All ICDs are also pacemakers (i.e. have pacing functionality) but pacemakers are not ICDs (i.e. do not have shocking functionality)
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)
Typically implanted in L upper chest wall
Contains device hardware and battery
Acts as a shocking electrode in defibrillation
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)
Pacing and sensing functionality
Typical bipolar (pacing and sensing are performed by two electrodes, located several millimeters apart at the tip of the 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)
Easily identified on Chest X-Ray and can hep differentiate an ICD from a pacemaker
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)
Secondary Prevention
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
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
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
Not indicated if VT/VF occurs <48 hours after myocardial infarction
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
Controversy exists over applying the above criteria to non-ischemic cardiomyopathy
Congenital long QT syndrome
High-risk HOCM
Brugada syndrome
ARVD
Other channelopathies
Any of the above with intraventricular conduction delay of >120ms
Can perform all functions of pacemakers
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
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
Delivery of a large electrical shock (up to 42 joules) from one electrode to the other in response to VT or VF
Placement of a magnet over the generator will deactivate anti-tachycardia pacing and defibrillation modes as long as the magnet is in place.
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
If anti-tachycardia pacing or defibrillation has occurred, there will be a large alert on the device's interrogation home screen
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)
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)
Does not help differentiate ICDs (different than pacemakers)
Nonmedical
Cell phones: do not interact with device
Airport security: may trigger alarm, no alteration of activity
Medical Sources
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
Cell phones: do not interact with device
Airport security: may trigger alarm, no alteration of activity
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
Implantable Cardioverter-Defibrillator complication
Acute arterial ischemia
Pacemaker complication
Acute coronary syndrome 
Left ventricular assist device complications
Cardiac ablation complications
Aortic endograft complications
Myocardial rupture