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Eur J Cardiothorac Surg 2002;22:490-491
© 2002 Elsevier Science NL
Letter to the Editor |
a Department of Neurology, University of Zürich, Frauenklinik Strasse 26, 8091 Zurich, Switzerland
b Department of Cardio-thoracic Surgery, University of Basel, Basel, Switzerland
Received 7 February 2002; accepted 28 May 2002.
* Corresponding author. Tel.: +41-1-255-5565; fax: +41-1-255-8864
e-mail: dg_de{at}yahoo.com
We read the recent article of Kofidis et al., concerning the clinical relevance of high-intensity transient signals (HITS) in patients with aortic valve replacement with interest [1]. Still, we feel that a number of issues require clarification:
(1) The authors use the term HITS throughout the paper, and even state that "the lack of correlation between the HITS rate and the occurrence of neurologic complications has caused a change of terminology in that microemboli are now called HITS". This statement is simply wrong: only two consensus meetings concerning embolus detection have been held to date; the first named these signals microembolic signals (MES) [2], and the second referred to microembolus detection and never mentioned the term HITS [3]. Thus, the term MES should be used instead of HITS, particularly since the characteristics of HITS (high intensity, short duration) unfortunately also apply to artifact signals.
(2) It does not appear reasonable to examine the clinical relevance of MES in 42 patients, as this group is far too small to allow any meaningful clinical conclusions. Furthermore, the authors failed to cite most studies on this issue, although these included markedly higher numbers of patients (Braekken et al., 1995, 92 patients; Georgiadis et al., 1994, 179 patients; Sliwka and Georgiadis, 1998, 580 patients) [4]. Additionally, this paper displays the same methodological weaknesses as most previous reports: Patients were examined on a single occasion, maybe months or even years after the neurological event (no exact time is stated in the paper). It cannot thus be excluded that MES do play an important role in that they are increased before the occurrence of the ischemic event.
(3) The authors should differentiate between MES detected in patients with prosthetic heart valves, which do not appear to be related to the prevalence of ischemic stroke, and MES detected in other patient categories, including intra- and postoperative monitoring in patients undergoing carotid surgery and patients with asymptomatic carotid stenosis which do have a clinical relevance [5]. Failure to do so leads to the assumption that MES detection is an ancillary investigation, which is certainly not the case.
(4) The authors discuss potential underlying embolic material in patients with mechanical prosthetic valves. Again, most relevant studies are ignored in the discussion. It has namely been shown that (a) MES counts are not related to serum levels of D-dimers, thrombin–antithrombin-complex and antithrombin-III (Georgiadis et al., 1994), (b) aspirin and heparin application do not influence MES counts (Muller et al., 1994; Sturzenegger et al., 1995), and (c) MES counts are significantly altered through inhalation of 100% oxygen (Kaps et al., 1997; Georgiadis et al., 1997) or hyperbaric exposure (Spencer et al., 1996) [4]. All these observations argue for gaseous embolic material. The observation that bubbles are able to pass through the pia arterioles and enter the venous circulation was not only demonstrated in animal studies, as stated by the authors, but also in a clinical study [6].
(5) The authors state that future studies on the clinical relevance of HITS should focus on new physiological and neurofunctional endpoints. We would like to point out that such studies have already been published [7,8].
(6) The statement that "based on the results of this study further progress in mechanical heart engineering will be essential for further improvement of the outcome following heart valve replacement" is certainly not supported by the results presented in this paper.
In conclusion, MES detection represents an intriguing technique providing both insight in pathophysiological concepts and – in certain patient groups – clinically relevant information. The clinical significance of MES in patients with prosthetic cardiac valves can only be determined by a large-scale prospective study.
References
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