Indications for ECGs

Abnormal Cardiovascular Physical Exam

Cardiac murmurs, gallop sounds and arrhythmias are some obvious physical exam abnormalities that are clear indications for an echocardiogram. Cardiac murmurs can arise from multiple underlying abnormalities in the heart. Murmurs can be pathologic or physiologic (also called functional) and these can only be definitively differentiated by a cardiologist’s interpretation of an echocardiogram. Gallop sounds occur when the clinician is able to auscultate an S3 or S4 in addition to the normal S1 and S2 sounds. This can often be an indication for diastolic dysfunction and an echocardiogram is always warranted when this occurs in dogs and cats. Arrhythmias can be caused by intracardiac or extracardiac disease. An echocardiogram helps rule out primary cardiomyopathy and/or infiltrative cardiac disease that may explain the arrhythmia. The echocardiogram also helps to determine appropriate anti-arrhythmic therapy for the individual patient.

Breed Screening

Many breeds of dog and cat have a heritable predisposition for heart disease. In some cases, auscultation by a board-certified cardiologist is indicated to rule out the presence of a murmur (for example breeds with a predisposition for Subaortic Stenosis include Golden Retrievers, Rottweilers, German Shepherds, Newfoundlands and Boxers). If a murmur is auscultated, then an echo is indicated for a complete evaluation. In some breeds, however, an echo is always indicated to screen for heart disease.

Many cat breeds should be screened prior to breeding with echo. Maine Coons, Bengals and Sphynx cats are popular breeds with known HCM in their lines. All Labrador Retrievers should be screened prior to breeding for Tricuspid Valve Dysplasia. A mildly affected dog may produce offspring with severe lesions. Not all mildly affected dogs have heart murmurs.

Finally, all Doberman Pinschers should be screened with echo prior to breeding to rule out occult Dilated Cardiomyopathy. Owners of pet Dobermans and Boxers are often curious about when and how to screen for cardiomyopathy in their dogs. Dobermans can be screened as early as 2 years of age. By age 5, most affected male Dobermans will have echo changes and by age 7, most affected females will have changes. Boxers should be screened with a Holter monitor. The above age grouping is appropriate for this breed as well.

Thoracic Radiographic Changes

Cardiomegaly noted on radiographs can be due to cardiac enlargement, pericardial fat accumulation and/or patient variability. An echocardiogram is the most specific tool for determining the size of each individual cardiac chamber and is a very useful tool in delineating a cause for radiographic cardiomegaly. For example, pulmonary hypertension may result in right-sided cardiomegaly and often presents without a distinguishable murmur. Pulmonary vasculature changes are another indication for echocardiograms. If enlarged, this can be indicative of a left-to-right cardiac shunt, pulmonary hypertension and/or impending congestive heart failure. If small, this can be indicative of a right-to-left cardiac shunt. Pulmonary parenchymal changes are another common indication for echocardiograms. The echocardiogram is highly specific and sensitive for congestive heart failure and pulmonary hypertension.

Feline Echocardiography

Cats can be particularly challenging cardiology patients because they can have severe cardiomyopathy despite the absence of physical exam abnormalities, radiographic changes and/or clinical signs. An echocardiogram is often the only appropriate diagnostic test that is both specific and sensitive for heart disease in cats. Purebred cats have a higher incidence of heart disease, and therefore echocardiographic evaluation is often high yield in these patients. It is our opinion that a screening echocardiogram is never inappropriate in a cat. Serum NTproBNP can also be considered in cats as a screening tool and is often utilized prior to anesthesia in adult cats. If this test results in suspected heart disease, an echocardiogram is recommended in these patients to confirm the presence of heart disease and determine the therapeutic needs of the patient.

Pre-Anesthetic Evaluation

Prior to placing a dog or cat under anesthesia, it can be helpful to obtain a complete understanding of the patient’s cardiovascular status. An echocardiogram is the most specific and sensitive test to accomplish this goal. Beyond an abnormal physical exam or radiographic changes, there are a variety of clinical signs that can increase a clinician’s suspicion for heart disease and increase the indication for an echocardiogram. These can include coughing, exercise intolerance, weakness and/or syncope.