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Mechanical Heartworm Removal from 2 Dogs with Caval Syndrome Using Modified Extraction Brushes
Sungwook Lee*,**, Jonghun Park** and Changbaig Hyun**1
*Su-Wan Animal Hospital, 1452 Suwan-dong, Kwang-Ju 506-304, Korea
**Section of Small Animal Internal Medicine, School of Veterinary Medicine and Institute of Veterinary Science, Kangwon National University, Chuncheon 201-100, Korea
(Accepted: December 14, 2012)
Abstract : Caval syndrome is a life threatening condition caused by heavy worm burden in right cardiac chambers including right atrium, right ventricle, and vena cava and results in mechanical interference in tricuspid valvular excursion and blood flow to lower pulmonary arteries. A mechanical worm removal is the choice of option for treating this condition in dogs. In this study, we developed a new mechanical worm removal method using modified extraction brushes for treating dogs with caval syndrome. With this newly developed method, we successfully removed heartworms in two dogs with caval syndrome. Although the number of cases applied was small, authors found this method can be a good alternative retrieval method for mechanical worm removal in dogs.
Key words : modified extraction brush, caval syndrome, heartworm, mechanical heartworm removal.
Introduction
Caval syndrome is a life threatening condition caused by heavy worm burden in right cardiac chambers including right atrium, right ventricle, and vena cava and results in mechanical interference in tricuspid valvular excursion and blood flow to lower pulmonary arteries (1,2,5). Clinical signs associated with caval syndrome include exercise intolerance, cough, dyspnea, syncope, weight loss, and lethargy (2-3,5-6). Although medi- cal adultcidal treatment is generally recommended for dogs with class III using split dosage method, the mechanical extraction may be also beneficial for these dogs, if the dogs have severe clinical signs associated with heartworm dis- eases (HWD). Therefore, a mechanical worm removal is the choice of option for treating this condition in dogs (3-4,7).
Mechanical removal using retrieval devices (i.e., alligator forceps, a basket retrieval device or a loop snare device) has been successfully applied in the veterinary field (3,8-9). The main advantages of this method are the reduced invasiveness of the procedure, less damage to the vascular endothelium and a shorter duration of general anesthesia (3,4). Also a catheter- guided technique for worm removal using retrieval baskets and tripod forceps has been also applied in dogs with heavy worm burden (4). These techniques have been known to improve access to the pulmonary arteries and to minimize vascular and intra-cardiac damage often associated with blind grasp-
ing of the retrieval forceps.
Case
The first case was 5-year-old intact mixed male dog weigh- ing 9.5 kg and having major complaints of severe cough, abdominal distension, exercise intolerance and cachexia. In the physical examination, muffled cardiac and pulmonary sounds, split S2 and a glade V/VI regurgitant murmur were heard over the right and left apex and base. The dog appeared ade- quately hydrated, mucous membranes were pale, and capillary refill time was > 2 seconds. Respiratory rate was 50 breaths/
min, and systolic blood pressure (Doppler method) was 125 mmHg. Laboratory tests revealed hypochromic anemia (packed cell volume 16.7%, reference range 37~55%; hemoglobin 5.2 g/dL, reference range 12~18 g/dL), leukocytosis (total number of white blood cells, 33.4 K/uL, reference range 6~17 K/uL), severe azotemia (BUN, 108.2 mg/dL, reference range 7~25 mg/
dL), hyperglycemia (143 mg/dL, reference range 60~120 mg/
dL), and high alkaline phosphatase activity (143 mg/dL, re- ference range 60~120 mg/dL). He was positive in heartworm antigen test (SNAP 4Dx; Idexx, USA) for adult worms and modified Knot’s test for microfilaria. Electrocardiogam re- vealed normal sinus rhythm with tachycardia. Thoracic radio- graphy revealed pleural effusion obscuring cardiac silhouette (Fig 1A). Emergency thoracocentesis was performed at the right hemithorax and removed 250 mL reddish fluid. The thoracic radiography taken after thoracocentesis revealed ‘re- vered D shaped heart’ indicating the dilation of right ventricle and main pulmonary artery (Fig 1B). Although the
1Corresponding author.
