RADIOGRAPHIC AND 2-D ECHOCARDIOGRAPHIC FINDINGS IN EIGHTEEN CATS EXPERIMENTALLY EXPOSED TO D. ZMMZTZS VIA MOSQUITO BITES

Eighteen cats were exposed to Dirofikria immitis infected mosquitoes. Thoracic radiography was performed prior to exposure and at 5, 7, and 9 month intervals following exposure. Immunologic testing for adult heartworm antigen was performed on days 168,195,210,224,237,254 and 271 post infection. Necropsies were performed on all cats. Adult heartworms were found in 61% of the exposed cats. Radiographic findings in heartworm positive cats included bronchointerstitial lung disease, lobar pulmonary arterial enlargement and pulmonary hyperinflation. In most heartworm positive cats, lobar arterial enlargement resolved as the disease progressed while pulmonary hyperinflation progressively became more common. Pulmonary patterns in heartworm positive cats remained abnormal throughoutthe study while abnormal pulmonary patterns resolved in over 50% of the heartworm negative cats. Cardiomegaly was seen in less than 50% of the cats with adult heartworms at necropsy. This study suggests that the radiographic appearance of heartworm disease is variable and radiographic changes are dependent on the time post infection at which cats are evaluated. Echocardiographic examinations were randomly performed on 16 of 18 cats. Heartworms were identified in 7 cats. No false positive identifications were made. Persistent pulmonary disease accompanied by resolving vascular disease in heartworm cats with pulmonary hyperinflation may be difficult to distinguish from cats with feline allergic lung disease. Echocardiograms may be helpful in identifying adult heartworms in cats in which the radiographic signs or immunodiagnostic data are insufficient to provide a diagnosis.     

CARDIAC AND PULMONARY ARTERY MENSURATION IN FELINE HEARTWORM DISEASE

A retrospective study was undertaken to quantify thoracic radiographic changes in cats with heartworm diseases, ( Dirofilaria immitis ). Using a blinded study format, the cardiac silhouette, thoracic cavity and pulmonary arteries were measured from thoracic radiographs of 21 cats with feline heartworm disease and 30 cats without known cardiac or pulmonary vessel pathology. Measured data were normalized to the thoracic cavity or bony structures within the radiographic field of view. The measurements were compared between the two groups of cats using an unpaired, two-tailed Student's t -test, with a p value of < 0.05 being considered significant. Cats with feline heartworm disease had enlargement of the craniocaudal aspect of the cardiac silhouette and normalized cardiac:thoracic ratio (p < 0.05) on the lateral view. Also, there was significant enlargement of the central and peripheral caudal lobar pulmonary arteries and their normalized ratios (p < 0.05) in the heartworm infected cats as visualized on the ventrodorsal projection. Tortuosity of the pulmonary arteries was seen in three of the 21 infected cats. Eleven of the 21 cats with feline heartworm disease had pulmonary parenchymal changes. Based on the present study, central and peripheral pulmonary artery enlargement as viewed on the ventrodorsal radiograph was the single best radiographic indicator of feline heartworm disease.     

Understanding feline heartworm infection: disease, diagnosis, and treatment

Feline heartworm disease is a very different clinical entity from canine heartworm disease. In cats, the arrival and death of immature heartworms in the pulmonary arteries can cause coughing and dyspnea as early as 3 months postinfection. Adult heartworms suppress the function of pulmonary intravascular macrophages and thus reduce clinical disease in chronic feline heartworm infection. Approximately 80% of asymptomatic cats self-cure. Median survival time for symptomatic cats is 1.5 years, or 4 years if only cats living beyond the day of presentation are considered. Aberrant worm migration is more frequent than it is in dogs, and sudden death can occur with no prior clinical signs. The bacterial endosymbiont Wolbachia likely contributes to the inflammatory pathology of heartworm disease, but its role is not yet fully clear. Unfortunately, the diagnosis, treatment, and management of feline heartworm disease are far from simple. Antemortem diagnosis is hampered by low worm burdens, the frequency of all-male infections, and nonspecific radiographic lesions. It is up to the veterinarian to determine the correct index of suspicion and choose the right combination of diagnostic tests to achieve an answer. Treatment is symptomatic because adulticide therapy is risky and does not increase survival time. Despite the dangers of feline heartworm disease, less than 5% of cats in the United States are on chemoprophylaxis. It is important for veterinarians to take a proactive preventive stance because heartworm infection in cats is a multisystemic disease that has no easy cure.     

