Tag Archives: electrical shock

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.

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,


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.