A12-week-old 6.2-kg (13.6-lb) female English Springer Spaniel was evaluated at the University of Missouri-Columbia Veterinary Medical Teaching Hospital because of suspected PDA. On physical examination, the dog was tachycardic (heart rate, 200 beats/min) and tachypneic (respiratory rate, 60 breaths/min); harsh lung sounds and hyperkinetic femoral pulses were detected. A grade 5/6 continuous heart murmur with the point of maximal intensity over the left heart base was auscultated. Thoracic radiography revealed a moderately large cardiac silhouette with a vertebral heart score of 12.5 (reference range, 8.5 to 10.6); a vertebral heart score is derived from measurements of the short and long axes of the heart in relation to vertebral bodies.1 Radiographically, pulmonary venous distension and a mild perihilar interstitial infiltrate were evident. These changes were consistent with left-sided congestive heart failure. Echocardiographic findings confirmed the diagnosis of PDA (left-to-right shunt). Continuouswave Doppler ultrasonography revealed that the peak velocity of systolic flow through the ductus was 5.82 m/s and end-diastolic flow velocity was 3.35 m/s. Mild mitral valve regurgitation was also present. Furosemide (2 mg/kg [0.91 mg/lb], PO, q 12 h) was administered for treatment of heart failure.
Two weeks later, the dog underwent coil occlusion of the PDA. Cefazolin (22 mg/kg [10 mg/lb], IV) was given at induction of anesthesia and every 90 minutes thereafter during the procedure. Once the dog was anesthetized, the ductus was approached percutaneously via the femoral artery. Results of angiography indicated that the ductus was 8 mm at its widest point and 4 mm at its narrowest point. The first coil deployed in the ductus embolized to the caudal lobe branch of the right pulmonary artery. Five additional coils were successfully placed into the ductus, and the coil mass protruded slightly into the pulmonary artery (Figure 1). Cefazolin (22 mg/kg, IV) was given every 6 hours for the first 24 hours after surgery, and then antimicrobial administration was discontinued.
Right lateral thoracic radiographic image obtained 24 hours after a coil occlusion procedure to treat PDA in a 12-week-old dog. The first coil embolized to the caudal lobe branch of the right pulmonary artery (solid arrow). Five additional coils were successfully placed in the ductus (open arrow). A small amount of persistent residual flow through the ductus was detected echocardiographically. Before surgery, the dog had a grade 5/6 left basilar continuous murmur; after surgery, only a 2/6 left basilar systolic murmur was detected.
Citation: Journal of the American Veterinary Medical Association 228, 12; 10.2460/javma.228.12.1901
Right lateral thoracic radiographic image obtained 24 hours after a coil occlusion procedure to treat PDA in a 12-week-old dog. The first coil embolized to the caudal lobe branch of the right pulmonary artery (solid arrow). Five additional coils were successfully placed in the ductus (open arrow). A small amount of persistent residual flow through the ductus was detected echocardiographically. Before surgery, the dog had a grade 5/6 left basilar continuous murmur; after surgery, only a 2/6 left basilar systolic murmur was detected.
Citation: Journal of the American Veterinary Medical Association 228, 12; 10.2460/javma.228.12.1901
Right lateral thoracic radiographic image obtained 24 hours after a coil occlusion procedure to treat PDA in a 12-week-old dog. The first coil embolized to the caudal lobe branch of the right pulmonary artery (solid arrow). Five additional coils were successfully placed in the ductus (open arrow). A small amount of persistent residual flow through the ductus was detected echocardiographically. Before surgery, the dog had a grade 5/6 left basilar continuous murmur; after surgery, only a 2/6 left basilar systolic murmur was detected.
Citation: Journal of the American Veterinary Medical Association 228, 12; 10.2460/javma.228.12.1901
Twenty-four hours after the procedure, echocardiography revealed mild residual flow through the ductus; the peak velocity of systolic flow was 2.80 m/s, and the amount of diastolic flow was negligible. The murmur was attenuated to a grade 2/6 left basilar systolic murmur. There was moderate bruising and mild swelling associated with the femoral puncture site. This was treated with warm packing for 2 weeks. The dog was discharged 1 day following the procedure.
