A sinoatrial block is a disturbance of the heart conduction system, in which an impulse can not advance from the sinus node toward the atrium. Sinoatrial blocks can be caused by excessive vagal stimulation, sinoatrial block acute infections, and atherosclerosis. It is identified in the electrocardiogram by an absent P wave. Treatment for symptomatic SA block includes the use of atropine and isoproterenol; an electronic pacemaker is used if drug therapy is ineffective.
Under normal conditions, electrical activity is spontaneously generated by the SA node, the physiological pacemaker. This electrical impulse is propagated throughout the right atrium, and through Bachmann's bundle to the left atrium, stimulating the myocardium of both atria to contract. The conduction of the electrical impulse throughout the left and right atria is seen on the ECG as the P wave.