5.3 Clinical diganosis of congenital heart disease
Identifying CHD depends on classification of cardiac murmurs, palpation of the arterial pulse and detection of other clinical signs such as precordial thrills, jugular distension and / or pulsation, peripheral oedema, tachypnoea and cyanosis. Foals with significant CHD may be poorly grown. Clinical evaluation is performed as described in Chapter 3.
A complicating factor in evaluating foals with cardiac murmurs is that functional murmurs are particularly common in the neonate. They may also be relatively loud (up to grade 4/6). Often these are functional murmurs due to non-laminar flow in the great arteries, of the same nature as those commonly found in adults. A continuous waxing and waning murmur can also be associated with flow through the ductus arteriosus in neonates. The time period during which normal closure of the ductus arteriosus is a matter of some debate and may depend on the technique used to document cessation of flow. The murmur usually disappears in the first 24 hours after birth; however, a systolic element may persist until there is complete closure of the ductus after three or four days.
Although cyanosis is uncommon in horses, it is an important finding in a small number of cases of CHD. It can be described as peripheral or central. Peripheral cyanosis is associated with poor local delivery of oxygenated blood and removal of deoxygenated blood reaching the systemic circulation, or severe pulmonary disease.