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Feline cardiomyopathies

image of Feline cardiomyopathies
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Abstract

Genetic and idiopathic myocardial diseases are often termed primary cardiomyopathies. These include hypertrophic (HCM), dilated (DCM), restrictive (RCM), arrhythmogenic right ventricular (ARVC) and unclassified (UCM) cardiomyopathies, as well as myocarditis (endomyocarditis). Myocardial infarction is a poorly characterized disorder in cats, which causes regional or global ventricular dysfunction. Of these conditions, HCM is most common. Secondary myocardial diseases develop from defined disorders such as systemic hypertension, hyperthyroidism, taurine deficiency and growth hormone excess (acromegaly). Echocardiographic findings overlap between primary and secondary myocardial disorders, but these conditions should be distinguished as patient management and long-term prognoses can differ. The chapter addresses History; Physical examination; Diagnostic studies; Specific feline cardiomyopathies; and Treating complications of feline cardiomyopathies.

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Figures

Image of 25.3
25.3 Clinical signs in feline cardiomyopathy. Cat presented with respiratory distress due to congestive heart failure undergoing emergency thoracocentesis. The patient is receiving oxygen and has been sedated. A small butterfly catheter was used to provide partial relief of the effusion. (Courtesy of S. Dennis.) Cat with decerebrate type posture following a suspected haemorrhagic stroke. The cat had severe systemic hypertension. Neurological signs improved significantly in this cat with just control of arterial blood pressure. Caudal image of a cat during the recovering phase from aortoiliac thromboembolism. The cat is ambulatory but there is extensor weakness in the left limb and proprioceptive deficits in the right limb. Ocular fundus of a cat with systemic hypertension. There is mild tortuosity noted in the retinal vessels and numerous focal active retinal detachments evident.
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25.4 Diagnostic approach to the cat with a cardiac murmur (see text for details). Note that: (i) serum thyroxine should be measured in cats >7 years of age; and (ii) abnormal NTproBNP, cTnI, thoracic radiographs (cardiomegaly) or ECG (cardiomegaly pattern, axis shift, rhythm disturbance) are indications for obtaining an echocardiographic study. Not all screening examinations are indicated in every case.
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25.6 ECGs in feline cardiomyopathy. Sinus rhythm with left axis deviation and increased QRS voltages in a cat with HCM. The frontal axis is left-cranial, with prominent positive voltages in leads aVL and I. There are progressively deeper S waves in leads II, aVF and III. Overall QRS voltages in lead III exceed 1 mV. (Paper speed 50 mm/s and standard calibration) Atrial fibrillation and probable right bundle branch block in a cat with cardiomyopathy. The overall rhythm is irregular and there are no consistent P waves evident. The QRS complex is widened, with terminal activation of the ventricle oriented to the right and cranially. Secondary T wave changes are evident.
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25.7 Radiography in feline cardiomyopathy. VD radiographs of two cats with HCM. The cardiac silhouette is significantly enlarged in each cat. The left panel shows marked LA dilatation (arrowed) with the apex shifting to the right. The right panel shows severe elongation of the heart compatible with LV enlargement. Lateral radiograph of a cat with RCM. The heart is moderately to severely enlarged. The caudal vena cava (VC) is dilated. The caudal lung lobes demonstrate a prominent pulmonary vascular pattern with interstitial lung densities. There is also a small pleural effusion (arrowed), which was shown to be chylothorax based on chemical analysis. VD radiographs of a cat with HCM before (left) and after (right) hospital therapy for CHF. The bilateral pulmonary interstitial and alveolar infiltrates are resolved in the follow-up film; however, the heart is still elongated with slight prominence of the LA.
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25.8 Echocardiography in feline cardiomyopathy. 2D colour Doppler echocardiogram from a cat with HCM of the LV, demonstrating: hypertrophy of the septum (IVS) and LV wall (LVW); LA dilatation; turbulence in the ascending aorta (Ao); and an eccentric jet of mitral regurgitation (arrowed) stemming from systolic anterior motion (SAM) of the mitral valve. Continuous wave (CW) Doppler study from a cat with HCM and dynamic LVOT obstruction. The cursor is aligned along a systolic signal that abruptly increases in velocity (arrows) at the time of SAM of the mitral valve. Diastolic flow waves (E and A) are also recorded since the CW cursor crosses the inflow signal of LV filling (these should not be analysed in this plane). Pulsed-wave Doppler recording of mitral valve filling from a cat with cardiomyopathy receiving atenolol. The filling pattern has become ‘restrictive’, characterized by a large E wave and attentuated A wave. These findings are suggestive of elevated pulmonary venous and mean LA pressures.
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25.9 Pathological features of feline cardiomyopathies. Opened LV from a cat with concentric hypertrophy due to HCM. The interventricular septum (IVS), papillary muscles (PM) and ventricular wall (LVW) are all thickened. There is some increase in fibrous tissue along the inner edge of the septum. Ao = Ascending aorta. RCM in a cat. The LV wall (W) is discoloured owing to diffuse infiltration with fibrous connective tissue. A segmental infarct is evident in the cut free wall (arrowed). The left auricular appendage (LAur) is moderately dilated. The RV is relatively spared. Histological section from a cat with endomyocarditis. Myocardium (Myo) is evident in this low-power photomicrograph. The zones beneath the endocardium (arrowed) are characterized by myocardial fibrosis and infiltration with inflammatory cells. Trichrome stain. Segment of descending aorta (DAo) cut near the origin of the internal and external (E) iliac arteries.

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