Abstract 12002: Increasing Heart Rate in Left Bundle Branch Block Results in Incomplete Relaxation and Increases Left Ventricular Diastolic Stiffness
Introduction: Left bundle branch block (LBBB) slows LV pressure decay and shortens diastole. At low heart rates (HR) this may not compromise filling as diastolic duration is sufficient for complete relaxation.
Purpose: We investigated if further abbreviation of diastole at increased HR could cause incomplete relaxation, particularly in the late activated LV lateral wall; thereby increasing diastolic LV stiffness, which may cause increased filling pressure.
Methods: We analyzed data from a study of 10 canines where HR was increased from 120 to 140 by atrial pacing before and after induction of LBBB. Ventricular and pericardial pressures, LV volume and regional segment lengths (SL) were measured. Global diastolic stiffness was calculated from end diastolic (ED) transmural LV pressure-volume (PV) relations and regional stiffness from pressure-SL relations in septum and lateral wall. A mathematical model was used to estimate the increase in filling pressure due to incomplete relaxation at HR 160 and 180.
Results: In LBBB, tau was prolonged and diastole abbreviated at both HR 120 and 140, compared to baseline (Fig. 1). Increased HR during LBBB stiffened the ventricle, seen as an upward shift of the ED PV relation by 1.4±1.7 mmHg (±SD), (p=0.03) whereas no shift (-0.9±1.5 mmHg) (NS) was seen at baseline (Fig. 2). Regional ED P-SL relations showed a larger upward shift of the lateral wall (1.1±1.8 mmHg) and hence a more pronounced stiffening compared to the septum (0.6±1.5 mmHg) (p<0.05), indicating more delayed lateral wall relaxation. Mathematical estimation showed an increase in filling pressure of 7 and 16 mmHg due to further diastolic abbreviation at HR 160 and 180, respectively.
Conclusions: LV diastolic stiffness is increased at high heart rates in LBBB due to incomplete relaxation, particularly of the late activated LV lateral wall. Diastolic stiffening by increased HR may lead to exercise intolerance and dyspnoea in LBBB patients due to elevated filling pressure.
- Heart failure
- Diastolic function
- Heart conduction system
- Intraventricular dyssynchrony
- Pressure - volume relation
Author Disclosures: O.S. Andersen: None. E. Boe: None. H. Skulstad: None. P. Storsten: None. H.H. Odland: None. O.A. Smiseth: None. E.W. Remme: None.
- © 2015 by American Heart Association, Inc.