title: Prospective evaluation of frequency and nature of transcranial high-intensity Doppler signals in prosthetic valve recipients.
abstract: OBJECTIVE
  In asymptomatic prosthetic valve recipients, high-intensity transient signals (HITS) observed with transcranial Doppler (TCD) are a phenomenon of obscure clinical relevance which nature has not yet been elucidated convincingly.
  
  
  METHODS
  Eighty-three patients without carotid disease, history of cerebrovascular accidents, and with negative preoperative TCD undergoing either valve replacement (mitral, n = 11; aortic, n = 56; mitral + aortic, n = 6; 40 mechanical prostheses, 29 biological prostheses, 10 homografts) or mitral repair (n = 10) were evaluated prospectively by means of TCD at discharge, three months and one year after surgery, to analyze the presence, incidence and characteristics of HITS. Furthermore, in 12 patients positive for HITS, TCD was repeated during a 30-min period of 100% O2 inhalation.
  
  
  RESULTS
  Twenty-five patients (30%) were positive for HITS at all postoperative controls, although no neurological symptoms were observed. Mechanical prostheses showed a significantly higher incidence of HITS (85%) than biological prostheses (10%, p <0.001), repaired mitral valves (0%, p <0.001) and homografts (0%, p <0.001). At multivariate analysis the presence of a mechanical prosthesis was the only significant predictor of detection of HITS after valve replacement. During O2 inhalation, a significant decrease in the number of HITS per hour (55 +/- 79 versus 22 +/- 31, p = 0.002) occurred, which returned to initial values when room-air breathing was resumed.
  
  
  CONCLUSIONS
  Prosthetic valve replacement, particularly when mechanical devices are used, is associated with the generation of HITS which persist throughout the follow up period, but remain clinically silent. The decrease of HITS during O2 inhalation strongly supports the hypothesis of the gaseous nature of such signals and confirms the validity of this method in helping to differentiate gaseous microemboli from solid microemboli in prosthetic valve recipients.
authors.affiliation: Cardio-Thoracic Department, University of Pisa Medical School, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Milano
authors.forename: A
authors.initials: A
authors.lastname: D'Alfonso
authors.forename: R
authors.initials: R
authors.lastname: Codecasa
authors.forename: M
authors.initials: M
authors.lastname: De Carlo
authors.forename: C
authors.initials: C
authors.lastname: Nardi
authors.forename: G
authors.initials: G
authors.lastname: Orlandi
authors.forename: L
authors.initials: L
authors.lastname: Landucci
authors.forename: U
authors.initials: U
authors.lastname: Bortolotti
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001021:Aortic Valve / Q000601:surgery; D002339:Carotid Arteries / Q000000981:diagnostic imaging; D004617:Embolism / Q000000981:diagnostic imaging* / Q000209:etiology; D005260:Female; D005500:Follow-Up Studies; D019918:Heart Valve Prosthesis Implantation / Q000009:adverse effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008943:Mitral Valve / Q000601:surgery; D015999:Multivariate Analysis; D011446:Prospective Studies; D017585:Ultrasonography, Doppler, Transcranial