burdens may be inactive and thus show few clinical signs or radiographic changes. Radiographic signs are mild-to-moderate in class II disease, but become more obvious in class III infections. The main pulmonary artery is enlarged,sup>1, 4</sup>, and the caudal lobar vessels appear tortuous<sup>1</sup> Ill-defined, fluffy infiltrates are apparent, and often surroung in the caudal lobar vessels. Right-sided cardiomegaly may be appreciated, and pleural and peritoneal effusions can be noted if right-sided congestive heart failure occurs<sup>4</sup>.
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In dogs, echocardiography is relatively unimportant as a diagnostic tool. Worms observed in the right heart and vena cava are associated with high-burden infection with or without caval syndrome. Severe, chronic pulmonary hypertension causes right ventricular hypertrophy, septal flattening, underloading of the left heart, and high-velocity tricuspid and pulmonic regurgitation. The ECG of infected dogs is usually normal. Right ventricular hypertrophy patterns are seen when there is severe, chronic pulmonary hypertension and are associated with overt or impending right-sided CHF (ascites). Heart rhythm disturbances are usually absent or mild, but atrial fibrillation is an occasional complication in dogs with Class III disease.
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Cardiac changes on thoracic radiography are less common in cats than dogs. The caudal lobar veins are enlarged (greater than 1.5 times the width of the ninth ribe), and the pulmonary arteries are blunted and tortuous<sup>3</sup>. Patchy parenchymal infiltrates may be seen in the region of vessels in animals showing respiratory signs<sup>1, 3</sup>. The main pulmonary artery cannot normally be seen in cats on radiography as it has a relatively midline position<sup>1</sup>. Thoracic radiography is an important
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tool for the diagnosis of feline heartworm
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disease. Despite thoracic abnormalities
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in few cases are absent or
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transient (Selcer et al., 1996), typical
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findings as enlarged peripheral branches
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of the pulmonary arteries accompanied
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by varying degrees of pulmonary
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parenchymal disease are strongly
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consistent with heartworm infection
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(Fig. 2). Enlargement of the main pulmonary
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artery cannot be observed
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because this tract of artery is obscured
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by cardiac silhouette. Right-sided cardiomegaly
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is not considered a typical
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finding in cat.
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Cardiac changes on thoracic radiography are less common in cats than dogs. The caudal lobar veins are enlarged (greater than 1.5 times the width of the ninth ribe), and the pulmonary arteries are blunted and tortuous<sup>3</sup>. Patchy parenchymal infiltrates may be seen in the region of vessels in animals showing respiratory signs<sup>1, 3</sup>. The main pulmonary artery cannot normally be seen in cats on radiography as it has a relatively midline position<sup.1</sup>.
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===Echocardiography===
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In dogs, echocardiography is relatively unimportant as a diagnostic tool. Worms observed in the right heart and vena cava are associated with high-burden infection with or without caval syndrome. Severe, chronic pulmonary hypertension causes right ventricular hypertrophy, septal flattening, underloading of the left heart, and high-velocity tricuspid and pulmonic regurgitation.
    
In cats, worms can usually be imaged on echocardiography. Parallel hyperechoic lines, which are an image from the heartworm cuticle, may be seen in the right heart and pulmonary arteries. High worm burdens may be associated with worms in the right heart. Echocardiography is more important in cats than dogs because of the increased difficulty of diagnosis and the high sensitivity of the test in experienced hands.
 
In cats, worms can usually be imaged on echocardiography. Parallel hyperechoic lines, which are an image from the heartworm cuticle, may be seen in the right heart and pulmonary arteries. High worm burdens may be associated with worms in the right heart. Echocardiography is more important in cats than dogs because of the increased difficulty of diagnosis and the high sensitivity of the test in experienced hands.
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===Electrocardiography===
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The ECG of infected dogs is usually normal. Right ventricular hypertrophy patterns are seen when there is severe, chronic pulmonary hypertension and are associated with overt or impending right-sided CHF (ascites). Heart rhythm disturbances are usually absent or mild, but atrial fibrillation is an occasional complication in dogs with Class III disease.
    
===Laboratory Tests===
 
===Laboratory Tests===
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