Feline heartworm (Dirofilaria immitis) infection: a statistical elaboration of the duration of the infection and life expectancy in asymptomatic cats

A study was conducted to assess the duration and the outcome (self-cure or death) of feline heartworm infection and the life expectancy of infected cats. To be included in the study, cats had to be positive for heartworm antibody (Ab) and heartworm antigen (Ag) and had to demonstrate the presence of worms by echocardiography. Self-cure was defined as (1) negative for heartworm Ag and (2) no further visualization of worms by echocardiography. Of the 1962 eligible cats, 364 (18.5%) were positive for heartworm Ag and 131 were positive for heartworm Ag and for echocardiography diagnosis (prevalence 6.7%). None of the cats was microfilaremic. Of 43 asymptomatic cats included into the follow-up study with owners' consent, 34 (79%) self-cured and nine (21%) died. Eleven (26%) cats remained asymptomatic and self cured within 21-48 months, 23 (53%) showed symptoms but self-cured within 18-49 months, 6 (14%) died within 8-41 months of follow-up and 3 (7%) suddenly died after 38-40 months, which was related to heartworm infection. The probability for death or sudden death increased significantly with age at diagnosis, but no difference was detected by gender, survival time after diagnosis, or the presence or absence of symptoms. The presence/absence of symptoms showed significant interaction with the age at diagnosis (i.e., symptomatic cats showed increasing duration of heartworm infection along with age at diagnosis compared to that for asymptomatic cats. Heartworm-infected cats survived significantly longer than heartworm-negative cats affected by hypertrophic cardiomyopathy, chronic renal failure, or neoplastic diseases.     

Prevalence and risk factors for heartworm infection in cats from northern Florida

Necropsies were performed on 630 adult cats in northern Florida to determine the prevalence and risk factors for heartworm infection in cats of this region. Heartworms were identified in 4.9% of cats, and serological evidence of heartworm exposure was present in 17% of cats. Not all cats from which heartworms were recovered were seropositive for heartworm antigen or antibody. There was no association between heartworm infection and co-infection with feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV). Male cats were at higher risk of infection with heartworm, FeLV, or FIV than were females. Because even a single heartworm can cause clinical disease or death in cats, the authors conclude that cats in this region should receive heartworm prophylaxis to prevent heartworm infection.     

Feline heartworm disease: a clinical review

Feline heartworm disease is caused by the filarial nematode Dirofilaria immitis, and is transmitted by mosquitoes in heartworm-endemic areas worldwide. While dogs are the definitive hosts for this parasite, cats can also be infected, and the overall prevalence in cats is between 5% and 10% of that in dogs in any given area. The spectrum of feline presentations varies from asymptomatic infections to chronic respiratory signs, sometimes accompanied by chronic vomiting to acute death with no premonitory signs. Ante-mortem diagnosis can be challenging and relies on a combination of tests, including antigen and antibody serology, thoracic radiography and echocardiography. As treatment with heartworm adulticidal drugs can be life-threatening and heartworm infection in cats is often self-limiting, infected cats are frequently managed with supportive treatment (corticosteroids, bronchodilators, and anti-emetics). Surgical removal of filariae using extraction devices may be considered in some acute cases where immediate curative treatment is necessary, but filarial breakage during the procedure may result in an acute fatal shock-like reaction. Necropsy findings are mainly pulmonary and include muscular hypertrophy of the pulmonary arteries and arterioles on histopathology. A number of safe and effective macrocytic lactone drugs are available for prophylaxis in cats. These drugs can kill a range of larval and adult life-cycle stage heartworms, which may be advantageous in cases of owner compliance failure or when heartworm infection status is undetermined at the time prophylaxis is commenced. An index of suspicion for feline heartworm disease is warranted in unprotected cats with respiratory signs, and perhaps chronic vomiting, in areas where canine heartworm disease is endemic. Many cats, once diagnosed and with appropriate supportive care and monitoring, will resolve their infection and be free of clinical signs.     

