View source for Implantable cardioverter-defibrillator complication

==Background==
===Nomenclature===
*All ICDs are also [[pacemaker]]s (i.e. have pacing functionality) but pacemakers are not ICDs (i.e. do not have shocking functionality)

===Parts===
*Pulse Generator
**Typically implanted in L upper chest wall
**Contains device hardware and battery
**Acts as a shocking electrode in defibrillation
*Leads
**Insulated and antimicrobial-coated
**Atrial lead
***Pacing and sensing functionality
***Typical bipolar (pacing and sensing are performed by two electrodes, located several millimeters apart at the tip of the lead)
**Right ventricular lead
***Pacing, sensing, and defibrillation functionality
***Has one or two coils to facilitate defibrillation
****Easily identified on Chest X-Ray and can hep differentiate an ICD from a pacemaker
***Typical bipolar (pacing and sensing are performed by two electrodes, located several millimeters apart at the tip of the lead)
**Left Ventricular Lead
***Pacing and sensing functionality
***Bipolar or unipolar (pacing and sensing are performed by one electrode at the tip of the LV lead and a second remote electrode, typically either one of the RV electrodes or the pulse generator)

===Indications for ICD implantation===
*Secondary Prevention<ref>Al-Khatib SM et al. 2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2018;72(14):e91. Epub 2018 Aug 16.</ref>
**Previous episode of unstable VT or VF
***'''Not indicated''' if VT/VF occurs <48 hours after [[myocardial infarction]]
**Sustained VT in setting of cardiomyopathy or channelopathy
*Primary Prevention<ref>Al-Khatib SM et al. 2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2018;72(14):e91. Epub 2018 Aug 16.</ref>
**[[Myocardial infarction]] >40 days ago with LVEF <30%
**[[Cardiomyopathy]] + NYHA Functional Class II or III, and LVEF <35%
***Controversy exists over applying the above criteria to non-ischemic cardiomyopathy
**Patients with underlying disorders placing them at high risk for unstable VT or VF
***Congenital [[long QT syndrome]]
***High-risk [[HOCM]]
***[[Brugada syndrome]]
***[[ARVD]]
***Other channelopathies
*Biventricular ICD (i.e. Cardiac Resynchronization Therapy)
**Any of the above with intraventricular conduction delay of >120ms

===Functions===
*Can perform all functions of [[pacemaker]]s
*Anti-tachycardia pacing
**In response to a ventricular rate within a pre-set range (typically ~150-220 bpm), the device will compare the ongoing QRS morphology to a saved image of a QRS complex that is known to be a sinus beat; if the ICD algorithm determines that the ongoing morphology is significantly different (i.e. is unlikely to be a sinus tachycardia), it will deliver a series of paced beats at a rate slightly faster than the ongoing rate in an attempt to break the re-entrant cycle
**A device will typically be programmed to attempt anti-tachycardia pacing several times; if unsuccessful, it will move on to defibrillation
*Defibrillation
**Delivery of a large electrical shock (up to 42 joules) from one electrode to the other in response to VT or VF
*Magnet Mode
**Placement of a magnet over the generator will deactivate anti-tachycardia pacing and defibrillation modes as long as the magnet is in place.
*Diagnostics
**Records rhythm strips of AF, VT, and VF episodes for later review
***If anti-tachycardia pacing or defibrillation has occurred, there will be a large alert on the device's interrogation home screen
**Keeps track of % of paced vs intrinsic beats
**Keeps a rate histogram, as well as % of time spent in AF

===Methods to Identify Manufacturer===
*Patient should carry a pocket card indicating manufacturer
*Manufacturer Hotline has patient database
**Medtronic Inc. (1-800-328-2518)
**St. Jude Medical Inc. (recently acquired by Abbott, Inc.) (1-800-722-3774)
**Boston Scientific Inc. (1-800-227-3422)
*Magnet mode
**Does not help differentiate ICDs (different than pacemakers)

===Electromagnetic Interference===
*Nonmedical
**Cell phones: do not interact with device
**Airport security: may trigger alarm, no alteration of activity
*Medical Sources
**[[MRI contraindications|MRI]]: mostly safe, consult cards on device specific recs
**Cardioversion: Use AP pads >8cm from device to minimize adverse effects
**Unipolar Cautery - can cause sensing and pacing malfunction as well as reprogramming

==Complications==
===Defibrillator Shocks===
*Approximately 1/3 - 1/2 of ICD patients receive a shock within one year of placement<ref>Sears SF Jr., Shea JB, Conti JB. Cardiology patient page. How to respond to an implantable cardioverter-defibrillator shock. Circulation. 2005;111:e380–e382</ref>
**Generally described by patients as a powerful "kick to the chest"
**Can be very distressing and a source of anxiety for patients

*Inappropriate Shocks
**Causes
***Misclassification by device of SVT or AF as VT or VF
***Electrical Noise
***Fractured Lead
**Can be diagnosed by interrogation of device after a reported shock

*Phantom Shocks
**The perception of a shock without a delivered shock
**Generally described by patients as a mild electrical pain or pain around the defibrillator site
**More common in patients who have never had an actual shock
**Occurs in 9% of patients each year<ref>Berg SK et al. Phantom shocks in patients with implantable cardioverter defibrillator: results from a randomized rehabilitation trial (COPE-ICD). Europace. 2013 Oct;15(10):1463-7. Epub 2013 Apr 18.</ref>

