Atrial Fibrillation: How Many Times Can You Shock The Heart?

The most effective method for getting a heart that is in atrial fibrillation back to normal rhythm is a called an electrical cardioversion.

I’ve tried to come up with a good alternative or descriptive term for this procedure for my patients, such as “resetting” or “rebooting” the heart, but the term that seems to best resonate with patients is “shocking” the heart.

How Does Electrical  Cardioversion Work?

Typically, we all can connect (excuse the pun) to the feeling of a low current electrical shock which occurs when touching an ungrounded electrical source.

Unless the current reaches a certain level, it only results in transient burns and discomfort.

However, at current levels greater than 50 mA, an AC electrical shock traveling through the chest can, if timed properly, cause the heart to go out of normal rhythm into ventricular fibrillation.

We use a “synchronized” electrical cardioversion (termed direct current or DC cardioversion (DCC)) to convert a fibrillating or fluttering atrium back to the normal rhythm by timing the electrical shock so that it doesn’t cause ventricular fibrillation but resets both ventricles and atria safely back to normal.

cardioversionAF
Recording from a recent cardioversion I performed on a patient with recurrent atrial flutter/fibrillation associated with heart failure. On the left is the heart rhythm before the shock, and on the right we can see resumption of normal sinus rhythm. The little squiggles labeled p waves represent the electrical activity of the sinus node preceding the big vertical deflections, which represent the electrical activity of the ventricles (QRS). The circled little arrow shows the timing of the shock concurrent with the QRS complexes. If the timing is not correct, the shock can cause ventricular fibrillation.

This may seem like a barbaric and unnecessarily crude and dramatic way to restore normal rhythm, but if patients are properly prepared for this procedure, it is very safe and very effective, resulting in resumption of the normal rhythm 99% of the time.

There are some medications that we can utilize to convert atrial fibrillation (afib) back to normal (antiarrhythmic drugs), but they are far less effective than the electrical cardioversion, and often can bring out more dangerous heart rhythms.

Typically, I do my cardioversions in conjunction with an anesthesiologist, who administers IV propofol (yes, this was Michael Jackson’s sleep aid, his “milk”) to obtain “deep  sedation.” At this level of anesthesia, the patient is breathing on his own but will only respond to painful stimulation. The propofol is short-acting and prevents the patient from feeling the intense pain of the cardioversion (often described as like a mule kicking one in the chest), and from recalling any of the events.

Electrical cadioversion
The skeptical cardiologist calmly prepares to push the “shock” button that will trigger the Zoll device to deliver 150 Joules of biphasic direct current to the electrodes attached to his patient’s chest thereby “ZAPPING” her back to NSR. Should the patient’s heart rhythm be too slow, the Zoll device also can serve as an external pacemaker, triggering cardiac contractions via lower level electrical currents delivered through the chest electrodes.

The electrical shock is administered through electrodes, consisting of large sticky pads with electrical conducting gel attached to the right anterior chest and the left posterior back (see this brief information from Zoll about optimal placement).
Since I began using “biphasic” energy, the initial cardioversion is successful >95% of the time in my experience, but the heart may revert back to atrial fibrillation anywhere from a few minutes to a few years after the shock. We can reduce the chances of reverting back by the use of anti-arrhythmic drugs.

Multiple Shocks: What Is The Limit?

The DCC may need to be repeated, and we may repeat it after starting one of those anti-arrhythmic drugs I mentioned, in order to increase the time that the heart stays in the normal rhythm.

A common question when I recommend a repeat cardioversion is:

“Doc, how many times can you have your heart shocked?”

One might think it is one and done with the shock but it is not a cure; it is merely a resetting of the chaotic, confused and futile activity of the atria, so that the synchronized and regular electrical pacing provided by the sinus node in the upper right atrium can again resume its rightful role as conductor of the cardiac electrical orchestra that creates the wondrous symphony of normal cardiac contraction.

The factors that brought on the afib in the first place likely are still present: if we don’t address correctable factors we are less likely to maintain the normal sinus rhythm (NSR). Correctable factors include:

  • abnormal thyroid function
  • abnormal potassium or magnesium
  • inflammation of adjacent lung or pericardium
  • severe infection
  • obesity (see my post on fat sheep and afib)
  • certain cardiac valve problems

There is no evidence that the cardioversion per se damages the heart in any way. The major risks of the procedure (again, assuming proper preparation, see below) are related to the anesthesia.

I am more inclined to recommend a repeat cardioversion if there is clear-cut evidence that the patient does poorly when the heart is in afib.

Why Shock The Heart?

In medicine, there are two reasons for giving medications and doing surgery/procedures: to make the patient feel better or to reduce the chances of dying/having a major complication.

The major complication of afib is stroke.  Proper anticoagulation is required to prevent this in patients with afib whether or not they are in normal rhythm.  Clots can form in the left atrial appendage within hours of the development of afib, and the electrical cardioversion can increase the chance of stroke as any clot present is more likely to be expelled when the quivering, ineffective atrium converts back to a normally pumping, vigorous  atrium.

Primarily, then, we utilize cardioversion for the purpose of making patients feel better.

