A pacemaker is a small implanted medical device that helps keep the heart beating at a safe and effective rhythm. It is most often used when the heart beats too slowly or pauses because the heart's natural electrical system is not working properly. The device does not replace the heart, but it supports the heart by sending carefully timed electrical signals.
Understanding pacemakers connects physics, electronics, and biology in a life-saving technology.
A pacemaker system usually includes a pulse generator placed under the skin and one or more insulated leads that enter the heart through a vein. The leads sense the heart's own electrical activity and can deliver a pacing pulse when the heartbeat is delayed. Inside the pulse generator, a battery and electronic circuitry measure timing, store settings, and control when pulses are sent.
Modern pacemakers can adjust pacing rate during activity and can be checked or programmed wirelessly by clinicians.
Key Facts
- A pacemaker treats abnormal heart rhythms by sensing heart activity and delivering electrical pulses when needed.
- The pulse generator contains the battery, microcircuitry, sensing electronics, and pulse output system.
- Pacemaker leads carry signals in two directions: heart signals to the generator and pacing pulses from the generator to the heart.
- Heart rate in beats per minute is HR = 60 / T, where T is the time between beats in seconds.
- Electrical energy delivered in a simple pulse can be estimated by E = VIt, where V is voltage, I is current, and t is pulse duration.
- A demand pacemaker waits for natural beats and only paces if the heart's own rhythm is too slow or absent.
Vocabulary
- Pacemaker
- A pacemaker is an implanted device that helps control heart rhythm by sending small electrical pulses to the heart.
- Pulse generator
- The pulse generator is the pacemaker body that contains the battery, control circuitry, and electronics that create pacing pulses.
- Lead
- A lead is an insulated wire that connects the pulse generator to heart tissue for sensing and pacing.
- Sensing
- Sensing is the process by which a pacemaker detects the heart's natural electrical signals before deciding whether to pace.
- Arrhythmia
- An arrhythmia is an abnormal heart rhythm that may be too fast, too slow, or irregular.
Common Mistakes to Avoid
- Thinking a pacemaker shocks the heart like a defibrillator is wrong because ordinary pacing uses small timed pulses, not high-energy emergency shocks.
- Assuming the pacemaker fires every beat is wrong because many devices are demand pacemakers that wait and pace only when the heart's own beat is late.
- Ignoring the leads is wrong because the pulse generator cannot sense or pace the heart effectively without a working electrical pathway to heart tissue.
- Confusing heart rate with pulse energy is wrong because heart rate measures timing in beats per minute, while pulse energy depends on voltage, current, and duration.
Practice Questions
- 1 A patient's heart beats once every 1.2 s. Calculate the heart rate in beats per minute using HR = 60 / T.
- 2 A pacing pulse has V = 2.5 V, I = 0.004 A, and t = 0.0005 s. Estimate the energy delivered using E = VIt.
- 3 A demand pacemaker senses a normal heartbeat just before it was scheduled to pace. Explain why the device should inhibit its pacing pulse and how this protects the heart's rhythm.