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Functional abnormalities in isolated left bundle branch block. The effect of interventricular asynchrony

C L Grines1, T M Bashore, H Boudoulas

  • 1Department of Internal Medicine, Ohio State University, Columbus.

Circulation
|April 1, 1989
PubMed

Insights

Left bundle branch block (LBBB) causes significant delays in left ventricular function, impacting diastolic time and heart sound amplitude. This leads to reduced septal contribution and overall reduced ejection fraction in LBBB patients.

Area of Science:

  • Cardiology
  • Cardiac Electrophysiology
  • Cardiovascular Imaging

Background:

  • Left bundle branch block (LBBB) is a cardiac conduction abnormality affecting ventricular activation sequence.
  • Understanding the functional consequences of LBBB on ventricular mechanics and hemodynamics is crucial for patient management.

Purpose of the Study:

  • To investigate the impact of isolated left bundle branch block (LBBB) on left and right ventricular function and timing.
  • To compare cardiac mechanical events in LBBB patients with normal subjects.

Main Methods:

  • Utilized a multimodal approach including apexcardiography, phonocardiography, electrocardiography, echocardiography (2D and dual M-mode), and radionuclide ventriculography (RNV).
  • Compared 18 patients with isolated LBBB to 10 normal control subjects.

Main Results:

  • LBBB demonstrated significant delays in left ventricular systolic and diastolic events, shortening diastole and increasing the right to left ventricular diastolic time ratio.
  • Decreased first heart sound (S1) amplitude (S1/S2 ratio) was observed in LBBB, attributed to widened separation of valvular contributors.
  • Abnormal interventricular septal motion in LBBB reflected asynchronous ventricular contraction and ejection.
  • RNV showed reduced septal regional ejection fraction and a lower global ejection fraction in LBBB patients compared to controls.

Conclusions:

  • Isolated LBBB disrupts normal interventricular synchrony, leading to impaired left ventricular function.
  • The study highlights significant alterations in diastolic timing, heart sound characteristics, and regional/global ejection fraction in LBBB.
  • These findings underscore the mechanical consequences of LBBB on overall cardiac performance.

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