Chapter 4 Cardiac disease and pathology
CARDIAC PATHOLOGICAL EXAMINATION
Most pathological techniques to examine the heart are designed to examine each chamber in isolation, usually opening the chamber along its border with the intraventricular septum and displaying its internal surface for examination and determination of weight.1 While this technique does have several advantages it does not enable the clinician to visualize the heart in the manner to which it has been examined by echocardiography. Therefore, a more clinically orientated approach to gross pathological examination of the heart is recommended.2 This approach is lesion orientated and therefore should commence by examining the side of the heart which is most affected by disease.
PRIMARY MYOCARDIAL PATHOLOGIES(
VMD)
Primary myocardial disease occurs rarely in the horse; dilated cardiomyopathies are occasionally reported and are described in Chapter 19. Myocardial fibrosis has been associated with ventricular tachycardia, presumably due to disruption of the cardiac conduction system of the ventricle, but can also be detected as an incidental finding.3 The gross appearance of these changes are of discolouration within the myocardium, but are rarely specific to a particular disease process (Fig. 4.2).
In most cases a local ischemic event was assumed to be the primary disease process whereas a primary inflammatory aetiology has also been implicated.4 However, as fibrosis is an end-stage process the primary disease process can be difficult to confirm. In a group of horses microemboli from parasitic lesions were suspected based on statistical associations.3 In human patients and animal models, fibrosis is associated with myocardial remodelling and this process is described below in more detail. Myocarditis is often a clinical diagnosis based on the presence of ventricular dysrhythmias with no apparent underlying cause, although viral and bacterial causes, including Streptococcus equi var equi, have been implicated;1 however, in many cases the primary initiating cause is unknown. ( ET)
Other primary myocardial pathologies are rare, although do occur sporadically (Fig. 4.3) and usually present clinically with cardiac dysrhythmias or signs of low cardiac output (see Chapter 19). ( CN)
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