Background— The effects of left ventricular (LV) loading conditions on LV dyssynchrony have not been elucidated. We modified LV loading conditions to reveal their effects on echocardiography-derived LV dyssynchrony index (LVdys) in patients with documented nonischemic dilated cardiomyopathy.
Methods and Results— Thirty-seven patients were consecutively enrolled. After baseline measurements, pneumatic compression of the lower extremities (Pcom) was used to increase LV afterload. Subsequently, sublingual nitroglycerin (SL-NG) was administered to modify preload. Conventional echocardiographic parameters, LVdys (by speckle-tracking radial strain analysis) and LV end-systolic wall stress (LV-ESWS), were calculated under each condition. LVdys-6 (defined as the maximal difference in time-to-peak radial strain between 6 myocardial segments) and LV-ESWS increased under Pcom (for LVdys-6, 159±117 at baseline versus 239±140 ms under Pcom, P<0.05; for LV-ESWS, 191±63 versus 228±80 g/m2, P<0.05) After SL-NG application, both parameters decreased significantly (for LVdys-6, 239±140 under Pcom versus 147±103 ms after SL-NG, P<0.05; for LV-ESWS, 228±80 under Pcom versus 189±67 g/m2 after SL-NG, P<0.05). When the presence of LV dyssynchrony was defined as the absolute difference in time-to-peak radial strain between the anteroseptal and posterior segments (LVdys-2), the results were unchanged. Using 130 ms as a cutoff value, the proportion of patients with LV dyssynchrony changed significantly (29.7% at baseline, 45.9% under Pcom, and 35.1% after SL-NG). When the presence of LV dyssynchrony was defined as standard deviation of the time to peak radial strain for 6 segments (LVdys-SD), the results were same. LVdys and LV-ESWS showed a modest but significant association with each other (r=0.47, P<0.001 for LVdys-6; r=0.41, P<0.001 for LVdys-2; r=0.46, P<0.001 for LVdys-SD).
Conclusions— To the best of our knowledge, the present study provides the first evidence of a significant association between LVdys and LV loading status, reflective of a dynamic nature of LVdys. Accordingly, LV loading conditions should be taken into account when echocardiographic LVdys is used for clinical decision-making of selecting candidates for cardiac resynchronization therapy or when it is used as a surrogate marker of prognosis.