What is the difference between Cardiac Contractility Modulation (CCM) and Cardiac Resynchronization Therapy (CRT) devices?

Differences Between Cardiac Contractility Modulation (CCM) and Cardiac Resynchronization Therapy (CRT) Devices

Cardiac Contractility Modulation (CCM) and Cardiac Resynchronization Therapy (CRT) are fundamentally different heart failure treatment modalities with distinct mechanisms of action, patient selection criteria, and clinical applications.

Key Differences

Mechanism of Action

• CRT: Delivers synchronized pacing to both ventricles to correct electrical dyssynchrony, improving ventricular contractility by restoring coordinated contraction in patients with conduction abnormalities 1
• CCM: Delivers non-excitatory high-energy stimulatory impulses during the absolute refractory period, enhancing cardiac contractility without affecting cardiac rhythm or requiring ventricular resynchronization 2

Patient Selection Criteria

• CRT: Primarily indicated for patients with:

  • QRS duration ≥150 ms (strongest evidence) 1
  • Left Bundle Branch Block (LBBB) morphology 1
  • LVEF ≤35% 1
  • NYHA class II-IV symptoms despite optimal medical therapy 1

• CCM: Indicated for patients with:

  • Normal or narrow QRS duration (typically <120 ms) 2, 3
  • LVEF ≤35% 3
  • Moderate to severe heart failure symptoms despite optimal medical therapy 2
  • May be considered for CRT non-responders as adjunctive therapy 4, 5

Device Types

• CRT: Available as:

  • CRT-P (with pacemaker function only) 1
  • CRT-D (with additional defibrillator capability) 1
  • Selection between CRT-P and CRT-D depends on patient risk factors and need for sudden cardiac death prevention 1

• CCM: Primarily focused on contractility enhancement without rhythm control or defibrillation capabilities, though can be used alongside ICDs in appropriate patients 2, 3

Clinical Outcomes

CRT Outcomes

• Reduces mortality by 24-36% in appropriate patients 1
• Decreases heart failure hospitalizations by approximately 30% 1
• Improves exercise capacity and quality of life 1
• Most effective in patients with LBBB and QRS ≥150 ms 1
• Induces favorable ventricular remodeling with reduction in chamber dimensions 1

CCM Outcomes

• Improves NYHA functional class and ejection fraction 5
• Enhances left ventricular contractility (measured by LV dP/dt) 5
• Can provide benefit in patients with normal QRS who are not candidates for CRT 2, 6
• May offer therapeutic option for CRT non-responders 4, 5
• Comparable improvements in functional status and ventricular remodeling to CRT in appropriate patients 3

Combined Use Considerations

• CCM and CRT devices can coexist without electrical interference in select patients 4, 5
• CCM may be considered as an adjunctive therapy in CRT non-responders 4, 5
• The combination requires careful technical planning and monitoring for potential complications 5

Clinical Decision-Making Algorithm

1. Assess QRS duration and morphology:

   • QRS ≥150 ms with LBBB: Consider CRT first 1
   • QRS 120-149 ms with LBBB: CRT may be beneficial 1
   • QRS <120 ms: Consider CCM 2, 6

2. Evaluate risk of sudden cardiac death:

   • High risk: Consider CRT-D 1
   • Lower risk: Consider CRT-P or CCM based on QRS criteria 1

3. For CRT non-responders:

   • Consider adding CCM as adjunctive therapy if symptoms persist 4, 5

Important Caveats

• CRT response rates are approximately 70-80%, leaving 20-30% as non-responders 5
• CCM shows similar left ventricular reverse remodeling to CRT in patients with mildly prolonged QRS, but less effect compared to CRT in patients with very wide QRS 6
• Mortality and complication rates may be higher when adding CCM to CRT non-responders due to the advanced disease state of these patients 5
• The evidence for CCM is less robust than for CRT, which has multiple large randomized controlled trials supporting its use 1