TPM... AAI vs VVI c tx of bradycardia

SEOBowhntr · Sep 11, 2005

Doug, i agree with ethelbsnrn here...if you could explain this it would be helpful.
The ep-docs i work with have explained to me that because of the chaotic 'electrical-static' nature of a-fib you're unable to 'capture' an atrium with a pacemaker because the atria arent depolarizing/repolarizing in and orderly fashion. Because of this, when you attempt to pace an atrium that is 'fibrillating' the myocardial cells simply are unable to respond (again becAUSE they're all firing randomly).
It would be cool to understand how you do this, and would be a novel 'trick'.....but in the many yeARS i've used temporary pacers, i'v never even tried to atrial pace an a-fib.

Dinith,

You can actually overdrive pace the Atria, and it will sometimes work, though it is rarely used, I've seen it maybe 5-6 times in my career, but if you have a slower rate A-Fib, you can check a sensing threshold by increasing mV until the pacer fires asynchronous, then you've achieved the atrial sensing threshold. You need to make sure you have the PVARP on and set to prevent pacer mediated tachycardia, and set your AV Interval on your pacer so that the ventricular side of the pacer will follow the atrial pacing. When you have a patient in slow A-Fib with poor output, you can pace over the fibrillation, getting a better atrial kick than you would have otherwise, with a VVI mode pacer in a slow A-Fib, and increase output significantly.

Doug

Dinith88 · Sep 12, 2005

Dinith,
You can actually overdrive pace the Atria, and it will sometimes work, though it is rarely used, I've seen it maybe 5-6 times in my career, but if you have a slower rate A-Fib, you can check a sensing threshold by increasing mV until the pacer fires asynchronous, then you've achieved the atrial sensing threshold. You need to make sure you have the PVARP on and set to prevent pacer mediated tachycardia, and set your AV Interval on your pacer so that the ventricular side of the pacer will follow the atrial pacing. When you have a patient in slow A-Fib with poor output, you can pace over the fibrillation, getting a better atrial kick than you would have otherwise, with a VVI mode pacer in a slow A-Fib, and increase output significantly.
Doug

Doug, i'll look into this and thanks for your input. The notion that you can pace/capture a fibrillating atria is a strange one. Regardless of the 'sensing threshold' stuff, when a pacer 'fires' on myocardium that is fibrillating (electro-static, random cell depolariozation/repolarization), it's simply impossible to get the atria to contract because the 'quivering' muscle isnt repolarizing/depolarizing in a normal fashion, and thus the impulse gets wasted on a bunch of cells that are unable to initiate any organized impulse (the desired impulse is unable to force a muscle contraction).

And going back to your stuff about sensing thresholds..., when a pacemaker 'senses' a heart chamber (atria or ventricle) it's sensing the chambers rate (sensing the rate of electrical depolarization in the chamber). A fibrillating heart chamber has no rate because it's not depolarizing/contracting. With this in mind, what is your pacemaker 'sensing' if looking at a fibrillating chamber???

Another angle/point that can be made regarding this argument is the exapmle of V-fib. IN v-fib the ventricle is fibrillating. Same thing, just diffierent chamber. Would it not make sense to simply pace someone in v-fib? Implanted pacemaker/aicd's can detect a fibrillating ventricle. If the fibrillating chamber could be 'captured' with a simple pacemaker impulse, i'm sure it would be done rather than resporting to a violent de-fibrillation discharge.

I hope you see why i'm resisting your position. It's not out of a desire to argue...it's just that it goes against conventional thought...

SEOBowhntr · Sep 12, 2005

And going back to your stuff about sensing thresholds..., when a pacemaker 'senses' a heart chamber (atria or ventricle) it's sensing the chambers rate (sensing the rate of electrical depolarization in the chamber). A fibrillating heart chamber has no rate because it's not depolarizing/contracting. With this in mind, what is your pacemaker 'sensing' if looking at a fibrillating chamber???
I hope you see why i'm resisting your position. It's not out of a desire to argue...it's just that it goes against conventional thought...

Actually, Dinith, what the pacemaker senses is electrical activity, thus the measurement "milliVolts. That is why many pacemakers will not dual chamber pace correctly in a patient in A-Fib. If you could easily reprogram a pacer, like we can external epicardial pacers, you could improve output for patients with permanent pacemakers also. I HAVE done this with epicardial pacers and had good outcomes several times. You can asynchronously pace the ventricle to, though in most cases it is not warranted and could potentially be dangerous, and yes, sometimes you will get capture and sometimes you will not, but the atria generally require lower mAmps to obtain full capture, therefore that is how I have achieved this in the past. Granted, there are occasions in which I have been unsuccessful, but those occasions were occasions when the wires were not functional.

