Customer Communications
Performance Note: Clinical Management of High-Voltage Lead System Oversensing

Performance Note: Clinical Management of High-Voltage Lead System Oversensing

ICD Leads
Original Date of Communication: July 1996

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Appropriate sensing by an ICD system refers to the sensing of cardiac events that may or may not require therapy delivery. ICD systems must sense relatively large QRS complexes while avoiding sensing of smaller T waves, yet continue to sense often small variable amplitude ventricular fibrillation. Thus, ICD systems attempt to dynamically adjust sensing of electrical events and discriminate between them based on detection algorithms and programmed settings.

Inappropriate sensing can occur when an ICD system classifies events of non-cardiac origin as QRS/VF events, or senses and counts T and far-field P waves as ventricular depolarizations. This is often referred to as “oversensing,” and may result in delivery of inappropriate high-voltage therapies. This is due, in part, to the desire to err on the side of delivering lifesaving high voltage therapy rather than withholding it. Thus, an ICD system that is experiencing oversensing issues will continue to deliver therapeutic shocks as required, but may also subject the patient to unnecessary shocks.

Oversensing can be difficult to manage, in that the precipitating cause of the oversensing can be problematic to isolate. Oversensing can be caused by many factors, including myopotentials/farfield sensing, electromagnetic interference, T wave sensing, connector issues, incomplete or complete conductor fractures, and insulation breaches. While the individual physician must exercise medical judgment in determination of appropriate clinical management of ICD systems, the chart below may assist in the process of causal factor differentiation and possible intervention.



Causal Factors



Myopotentials/Far-field sensing

Diaphragmatic muscle potentials in breathing, wide tip-to-ring (coil on integrated bipolar leads) spacing

Nonphysiological sensed event on EGM, which may confuse detection potentially resulting in false positive shocks

Check R waves for deterioration. Reprogram sensitivity. Try repositioning lead. Consider change-out to true bipolar lead, or if true bipolar lead in use, one with closer tip-to-ring spacing than current lead.

EMI (Electro-Magnetic Interference)

Arc welders, electrical generators, store walk-through security scanners, poorly insulated electrical equipment

Multiple and consecutive short intervals (< 140 ms) independent of underlying sinus beats. Associated with proximity to the EMI source.

Avoid EMI areas. True bipolar leads less susceptible.

T-wave sensing

Drugs, ischemic tissue, exercise, Long QT syndrome, electrolyte imbalance

Sense markers seen on EGM related to T wave. False positive detection.

Check for R wave deterioration and characteristics. If R wave > 3.0 mV, reprogram sensitivity. If R wave < 3.0 mV, reposition/replace lead. Address causal factor (e.g., drugs [if appropriate/medically viable]).

Connector problems

Loose setscrew, cross-threaded setscrew, incomplete lead insertion into header

This is an acute phenomenon seen within 6 months of implant (usually sooner)

Requires invasive check of connections. May be reproducible with pocket manipulation.

Incomplete conductor fracture

One or more filars of a multifilar conductor fracturing while leaving enough filars intact to provide a conduction circuit

Characterized by chaotic oversensing related to motion of the fracture site

Check EGMs and x-rays. Manipulate lead at suspected fracture site if possible as a provocative test. If confirmed, replace lead.

Lead insulation breach

Cuts, tears, metal ion oxidization, abrasion, cold flow, environmental stress cracking

Characterized by cyclical and/or erratic, intermittent, spontaneous oversensing; often post-pace or post-shock can cause false positives

Replace lead. If acute, usually secondary to implant damage/replacement damage. If late, material characteristic.

Oversensing during interrogation with programming head (not wireless telemetry) with complete lead fracture

Interrogation with a programming head in combination with complete lead fracture that creates an open circuit can induce noise on the sensing circuitry inside the ICD can

Nonphysiologic sensed event on EGM. If detection is enabled during interrogation, oversensing may result in inappropriate therapy.

Quickly remove the programming head. CANCEL the interrupted interrogation and manually load the software for the specific device model. Reposition the programmer head over the device and immediately select SUSPEND. Device will resume detection when programming head is removed, or when RESUME is selected. Replace lead.


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Specific Models This Applies To 726050