We work through every interrogation using the PBL-STOP framework: Presenting rhythm, Battery, Lead impedance, Sensing, Threshold, Observations, Program & Print. On an ICD the O section gets the most clock time, because every ATP and every shock since the last visit deserves an EGM walk.
Device overview
An ICD does everything a pacemaker does, plus it monitors for ventricular tachycardia and fibrillation and delivers ATP or shocks when criteria are met. Every clinic visit answers two questions: is the device working, and did the device make any decisions since the last visit — and were they correct?
PBL-STOP walkthrough
P — Presenting Rhythm
The live picture before anything else.
- Intrinsic vs paced on the rhythm strip and EGM
- Snapshot %A-paced and %V-paced for this session
- Baseline QRS morphology — useful for comparing to stored episode EGMs later
- Any ongoing arrhythmia the patient walked in with (AF with RVR, frequent PVCs, sustained NSVT)
- Symptom check: palpitations, near-syncope, perceived or witnessed shocks
This anchors every subsequent number — a patient who is 80% V-paced has different battery and threshold expectations than one who is 0%.
B — Battery Status
- Voltage compared against the model-specific RRT/ERI threshold
- Percent remaining, projected months of service
- BOL / MOL / ERI / EOL status
- ICD-specific drivers of accelerated drain:
- Frequent shock deliveries — each charge is expensive
- Frequent capacitor reforming
- High RV pacing burden
- CRT-D configurations with high LV outputs
After a shock cluster, recompute longevity — the projection from the prior visit no longer applies.
L — Lead Impedance
Pacing and high-voltage values, both with trends.
- RA and RV pacing impedance: 400–1200 ohms
- Sudden drop: insulation breach
- Sudden rise: conductor fracture or microdislodgement
- RV shock (HV) impedance: 30–80 ohms typical
- Change >20 ohms suggests a coil, SVC-coil, or HV conductor issue and warrants a same-day call
- Sudden swing in any of these is more important than the absolute number — open the trend graph and look back at least three prior values
S — Sensing
- R-wave amplitude: typically >5 mV on the RV channel; drop >50% from baseline triggers a closer look for undersensing
- T-wave oversensing screen — discriminator zones, decay constants, sensing-vector alternatives if available
- Far-field R-wave on the atrial channel — can drive inappropriate mode switches and confuse SVT discriminators
- Noise on the HV channel — non-physiological short intervals are the canary for lead fracture or loose set-screw
- Atrial P-wave amplitude where applicable
T — Threshold
- Capture threshold per lead at 0.5 ms — auto-test plus manual confirmation when the trend is rising or borderline
- Safety margin programmed at 2× threshold; tighten in EOL planning where appropriate
- DFT testing is rarely repeated in clinic in 2026 — flag to the attending if there is concern about defibrillation safety margin (subcutaneous ICD upgrade, high HV impedance, post-revision)
- Morphology template re-acquisition if the QRS has changed since implant or after lead revision
O — Observations
The heart of the ICD interrogation. Counters, episodes, and therapy delivered.
Counters and histograms
- %V-paced and %A-paced since last reset
- Rate histograms and patient-triggered transmissions
- AT/AF burden — episode count, duration, fastest atrial rate; AHRE >6 minutes triggers an anticoagulation discussion
- NSVT in the monitor zone — frequency, fastest rate, longest run
Therapy episodes — EGM walk for every one
For every ATP and every shock since the last visit:
- Open the stored EGM and confirm classification — VT, VF, SVT, noise, oversensing
- Intervals consistent with the classification?
- For ATP: did it terminate, was it ineffective, or did it accelerate?
- For shock: first-shock efficacy, redetect behavior, post-shock rhythm
- Sensing clean throughout — no T-wave double-count, no lead noise masquerading as VF
- For inappropriate therapy, classify the cause:
Storm flag
- ≥3 sustained VT/VF episodes in 24 hours = VT storm, call the EP attending before the patient leaves
P — Program & Print
Close the loop with explicit therapy programming.
Detection zones
- VT monitor zone: counts only, no therapy
- VT zone: cutoff typically 170–188 bpm — ATP then shocks
- VF zone: cutoff typically 188–220 bpm — shocks (with ATP during charging on most platforms)
- Long detection (30/40 intervals or ~12 s) to cut avoidable shocks for self-terminating runs
SVT discriminators
- Onset, stability, morphology, A:V relationship — tightened or loosened based on the appropriateness review under O
ATP and shock energy
- ATP burst sequences before the first shock in the VT zone, and during charging in the VF zone
- First-shock energy at maximum on most platforms; review after any failed shock
Post-shock pacing
- Rate typically 90 bpm, duration 30 s to a few minutes
- Outputs with generous safety margin — capture matters more than battery here
Bradycardia and general pacing
- Mode, lower rate, AV delay favoring intrinsic conduction, MVP/AV search on for primary-prevention patients, rate response off unless documented chronotropic incompetence
Wrap-up
- Document each change with prior value and rationale
- Re-interrogate after the change
- Save and print the summary report plus any reviewed episode EGMs to the chart
- Patient education after any shock — same-day, before they leave the office
- Set next remote and next in-office visit
- Escalate to the EP attending for: any shock, inappropriate detection from oversensing, HV impedance alert, VT storm, failed shock, phantom shock with no device-recorded therapy
Reference
Framework reference: “Keeping the Pace using PBL-STOP” — Chart Healthcare Academy