The heart is composed of four chambers. The upper two chambers are called atria (singular atrium) and lower two chambers are called ventricles. An electrical impulse generated from sinoatrial (SA) node makes these chambers contract in a synchronized manner in order the pump the blood to the lungs and the rest of the body. The heart's electrical activity is detected by means of electrocardiogram (ECG). The P waves in the ECG are associated with electrical activity in the atrial.
Atrial Standstill refers to complete or partial inactivity of atrial which appears as absent of P waves on ECG recordings. This complete or partial inactivity of the atrial results from failure of atrial depolarisation. The ventricles, however, work normally. Atrial standstill is an abnormal heart rhythm characterized by absence of P waves on ECG. The P wave is the first upward deflection of the ECG tracing that looks like a “bump” in the tracing and is a measure of the electrical activity of the atria. Along with absent P waves, a slow heart rate and regular or irregular heart rhythm may also be indicated on ECG.
Atrial standstill can be temporary, persistent or terminal in nature. English Springer Spaniels are the most commonly affected dogs.
Common symptoms associated with atrial standstill include
Skeletal muscle wasting of the forearms and shoulders
Slow heart rate (bradycardia)
A spontaneous loss of consciousness (syncope)
Signs of congestive heart failure (coughing, difficulty breathing, bluish skin, moist membrane)