confused.. Non-conducted PAC vs Type II AV block?

A blocked, or non-conducted PAC is what the name implies... A premature atrial beat that is not conducted to the ventricles; P wave but no QRS. The key is the fact that it is early. So take your calipers and measure out the P-P interval then measure form the last normal p wave and look where the calipers land. Does the non conducted P wave come sooner than where your calipers land? If so then it is a blocked PAC. They commonly are buried in the preceding T wave so look closely for changes in T wave moroplogy. There may be an extra hump or taller peak. Now with Second degree type 2 there is not a premature beat, there is an intermittent failure of conduction to the ventricles. So same as before take your calipers, get the P-P and measure out from the last normal P. Is there a non conducted P wave exactly where your calipers land? That is second degree hesrt block. Slide your calipers from that non conducted P wave and they should land exactly on another P wave, this time with an associated QRS. This is what people refer to as "marching out". With a second degree type 1 (Wenckeback) there is no marching out of p waves. Each consecutive PR Interval increases until there is a non conducted p wave. Longer, longer, dropped then the cycle repeats. So fixed PRI for the beats preceding a dropped best is not Wenckeback, most likely a PAC or 2nd degree type 2. Hope that helps, I typed this on my IPad so sorry for the format and typos