Incidence of positive heartworm antibody and antigen tests at IDEXX Laboratories: trends and potential impact on feline heartworm awareness and prevention

Data from the IDEXX Laboratories Reference Laboratory Network were retrospectively examined for feline heartworm testing trends in testing frequency, geographic bias, and prevalence for the years 2000--2006. Examination of the data supports the commonly held view that veterinarians do not embrace heartworm disease testing or prevention in cats to the same degree they do in dogs. Despite significant awareness and adoption of heartworm testing and prevention in dogs, we hypothesized that heartworm testing rates are lower for cats than for dogs despite a significant prevalence of feline infection. This is important because a perceived low rate of infection in cats is likely to manifest in a low adoption of testing and prevention. In reality, the overall feline heartworm antigen-positive rate is significant--on average 0.9% over the period studied--and in some regions was estimated to be as high as 4.6%. This compares with an average canine heartworm prevalence rate of 1.2%, a feline leukemia virus prevalence of 1.9%, and a feline immunodeficiency prevalence of 1.0%. Based on the low rate of testing and these prevalence rates, practitioners are routinely missing cases of adult feline heartworm infections and the recently defined heartworm-associated respiratory disease (H.A.R.D). Increased antigen testing would result in detection of a significant number of positive cases. In addition, this population of infected cats would represent the "tip of the iceberg" relative to the greater number of cats that have early infection or are at risk for infection.     

THORACIC RADIOGRAPHIC ABNORMALITIES IN 200 DOGS WITH SPONTANEOUS HEARTWORM INFESTATION

Thoracic radiographs of 200 dogs with spontaneously occurring heartworm disease were reviewed. Radiographs of 28 dogs (14%) were normal. In the remaining 172 dogs various combinations of cardiopulmonary abnormalties were found. The most frequently observed combination, noted in 61 of 200 dogs, was right ventricular, main pulmonary, and right cranial lobar pulmonary artery enlargemetn. Dogs with severe increse of one parameter generally had severe increase of the other two parameters also. One hundred five of the 200 dogs had a right cranial lobar pulmonary artery of normal size. Thus, right cranial lobar pulmonary artery size, when normal, is not a sensitive indicator of the absence of heartworm disease. There was a statistically significant positive relation between the size of the caudal vena cava and that of the right ventricle.     

RADIOGRAPHIC EVALUATION OF CANINE HEARTWORM DISEASE COEXISTING WITH RIGHT HEART FAILURE

Thoracic radiographs of 28 dogs with heartworm disease and right heart failure were evaluated subjectively and objectively. Radiographs of all dogs were abnormal. Abnormalities were consistent with those previously reported for heartworm disease but were more severe than those identified in another group of heartworm dogs that did not have right heart failure. The right ventricle and right caudal labor pulmonary artery were enlarged in every dog. The main pulmonary artery, right cranial lobar pulmonary artery, and caudal vena cava were enlarged in 24, 25, and 17 dogs, respectively. Radiographically apparent pathologic pulmonary conditions were present in 25 dogs. Pleural effusion was not identified.     

Structural and ultrastructural changes in the lungs of cats Felis catus (Linnaeus, 1758) experimentally infected with D. immitis (Leidy, 1856)

Clinical signs are seldom observed in feline heartworm disease, and the pathophysiological changes in the lungs of infected animals remain undefined. The goal of this study was to evaluate the structural and ultrastructural changes in the lungs of cats experimentally infected with Dirofilaria immitis. Six healthy cats were each infected with two adult heartworms by intravenous transplantation (Receptor Group, RG). The control group consisted of two uninfected animals kept under the same conditions as the RG. At 42 days after transplantation, all cats were euthanized and necropsied for worm recovery and collection of lung samples for examination by light microscopy (LM) and transmission electron microscopy. By LM, lung sections from the six infected cats exhibited bronchial and bronchiolar lesions. Alterations in all tissues of the pulmonary arteries were observed in the infected animals. In conclusion, cats infected experimentally with D. immitis developed lesions in their lungs as a consequence of arterial disease and intense interstitial pneumonia.     

Renal effects of Dirofilaria immitis in experimentally and naturally infected cats