One week after the procedure, the dog became anorexic and lethargic, began vomiting, and had a rectal temperature of 40.2°C (104.5°F). The swelling associated with the femoral puncture site had abated, but mild skin discoloration was still present. Abnormalities detected via CBC included mild normocytic, normochromic anemia (Hct, 33%; reference range, 37% to 55%), neutrophilia (11,660 cells/mL; reference range, 3,000 to 11,500 cells/mL) with a left shift (3,040 band neutrophils/mL; reference range, 0 to 300 bands/mL), and thrombocytopenia (14,200 platelets/mL; reference range, 200,000 to 500,000 platelets/mL). Toxic effects on neutrophils were detected on examination of a blood smear. No notable abnormalities were identified via serum biochemical analyses. A coagulation profile was obtained. Prothrombin time was prolonged (7.8 seconds; reference range, 5.4 to 7.4 seconds) and fibrin degradation products concentration was high (> 20 mg/mL; upper reference limit, < 5 mg/mL). The activated partial thromboplastin time was within reference limits. The result of a parvovirus antigen test was negative. Urinalysis revealed proteinuria (2+), and urine specific gravity was 1.044 (reference range,2 1.001 to 1.065), but no other abnormalities were identified. Bacteriologic culture of urine yielded negative results; however, Pasteurella multocida was cultured from 3 blood samples obtained aseptically from a jugular vein at 1-hour intervals. Radiographically, the vertebral heart score was 11.0, and there was no evidence of congestive heart failure. The position of the coil mass was unchanged. Echocardiographically, there were no important changes, compared with previous postoperative findings.
The dog was admitted to the intensive care unit for treatment of sepsis because the presumptive diagnosis was infection of the implanted coils. Treatment with ticarcillin-clavulanic acid (50 mg/kg [22.7 mg/lb], IV, q 6 h) was initiated along with IV fluid therapy. Clinical signs of sepsis resolved within 48 hours. The femoral puncture site appeared normal within 1 week. After 2 weeks, IV treatment with the antimicrobial drug combination was discontinued and the dog received amoxicillin-clavulanic acid orally (13.75 mg/kg [6.3 mg/lb], q 12 h). The leukogram and platelet count were within reference range 1 month after starting treatment with ticarcillin-clavulanic acid.
Six weeks after the initial evaluation of the dog because of sepsis (at a time when it was still receiving antimicrobials), it was examined because of signs of congestive heart failure. Physical examination revealed a 5/6 continuous heart murmur with the point of maximal intensity over the left heart base, harsh lung sounds, and tachypnea. Thoracic radiography revealed the presence of pulmonary interstitial infiltrates in the caudal and dorsal portions of the lungs, which was consistent with congestive heart failure, and partial migration of the coils into the pulmonary artery (Figure 2). The vertebral heart score was 12.0. Echocardiography revealed that the left ventricular diastolic and left atrial systolic dimensions had increased by approximately 30%, compared with findings after surgery. Flow through the ductus had increased; the peak velocity of systolic flow was 4.43 m/s, and the end-diastolic flow velocity was 2.43 m/s. Treatment with furosemide (3.3 mg/kg [1.5 mg/lb], PO, q 12 h) and enalapril (0.5 mg/kg [0.23 mg/lb], PO, q 12 h) was initiated.
Right lateral thoracic radiographic image obtained 6 weeks after a coil occlusion procedure to treat PDA in the dog in Figure 1. The dog had been successfully treated for signs of sepsis that had developed 1 week after the implant procedure. At this time, the dog had tachypnea, tachycardia, and a grade 5/6 left basilar continuous murmur. Notice the large cardiac silhouette, interstitial infiltrates in the caudal and dorsal portions of the lungs, and pulmonary vascular distension consistent with congestive heart failure. The position of the coil mass has shifted in the ductus (dashed arrow), compared with its radiographic location 24 hours after surgery.
Citation: Journal of the American Veterinary Medical Association 228, 12; 10.2460/javma.228.12.1901
Right lateral thoracic radiographic image obtained 6 weeks after a coil occlusion procedure to treat PDA in the dog in Figure 1. The dog had been successfully treated for signs of sepsis that had developed 1 week after the implant procedure. At this time, the dog had tachypnea, tachycardia, and a grade 5/6 left basilar continuous murmur. Notice the large cardiac silhouette, interstitial infiltrates in the caudal and dorsal portions of the lungs, and pulmonary vascular distension consistent with congestive heart failure. The position of the coil mass has shifted in the ductus (dashed arrow), compared with its radiographic location 24 hours after surgery.
