Cardiac Pacing Leads : Pacing Lead Performance and Longevity
Types of Cardiac Pacemaker Leads
There are different types of cardiac pacing leads used for different purposes. The main types include:
- Atrial leads: These thin insulated wires are placed in the right atrium and are used to pace the atrium. Atrial leads help maintain normal sinus rhythm and atrioventricular synchrony.
- Ventricular leads: As the name suggests, ventricular leads are implanted in the right ventricle. They are used for ventricular pacing to treat conditions like complete heart block or slow ventricular rates.
- Bipolar leads: Both bipolar atrial and Cardiac Pacing Leads have two electrode surfaces - one at the tip and one on the lead body a few centimeters proximal. This helps reduce ventricular pacing thresholds.
- Unipolar leads: Unipolar leads have a single electrode at the tip and use the metal case of the pacemaker as the other electrode. They are cheaper but have higher pacing thresholds.
- Balloon-expandable leads: For patients with thin vessel walls or trabeculated hearts, balloon-expandable leads which can be expanded inside heart chambers are preferred.
- Myocardial leads: Used for CRT devices, myocardial leads are screwed directly into heart muscle to provide pacing at multiple sites.
Lead Implantation Procedure
Pacemaker leads are implanted by cardiologists in a minor surgical procedure under local anesthesia. A small incision is made in the upper chest and the lead is inserted into a large vein and guided to the right atrium or ventricle using state-of-the-art lead delivery systems.
In the heart chamber, the lead is secured to the endocardium either actively by screwing in or passively by tines or passive fixation mechanisms. Different heart chambers may require different approaches. The proximal end of the lead is then tunneled subcutaneously and connected to the pacemaker generator which is implanted in a subcutaneous pocket.
Lead Stabilization and Anchoring
Proper stabilization and anchoring of the pacing lead is critical for ensuring adequate contact between the electrode and cardiac tissue over the long-term. Active fixation leads have screw-in electrodes that help achieve primary stability through mechanical engagement in heart muscle.
Passive fixation leads rely on tines, fibrous tissue ingrowth or silicone rubber sleeves to achieve secondary stability gradually over weeks. Dual anchor mechanisms combining passive and active features are also available. Improper fixation can lead to lead dislodgements or increased pacing thresholds over time.
Lead Performance Parameters
Some key performance parameters to assess functional status of implanted cardiac pacing leads include:
- Impedance: Measured in ohms, high impedance could indicate lead fracture or insulation breach.
- Threshold: Minimum pacing voltage needed to capture the heart. Rising thresholds over time suggest loss of contact.
-R wave amplitude: Strength of intrinsic cardiac signal detected by the lead. Low amplitudes indicate poor lead position.
-P-wave amplitude: For atrial leads to ensure effective atrial sensing.
-Capture threshold testing: Periodic testing to ensure consistent safety margins for pacing.
Lead Extraction
On rare occasions, infected or malfunctioning pacing leads may need to be extracted. Lead extraction requires special equipment, training and is carried out in electrophysiology labs equipped to handle potential complications. Laser sheath techniques and mechanical dilators and locked stylets help fragment and remove leads through the large veins.
Extraction is a challenging procedure associated with risks of pericardial effusion, cardiac tamponade or vessel injury. Hence it is only recommended for leads that are truly non-functional, infected or causing significant complications like cardiac perforation or thrombosis. Abandoning malfunctioning leads should otherwise be avoided.
cardiac pacing leads play a critical role in ensuring effective delivery of electrical stimulation from implantable pacemakers to the appropriate cardiac chambers. Optimizing lead performance and developing safer lead extraction techniques remain active areas of research.
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