Subclavian crush

Still a third failure mechanism was not seen in animal studies, but was discovered clinically. Explanted and returned leads with crushed, flattened, and fractured conductor coils began to show up in the mid 1980s (Fig. 7) [17]. When polyurethane leads were introduced for human use, a new implant technique was developed. Instead of inserting the leads through a cephalic or jugular vein cut down, they were 

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Before starting the procedure, in the presence of a noninfective indication and if an implant of a new lead is planned, I perform a venography through an antecubital vein in order to assess venous patency and visualize the zone where a safe and effective venous puncture can be performed. In the presence of venous patency, I prefer creating a new access into the vein rather than inserting the new lead inside the sheath after lead removal. In this way, it is possible to avoid a risky lead position (in case of subclavian crush, for example), and the positioning of the new lead is easier outside of the fibrous endovascular tunnel. The intraoperative checklist is then completed. 

Spontaneous fracture of a lead is not common, and the most frequent cause is subclavian crush (Fig. 10.1). 

Fig 10 1 (a) X-Ray of the costoclavicular region in two pacemaker patients, (b) Note the spontaneous fracture of leads in this region due to subclavian crush arrows)... 

As mentioned, extraction techniques and related tools are mainly designed for leads in normal condition. Any damage to the lead, due to its characteristics or failure (subclavian crush, loss of insulation, wire protrusion) or to previous ineffective attempts at removal, may heavily impact the transvenous removal procedure, often requiring unconventional approaches. In the following paragraphs the most common situations are addressed. 

The axillary vein is becoming a common venous access site for pacemaker and defibrillator implantations, given the concerns of the subclavian crush and the requirement for insertion of multiple electrodes for dual-chambered pacing and a large complex electrode for transvenous nonthoracotomy defibrillation. There are now a number of reliable techniques for axillary venous access (Table 4.11). 

Venous access. In adnlt pacemaker practice, it is common to obtain a cut-down on the cephalic vein that will accommodate one or two leads. However, in children, becanse of the size of the vein, this is less likely. Still, the cephalic approach is preferable to the snbclavian approach, when available, as it completely avoids the complication of subclavian crush injury to the lead (39,40). Subclavian crnsh injnry resnlts from entrapment of the lead between the clavicle and the first rib, where it is subject to great stress with patient movement. 

Another approach is the placement of a catheter in the subclavian vein via the femoral vein, which may be used to perform a radiographic contrast injection for outlining the venous structures, and may also be left as a target for subclavian needle entry. The catheter is advanced far laterally to the junction between the subclavian and axillary veins, and the use of this as a target allows for a very lateral entry and thereby avoids the problem of subclavian crush injury to the leads (41). The use of such a catheter for angiograms will also identify venous abnormalities, such as a persistent left superior vena cava prior to creation of the pacemaker pocket. 

Fig. 7 An x-ray showing several leads implanted via the subclavian vein. One lead has fractured conductors due to crush (at the arrow, left). A photograph of an explanted lead rendered inoperable by subclavian crush (right)...

To this day, we still hear people claim that in vitro testing of materials alone shows that they are suitable for use in chronically implanted devices. Others continue to say that I proved the materials are biocompatible and biostable, so I don t have to do any device testing. This statement can be very far from the truth. In vitro testing has its place, primarily to screen materials and processes for further testing. In some cases where no suitable in vitro test exists, one may be forced to develop accelerated in vivo materials tests. Once the preliminary testing is accomplished, however, one must test the device per se in animals. A biocompatible material does not necessarily make a biocompatible device. The same may be said about biostability. These statements are true because shape, size, surface finish, interactions between the materials in the device, etc., all can affect its biocompatibility and biostability. But even well-performed animal studies may not unveil previously unknown mechanisms, because animals do not perfectly mimic the human in vivo environment. An excellent example of this is the subclavian crush in humans (clamping a lead between the clavicle and first rib), which is impossible to discover in animals with no clavicles. With the right protocol for the device in question, only postmarket surveillance appropriate for the device in question can determine for certain that the device does or does not meet expectations. 

Historically, surgeons believed that the subclavian vein could be entered at the junction of the middle and the inner thirds of the clavicle, creating a very medial approach to the vein. There is now evidence, however, that this traditional percutaneous subclavian approach predisposes the lead to crush injury between the clavicle and the first rib. At this point, the lead may become entrapped... 

As with pacemaker leads, the leads of an ICD system can fracture at the first rib and clavicle due to crush injury between the two bones, especially when inserted by a subclavian vein puncture, in my experience. 

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