===Pacemaker Malfunctions===

====Problems with pocket====
*Infection
**Most commonly S. aureus or S. epidermidis
**2% local wound infection; 1% sepsis/bacteremia
*Hematoma
**Typically occurs shortly after placement

====Problems with leads==== 
*Dislodgment
*Perforation (most commonly at RV apex)
*Infection can cause severe sepsis
*Tricuspid regurgitation
*Coiling (ie: [[Twiddler's Syndrome]]) [[File:Twiddler Syndrome.png|thumb|Twiddler Syndrome after large pocket and defibrillator wires coiled around the generator]]

===Failure to Capture===
*Delivery of pacing stimulus without depolarization
**Functional - refractory myocardium, desensitized local tissue around the lead
**Medical - drugs, myocardial disease, electrolytes
**Technical - insufficient device output, lead dislodgment, fracture, insulation defect, ventricular wall perforation
*Battery of End of Life (EOL)

===Failure to Pace===
*Failure to deliver a stimulus to the heart
**Oversensing - most common cause: retrograde P’s, T’s, skeletal muscle myopotentials, 
**Crosstalk - type of oversensing where the ventricular lead senses atrial pacing stimulus, and ventilator output inhibited

===Failure to Sense===
*Normal function: a sensed myocardial depolarization greater than the programmed threshold causes inhibition of pacing
*Failure to sense results in a paced beat on top of an intrinsic beat (as the device is "unaware" of the intrinsic beat")
**Voltages of patient's intrinsic QRS complex is too low to be detected
**New intrinsic arrhythmia (AF has a smaller depolarization than sinus beat), AMI, electrolyte abnormalities, lead separation, battery depletion

===Runaway Pacing===
*Physiologic electrical activity (T waves, muscle potentials)
*External electromagnetic interference
*Signals generated by interaction of different portions of the pacing system
*Potentially life-threatening as it can cause V-Fib or (paradoxically) bradycardia due to failure to capture

===Pacemaker Mediated Tachycardia===
*Also known as Endless Loop Tachycardia
*Formation of a re-entrant circuit causing inappropriate tachycardia
**Most commonly: paced ventricular beat ->  retrograde AV node conduction -> intrinsic P wave -> device reacts to intrinsic P wave by looking for intrinsic QRS, but since AV node is now refractory it delivers a paced beat at the programmed P-R interval (typically ~200-250ms), starting the process anew
*Tachycardia does not exceed programmed upper limit rate on pacemaker

==Evaluation==
===Work-Up===
*BMP and Mg
*[[CXR]]
*[[ECG]]
*[[Troponin]]
*Interrogation
**Each company has on-call representatives who will come interrogate a device 24/7 (phone numbers above)
**Most cath labs will have machines capable of interrogating each brand

===Expected ECG Patterns===
*Absence of pacer artifact indicates intrinsic depolarization
**With newer pacemakers, pacer spikes may not appear on some or all paced beats, depending on EKG machine
*Pacing artifacts preceding depolarizations indicate successful pacing and capture
*Leads in RV apex produce LBBB pattern with appropriate discordance
*New RBBB pattern may indicate lead in LV
* Bi-ventricular devices can produce paced QRS complexes that are either narrow or wide and bizarre, depending on device programming
*Simultaneous depolarization of ventricles produces dominant R wave in V1

===Plain Film Findings===
*Obtain PA/Lateral Films to confirm pulse generator, manufacturer, lead placement/number/integrity
*R atrial lead J shaped(tip medially on AP) entering right atrial appendage
*RV leads point downward with tip between left spine and cardiac apex--lateral XR shows inferior and anterior
*Coronary sinus lead- courses posteriorly on lateral XR
*Extra leads may be appropriately abandoned and capped
*ICD component appears as thickened shock coil

==Management==
*Reported Shock
**If unable to prove a phantom shock, electrophysiology or cardiology consult is often needed
**Interrogation is mandatory, either by an experienced clinician or by device representative
***Some devices can be remotely interrogated; contact the respective company representative at the above phone numbers to discuss this possibility

*Repeated Shocks
**Before placement of a magnet or changing the device parameters, you must determine if the shocks are appropriate (i.e. the patient is in VT storm or having recurrent episodes of VF) or inappropriate
***If it is determined that the shocks are inappropriate, a magnet will deactivate the shocking function while placed over the device
**Electrophysiology consult

*Pacemaker Mediated Tachycardia
**Break with [[adenosine]] - magnet will not fix PMT in a patient with a defibrillator

==Disposition==
*Consider discharge if:
**Proven Phantom Shock
**Resolved Pacemaker Mediated Tachycardia
**Single shock only AND Currently asymptomatic AND No concerning associated symptoms (e.g. chest pain, dyspnea, syncope) 
***Ensure patient has Electrophysiology/Cardiology follow-up
***Consider Electrophysiology/Cardiology consult
*Admit all others

==See Also==
*[[Pacemaker complication]]
*[[Medical device complications]]

==External Links==
*[http://www.emdocs.net/ecg-pointers-icds-and-when-they-malfunction/ ECG Pointers: ICDs and when they malfunction]

==References==
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[[Category:Cardiology]]