Some patients feel terrible the moment they go into afib: symptoms of palpitations, chest pain, or shortness of breath predominate and are especially prominent if the heart rate is high. Controlling the high heart rate with beta-blockers or diltiazem will reduce many of these symptoms, but I have a large number of patients who still feel terrible when they are “out of rhythm,” even if the heart rate is normal. Such patients who persist in afib are good candidates for one or multiple cardioversions, with or without the addition of anti-arrhythmic drugs.

A second group of patients, I think, benefits the most from maintaining sinus rhythm (rhythm control strategy): patients who develop heart failure when they go into AF.

These patients may not even know they are in AF because they don’t feel the typical symptoms initially.  After a few days or weeks or months of being in afib silently, however, they develop shortness of breath, weakness and leg  swelling – classic signs of heart failure.

When we look at the heart of such a patient by echocardiography, we often find one of two things causing the heart failure: a weakening of the heart muscle (cardiomyopathy) or significant leakage/backflow from the mitral valve (mitral regurgitation). Following cardioversion and maintenance of SR for weeks to months, the heart muscle strengthens back to normal and/or the mitral regurgitation improves dramatically and the heart failure resolves.

Multiple Shocks: Rationale

Yesterday I did an electrical cardioversion on an elderly patient of mine  for atrial fibrillation/flutter; this was her fifth DCC in the last year.

She falls into the second category of afib patients; she had developed severe heart failure due to mitral regurgitation after silently going into afib a year earlier. After long-term loading on the anti-arrhythmic drug amiodarone, followed by her fourth cardioversion, she had stayed in NSR for 10 months, her MR resolved, and she felt great. In patients like her, I think it is particularly important to maintain NSR and thus, multiple shocks are definitely warranted.

On the other hand, if you feel fine in afib without any evidence that it is effecting your heart muscle or valves, then it is hard to justify multiple attempts to shock the heart.

Any patient that has recurrent symptomatic afib or afib associated with heart failure, should be considered a candidate for an atrial fibrillation ablation.  The risks and benefits of afib ablation are worthy of another blog post, but the patient-centered afib website stopafib.org has a reasonable discussion here. Suffice it to say, it is a much more complicated and risky procedure than a cardioversion, but it attempts to address the underlying cause(s) of afib, and in some cases creates what could be considered a “cure.”

Cardiovertly Yours,

-ACP

For additional reading:

Here’s a good article from the European Society of Cardiology on cardioversion (https://www.escardio.org/Guidelines-&-Education/Journals-and-publications/ESC-journals-family/E-journal-of-Cardiology-Practice/Volume-11/Cardioversion-in-Atrial-Fibrillation-Described)

and check out what Dr. John Mandrola, an electrophyiologist (cardiologist who specializes in electrical problems of the heart) has to say about afib ablations at Drjohnm.org (http://www.drjohnm.org/2015/09/a-cautionary-note-on-af-ablation-in-2015/)

Credits-Life Coach of the Skeptical Cardiologist (LCOSC) for review of electrical engineering stuff.

 

 

 

18 thoughts on “Atrial Fibrillation: How Many Times Can You Shock The Heart?”

  1. I’m a fan of cardioversion, having had one to eliminate a mixed AF/atrial tachycardia. A nasty combination.
    It worked in one. Except for the sticky pads and the normal rhythm, I’d never have known they did it.

    My question is about those antiarrhythmia drugs. None is ideal. They range from hardly effective, through dangerous in the context of heart disease, to downright poisonous – as in amioderone.
    Could you discuss them?
    Rank them?

    1. I would love to discuss the anti-arrhythmic drugs and my personal approach to them. Definitely a complicated area and I don’t want to give it a superficial treatment. I’ll post my summary down the line when time permits.
      I will say that I use two drugs for 95% of my patients and that I know these two drugs inside and out and with extreme vigilance and meticulous monitoring coupled with 20 years of experience I find them to be safe and effective.

  2. As an atrial flutter participant, and a lay person,
    Your blog was understandable, informative
    Important for family member knowledge.
    Very comforting as well. Your picture may need
    Some George Lucas help, but yet, good.
    Thanks Doc, that’s one of the things I like about you, which is communication.
    Continue your fine approach to medicine!

  3. Hola Dr.,

    Just became a “follower”, (man does that sound cult-ish), and I am so excited to start reading your posts.

    I am the son of an elderly parent who has myriad heart issues – one of which is A-fib. We have done the Caridoversion thing, and it worked very well.

    I’ve often found myself having to simplify jargon for my parent, and this was no exception. It helps to calm the nerves by distilling the scary bits down to that which is giggle-some. It also serves to quell fears of distant family who are concerned about such processes.

    To that end; I’d like to add/propose my renditions of non threatening names for this procedure – if you will allow.

    I have used: “Defribu-Lite”, “Fribu-later Alligator”, and (for the 50 Shades fraternity), “A Firm Yet Gentle Paddling for That Saucy Ticker”.

    Please keep the blogs coming.

