Infundibular pulmonic stenosis in a Moluccan cockatoo (Cacatua moluccensis).
Key words: foot clenching, cardiac outflow obstruction, subvalvular disease, congenital heart disease, atherosclerosis, bird, avian, Moluccan cockatoo, Cacatua moluccensis
A 31-year-old female Moluccan cockatoo (Cacatua moluccensis) was presented to the William R. Pritchard Veterinary Medical Teaching Hospital of the University of California, Davis, for a 4-month history of episodic foot clenching and disorientation. The bird had a historical left-sided wing droop for an unknown period of time and had been unable to fly since adoption by the current owners 13 years previously. The bird had been fed a seed-only diet before its adoption. The current diet was 25% pelleted food (Harrison's Adult Lifetime Course, Brentwood, TN, USA) and 75% high-fat table food such as cheese and pancakes, as well as fruits. Foot-clenching episodes were observed once per week, occurred on either side, and lasted approximately 1 to 3 minutes. During the episodes, the bird appeared moderately disoriented but did not appear to be in pain and was able to put weight on the spastic leg. The referring veterinarian evaluated the bird at the onset of clinical signs without identifying significant findings on the physical or neurologic examination. A therapeutic trial of calcium glubionate (60 mg/kg PO q24h for 30 days) and meloxicam (0.3 mg/kg PO, frequency unknown, for 21 days) was associated with a decreased frequency of clenching episodes. However, the signs eventually became more frequent, and the cockatoo fell from the perch the day before presentation.
On presentation, the bird was bright, alert, and responsive. Visual examination revealed a purposeful, symmetric, and coordinated gait, as well as a left wing droop at the level of the elbow. The bird was nervous, and physical examination was performed under sedation with midazolam (1 mg/ kg IM) and butorphanol (1 mg/kg IM; Torbugesic, Fort Dodge Laboratories Inc, Madison, NJ, USA) to reduce restraint-associated stress. An area of feather loss was present over the right carpus. Primary feathers were worn at the margins, with discontinuous barbules between barbs, and the calamus was occasionally pinched. The bird weighed 805 g with an optimal body condition score of 4/7 and was appropriately hydrated. (1) The heart rate of 260 beats/min was regular and within the reference interval (222-545 beats/min) (2) without identifiable murmurs or arrhythmias. Ulnar vein refill time was less than 1 second, and the mucous membranes were pink. Examination of the oropharyngeal cavity revealed severely blunted choanal papillae, and ophthalmologic evaluation showed bilateral immature cataracts. Musculoskeletal evaluation of pelvic limbs revealed no abnormalities, but extension of the left carpus was reduced by 80%. No appreciable neurologic deficits were noticed, as the bird had symmetric strong grip, normal proprioception, and normal sensation. Whole-body survey radiographs were obtained under sedation as described above. Degenerative joint disease of several thoracic intervertebral joints was noted (Fig 1). Thoracic and pelvic limbs showed no osteoarticular lesions. A 3-mL blood sample was collected from the right jugular vein for a complete blood count, plasma biochemical analysis, and toxicologic screening. Results of the complete blood cell count and biochemical analysis were within reference intervals. (3) Toxicologic screening and trace element analysis revealed lead and copper concentrations under detectable limits. The plasma copper concentration was under the detectable limit of 0.1 pprn (reference interval, 0.07-0.33 ppm), (4) and potential hypocupremia was considered.
