title: Critical appraisal of methods to assess mechanical dyssynchrony.
abstract: OBJECTIVE
  To analyze the strength and weakness of various imaging tools for systolic dyssynchrony assessment in the cardiac resynchronization therapy (CRT) era. Also, controversies and problematic issues of the recent predictors of response to cardiac resynchronization therapy study were addressed.
  
  
  RESULTS
  Despite published data from experienced centers that echocardiographic parameters of systolic dyssynchrony assessment with defined cutoff values were able to predict favorable response to CRT (septal-to-posterior wall delay by M-mode of 130 ms, tissue Doppler imaging of septal-to-lateral wall delay of 65 ms and Ts-SD of 33 ms, and speckle tracking delay in septal-to-posterior wall radial strain of 130 ms), the recent predictors of response to cardiac resynchronization therapy (PROSPECT) study did not concur with the observations. However, the latter study was flawed in multiple areas including site selection bias, dyssynchrony training, and selection of echocardiography equipment, echo core-laboratory experience and echocardiographic image quality surveillance. These factors acting in concert contributed to the high variability of dyssynchrony parameters, high echocardiographic data missing rate, and inconsistent measurement, which will not determine if dyssynchrony predicts a higher response rate than QRS duration alone.
  
  
  CONCLUSIONS
  There is a learning curve for dyssynchrony assessment. Without proper dyssynchrony training and experience accumulation in a large number of implanting centers worldwide, a rush into multicenter trials that only focus on experienced device implantation will not be possible to replicate the role of dyssynchrony assessment.
authors.affiliation: Institute of Vascular Medicine, Division of Cardiology, Department of Medicine and Therapeutics, Prince of Wales Hospital, The Chinese University ofHong Kong, Shatin, NT Hong Kong. cmyu@cuhk.edu.hk
authors.forename: Cheuk-Man
authors.initials: CM
authors.lastname: Yu
authors.forename: Jeroen J
authors.initials: JJ
authors.lastname: Bax
authors.forename: John
authors.initials: J
authors.lastname: Gorcsan
mesh_terms: D004452:Echocardiography / Q000379:methods*; D006801:Humans; D008279:Magnetic Resonance Imaging; D015337:Multicenter Studies as Topic; D010138:Pacemaker, Artificial; D011875:Radionuclide Angiography; D018754:Ventricular Dysfunction / Q000175:diagnosis* / Q000000981:diagnostic imaging