In Question 13 from the second paper of 2001, the candidates were presented with an elective ICU admission who happens to also have an AICD. "How does this device affect your management" they asked. Conditions which pose as indications for the insertion of an AICD are farm more threatening than the AICD itself, in my opinion. However, there are implications to having an angry electric eel in your chest. There is a beautiful and freely available article by Sergio Pinski (2000) which lists not only the common AICD-related problems, but also the solutions to them. This article is paraphrased here to simplify revision.
AICD device malfunction
Total device failure: there is no pacing or AICD activity. The device appears dead for all intents and purposes. There are several possible causes for this:
- Its battery may run out if it has not been checked recently.
- The surgery may have damaged it, rendering it inoperable.
- The anaesthetist had it turned off, in order to allow safe diathermy, and failed to turn it back on again.
- The patient was externally defibrillated, and a 200J shock has completely fried the AICD circuitry.
Pacing failure: the device seems to be working (pacing spikes are seen on ECG) but there is no capture. This usually means something has happened to its interface with the myocardium.
- The leads have become dislodged, eg. in moving the patient, or in the process of CVC insertion (classically, the PA catheter is to blame)
- The whole device has been dislodged in some way, also pulling out the leads. Classically, this is associated with a demented patient who fiddles with their device.
- The myocardium underlying the pacing lead has infarcted.
- The lead has become infected
Failure to defibrillate VT or VF: the patient is clearly dying but the AICD for some reason refuses to rescue them. Why might that be? It is usually some sort of programing error. For instance:
- Inappropriately high rate cutoff: the VT is not fast enough
- Failure to satisfy multiple detection criteria (too many criteria)
- Completed cycle, exhaustion of therapies (the AICD has run out of ideas)
- Cross-inhibition by separate pacemaker
Consequences of normal AICD function
Overenthusiastic defibrillation: the device is shocking the patient relentlessly.
- There is a genuine VT storm,
- There is electrical interference, eg. from diathermy
- The AICD is suffering a software error and is misinterpreting normal cardiac function or diaphragmatic myopotentials, delivering "spurious" shocks.
Inappropriately normal function: the device missed the family conference, and does not realise the patient is being palliated. In these situations the AICD should be disabled. Ethical issues arise if the patient has an underlying complete heart block or something similar (in which you might want to merely disable the defib function).
Logistic consequences of having an implantable device
- it may act as a nidus for infection
- it interferes with line placement
- it makes MRI impossible
- it creates CT artifact, obscuring chest pathology