The bird was discharged with recommendations to increase dietary copper through incorporation of peas, sweet potatoes, and grapes in the ration and to provide a more balanced diet. Monitoring of foot-clenching episodes for frequency and duration was also recommended. Nonsteroidal anti-inflammatory therapy was considered but was not initiated because clinical signs had resolved. After a diet change and 6 months without exhibiting clenching signs, the bird was re-examined because of intermittent knuckling, affecting alternatively one foot or the other without perceived pain or disorientation. The affected foot was described as paretic. These episodes of foot weakness were recorded every 2 days during the 10 previous days and lasted between 2 and 5 minutes. Episodes were occasionally associated with head shaking. Physical examination revealed no other abnormalities compared with the evaluation during the first visit. Plasma biochemical analysis, trace element concentration, and a lipoprotein panel were performed. The only abnormality was plasma copper concentrations again below the detectable limit. (4)
The bird was sedated with midazolam (1 mg/kg IM) and butorphanol (1 mg/kg IM). Crystalloid fluids (lactated Ringer's solution, 60 mL/kg SC) were administered during sedation. Indirect systolic arterial pressure was measured 3 times with a no. 2 neonate cuff on the left pelvic limb without removing the cuff between measurements (5); the mean value was considered normal at 105 mrnHg (reference interval, 104-197 mm Hg). (6) At that time, radiographic review of the radiographs taken 6 months prior suggested mild pulmonary trunk enlargement on the lateral view (Fig 1A and B).
Echocardiography was pursued to investigate potential cardiovascular causes for the clinical signs. A transcoelomic ventromedial approach was elected, and the sedated bird was held between dorsal and upright recumbency as previously described. (7) Maximal velocity through the aortic valve was normal (0.94 m/s; reference value, 0.78 [+ or -] 0.19 m/s). (7) The right ventricle was mildly to moderately dilated, and this chamber could be seen on both sides of the left ventricle in standard longaxis views. All right ventricular measurements exceeded the published means for cockatoos. (8) Right ventricular long-axis systolic dimension measured 11.7 mm (reference value, 10.3 [+ or -] 1.2), and diastolic dimension was 15.6 mm (reference value, 11.3 [+ or -] 2.3). The right ventricular transverse measurement in systole was 3.6 mm (reference value, 2.3 [+ or -] 0) and in diastole was 4.9 mm (reference value, 3.5 [+ or -] 0.5), giving a fractional shortening within the reference interval (26.5%; reference value, 33.3 [+ or -] 10.3%). Subjective assessment of the right atrioventricular valve was unremarkable. Hepatic parenchyma and hepatic veins subjectively showed no sign of congestion. Right atrial dimensions were subjectively normal. Turbulent flow of unknown origin was identified in the right ventricular outflow tract (RVOT) (Fig 2A). However, spectral Doppler tracing could not be obtained because of poor alignment limited by patient size and imaging windows. Further Doppler evaluation identified trivial mitral regurgitation with a centrally directed jet. Aortic valve regurgitation was also noted and characterized by a peak aortic regurgitation velocity of 5.07 m/s and a pressure half-time of aortic regurgitation of 584 ms with no overt left-sided chamber enlargement (Fig 2B). Left ventricular long-axis measurements were normal in both diastole (19.9 mm; reference value, 19.4 [+ or -] 1.8 mm) (8) and systole (17.8 mm; reference value, 18.9 [+ or -] 1.7 mm). (8) The left ventricular transverse measurements were also normal in diastole (8.3 mm; reference value, 8.8 [+ or -] 1.8 mm) and in systole (5.5 mm; reference value, 6.6 [+ or -] 1.7 mm), giving a fractional shortening within the reference interval (33.7%; reference value, 25.6 [+ or -] 7.0%). (8) Left atrial dimensions were subjectively normal. Although the proximal aorta appeared dilated, outflow velocities were normal. There was some echo dropout at the level of the interventricular septum, and the aortic insufficiency was seen to course in this direction. The absence of a ventricular septal defect was confirmed with a bubble study; 3 mL of microaerated saline was injected through a 24-gauge catheter placed into the right medial metatarsal vein. No bubbles were seen within the left atrium, left ventricle, or aorta, which ruled out a right-to-left shunt. Additionally, no negative contrast effect was seen within the contrast-enhanced right ventricle, excluding the presence of any left-to-right ventricular shunting. A rhythm strip electrocardiogram was recorded under sedation throughout the echocardiogram and revealed a sinus rhythm and normal-appearing complexes. (2)
The bird was discharged with owner instructions to decrease fat content and increase vegetables like dark leafy greens, celery, and carrots in the diet. Advanced diagnostic imaging, such as nonselective fluoroscopic angiography or computed tomography angiography, was recommended but declined by the owners. Because no treatable condition had been identified, environmental modifications were recommended to prevent traumatic injury in case the bird fell.
