title: Impact of scar thickness on the assessment of viability using dobutamine echocardiography and thallium single-photon emission computed tomography: a comparison with contrast-enhanced magnetic resonance imaging.
abstract: OBJECTIVE
  We sought to determine whether the transmural extent of scar (TES) explains discordances between dobutamine echocardiography (DbE) and thallium single-photon emission computed tomography (Tl-SPECT) in the detection of viable myocardium (VM).
  
  
  BACKGROUND
  Discrepancies between DbE and Tl-SPECT are often attributed to differences between contractile reserve and membrane integrity, but may also reflect a disproportionate influence of nontransmural scar on thickening at DbE.
  
  
  METHODS
  Sixty patients (age 62 +/- 12 years; 10 women and 50 men) with postinfarction left ventricular dysfunction underwent standard rest-late redistribution Tl-SPECT and DbE. Viable myocardium was identified when dysfunctional segments showed Tl activity >60% on the late-redistribution image or by low-dose augmentation at DbE. Contrast-enhanced magnetic resonance imaging (ceMRI) was used to divide TES into five groups: 0%, <25%, 26% to 50%, 51% to 75%, and >75% of the wall thickness replaced by scar.
  
  
  RESULTS
  As TES increased, both the mean Tl uptake and change in wall motion score decreased significantly (both p < 0.001). However, the presence of subendocardial scar was insufficient to prevent thickening; >50% of segments still showed contractile function with TES of 25% to 75%, although residual function was uncommon with TES >75%. The relationship of both tests to increasing TES was similar, but Tl-SPECT identified VM more frequently than DbE in all groups. Among segments without scar or with small amounts of scar (<25% TES), >50% were viable by SPECT.
  
  
  CONCLUSIONS
  Both contractile reserve and perfusion are sensitive to the extent of scar. However, contractile reserve may be impaired in the face of no or minor scar, and thickening may still occur with extensive scar.
authors.affiliation: University of Queensland, Brisbane, Australia.
authors.forename: Charles
authors.initials: C
authors.lastname: Nelson
authors.forename: Jane
authors.initials: J
authors.lastname: McCrohon
authors.forename: Frederick
authors.initials: F
authors.lastname: Khafagi
authors.forename: Stephen
authors.initials: S
authors.lastname: Rose
authors.forename: Rodel
authors.initials: R
authors.lastname: Leano
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Marwick
mesh_terms: D000318:Adrenergic beta-Agonists; D000368:Aged; D003287:Contrast Media; D004280:Dobutamine; D004452:Echocardiography; D005260:Female; D006801:Humans; D007089:Image Enhancement; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000502:physiology; D009203:Myocardial Infarction / Q000175:diagnosis / Q000503:physiopathology; D013223:Statistics as Topic; D013794:Thallium Radioisotopes; D015899:Tomography, Emission-Computed, Single-Photon; D018487:Ventricular Dysfunction, Left / Q000175:diagnosis / Q000503:physiopathology
chemical_list: D000318:Adrenergic beta-Agonists; D003287:Contrast Media; D013794:Thallium Radioisotopes; D004280:Dobutamine