Friday, 28 February 2014

Pacemakers

"Understand pacemakers and their failure" - what a broad statement to put in a syllabus. Luckily, some excellent resources exist to help us to do just that. The best resource has to be from EnlightenMe (especially good as that's for EM docs anyway).

EnlightenMe
http://www.enlightenme.org/knowledge-bank/cempaedia/cardiac-implantable-devices


GoogleFOAM
http://www.eperc.mcw.edu/EPERC/FastFactsIndex/ff_111.htm
http://journals.lww.com/em-news/Fulltext/2007/01000/Diagnosis__Pacemaker_Failure_to_Capture.9.aspx
http://lifeinthefastlane.com/education/ccc/pacemakers/ 
http://www.cardiacengineering.com/pacemakers-wallace.pdf
http://lifeinthefastlane.com/education/ccc/temporary-pacemaker-troubleshooting/
http://emcrit.org/blogpost/understanding-pacemakers/
http://www.mededmasters.com/sgarbossa-criteria---ami-in-presence-of-pacemaker.html http://lifeinthefastlane.com/ecg-library/pacemaker-malfunction/
http://expensivecare.com/2013/12/03/pacemakers-defibrillators-and-immortality/
http://archinte.jamanetwork.com/article.aspx?articleid=1783304
http://annals.org/article.aspx?articleid=706782
http://drgdh.wordpress.com/2011/07/11/pacemaker-emergencies/  

BMJLearning - nothing
Doctors.net - nothing

Pacemakers

 There are lots of different types of pacemakers, and these are catagorised using "NGB codes". The code should be in the patient's passport. This NGB code explains which chambers of the right heart are involved, as well as the way in which the device interprets electrical signals. Modern pacemakers are able to recognise intrinsic depolarisations (“sensing”) and provide artificial stimuli (“pacing”).
1st letter: the chamber paced: A(trium), V(entricle), or D(ual)
2nd letter: the chamber sensed: again, A,V, D, or very occasionally, neither (O)
3rd letter: the way in which the signals determine the activity of the pacemaker itself: I(nhibited), T(riggered), or D(ual). The differences between these are not relevant here.
       
Common modes of pacing are

- VVI: a single lead to the RV provides both sensing information and pacing 
- DDD: leads are positioned in both the RA and RV, and can both sense and pace 

Pacemaker problems
Device failure: failure to sense and/or pace appropriately. Don't be mislead by hysteresis. Consider a patient with a pacemaker and a lower acceptable heart rate of 50/min would start pacing as soon as the intrinsic rate fell to 49/min. Hysteresis is the separation of the lower pacing rate from the lower sensing rate. meaning that the device will pace at 50/min, but only when the intrinsic rate drops to, for example, 40/min. It is easy to see why this might give the impression that the device has malfunctioned, if the patient’s own rate is perhaps 42/min, but the pacemaker has not stepped in.
Lead failure: in the immediate post-implant period the leads may displace which might be quite subtle. Displacement can cause "Twiddler's Syndrome" where the patient manipulates the pulse generator, the pacemaker rotates and the leads dislodge. This can cause diaphragmatic or brachial plexus pacing!
Pocket problems: the pacemaker is implanted in a pocket in the deep issues of the chest. This may get infected. Antibiotics may help but the pacemaker may need changing.  


Questions
Check:
  1. What device is implanted, and when?
  2. How is the device set up, in terms of mode and rate etc.?
  3. What is the patient’s own intrinsic rhythm and rate?
  4. Is there evidence of appropriate pacing activity on the surface ECG?
  5. Is there evidence of appropriate sensing on the surface ECG?
  6. If no to 4 and 5, is there evidence of inappropriate pacing/sensing?
  7. Is there any evidence of a mechanical complication, i.e., lead displacement, fracture etc.?
  8. Is there evidence of a local complication such as infection
Presenting Complaints
 Delivered shock therapy whilst conscious
- Was this appropriate (for VF/untreated VT), or inappropriate (usually due to misidentification of the rhythm, or “noise” artifact secondary to lead fracture).
Clinical assessment within the ED will include the following:
  • Check electrolytes, especially magnesium and potassium
  • Look for myocardial ischaemia - if in doubt, treat as ACS
  • Look for lead fracture: a plain chest x-ray is helpful

    A patient who is well, with a stable rhythm, and who has had a very limited number of shocks, does not necessarily require admission and can be discharged with next day follow up.
Syncope
Check syncope is really due to a cardiac cause. Remember: 
  • Sustained bradycardia is unlikely if the ICD has pacing functions, but is possible if there is any evidence suggestive of pacemaker failure
  • VF will rapidly lead to loss of consciousness.
  • Patients who have had sustained VT  may or may not be aware of palpitations immediately beforehand, and there is often a degree of retrograde amnesia following a shock / collapse; a normal ECG at presentation does not exclude this as a cause
Associated cardiac symptoms
Chest pain, palpitations and dyspnoea may all be seen in ICD patients attending the ED, either from the underlying cardiac condition, or as a manifestation of issues around therapy from the device. In general, these should be approached as they would for any other patient.

Palliative PatientsIf possible, reprogramme the ICD with the tachyarrhythmia therapy disabled. If this isn't possible, tape an external magnet above the device.
Pacemakers don't keep dying patients alive as terminal events are normally associated with such a sick myocardium that the patient doesn't respond to the pacemaker.
If the patient is not imminently going to die, don't automatically switch off the pacemaker as you may cause symptomatic bradycardia and heart failure.


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