Norpace Flop

After almost a year of unmanageable SVT (Atrial Tachycardia), we tried the latest med, Norpace. It was a horrendous experience. It gave me daily Inappropriate Sinus Tachycardia and caused the Atrial Tachycardia to worsen, and episodes to lengthen. It was an awful week. I was awake every night with terrible runs if SVT (hours). Finally stopped it and the side effects lessened. The SVT is still not fun, but not incessant likebit was. Has anyone heard of the Anti-Dysrhythmics making Atrial rhythms worse? What does that mean in the EP world? In don't quite understand the Physiology of what would make that happen. Hoping someone with more knowledge can weigh in!

Also, if the Beta Blocker stopped working and didn't stop the rhythm, are all beta blockers out? Or would another one possible work? Metoprolol and Propranolol stopped working, but didn't try any others.



Edited 1 time(s). Last edit at 09/06/2023 11:33AM by MeganMN.

Sorry to see you are living this experience. Must be awful.

The beta blockers only slow the heart, they have no effect on arrhythmia. And yes, several people on this board have reported several undesired side-effects when taking both calcium channel blockers and anti-arrhythmic medications. Fortunately the other life saver, the new oral anti-coagulant drugs, such as apixaban, are well tolerated almost universally.

Norpace is a class I antiarrhythmic and those are definitely known to be pro-arrhythmic in some people. They can even go from being effective to being pro-arrhythmic in someone who's been taking it for years.

Like gloaming said, beta blockers only slow your heart rate. They won't stop or prevent an arrhythmia.

Thank you for the replies. We are going to try Propafenone next. I really hope it works!

Good luck and let us know how it goes!

Have you tried a calcium channel blocker, like Diltiazem?



Edited 1 time(s). Last edit at 09/07/2023 05:27PM by The Anti-Fib.

So I am on Day 3 of Propafenone. My SVT episodes are getting longer, just like they did with the Norpace. I just doubled the dose as directed but it seems to be following the same pattern as the Norpace. I got orthostatic tachycardia and my SVT episodes worsened and lasted longer. Anyone know why this is happening with the sodium channel blockers? The doctor seems puzzled. I don't understand it.

If I were you I would stop the propafenone. It's the same class of drug as flecainide and seems to be behaving the same, so I would just stop. Talk to them about something entirely different like Multaq or sotalol.

Thanks, Carey. I have been in SVT now for over three hours, and already took the higher dose for tonight. Will tough it out and talk with them in the morning. They seemed skeptical last time, but it had to be something with the sodium channel blockers that my heart doesn't like. Try again....

Can anyone explain the actual physiology of why some anti arrythmics cause atrial tachycardia?

I would have to wade through all this to learn and to figure out how to explain it in my own words. Would you like to give it a shot?

[www.ahajournals.org]

Perfect! That is EXACTLY what my nursing brain was looking for!!

I think the narrowing of the refractory period would be the main culprit. When you make the refractory period shorter, it gives more time for an errant impulse to trigger a response. I saw this firsthand when I learned how to control my flutter with potassium. Potassium does the opposite and widens the refractory period, and if you widen it enough it can stop the repeating circle of flutter by causing the impulses to arrive too late to trigger another beat. The same general principle would apply to afib: wider refractory period, less arrhythmia (within limits, obviously).

Quote
Carey
I think the narrowing of the refractory period would be the main culprit. When you make the refractory period shorter, it gives more time for an errant impulse to trigger a response. I saw this firsthand when I learned how to control my flutter with potassium. Potassium does the opposite and widens the refractory period, and if you widen it enough it can stop the repeating circle of flutter by causing the impulses to arrive too late to trigger another beat. The same general principle would apply to afib: wider refractory period, less arrhythmia (within limits, obviously).

Hmm

"In man, Norpace at therapeutic plasma levels shortens the sinus node recovery time, lengthens the effective refractory period of the atrium, and has a minimal effect on the effective refractory period of the AV node. Little effect has been shown on AV-nodal and His-Purkinje conduction times or QRS duration." Source

For Propafenone: "Atrial and ventricular refractory periods were prolonged significantly in a dose-dependent fashion." Source

I certainly agree generally with "wider refractory period, less arrhythmia."

[quote

Hmm

"In man, Norpace at therapeutic plasma levels shortens the sinus node recovery time, lengthens the effective refractory period of the atrium, and has a minimal effect on the effective refractory period of the AV node. Little effect has been shown on AV-nodal and His-Purkinje conduction times or QRS duration." Source

For Propafenone: "Atrial and ventricular refractory periods were prolonged significantly in a dose-dependent fashion." Source

I certainly agree generally with "wider refractory period, less arrhythmia."[/quote]


So it appears that in Norpace and Propafenone, they lengthen the refractory period of the atrium. So I still can't figure out why those two drugs have worsened the atrial tachycardia. Unless I have some issue with my sodium channels. Just trying to sort some of this out before I speak with my EP because they are beginning to run out of options for meds.

Quote
MeganMN
So it appears that in Norpace and Propafenone, they lengthen the refractory period of the atrium. So I still can't figure out why those two drugs have worsened the atrial tachycardia.

Because the class I antiarrhythmics are known for that. I don't think there's a definitive answer to your question about mechanism.

There are a half-dozen other antiarrhythmics to try, so your EP shouldn't be running out of options.