Exam 5 - Pacemakers

Question 1

Pacemakers

Answer 1

• Inserted into RA and/or RV
• Can sense and stimulate electrical activity
• Can be programmed externally

Question 2

Pacemaker uses

Answer 2

• Can be used to “overdrive” tachycardias
  - need cardioversion available as backup
• 3rd degree av block
• lesser degree av block/bradycardia
• AV blocks +/- BBBs

Question 3

J.A. McWilliam

Answer 3

• 1899

- Zapping heart with electrical stimuli can cause heart to contract

Question 4

Dr. William Weirich

Answer 4

• 1957
• used myocardial electrodes to restore HR, CO, and MAP in animals
• allowed open heart surgery to expand dramatically

Question 5

Arne Larson

Answer 5

• 1958
• Swedish patient who got 26 pacemakers in his life
• Problem with early pacemakers was mercury batteries

Question 6

Lithium iodide batteries

Answer 6

• Revolutionized pacemakers
• 1971
• more reliable and lasted longer

Question 7

Pacemaker components

Answer 7

• generator (holds battery, electronics, and header)
  - can be MRI safe (titanium) or MRI bad
• leads: unipolar (talks to generator) or bipolar (talks to lead itself)
  
  • attached to inside heart muscle passively (hook) or actively (screw)
  • unipolar more sensitive but bipolar less affected by muscle movement and magnetic fields
• electrode tip

Question 8

Temporary pacemaker types

Answer 8

• transcutaneous: emergency use w/ external pacing/defib unit
• transvenous: emergency use w/ external pacemaker
• epicardial: wires sutured to RA (exit R of sternum) and RV (exit L of sternum)
• used for short periods of time
• In CPB…placed post x-clamp removal….before CPB termination

Question 9

Single chamber permanent pacemaker

Answer 9

• One lead into either RA or RV

- Used to fix slow/irregular heartbeat caused by heart block

Question 10

Dual chamber pacemaker

Answer 10

• One lead in A….one in V
• Can create the atrial kick like in normal heart beat
• leads to good CO

Question 11

Triple chamber pacemaker

Answer 11

• aka Bi-ventricular
• aka Cardiac resynchrinization therapy (CRT)
• Used on very sick hearts
• lead in RA, RV, LV (via coronary sinus)

Question 12

Demand pacemaker

Answer 12

• fixes slow or irregular heart beats
• senses when no electrical activity is detected…. and fires
• after each detected native beat…timer resets

Question 13

Fixed rate pacemaker

Answer 13

• discharge at steady rate regardless of native heart activity
• can lead to competition of native and pacemaker beats are too similar

Question 14

Rate-responsive pacemaker

Answer 14

• adjust pacing to patients level of physical activity

Question 15

Implantable cardiac defibrillators

Answer 15

• ICDs
• when tachycardia is sensed…it shocks heart back into normal rhythm
• very sophisticated algorithms
• can also help w/ bradycardia, do low energy cardioversion, high energy defibrillation

Question 16

Defibrillation

Answer 16

• enough energy to cause all cardiomyocytes to contract
• stops the cells and arrhythmias
• forces all cells to enter refractory phase at same time
• hopefully puts heart back in normal rhythm

Question 17

AC defib

Answer 17

• no longer used
• difficult to control
• low conversion rate
• only good on ventricular arrhythmias
• causes voltage drops in hospital

Question 18

DC defib

Answer 18

• 1962 by Dr. Bernard Lown
• electrical charge is stored rather than delivered
• need high voltage over short time span to be effective
• defib in v-tach or v-fib

Question 19

Cardioversion

Answer 19

• special shock 30 ms after r wave
• done with algorithm
• fixes a-fib, a-flutter, a-tach, SVTs

Question 20

Pacemaker nomenclature

Answer 20

- Paced - Sensed - Response - (adaptive?)
A = atria
V = ventricle
D = dual
O = none
S = single
T = trigger
I = inhibit
R = responsive to physical activity

Question 21

5th letter

Answer 21

• if present
• response to tachyarrhythmias
  P = pacing response
  S = shock response
  D = dual
  O = no response

Question 22

Failure to capture

Answer 22

• pacer spike…but no cardiac response

Question 23

Failure to pace

Answer 23

• no pacer spike but should be

Question 24

Failure to sense

Answer 24

• pacer fires randomly during cardiac cycle

Question 25

Pacer problems that can be fixed w/ reprogramming

Answer 25

• Under-sensing: cant detect cardiac activity
• Over-sensing: detecting muscle movement as cardiac activity
• Loss of capture: pacer stimulation fails to make a heartbeat
• crosstalk: when dual chamber device interprets atrial output as vent output
• Pacemaker-sustained endless loop arrhythmia: tachycardia sustained by pacemaker