1st 2nd 3rd degree blocks

[Shishkabob]

Let's see if I understand these right;

1st degree is a lengthened PR interval caused by slow conduction.

2nd Mobitz 1 is a gradually increasing PR interval until a QRS is skipped.

Mobitz II is normal P to P interval with QRS skipped 2:1,3:1,4:1 usually.

3rd is ventricular foci not being affected by atrial foci at all, so P waves will have a different rate then the QRS'.


So do I pretty much have em down?

Don't get me started on ventricular arthymias yet. Gah


Thanks

 

[Sasha]

My understanding and what I've seen (although I've seen very few complete/3rd degree) is if you march out the P waves and QRS's on a third degree, they will match up with eachother, like P to P will be equal, but there is no correlation to the QRS.

In a 3rd degree they're both marching to their own drum.

Could be wrong, but that's my understanding of it.

 

[Shishkabob]

That's what I've come to believe so I just wanted to see if it was true or not.

Which begs the question; what's the difference between 3rd and an escape beat from the ventricals?

 

[ResTech]

My understanding of 3rd degree block is there is a complete blockage of impulse conduction at the AV junction resulting in a complete dissociation between atrial and ventricular firing. The atria and ventricles are firing but doing so on their own without coordination.

On the EKG, its pretty easy to note as their is no correlation between P's and QRS... you can see the P's march right on through the QRS complexes.

 

[Epi-do]

3rd degree is like you both said - the atria and ventricles are each doing their own thing. There is no correlation between the two of them. I've seen a couple of these patients during clinicals, and have actually transported one since getting cleared to work as a medic on my own. These patients typically end up with a pacemaker. They may present similar to a bradycardic patient.

With a ventricular escape beat, the patient will be in XYZ rhythm, for instance, a sinus rhythm or sinus tach. An escape beat is as the name implies. The ventricles will have a random, or escaped, beat and then resume the underlying rhythm. The patient may have more than one escape beat in a row. I was taught that if there are more than three in a row, it is considered a run of v-tach. Although lots of things can cause escape beats, alot of times, putting the patient on oxygen will help tremendously in either decreasing the number of escape beats you see, or resolve them all together.

 

[TomB]

Here's a tip for you. The only two AV blocks with variable PR intervals are 2AVB Type I and 3AVB. With 2AVB Type I you will typically have clustering of the QRS complexes in a repeating pattern. With 3AVB the QRS complexes will have a regular R-R interval. That's the easiest and fastest way to tell them apart.

Tom

 

[marineman]

Since TomB didn't post it I will, here's his site ems12lead.blogspot.com

there's some great information on there. I learned more from reading his site than I did during our cardiology class.

 

[Ridryder911]

Simply put they are NOT really heart blocks but AV Dissassociation(s).

1'st degree- prolonged PR interval.

Second Degree:
Type I/ Wenkeback- (baby foot steps -gets longer and longer until they fall down)
Type II: Appears to be normal but will drop a QRS in a certain period. Don't confuse with ventricle drop beats.

Thrid Degree/Complete Heart Block: No corelation to the atrium or ventricles. Each are independently firing.

Which is worst?.... Hint it's not the third degree...

R/r 911

 

[Epi-do]

Which is worst?.... Hint it's not the third degree...

R/r 911

That would be a second degree type II. This particular block has a very high degree of likely hood of progressing to a third degree block, but may also be associated with an anterior wall MI. The increased mortality is due to the risk of ventricular arrhythmias and left-sided heart failure.

Not only can heartblocks be caused by damage/injury, they can also be congenital, or due to pharmacology/toxicology, infections, electrolyte disturbances, or hypothermia, to name a few other causes.

 

[Ridryder911]

That would be a second degree type II. This particular block has a very high degree of likely hood of progressing to a third degree block, but may also be associated with an anterior wall MI. The increased mortality is due to the risk of ventricular arrhythmias and left-sided heart failure.

Not only can heartblocks be caused by damage/injury, they can also be congenital, or due to pharmacology/toxicology, infections, electrolyte disturbances, or hypothermia, to name a few other causes.

Ding....ding...ding...We have a winner.

I took a Marriott ECG interpertation course, and most always assume it is the 3 degree as it r/t in burns. Most of the time, third degree blocks the damage has already occurred but keeping the ventricular rate up for perfusion is the hard part.

Even the old Dirst Degree Block can be nasty, as many will "blow it off" and ignore it as something we do not tx. Any sedative or paralytic agents can easily induce these into an AMI as well.

Nice going!
R/r 911

 

[Shishkabob]

Can't 3rd degree turn into Vfib?

Could have sworn I read that somewhere.

 

[Melbourne MICA]

"AV dissociation"

The most important feature of third degree AV block to understand is AV dissociation. Also that it can be caused by many things and is a feature of a number of conduction irregularities.

The sinus node fires an impulse but it is not conducted through to the ventricles (because the normal conduction pathway is blocked) so you see a regular p wave in the rhythm but no QRS attached to it. In the absence of detecting conduction from the sinus node or junctional node (their are pacemaker sites in each - the junctional node doesn't engage here because the sinus node conducted an impulse at least as far as the junction) so the ventricles have to generate their own impulse. Which they do at the ventricular rate you typically see in such pts -15-40 beats per minute.

I don't know if I'd call it the "atria and ventricles doing their own thing". One leads to the other. AV dissociation occurs in other dysrhythmias a favourite being VT of course.

MM