Microemboli in Cerebral Circulation and Alteration of Cognitive Abilities in Patients With Mechanical Prosthetic Heart Valves
To the Editor:
We have read with great interest the article by Deklunder and coworkers1 in which the authors so elegantly demonstrate the high incidence of microemboli through the brain circulation of patients with mechanical prosthetic heart valves. They also speculate on the relationship of such episodes to cognitive impairment.
However, after reading the method carried out to detect high-intensity transient signal (HITS), we entertain several doubts.
In the first place, we would like to know why the authors have used the duplex scan, a procedure that carries the disadvantage of a high incidence of inadequate acoustic windows.2 The equipment used, an Acuson 128XP, has a large and heavy 2-Mhz transducer that is difficult to hold upright at a given point during long periods of time, which would explain why the authors monitored their population during very brief time spans.3 The loss of the window and the appearance of artifacts may be high when a transducer of this type is used. Because of the latter, monitoring with transducers held by halos would seem more reasonable to us.
Finally, we would like to comment that for studies of this kind, multigated equipment appears to provide better information.4 These devices assess the presence of HITS at 2 different depths, which allows for measurement of HITS velocity and further adds to the differential diagnosis with artifacts.
- Copyright © 1999 by American Heart Association
Deklunder G, Roussel M, Lecroat JL, Prat A, Gautier C. Microemboli in cerebral circulation and alteration of cognitive abilities in patients with mechanical prosthetic heart valves. Stroke.. 1998;29:1821–1826.
Geiser T, Sturzenegger M, Genewein V, Haeberli A, Beer J. Mechanism of cerebrovascular events as assessed by procoagulant activity, cerebral microemboli, and platelet microparticles in patients with prosthetic heart valves. Stroke.. 1998;29:1770–1777.
Georgiadis D, Goeke J, König M, Hilll M, Nabavi DG, Stögbaver F, Zunker P, Ringelstein EB. A novel technique for identification of Doppler microembolic signals based on the coincidence method: in vitro and in vivo evaluation. Stroke.. 1996;27:683–686.
In their letter, Drs Lagos and Cabezas address the question of the pertinence of the use of an Acuson 128XP for HITS detection in our study on the cognitive effects of microemboli in patients with mechanical prosthetic heart valves. Use of this class of equipment imposes handling constraints, as pointed out by Lagos and Cabezas. The reason this machine has been used in our study lies in the fact that it was the only TCD equipment available with an accurate spectral analyzer in our unit at the outset of the study. Nevertheless, the method we used to assess the HITS rate was the one commonly accepted.R1 Under these conditions of HITS detection, we could have underestimated the number of HITS in the middle cerebral artery. Obviously, a more recent model of equipment could lead to greater accuracy in HITS counting, especially through increase of the monitoring duration, which is all the more important because HITS production appears to be an irregular phenomenon over time.
However, the main objective of the study was to demonstrate the reality of cognitive impairments in patients with MHV; the accuracy of HITS counting was thus less crucial than had we sought to correlate HITS rate and impairment degree, for example.
Spencer MP. Detection of cerebral arterial emboli. In: Newell DW, Aaslid R, eds. Transcranial Doppler. New York, NY: Raven Press; 1992:215–230.