Prospective evaluation of frequency and nature of transcranial high-intensity Doppler signals in prosthetic valve recipients

Background and nim of the study: In asymptomatic prosthetic valve recipient s, high-intensity transient signals (HITS) observed with transcranial Doppl er (TCD) are a phenomenon of obscure clinical relevance which nature has no t yet been elucidated convincingly. Methods: Eighty-three patients without carotid disease, history of cerebrov ascular accidents, and with negative preoperative TCD undergoing either val ve replacement (mitral, n = 11; aortic, n = 56; mitral + aortic, n = 6; 40 mechanical prostheses, 29 biological prostheses, 10 homografts) or mitral r epair (n = 10) were evaluated prospectively by means of TCD at discharge, t hree 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% O-2 inhalation. Results: Twenty-five patients (30%) were positive for HITS at all postopera tive controls, although no neurological symptoms were observed. Mechanical prostheses showed a significantly higher incidence of HITS (85%) than biolo gical 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 mech anical prosthesis was the only significant predictor of detection of HITS a fter valve replacement. During O-2 inhalation, a significant decrease in th e 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 dev ices are used, is associated with the generation of HITS which persist thro ughout the follow up period, but remain clinically silent. The decrease of HITS during O-2 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 v alve recipients.