EP Staff Education Clinical Staff Ilyas Colombowala, MD, FACC, FHRS →
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Device

Loop Recorder Remote / In-Office Check

Implantable loop recorder review workflow — battery, sensing, episode triage, and how to handle the high volume of false positives that come with long-term continuous monitoring.

Interrogation walk-through

  • ▸P — Chart review: indication, implant date, symptom diary, prior episodes reviewed.
  • ▸B — Battery voltage, % remaining, projected months to EOS.
  • ▸L — Sensing amplitude only (no pacing leads); confirm R-wave >0.3 mV.
  • ▸S — Episode list with patient-activated first, then auto-detected by severity; EGM review of every clinically relevant strip.
  • ▸P — Threshold adjustments, patient education, next transmission window, attending escalation as needed.

Common issues / troubleshooting

  • ▸False-positive AF detection from PAC runs or undersensing
  • ▸False-positive pause detection from R-wave undersensing
  • ▸Episode memory overflow from high event volume between transmissions
  • ▸Patient-activated events with no captured arrhythmia
  • ▸Sensing decline as the device migrates or scar tissue matures

We work through every interrogation using the PBL-STOP framework — a quick mental checklist so nothing gets missed. The ILR is a monitor, not a therapeutic device, so we use an abbreviated version: P, B, L (sensing only), S (the main event), and P. T and O are explicitly skipped.

Device overview

An implantable loop recorder is a small subcutaneous monitor placed in the left parasternal area. It records a single-channel ECG continuously and stores episodes triggered automatically by algorithm or by the patient with a handheld activator or smartphone app. Most ILR follow-up is remote, with in-office visits reserved for specific issues — sensing problems, episode review for borderline findings, or end-of-indication decisions. Indications are narrow but important: unexplained syncope, palpitations without documented arrhythmia, cryptogenic stroke (AF surveillance), and post-ablation AF monitoring.

PBL-STOP walkthrough (abbreviated)

P — Presentation / Pre-interrogation review

  • Manufacturer, model, serial, implant date
  • Indication: syncope, palpitations, cryptogenic stroke, post-ablation AF surveillance
  • Symptom diary entries since last review
  • Episodes already adjudicated at prior transmissions
  • Current rhythm-relevant medications (rate-control, antiarrhythmics, anticoagulation status)
  • Outstanding clinical questions: are we still looking for the same arrhythmia, or has the clinical situation evolved?

A 30-second chart pass before opening the episode list keeps the review focused — you want to know what question the ILR is answering before you start clicking through strips.

B — Battery / longevity

  • Voltage and estimated remaining longevity
  • Expected total service typically 3–4.5 years depending on platform and episode volume
  • Plan ahead:
    • >12 months remaining: continue monitoring per indication
    • 6–12 months: confirm whether the clinical indication still exists
    • <6 months: plan explant vs replacement based on whether the diagnostic question is unresolved

ILR replacement is uncommon — most devices are pulled at diagnosis or end-of-indication. Battery alone rarely drives a replace-vs-explant decision; the clinical question does.

L — Lead measurements (sensing margin only)

The ILR has no pacing leads — there is no impedance, no capture threshold. The L section reduces to sensing.

  • R-wave amplitude: should be >0.3 mV
    • Trend it across visits — declining sensing is the leading cause of new false positives
    • Sustained R-wave <0.2 mV will degrade every algorithm downstream
  • Body position effects — some platforms show sensing in supine vs upright
  • Note any signal saturation, baseline drift, or noise artifact patterns in the strip
  • If sensing has dropped meaningfully, consider:
    • Device migration
    • Scar maturation around the electrodes
    • Patient body habitus change
    • Need to re-position or reprogram sensing gain

S — Stored events / Sensed rhythm

This is the main event of an ILR check — everything else exists to support this section.

Triage order

  • Patient-activated symptomatic episodes first — these are tied to symptoms and have the highest diagnostic value
  • Then auto-detected episodes by clinical severity:
    • Asystole / long pause
    • AF
    • Sustained tachycardia
    • Bradycardia
    • Non-sustained tachycardia

EGM review for every flagged episode

  • AF claims: irregular RR with no organized P-waves vs noise vs SVT vs frequent PACs
  • Pause claims: true asystole vs R-wave undersensing vs lead artifact vs T-wave/P-wave dropout
  • Tachycardia claims: sinus vs SVT vs VT — width matters, onset matters
  • Bradycardia claims: true sinus brady vs sensed pause from undersensing

Symptom correlation

  • Cross-reference each device episode with the patient diary
  • Symptomatic episode + documented arrhythmia = diagnostic
  • Symptomatic episode + sinus rhythm = also diagnostic (rules out arrhythmic cause)
  • Asymptomatic AF in a cryptogenic stroke patient = anticoagulation discussion

Memory management

  • Clear reviewed episodes to free storage
  • High event volume between transmissions can overflow memory and lose data
  • If overflow is happening, tighten the detection thresholds or shorten the transmission interval

Detection threshold adjustments

  • Tighten if false positives are overwhelming the workflow
  • Loosen if the clinical question demands maximum sensitivity (e.g., active cryptogenic stroke workup)

T — Therapy

Not applicable — the ILR does not deliver therapy or pace.

O — Optimization

Not applicable — the ILR does not deliver therapy or pace.

P — Plan / Programming changes

  • Document every threshold change with prior value and rationale
  • Save EGM strips of any clinically relevant episode to the EMR
  • Reset counters and clear reviewed episodes
  • Patient education refresh: activator use, what to do if symptomatic, when to call
  • Set next remote transmission and next in-office visit
  • Escalate to the EP attending for:
    • Asystole >6 seconds, regardless of symptoms
    • AF with stroke risk and no anticoagulation
    • Any wide-complex tachycardia
    • Syncope with a corresponding device-recorded arrhythmia
    • Worsening symptoms with no device correlation — may need a different monitoring strategy
    • End-of-indication explant decisions

A note on volume

The biggest workflow challenge with ILRs is volume. A single patient with a borderline AF algorithm can generate dozens of false positives per week. Triage policies — who reviews what, what gets escalated, and how often we revisit detection thresholds — keep the device clinic functional. A trained ILR reader who knows the difference between noise, pseudo-AF from PACs, and true AF saves the practice an enormous number of hours.

Last reviewed by Dr. Colombowala on May 22, 2026.

Not medical advice. This page is educational. Your situation may differ — discuss it with Dr. Colombowala or your treating physician before making decisions.