Citation: Journal of the American Veterinary Medical Association 228, 12; 10.2460/javma.228.12.1901
Right lateral thoracic radiographic image obtained 6 weeks after a coil occlusion procedure to treat PDA in the dog in Figure 1. The dog had been successfully treated for signs of sepsis that had developed 1 week after the implant procedure. At this time, the dog had tachypnea, tachycardia, and a grade 5/6 left basilar continuous murmur. Notice the large cardiac silhouette, interstitial infiltrates in the caudal and dorsal portions of the lungs, and pulmonary vascular distension consistent with congestive heart failure. The position of the coil mass has shifted in the ductus (dashed arrow), compared with its radiographic location 24 hours after surgery.
Citation: Journal of the American Veterinary Medical Association 228, 12; 10.2460/javma.228.12.1901
Two months after signs of heart failure initially developed, the dog was taken to Michigan State University's Veterinary Teaching Hospital for removal of the coils and closure of the PDA. Briefly, the dog was anesthetized and prepared routinely for surgery. The left femoral and left carotid arteries were isolated in case cardiac bypass became necessary. A left lateral thoracotomy was performed, and the PDA was approached as if for routine ligation. The ductus was clamped at its intersection with the aorta by use of Satinsky clamps and at its intersection with the pulmonary artery by use of ductus clamps. The ductus was incised to expose the coils, which were located partially within the ductus and partially in the pulmonary artery. Attempts to remove the coils by use of tension initially failed because of multiple adhesions that had formed between the coils and endothelium. The coils were also held by the ductus clamps at the point where they had migrated into the pulmonary artery. Inflow occlusion was performed 6 times, which enabled the coils to be freed from the pulmonary artery. The shortest inflow occlusion time was 5 seconds, whereas the longest inflow occlusion time was 90 seconds. The coils were cut into pieces and dissected free of the endothelium. The coil in the right pulmonary artery was left in place because it was inaccessible via a left lateral approach. Moderate hemorrhage occurred during the procedure, necessitating transfusion with several units of blood. The entire ductus was excised. The aorta and pulmonary artery were closed by use of 4-0 polypropylene suture in a mattress pattern. A thoracic tube was placed, and routine closure was performed. The coils and ductus tissue were submitted for bacteriologic culture, which yielded no growth of aerobic or anaerobic bacteria. The dog was discharged from the hospital 36 hours after surgery; the owner was instructed to administer amoxicillin-clavulanic acid (13.75 mg/kg, PO, q 12 h for 6 weeks), enalapril (0.5 mg/kg, PO, q 12 h for 2 weeks), and meloxicam (0.1 mg/kg [0.045 mg/lb], PO, q 24 h for 10 days).
Although the coil that embolized to the pulmonary vasculature was left in place, the dog had remained free of clinical signs for > 9 months at the time of this report. Two months after surgical treatment of the PDA, the dog underwent ovariohysterectomy without complications. Except for treatment with antimicrobials for 10 days after the ovariohysterectomy, the dog did not receive other antimicrobials during the followup period.
Discussion
In the dog of this report, the authors presumed that septicemia was associated with bacterial infection of the vascular occlusion coils used to treat the PDA and that administration of antimicrobials was effective against that infection; thus, results of bacteriologic culture of the coils were negative. However, these assumptions cannot be proven because bacteriologic culture of the coils was not performed when signs of sepsis were present. However, septicemia in a young dog with a PDA closure device has been reported.a In that dog, Pasteurella canis was cultured from blood samples and the presence of bacteria within the device was detected at necropsy.
Infection of a surgical implant is a devastating complication because of the difficulty of successfully treating such infections. In the human medical literature, implant-related infections are associated with prolonged hospitalization and great economic expense and have a major impact on the patient's quality of life.3 Infection of cardiac defect closure devices is rare in humans.4 Therefore, decisions regarding treatment of the dog of this report were based on extrapolations from reports of other types of cardiovascular device infection. Of these, pacemaker infections are reported most frequently. In dogs, the infection rate associated with transvenously placed pacemakers ranges from 5% to 16%.5–8 In humans, the infection rate associated with pacemakers ranges from 0.13% to 19.9%.4,8–11
The causative agents of most intravascular devicerelated infections in humans are various species of staphylococci.3,4,9,12 In 1 report,13 Staphylococcus aureus accounted for 20%, coagulase-negative staphylococci accounted for 14%, and Enterococcus spp accounted for 12% of surgical site infections in humans. In a study14 in dogs, S aureus was more commonly associated with infections that developed within days to months of the operation, whereas Staphylococcus epidermis was detected more often in infections that developed years later. In another report,15 S aureus was also the most commonly implicated pathogen in human cases of valvular endocarditis, whereas S epidermidis was more frequently associated with foreign bodies.
