Hello folks,
Today’s POTD will be a quick overview of implantable cardioverter-defibrillators (ICDs) and their common complications.
Why do patients have an ICD in place?
Secondary prevention in previous episodes of unstable VT or VF.
Primary prevention if pt has hx of severe heart failure or underlying congenital arrhythmias.
Exact indications listed below:
Hx of MI within last 40 days with LVEF of <30%, NYHA Class II or III heart failure with an LVEF <35%, underlying disorders which place them at high risk of unstable VT or VF such as congenital long QT syndrome, HOCM, Brugada, ARVD
What does an ICD do?
Note that all ICDs are also pacemakers, but the reverse is not true (pacemakers do not have defibrillator/shocking functionalities).
Anti-tachycardia function: If the patient is tachycardic above a pre-set range (usually 150-220) the ICD will compare QRS morphology to a known sinus beat and if determined to be different, will deliver a series of paced beats at a rate slightly faster than the native rate to break the re-entrant cycle.
Defibrillation in response to sensed VT or VF
What can go wrong with ICDs?
In short, problems with ICDs/pacemakers come down to a failure of sensing or a failure of pacing.
Pacing malfunction:
Failure to pace: pacemaker doesn’t deliver a stimulus at all, resulting in return of the underlying rhythm.
Failure to capture: pacemaker delivers a stimulus, but the stimulus does not result in depolarization. EKG will show pacer spikes that are not followed by P waves or QRS complexes.
Sensing malfunction:
Failure of sensing: pacemaker fails to sense normal cardiac activity so an impulse is delivered inappropriately. EKG will show intermittent pacer spikes.
Oversensing: pacemaker identifies external signals such as from skeletal muscle contraction as “appropriate” and will not send an impulse when one is required.
Other problems:
Pacemaker mediated tachycardia: formation of a re-entrant circuit from retrograde p waves being sensed as native atrial activity, causing inappropriate tachycardia. This tachycardia does not exceed the programmed upper limit of the ICD.
Twiddler syndrome: accidental or intentional manipulation of the pulse generator resulting in dislodgement of pacing leads resulting in sx such as diaphragmatic or brachial plexus pacing. Will manifest as arm twitching or uncontrollable hiccups depending on where lead has migrated.
Miscellaneous pearls
Because most ICDs have only a lead in the RV, a LBBB pattern is expected on EKG; new RBBB pattern/axis deviation may indicate lead migration/dysfunction.
If you need to externally cardiovert or defibrillate, place pads at least 8cm away from device in anterior-posterior orientation.
Placing a magnet over the device will remove the defibrillator function of an ICD, but pacing function will be kept. This will be helpful in the setting of inappropriate shocks. Kept in charge nurse desk on north side usually!
Every patient should carry a pocket card indicating the manufacturer of their ICD, but it can also be ID’d by CXR and using an app called Pacemaker!
We’re lucky we have electrophysiology as a consult service here at Maimo that can interrogate a device for us, but each company has on-call representatives that will come interrogate a device 24/7.
Medtronic Inc. (1-800-328-2518)
St. Jude Medical Inc.(1-800-722-3774)
Boston Scientific Inc. (1-800-227-3422)
References
https://www.emdocs.net/ecg-pointers-icds-and-when-they-malfunction/
https://www.emdocs.net/em3am-pacemaker-aicd-complications/
https://www.emdocs.net/pacemaker-and-aicd-management-in-the-emergency-department/
https://rebelem.com/pacemaker-basics/