Sunday, May 17, 2015

Pacemaker's lead Active versus passive fixation

Pacing leads must be secured in the inside of the heart. Ventricular leads often use passive-fixation mechanisms, such as fins or tines, which lodge in the trabeculae lining the interior of the ventricle. The fins or tines snag the lead into position, and over time, fibrosis grows over the interface between lead and tissue such that the lead is firmly in place in the heart. In fact, chronic leads are so securely fixated by fibrosis that they can be difficult to extract if that is ever necessary.

 Atrial leads typically use active-fixation mechanisms because the interior of the atria tends to be smooth walled and possesses no trabeculae. Of course, active-fixation leads can also be used in the ventricles, if the implanting physician chooses. An active-fixation lead has a corkscrew or helix or another mechanism that is deployed and twisted or screwed into the heart. There are a number of active-fixation leads on the market and most usually involve a small tool to twist or turn to deploy the active-fixation mechanism. These leads are securely fixated right at implant and can be easier to remove, if necessary. Implanting physicians may have ideas as to where they want the leads to be fixated, such as the right ventricular outflow tract, but finding the optimal lead location can involve some trial and error. Once a lead is secured in the heart, it has to be tested to be sure that the electrical characteristics are acceptable. A lead can be properly placed mechanically but yield suboptimal electrical results. In such cases, the physician moves the lead to a new spot and tests it again. It is not at all unusual during implant for a physician to move the leads a few times to achieve the desired electrical performance.

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