The cockatoo was presented again after a 3-week period during which episodes of unilateral clenching and weakness of the right and left feet were observed every 2 days and lasted 1-5 minutes. Physical examination findings were unchanged except that the right pelvic limb was weak and showed muscle atrophy. Blood copper concentration was measured and revealed normal cupremia (0.33 ppm) (4)
Nonselective fluoroscopic angiography was pursued to further assess the right heart enlargement, mildly dilated aorta, source of RVOT turbulence, and a potential vascular cause for intermittent foot weakness and spasticity. The bird was premedicated as described above and induced with isoflurane in oxygen (1.25% in 1 L/min) by face mask, then intubated and maintained on anesthesia with 2% isoflurane. During anesthesia, the cockatoo was monitored via capnography and pulse oximetry and received crystalloid fluids (10 mL/kg per hour; lactated Ringer's solution) through a 24-gauge catheter placed into the left ulnar vein. The bird was positioned in right lateral recumbency, and C-arm fluoroscopy (OEC 9800 unit, General Electric, Waukesha, WI, USA) was done. A nonionic iodinate contrast medium (1.4 mL total volume; 760 mg/kg IV; Isovue-300, Bracco Diagnostics Inc, Princeton, NJ, USA) was administered at a constant rate of 1-2 mL/kg per minute through the catheter placed in the left ulnar vein during video acquisition. (9) Video loops were acquired throughout the injection and until contrast was observed to clear the left side of the heart. The bird was then placed in ventrodorsal recumbency, and the same procedure was repeated after injection of a second bolus of contrast media. Total dose of injected iodinate contrast medium was 840 mg. Lateral and ventrodorsal angiograms showed a narrowing proximal to the pulmonic valve in the infundibular region of the RVOT. This narrowing was persistent throughout the angiogram and did not appear to be dynamic, consistent with an infundibular pulmonic stenosis. Poststenotic dilation of the pulmonic trunk and proximal main pulmonary arteries were also noted. Mild luminal narrowing was observed in the descending aorta after the arch (Fig 3A and B). The diagnosis was infundibular pulmonic stenosis with poststenotic dilatation of the proximal pulmonary trunk. Additionally, narrowing of the aortic lumen diameter associated with epidemiologic data was suggestive of atherosclerosis. The bird was discharged without medication and experienced a few clenching episodes in the days after the last visit. An annual follow-up was recommended to the owner as well as a regular monitoring every 6-12 months with ultrasonographic recheck to evaluate development of right-sided congestive heart failure. The client elected not to return the bird for a recheck examination. The owners reported that clinical signs have not recurred during the 18month follow-up period.
This report describes the diagnosis of infundibular pulmonic stenosis in a Moluccan cockatoo and illustrates ancillary imaging modalities that can be used in avian cardiology. To our knowledge, this is the first case of infundibular pulmonic stenosis reported in a bird.
The RVOT, or infundibulum, is the outlet structure of the right ventricle carrying blood from the right ventricle to the pulmonary trunk. In mammals, the infundibulum refers to the anatomic region precisely located between the supraventricular crest and the pulmonic valve. Avian heart anatomy differs in many aspects from its mammalian counterpart, but the RVOT is similar in both taxonomic groups, (10) except that the singular right atrioventricular valve functionally replaces the supraventricular crest. (11) The pulmonic valve has 3 semilunar cusps and prevents regurgitation from the pulmonary trunk into the right ventricle during diastole. The pulmonary trunk is short and rapidly divides into the left and right pulmonary arteries.