Canine heartworm infection has been associated with glomerular disease and proteinuria. We hypothesized that proteinuria, likely due to glomerular damage, would also be found in cats experimentally and naturally infected with Dirofilaria immitis. Two populations of cats were evaluated, including 80 that were each experimentally infected with 60 infective heartworm larvae as part of a drug safety study, and 31 that were naturally infected with D. immitis. Each had a control population with which to be compared. In the experimentally infected group, we evaluated urine from 64 cats. Ten of these cats were shown to have microalbuminuria 8 months post infection. No cat refractory to infection with larvae and no cats from the control group demonstrated microalbuminuria. All 10 microalbuminuric cats were shown to have significant proteinuria, as measured by the urine protein:creatinine ratio. There was a subtle, but significant, association between worm burden and proteinuria, and although the presence of adult heartworms was required for the development of proteinuria, both microfilaremic and amicrofilaremic cats were affected. Neither the presence of circulating heartworm antibodies and antigen nor the presence of antigenuria predicted the development of proteinuria. Both heavily infected cats (5-25 adult heartworms) and cats with worm burdens compatible with natural infections (1-4 adult heartworms) developed proteinuria, and the relative numbers of cats so affected were similar between heavily and more lightly infected cats. Naturally infected cats, for which only dipstick protein determinations were available, were shown to have a significantly greater incidence of proteinuria (90% vs 35%) than did those in an age- and gender-matched control population. Additionally, the proteinuria in heartworm-infected cats was 3- to 5-fold greater in severity. We conclude that cats infected with mature adult heartworms are at risk for developing proteinuria and that this is recognized relatively soon after infection. While heavier infections may predispose cats to developing proteinuria, this complication is seen in naturally infected cats and experimental cats with worm burdens similar to those seen in natural infections (i.e., "clinically appropriate" worm burdens). The clinical relevance of heartworm-associated proteinuria is yet to be determined.     

Diagnostic, treatment, and prevention protocols for feline heartworm infection in animal sheltering agencies

Cats are at risk for heartworm infection (Dirofilaria immitis) wherever the disease is endemic in dogs. Diagnosis is more difficult in cats, and little information is available regarding effective palliative and curative treatments for infected cats. In contrast to the challenges of diagnosis and treatment, chemoprophylaxis is highly effective, and current guidelines call for preventive medications to be administered to all cats in endemic areas. The purpose of this study was to survey feline heartworm management protocols used by 400 animal shelters and foster programs in the endemic states of Alabama, Florida, Georgia, and Mississippi. Only 23% of shelters performed feline heartworm testing. The most common reasons for not testing were expense (36%), lack of treatment options for infected cats (18%), and because the agency considers heartworm infections in cats to be less important than in dogs (12%). Most agencies (69%) did not provide preventive medication to cats. Reasons included because testing was not performed (36%), expense (35%), and the perception that local heartworm risk was low (10%). When preventive was provided, feline-labeled broad-spectrum products were used more commonly (81%) than livestock products (14%). The survey also indicated that many policy decisions were based on inaccurate knowledge of feline heartworm prevalence and pathogenesis. Issues of cost, feasibility, and education prevent most Southeastern sheltering agencies from adequately protecting cats against heartworm disease. Practical guidelines tailored to the needs of these agencies should be developed. Subsidized testing and preventive products may facilitate implementation of feline heartworm management protocols in sheltering agencies.     

Use of echocardiography for the diagnosis of heartworm disease in cats: 43 cases (1985-1997)

OBJECTIVE: To determine the usefulness of echocardiography in the diagnosis of heartworm disease in cats and to compare this modality with other tests. DESIGN: Retrospective study. ANIMALS: 43 cats with heartworm infection that had echocardiographic examinations at 2 veterinary teaching hospitals between 1985 and 1997. Twenty-two of these 43 cats also underwent radiography of the thorax and heartworm antibody and heartworm antigen testing. PROCEDURE: Cats were determined to be infected with Dirofilaria immitis infection on the basis of 1 or more of the following findings: positive modified Knott or antigen test result, echocardiographic evidence of heartworm disease, or confirmation of the disease on postmortem examination. The percentage of echocardiographs in which heartworms were evident was compared with the percentage of radiographs in which pulmonary artery enlargement was evident and results of antigen or antibody tests in cats in which all tests were performed. RESULTS: Overall, heartworms were detectable by use of echocardiography in 17 of 43 cats, most often in the pulmonary arteries. In the 22 cats in which all tests were performed, antibody test results were positive in 18, antigen test results were positive in 12, and pulmonary artery enlargement was evident radiographically and heartworms were identifiable echocardiographically in 14. Heartworm infection was diagnosed exclusively by use of echocardiography in 5 cats in which the antigen test result was negative. CONCLUSIONS AND CLINICAL RELEVANCE: Although echocardiography was less sensitive than antigen testing, it was a useful adjunctive test in cats that had negative antigen test results in which there was a suspicion of heartworm disease. The pulmonary arteries should be evaluated carefully to increase the likelihood of detection of heartworms echocardiographically.     

