CASE ROUTES h CARDIOLOGY h PEER REVIEWED Subclinical Subaortic Stenosis in a Golden Retriever Kursten Pierce, DVM, DACVIM (Cardiology) Colorado State University THE CASE THE CASE A 12-month-old intact female golden retriever is pre- Diagnostic investigation of the heart murmur via echo- sented for a wellness examination and to discuss the cardiography is discussed with the owner but declined pros and cons of breeding the patient versus pursuing due to the patient’s lack of clinical signs and the costs ovariohysterectomy. The owner would like her to pro- associated with additional testing. duce one litter of puppies prior to being spayed. What are the next steps? On physical examination, the patient is bright, alert, and responsive. She is extremely energetic with a good THE CHOICE IS YOURS … BCS (4/9) and appropriate musculature. Cardiovascu- CASE ROUTE 1 lar examination reveals pink mucous membranes, no To provide information on breeding and caring for a obvious jugular venous distension, and a normal heart pregnant bitch and neonatal puppies and plan to spay rate and rhythm with normal synchronous femoral the patient after the puppies have been weaned, go to pulses. Auscultation is difficult and brief because the page 28. patient is rambunctious and panting. Despite the pant- ing, she is eupneic with clear bronchovesicular sounds. CASE ROUTE 2 A grade II/VI left basilar systolic heart murmur is aus- To avoid providing additional recommendations cultated. A murmur had not previously been docu- regarding breeding and ovariohysterectomy to the mented at her puppy wellness visits. The owner has not owner until a diagnostic investigation with a cardiolo- observed any coughing, trouble breathing, exercise gist has been pursued, go to page 32. intolerance, or syncope at home, and the patient appears subclinically affected. November 2018 cliniciansbrief.com 27 CASE ROUTES h CARDIOLOGY h PEER REVIEWED weaned. On patient auscultation as part of the CASE ROUTE 1 preanesthetic examination for ovariohysterectomy, the same grade II/VI left basilar systolic murmur is Because the patient appears healthy and observed. The patient is in excellent health and subclinically affected by the soft murmur, encountered no complications during pregnancy or birth, so an ovariohysterectomy is pursued using you suspect an innocent, benign flow typical anesthetic and surgical protocols. murmur. There is no urgency to push for expensive echocardiography that may Clinical Considerations Incidental murmurs are common in small animals, reveal no abnormalities. Thus, you provide particularly in young dogs or dogs that may be sub- information on breeding and caring for a jected to high-stress environments,1,2 and deter- pregnant bitch and neonatal puppies and mining whether a grade I/VI to grade III/VI systolic murmur is pathologic (ie, structural cardiovascular plan to spay the patient after the puppies lesion is present) or nonpathologic (ie, functional have been weaned. or innocent murmur) based on auscultation alone can be difficult. Guidelines are available to help Case Progression determine the best approach for treating these mur- The pros and cons of echocardiography at this murs.3,4 Criteria such as a murmur that can be stage are discussed with the owner. Based on the heard at all times (at rest or with activity), that is location and intensity of the heart murmur and loud through the majority of systole, that is dia- the patient’s breed, the most likely differentials stolic or continuous in nature, that is grade III/VI include a benign aortic flow murmur and subclini- or higher intensity, or that is accompanied by cal subaortic stenosis (SAS). Even with mild SAS, abnormal heart sounds (eg, gallop rhythms, split dogs typically have a normal lifespan. The owner heart sounds, clicks, arrhythmias) is more likely to is relieved that the dog is likely to have a normal be pathologic in nature as compared with a murmur lifespan and elects not to spend additional money that is characterized as soft, focal, or short or with on echocardiography. a systolic murmur that is softer or absent at rest, which is more likely to represent a nonpathologic The patient is bred and uneventfully gives birth murmur. Localization of the point of maximal to 5 healthy puppies. The puppies are successfully intensity, timing, and grade of the murmur in con- junction with patient signalment can help either heighten or decrease the concern for any potential underlying cardiovascular disease. A grade II/VI murmur in a young healthy golden retriever, as in SAS is a common obstructive this patient, could represent a functional murmur congenital heart defect in or indicate a lesion such as mild SAS. Even if mild SAS is present, it is unlikely to substantially impact