Pulmonic stenosis refers to a narrowing of the RVOT or downstream structures and can be classified as submandibular, infundibular, valvular, or supravalvular. (12) Regardless of their precise localization, stenotic lesions share pathophysiologic similarities, as they functionally divide the right ventricle into a proximal high- and a distal low-pressure chamber, leading to muscular hypertrophy of the chamber proximal to the obstruction. (13) In birds, the right atrioventricular valve consists of a muscular flap of myocardium. (10) Right ventricular hypertrophy has been associated with hypertrophy of the muscular right atrioventricular valve in chickens with pulmonary hypertension. (14) This situation results in atrioventricular regurgitation, which leads to right-sided congestive heart failure. The same pathophysiology is expected to occur regardless of the primary cause of right ventricular wall hypertrophy. (15) In people, subvalvular pulmonic stenosis tends to worsen with time and may be discovered in adulthood only when signs manifest. (16)
In people and dogs, infundibular pulmonic stenosis is frequently congenital and associated with other congenital abnormalities, such as ventricular septal defect or tetralogy of Fallot. (16,17) In this cockatoo, a congenital cause of stenosis was considered most probable. Other potential causes are upstream pressure overload generating asymmetric right ventricular hypertrophy, isolated right ventricular hypertrophic cardiomyopathy, neoplasia, or granuloma. In this bird, these causes were considered extremely unlikely with regards to ultrasonographic findings and the clinical history. No other congenital lesions were identified by echocardiography or angiographic studies. Isolated infundibular pulmonic stenosis is a rare congenital disorder representing 0.45% of congenital heart disease in people, (18) whereas subvalvular stenosis has been reported to account for 1.98% of congenital heart disease in dogs. (19) Two large-scale retrospective studies of postmortem findings in psittacine birds identified no congenital cardiac abnormalities. (15,20) Congenital cardiovascular anomalies have been seldom reported in birds. (21) Reports of narrowing of the outflow tract in birds are rare and are limited to left outflow tract narrowing associated with a ventricular septal defect in a Moluccan cockatoo (22) and subaortic valvular stenosis associated with mitral stenosis in a duck (Anas platyrhynchos). (23) The diagnostic confirmation of infundibular pulmonic stenosis relies on visualizing the RVOT narrowing. Further diagnostic testing aims to provide information such as location, severity, and nature of the stricture and its association with other cardiac abnormalities. These parameters are associated with prognosis and are mandatory to adapt therapeutic strategy. Electrocardiography can show right axis deviation in people and in cats and dogs suffering from RVOT obstruction.
Foot clenching and weakness have been described in birds with cardiovascular disease (endocarditis, atherosclerosis), (24,25) poisoning (organophosphate, heavy metal), (26) orthopedic abnormalities (appendicular fracture, spinal trauma, degenerative joint disease), (27) metabolic abnormalities (hypocalcemia, hypovitaminosis B2, vitamin E and selenium deficiency), and neurologic disease (infectious or parasitic polioencephalomyelitis, poliomalacia, and ischiatic nerve compression), (28) but some cases remain idiopathic. In this case, degenerative joint disease of multiple intervertebral joints was observed radiographically and could account for the neurologic signs observed in the case of spinal cord compression. However, the intermittent expression of clinical signs occasionally associated with disorientation, considered along with the history, physical examination findings, and diagnostic test results, increased the presumption of a vascular disorder. Clinical signs of right ventricular outflow obstruction are unknown in birds. In mammals, infundibular stenosis can be subclinical or associated with nonspecific clinical signs such as exercise intolerance, (29) dizziness, dyspnea, and syncope. (30) It is unlikely that the infundibular pulmonic stenosis would result in the clinical signs expressed by the bird, but atherosclerotic lesions of the aorta or vessels of the hind limbs as well as thromboembolic disease could lead to insufficient perfusion of the extremities. (25)
In one study of infundibular pulmonic stenosis in cats, radiographs were found to have poor sensitivity in diagnosis. (12) Radiographs can reveal nonspecific signs of congestive heart failure, great vessel dilation, or chamber enlargements. Reference values of radiographic cardiac silhouette measurements have been established in various psittacine species, but not in cockatoos. The anatomy of clavicular and cranial thoracic air sacs in Cacatua species provides normal negative contrast, allowing for better cardiac visualization. (31) However, definitive diagnosis and thorough evaluation of infundibular pulmonic stenosis require more advanced imaging techniques.
