Canine dilated cardiomyopathy

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Dilated cardiomyopathy (DCM) is a primary myocardial disease characterized by ventricular dilatation and systolic dysfunction with eccentric hypertrophy (increased left ventricular mass, but relatively thin walls). Remodelling leads to a round rather than elliptical left ventricle (LV) (increased sphericity). It is important to note that DCM is a diagnosis of exclusion; other congenital and acquired cardiac diseases and systemic conditions that may lead to these changes should be actively excluded prior to making this diagnosis. This chapter looks at Aetiology and inheritance; Pathophysiology and histopathology; Pathophysiology; Clinical signs; Diagnostic approach; and Treatment.

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23.2 Post-mortem specimen from a 10-year-old Newfoundland that had been treated for 4 years for CHF associated with DCM with AF. The patient was eventually euthanased due to refractory congestive failure. Note that all four chambers are markedly dilated and the ventricular myocardium is flabby.
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23.5 Radiographs from a 6-month-old Great Dane with DCM following initial treatment for pulmonary oedema. Right lateral recumbent view showing generalized cardiomegaly (vertebral heart size 12.1), particularly due to left atrial and ventricular enlargement. The outline of the cardiac silhouette is very sharp, due to loss of normal systolic–diastolic movement blur. There is a generalized increase in interstitial pulmonary pattern, which is predominantly perihilar, consistent with residual pulmonary oedema. Loss of serosal detail in the abdomen is associated with very poor body condition. Dorsoventral view confirming four-chamber enlargement of the cardiac silhouette, pulmonary venous distension and a generalized increase in interstitial markings.
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23.6 Echocardiographic images from a 20-week-old Great Dane with DCM and CHF in sinus rhythm. Right parasternal long-axis four-chamber view, showing a dilated, relatively thin-walled, rounded left ventricle (LV) in systole. Left ventricular M-mode at the level of chordae tendinae, obtained from a short-axis view. The dilated LV chamber, with proportionately thin-walled interventricular septum and left ventricular free wall, and marked hypokinesis can be appreciated. In this case, the mean left ventricular diameter during diastole (LVDd) was 74.5 mm and during systole (LVDs) was 65.9 mm, with a fractional shortening of 11.6%. Colour flow Doppler image of the mitral valve/left atrium on a right parasternal long-axis four-chamber view during systole, showing mitral regurgitation as a consequence of altered LV geometry.
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23.7 Six-lead ECG from a German Shepherd Dog with AF. Note the normal appearance of the QRS complexes, completely irregular RR interval and the absence of P waves. The ventricular rate in this case is over 260 beats/minute. A cursory glance at the ECG fails to appreciate the very irregular RR intervals at very fast heart rates; human ears are better at detecting the chaotic rhythm. Paper speed 50 mm/s; gain 0.5 cm/mV. Six-lead ECG from the same dog following 10 days of treatment with both digoxin and diltiazem. The ventricular rate is now better controlled at about 180 beats/minute. Note that this rate control is still not optimal if the rate persists at 180 beats/minute over 24 hours. Paper speed 50 mm/s; gain 0.5 cm/mV.
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23.8 Lead I ECG from an Irish Wolfhound with AF and a slow ventricular rate, prior to development of CHF or any clinical signs evident to the owner. Ventricular rate is about 120 beats/minute. Note that fibrillation waves are evident affecting the base line, but their presence is not required to make the diagnosis of AF in dogs. Paper speed 50 mm/s; gain 1 cm/mV.
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23.9 Leads I, II and III from a Boxer with ARVC. One sinus complex precedes sustained ventricular tachycardia. The left bundle branch-block morphology of the ventricular ectopics suggests right ventricular origin. The rate of the ventricular tachycardia is 340 beats/minute. Paper speed 50 mm/s; gain 0.5 cm/mV.
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23.10 Channel from an ambulatory ECG recording (Holter monitor) from a Dobermann diagnosed with DCM showing paroxysms of ventricular tachycardia, with only occasional sinus complexes in this section. The initial ECG showed sinus rhythm with occasional VPCs. Paper speed 25 mm/s.

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