Cardiac Resynchronization Therapy (CRT) is a device-based treatment for patients with heart failure caused by ventricular dyssynchrony. CRT improves symptoms, reduces hospitalizations, enhances quality of life, and reduces mortality by coordinating the timing of right and left ventricular contraction.

CRT may be delivered through:

• CRT-P (biventricular pacemaker)
• CRT-D (biventricular pacemaker + ICD capabilities)

This page summarizes guideline-based indications for CRT according to ACC/AHA/HRS and ESC recommendations.

Primary Reference: ACC/AHA/HRS 2017 Ventricular Arrhythmia & SCD Prevention Guideline ESC Heart Failure Guidelines

CRT improves cardiac performance by:

• Resynchronizing ventricular contraction
• Reducing QRS duration
• Improving left ventricular ejection fraction (LVEF)
• Enhancing stroke volume and cardiac output
• Reducing functional mitral regurgitation

CRT is specifically intended for:

• Left bundle branch block (LBBB) or intraventricular conduction delay
• Reduced LVEF
• Symptomatic heart failure despite optimal therapy

CRT is recommended for patients with:

• LVEF ≤ 35%
• Sinus rhythm
• LBBB with QRS duration ≥ 150 ms
• NYHA Class II, III, or ambulatory IV symptoms
• On optimal guideline-directed medical therapy (GDMT)

CRT reduces mortality and HF hospitalizations in this group.

CRT is reasonable for:

• LBBB with QRS 120–149 ms (LVEF ≤ 35%, NYHA II–IV)
• Non-LBBB conduction with QRS ≥ 150 ms
• Atrial fibrillation requiring AV node ablation to ensure biventricular pacing
• Patients expected to require >40% ventricular pacing with LVEF ≤ 35%
• Patients receiving a new pacemaker/ICD with anticipated high RV pacing burden

Reference: ACC/HRS Bradycardia & Conduction Delay Guideline Summary

CRT *may be considered* for:

• Non-LBBB pattern with QRS 120–149 ms
• NYHA Class I symptoms with LVEF ≤ 30% and LBBB ≥ 150 ms
• Pacemaker-dependent patients with borderline CRT indications

CRT benefit is less predictable in non-LBBB QRS patterns.

CRT is not recommended for:

• QRS < 120 ms (no electrical dyssynchrony)
• LVEF > 35%
• NYHA Class I without other qualifying factors
• Patients whose comorbidities limit survival to < 1 year
• Atrial fibrillation without capacity for near-100% biventricular pacing
• Heart failure primarily due to non-electrical causes (e.g., severe valvular disease untreated)

Reference: NICE: CRT Device Recommendations

CRT may be used if:

• LVEF ≤ 35%
• QRS ≥ 130–150 ms
• AV node ablation or strict rate control ensures >95% biventricular pacing

CRT is beneficial in patients undergoing AV node ablation for AF with:

• LVEF ≤ 50%
• Anticipated dependence on ventricular pacing

CRT can improve EF and symptoms in patients with:

• Declining EF due to chronic RV pacing
• High pacing burden (>40%)

Reference: RV Pacing-Induced Cardiomyopathy – Evidence Review

• CRT is a powerful therapy for HFrEF with electrical dyssynchrony.
• Greatest benefit occurs in LBBB ≥ 150 ms with LVEF ≤ 35%.
• Non-LBBB patients benefit less but may still qualify with wide QRS.
• Near-100% biventricular pacing is required in atrial fibrillation.
• CRT-P vs CRT-D depends on arrhythmia risk and ICD indications.
• Device decisions follow ACC/AHA/HRS and ESC guideline recommendations.

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