Pasteurella multocida is reported16 to be a rare cause of acute bacterial endocarditis in humans. Affected humans are usually immunocompromised and have a history of exposure to dog or cat saliva, wherein the organism resides. Fortunately, P multocida is usually susceptible to penicillins and cephalosporins. Humans that were infected with this organism have been treated with antimicrobials and supportive care for a minimum of 6 weeks. Some cures were achieved with medical treatment alone; however, most patients required surgery to provide complete resolution of the infection.
In humans, 2 mechanisms have been proposed to explain the development of implant-related infections.4 The first mechanism involves inoculation of the microorganism directly at the time of surgery or from a cutaneous infection following postoperative manipulations. This hypothesis explains the high rate of implant-related infections involving organisms that are commonly found on the skin. The other mechanism involves the hematogenous seeding of the implant as a result of an unrelated bacteremia.10,12 In the dog of this report, it would appear that hematogenous spread of bacteria most likely occurred because P multocida is part of the normal microflora of the oral cavity and respiratory tract of dogs.16
The specific pathogenesis of the dog's infection is unknown. In humans, uncorrected PDA or persistent residual flow after intervention is considered a moderate risk factor for development of bacterial endocarditis.17 The overall prevalence of infective endocarditis in dogs is low.18 Congenital cardiac abnormalities, including PDA, have been associated with infective endocarditis but appear to be rare risk factors.19,20 A risk factor for pacemaker-related endocarditis in humans is the development of hematomas at the pacemaker site.10 The dog of this report had mild hematoma formation at the introduction site of the femoral catheter; it is very likely that the dog licked and groomed the hematoma site, which may have increased its risk of developing an infection.
Ideal management of an infected implant includes its surgical removal. Antimicrobial treatment is recommended for a minimum of 14 days after bacteriologic culture of blood yields negative results or for a period of at least 4 weeks.4 However, for humans and other animals, surgical intervention is not always an option. If the implant cannot be removed, long-term (often lifelong) antimicrobial administration is recommended.4,12 In 1 study12 of intravascular device-related infections in humans, the duration of antimicrobial treatment ranged from 3 to 120 months and 26 of 51 (51%) patients required treatment for 1 year or longer.
Pending results of bacteriologic culture of blood and antimicrobial susceptibility testing, empirical antimicrobial treatment of an implant-related infection should be initiated. Cephalosporins are commonly used because they are active against many of the organisms isolated from infected implants.9,14
Recommendations for prevention of device-related infections in humans include IV administration of antimicrobials 1 to 2 hours prior to surgery.9,21 Cefazolin is a commonly recommended antimicrobial for prophylaxis in humans undergoing cardiothoracic and vascular surgery21; after the first dose is given, antimicrobial administration should be repeated if the surgical procedure is still in progress after a period that is equivalent to 2 half-lives of the drug has elapsed.
There is considerable debate concerning the appropriate use of antimicrobials in humans to prevent the development of bacteremia and implant infection after surgery. Prolongation of antimicrobial treatment can result in superinfection with less commonly recognized organisms or the development of resistant organisms.17 Most authors suggest continuing postoperative administration of antimicrobials for no longer than 6 to 8 hours, unless a cardiac procedure is performed, in which case treatment should be continued for 24 to 72 hours.14,17,21 Whether these recommendations are appropriate for veterinary patients is unknown. Given the potential for less-than-optimal hygienic conditions during the healing process, it is probably prudent to continue prophylactic administration of antimicrobials orally for 10 to 14 days after implant placement in animals.
In instances of infected cardiac defect closure devices in humans, surgical removal of the device has been required as part of the treatment.4 It was assumed that the implants in the dog of this report were infected and that the negative results obtained after bacteriologic culture of the coils indicated that infection of the coil mass was successfully resolved via medical treatment. However, surgical intervention was necessary because of the migration of the coils, which may have occurred as a complication of the infection or because the residual ductal flow pushed the coils further into the pulmonary artery. Thus, whether other instances of septicemia associated with PDA occlusion devices can be managed with medical treatment alone is unknown. As PDA occlusion coils become more commonly used in veterinary medicine, additional cases of sepsis are likely to occur and clinicians should be prepared to treat the infection in affected animals aggressively.
ABBREVIATIONS
| PDA | Patent ductus arteriosus |
Fine DM, Tobias AH, Spier AW. Cardiovascular device related infections (abstr), in Proceedings. 2005 Am Coll Vet Internal Med Forum. J Vet Intern Med 2005;19:456.
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