E-mail: hyun5188@kangwon.ac.kr
lung field was relatively clear, there was marked dilation of caudal pulmonary arteries (Fig 1B). Two-dimensional echo- cardiography revealed right atrial and ventricular enlargement,
marked dilation main pulmonary artery (Fig 2A), marked thickening and flattening of interventricular septum (Fig 2B) and hyperechogenic heartworms moving between the right ventricle and right atrium (Fig 2). Color and spectral Doppler echocardiography also revealed tricuspid (4.5 m/s) and pul- monic regurgitation (3.7 m/s; Fig 3).
The second case was a 4-year-old intact mixed male dog weighing 4.2 kg and having major complaints of hemoglo- binuria, mild cough, exercise intolerance and anorexia. Heart auscultation revealed a grade IV/VI systolic regurgitant mur- mur in the right and left chest. The main laboratory findings were hypochromic anemia (packed cell volume 26.3%, re- ference range 37~55%; haemoglobin 9.1 g/dL, reference range 12~18 g/dL), hyperbilirubinemia (bilirubin, 1.4 mg/dL, refer- ence range 0.3~0.9 mg/dL), and prerenal azotemia (blood urea nitrogen, 32 mg/dL, reference range 7~25 mg/dL; creatinine, 1.8 mg/dL, reference range 0.6-1.4 mg/dL). He was positive in heartworm antigen test (SNAP 4Dx; Idexx, USA) for adult worms and modified Knot’s test for microfilaria. Thoracic radiography revealed a right-sided cardiomegaly with marked dilation of pulmonary arteries and diffuse interstitial pulmonary infiltration. Two-dimensional echocardiography revealed right atrial and ventricular enlargement and marked thickening and flattening of interventricular septum (due to a marked elevation Fig 1. Ventrodorsal projection of thoracic radiography in dog 1.
(A) Pleural effusion was obscuring cardiac silhouette in this dog.
(B) After emergency thoracocentesis, the thoracic radiography revealed ‘revered D shaped heart’ indicating the dilation of right ventricle and main pulmonary artery. However the lung field was relatively clear, although there was marked dilation of caudal pulmonary arteries.
Fig 2. Echocardiography of dog 1. (A) Right parasternal short axis view at pulmonary artery level: There were right atrial and ven- tricular enlargement, marked dilation main pulmonary artery, and hyperechogenic heartworms (arrow) moving between the right ventricle and right atrium. (B) Right parasternal short axis view at papillary muscle level: There was marked enlargement of right ventricle, marked thickening and flattening of interventricular septum. Hyperechogenic clumps (suspecting heartworms; arrows) were clearly visible from the ventricle. RV, right ventricle; LV: left ventricle, MPA, main pulmonary artery, Ao: aorta.
Fig 3. Echocardiography of dog 1. (A) Color Doppler echocardiography revealed pulmonic regurgitation. (B) Spectral Doppler echocardiography confirmed pulmonic regurgitation with maximal velocity of 3.7 m/s (pressure gradient ~50 mmHg).
of right ventricular pressure). Hyperechogenic clumps (sus- pecting adult heartworms) moving between the right ventricle and right atrium were clearly visualized by echocardiography (Fig 4A and 4B). Color and spectral Doppler echocar- diography revealed high-velocity regurgitation jet flow across
the tricuspid (4.2 m/s) and pulmonic valves (3.1 m/s) indicating severe pulmonary hypertension.
