Troubleshooting Implanted Cardioverter Defibrillator Sensing Problems I

Abstract

electrograms from floating bipolar atrial electrodes on defibrillation leads. 12,13 The former requires a dual-coil lead and the latter a specialized lead. Evaluating Sensing From ICD ElectrogramsFilter settings may influence electrogram appearance (Figure 2). Wideband signals with minimal filtering reproduce QRS complexes accurately and retain the distinctive, rounded appearance of T waves. Highly filtered narrowband signals display the signal that is compared with the sensing threshold in the sensing process, but they alter signal amplitude and polarity, markedly reducing the amplitude of signals with prominent low-frequency components, such as T waves and some components of VF ( Figure I in the Data Supplement). Programmable filter settings (St. Jude Medical and Biotronik) permit assessing the effect of filtering on R-and T-wave amplitude.Sampling is the process of converting an analog signal into a digital sequence. It must be performed at ≥2× the source's signal frequency to reproduce the source's information content completely. ICD telemetry reproduces cardiac signals completely because it samples at 128 to 256 Hz per channel, but it may distort nonphysiological signals periodically (Figure II in the Data Supplement) 14 and it may not completely reproduce myopotentials that have frequency content >100 Hz. Stored Versus Real-Time ElectrogramsStored electrograms and their corresponding interval and episode data are the primary sources for diagnosing devicedetected tachycardias. Real-time electrograms are useful in troubleshooting reproducible oversensing: lead or connector problems in the pocket may be identified by pocket manipulation, pectoral or diaphragmatic myopotentials can be provoked by pectoral muscle contraction and straining or deep breathing, respectively (Figure III in the Data Supplement). Differential electrograms recorded simultaneously between 1 common electrode and 2 different electrodes are useful when lead or connector-related oversensing is suspected (Figure 3). Role of Additional Diagnostics, Alerts, and Remote MonitoringTrend plots of P-and R-wave amplitude, impedance measurements and trends, and algorithms that identify oversensing facilitate electrogram interpretation as discussed below. Alerts for suspected oversensing may notify the patient using audible tones or pulse generator vibration, may be transmitted via internet-based remote-monitoring networks, or both. Remote monitoring has transformed follow-up of sensing problems, permitting rapid determination of cause of an alert and implementation of a response plan, especially for devices with wireless telemetry.16,17 Troubleshooting Ventricular OversensingPresentation, Classification, and Recognition Clinical PresentationIn ICD patients, ventricular oversensing of rapid signals presents as oversensing alerts or inappropriate detection of VT/ VF, often resulting in inappropriate shocks. In pacemakerdependent patients it also presents as failure to deliver bradycardia pacing. ClassificationOversensing can be classified by electro...

Loss of Biventricular Pacing During Exercise: What Is the Mechanism?

“…In the presence of high‐amplitude R waves, reducing programmed sensitivity may be all that is required . Indeed, in the present case, altering the ventricular sensitivity from 0.3 mV to 0.45 mV abolished post‐pacing TWOS.…”

“…Indeed, in the present case, altering the ventricular sensitivity from 0.3 mV to 0.45 mV abolished post‐pacing TWOS. On the other hand, in the presence of small R‐waves, alternative strategies include changing from dedicated bipolar to integrated bipolar sensing and consideration of lead repositioning.…”

Recurrent shocks in a dual chamber implantable cardioverter defibrillator: Making sense of the chaos

“…White squares, representing atrial cycle length (AA interval) were tied with the VV cycle length for much of the time. However, there were two groups of AA intervals which appeared to be multiples of the VV TCL 480 ms. Morphologically, it was reminiscent of a rail road track and sometimes described as the “tram‐track sign” . The pattern in which the AA intervals fell into two discrete TCL groups, in multiples of the ventricular TCL was suggestive of undersensing in the atrial channel, with the AA cycle length clearly linked to the VV cycle length.…”

Technologies for Prolonging Cardiac Implantable Electronic Device Longevity

“…Continuous electrogram storage (in contradistinction to only posttachycardia detection) may be desirable but is also optional in a practical sense. Filtering (by frequency) can significantly reduce the amount of data representing an electrogram, and hence the energy required of store them . Continuous storage of filtered electrograms has minimal impact on device longevity and is generally a default feature that cannot be switched off in ICD and CRTD models that implement it.…”