What is cardiac resynchronization therapy (CRT) used for in patients with heart failure?

Cardiac Resynchronization Therapy for Heart Failure

Cardiac resynchronization therapy (CRT) is primarily indicated for patients with heart failure who have reduced left ventricular ejection fraction (≤35%), QRS prolongation (≥120 ms), and persistent symptoms despite optimal medical therapy. 1

Primary Indications for CRT

CRT is recommended for the following patient populations:

• Strong evidence (Class I):

  • Patients with LVEF ≤35%, LBBB, and QRS duration ≥150 ms with NYHA class II-IV symptoms despite optimal medical therapy 1
  • Patients with LVEF ≤35%, LBBB, and QRS duration 120-149 ms with NYHA class II-IV symptoms on guideline-directed medical therapy (GDMT) 1
  • Patients with NYHA class III or ambulatory class IV heart failure with LVEF ≤35% and QRS ≥120 ms 2

• Moderate evidence (Class IIa):

  • Patients with LVEF ≤35% and permanent atrial fibrillation requiring ventricular pacing or meeting other CRT criteria 1
  • Patients with LVEF ≤35% undergoing new device placement with anticipated requirement for significant (≥40%) ventricular pacing 1
  • Patients with LVEF ≤35%, non-LBBB pattern, and QRS ≥150 ms with NYHA class III/ambulatory IV symptoms 1

Clinical Benefits of CRT

CRT provides multiple benefits for appropriate patients:

1. Mortality reduction: 22-36% reduction in all-cause mortality 1
2. Reduced hospitalizations: 37-52% decrease in heart failure hospitalizations 1, 2
3. Improved cardiac function:
   • Increased LVEF by approximately 3-6.9% in responders 1
   • Reverse remodeling with reduction in LV volumes 1, 2
4. Enhanced quality of life:
   • Improved functional status and NYHA class 2, 1
   • Increased exercise capacity with 20% improvement in 6-minute walk distance 1
   • 10-15% increase in peak oxygen consumption 1

Predictors of Response to CRT

Certain factors predict better response to CRT:

• Positive predictors:

  • LBBB morphology 1, 2
  • QRS duration ≥150 ms 1, 2
  • Non-ischemic cardiomyopathy 1

• Negative predictors:

  • QRS <120 ms 1
  • Non-LBBB pattern, especially right bundle branch block (RBBB) 1, 3
  • Extensive myocardial scarring 2

Device Selection: CRT-P vs. CRT-D

The choice between CRT with pacemaker (CRT-P) or CRT with defibrillator (CRT-D) depends on:

• CRT-D is preferred for:

  • Patients meeting criteria for both CRT and ICD 1
  • Secondary prevention ICD indications 1
  • Ischemic cardiomyopathy with LVEF ≤30% and QRS ≥150 ms with LBBB pattern 1
  • Patients with reasonable survival expectation >1 year with good functional status 1

• CRT-P is appropriate for:

  • Patients with significant comorbidities limiting survival 1, 2
  • Patients with contraindications to ICD therapy 1
  • Elderly patients with primary prevention indications 1

Contraindications and Limitations

CRT is not recommended for:

• Patients with NYHA class I or II symptoms, non-LBBB pattern, and QRS <150 ms 1
• Patients with QRS duration <120 ms without evidence of electrical dyssynchrony 1, 2
• Patients with comorbidities limiting survival with good functional capacity to less than 1 year 1

Optimization and Follow-up

For optimal CRT effectiveness:

• Ensure high percentage (≥95%) of biventricular pacing 1
• Target LV lead placement to the latest activated areas (typically lateral or posterolateral vein) 1
• Avoid apical lead placement when possible 1
• Consider AV nodal ablation in patients with atrial fibrillation to ensure adequate biventricular capture 1, 2
• Program AV delay typically between 100-120 ms 1

Special Considerations

1. Patients with mild heart failure (NYHA I-II):

   • CRT can provide significant reverse remodeling and reduce heart failure hospitalizations 2
   • MADIT-CRT and REVERSE trials demonstrated benefits in NYHA class I-II patients 2

2. Patients with narrow QRS complex (<120 ms):

   • Generally not recommended for CRT regardless of echocardiographic evidence of dyssynchrony 1, 2
   • The RethinQ trial failed to show significant improvement in peak oxygen consumption in these patients 2

3. Patients with atrial fibrillation:

   • May benefit from CRT if adequate biventricular pacing can be achieved 2, 1
   • AV nodal ablation often required to ensure high percentage of biventricular capture 1

4. Patients requiring conventional pacing:

   • Biventricular pacing preferred over RV pacing in patients with LV dysfunction 2
   • BLOCK-HF study showed 26% reduction in combined endpoint of mortality, HF-related urgent care, and increase in LV end-systolic volume with biventricular pacing compared to RV pacing 2

By carefully selecting appropriate candidates and optimizing device programming, CRT can significantly improve outcomes for heart failure patients with ventricular dyssynchrony.