    Brian, London Ontario Canada

  4. This was very interesting information … as your posts usually are. It’s been a very long time — 10 years since I participated as a nurse in the assistance of treatment of patients undergoing cardioversion for a-fib. It was never a dull moment for me and MY adrenaline (or epinephrine) level was always high. I was always scared for the patient but knew this was a good treatment for them and just loved successful outcomes for them — which seemed to be most of the time!

    I’ve always found it interesting when I talk to patients how some know they have a-fib going on and others don’t notice a thing. I think cardioversion is obviously more preferable to being on a medication when possible.

    You’ve inspired me to do some more continuing ed in the cardiac arena! ❤

    1. Thank you. I too am totally fascinated by the difference in how patient’s feel when in Afib. I think it has to do with how the patient feels discomfort/pain in general-some are naturally stoics, others with extremely low threshold for any body disturbance. More research definitely needed in this area!

      1. Off topic … but kind of on topic (the heart) … I asked an anesthesiologist which was more accurate in determining LVEF (ejection fraction) — an echocardiogram (not TEE) or myocardial perfusion stress test. The anesthesiologist said an echo. I would have thought the myocardial perfusion.

        Can you answer why (or better yet) make a post? Just wondering. I know I could Google the heck out of the answer, but there’s some special hearing an answer from a “real life” specialist.

      2. Wow!. The things I could write about ejection fraction, the main measure that we have of the pumping function of the heart.
        Good topic for discussion. I can tell you briefly what I teach my residents and previously taught cardiology fellows.
        A well-done, well interpreted transthoracic echo EF is far more trustworthy than an ejection fraction obtained from a nuclear or myocardial perfusion stress test. I read them both on a regular basis in multiple areas and have done so at multiple hospitals.
        Briefly, the limitations of the nuclear gated imaging-unreliable if heart rhythm irregular, cannot reliably assess if large prior heart attack, unreliably high in people with small hearts. I can’t tell you how many times we’ve gotten a questionably low EF from nuclear and verified normality by echo.
        Now, since I review personally the echo on my patients, I can be guaranteed that the EF is correct and is “well done and well interpreted”. If you have read my postings on botched echocardiograms you know that is not always the case 🙂

      3. I’ll have to go back and read many of your posts. I’m happy that the anesthesiologist and his cohorts all agreed with what you’re saying — that the transthoracic echo was more accurate with EF — they said it without hesitation.

        While I don’t work directly with cardiologists, I do obtain cardiology records — echos, stress tests, pacer checks, EKGs and office notes.

        I read most of them most of the time and yesterday I had an echo that said 60-65% EF and the myocardial perfusion said 81% — I was thinking this was quite a difference since they were performed on the same day. I finally thought to ask the question which was more accurate because I like to document in my nursing history (that is read by the anesthesiologists) the EF … but didn’t know which one to put because of the difference. I wanted to put the higher number, but thought I’d ask. The question had never dawned on me before. I had always thought the two tests would have relatively same results regarding EF … not so yesterday.

      4. That is a typical scenario, abnormally high EF by MPI (likely smallish woman with smallish , normally functioning heart) with echo EF more accurately reflecting the true systolic function.
        I would also point out that with echo we are directly looking at the heart muscle on a beat to beat basis.
        With MPI it’s a totally indirect image compiled from thousands of beats and the heavily processed and manipulated.

      5. Yes, if my memory does serve me correctly it was a smallish woman — weight no greater than 140 lbs. sent for testing due to abnl EKG, but the stress and echo turned out fine except for some mild MR.

      6. OK, back on topic.
        I could not believe it when I first read of some people not actually knowing they were in AF.
        Going into AF, to me, means suddenly knowing something is drastically wrong. My ribs are being thrashed from inside by something frightened – wanting to escape. Adrenalin spurts, and then the fright is mine. If I quieten and sit – which I must to catch my breath – I can sense the low buzz of the fibrillation.
        I’m thin. Not much covering those ribs.
        I wonder – is there a correspondence of cushioning obesity with “silent” AF?

      7. I really think there is. This is based on my anecdotal experience. Some day, I’d like to review all my patients and classify them as silent afibbers or symptomatic afibbers and compare BMI.
        That being said, I did see my very thin 94 year old lady yesterday (who self monitors for afib with her iphone/alivecor) who when I first saw her was in afib at 140 BPM and was totally unaware.

  5. I recall a friend having what I believe to be this procedure 8 years ago without any sedation, and she begged to stop but they said once you started, you couldn’t stop. Is this the same procedure? If so, why was it originally done with no sedation or anesthesia?

    1. In rare circumstances (usually when patient is in shock with extremely low blood pressure) it is necessary to do a cardioversion for atrial fibrillation immediately and without appropriate sedation or anesthesia. The rationale is that the sedating agents can further and potentially dangerously drop the blood pressure.
      The other possibility for your friend is that she was in ventricular tachycardia (VT) which is a much more life threatening arrhythmia. VT is usually associated with profound symptoms and low blood pressure, often with the patient being unconscious, thus sedation/anesthesia not required. Sometimes, however patients develop a less malignant form of VT that is sustained and are mentating on arrival to ER.
      With this type of patient it is often possible to use medications to convert the rhythm, however, a particularly eager and aggressive ER doctor could conceivably rush in and do an electrical cardioversion right away.

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