title: Time to onset of regional relaxation: feasibility, variability and utility of a novel index of regional myocardial function by strain rate imaging.
abstract: OBJECTIVE
  Time to onset of regional relaxation (T(R)) has been proposed as a novel index of regional myocardial function. This study sought to prospectively establish the feasibility and variability of T(R) in healthy volunteers (CONTROL) and to examine its utility in patients with inducible ischemia (PATIENT).
  
  
  BACKGROUND
  Strain rate imaging (SRI) depicts myocardial deformation and enables quantitation of regional myocardial function with high temporal and spatial resolution. Thus, regional mechanical events can be accurately timed with SRI. The time point of regional transition from contraction to relaxation is altered in pathologic states.
  
  
  METHODS
  Resting mean segmental T(R) was determined in 60 subjects: 20 in the CONTROL group and 40 in the PATIENT group. T(R) was also measured at peak dobutamine stress in the PATIENT group. An automated image analysis program determined the time point of transition from regional contraction to relaxation activity, and calculated T(R), defined as the time, in milliseconds, from the electrocardiogram R-wave to this transition point.
  
  
  RESULTS
  Automated T(R) measurements were feasible in more than 90% of the segments in CONTROL and PATIENT groups. Mean T(R) was 353 +/- 24 ms and was shorter in the mid segments compared to apical and basal segments. Intra- and interobserver variability were low (6% and 9%, respectively). In the PATIENT group, the percent decrease in T(R) during dobutamine stress was significantly higher in normal compared to ischemic segments (30% vs. 19%, respectively, p = 0.01). A percent change >20% in T(R) identified patients with an ischemic response during dobutamine infusion (sensitivity 92%, specificity 75%).
  
  
  CONCLUSIONS
  T(R), a novel quantitative index of regional myocardial function, can be determined with low variability and satisfactory feasibility in routine clinical settings. Percent change in T(R) identifies ischemic segments during dobutamine stress echocardiography (DSE) and may allow quantitative assessment of DSE.
authors: Division of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota 55905, USA.abraham.theodore@mayo.edu
authors: Theodore P
authors: TP
authors: Abraham
authors: Marek
authors: M
authors: Belohlavek
authors: Helen L
authors: HL
authors: Thomson
authors: Cristina
authors: C
authors: Pislaru
authors: Bijoy
authors: B
authors: Khandheria
authors: James B
authors: JB
authors: Seward
authors: Patricia A
authors: PA
authors: Pellikka
mesh_terms: D000328:Adult; D000368:Aged; D004280:Dobutamine; D025401:Echocardiography, Stress; D005080:Exercise Test; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000502:physiology*; D017202:Myocardial Ischemia / Q000175:diagnosis* / Q000503:physiopathology; D015588:Observer Variation; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013997:Time Factors
chemical_list: D004280:Dobutamine