title: Impact of loading condition on the 2D speckle tracking-derived left ventricular dyssynchrony index in nonischemic dilated cardiomyopathy.
abstract: 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.
  
  
  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/m(2), 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/m(2) 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.
authors.affiliation: Division of Cardiology, Department of Internal Medicine, Cardiovascular Center, Seoul National University Hospital, Seoul, Korea.
authors.forename: Hyo Eun
authors.initials: HE
authors.lastname: Park
authors.forename: Sung-A
authors.initials: SA
authors.lastname: Chang
authors.forename: Hyung-Kwan
authors.initials: HK
authors.lastname: Kim
authors.forename: Dong-Ho
authors.initials: DH
authors.lastname: Shin
authors.forename: Ji-Hyun
authors.initials: JH
authors.lastname: Kim
authors.forename: Myung-Ki
authors.initials: MK
authors.lastname: Seo
authors.forename: Yong-Jin
authors.initials: YJ
authors.lastname: Kim
authors.forename: Goo-Yeong
authors.initials: GY
authors.lastname: Cho
authors.forename: Dae-Won
authors.initials: DW
authors.lastname: Sohn
authors.forename: Byung-Hee
authors.initials: BH
authors.lastname: Oh
authors.forename: Young-Bae
authors.initials: YB
authors.lastname: Park
mesh_terms: D001794:Blood Pressure; D002311:Cardiomyopathy, Dilated / Q000150:complications / Q000000981:diagnostic imaging*; D015150:Echocardiography, Doppler / Q000379:methods; D005260:Female; D006339:Heart Rate; D006352:Heart Ventricles / Q000000981:diagnostic imaging*; D006801:Humans; D048228:Intermittent Pneumatic Compression Devices; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D018487:Ventricular Dysfunction, Left / Q000150:complications / Q000000981:diagnostic imaging*