Indications for CRT-P in Complete Heart Block with LBBB
In patients with complete heart block and LBBB, cardiac resynchronization therapy with pacemaker (CRT-P) is reasonable to reduce total mortality, reduce hospitalizations, and improve symptoms and quality of life when the LVEF is 36% to 50%. 1
Primary Indications Based on Ejection Fraction
- For patients with high-degree or complete heart block and LVEF of 36% to 50%, CRT is recommended as a Class IIa indication (Level of Evidence B-R) to improve clinical outcomes 1
- For patients with LVEF ≤35%, sinus rhythm, LBBB with QRS duration ≥150 ms, and NYHA class II, III, or ambulatory IV symptoms on guideline-directed medical therapy (GDMT), CRT is indicated as a Class I recommendation 1
- For patients with LVEF ≤35%, sinus rhythm, LBBB with QRS duration 120-149 ms, and NYHA class II, III, or ambulatory IV symptoms on GDMT, CRT is recommended as a Class IIa recommendation 1
Indications Based on Pacing Requirements
- CRT is reasonable for patients on GDMT who have LVEF ≤35% and are undergoing placement of a new or replacement device with anticipated requirement for significant (>40%) ventricular pacing 1, 2
- Patients with conventional pacemakers who develop heart failure with LVEF ≤35% and have a high percentage of ventricular pacing should be upgraded to CRT if they remain in NYHA class III or ambulatory IV despite adequate medical treatment 1, 2
- De novo CRT should be considered in heart failure patients with reduced EF and expected high percentage of ventricular pacing to decrease the risk of worsening heart failure 1, 2
QRS Duration and Morphology Considerations
- The strongest evidence for CRT benefit is in patients with typical LBBB morphology 1, 3
- QRS duration ≥150 ms is associated with greater benefit from CRT compared to QRS duration 120-149 ms 1
- CRT is not recommended for patients with QRS duration <120 ms regardless of heart block or LBBB status 1
Patient Selection Considerations
- Ambulatory NYHA class IV patients (no scheduled or unscheduled HF hospitalizations in the last month) with a life expectancy >6 months can benefit from CRT 1, 3
- Patients should have a reasonable expectation of survival with good functional status for >1 year to receive maximum benefit from CRT 1, 2
- Patients should generally not be implanted during admission for acute decompensated heart failure; guideline-directed medical therapy should be optimized first 1
Special Considerations for Complete Heart Block
- Chronic right ventricular pacing in patients with pre-existing LV dysfunction can induce left ventricular dyssynchrony and worsen heart failure symptoms 2, 4
- Patients with complete heart block and existing RV pacing have similar dyssynchrony patterns as patients with intrinsic LBBB 4
- CRT leads to improvements in LV global function, dyssynchrony variables, and symptoms in patients chronically paced from the RV that are similar to those observed in patients with intrinsic LBBB 4
Emerging Alternatives to Traditional Biventricular Pacing
- Left bundle branch area pacing (LBBAP) has shown promise as an alternative CRT technique in patients with heart failure and LBBB 5, 6
- Permanent His bundle pacing has demonstrated significant narrowing of QRS duration and improvement in LV function in patients with RBBB and reduced LVEF 7
- Recent randomized trial data suggests LBBP-CRT may provide greater LVEF improvement than traditional biventricular pacing CRT in patients with nonischemic cardiomyopathy and LBBB 6
Common Pitfalls and Caveats
- CRT remains underutilized, with only about one-third of eligible patients receiving devices 3
- Non-response to CRT occurs in approximately 20-40% of patients, depending on the response criteria used 3
- Optimization of medical therapy before and after CRT implantation is crucial for maximizing benefits 3, 2
- For patients with atrial fibrillation, AV nodal ablation or pharmacological rate control is often necessary to ensure near 100% ventricular pacing with CRT 1, 2