How does His (bundle) pacing correct Right Bundle Branch Block (RBBB)?

How His Bundle Pacing Corrects Right Bundle Branch Block

His bundle pacing (HBP) corrects right bundle branch block (RBBB) by directly capturing and activating the His bundle proximal to the site of conduction block, allowing electrical impulses to bypass the diseased right bundle branch and restore physiologic ventricular activation. 1

Mechanism of RBBB Correction with His Bundle Pacing

His bundle pacing works through several key mechanisms:

1. Anatomical Basis:

   • The His bundle contains fibers destined for both the left and right bundle branches
   • In RBBB, the block typically occurs distal to the His bundle in the right bundle branch itself
   • HBP delivers electrical stimulation proximal to this block

2. Types of RBBB Correction:

   • Selective His Capture: Directly captures the His bundle fibers without capturing surrounding myocardium
   • Non-selective His Capture: Captures both the His bundle and adjacent ventricular myocardium

3. Physiologic Activation Sequence:

   • HBP restores the natural electrical activation pattern through the native conduction system
   • This prevents the ventricular dyssynchrony typically seen with right ventricular pacing 1

Clinical Evidence for RBBB Correction

HBP has demonstrated significant efficacy in correcting RBBB:

• In patients with heart failure and RBBB, HBP successfully corrected RBBB in 78% of cases 2
• Successful HBP in RBBB patients led to:
  • Significant QRS narrowing from 158±24ms to 127±17ms
  • Improvement in left ventricular ejection fraction from 31±10% to 39±13%
  • Improvement in NYHA functional class from 2.8±0.6 to 2±0.7 2

Advantages Over Traditional Pacing

HBP offers several advantages over conventional right ventricular pacing:

• Prevents Ventricular Dyssynchrony: HBP mitigates the ventricular dyssynchrony and adverse mechanical remodeling observed with right ventricular pacing 1
• Reduces Heart Failure Hospitalizations: HBP is associated with a significant decrease in heart failure hospitalizations, particularly in patients with ventricular pacing >20% compared with RV pacing 1
• Improves Cardiac Function: Studies show reduction in left ventricular end-systolic volume index and improvement in LVEF with HBP 1

Technical Considerations

When implementing HBP for RBBB correction:

• Implantation Success Rate: With improved tools and techniques, HBP can be successfully applied in >90% of patients 3
• Pacing Thresholds: His capture and bundle branch block correction thresholds average 1.1±0.6V and 1.4±0.7V at 1ms pulse width, respectively 2
• Lead Stability: Rate of lead dislodgement and threshold increase is similar to conventional pacemaker systems 3

Limitations and Challenges

Despite its benefits, HBP has some limitations:

• Higher Pacing Thresholds: HBP typically requires higher pacing outputs compared to conventional RV pacing
• Technical Difficulty: HBP implantation can be more challenging than traditional pacing approaches
• Limited Efficacy in Distal Block: HBP may be less effective if the RBBB occurs very distal in the conduction system

Alternative: Left Bundle Branch Pacing

For cases where HBP is challenging or ineffective:

• Left bundle branch pacing (LBBP) has emerged as an alternative approach
• LBBP may be easier to implant and possible in a wider anatomic area
• However, LBBP requires active screw-in of the lead deep into the ventricular septum, and long-term data is limited 3

HBP represents a significant advancement in physiologic pacing that can effectively correct RBBB and improve clinical outcomes in patients with heart failure and conduction disorders.