A first-degree, or 1 st degree, AV block is indicated on the ECG by a prolonged PR interval, as seen below. Recall that the P wave indicates atrial depolarization, initiated by firing of the SA node.

A trifascicular block is the combination of a right bundle branch block, left anterior or posterior fascicular block and a first-degree AV block (prolonged PR interval). The term “trifascicular ...