title: Dynamic dyssynchrony and impaired contractile reserve of the left ventricle in beta-thalassaemia major: an exercise echocardiographic study.
abstract: BACKGROUND
  Performance of the left ventricle during exercise stress in thalassaemia patients is uncertain. We aimed to explore the phenomenon of dynamic dyssynchrony and assess contractile reserve in patients with beta-thalassaemia major and determine their relationships with myocardial iron load.
  
  
  RESULTS
  Thirty-two thalassaemia patients (16 males), aged 26.8 ± 6.9 years, without heart failure and 17 healthy controls were studied. Their left ventricular (LV) volumes, ejection fraction, systolic dyssynchrony index (SDI), and myocardial acceleration during isovolumic LV contraction (IVA) were determined at rest and during submaximal bicycle exercise testing using 3-dimensional and tissue Doppler echocardiography. Myocardial iron load as assessed by T2* cardiac magnetic resonance in patients were further related to indices of LV dyssynchrony and contractile reserve. At rest, patients had significantly greater LV SDI (p<0.001) but similar IVA (p = 0.22) compared with controls. With exercise stress, the prevalence of mechanical dyssynchrony (SDI>4.6%, control+2SD) increased from baseline 25% to 84% in patients. Δ SDI(exercise-baseline) correlated with exercise-baseline differences in LV ejection fraction (p<0.001) and stroke volume (p = 0.006). Compared with controls, patients had significantly less exercise-induced increase in LV ejection fraction, cardiac index, and IVA (interaction, all p<0.05) and had impaired contractile reserve as reflected by the gentler IVA-heart rate slope (p = 0.018). Cardiac T2* in patients correlated with baseline LV SDI (r = -0.44, p = 0.011) and IVA-heart rate slope (r = 0.36, p = 0.044).
  
  
  CONCLUSIONS
  Resting LV dyssynchrony is associated with myocardial iron load. Exercise stress further unveils LV dynamic dyssynchrony and impaired contractile reserve in patients with beta-thalassaemia major.
authors.affiliation: Division of Paediatric Cardiology, Queen Mary Hospital, The University of Hong Kong, Hong Kong, China. xfcheung@hku.hk
authors.forename: Yiu-fai
authors.initials: YF
authors.lastname: Cheung
authors.forename: Wei
authors.initials: W
authors.lastname: Yu
authors.forename: Shu-na
authors.initials: SN
authors.lastname: Li
authors.forename: Wendy W M
authors.initials: WW
authors.lastname: Lam
authors.forename: Yuen-chi
authors.initials: YC
authors.lastname: Ho
authors.forename: Sophia J
authors.initials: SJ
authors.lastname: Wong
authors.forename: Godfrey C F
authors.initials: GC
authors.lastname: Chan
authors.forename: Shau-yin
authors.initials: SY
authors.lastname: Ha
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D015150:Echocardiography, Doppler; D005080:Exercise Test; D005260:Female; D006352:Heart Ventricles / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D006801:Humans; D007501:Iron / Q000032:analysis; D008279:Magnetic Resonance Imaging; D008297:Male; D009200:Myocardial Contraction; D009206:Myocardium / Q000737:chemistry / Q000473:pathology*; D013318:Stroke Volume; D018487:Ventricular Dysfunction, Left / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D017086:beta-Thalassemia / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*
chemical_list: D007501:Iron