Prior to mechanical heart worm removal, the dogs were premedicated with prednisolone (0.5 mg/kg, BID, PO; Dae- woo, Korea), doxycycline (5 mg/kg, BID, PO; Pfizer, USA) and clopidogrel (2 mg/kg, SID, PO; Sanfi-Aventis, France) for 1 week. For surgical anesthesia, the dogs were premedi- cated with tramadol (2 mg/kg, subcutaneous administration, Daewoong, Korea) and butorphanol (0.2 mg/kg, intramuscular administration, Myungmun, Korea), with subsequent induc- tion of propofol (induction 6 mg/kg, intravenous administra- tion; Handok, Korea) and maintenance of 2-5% isoflurane with oxygen. The right jugular vein was exposed for inser- tion of the extract brush (Figs 5, 6). The extraction brush was inserted into the right atrium under echocardiographic guid- ance. After insertion of the extraction brush, we rotated the brush 4-5 times, and then gently pull out the brush. The pro- cedure was repeated until no worms were visible by echocar- diography. From the first case of dog, 21 heartworms were removed (Fig 7), while 15 heartworms were removed from the second case of dog. After heartworm removals, the right jugular vein was ligated and the skin was closed routinely.
Both dogs were recovered from anesthesia without complica- tion. Clinical signs associated with caval syndrome (i.e. hemo- Fig 4. Echocardiography of dog 2. (A) Right parasternal short axis view at pulmonary artery level: There were right atrial and ventricular enlargement and hyperechogenic heartworms (arrow) moving between the right ventricle and right atrium. (B) Right parasternal long axis view: There was marked enlargement of right ventricle. Hyperechogenic clumps (suspecting heartworms; arrows) were clearly visible from the ventricle. RA, right atrium; RV, right ventricle; LA, left atrium, LV: left ventricle, HW, heartworm.
Fig 5. Extraction brushes used in this study. (A) The first brush was made of frame of surgical wire (No. 500) threaded with 3-0 maxon (each 6 cm in length) (B) The second brush was made of frame of feeding tube (5 Fr) threaded with 3-0 maxon (each 6 cm in length).
Fig 6. Mechanical heartworm removal using extraction brushes. (A) Insertion of extraction brush (made of surgical wire) into the exposed right jugular vein. (B) Insertion of extraction brush (made of feeding tube) into the exposed right jugular vein.
globinuria, pleural effusion, exercise intolerance) were re- markably improved from the next day after heartworm re- moval. Although the echocardiography revealed complete worm removals from the right atrium and ventricle (Fig 8A), there was residual worms at pulmonary artery (Fig 8B) in dog 2. Both dogs were treated with prednisolone (0.5 mg/kg, BID, PO), doxycycline (5 mg/kg, BID, PO), and clopidogrel (2 mg/kg, SID, PO) for a week, to prevent complications from surgical worm removal and heartworm related diseases.
Both dogs were treated with heartworm preventives (Revolu- tion; Pfizer, USA) after one month of mechanical worm removal. Furthermore the adultcidal therapy using standard protocol were performed using melarsomine (2.5 mg/kg, IM, Merial, USA) for treating residual infection after the dogs were fully recovered.
For percutaneous heartworm removal, several catheters such as alligator forceps, flexible alligators, basket catheters, snares, and horsehair brushes have been widely used (3). The extraction brush used in this study was similar to horsehair brush which was used in heartworm removal from the pul- monary artery of cat (9). A main obstacle of horsehair brush was that only small number of worms can be retrieved. For
animals with heavy worm burden, it still required other type of retrieval devices (i.e. alligator forceps or baskets). In this study, we developed two forms of modified extraction brushes which were more flexible and cheaper. Since the brushes were made with either feeding tube or surgical wire and 3-0 maxon (each 6 cm in length), the cost for brush is relatively cheaper than any other retrieval devices. Also these brushes can be made instantly before mechanical heartworm removal.
Furthermore the flexibility of this extraction catheter was able to minimize intracardiac damages by the mechanical heart worm removal. Although the fluoroscopic guidance might be shorten the time for complete worm removal, the echocardio- graphic guidance was also able to remove heartworms from the right cardiac chambers. However, one problem for this method was that there was no control knob (aids) for inserting this brush into pulmonary artery. Therefore, for the removal of heartworms from the pulmonary arteries, other retrieval devices were necessary. In this study, we also found a few worms were still visible at the pulmonary arteries after heart- worm removal, although the clinical signs were markedly improved after the heartworms were removed from right atrium and ventricle. We used adulticidal therapy for residual infection rather than mechanical heartworm removal using other retrieval devices. Fortunately, two dogs were success- fully treated with this method. However, further study will be necessary to improve the insertion of extraction brush into pulmonary artery.
