Basic Rhythm Course

What exactly are you having trouble with regarding blocks? Trying to teach them in an understandable way?

1st degree blocks are easy. Just remember a prolonged PR interval, >0.20sec. Not really anything to worry about.

Causes: digoxin, beta blockers, CCBs, increased vagal tone, hyperkalemia, MI, degeneration of conduction pathways associated with aging or idiopathic.

For the others, I used mnemonics to help me because I had a hard time keeping them straight.

Long, longer, drop...then you have a Wenckebach (2nd degree type 1). Recall that with this block you have a PR interval that progressively becomes long, then longer and then you have a dropped beat (no QRS). This block isn't very concerning. It can progress to a higher level block, though. Just monitor for symptoms that = compromised hemodynamic status.

Causes: same as above. Commonly follows an acute inferior wall MI.

If your P's don't always go through, then you have a Mobitz II (2nd degree type 2). This block is more serious than a Wenckebach. It can quickly progress to a 3rd degree block (the most serious of all!) or progress to ventricular standstill without warning. There is usually more than 1 P wave (sometimes 2 or 3 or more) before a QRS (P's don't always go through to the Q!).

Causes: acute anterior wall MI, acute myocarditis, age-related conduction pathway degeneration. Usually not drug-related unlike Wenckebach and 1st degree blocks.

If your P's and Q's don't agree, then you have a 3rd degree. With this type of block, you have complete AV-dissociation. The P's are doing their own thing and the QRS' are doing their own thing (they're not "married" to each other) - there is no relationship between them. A majority of the time these rhythms are slow (ventricular rate will vary from 20-60bpm depending if they are paced by the AV junction or ventricles) and these patients look like CRAP, oftentimes hemodynamically-compromised. These patients NEED a pacemaker. Slap on some transcutaneous pacer pads until a more permanent (or permanent) pacemaker can be placed. This rhythm can also lead to ventricular standstill without warning.

Causes: inferior wall MI, ischemic heart disease, drugs (dig, beta blockers, CCBs, though usually this doesn't occur with drug toxicity), acute anterior MI, hyperkalemia, acute rheumatic fever.

A Mobitz II vs. a 3rd degree block may look similar. The key is to look at the PR interval. In a Mobitz II (2nd degree type 2) block, you will see a consistent PR interval. It may be WNL or it may be prolonged (>0.20 sec) but it remains consistent.

In a 3rd degree block, the PR interval is variable. It may be 0.60 sec one moment and then 0.20 sec the next or something.

Hope this helps! Good luck!