Chapter 10: Cardiac Pacing

Question 1

What happens when complete heart block occurs at the level of the AV node?

Answer 1

HR around 50bpm

Stable escape rhythm - unlikely to suddenly fail and cause asystole

Narrow QRS due to intact bundle branches and bundle of his

May be due to inferior MI

May not req. pacing

Question 2

What can cause complete heart block lower than the AV node?

Answer 2

Degenerative conducting fibrosis

Extensive anteroseptal MI - affect all fibres of bundle branches

Cardiomyopathies

Calcific valve disease

Question 3

What happens in a complete heart block lower than the AV node?

Answer 3

Activity from Purkinje fibres or myocardium

Slow and unreliable

Wide QRS

Fail transiently to cause Syncope (stokes-adams attack) or ventricular standstill and cardiac arrest

Req. urgent pacing - esp. if long ventricular pauses (>3s)

Question 4

What makes pacing more likely to be successful?

Answer 4

Presence of p waves - heart more likely to respond to pacing stimulus

Question 5

What does capture mean in reference to pacing?

Answer 5

Immediate QRS following pacing stimulus

Check to see if there is a pulse

Question 6

What are the types of pacing?

Answer 6

Non-invasive:

• Percussion (mechanical - fist)
• Transcutaneous (electrical)

Invasive:

• Temporary transvenous pacing
• Permanent pacing - implanted pacemaker

Question 7

What are some indications for implanted pacemakers?

Answer 7

Treatment of bradycardia

Biventricular pacemakers for heart failure - cardiac resynchronisation therapy

Implanted cardioverter defibrillator which have pacing function

Question 8

When is percussion pacing used in preference to CPR?

Answer 8

Bradycardia so profound it causes clinical cardiac arrest

More likely to be successful when ventricular standstill accompanied by p waves

Question 9

How do you perform percussion pacing?

Answer 9

Deliver firm thump to precordium (lateral to lower left sternal edge)

Monitor ECG and 2nd person check for pulse

Question 10

What should you do if percussion pacing does not promptly trigger return of a pulse?

Answer 10

Start CPR immediately regardless of whether QRS complexes are generated

Question 11

When is transcutaneous pacing used?

Answer 11

Whilst waiting to establish transvenous pacing

Question 12

What are the advantages to transcutaneous pacing?

Answer 12

Established quickly
Non invasive
Easy to perform and req. minimal training

Question 13

What are the disadvantages to transcutaneous pacing?

Answer 13

Discomfort in conscious patient - stimulate painful contractions of chest wall muscles

Question 14

What can be used to deliver transcutaneous pacing?

Answer 14

Some defibrillators have ability

Stand-alone pacing devices may be available

Most systems capable of demand pacing - deliver impulse when req.

Question 15

How do you perform transcutaneous pacing?

Answer 15

Ensure area for pads is dry and remove hair

Position pads in same position as defibrillator pads

Use machine as per instructions

Avoid causing movement artefact - may prevent pacing stimulus

Set pacing rate - 60-90bpm typical, can be 30/40 if sudden ventricular standstill or extreme bradycardia

Set energy value at lowest value, gradually increase as observing pt and ECG - until pacing spike followed by QRS and subsequent t wave

Check for pulse

Question 16

What is a typical energy range for a transcutaneous pacing device?

Answer 16

50-100mA

Question 17

What should you do if the highest energy on transcutaneous pacing doesn’t achieve electrical capture?

Answer 17

Try different electrode positions

If continued - likely myocardium non-viable

Could be caused by other conditions such as severe hyperkalaemia

Question 18

Should you use transvenous pacing during a cardiac arrest?

Answer 18

No - attempt non-invasive before seeking expert help with transvenous pacing

Question 19

What can cause transvenous pacing systems to fail and what is the issue?

Answer 19

It may cause cardiac arrest, esp. in those who are pacing dependent. Fail in 3 ways:

1 High threshold
2 Connection Failure
3 Lead displacement

Question 20

When using temporary transvenous pacing, what happens to the pacing threshold?

Answer 20

Gradually reduce voltage to minimum to stimulate ventricle. Aim for <1V. Higher indicate insufficient myocardium contact

Pace at 3-4V (higher than the minimum threshold).

Over first days threshold transiently rise

Must check to ensure output remains over the threshold value

Question 21

What should you do if you lose capture due to high threshold?

Answer 21

Increase output of cardiac pacemaker

May cause lead displacement so req. expert assistance

Question 22

How can you get connection failure in transvenous pacing?

Answer 22

Electrodes usually bipolar - 2 electrodes

Each electrode seperately connected by lead outside patient and inserted into socket and subsequent pacemaker

Failure in any connections can prevent delivery of pacing stimulus

Question 23

When transvenous pacing failure is accompanied with loss of pacing spike, what should you do?

Answer 23

Check connections
Check pacemaker not turned off or batteries died

If these not issue, likely fracture in connecting cable - change

Question 24

Where and how is the tip of an endocardial transvenous pacing lead placed?

Answer 24

Apex of right ventricle

Must be enough slack in right atrium for movement due to posture change/inspiration but not so much to encourage displacement

Question 25

What is a complication of transvenous pacing?

Answer 25

Tip can perforate RV wall and enter pericardium –> cardiac tamponade

Question 26

If transvenous pacing fails due to lead displacement or perforation, what is seen?

Answer 26

ECG show pacing spike

Likely intermittent or complete loss of capture

If displace but still in RV - can cause ventricular extrasystoles and VT/VF

Question 27

What can happen if transvenous pacing fails?

Answer 27

Ventricular standstill

May be short lived and cause syncope

May be prolonged and cause cardiac arrest in asystole - if so use non-invasive pacing until transvenous pacing reestablished

Question 28

Are issues with implanted permanent pacemakers common?

Answer 28

No as the connections are much more secure

Question 29

What issues may be seen with implanted permanent pacemakers?

Answer 29

Lead displacement - early, less likely over time and rare after 4-6 weeks

Fracture of permanent pacing lead - usually following trauma

Question 30

What are the types of implanted pacemaker?

Answer 30

Device under clavicle

Leadless - transvenous within RV

Question 31

What are the reasons for having an implanted pacemaker?

Answer 31

Treat bradycardia - AV or SA node malfunction

Heart failure - biventricular pacing - cardiac resynchronisation - improve co-ordination of ventricular contraction

Question 32

What can happen if you get a failure in a biventricular pacing system?

Answer 32

Doesn’t lead to major change in HR or dangerous rhythm abnormality

Unlike if implanted pacemaker inserted for bradycardia

Question 33

What is an implanted cardioverter-defibrillator?

Answer 33

Device that primarily terminates life threatening tachyarrhythmia’s but also can deliver pacing stimuli

Question 34

If a patient with an ICD has a cardiac arrest, what should you do?

Answer 34

Deliver CPR as normal - no major risk even if ICD deliver shock

Rare reports of shocks from ICD causing transient myalgia and paraesthesia

Question 35

What should you consider in patients who have been resuscitated from cardiac arrest in shockable rhythm outside of context of acute MI?

Answer 35

ICD implantation

Question 36

What should be done for patients with and ICD after death?

Answer 36

Arrange for deactivation

Must be done before removal from body or performance of autopsy

Must be removed before cremation