Persistent atrial standstill, a form of cardiomyopathy resulting in destruction of the atrial myocardium (which may also affect the ventricular myocardium), has been reported in dogs. Affected breeds include English Springer Spaniels, Old English Sheepdogs, Shih Tzus, German Shorthaired Pointers, and mixed-breed dogs. The disease has also been reported in some cats with concurrent cardiomyopathy. Initially, atrial myocardial destruction leading to atrial standstill (no atrial electrical or mechanical activity) and an atrioventricular nodal escape rhythm is noted. Mitral regurgitation that may be severe often occurs at this stage. Eventually, myocardial failure may ensue. Clinical signs are similar to those in animals with dilated cardiomyopathy, with right heart failure or left heart failure being noted. Pacemaker implantation may improve heart rate and cardiac output. Other treatment aims to palliate clinical signs of CHF.
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