Impulse propagation may also be blocked in atrial tissues surrounding the sinus node, causing sinoatrial (SA) block. Thus, slowing of the ventricular rate and/or pauses may be caused not only by slowing of the rate of sinus node discharge, but also by SA block, by block in the AV node and/or by block in the more distal conduction system. We will first discuss atrioventricular (AV) conduction disturbances, and then discuss sinoatrial (SA) conduction disturbances.