Echocardiography is crucial to demonstrate and localize stenosis accurately, and in people, it has a detection rate of 72%-95%. In the case of infundibular stenosis, 2-dimensional imaging can reveal muscular hypertrophy proximal to the stenosis or systolic fluttering of the pulmonary valve. (32) While color Doppler allows for assessment of flow turbulence, continuous-wave Doppler helps in estimating pressure gradients and severity of the obstruction. (2). Two-dimensional transcoelomic echocardiography (TCE) and reference intervals have been described in psittacine species, including cockatoos. (7,8) However, echocardiographic measurements are not highly reliable in birds, and the RVOT is difficult to evaluate because it is curved in a spiral fashion from the right ventricle along the interventricular septum cranially and then abaxially to the lungs, and the imaging windows that can be obtained from TCE are highly dependent on patient cooperation and size. (20,33) In the case we describe, TCE revealed abnormalities leading to the suspicion of infundibular stenosis, but this procedure was not sufficient to provide a definitive diagnosis. Transesophageal echocardiography (TEE) is recommended in mammals to improve ultrasonic image quality and Doppler-derived systolic pressure gradients. (30) Although reference values have not been published, TEE has been used successfully in birds. However, the procedure is not recommended in psittacine birds weighing less than 900 g because of the risk of esophageal perforation. (34) The risk-benefit ratio of TEE was considered too high in this cockatoo. Therefore, nonselective angiography was elected as the safest diagnostic procedure.
Nonselective fluoroscopic angiography has been described in avian medicine to evaluate heart chambers and vascular structure in real time. (9) It is different from traditional selective angiography, where catheters are directed through the vessels into the chamber of interest and contrast is delivered within the heart or vascular structure of interest. (35) In nonselective angiography, the contrast is injected peripherally through a venous catheter and carried to the right and subsequently left side of the heart. This technique is less selective but provides good resolution in small patients with rapid heart rates such as cats and birds. This technique cannot replace echocardiography but can provide complementary information when anatomic constraints limit echocardiographic evaluation. (36) Because of the rapid heart rate, evaluation of cardiac contractility in birds may be difficult. However, it is possible to detect ventricular hypertrophy or dilation, atrial dilation, vessel or cardiac valve stenosis, and vascular aneurysms. (36) Other imaging options, such as magnetic resonance imaging and computed tomography (CT), are used in human, (37) canine, (29) and feline (38) patients because these techniques provide excellent anatomic detail and 3-dimensional reconstitution, as well as precise functional data. (37) In birds, computed tomography is efficient to evaluate walls and lumens of the great vessels and to perform 3-dimensional reconstruction of the heart. However, detailed evaluation of the chambers can be limited by motion artifacts. (9) This modality failed to diagnose a pericardial mesothelioma extending from the atria to the ventricles and infiltrating the myocardium in an Amazon parrot (Amazona auropalliata). (39) Fluoroscopy allows capture of 8 frames per second, avoiding the risk of missing the filling phase with CT. In human medicine, definitive diagnosis of a double-chambered right ventricle relies on cardiac catheterization to delineate high-pressure inflow and low-pressure outflow chambers, (16) but this procedure has not been reported in psittacine birds. Computed tomography was recommended in this patient to investigate spinal disorders related to degenerative joint disease, as well as stenosis of the aorta or its branches to the pelvic limbs, but further imaging was declined because of financial constraints.
Treatment of infundibular pulmonic stenosis in mammals is usually recommended when the abnormality is associated with hemodynamic compromise evidenced by severe tricuspid regurgitation, marked atrial enlargement, or high pressure gradients across the stenosis or when clinical signs are present. (40) Surgical options in people include surgical excision of the fibromuscular obstruction, balloon dilatation, (41) alcoholic ablation, (42) and stenting procedures. (43) Conventional therapy for dogs with severe RVOT stenosis often includes the use of oral beta-blockers to reduce the pressure gradient, reduce myocardial oxygen demand, improve coronary perfusion, and limit turbulence. Angiotensin-converting enzyme inhibitors or [beta]-blockers could have been of therapeutic benefit in this case, but they should be used with caution in birds because their effects on arterial blood pressure are not defined. Pharmacokinetics and pharmacodynamics of a few cardiovascular agents like enalapril, (44) digoxin, (45) furosemide, (46) and spironolactone46 have been studied in birds. Various empirical treatments have been reported for birds suffering from congestive heart failure, including furosemide, spironolactone, enalapril, pimobendan, (47) and supportive care. (48) In the case we describe, the bird showed no evidence of congestive heart failure. Cardiac supportive treatment was not indicated, and clinical signs resolved without specific treatment.
