There are many indications for referral of patients with heart disease to a veterinary cardiologist, but there are also numerous scenarios that veterinarians encounter where referral is not a feasible option for pet owners. It is important to remember the goal when deciding how to approach a clinical situation where finances or other factors dictate minimal diagnostics and referral isn’t possible.
Usually this goal is to identify patients who are at risk for adverse outcomes and to intervene if possible.
Detecting those patients with heart disease is the first step; patient profiling, good history taking and physical examination can go a long way towards determining which tests will provide the best value. It is helpful to formulate several plans that can be used depending on the resources available. Radiographs are accessible in most situations and so it is helpful to understand what radiographs can and can’t determine when it comes to diagnosing heart disease. Radiographs are useful for distinguishing ACVIM Stage B1 from B2 disease in dogs with preclinical mitral valve disease and are the test of choice for diagnosis of congestive heart failure. Therefore, radiographs are a very good choice for staging of dogs with mitral valve disease. Although they are not useful for evaluating cardiac function or internal size, in most instances, thoracic radiographs can provide sufficient information to formulate a treatment plan for dogs and cats, even if a definitive cardiac diagnosis is not known. Several studies have shown that thoracic radiographs can detect Stage B2 in dogs if conservative cutoffs are used (VHS >11.5, VLAS >2.3), therefore allowing the clinician to practice evidence-based medicine to start pimobendan in Stage B2 dogs with mitral valve disease. Thoracic radiographs are also very useful for understanding the cause of cough in dogs with heart disease, which in many cases is due to concomitant airway disease or mainstem bronchus compression.
Home resting respiratory rate monitoring allows for early detection of congestive heart failure by the owner in the home environment. If the veterinarian and owner have good communication, mild increases in resting respiratory can trigger an early discussion about medication adjustments which might prevent the need for hospitalization and associated expenses. Most healthy dogs and dogs with controlled congestive heart failure have resting or sleeping respiratory rates below 30/minute, so increases above that or significant changes from the dog’s baseline might indicate the development of congestive heart failure. This is a simple and powerful monitoring tool in the home environment.
Thoracic radiographs can also be useful for detection of cardiomegaly and congestive heart failure in cats, although diagnosis of the specific underlying cardiomyopathy requires echocardiography. However, since no medications have been shown to delay progression in preclinical disease, this information is not essential to initiate close monitoring of the cat and clopidogrel.
If radiographic cardiomegaly is present, then the left atrium is likely enlarged which carries a risk of thromboembolic disease; therefore, even without knowledge of the cardiomyopathy type, anti thrombotic therapy is likely indicated.
For dyspneic or tachypneic cats, thoracic radiographs provide confirmation of congestive heart failure. The SNAP NTproBNP test can be helpful in the emergency situation when it is unclear if the cat is dyspneic from respiratory disease or congestive heart failure.
Cage-side ultrasound (POCUS, TFAST) can be viewed as an extension of the physical examination and has a role in rapid diagnosis and treatment of dogs and cats presented for acute signs of heart disease, usually in the emergency setting. Body cavity effusions might indicate congestive heart failure if other findings corroborate severe heart disease. Left atrial size, left and right ventricular size, and subjective assessment of function utilize basic views to help the clinician rapidly determine if heart disease is severe enough to cause the clinical signs. With basic training, clinicians can become comfortable utilizing cage side ultrasound in the emergency setting to rapidly direct treatment. This should be viewed as complementary to the exam and thoracic radiographs with the understanding that a full echocardiogram is needed to evaluate all aspects of cardiac size and function and come to a definitive diagnosis.
Despite best efforts, there are some instances where referral to a cardiologist is needed to adequately diagnose or treat patients. These situations include a loud or persistent murmur in a young animal suggestive of congenital heart disease, when the cause of clinical signs remains unclear despite basic testing, and when there is a poor response to treatment suggesting there might be an alternative diagnosis to the one being treated for. However, these are rare situations, and mitral valve disease, the most common heart disease seen in practice, can often be treated appropriately based on examination and thoracic radiographs.
About the Author
DARCY ADIN | DVM, DACVIM (CARDIOLOGY)
Dr. Darcy Adin is a Clinical Professor of Cardiology at the University of Florida, College of Veterinary Medicine. She received her DVM from Cornell University in 1996. She completed a rotating internship at VCA South Shore Animal Hospital in 1997 and a cardiology residency at the University of California, Davis in 1999, with ACVIM board certifi cation in Cardiology in 2000. Dr. Adin has held positions in both academic and private specialty practice. Her clinical research focuses on the investigation of diuretic treatments and neurohormonal modulation of congestive heart failure.