What is a pacemaker and how does it work?

What is a Pacemaker and How Does it Work?

A pacemaker is an implantable medical device that uses electrical impulses delivered through electrodes to regulate the beating of the heart when the heart's natural pacemaker is not functioning properly or when there is a block in the heart's electrical conduction system. 1

Basic Function and Components

A pacemaker system typically consists of:

• Pulse generator: Contains the battery and electronic circuitry that controls the timing of electrical impulses
• Leads: Insulated wires that deliver electrical impulses from the generator to the heart
• Electrodes: The tips of the leads that contact the heart muscle

The pacemaker monitors the heart's electrical activity and delivers electrical stimulation when needed to maintain an adequate heart rate.

Types of Pacemakers

Modern pacemakers come in various configurations:

1. Single-chamber pacemakers: Stimulate either the right atrium or right ventricle
2. Dual-chamber pacemakers: Stimulate both the right atrium and right ventricle to maintain synchrony between chambers
3. Biventricular pacemakers (Cardiac Resynchronization Therapy): Stimulate both ventricles to restore synchrony in heart failure patients
4. Leadless pacemakers: Newer, self-contained devices implanted directly into the heart chamber without traditional leads 2

Pacing Modes

Pacemakers use a standardized code to describe their functionality:

• AAI: Atrial pacing inhibited by sensed atrial activity
• VVI: Ventricular pacing inhibited by sensed ventricular activity
• DDD: Dual chamber pacing with sensing and response in both chambers
• Rate-responsive pacemakers (AAIR, VVIR, DDDR): Adjust pacing rate based on physical activity or metabolic needs 1

Clinical Indications

Pacemakers are primarily implanted for:

• Symptomatic bradycardia due to sinus node dysfunction or AV block
• Heart block (second or third degree)
• Certain tachyarrhythmias that can be managed with specialized pacing
• Heart failure with conduction delays (cardiac resynchronization therapy)
• Syncope related to bradyarrhythmias 1

Implantation Procedure

The implantation procedure is typically performed under local anesthesia:

1. A small incision is made, usually below the collarbone
2. The leads are threaded through veins into the appropriate heart chambers
3. The leads are tested to ensure proper positioning and function
4. The pulse generator is connected to the leads and placed in a pocket created under the skin
5. The incision is closed and the device is programmed 3

Benefits and Outcomes

Pacemaker therapy has been shown to:

• Reduce symptoms such as fatigue, dizziness, and syncope
• Improve quality of life by allowing patients to resume normal activities
• Reduce mortality in certain patient populations
• Prevent complications associated with bradyarrhythmias 1, 2

Important Precautions for Patients with Pacemakers

Patients with pacemakers should be aware of:

• Electromagnetic interference: Strong electromagnetic fields can potentially interfere with pacemaker function

  • Keep cell phones at least 6 inches away from the device
  • Avoid lingering near security systems
  • Inform healthcare providers about the pacemaker before procedures 4

• Physical activity:

  • Avoid contact sports that could damage the device
  • Avoid extreme arm movements on the implant side for 4-6 weeks after implantation 4

• Medical procedures:

  • Special precautions are needed for procedures involving electromagnetic fields
  • MRI-conditional pacemakers may be safe for MRI under specific conditions
  • Electrocautery during surgery requires special precautions 4

• Follow-up care:

  • Regular device checks (initially 2-4 weeks after implantation, then every 3-6 months)
  • Remote monitoring may supplement in-person visits 4

Conclusion

Pacemakers have evolved significantly since their introduction in 1958, becoming smaller, more sophisticated, and capable of treating a wider range of cardiac conditions. They remain a cornerstone therapy for managing bradyarrhythmias and have expanded to treat certain tachyarrhythmias and heart failure, significantly improving patients' quality of life and survival.