Could you pace V-Fib???? I don't know for sure, I don't know if anyone has ever tried it, (could be a risky proposition, but also could be effective, one might think) but you can defibrillate it and correct it on occasion. One thing to note, basically, the charge that comes from an AICD is significantly less than an external defibrillator, and you generally will need less powerful shocks to reset the atria.

You do bring up some good points, however, I can tell you that in my practice, I have used all of these things which I advocate and had multiple successes. On the occasions I was unsuccessful, the problem lay in the wires themselves, which were dislogded or non-functional, resulting in no sensing or pacing, which begins another story in which I've screamed at a doctor or two on occasion.

Doug

Dinith88 · Sep 12, 2005

. If my patient has sinus bradycardia symptomatic or asymptomatic, which is the best mode to place my tpm in? :)

A question to you would be 'why' would you desire to pace an asymptomatic sinus bradycardia??

Secondly, symptomatic sinus brady is rare... usually caused by meds, vagal stim., etc. and usually resolves if these underlying causes are identified and corrected. In the meantime, if the patient is being paced, AAI would certainly work...and perhaps a better mode than VVI (d/t atrial kick). However, if you're able, DDD would be superior as it would protect in the event of a deterioration of your rhythm (into a block, v-standstill, etc.), and enables you to manipulate pr-interval if desired. In DDD mode, the pacer'll work exactly the same way as AAI in sinus brady because the DDD senses/watches both the atrial rate and ventricular rate. If the paced atrium is followed by a corresponding ventricular contraction/QRS (with good pr-interval), then the ventricular leads wouldnt fire as the PM would 'sense' an adequate ventricular rate.

So...i guess my answer would be that in sinus bradycardia AAI is fine, but DDD is better because it would function similarly to AAI and has the added bonus that it protects against worsening rhythms. My best guess...

Dinith88 · Sep 12, 2005

Actually, Dinith, what the pacemaker senses is electrical activity, thus the measurement "milliVolts. That is why many pacemakers
Doug

Indeed it does sense electrical activity. However, to go further...it senses the electrical 'depolarization' of the atria...which in essence is the atrial contraction. Unfortunately, In a-fib the atria do not depolarize/contract normaly.

To make it as simple as possible...pretend the sensing pacemaker is an 'eyeball' that watches the atrial EKG baseline (electrical activity) for p-waves (atrial depolarization). When you adjust pacemaker sensitivy, all you're doing is fine-tuning this 'eye' to respond to different 'heights' of these p-waves. Now...regardless of how you adjust and/or fine-tune this sensing 'eye', if it sees a fibrillating ekg baseline (in a-fib), it is impossible to 'sense' anything because there're no p-waves. And...even if the atrial wire discharges at a set rate it CANT capture the atrium because they never repolarize (d/t the chaotic electrical activity in fib.)/ You can only truly 'pace' a heart chamber that is repolarized ('loaded and ready to fire').

Sure...with a TPM you can set an atrial rate and attempt to pace the underlying fib...and you'll even see spikes,...but it's probably a waste of time and of questionable value. Of course, i'll ask some of the EP docs i work with to confirm this stuff...but i dont beleive i'm far off the mark.

Dinith88 · Sep 12, 2005

One thing to note, basically, the charge that comes from an AICD is significantly less than an external defibrillator, and you generally will need less powerful shocks to reset the atria.
Doug

Have you ever seen someone get whapped by one of these? It's awful. They say it feels like getting kicked in the chest by a horse. Quite different from a pacemaker discharge...even if it is less powerful than an external defib.

SEOBowhntr · Sep 12, 2005

Have you ever seen someone get whapped by one of these? It's awful. They say it feels like getting kicked in the chest by a horse. Quite different from a pacemaker discharge...even if it is less powerful than an external defib.

Dinith,

Yes I have, several times, but that charge is definitely less powerful than when I put paddles on them and zap them myself.

To make it as simple as possible...pretend the sensing pacemaker is an 'eyeball' that watches the atrial EKG baseline (electrical activity) for p-waves (atrial depolarization). When you adjust pacemaker sensitivy, all you're doing is fine-tuning this 'eye' to respond to different 'heights' of these p-waves. Now...regardless of how you adjust and/or fine-tune this sensing 'eye', if it sees a fibrillating ekg baseline (in a-fib), it is impossible to 'sense' anything because there're no p-waves. And...even if the atrial wire discharges at a set rate it CANT capture the atrium because they never repolarize (d/t the chaotic electrical activity in fib.)/ You can only truly 'pace' a heart chamber that is repolarized ('loaded and ready to fire').