Activity of pulmonary intravascular macrophages in cats and dogs with and without adult Dirofilaria immitis

Pulmonary intravascular macrophages (PIMs), large (20-80 microm diameter) monocytes are present in sheep, pigs, and horses, but not in dogs, rats, rabbits, or primates. The present study evaluated the phagocytic activity of various organs in cats and dogs and determined the influence of Dirofilaria immitis infections on PIM activity. Live or dead adult heartworm (HW) was transplanted via jugular venotomy into cats and dogs. Cats (four per group) were allocated to five groups: surgical controls--no HW, dead HW for 1 week, live HW for 1 week, dead HW for 3 weeks, or live HW for 3 weeks. Radioactive technetium (Tc-99m, 1.2mCi in 0.3ml) sulfa-colloid was injected intravenously. All cats with HW were clinically asymptomatic and developed radiographic pulmonary parenchymal changes. No gross changes were visible at necropsy for cats with HW; inflammatory changes were less severe in cats with live HW. In cats with dead HW for 3 weeks, worms were present but folded, flattened, and located in distal pulmonary arteries. Uninfected control dogs and those with dead HW did not demonstrate any PIM activity. In control cats, lungs were the primary phagocytic organ after systemic IV colloid injection (72.5% of the total recovered radioactive dose). The lung and liver together represented over 95% of the recovered Tc-99m colloid in all cats. In each group of cats with HW, phagocytic activity of the lung was significantly less (p < 0.001) than the PIM activity of controls. Cats with dead HW at 1 week (50.1%) had a significant (p < 0.019) decrease in PIM activity compared with cats with dead HW at 3 weeks (59.5%). The PIM activity in cats with live HW was significantly decreased (p < 0.001) from that in groups with dead HW, but there was no significant difference between the two groups infected with live worms. There were no significant differences in recovery between any groups in pairwise analysis of the spleen, heart, skeletal muscle, kidney, bone marrow, or blood. Significant increases (p < 0.001) in liver activity for each group inversely reflected the decreased lung activity; consistent with increased hepatic uptake of Tc colloid "escaping" a relatively suppressed lung macrophage system. Transmission electron microscopy confirmed PIM glycocalyx changes and vacuolization, moderate Type 1 cell damage and Type II cell hypertrophy in cats with dead HW. There was no evidence of PIM death. The significant decrease in PIM activity in groups with dead HW and a greater decrease in groups with live HW are consistent with a down-regulation of PIM function in cats with live HW.     

Endogenous lipid pneumonia in cats: 24 cases (1985-1998)

OBJECTIVE: To determine clinical signs, radiographic and histologic abnormalities, and concurrent diseases in cats with endogenous lipid pneumonia (EnLP) and to determine the pathologic importance of EnLP in cats. DESIGN: Retrospective study. ANIMALS: 24 cats. PROCEDURE: Medical records of cats in which EnLP was confirmed by histologic examination of necropsy specimens were reviewed. Information collected from the medical records included signalment, body weight, clinical signs, and results of clinicopathologic tests. Thoracic radiographs were reviewed by a radiologist; histologic specimens were reviewed by a pathologist. RESULTS: All cats had nonspecific clinical abnormalities, such as lethargy, anorexia, or weight loss; 16 had signs of respiratory tract disease. All cats had concurrent systemic diseases, and clinicopathologic abnormalities were reflective of these conditions. Nonspecific abnormalities were detected on thoracic radiographs from 9 of 11 cats. Most cats had macroscopic, multifocal, subpleural lesions; inflammatory infiltrates, cholesterol clefts, and multinucleated giant cells were common. Ten cats had an underlying obstructive pulmonary disease that was the likely cause of EnLP. Lesions of EnLP were not considered to be severe enough or extensive enough to be the cause of death in any of these cats. CONCLUSIONS AND CLINICAL RELEVANCE: EnLP is an uncommon respiratory tract disorder of cats with no pathognomonic clinical, laboratory, or radiographic findings. Although EnLP was not the cause of death in any of these cats, results of the present study do suggest that EnLP may be a marker for potentially severe underlying obstructive pulmonary disease.     

Catheter-guided percutaneous heartworm removal using a nitinol basket in dogs with caval syndrome

Carval syndrome is a severe heartworm infection where the worms have migrated to the right atrium and vena cava; this condition is associated with a myriad of clinical signs. Several non-surgical and interventional methods are currently used for mechanical worm removal. However, the success rate and complications related to these methods are heavily dependent on methodology and retrieval devices used. In this study, we developed a catheter-guided heartworm removal method using a retrieval basket that can easily access pulmonary arteries and increase the number of worms removed per procedure. With this technique, we successfully treated four dogs with caval syndrome.     

