Implantable cardioverter defibrillators (ICDs) and pacemakers are two devices that are sometimes implanted into a person’s upper chest to help them maintain (or restore) a normal heart rhythm.
The main difference between a pacemaker vs defibrillator is that a pacemaker helps to maintain a steady heart rhythm while an implantable cardioverter defibrillator sends either a low-energy shock or high-energy shock when it detects abnormal heart rhythms that are shockable—such as ventricular fibrillation or ventricular tachycardia.
If you have a heart condition or have experienced a heart attack or sudden cardiac arrest, understanding the differences between a defibrillator vs pacemaker can help you prepare yourself for the treatment that your doctor or cardiologist recommends.
Similarities Between Defibrillators and Pacemakers
Pacemakers and implantable cardioverter defibrillators are both small devices with a sealed lithium battery, circuitry, leads (in most cases), and electrodes. They have several features in common:
- With the exception of leadless pacemakers, both devices have leads that are threaded through a blood vessel into the heart.
- Both are typically implanted via surgery under local anesthesia and require a few days to a few weeks of recovery time.
- Both can improve eligible patients’ length and quality of life.
- Both have surgery- and device-related risks, although fortunately, serious risks are rare.
Key Differences Between a Defibrillator vs. Pacemaker
How They Work
Implantable defibrillators work much like automated external defibrillators (you might have seen these before–popular models include the Philips HeartStart FRx and HeartSine Samaritan PAD 350P). When they sense an AED shockable rhythm, they send an electric shock to the heart immediately to shut down the heart’s fluttering so that it can restart with a normal rhythm.
In contrast to an external defibrillator:
- An implantable defibrillator is present and ready to deliver a shock at all times.
- An ICD delivers shocks automatically (without anyone needing to connect the electrodes to your chest or press a button) to prevent sudden cardiac death.
- Many implantable cardioverter defibrillators also function as pacemakers.
Whereas an implantable cardioverter defibrillator is on standby to deliver shocks reactively, a pacemaker’s pulse generator sends electrical signals to the heart on a regular basis to bring an abnormal heart rhythm back into the healthy range. This typically occurs when the heart beats too slowly (referred to as “bradycardia”) rather than when it’s too fast (referred to as “tachycardia”).
For people who need both functions, there are implantable cardioverter defibrillators that also function as pacemakers.
Relevant Heart Conditions
Implantable cardioverter defibrillators are often recommended for people who:
- Have survived a sudden cardiac arrest
- Suffer from heart failure, especially heart failure that is getting worse
- Suffer from cardiomyopathy
- Are awaiting a heart transplant
- Have irregular heartbeats due to a structural issue
- Developed an abnormal heartbeat after suffering a heart attack
Pacemakers are often recommended for people who:
- Have congenital heart defects (structural problems with the heart)
- Have specific types of muscular dystrophy
- Have suffered a heart attack
Both devices are recommended for people who have issues with their heart’s electrical system.
Primary Risks Associated With ICDs & Pacemakers
The risks of having an ICD or pacemaker implanted are similar and are largely related to the surgery itself. Apart from bruising and swelling (which is usually temporary), ICD or pacemaker implantation can lead to:
- Blood clots
- Damage to a blood vessel or nerve
- Heart infection
- Punctured or collapsed lung
To circumvent these risks, some patients might be eligible for wearable cardioverter defibrillators (WCDs), which are worn like a vest under the patient’s clothing and have electrodes attached to the chest that can sense abnormal heart rhythms and deliver a shock.
Other patients with mild symptoms may be able to simply keep an AED with them at all times. For instance, the Philips HeartStart OnSite is extremely easy to use, making it one of the best AEDs to use in the home. It’s important to discuss all of the options with your doctor to see which might be the most appropriate for you.
Types of Pacemakers
There are several types of pacemakers that are wired slightly differently:
- Single-chamber pacemaker. The lead is wired to either the right ventricle or right atrium.
- Dual-chamber pacemaker. There are two leads—one wired to the right ventricle and the other to the right atrium.
- Biventricular pacemaker. Two leads are also used except that they connect to the right and left ventricles to keep both sides of the heart in sync. A biventricular pacemaker is also referred to as a cardiac resynchronization therapy (CRT) pacemaker.
- Leadless pacemaker. A leadless pacemaker combines the electrode and pulse generator into one small device–the size of a pill–that is installed directly on the ventricle wall. It activates when the heart rate falls below a predetermined value.
Protecting a Pacemaker or ICD
As electrical devices, pacemakers and ICDs are sensitive to other devices with a strong magnetic field. In particular, people who have these devices will need to be careful about coming too close to:
- Cell phones
- High-tension electrical wires
- Electrical generators
- Power plants
- Airport security
- Metal detectors
- Strong magnets
If you need an MRI or shockwave therapy for kidney stones, tell the doctor that you have a pacemaker or ICD and which kind you have. Every 3 or 6 months, your doctor will check that the device is working and the leads are in place. Some may also check heartbeat data from the device.
Treating Sudden Cardiac Arrest with a Pacemaker or Implantable Defibrillator
People with a pacemaker or ICD implanted can still go into cardiac arrest—especially if the device stops working. When treating a victim of SCA, check for a small box in the upper left side of the chest, upper right side (less common), or abdomen (in children). An ICD will be slightly larger than a pacemaker.
To treat the victim, call 911, commence high-quality CPR immediately, and send someone to fetch an AED (if available). Place the closest electrode pad at least a few inches from the pacemaker or ICD—never directly on top because the device could stop the shock from reaching the heart.
The Right Device for the Right Purpose
If you are concerned about heart symptoms or have suffered a heart attack or sudden cardiac arrest in the past, your doctor can explain the potential treatment options and order tests for a clear diagnosis.
Whether your doctor recommends a pacemaker, ICD, wearable cardioverter defibrillator, portable defibrillator, medications, lifestyle changes, or a combination of these, the right measures can help you live a longer and more active life.