A Brief Synopsis of AFP's "Sudden Cardiac Death and Implantable Cardioverter-Defibrillators"

Sudden Cardiac Death and Implantable Cardioverter-Defibrillators
MINTU P. TURAKHIA, MD, MAS, Veterans Affairs Palo Alto Health Care System, Palo Alto, California, and Stanford University School of Medicine, Stanford, California
Am Fam Physician. 2010 Dec 1;82(11):1357-1366. 
http://www.aafp.org/afp/2010/1201/p1357.pdf

     Implantable cardioverter-defibrillators (ICDs) are used to prevent sudden cardiac death (SCD) from arrhythmia. Sudden cardiac death (SCD) will either occur from ventricular tachycardia, progressing to ventricular fibrillation or from bradyarrhythmias, electromechanical dissociation, or advanced heart failure. Risk factors for SCD include coronary artery disease, heart failure, arrhythmias, structural disease, or electrical disease.
    An ICD consists of a generator and a lead. The generator includes the battery, capacitor and microprocessor (the big round thing in the chest wall). The lead consists of the pacing tip electrode and one or two shock coils. The lead parts are placed around the right ventricle, or around the left ventricle (specifically the coronary sinus ostium and a coronary sinus vein) in the case of biventricular pacing. The purpose of the ICD is to stop VT or VF with pacing, cardioversion or defibrillation (FYI "synchronized" cardioversion is defined as giving the the heart a synchronized shock (low voltage at the peak of the R wave) to help the heart get back to normal sinus rhythm. Defibrillation, also known as "unsynchronized" cardioversion, is done to get PEA or VF back into a sinus rhythm. It is high voltage at any point along the ECG).
     ICD placement is helpful in primary prevention because the first event of arrhythmia is often fatal. The best predictor of  SCD is LV ejection fraction. Indications for ICD placement include prior VT, VF or syncope, and an ejection fraction below 30-35%. Implantation for secondary prevention includes patients who have survived previous episodes of cardiac arrest from a VT or VF, or those presenting with structural disease.  Candidates for placement should have a life expectancy of at least 7 years for it to be cost beneficial.
     Evaluation of patients who already have an ICD include LV injection fraction, underlying cardiac disease, indication for placement, underlying rhythm, and device manufacturer. Patients who experience an ICD shock should be examined to determine if the shock was appropriate.  Inappropriate causes include SVT's (atrial, junctional or sinus tachycardia as well as PVC's) and device oversensing. Repeated shocks could be due to a recurrent ventricular arrhythmias or a broken lead.
     MRI's are generally contraindicated, although a special magnet can be placed over the ICD to protect it if the imaging is absolutely necessary. Patient undergoing a surgical procedure should not have central venous access on the same side as ICD lead placement.