In this report we describe multiple cardiovascular abnormalities in a cockatoo with concurrent intermittent foot clenching and weakness. This case illustrates the application of basic and advanced diagnostic imaging modalities in evaluating cardiac disease in a bird. More information regarding the prevalence and causes of structural cardiovascular disorders and their clinical significance in birds, as well as their respective natural histories, are required.
Graham Zoller, DVM, IPSAV, David Sanchez-Migallon Guzman, LV, MS, Dipl ECZM (Avian, Small Mammal), Dipl ACZM, Noemie Summa, DVM, IPSAV, Krista A. Keller, DVM, Dipl ACZM, Sarah J. Silverman, DVM, Dipl ACVIM (Cardiology), and Joshua A. Stern, DVM, PhD, Dipl ACVIM (Cardiology)
From the Exotic Pet Department, Centre Hospitalier Veterinaire Fregis, 43 avenue Aristide Briand 94110 Arcueil, France (Zoller); and the William R. Pritchard Veterinary Medical Teaching Hospital (Summa, Keller. Silverman) and Department of Medicine and Epidemiology (Guzman, Stern), School of Veterinary Medicine, University of California, Davis, Davis, CA 95616, USA. Present address: BluePearl Veterinary Partners, 820 W Frontage Road, Northfield, IL 60093, USA (Silverman); Vida Veterinary Care, 4175 East Warren Avenue, Denver, CO 80222, USA (Keller).
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Caption: Figure 1. (A) Ventrodorsal radiographic view of a Moluccan cockatoo with thoracic intervertebral degenerative joint disease lesions. (B) Right lateral radiographic view of the same Moluccan cockatoo showing the thoracic intervertebral degenerative joint disease and mildly enlarged pulmonary trunk (arrow).
Caption: Figure 2. (A) A transcoelomic ventromedial 2dimensional and color Doppler image of the cockatoo described in Figure 1. Blood flow is seen going away from the transducer in 2 outflow tracts. The laminar pure blue flow is aortic outflow (*). The flow observed to the right is turbulent and displays multiple color signals (+). This turbulent flow is within the right ventricle but not optimized from this imaging window. (B) Continuous-wave spectral Doppler image obtained from a transcoelomic ventromedial approach depicting the high-velocity aortic regurgitation.
Caption: Figure 3. (A) Still frame in ventrodorsal view from nonselective angiography is captured at the time of peak right ventricular ejection in the Moluccan cockatoo described in Figure 1. Contrast-rich blood is seen to flow into the right atrium originating at the site of injection. The pulmonic trunk is dilated as a consequence of poststenotic turbulences. The left (L) and right (R) pulmonary arteries are labeled. (B) Still frames from nonselective angiography in a lateral view. The head is to the left of the images, (a) Capture at the time contrast flows into the right atrium, (b) Capture at the time of peak right ventricular ejection. Contrast medium is seen within the right atrium. A thin column of contrast is seen in the right ventricular outflow tract indicating infundibular narrowing (arrow). Poststenotic dilatation of the pulmonary trunk and the proximal pulmonary arteries are seen as these structures are opacified (*). The left and right pulmonary arteries overlap and faint contrast is seen to outline the vascular supply within the lungs, (c) A still frame from nonselective angiography capture during levophase when contrast has had time to return to the left ventricle. Left atrium and ventricle, pulmonary veins, left ventricular outflow, superimposed left and right brachiocephalic trunks, aortic root, and descending aorta are opacified with contrast. Note the mild narrowing of the contrast column within the descending aorta (arrow).
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|Author:||Zoller, Graham; Guzman, David Sanchez-Migallon; Summa, Noemie; Keller, Krista A.; Silverman, Sarah J|
|Publication:||Journal of Avian Medicine and Surgery|
|Date:||Mar 1, 2017|
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