student with a question-

  1. I was hoping some of you cardiac folks could help me. I am in Physiology and we just finished a unit on the cardiovascular system. I came up with a question my instructor couldnt answer Our text was discussing the SA node and how it is the pacemaker for the heart. The text also said other cells in the heart are capable of generating action potentials as well. My question is: when a patient is in PEA, is this what is happening? Are these other cells trying to fire action potentials and take over for the SA node? Our text isnt clear on the subjuect and I have been looking around in Taber's and on some sites but so far all I have found is how to treat PEA, definitions of Pea, etc. I am curious so let me know. Believe it or not, my physiology instructor didnt know what PEA was I couldnt believe it.


    Laura
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  2. 13 Comments

  3. by   dianah
    My understanding of PEA is: Pulseless Electrical Activity. There IS electrical activity, you WILL see activity on the EKG: it may be NSR, or some sort of AV block or whatever, but you will see a rhythm = Electrical Activity. BUT, there will be NO PULSE. It's not a question of what's competing for origin of the rhythm. The main problem, for whatever reason, is the heart is not beating, therefore NO PULSE. So you consult the algorithm for 1) reasons why and 2) treatment/support.
    Anyone else??
  4. by   obeyacts2
    Quote from dianah
    My understanding of PEA is: Pulseless Electrical Activity. There IS electrical activity, you WILL see activity on the EKG: it may be NSR, or some sort of AV block or whatever, but you will see a rhythm = Electrical Activity. BUT, there will be NO PULSE. It's not a question of what's competing for origin of the rhythm. The main problem, for whatever reason, is the heart is not beating, therefore NO PULSE. So you consult the algorithm for 1) reasons why and 2) treatment/support.
    Anyone else??
    Okay, I understand that PEA is no pulse and the heart is not beating: my question is: what is causing the electrical activity? Is it other cells trying to take over for the SA node?

    Laura
  5. by   Ted
    During PEA, the heart's electrical system can very well be functioning properly. Something else is keeping the heart from beating! Could be cardiac tampenode (sp?) where fluid within the cardiac sack is literally preventing the heart from beating. It could be a pulmonary embolism where where blood is prevented to to into the heart by a HUGE blood clot(s) in the lung. It could be a drug overdose. It could be a significant electrolye imbalance.

    Check out the American Heart Association's Advanced Cardiac Life Support (ACLS) text books. They do a fairly good job explaining PEA.

    Remember: PEA is a life threatening situation. The heart's electrical system may very well be working just fine as evidenced by an EKG. But the heart is NOT pumping blood!!!

    Hope this is helpful!

    Ted

    P. S. I've seen and dealt with PEA a few times. It's wierd and scary. You see the cardiac rhythms on the monitor, but you can't feel the freakin' pulse! In all the cases that I dealt with PEA, it involved a huge pulmonary embolism. Despite CPR (well performed chest compressions), one could NOT feel the pulse! The ENTIRE cardiao/pulmonary/peripheral vasculature was blocked by a huge clot(s). Very wierd! Very scary! Very sad!

    Ted
    Last edit by Ted on Mar 20, '04
  6. by   dianah
    Whatever the rhythm is on the screen, that's where the electrical activity is originating: a normal sinus rhythm or even a sinus tachycardia, is originating at or near the SA node. If it's any kind of an AV block, you'll see that on the rhythm. The electrical activity is still going thru its pathway(s), there is just no response from the heart muscle. Howzat??!!
  7. by   Ted
    Quote from dianah
    Whatever the rhythm is on the screen, that's where the electrical activity is originating: a normal sinus rhythm or even a sinus tachycardia, is originating at or near the SA node. If it's any kind of an AV block, you'll see that on the rhythm. The electrical activity is still going thru its pathway(s), there is just no response from the heart muscle. Howzat??!!
    The heart muscle may not be able to respond. For example, let's take cardiac tampenode (sp??). In cardiac tampenod, there's fluid in between the outer layer of the heart, the cardiac sac (or some similar name to like that), and the actual myocardium or heart muscle. That fluid (blood, whatever) is trapped between the two. There is a point when the volume of this fluid gets so great (and remember it's trapped between the heart's protective outter sac layer and the heart's muscle) the heart's muscle simply has no room to expand/fill with blood then pump blood out of itself to either the lungs or body. The chambers of the heart are prevented from filling because of the trapped fluid. Yes! There's still electrical activity. But that activity is useless because the heart simply doesn't have room to pump.

    What can cause cardiac tampanod?? Two main causes are trauma and infection. Each can cause some kind of fluid to be trapped in between the outter sac and the heart muscle.

    Take Pulmonary embolism for another example. Basically there's a big ol' clot that damming up the plumbing. It's like a big old turd stuck in a toilet pipe! No water can't get pass that turd. Except in the case of the heart and body's vasculature, no blood can get pass the clot.

    All it takes is one big ol' turd of a clot to cause a PE. Does the heart's electrical system still work? Yes! But basically the heart is prevented from pumping. . . Circulating. . . blood because of the turd/clot dam. So all of that electrical activity is again useless.