Have you set up many pacers??? Actually, when setting up a DDD pacer on a patient in A-fib, if the sensitivity is set to the highest setting (.4mV) on my pacers, it will sense continually. That is why I do a sensing threshold, and then override the pacer to basically asynchronously pace the atria, it does work and it works quite well.

Think about it like this, you have an isoelectric line on you ECG tracing, and in SR-SB, between your T-wave and your P-wave the electrical activity is 0 mV, then you get about 1.2mV of activity that is your P-Wave. Well in A-fib, after your T-wave, you have the continual fibrillation and depending on the fineness or coursness, it may fibrillate at .4-1.0mV, therefore if you set your sensing level to sense at 1.4mV, then that pacer will fire on that fibrillating atria, and make it contract moreso than it is while it is fibrillating. Kind of going on the same theory but different than defibrillating V-fib, only using much less energy. And yes, it is basically an "Atrial Defibrillation" as it is not able to sync as you would in a cardioversion, only using much less voltage. It would be interesting to see if you could selectively send enough energy through those atrial pacing leads to cardiovert the heart, though I am not sure exactly how you'd do that, you'd think it possible. I don't know everything, but pacemakers are one thing that I do know, Dinith, as I've reprogrammed and set up many of them, and have seen the varying capabilities of each from Transvenous to Epicardial to Permanent, and the Epicardial are by far the most nurse friendly because we can fine tune them with out having to obtain some piece of equipment like a permanent, and we can pace both chambers of the heart unlike a Transvenous.

Doug

Dinith88 · Sep 14, 2005

Dinith,
Yes I have, several times, but that charge is definitely less powerful than when I put paddles on them and zap them myself.
Have you set up many pacers??? Actually, when setting up a DDD pacer on a patient in A-fib, if the sensitivity is set to the highest setting (.4mV) on my pacers, it will sense continually. That is why I do a sensing threshold, and then override the pacer to basically asynchronously pace the atria, it does work and it works quite well.
Think about it like this, you have an isoelectric line on you ECG tracing, and in SR-SB, between your T-wave and your P-wave the electrical activity is 0 mV, then you get about 1.2mV of activity that is your P-Wave. Well in A-fib, after your T-wave, you have the continual fibrillation and depending on the fineness or coursness, it may fibrillate at .4-1.0mV, therefore if you set your sensing level to sense at 1.4mV, then that pacer will fire on that fibrillating atria, and make it contract moreso than it is while it is fibrillating. Kind of going on the same theory but different than defibrillating V-fib, only using much less energy. And yes, it is basically an "Atrial Defibrillation" as it is not able to sync as you would in a cardioversion, only using much less voltage. It would be interesting to see if you could selectively send enough energy through those atrial pacing leads to cardiovert the heart, though I am not sure exactly how you'd do that, you'd think it possible. I don't know everything, but pacemakers are one thing that I do know, Dinith, as I've reprogrammed and set up many of them, and have seen the varying capabilities of each from Transvenous to Epicardial to Permanent, and the Epicardial are by far the most nurse friendly because we can fine tune them with out having to obtain some piece of equipment like a permanent, and we can pace both chambers of the heart unlike a Transvenous.
Doug

OK doug, earlier at work i had a discussion with the head-nurse of the Ep-dept. at my place of employment. According to her, as i've said repeatedly, an atrium that is in a-fib cannot be paced....for the reasons i've already stated. Sensing is an entirely different 'animal' than pacing...and i agree with your sensing thresh-hold stuff..but it's irrelevant because even 'asynchronous' pacing of the atria will not produce an atrial systole (leading to a ventricular response/contraction/p-wave) if the atrium is fibrillating...and thus would make the notion of an atrial kick a moot point, because without an organized contraction of atria,...etc...

If you still disagree with this premise, i suppose i can ask the ep physicians themselves and relay their input on the matter.

SEOBowhntr · Sep 14, 2005

OK doug, earlier at work i had a discussion with the head-nurse of the Ep-dept. at my place of employment. According to her, as i've said repeatedly, an atrium that is in a-fib cannot be paced....for the reasons i've already stated. Sensing is an entirely different 'animal' than pacing...and i agree with your sensing thresh-hold stuff..but it's irrelevant because even 'asynchronous' pacing of the atria will not produce an atrial systole (leading to a ventricular response/contraction/p-wave) if the atrium is fibrillating...and thus would make the notion of an atrial kick a moot point, because without an organized contraction of atria,...etc...
If you still disagree with this premise, i suppose i can ask the ep physicians themselves and relay their input on the matter.