In conclusion, we developed new heartworm removal method using modified extraction brushes and successfully treated dogs with caval syndrome using this heartworm removal method.
References
1. Nelson CT, McCall JW, Rubin SB, Buzhardt LF, Dorion DW, Graham W, Lonqhofer SL, Guerrero J, Robertson-Plouch C, Paul A. 2005 Guidelines for the diagnosis, prevention and management of heartworm (Dirofilaria immitis) infection in dogs. Vet Parasitol 2005; 133: 255-266.
Fig 7. Heartworms removed from the dog 1.
Fig 8. Echocardiography taken one day after heartworm removal from the dog 2. (A) Left apical four chamber view: There were no heartworms visible at right atrium and ventricle. (B) Right parasternal short axis view, pulmonary valve level: There still was marked dilation of main pulmonary artery. Also there were few worms still visible at pulmonary artery. RA, right atrium; RV, right ventricle;
LA, left atrium, LV: left ventricle; Ao; aorta, PA; pulmonary artery.
2. Bové CM, Gordon SG, Saunders AB, Miller MW, Roland RM, Achen SE, Drourr LT, Boqqess MM. Outcome of mini- mally invasive surgical treatment of heartworm caval syn- drome in dogs: 42 cases (1999-2007). J Am Vet Med Assoc 2010; 236: 187-192.
3. Atkins C. Canine heartworm disease. In: Ettinger SJ, Feldman EC, eds. Textbook of veterinary internal medicine. 6th ed.
Philadelphia: Elsevier Inc. 2005; 1118-1136.
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5. Calvert CA, Rawlings CA, McCall J. Canine heartworm disease. In: Fox PR, Sisson D, Moise NS, eds. Textbook of canine and feline cardiology. 2nd ed. Philadelphia: WB Saunders Co. 1999; 702-726.
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life cycle, pathophysiology, and diagnosis. Compend Contin Educ Pract Vet 2008; 30:133-140.
7. Arita N, Yamane I, Takemura N. Comparison of canine heart- worm removal rates using flexible alligator forceps guided by transesophageal echocardiography and fluoroscopy. J Vet Med Sci 2003; 65: 259-261.
8. Lee SG, Moon HS, Hyun C. Percutaneous heartworm removal from dogs with severe heart worm (Dirofilaria immitis) in- festation. J Vet Sci 2008; 9: 197-202.
9. Glaus TM, Jacobs GJ, Rawlings CA, Watson ED, Calvert CA. Surgical removal of heartworms from a cat with caval syndrome. J Am Vet Med Assoc 1995; 206: 663-666.
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카발신드롬에 이환된 2마리의 개에서
modified extraction brushes를 이용한 심장사상충 제거술
이성욱*,**·박종훈**·현창백**1
*수완동물병원, 광주광역시 수완동 1452번지, **강원대학교 수의과대학 소동물 내과교실
요 약 : Caval syndrome은 감염된 다수의 심장사상충이 우심방, 우심실을 포함한 우심계와 대정맥으로 이동하여 삼첨 판의 움직임을 물리적으로 방해하고 폐동맥으로 가는 혈류의 장애를 유발하여 생명을 위협하는 질환이다. 이 질환의 치료를 위해 외과적인 사상충의 제거가 필요하다. 본 증례는 modified extraction brushes를 이용한 새로운 방법의 심 장사상충 제거 방법에 대한 보고이다. 본 연구에서 새롭게 만들어진 사상충 제거 카테터를 사용하여 caval syndrome 에 감염된 두 마리의 개를 성공적으로 치료하였다. 비록 새로운 시술법의 적용이 단지 두 증례에 불과하지만, 본 시술 법은 심장 사상충 치료를 위한 외과적 제거방법 중 하나로 선택할 수 있다.
주요어 : modified extraction brush, 카발신드롬, 심장사상충, 외과적 사상충 제거