large-breed dogs, with a the lifespan and health of this patient.5,6 More strong prevalence in golden important clinical implications arise in patients 7 being considered for breeding. retrievers. SAS is a common obstructive congenital heart defect in large-breed dogs, with a strong preva- CHF = congestive heart failure lence in golden retrievers.7 Hereditary transmis- SAS = subaortic stenosis sion is suspected via an autosomal recessive trait.8 28 cliniciansbrief.com November 2018 Dogs with moderate-to-severe SAS are at an sary, their use is common among some cardiolo- increased risk for arrhythmias, sudden death, gists, in part due to the difficulty of treating infective endocarditis,9,10 and other complications endocarditis if it develops and the serious sequelae (eg, congestive heart failure [CHF]).5 that may result (eg, acute CHF, immune-mediated disease [eg, glomerulonephritis, polyarthritis], Anesthetic considerations for cardiac disease are thromboembolic disease, arrhythmias). Endocar- best determined via echocardiography to evaluate ditis can result in permanent damage to the car- the severity of the cardiovascular lesion and sec- diac valves, causing significant regurgitation, and ondary chamber enlargement, cardiac function, is difficult to treat due to the relatively avascular and fluid tolerance. General recommendations and composition of the heart valves. Therefore, anti- anesthetic goals for patients with underlying biotics are sometimes administered intra- and structural cardiac disease include maintaining postoperatively if there is a concern about an heart rate and limiting vasodilation. Extreme fluc- increased risk for endocarditis; it may be easier tuations in heart rate and blood pressure should (and less costly) to prevent endocarditis and/or be avoided. Tachycardia and hypertension should prophylactically treat it with antibiotics as com- be avoided in patients with aortic stenosis, as pared with treating the endocarditis itself. Antibi- there are fewer cardiovascular reserves and these otics should not be administered to every patient; extremes may worsen myocardial work against a the cardiologist should discuss with the pet owner fixed obstruction. the degree of risk for the development of endocar- ditis and determine appropriate antibiotic use It is important to maintain adequate preload and based on the severity of the lesion. optimize ventricular filling in patients with SAS or other underlying disease processes that can Outcome impair ventricular compliance (eg, hypertrophic The patient recovers from anesthesia and surgery cardiomyopathy). Inappropriate preload or volume uneventfully and is discharged the next day. Five contraction can contribute to myocardial oxygen days later, the patient is presented for evaluation deficit, which may precipitate arrhythmias. Car- of lethargy and inappetence. On auscultation, the diac output for these patients can be highly depen- grade II/VI systolic murmur is still present and a dent on heart rate; thus, bradycardia can result in new diastolic murmur is audible. Other examina- a significant decrease in cardiac output. Cardiac tion findings include hyperkinetic pulses with a output is a product of heart rate and stroke vol- wide pulse pressure and fever (104.1°F [40.1°C]). ume. Alternatively, tachycardia can result in Neutrophilia with a left shift and monocytosis are decreased coronary artery perfusion. present on CBC results. An echocardiogram reveals mild SAS with moderate aortic insuffi- The use of certain drugs that can alter hemody- ciency and aortic valve endocarditis. namics and/or precipitate arrhythmias should be avoided, including α2 agonists (eg, dexmedeto- midine), ketamine (due to increased myocardial oxygen demand), acepromazine, and anticholiner- gics (unless indicated for bradycardia).11 Because patients with SAS have an increased risk for endocarditis due to blood flow turbulence and Inappropriate preload or volume endothelial damage, prophylactic antibiotics contraction can contribute to (eg, cefazolin) are recommended intraoperatively. Although there is no evidence-based medicine to myocardial oxygen deficit, which support that postoperative antibiotics are neces- may precipitate arrhythmias. November 2018 cliniciansbrief.com 29 h h CASE ROUTES CARDIOLOGY PEER REVIEWED ® 30 mg/mL BRIEF SUMMARY: Before using this product, please consult the full product insert for more information. For oral use in dogs only The patient is hospitalized for 6 days for supportive care and treat- Appetite Stimulant ment. Paired blood cultures (obtained prior to starting antibiotics to Caution: Federal (USA) law restricts this drug to use by or on the order of a reduce the chance of a false negative result) are submitted, and amoxi- licensed veterinarian.