si·nu·a·tri·al block, S-A blocksinus block
blockade of the impulse leaving the sinus node before it can activate atrial muscle.
Synonym(s): sinoauricular block
si·nu·a·tri·al block, sinoatrial block (sin'yū-ā'trē-ăl blok, sī'nō-)
Blockade of an impulse leaving the sinuatrial node before it can activate atrial muscle or be propagated to the atrioventricular node. The condition is indicated on electrocardiography by the absence of some P waves.