Does cardiac cough exist?
Cough has been traditionally attributed to heart failure for decades, especially in veterinary medicine. However, cough cannot be caused by pulmonary oedema, as commonly reported in some veterinary textbooks. This can be easily extrapolated by the fact that the reflex is not evoked in the deeper respiratory tract where pulmonary oedema occurs, such as respiratory bronchioles or alveolar space. Conversely, patients with pulmonary oedema will almost inevitably present with tachypnoea and/or dyspnoea. They may occasionally cough if there is a massive accumulation of fluid in the alveolar space severe enough to flood higher airways and mechanically stimulate coughing receptors.
Most cardiac patients are geriatric animals (primarily toy-small breeds) who suffer from concomitant airway disease. In most cases, these dogs are bright, alert, not dyspnoeic and may also present an obvious sinus arrhythmia, which are all signs compatible with airway disease but unlikely associated with congestive heart failure. Cardiomegaly, in particular left atrial enlargement (LAE), is however associated with an increased risk of cough in dogs with chronic degenerative mitral valve disease, and there is a ten-fold increased risk of coughing if LAE and airway disease coexist, even in the absence of pulmonary oedema.
Therefore, in cardiac patients presenting with a cough, our differential diagnosis should also include other causes of coughing, such as infectious tracheobronchitis, tracheal collapse, bronchomalacia, gastro-oesophageal reflux, gagging reflex.