ICDs Flashcards
Functions of an ICD
Deliver shock in the setting of VF/VT.
All ICDs are also pacemakers but not all pacemakers are ICDs.
Parts of an ICD
1) Pulse generator: Acts as a shocking electrode in defibrillation
2) Leads
- Arterial lead (sensing/pacing functionality)
- RV lead (pacing, sensing, defib functionality)
- LV lead (pacing/sensing function)
Indications for ICD implantation
1) Secondary prevention:
- previous episode of unstable VF/VT (but NOT INDICATED if VF/VT occurs <48hrs after MI)
- Sustained VT in setting of CDM or channelopathy
2) Primary prevention:
- MI >40d prior and LVEF <30%
- CDM and NYHA II+ with LVEF <35%
- Pts with underlying disease that puts them at high risk (congenital long QT, high risk HOCM, Brugada, other channelopathies)
How anti-tachycardia pacing works with an ICD
In response to a pre-set ventricular rate (typically ~150-200), device will compare the QRS morphology to a saved image of a QRS complex that is known to be sinus. If the ICD algorithm determines the ongoing morphology is significantly different from a sinus beat (i.e. unlikely sinus tach), it will deliver a series of paced beats at a rate faster than the only going rate in attempt to break the re-entrant cycle.
Devices will typically be programmed to attempt anit-tachycardia pacing several times then if unsuccessful, will move on to defibrillation.
MOA of ICD defibrillation
Delivery of a large shock (up to 42J) from one electrode to the other in response to VF or VT
What is magnet mode
placement of a magnet over the generator will deactivate anti-tachycardia pacing and defibrillation as long as the magnet is in place.
Causes of inappropriate ICD shocks
1) Recurrent non-sustained VT
2) SVT (or AF) with rapid ventricular response inappropriately sensed as VT/VF
3) Oversensing T waves as QRS complexes
4) Artifact oversensing/’electrical noise’ (muscular activity, shivering, fasciculations from sux)
5) Fractured/displaced lead
What is a ‘phantom shock’
Perception of a shock without a delivered shock.
Generally described as a mild electrical pain or pain around the defibrillator site.
Occurs in ~9% of patients/year
General approach to patients who report an ICD shock
1) Pt reported shocks may be appropriate (underlying VT/VF), inappropriate shocks or phantom shocks (pt perceives shock but did not occur)
2) Call cardio for interrogation
3) If pt on anti-arrhythmic and BB, ask if they have had their dose that day and if not, consider giving
4) Consider causes of appropriate shocks: VT/VF, electrolyte abnormalities, ACS, medications (proarrhythmic drugs, noncompliance)
5) Consider causes of inappropriate shocks (SVT/AF, oversensing Ts, nonsustained VT, artifact oversensing, broken/misplaced leads)
6) Get ECG- look for arrhythm, signs ischemia, signs of electrolyte imbalances
7) Labs: cardiac routines, extended lytes, lytes
8) Get CXR to evaluate for fractured/broken leads
Key investigations to consider for pts that report an ICD shock
1) CXR: look for fractured/broken leads
2) ECG: look for ischemia, electrolyte abnormalities, check QT
3) Troponin, lytes, extended lytes
What misleading finding may appear on ECG in the first 5-15 min following a shock?
Post-shock ECG may show transient ST elevation or depression
What should you do if you suspect that the ICD is firing inappropriately?
Apply an ICD magnet over the chest.
Magnet will NOT disable backup pacing.
Return of ICD function after magnet removal is manufacturer dependent.
Causes of implantable cardioverter-defibrillator failure
1) Component failure: lead #/displacement
2) Battery depletion
3) Interference with pacemakers
4) Inadvertent inactivation: any strong magnetic force can cause temporary or permanent (device dep) failure.
5) Resistant VT/VF: Device functioning but rhythm resistant to internal defibrillation
Should you deliver external shocks to someone with an ICD in VF/VT?
Yes. Perform external defibrillation for VT/VF if not resolved with internal defibrillation.
Use standard paddles on front/back of chest and place >/10 CM AWAY FROM generator!
