Cardiac pacing leads play a vital role in cardiac pacing by delivering electrical impulses from the pacemaker to the heart. They come in a variety of configurations tailored for specific clinical needs. This article discusses the different types of pacing leads commonly used.
Single-Chamber Pacing Leads
Single-chamber pacing leads are used for single-chamber pacing of either the right atrium or right ventricle. The most basic configuration is the unipolar lead which consists of a single coil electrode at the lead tip and the pacemaker case serving as the ground electrode. Unipolar leads are easy to implant but can cause muscle stimulation at high output settings due to current spread.
Dual-chamber pacing systems employ bipolar leads which have two separate electrodes - one at the lead tip and the other a few centimeters proximal. This electrode configuration localizes the electric field and reduces muscle stimulation. Bipolar leads have become the standard for atrial and ventricular pacing. Modern bipolar leads often have retractable tines or other fixation mechanisms to provide reliable lead anchoring in the heart chamber.
Lead Technology Advances
Lead technology continues to evolve with new construction materials and designs. Some newer single-chamber leads incorporate accelerometers that can detect lead motion or dislodgment and adjust pacing output accordingly. Steroid-eluting leads use controlled steroid drug release from the lead tip to reduce pain and pacing thresholds during the acute phase post-implantation. Pre-formed stylets inside the lead allow shaping of the lead curvature for easier maneuvering within the heart.
Dual-Chamber Pacing Leads
Dual-chamber pacing systems employ two separate leads - one for atrial pacing and the other for ventricular pacing. This allows pacing and sensing of both chambers in a physiologic manner.
The most commonly used dual-chamber leads are bipolar leads placed in the right atrial appendage and right ventricular apex. A few manufacturers offer unipolar/bipolar leads that can operate in either mode for added versatility.
Some advanced dual-chamber leads have interconnectable electrodes that allow pacing between leads for resynchronization therapy. Cardiac Pacing Leads designs incorporating fixation sleeves or passive fixation helixes have improved the reliability of atrial lead placement and stability over time. Additional technological advances in dual-chamber leads parallel those seen in single-chamber leads.
Biventricular Pacing Leads
Around one-third of heart failure patients have intraventricular or interventricular conduction delays that can be improved with cardiac resynchronization therapy (CRT). CRT uses three leads - one each in the right atrium, right ventricle, and left ventricle.
Left ventricular (LV) pacing is achieved using either transvenous or epicardial leads. Transvenous LV leads are advanced from the right ventricle into a cardiac vein near the LV free wall. These coronary sinus leads have either an active or passive fixation mechanism and vary in construction material and flexibility. Epicardial LV leads are surgically placed on the epicardium during cardiac surgery.
Technological advances in LV leads include smaller cross-sectional sizes for easier placement, stylets to aid lead manipulation, and steroid-eluting electrodes. Directional LV leads with multiple electrodes allow assessment and optimization of pacing vector for best response. Interconnectable LV-RV leads that allow biventricular pacing using only two leads are also available.
Lead Extraction
Over time, a small percentage of implanted leads become ineffective, infected or pose other clinical issues requiring extraction. Lead extraction tools and techniques have advanced significantly to safely remove even older, adherent leads. Modern extraction kits include locking stylets, dilators, snares and sheaths in graduated sizes to dissect fibrotic lead attachments through an evolutionarily careful, step-wise approach.
Laser and mechanical powered sheaths that create a controlled cutting zone combined with gentle countertraction have improved extraction success and reduced complications compared to manual methods. Several large studies have demonstrated high extraction success and low mortality using these advanced techniques even for leads implanted for several years. Fluoroscopic visualization throughout the procedure and on-site cardiovascular surgical backup are standard recommendations.
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