A pacemaker is a small device implanted in the chest. It sends electrical signals to start or regulate a slow heartbeat. It’s most often placed in the chest just under the collarbone. A pacemaker may be used if the heart’s natural pacemaker (the SA node) is not working properly causing a slow heart rate or rhythm, or if the electrical pathways are blocked. 

Another type of pacemaker is called a biventricular pacemaker. It’s used for ventricles that don’t contract at the same time. This can make heart failure worse. A biventricular pacemaker paces both ventricles at the same time. This increases the amount of blood pumped by the heart. This treatment is called cardiac resynchronization therapy (CRT).

In some cases, a newer type of system called a leadless pacemaker may be used. This device is implanted within the heart itself. It does not use leads to stimulate the heart. 

What is an implantable cardioverter defibrillator (ICD)? 

An implantable cardioverter defibrillator (ICD) looks like a pacemaker, though slightly larger. It works very much like a pacemaker. But the ICD can send an energy shock that resets an abnormal heartbeat back to normal. 

Many devices combine a pacemaker and ICD in one unit for people who need both functions. After the shock is delivered, a “back-up” pacing mode is available if needed for a short while. 

The ICD has another type of treatment for certain fast rhythms called anti-tachycardia pacing (ATP). This is a fast-pacing impulse sent to correct the rhythm. This can be used instead of shocking the heart in some cases. 

Another type of ICD called a subcutaneous ICD does not involve placing a wire in the heart. Instead, this device is implanted in the left axillary region. Ann ICD lead is tunneled under the skin over the sternum. It can deliver energy shocks to treat life-threatening heart rhythms. But it can’t act as a pacemaker.