Comments

This is a fascinating set of EKG tracings associated with a classic chest x-ray illustrating the subclavian crush.

The patient has a dual chamber pacemaker that required the insertion of two leads. This need to implant more than one lead usually leads to a subclavian puncture as opposed to a cephalic vein cut down. Although the cephalic vein cut down usually can only handle one lead and is a more tedious procedure it dose seem to ensure that the lead will have a smooth passage over the first rib. This is not the case for the puncture technique where the lead may be entrapped in the tissues near the junction of the first rib and the clavicle and be subject to a "crush".

The series of x-rays clearly show an insulation break at the level of the first rib and the clavicle. The lead impedance measurement sounded an alarm as the lying value is grossly elevated. Curiously the sitting value of the lead impedance, while still high is less as is the pacing threshold. The current thresholds at 3.5 ma and 3.1 ma (calculating current by dividing the voltage by the resistance) are similar. This being said the change in position obviously changed the conduction down the outer conductor. The failure of the outer conductor is confirmed with the excellent threshold in the unipolar mode that does not use the external conductor. One has to assume that the conductor itself is damaged as the loss of the insulation alone would have lowered the impedance of the lead. Finally it would seem to be only a matter of time before the inner conductor would suffer the same fate.

At this point it might be best to try a cephalic approach for a new venticular lead to avoid the possibitlity of hitting the good atrial lead with a puncture needle and also to ensure that the new lead does not suffer the same fate as the old one. One could also ask if sleeves could not be devised to slide over leads to protect them from the crush.

Mike Rosengarten