Implanted defibrillators give life-saving shocks, but if you have atrial fibrillation, may go off for the wrong reasons.
Defibrillators are little devices that monitor every heartbeat, and when a defibrillator detects that a patient has gone into cardiac arrest it will immediately deliver a life-saving shock. But these shocks can sometimes happen for the wrong reasons — and do at a surprisingly high rate.
What does it feel like if one of these implanted defibrillators fires? My patients often describe a “shock” from their defibrillator as a bomb going off inside the chest. Most patients would gladly exchange this very short and intense burst of pain for extra years of life.
My colleagues and I studied this question (the results of our study were published in October 2013 in the Journal of the American College of Cardiology. We looked at what happened to 3,809 patients who received a shock from an implantable defibrillator. We then compared the outcomes of these 3,809 patients with 3,630 matched defibrillator patients who did not receive a shock.
Here’s what we found over the three-year follow-up period:
- If the shock was to end a cardiac arrest (ventricular fibrillation), patients were 2.1 times more likely to die over the next three years.
- If the shock was to stop ventricular tachycardia, a type of arrhythmia, patients were 1.7 times more likely to die over the next three years.
- If the shock was from atrial fibrillation, patients were 1.6 times more likely to die over the next three years. It should be noted here that defibrillators are designed to not deliver a shock for atrial fibrillation. But if the atrial fibrillation is fast enough it can “fool” the defibrillator, and a shock will be delivered.
- If the shock was for a very fast, benign arrhythmia or a device malfunction (the device was fooled), there was no increased risk of dying.
Interpreting the Defibrillator’s Shock
What do these findings mean? The majority of the time the defibrillators went off for the right reasons (ventricular tachycardia or ventricular fibrillation). But 41 percent of the shocks were because a device was fooled by a non-life-threatening arrhythmia, or because of a device malfunction.
Clearly, these devices aren’t doing a very good job if they fire for the right reason only 59 percent of the time.
First, in my opinion, this study should be a wake-up call for defibrillator manufacturers to create a more reliable device that is less likely to go off for the wrong reasons.
Second, if a patient receives a shock for any arrhythmia from the ventricles or for atrial fibrillation, this is a cry for help from the patient’s heart. These patients are at high risk of dying and need to be evaluated and treated quickly.
Often what we see is that these patients have gone into heart failure, or may have a blockage of one of the arteries in their heart. So patients who have received a shock for a ventricular arrhythmia or atrial fibrillation require prompt medical attention. With a thorough evaluation and treatment, including lifestyle changes, the heart may be given a chance to heal and reduce the risk of premature death.
Third, these results are reassuring in that there was no increased risk of death if the defibrillator went off for a benign rhythm or device malfunction. This also helps to answer the long-standing debate among cardiologists as to whether shocks, in and of themselves, are dangerous or not.
Fortunately, the danger is not from the shock but rather from the underlying cardiac condition.
At the end of the day, shocks, both appropriate and inappropriate ones, are just a part of implantable defibrillator therapy. It is my hope that from this study, device manufacturers will work to create better algorithms and software, so that these devices are not so easily fooled, and so that physicians caring for patients who have received a shock for ventricular fibrillation, ventricular tachycardia, or atrial fibrillation will realize the significance of this event and take rapid measures to prevent premature death in these patients.
Who Needs an Implantable Defibrillator?
Implantable defibrillators are reserved for patients who have either already survived a cardiac arrest or are at high risk for a cardiac arrest. Defibrillators are specifically designed to treat life-threatening arrhythmias in the ventricles, or the lower chambers of the heart.
Arrhythmias of the upper chamber of the heart, like atrial fibrillation, do not require an implantable defibrillator.
What Is It Like to Live With a Defibrillator?
While these implanted devices generally don’t cause much discomfort, patients can certainly feel them under the skin. If a person is wearing a swimming suit, you can see the outward bulge of the defibrillator device on their chest.
These devices help many patients feel more secure because they know that every heartbeat is being monitored. But for other patients it can be a huge source of anxiety, since they never know whether the device is going to deliver a shock.
Unfortunately, these devices aren’t foolproof: Sometimes a patient will receive a shock for a non-life-threatening event or a device malfunction, as our study demonstrated.
John D. Day, MD, is a cardiologist specializing in heart rhythm disorders at the Intermountain Medical Center Heart Institute. He is the immediate past president of the Heart Rhythm Society and is the editor-in-chief of the Journal of Innovations in Cardiac Rhythm Management. He has published more than 100 medical articles and has an upcoming book entitled The Longevity Plan: Seven Lessons From the World’s Happiest and Healthiest Village.