Abstract 14719: Wasted Work Fraction - A Novel Method For Assessing Dyssynchrony In Patients With Left Bundle Branch Block
Background: In patients with left bundle branch block (LBBB) left ventricular (LV) late activated segments are stretched initially by the contraction of early activated segments and early activated segments are stretched (after initial contraction) when late activated segments start to contract. The result of this dyssynchrony is that substantial amounts of LV work does not contribute to ejection and is “wasted”. We therefore introduce “wasted work fraction” (WWF) which may be used to quantify LV wasted work.
Methods: In a dog model (n=7) and in patients (n=14) with LBBB we measured segmental strain by speckle tracking echocardiography (dogs and patients) and sonomicrometry (dogs) and LV pressure (LVP) by micromanometry. Regional work was calculated using strain to assess regional shorting and LVP as an analog for wall stress. Instantaneous strain rate and LVP were multiplied resulting in a measure of instantaneous power. Power was then integrated over time to give work displayed as a function of time. Work during segmental shortening was defined as positive (black line in fig 1) and work during segmental lengthening as negative (grey line in fig 1), the latter was considered as wasted work. WWF could then be calculated as percent negative work of total positive work for a specific segment and as a mean WWF incorporating all LV walls (global).
Results: In the dogs global WWF increased significantly from baseline to LBBB (mean ±SD, 15±8 vs. 36±15% and 16±5 vs. 34±9%) using sonomicrometry (Fig 2) and STE, respectively. Patients with LBBB also had a large degree of WWF (30±9%). Figure 1 shows regional work analysis for two segments in a patient with cardiac resynchronization therapy (CRT).
Conclusions: In a clinical setting WWF may be used to quantify the cardiac mechanical disadvantage of dyssynchrony and the WWF may indicate the potential for improvement in function by CRT. This analysis may serve as an important tool when evaluating patients for CRT and optimizing device settings.
- © 2011 by American Heart Association, Inc.