Back to basics: clinical cardiovascular exam and diagnostic testing (Proceedings)
Although there are highly sophisticated and advanced diagnostic modalities in cardiology, the basic technique of a good cardiovascular examination is still an essential fundamental element of the cardiovascular workup. Other basic diagnostic modalities that are readily available in most practices include thoracic radiographs, electrocardiography, and blood pressure measurement.
The initial assessment of the patient begins with the signalment and history. In pediatric or juvenile patients, signalment helps increase suspicion for certain congenital defects. Rottweiler, Golden Retriever, Great Dane, Boxer, and German Shepherd dogs are particularly predisposed to develop subaortic stenosis. In contrast, terriers and small breed dogs are more likely to develop pulmonic stenosis. Tricuspid valve dysplasia +/- mitral valve dysplasia are the most common defects of Labrador Retrievers, which cannot be excluded based on the absence of a murmur on physical examination. Small breed dogs such as the poodle, Yorkshire terrier, Shetland sheep dog, and many others typically develop patent ductus arteriosus. Developmental heart diseases are more common in middle age to older animals, and include myxomatous mitral valve disease in small dogs (especially the Cavalier King Charles Spaniel),dilated cardiomyopathy in large breed dogs, and hypertrophic cardiomyopathy in cats. Highly predilected breeds for development of DCM include Boxer dogs, Doberman Pinschers, and giant breed dogs.
Objectives for cardiac auscultation include assessment for a murmur, extra heart sound (gallop or systolic click), or arrhythmia. The murmur is localized to left or right side, basilar versus apical point of maximal intensity, with the timing defined as systolic (90% of murmurs), diastolic, continuous, or to-and-fro. Certain murmur characteristics are pathognomic for specific diseases, such as a continuous left basilar murmur heard in patients with a patent ductus arteriosus. Murmurs in cats may be present due to underlying heart disease, systemic diseases causing volume overload to the heart or high output state (significant anemia, fluid overload, hyperthyroidism, fever), or may be innocent. Most innocent murmurs are relatively soft, whereas loud murmurs are most common in hypertrophic obstructive cardiomyopathy or congenital heart defects. The typical murmur of mitral regurgitation is a left apical holosystolic or pansystolic murmur. Pansystolic murmurs obscure the second heart sound, and are usually present in the face of severe mitral regurgitation. The murmur intensity roughly parallels the degree of mitral regurgitation, with soft murmurs (I-II) correlated with mild mitral regurgitation, and loud murmurs (≥ IV) correlated with severe mitral regurgitation. The typical auscultation abnormalities in dilated cardiomyopathy include a soft left apical holosystolic murmur and a S3 gallop.Extra heart sounds include either a gallop heart sound, a systolic click, or split heart sounds, and sometimes can be difficult to differentiate, especially in the presence of tachycardia. A gallop heart sound is an extra heart sound, either S3 or S4, and occurs in diseases causing a stiff left ventricle (in cats mostly) or significant volume overload to the heart (cats: anemia, hyperthyroidism, fluid overload; dogs: severe AV insufficiency, dilated cardiomyopathy). A mid-systolic click is a classic feature of mitral valve prolapse and myxomatous valve degeneration, and is often heard when the mitral regurgitation is mild.
Arrhythmias may consist of premature beats, runs of tachycardia, irregularly irregularly rhythm, or bradycardia. Auscultation alone cannot diagnose the type of premature beat (ventricular versus atrial premature complex), and an electrocardiogram must be done to diagnose the specific rhythm abnormality. An irregularly irregular rhythm may be caused by atrial fibrillation or frequent atrial or ventricular premature complexes, and must be distinguished by an ECG.
Assessment of femoral arterial pulse intensity and whether pulses are synchronous with the heart beat are also essential objectives in the cardiac examination. Femoral pulses reflect the pulse pressure which is the difference between the systolic and the diastolic arterial blood pressure. Decreased femoral arterial pulse strength may be present in dogs with significant left ventricular outflow tract obstruction such as subaortic stenosis, or in dogs with very low cardiac output (most commonly due to dilated cardiomyopathy or cardiac tamponade). Bounding femoral arterial pulses are present in diseases with increased pulse pressure such as patent ductus arteriosus or aortic insufficiency, which cause a diastolic runoff of blood from the aorta to the pulmonary artery or left ventricle respectively. Jugular venous distension or pulsation may reflect elevated right heart diastolic pressure in dogs with right heart failure. Concurrent abnormalities typically include hepatomegaly and abdominal effusion.
Evaluation of respiratory abnormalities is initially done by observation of the animal's breathing pattern in the examination room prior to handling the animal. Abnormal respiratory patterns include tachypnea, dyspnea, orthopnea, or cough. Cough is not specific for heart failure, and is often present in dogs with respiratory disease including collapsing trachea or chronic bronchitis. Dogs with heart failure may cough due to pulmonary edema or compression of the left mainstem bronchial compression by an enlarged left atrium. A cardiac cough is typically soft, compared to the loud honking cough caused by collapsing trachea, or the loud, productive hacking cough typical of chronic bronchitis. Animals with heart failure may have increased adventitious lung sounds, although harsh crackles are more common in animals with primary respiratory disease. Muffled lung sounds are common in animals with pleural effusion, and are typically coupled with a restrictive breathing pattern (fast, shallow breaths). Absence of adventitious lung sounds does not eliminate congestive heart failure, as many animals with mild cardiogenic pulmonary edema do not have increased lung sounds.