quick question:

[realruby2000]

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anyone know why lidocaine and atropine are contraindicated in a third degree heart block? I thought I knew the answer but one resident totally confused me today 😕

 

[FoughtFyr]

anyone know why lidocaine and atropine are contraindicated in a third degree heart block? I thought I knew the answer but one resident totally confused me today 😕

Remember that a third degree block is a total disruption of the AV node. It is completely blocked. So the heart is beating because of the automaticity of the fibers of the ventricle. Therefore, atropine, which works by blocking vagal tone into the SA node (above the block) is rendered ineffective, it can't work by speeding up the atria because they are not transmitting to the ventricles. Lidocaine is a class 1B antiarrhythmic, it suppresses automaticity and shortens the effective refractory period and action potential durationof His-Purkinje fibers. Thus, it would act to supress the only action keeping any circulation going.

So, short answer:
Atropine - won't work
Lidocaine - will work against you

- H

 

[jf]

Agree with above!

Treatment of choice - pacemaker!

 

[realruby2000]

Remember that a third degree block is a total disruption of the AV node. It is completely blocked. So the heart is beating because of the automaticity of the fibers of the ventricle. Therefore, atropine, which works by blocking vagal tone into the SA node (above the block) is rendered ineffective, it can't work by speeding up the atria because they are not transmitting to the ventricles. Lidocaine is a class 1B antiarrhythmic, it suppresses automaticity and shortens the effective refractory period and action potential durationof His-Purkinje fibers. Thus, it would act to supress the only action keeping any circulation going.

So, short answer:
Atropine - won't work
Lidocaine - will work against you

- H

Excellent... Now I'm assuming the above reason is true even for a pt who is hemodynamically stable correct?

thanks 🙂

 

[ISU_Steve]

Yes, because you will make the patient unstable (or quite possibly dead).

 

[FoughtFyr]

Excellent... Now I'm assuming the above reason is true even for a pt who is hemodynamically stable correct?

thanks 🙂

Absolutely. The pharmacokinetics are not related to BP. Of the two lidocaine is by far the more dangerous.

- H

 

[pushinepi2]

Yes, because you will make the patient unstable (or quite possibly dead).

The treatment for third degree heart block is, without question, pacer therapy. I wonder if its appropriate to label atropine as contraindicated. While third degree heart block is characterized by dissociation, it is still not impossible for an occasional supraventricular impluse to be conducted. On more than one occasion, I have administered atropine as a temporizing measure prior to seeting up pacer pads. If the AV block is, "high enough," then additional (or accelerated) stimulus from the SA/atrial pacemakers might induce capture. Clearly, patients deteriorating into third degree heart block need definitive therapy. If, for whatever reason, there is a delay in setting up pacer capability, then it might make good clinical sense to at least try a dose of atropine, no?

Just so you know I'm not making this up:

"Hemodynamically unstable patients may be treated with atropine, although this will be ineffective in patients with a wide complex escape rhythm. Use caution in administering atropine in the setting of a suspected acute MI, as the resulting vagolysis leads to unopposed sympathetic stimulation, causing increased ventricular irritability and, potentially, ventricular tachycardia (VT)/ventricular fibrillation (VF)."

Emedicine.com

 

[Jeff698]

If the AV block is, "high enough," then additional (or accelerated) stimulus from the SA/atrial pacemakers might induce capture.

Although it is really an academic point as opposed to a useful clinical one, there may be some parasympathetic innervation of the purkinje system/ventricles right around the AV node. For this reason, atropine could be effective in some very high 3rd degree blocks. These are the ones with a narrow QRS that has AV dissocation.

In any case, as everyone has said, lido is bad and pacing is good.

Take care,
Jeff

 

[ERMudPhud]

I remember a pre-hospital M&M from a few years ago where the patient had an accelerated idioventricular rhythym at about 110bpm. They were also a bit hypotensive from what was probably sepsis. The paramedics thought the aivr was v-tach and gave lidocaine. The resultant asystole was quite dramatic.

 

[ISU_Steve]

I remember a pre-hospital M&M from a few years ago where the patient had an accelerated idioventricular rhythym at about 110bpm. They were also a bit hypotensive from what was probably sepsis. The paramedics thought the aivr was v-tach and gave lidocaine. The resultant asystole was quite dramatic.

Oops.

 

[EMIMG]

Yes, because you will make the patient unstable (or quite possibly dead).

One of the worse terms of all time - stable...because it implies no change. SO, I would argue that someone with no pulse, no respirations, and no blood pressure is stable.....they are dead..and therefore there vitals typically don't change over time.

 

[a_ditchdoc]

Some years ago I had a patient in 3rd degree block with intermittant, unstable, v-tach. To be honest, I was in a bit of a quandry as to what to treat first as the polymorphic V-tach was becoming more prominant that the block (with syncope, fluctuating LOC...). In retrospect maybe I should have treated the block with pacing to try to abolish the V-tach. But, I remember thinking she was going to degenerate into v-fib at any moment. So, what I actually did was attach pacing pads, set the rate, and give a bolus of lidocaine. And, just like the book said would happen, I knocked out all ventricular rythm. I turned the amps up on the pacer and got a sweet, much hoped for, capture. She never even fully lost consciousness. Of course, then I sedated her so she would stop saying "Oww.....Oww.....Oww....."

I'm just curious, what do you guys think would be the best way to handle a patient like this? I know what I did was risky, but I felt not doing it was even riskier.

 

[ERMudPhud]

I think I would have put the pads on and overdrive paced her before the lidocaine. First because that would confirm that I was going to be able consistenly pace her if need be and two pacing her at a higher rate might help supress the v-tach. Only when the pacer was working and if needed would I have given the lidocaine. Then I'd call the cardiologist and ask them to come put in an AICD right quick.

 

[a_ditchdoc]

I would have put the pads on and overdrive paced her before the lidocaine

In retrospect I suppose that was the way to go, especially since I had the pads on her already. I just had a bad feeling about fib as her v-tach was not that well organized. And I have to admit that my ass was puckered up while waiting for capture...

Some patients live because of what we do, some in spite of it...