What are the differences between right ventricular (RV) apical, septal, and left ventricular (LV) septal pacing in terms of conduction and cardiac function?

Differences Between RV Apical, Septal, and LV Septal Pacing

Physiologic pacing methods such as right ventricular septal, His bundle, or left ventricular septal pacing provide better cardiac function outcomes compared to traditional right ventricular apical pacing by preserving more natural ventricular activation patterns and reducing ventricular dyssynchrony.

Conduction Patterns and Cardiac Function by Pacing Site

Right Ventricular Apical (RVA) Pacing

• Creates non-physiologic ventricular activation pattern with significant electrical and mechanical dyssynchrony 1
• Results in:
  • Prolonged QRS duration (average 154-172 ms) 2, 3
  • Reduced left ventricular ejection fraction (LVEF) 2
  • Increased left ventricular end-systolic and end-diastolic volumes 1
  • Decreased stroke volume 2
  • Greater risk of heart failure when pacing exceeds 40% of the time 1
• Long-term RVA pacing can lead to adverse cardiac remodeling and heart failure, especially in patients with pre-existing cardiac dysfunction 1

Right Ventricular Septal (RVS) Pacing

• Produces more physiologic conduction than RVA pacing but still creates dyssynchrony
• Characteristics include:
  • Shorter QRS duration than RVA pacing (average 147 ms vs. 154 ms) 2
  • Better preservation of LVEF compared to RVA pacing 2
  • Less dyssynchrony than RVA pacing 2
  • Still reduces LVdP/dtmax (measure of contractility) by approximately 6.9% compared to baseline 3

Left Ventricular Septal (LVS) Pacing

• Provides most physiologic activation pattern of the three approaches
• Advantages include:
  • Shortest QRS duration (average 144 ms) 3
  • Maintains LVdP/dtmax at baseline levels (preserves contractility) 3
  • Better preservation of cardiac synchrony 3, 4
  • May improve LVEF over time rather than just maintaining it 5
  • Activates the working myocardium first at the LV endocardium in low septal and anterior free-wall regions, mimicking normal conduction 4

Clinical Implications and Considerations

Patient Selection

• Patients requiring high percentage of ventricular pacing (>40%) benefit most from physiologic pacing methods 1
• Patients with intermediate LVEF (>35% but ≤52%) show greatest benefit from physiologic pacing compared to RVA pacing 1
• Patients with hypertrophic cardiomyopathy and left ventricular outflow tract obstruction may specifically benefit from RVA pacing with short AV intervals to reduce outflow gradient 1

Technical Considerations

• LVS pacing requires more advanced techniques but is becoming more feasible with specialized leads and delivery systems 3, 4
• RVS pacing sites can be heterogeneous when using standard implantation techniques, leading to inconsistent results 6
• His bundle pacing and left bundle branch pacing are additional physiologic pacing options with specific advantages and technical challenges 4

Long-term Outcomes

• Physiologic pacing methods (LVS, His bundle) show:
  • Reduced adverse cardiac remodeling 1
  • Better preservation of LVEF 1
  • Fewer heart failure hospitalizations when pacing exceeds 40% 1
  • No demonstrated mortality benefit in current studies 1

Common Pitfalls and Caveats

1. RVS pacing is often incorrectly positioned, resulting in heterogeneous pacing sites and potentially worse outcomes than properly positioned RVA pacing 6

2. Physiologic pacing methods (His bundle, LVS) may have higher complication rates:

   • Higher risk of lead revision due to elevated thresholds or dislodgement 1
   • Potentially shorter battery longevity with biventricular pacing 1

3. The benefit of physiologic pacing may be minimal in patients with normal baseline cardiac function or those requiring minimal ventricular pacing 1

4. Accurate lead placement verification requires more than just fluoroscopy and ECG - echocardiographic confirmation is valuable 6

5. Long-term data on LVS pacing outcomes are still limited compared to the extensive experience with RVA pacing 4