Not really worth arguing about, but like I said, I've done it numerous times in the past and seen a significant improvement. Ask one of the doc's they may agree with you HN, but I've seen it. I agree, it would be one of those "See it to Believe it," type things, that's why I believe it. Similar to pacing an asystole if you will or defibrillating a pt. in V-fib, only you keep doing it at a rate of 60-80/min. It may not break the fibrillation, but that shock will cause the muscle to contract, increasing the "atrial output."

Doug

Dinith88 · Sep 15, 2005

defibrillating a pt. in V-fib, only you keep doing it at a rate of 60-80/min. It may not break the fibrillation, but that shock will cause the muscle to contract, increasing the "atrial output."
Doug

...OK, now you're talking silly. Listen, if you defibrilate a heart chamber it doesnt generate any measurable output/systole. Also, shocking an a-fib is how you convert (ATTEMPT to convert) a-fib, not capture a chamber...if you defibrillated an a-fibbing atria 60-80 times a minute you'd fry the thing up...on top of not generating a contraction...on top of absolutely torturing the patient...

But i'll take your word for it. You have to see it to believe it...

SEOBowhntr · Sep 15, 2005

...OK, now you're talking silly. Listen, if you defibrilate a heart chamber it doesnt generate any measurable output/systole. Also, shocking an a-fib is how you convert (ATTEMPT to convert) a-fib, not capture a chamber...if you defibrillated an a-fibbing atria 60-80 times a minute you'd fry the thing up...on top of not generating a contraction...on top of absolutely torturing the patient...
But i'll take your word for it. You have to see it to believe it...

You see, that's where you misunderstand, it doesn't torture the patient at all, have you ever heard a patient complain that their pacemaker is shocking them???? As far as not generating a contraction, the electrical shock delivered, WILL cause a contraction, trust me. Ever use a "train of four???" Not exactly the same, but similar concept. Even a tetanic muscle would contract when smacked with a "stimulator" on high voltage, similar to a fibrillating atria.

Actually, thinking about pacing a V-Fib, got me going on searches, check this out: http://heart.bmjjournals.com/cgi/content/abstract/83/2/178 , can't see the whole article, but I guess I'm not the first one to think of attempting to pace V-Fib. I am unconventional, but I've also have good results from it. Atrial pacing A-fib has never converted it, and is unneeded in a patient with a sufficient cardiac output, but in a patient in low voltage A-Fib, with poor Cardiac output, it CAN be done and CAN improve a patients hemodynamic status.

Doug

Dinith88 · Sep 17, 2005

You see, that's where you misunderstand, it doesn't torture the patient at all, have you ever heard a patient complain that their pacemaker is shocking them???? As far as not generating a contraction, the electrical shock delivered, WILL cause a contraction, trust me. Ever use a "train of four???" Not exactly the same, but similar concept. Even a tetanic muscle would contract when smacked with a "stimulator" on high voltage, similar to a fibrillating atria.
Actually, thinking about pacing a V-Fib, got me going on searches, check this out: http://heart.bmjjournals.com/cgi/content/abstract/83/2/178 , can't see the whole article, but I guess I'm not the first one to think of attempting to pace V-Fib. I am unconventional, but I've also have good results from it. Atrial pacing A-fib has never converted it, and is unneeded in a patient with a sufficient cardiac output, but in a patient in low voltage A-Fib, with poor Cardiac output, it CAN be done and CAN improve a patients hemodynamic status.
Doug

Doug...i thought i was done with this but you keep drawing me back :)

First off..that study you linked has nothing to with anything we've discussed. To put it simply: the study is mentioning rapid ventricular pacing (in a NON-fibbing ventricle) in an ep-study/NIPS...and whether or not the procedure can inadvertantly induce a-fib. In this procedure, the ep-doc will rapidly pace the ventricle TO INDUCE v-fib...then he/she shocks the v-fib to ensure the aicd is working properly. The study was trying to determine a corrolation(sp?) between this procedure and accidental a-fib induction. You need to research a little harder.

And also the difference between defbrillating an atria and pacing an atria is like comparing mountains and mole-hills...or ponds and oceans. pacing IS NOT like defibrillating.

Lastly, i'm sure you've set up tpm's to do this, and i'm sure you saw spikes...but again.. It is impossible (and thus useless) to capture a fibrillating atria with a pacer...and would therefore be useless/incapable of generating any type of atrial kick to improve cardiac output. Period.