Understanding Pacemakers and Defibrillators

Aug 12, 2024

Implantable Pacemakers and Defibrillators

Overview

  • Implantable pacemakers and defibrillators are devices that apply electric shocks to maintain the heart rhythm and, if necessary, restart it.
  • The number of devices being implanted is steadily increasing, exceeding half a million per year.

Heart Anatomy

  • The heart consists of four chambers:
    • Two atria
    • Two ventricles
  • Each atrium is connected to its respective ventricle by a one-way valve.
  • Blood is pumped as the chambers contract and relax in a coordinated manner.

Heartbeat Regulation

  • Healthy heart beating is regulated by electrical impulses.
  • Sequence of events:
    1. Atria fill with deoxygenated blood (right side) and oxygenated blood (left side).
    2. Electrical signal from the sinoatrial (SA) node causes atrial contraction, pushing blood into ventricles.
    3. Signal is picked up by the atrioventricular (AV) node and directed to the Purkinje fibers in the ventricle walls, causing ventricular contraction.
    4. Blood is pumped through the pulmonary valve (to lungs) and aortic valve (to body).
    5. Cycle restarts.

Artificial Pacemakers

  • When the SA node fails, an artificial pacemaker can be implanted.
  • Pacemakers deliver small, evenly timed electric shocks.
  • Implantation process involves:
    • Inserting electrodes into heart chambers.
    • Inserting leads into a vein near the collarbone.
    • Implanting a generator device under the skin.

Implantable Cardioverter Defibrillators (ICDs)

  • Used for severe heart conditions.
  • Capable of sensing a stopped heart and delivering a powerful electric shock to restart it.

Advanced Devices

  • Cardiac Resynchronization Therapy (CRT) ICD:
    • Uses a third lead inserted into the left ventricle to resynchronize ventricles.

Challenges with Leads

  • Patients with ICDs face a 20% chance of lead failure within 10 years.
  • Lead replacement may require open-heart surgery (about 2% of cases).

Innovations in Pacemaker Design

  • Development of new pacemakers that do not rely on leads inside the heart.
  • Subcutaneous ICD:
    • Places the lead just outside the heart, under the skin.
  • Wireless designs are being developed to eliminate the need for leads altogether.