Evidence of severe heart disease on physical examination
Diagnosis of LCHF usually entails significant dyspnea/respiratory effort and tachypnea; there is the occasional dog (e.g. Dobermans) that can be walking around with fairly severe pulmonary infiltrates but little outward evidence of respiratory compromise. In most little dogs with mitral endocardiosis causing LCHF we expect to hear a readily audible murmur (grade III/VI or louder) but there are exceptions to this rule. A murmur may be relatively inaudible if dyspnea and respiratory sounds are so great as to obscure the murmur. Acute chordal rupture resulting in LCHF may not produce an obvious murmur. Large breed dogs with DCM may not have a loud murmur, or any; this, in fact, is one of the distinguishing features between DCM and mitral regurgitation (MR) due to endocardiosis. MR secondary to DCM is typically produced by a dilated, hypofunctional ventricle and murmurs may be subtle. LCHF in association with a soft murmur due to endocardiosis is unlikley (but possible). Listen carefully for a gallop sound in all cases. A reliable gallop (S3 or S4) is comparatively specific sign of significant heart disease in a small animal, i.e. consistent with LCHF. With great uniformity, a dog with LCHF is expected to have an “elevated” heart rate (e.g. 140/min or greater) and loss of sinus arrhythmia due to sympathetic activation. Exceptions to this rule include the presence of medications that artificially lower the heart rate (pimobendan, beta-blockers). If a dog's heart rate is 120/min or lower, you should be strongly aware of the possibility that LCHF is not present. Inspiratory crackles are supportive evidence of alveolar pulmonary edema due to LCHF. However, LCHF is not the only cause of crackles and any alveolar (pneumonia, noncardiogenic edema) or bronchial infiltrates (bronchopneumonia, collapsing airway syndromes, “pulmonary fibrosis”, reactive airway disease) may result in these sounds! Supportive evidence for LCHF in cats includes the presence of a murmur or gallop sound but there are many cats with severe heart disease and virtually no detectable physical abnormalities until the onset of LCHF. Tachycardia is not consistently present. Some cats actually present with bradycardia and this, in association with hypothermia, may be an ominous finding.