SCEOND DEGREE AV BLOCK ËÅѡࡳ±ì¡ÒÃÇÔ¹Ô¨©Ñ         May occur with any supraventricular rhythm and is due to intermittent conduction from the atria to the ventricles   Type 1 (Wenckebach) R-R interval is irregular R-R interval is continuously irregular R-R interval progressively shortens, then prolongs for one interval P-P interval is regular PR interval progressively lengthens until a single P wave is not followed by a QRS complex   Fixed type II R-R interval is regular P-P interval is regular P rate is a multiple of the QRS rate (2:1, 3:1, or 4:1) There is a fixed relationship of P wave to QRS complexes   Varying type II R-R interval is irregular R-R interval varies continuously P-P interval is regular R-R interval is a varying multiple of P-P interval (alternating 2:1 and 3:1) All R waves are preceded by a P wave with the same PR interval ¡ÒÃÇÔ¹Ô¨©ÑÂá¡âä Premature atrial contraction AV dissociation First degree AV block, third degree AV block