Attraction of mosquitoes to domestic cats in a heartworm enzootic region

Heartworm disease is caused by a mosquito-borne parasite that can affect many different mammalian species and has worldwide distribution. The agent, Dirofilaria immitis (Leidy 1856), infect mainly dogs but feline infection have been frequently reported in the last decade. Feline heartworm infection is difficult to detect, therefore, low reported prevalence could reflect true low prevalence or poor diagnostic efficiency. As mosquitoes are known to be attracted differently by different mammalian species, mosquitoes were collected from both a cattery and a contiguous home located in a canine heartworm enzootic area in Niterói, state of Rio de Janeiro, Brazil. For 14 months, mosquitoes were collected weekly for genus identification, speciation when possible, and for individual blood meal identification. Culex species mosquitoes were the most captured and those most frequently found with feline blood meal, followed by Aedes species that, although captured in lower numbers, also fed on feline blood. While Culex species mosquitoes have been reported as potential secondary heartworm vectors for dogs and primary vectors for cats, the present results suggest that Aedes species mosquitoes may also be involved in feline heartworm transmission in a larger proportion than previously thought.     

RADIOGRAPHIC AND ANGIOGRAPHIC EVALUATIONS OF FERRETS EXPERIMENTALLY INFECTED WITH DIROFILARIA IMMITIS

Five ferrets of each sex were each inoculated with 15 third-stage infective larvae of Dirofilaria immitis to study radiographic and angiographic changes in the cardiopulmonary system following heartworm infection; 5 additional ferrets of each sex served as noninfected controls. Prior to inoculation and every 8 weeks thereafter until 40 weeks, the infected and noninfected ferrets were radiographed; angiographic examinations were done prior to necropsy. At necropsy, the worms in the heart, lungs, and associated vessels were counted, and lung histosections were prepared and examined for changes. Radiographic changes were seen in the right side of the heart and associated vessels of infected ferrets as compared with the noninfected ferrets, but changes were less prominent than those seen in heartworm-infected dogs and cats. The changes were primarily an increase in the size of the right side of the heart, especially the right atrium. Radiographically, no changes could be visualized in the pulmonary vascular system. Worms in the enlarged cranial vena cava, azygous vein, and left caudal lobar pulmonary artery of infected animals were delineated by angiography. Histologically, no changes were seen in the pulmonary vascular tissues.     

Clinical, hematologic, and survival data from cats infected with feline immunodeficiency virus: 42 cases (1983-1988).

A retrospective study of stored feline serum samples was done to determine the infection rate of feline immunodeficiency virus in cats in central Missouri. Infected cats were compared with uninfected cats subjected to the same selection criteria on the basis of signalment, clinical signs, and CBC abnormalities. A significant incidence of virus infection was found in male cats. Neither age nor breed predilection could be identified. Infected cats were more likely to be anemic and leukopenic because of neutropenia. Cellulitis and neoplasia were more common in infected cats. A spectrum of disease severity was seen in infected cats ranging from no clinical signs to signs of severe chronic inflammatory disease. Infected cats were more likely to have clinical disease. Mean survival of infected cats was 24.4 months from the time of diagnosis.     

COMPUTED TOMOGRAPHY ANGIOGRAPHY FOR EVALUATION OF PULMONARY EMBOLISM IN AN EXPERIMENTAL MODEL AND HEARTWORM INFESTED DOGS

This study was performed to characterize pulmonary embolism with computed tomography pulmonary angiography in experimental pulmonary embolism and heartworm infected dogs. In the experimental group, there were pulmonary changes after pulmonary embolism induction as follows: hypoattenuating round filling defects in pulmonary arteries, arterial dilations with straight and abrupt cut‐off appearances in the pulmonary embolism regions, pulmonary infarctions, a cavity formation and spontaneous pneumothorax, and emboli migration. In the heartworm‐infected group, three out of eight dogs developed pulmonary embolism, especially in the right caudal arteries. Arterial dilations with typical tortuosity were also identified, mainly in the right caudal arteries in five dogs. Computed tomography pulmonary angiography can be an important imaging modality in the diagnosis of pulmonary embolism and the evaluation of pulmonary arterial and parenchymal changes in dogs.