Chapter 10: Cardiac Pacing Flashcards
What happens when complete heart block occurs at the level of the AV node?
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
What can cause complete heart block lower than the AV node?
Degenerative conducting fibrosis
Extensive anteroseptal MI - affect all fibres of bundle branches
Cardiomyopathies
Calcific valve disease
What happens in a complete heart block lower than the AV node?
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)
What makes pacing more likely to be successful?
Presence of p waves - heart more likely to respond to pacing stimulus
What does capture mean in reference to pacing?
Immediate QRS following pacing stimulus
Check to see if there is a pulse
What are the types of pacing?
Non-invasive:
- Percussion (mechanical - fist)
- Transcutaneous (electrical)
Invasive:
- Temporary transvenous pacing
- Permanent pacing - implanted pacemaker
What are some indications for implanted pacemakers?
Treatment of bradycardia
Biventricular pacemakers for heart failure - cardiac resynchronisation therapy
Implanted cardioverter defibrillator which have pacing function
When is percussion pacing used in preference to CPR?
Bradycardia so profound it causes clinical cardiac arrest
More likely to be successful when ventricular standstill accompanied by p waves
How do you perform percussion pacing?
Deliver firm thump to precordium (lateral to lower left sternal edge)
Monitor ECG and 2nd person check for pulse
What should you do if percussion pacing does not promptly trigger return of a pulse?
Start CPR immediately regardless of whether QRS complexes are generated
When is transcutaneous pacing used?
Whilst waiting to establish transvenous pacing
What are the advantages to transcutaneous pacing?
Established quickly
Non invasive
Easy to perform and req. minimal training
What are the disadvantages to transcutaneous pacing?
Discomfort in conscious patient - stimulate painful contractions of chest wall muscles
What can be used to deliver transcutaneous pacing?
Some defibrillators have ability
Stand-alone pacing devices may be available
Most systems capable of demand pacing - deliver impulse when req.
How do you perform transcutaneous pacing?
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
What is a typical energy range for a transcutaneous pacing device?
50-100mA
What should you do if the highest energy on transcutaneous pacing doesn’t achieve electrical capture?
Try different electrode positions
If continued - likely myocardium non-viable
Could be caused by other conditions such as severe hyperkalaemia
Should you use transvenous pacing during a cardiac arrest?
No - attempt non-invasive before seeking expert help with transvenous pacing
What can cause transvenous pacing systems to fail and what is the issue?
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
When using temporary transvenous pacing, what happens to the pacing threshold?
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
What should you do if you lose capture due to high threshold?
Increase output of cardiac pacemaker
May cause lead displacement so req. expert assistance
How can you get connection failure in transvenous pacing?
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
When transvenous pacing failure is accompanied with loss of pacing spike, what should you do?
Check connections
Check pacemaker not turned off or batteries died
If these not issue, likely fracture in connecting cable - change
Where and how is the tip of an endocardial transvenous pacing lead placed?
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
What is a complication of transvenous pacing?
Tip can perforate RV wall and enter pericardium –> cardiac tamponade
If transvenous pacing fails due to lead displacement or perforation, what is seen?
ECG show pacing spike
Likely intermittent or complete loss of capture
If displace but still in RV - can cause ventricular extrasystoles and VT/VF
What can happen if transvenous pacing fails?
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
Are issues with implanted permanent pacemakers common?
No as the connections are much more secure
What issues may be seen with implanted permanent pacemakers?
Lead displacement - early, less likely over time and rare after 4-6 weeks
Fracture of permanent pacing lead - usually following trauma
What are the types of implanted pacemaker?
Device under clavicle
Leadless - transvenous within RV
What are the reasons for having an implanted pacemaker?
Treat bradycardia - AV or SA node malfunction
Heart failure - biventricular pacing - cardiac resynchronisation - improve co-ordination of ventricular contraction
What can happen if you get a failure in a biventricular pacing system?
Doesn’t lead to major change in HR or dangerous rhythm abnormality
Unlike if implanted pacemaker inserted for bradycardia
What is an implanted cardioverter-defibrillator?
Device that primarily terminates life threatening tachyarrhythmia’s but also can deliver pacing stimuli
If a patient with an ICD has a cardiac arrest, what should you do?
Deliver CPR as normal - no major risk even if ICD deliver shock
Rare reports of shocks from ICD causing transient myalgia and paraesthesia
What should you consider in patients who have been resuscitated from cardiac arrest in shockable rhythm outside of context of acute MI?
ICD implantation
What should be done for patients with and ICD after death?
Arrange for deactivation
Must be done before removal from body or performance of autopsy
Must be removed before cremation
