Intro to Pacemakers

by Atul Jaidka

Pacemakers

  • Single Chamber
  • Dual Chamber
  • Leadless
  • CRT-P
  • Left Bundle/His

Defibrillators

  • ICD
  • Dual Chamber ICD
  • CRT-D
  • Subcutaneous ICD
  • LifeVest Wearable Defibrillator

Note: All defibrillators are pacemakers

Pacemakers

  • Constantly monitors for need to pace
  • Depending on programming will pace at varying lower and upper rates

Single Chamber

  • Most common
  • RV Lead

Dual Chamber

  • RA Lead
  • RV Lead

Note: LBBB like QRS

What do pacemakers do?

  • Pace
  • Sense
  • (Defibrillate)

Pacemaker Modes

Common Modes: VVI, DDD, AAI, VOO

VOO

https://derangedphysiology.com/main/required-reading/cardiothoracic-intensive-care/Chapter%209.1.2.7/single-and-dual-chamber-pacing-modes

DDD

https://derangedphysiology.com/main/required-reading/cardiothoracic-intensive-care/Chapter%209.1.2.7/single-and-dual-chamber-pacing-modes

Pacemaker Issues

  • Threshold
  • Sensing
  • Algorithms

 

 

 

 

 

Note: Pacemaker is usually not the problem

Threshold

  • Testing how much output is needed to achieve pacing
  • Set rate higher than patients intrinsic
  • Progressively reduce output till lose capture (watch morphology change)
  • Threshold is one above and set pacemaker to 3x or more

Failure to Capture

  • Note enough output to achieve a QRS
  • Example: lead fracture or lead dislodgement

Over and Under Sensing

  • If spikes are where they shouldn't be or rate is much lower than the set lower rate, think about sensing issues

Sensing

  • Pacemaker needs to be able to sense to know when to pace or not pace
  • If it under-senses (b), it will miss QRS and pace when not needed
    • extra spikes
  • If it over-sense (c), it will think other waves are QRS and not pace when needed
    • less spikes

Sitting

Leadless Pacemaker

Implanted in the RV

Note: may not see pacer spikes

ICD

  • Acts as a pacemaker (ie. watching for need to pace)
  • Monitors for arrhythmia
  • If ICD senses ventricular arrhythmia will either try ATP (anti-tachycardia pacing) or shock depending on programming
  • Indicated for EF<35 and on optimal medical therapy

CRT

  • Patients with wide QRS have dyssynchronous LV and RV contraction causing reduced effeciency
  • By sensing the atria and then pacing the LV and RV at the same time, the heart is resynchronized to try and improve efficiency and thus symptoms
  • Indicated for LBBB>140ms, NYHA II-IV, EF <35, on optimal medical therapy

His/LBBB

  • Putting a pacemaker lead in the His or LBBB to achieve a narrow QRS and LV and RV synchrony
  • Ongoing area of advancement