Atrial standstill (Sinoventricular conduction) is a heart disease characterized by sinoatrial inactivity, translating as an absence of P waves.
This condition can be defined by cause:
- Temporary - hyperkalemia, myocarditis
- Persistent - atrioventricular muscle dystrophy, cardiomyopathy, hypothyroidism, hypoadrenocorticism, immune-mediated polymyositis, nemaline myopathy, double-chambered right ventricle
- Terminal - congestive heart failure
Initially, atrial myocardial destruction leading to sinoatrial standstill and an AV nodal escape rhythm is noted. Eventually, myocardial failure ensues.
Clinical signs are observed commonly in younger dogs and include weakness, lethargy and in patients with persistent atrial standstill, abdominal distension and atrophy of skeletal muscles may be observed.
A presumptive diagnosis can be established from an electrocardiogram which usually reveals an absence of a P wave but normal QRS complexes with mild bradycardia.
A differential diagnosis would include atrial fibrillation and sinus bradycardia.
In affected patients, heart rate does not increase following injections of atropine.
Treatment is typically unnecessary in persistent atrial standstill although implanted pacemakers may regulate rate and rhythm. In many cases, correction of underlying disorder and correction of hyperkalemia with calcium gluconate may afford a better prognosis.
Some cases may require digoxin and diuretics and ACE inhibitors if congestive heart failure ensues.
- Lai SR (2009) Atrioventricular muscular dystrophy in a 5-month-old English springer spaniel. Can Vet J 50(12):1286-1287
- Warman S et al (2008) Dilatation of the right atrium in a dog with polymyositis and myocarditis. J Small Anim Pract 49(6):302-305
- Nakamura RK et al (2012) Adult-onset nemaline myopathy in a dog presenting with persistent atrial standstill and primary hypothyroidism. J Small Anim Pract 53(6):357-360
- Fukushima R et al (2011) Epidemiological and morphological studies of double-chambered right ventricle in dogs. J Vet Med Sci 73(10):1287-1293