Leads are used to deliver electrical energy into the heart in the form of pacing pulses or higher field voltages to elicit defibrillation. An array of catheters, stylets, and/or guide wires can be used to deliver leads to their desired locations within the heart. Once there, the leads can be passively fixed with tines in the trabeculations of the heart or more commonly, actively fixed using a helix that can be rotated into the heart tissue.
Pacing Leads: Low power bradycardia leads are typically implanted in the right atrium and/or the right ventricle. The most common indications for these pacemaker leads are
- Symptomatic bradycardia: Slow heart rate with symptoms such as syncope (fainting), dizziness, fatigue, and chest pains.
- Sick Sinus Syndrome: The heart's sinus node does not function properly. The sinus node consists of specialized cells in the right atrium that act as the natural pacemaker of the heart. Sick Sinus Syndrome can entail rhythms that are too slow and too fast.
- AV block: Problems with signal conduction from the atria to the ventricles. As a result, the heart can beat too slowly.
- Chronotropic Incompetence: The inability to adjust the heart rate in response to activity.
Defibrillation Leads: High power defibrillation leads are used to deliver high and low power therapies to treat dangerously fast ventricular heart rhythms. These leads are typically placed in the apex of the right ventricle.
Fast ventricular rates (ventricular tachycardia) can be treated with antitachycardia pacing, where the lead delivers electrical stimuli at a rate faster than the intrinsic ventricular rate in order to obtain control and subsequently decrease the rate. If antitachycardia pacing is not successful or ventricular fibrillation is detected, the lead can deliver a high energy shock to reset the heart's signal conduction. Ventricular fibrillation involves fast erratic impulses that do not allow the ventricles to pump. If ventricular fibrillation is not treated immediately sudden cardiac death can occur.
Defibrillation leads can have two coils, one in the right ventricle and one in the superior vena cava, or one single coil in the right ventricle. The connector can be a DF-4 connector or a trifurcated DF-1 connector depending on the configuration of the associated device can.
Heart Failure Leads: Heart failure leads can be used to treat heart failure patients with electrical dyssynchrony. A typical cardiac resynchronization therapy system consists of a right atrial pacing lead, a right ventricular pacing or defibrillation lead, and a heart failure lead in a coronary vein (see Coronary System Tutorial/Biomedical Applications of the Coronary Venous System).
Epicardial Leads: When endocardial pacing is not an option, leads can be placed on the epicardial surface of the heart. Leads can be placed via a subxiphoid approach, left thoracotomy, or median sternotomy. Epicardial leads may be used in pediatric patients.
Lead extraction: Lead extraction can be performed as a response to (but not limited to) infection, an occluded vessel, an identified risk caused by the system (such as perforation, extracardiac stimulation, pain, arrhythmia), dislodgement, or removal of non-functional leads . Lead extraction can be performed with simple traction or traction with a locking stylet. More difficult chronic leads may require laser, rf, or mechanical sheaths for extraction.
1. Epstein, Laurence M., Richard A. Friedman, and E. H. Charles. "Transvenous Lead Extraction: Heart Rhythm Society Expert Consensus on Facilities, Training, Indications, and Patient Management."