When Is a Patient a Good Candidate for Cardiac Resynchronization Therapy (CRT)?
Quick, clinician-friendly criteria summarizing guideline-focused indications for biventricular pacing / CRT (including CRT-D when defibrillation is indicated).
Core Eligibility
Clinical
- Symptomatic heart failure (NYHA II–ambulatory IV) despite optimized GDMT (≈ ≥3 months).
- LVEF ≤ 35% on echocardiography.
- Usually in sinus rhythm (see AF below).
Electrical
- LBBB morphology with QRS ≥ 150 ms → strongest evidence (Class I).
- LBBB with QRS 130–149 ms → reasonable benefit (Class IIa).
- Non‑LBBB with QRS ≥ 150 ms → selective benefit (Class IIa/IIb depending on context).
Special Populations & Practical Nuances
- Atrial fibrillation CRT is appropriate if near‑100% biventricular capture can be ensured; consider AV nodal ablation when needed.
- High RV pacing burden If LV dysfunction is present and RV pacing is expected >40–50%, CRT can prevent pacing‑induced cardiomyopathy.
- Post AV node ablation HF patients with LVEF ≤35% benefit from CRT if paced‑dependent.
- Ischaemic vs non‑ischaemic Both benefit; balance defibrillator need (CRT‑D) using standard SCD risk criteria.
- CSP / LBBAP as CRT Conduction‑system pacing (e.g., LBBAP) may be used for CRT in selected cases; program AV/VV carefully to ensure resynchronization.
Quick Reference Table
| Criterion | Threshold | Typical Class |
|---|---|---|
| LVEF | ≤ 35% | Class I |
| NYHA class | II–ambulatory IV | Class I |
| QRS (LBBB) | ≥ 150 ms | Class I |
| QRS (LBBB) | 130–149 ms | Class IIa |
| QRS (non‑LBBB) | ≥ 150 ms | Class IIa–IIb |
| AF with ensured BiV pacing | >95% capture | Class IIa |
| Anticipated RV pacing burden | >40–50% with LV dysfunction | Class IIa |
Classes reflect common international guideline framing; individual society wordings vary slightly.
Who Usually Does Not Benefit?
- QRS < 120–130 ms with no dyssynchrony (most cases).
- LVEF > 35% without other pacing indications.
- Inability to achieve reliable LV/BiV capture (e.g., unfavorable venous anatomy and no alternative CRT approach planned).
Notes for Practice
- Confirm QRS morphology/duration on a clean 12‑lead ECG (average multiple beats).
- Optimize GDMT before referral; re‑assess LVEF after GDMT titration when feasible.
- For AF, plan for pacing strategy (rate control ± AV node ablation) to secure near‑continuous BiV capture.
- If using conduction‑system pacing (e.g., LBBAP) for CRT, document capture criteria and optimize AV/VV delays by ECG.