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N418 Exam 2 AV Blocks and Pacemakers

Terms in this set (66)

With 2nd degree AV blocks, we have 2 types: Type I ( Mobitz Type I, Wenckebach) and Type II (Mobitz Type II). Which of these is described below?

· Rate
o Depends on AV conduction ratio, may be less than 60
o Depends on how many impulses (P waves) are getting down into the ventricle (the more that are blocked, the more significant its going to be for the patient because the HR will be much slower—can be significant if its <60)

o Clinical significance depends on the rate
§ If the patient is very bradycardic then they may be very symptomatic
o Can be unstable if a significant amount of P waves are blocked (its all about the rate)

· Rhythm
o Irregular
· P wave
o Normal, some P waves are not followed by a QRS (conduction ratios are 3:2, 4:3, 5:4 etc.)

· PRI
o Progressively lengthens until one p wave is not conducted (missing QRS)
o Prolonging PR interval until one beat is blocked then it kind of resets itself and you might have a normal PR interval, then the next beat might be a little longer, then the next beat a little longer until one of those P waves are blocked
§ Its taking longer and longer for the impulse to get down into the ventricle and so eventually one for the P waves fires but the ventricles are not repolarizing and are not ready to accept a beat so that beat is blocked

· QRS
o Normal
· Grouped beating due to unconducted beats.

· Treatment:
o If the patient is bradycardic then follow the bradycardia algorithm
§ First drug is atropine (a vagolytic)
· Will block the parasympathetic nervous system (responsible for slowing the HR)—the sympathetic nervous system will be unopposed and increase the rate of fire of the SA node
· If this doesn't work, then try an external pacemaker (transcutaneous pacemaker) until a mor permanent solution can be implemented (transvenous pacemaker, permanent pacemaker, resolve whatever disease process they have, adjust the meds)
o If its new onset then notify the physician (they need to look at their disease processes—it could be because the patient had an MI or they are having respiratory problems, electrolyte problems, drugs that we are giving them)
o Depending on the rate, the patient may need a pacemaker if it cant be resolved
With 2nd degree AV blocks, we have 2 types: Type I ( Mobitz Type I, Wenckebach) and Type II (Mobitz Type II). Which of these is described below?

· Generally considered to be more significant—patient could be more hemodynamically unstable
o A lot of the times, these patients end up with a permanent pacemaker

· Rate
o Depends on AV conduction ratio (how many beats get through and how many don't), usually the rate is less than 60
o The degree of block will determine how fats or slow the HR is and ow clinically significant it is
· Rhythm
o Irregular—because some beats are conducted and some are not

· P wave
o Normal, some P waves are not followed by a QRS (conduction ratios are 2:1, 3:1, 4:1 etc.)
o Some P waves are conducted, and some are not
o The more P waves that are blocked, the lower the HR, the more significant the bradycardia, and the less likely the patient is to tolerate it

· PRI
o May be normal or prolonged: constant before the conducted beats.
o The difference between type I and type II is that you do not have that prolonging PR interval (all the PR intervals measure out to be the same—they don't get progressively longer and longer like they do in type I)
o May be prolonged but They are consistent—its just that some of them get through and some of them don't
§ If its 0.16 then they will all be 0.16

· QRS
o May be normal or wide/greater than 0.12 seconds
o If the block is low, then you will end up with a wide QRS because one side of the ventricle is going o depolarize before the other
o If the block is high in the AV, then you will probably have a normal or narrow QRS

· Treatment:
o Bradycardia algorithm
§ 1st line treatment is typically atropine but it may or may not work—there is some theory out there that says it may even make it worse because if you increase the rate of the sinus rhythm it may block down more
§ Transcutaneous pacemaker
§ Drip of epinephrine and a drip of dopamine
· Both increase HR—chronotropic effects (they stimulate sinus rate)
o Notify the HCP because this patient will probably need a pacemaker
o If it's because they are having some kind of acute event like an MI, then the patient probably needs to go to the Cath lab and have PCI

· Sometimes it can look like you are just having some unconducted PACs, but you can tell it's not PACS because if you measured out your P waves they would all be regular (they all walk out on time)
o In PACs, the P wave would be early or premature (premature ventricular contractions)
· Can have every other beat that is blocked (called a 2:1 conduction)—in those cases you usually have a pretty significant bradycardia
The following is information about ______ _____ blocks:

· Patients usually tolerate these well
o Some patients live with ____ ____ blocks

· Two major bundles:
o Right bundle branch—depolarizes the right ventricle
o Left bundle branch—depolarizes the left ventricle
§ The left bundle also has another little branch off of it (dual branches)

· Sinus node is working fine, AV node is working fine, but somewhere down in the bundles the impulse is blocked
o The impulse goes down the unblocked bundle and depolarizes that ventricle and then from cell to cell conduction it depolarizes the other ventricle
§ End up seeing a big, wide QRS (> 0.12 seconds) on your EKG with the T wave in the opposite polarity
· Will see a P wave before the QRS

§ It basically looks like a ventricular beat because it follows the path of a ventricular beat
· Normal beat goes through the SA node, to the AV node and depolarizes both of the ventricles at the same time (end up with your normal RQS of <0.12 seconds)

· If it's a beat that is initiated in the ventricles (like PVC), then it doesn't go down the bundles at the same time—it uses that cell to cell conduction to depolarize one side and then the other and then you get that wide, bizarre QRS with a T wave in opposite polarity
o Looks very similar when you have a ____ ____ block
o Difference between a PVC and a ___ ____ block is with a PVC you are not going to see a P wave before it
§ Aa ____ _____ block also will not come early, its going to be regular (its not premature)