    The heart needs to be able to beat freely: expand and contract, expand and contract. The heart also need all of the veins and arteries to be clot free too! The pipes need to be free of turds.



    Hope that's helpful!

    Ted
  8. by   dianah
    (he said "turds," lol!)

    Is that a medical term Ted? Like medical doo-hickey and medical thingey?
  9. by   Ted
    Quote from dianah
    (he said "turds," lol!)

    Is that a medical term Ted? Like medical doo-hickey and medical thingey?
    Well, if it's not a medical term, it should be!

    Honestly, though. . . thinking in terms of the absurdly silly helps me remember stuff like this.

    Cheers!

    Ted
  10. by   zambezi
    PEA is a type of asystole. As Ted mentioned, electrical activity is preserved (hence the ekg tracing) but the heart can't contract--no pulse, no bp.
    Some causes: hypovolemia, hypoxia, acidosis, tension pneumo, tamponade, pe, hypo/hyperkalemia, hypothermia, overdose, huge mi. Treatment is the same as asystole, identifying the cause will help guide further interventions.

    The one time I have seen PEA, the patient was septic...and very acidotic, despite multiple bicarbs (she actually got worse after the bicarb...) She bradys down...we code her get her back...at some point she went pea (but dr. had talked to fam. and changed code status)--of course, family is watching monitor and seeing heart rhythm (pt vented, max epi/dopa/vasopressin and fluids...) I am pretty sure that soon after code the patient passes away as no one could feel a pulse for about an hour (further interventions, ie: echo to confirm pea were not done due to accumulation of poor circumstances which led to change to DNR status)...pt cold (with temp of 42, so we did have a cooling blanket on), levidity setting in so she was purple (with help from the vasopressors, I'm sure).
    It was pretty sad...an ugly situation all the way around--I just hope that we allowed the family some time grieve and to be with their loved one (all of them sitting in the room, watching the heart rate slowly dwindle down...). What an experience.
  11. by   athomas91
    like everyone else has said....with PEA there is electrical activity and it very well may be origionated in the SA node...but there is a dissociation between the electrical system and the muscular system...thus you have electrical activity which may be normal...but the muscle will not/ does not respond.
  12. by   wv_nurse 2003
    It is true that all cardiac cells have the potential to initiate electrical activity. The SA node (pacemaker) has an intrinsic rate of about 60-100 impulses per minute (the basis for "normal" heart rate). If the SA node fails (for any number of reasons)--the "pacing" responsibilities drop down to less reliable cells with slower intrinsic rates: {follow normal cardiac electrical conduction patterns}: cells located in the AV juncion with a rate of 40-60; cells located in the ventricles themselves with a rate of 20-40. Consider it your heart's "back-up" plan.
    Electrical signals in PEA can originate in any of these areas--and thus will determine the rhythm seen on the monitor. (If its the SA node firing--the PEA will be a sinus rhythm--I will guess that is rare). Usually PEA comes from a lower pacemaker--but depends on the underlying pathology that caused the PEA.
    Hope that helps!
  13. by   obeyacts2
    Quote from wv_nurse 2003
    It is true that all cardiac cells have the potential to initiate electrical activity. The SA node (pacemaker) has an intrinsic rate of about 60-100 impulses per minute (the basis for "normal" heart rate). If the SA node fails (for any number of reasons)--the "pacing" responsibilities drop down to less reliable cells with slower intrinsic rates: {follow normal cardiac electrical conduction patterns}: cells located in the AV juncion with a rate of 40-60; cells located in the ventricles themselves with a rate of 20-40. Consider it your heart's "back-up" plan.
    Electrical signals in PEA can originate in any of these areas--and thus will determine the rhythm seen on the monitor. (If its the SA node firing--the PEA will be a sinus rhythm--I will guess that is rare). Usually PEA comes from a lower pacemaker--but depends on the underlying pathology that caused the PEA.
    Hope that helps!
    Thank you for answering my question. Laura
  14. by   rnmaven
    Quote from obeyacts2
    I was hoping some of you cardiac folks could help me. I am in Physiology and we just finished a unit on the cardiovascular system. I came up with a question my instructor couldnt answer Our text was discussing the SA node and how it is the pacemaker for the heart. The text also said other cells in the heart are capable of generating action potentials as well. My question is: when a patient is in PEA, is this what is happening? Are these other cells trying to fire action potentials and take over for the SA node? Our text isnt clear on the subjuect and I have been looking around in Taber's and on some sites but so far all I have found is how to treat PEA, definitions of Pea, etc. I am curious so let me know. Believe it or not, my physiology instructor didnt know what PEA was I couldnt believe it.


    Laura
    Laura,

    Maybe you better send your instructor the ACLS guidelines......maybe the algorithm for PEA will help him/her understand the concept. That's why you have to have a documented flat line to be actually considered dead!

    Good luck in school.

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