title: Adenosine stress native T1 mapping in severe aortic stenosis: evidence for a role of the intravascular compartment on myocardial T1 values.
abstract: BACKGROUND
  Myocardial T1 relaxation times have been reported to be markedly abnormal in diverse myocardial pathologies, ascribed to interstitial changes, evaluated by T1 mapping and calculation of extracellular volume (ECV). T1 mapping is sensitive to myocardial water content of both intra- and extracellular in origin, but the effect of intravascular compartment changes on T1 has been largely neglected. We aimed to assess the role of intravascular compartment on native (pre-contrast) T1 values by studying the effect of adenosine-induced vasodilatation in patients with severe aortic stenosis (AS) before and after aortic valve replacement (AVR).
  
  
  METHODS
  42 subjects (26 patients with severe AS without obstructive coronary artery disease and 16 controls) underwent cardiovascular magnetic resonance at 3 T for native T1-mapping (ShMOLLI), first-pass perfusion (myocardial perfusion reserve index-MPRI) at rest and during adenosine stress, and late gadolinium enhancement (LGE).
  
  
  RESULTS
  AS patients had increased resting myocardial T1 (1196±47 ms vs. 1168±27 ms, p=0.037), reduced MPRI (0.92±0.31 vs. 1.74±0.32, p<0.001), and increased left ventricular mass index (LVMI) and LGE volume compared to controls. During adenosine stress, T1 in AS was similar to controls (1240±51 ms vs. 1238±54 ms, p=0.88), possibly reflecting a similar level of maximal coronary vasodilatation in both groups. Conversely, the T1 response to stress was blunted in AS (ΔT1 3.7±2.7% vs. 6.0±4.2% in controls, p=0.013). Seven months after AVR (n=16) myocardial T1 and response to adenosine stress recovered towards normal. Native T1 values correlated with reduced MPRI, aortic valve area, and increased LVMI.
  
  
  CONCLUSIONS
  Our study suggests that native myocardial T1 values are not only influenced by interstitial and intracellular water changes, but also by changes in the intravascular compartment. Performing T1 mapping during or soon after vasodilator stress may affect ECV measurements given that hyperemia alone appears to substantially alter T1 values.
authors.affiliation: University of Oxford Centre for Clinical Magnetic Resonance Research (OCMR), Division of Cardiovascular Medicine, Radcliffe Department of Medicine, John Radcliffe Hospital, Oxford OX3 9DU, UK. masliza.mahmod@cardiov.ox.ac.uk.
authors.forename: Masliza
authors.initials: M
authors.lastname: Mahmod
authors.forename: Stefan K
authors.initials: SK
authors.lastname: Piechnik
authors.forename: Eylem
authors.initials: E
authors.lastname: Levelt
authors.forename: Vanessa M
authors.initials: VM
authors.lastname: Ferreira
authors.forename: Jane M
authors.initials: JM
authors.lastname: Francis
authors.forename: Andrew
authors.initials: A
authors.lastname: Lewis
authors.forename: Nikhil
authors.initials: N
authors.lastname: Pal
authors.forename: Sairia
authors.initials: S
authors.lastname: Dass
authors.forename: Houman
authors.initials: H
authors.lastname: Ashrafian
authors.forename: Stefan
authors.initials: S
authors.lastname: Neubauer
authors.forename: Theodoros D
authors.initials: TD
authors.lastname: Karamitsos
mesh_terms: D000241:Adenosine; D000368:Aged; D001021:Aortic Valve / Q000503:physiopathology / Q000601:surgery; D001024:Aortic Valve Stenosis / Q000175:diagnosis* / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D016022:Case-Control Studies; D003287:Contrast Media; D003326:Coronary Circulation; D005260:Female; D005355:Fibrosis; D019786:Gadolinium DTPA; D019918:Heart Valve Prosthesis Implantation; D006801:Humans; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction; D055414:Myocardial Perfusion Imaging / Q000379:methods*; D009206:Myocardium / Q000473:pathology; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012720:Severity of Illness Index; D016896:Treatment Outcome; D014664:Vasodilation; D014665:Vasodilator Agents; D016277:Ventricular Function, Left
chemical_list: D003287:Contrast Media; D014665:Vasodilator Agents; C064925:gadodiamide; D019786:Gadolinium DTPA; D000241:Adenosine