There are acute and long-term failure modes for pacemaker/ICD leads. Failure modes can cause a spectrum of issues from minor annoyances to catastrophic failure and death. Many of the failures require replacement of the generator or leads or both, which can cause its own complications for the patient.

Electrical Leads of a Pacemaker

Examples of failure modes include:

  • Acute perforation
  • Dislodgement
  • Infection
  • Vein thrombosis
  • Migration
  • Conduction failure
  • Insulation damage/Externalization

Silicone Structural Failure

The last item, insulation failure has been seen in several lead designs. The silicone casing around transvenous leads is subjected to conditions that can lead to fracture and structural failure.

The proximal length undergoes high muscular stress from the pectoral muscles. Being above the bony thorax wall it is also subjective to crush, causing lead-to-lead or lead-to-can disruption. The distal segment experiences high intracardiac forces and dynamic flexing. There are also fatigue initiation points where the shocking coil is attached to the silicone. The most common site was the part of the lead just below the tricuspid valve.

The failure rate is higher in lead designs with dual shocking coils, which has contributed to recommendations against their use.

When the insulin fails, the defibrillation or sensing wires can be externalized. If their ETFE coating remains intact the externalized conductors remain electrically silent, and no detectable electrical abnormalities may be seen. However, the ETFE coating is not design to withstand the externalized environment. The coating often quickly becomes damaged, and leads to electrical short circuits.

ICD Lead Externalized Wire

Structural failure of the pacemaker/ICD lead silicone casing and externalized conductors.

Asymmetric Lead Design

This problem was faced by St. Jude Medical with their Riata silicone-insulated leads, and led to a physician advisory. The cross section of a typical asymmetrical lead design (Riata family) is shown below.