title: Evidence-based recommendations for PISA measurements in mitral regurgitation: systematic review, clinical and in-vitro study.
abstract: BACKGROUND
  Guidelines for quantifying mitral regurgitation (MR) using "proximal isovelocity surface area" (PISA) instruct operators to measure the PISA radius from valve orifice to Doppler flow convergence "hemisphere". Using clinical data and a physically-constructed MR model we (A) analyse the actually-observed colour Doppler PISA shape and (B) test whether instructions to measure a "hemisphere" are helpful.
  
  
  RESULTS
  In part A, the true shape of PISA shells was investigated using three separate approaches. First, a systematic review of published examples consistently showed non-hemispherical, "urchinoid" shapes. Second, our clinical data confirmed that the Doppler-visualized surface is non-hemispherical. Third, in-vitro experiments showed that round orifices never produce a colour Doppler hemisphere. In part B, six observers were instructed to measure hemisphere radius rh and (on a second viewing) urchinoid distance (du) in 11 clinical PISA datasets; 6 established experts also measured PISA distance as the gold standard. rh measurements, generated using the hemisphere instruction significantly underestimated expert values (-28%, p<0.0005), meaning r(h)(2) was underestimated by approximately 2-fold. du measurements, generated using the non-hemisphere instruction were less biased (+7%, p=0.03). Finally, frame-to-frame variability in PISA distance was found to have a coefficient of variation (CV) of 25% in patients and 9% in in-vitro data. Beat-to-beat variability had a CV of 15% in patients.
  
  
  CONCLUSIONS
  Doppler-visualized PISA shells are not hemispherical: we should avoid advising observers to measure a hemispherical radius because it encourages underestimation of orifice area by approximately two-fold. If precision is needed (e.g. to detect changes reliably) multi-frame averaging is essential.
authors.affiliation: International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College, 59-61 North Wharf Road, London W21LA, UK. Electronic address: michela.moraldo@gmail.com.
authors.forename: Michela
authors.initials: M
authors.lastname: Moraldo
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Cecaro
authors.forename: Matthew
authors.initials: M
authors.lastname: Shun-Shin
authors.forename: Punam A
authors.initials: PA
authors.lastname: Pabari
authors.forename: Justin E
authors.initials: JE
authors.lastname: Davies
authors.forename: Xiao Y
authors.initials: XY
authors.lastname: Xu
authors.forename: Alun D
authors.initials: AD
authors.lastname: Hughes
authors.forename: Charlotte
authors.initials: C
authors.lastname: Manisty
authors.forename: Darrel P
authors.initials: DP
authors.lastname: Francis
mesh_terms: D018618:Echocardiography, Doppler, Color / Q000379:methods / Q000592:standards*; D019317:Evidence-Based Medicine / Q000379:methods / Q000592:standards*; D006801:Humans; D008944:Mitral Valve Insufficiency / Q000000981:diagnostic imaging* / Q000628:therapy; D017410:Practice Guidelines as Topic / Q000592:standards*