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Herz- und Diabetes Zentrum NRW, Thorax- und Kardiovaskularchirurgie, Georgstr. 11, Bad Oeynhausen 32545, Germany
(Email: dfritzsche{at}hdz-nrw.de).
We acknowledge the comments by Drs Hettich and colleagues [1] regarding our article [2]. The work depicts the use of the ThromboCheck device (Cardiosignal GmbH, Hamburg, Germany) in a clinical setting (ie, identification of patients with dysfunction of their mechanical heart valve prostheses). We have information we would like to share with the readers of The Annals of Thoracic Surgery.
Hettich and colleagues [1] challenge our claim of a high sensitivity of the ThromboCheck device in identifying valve-related dysfunction. Specifically, they ask for extended imaging studies in all patients with normal digital frequency spectra as computed by the ThromboCheck device. Their rationale is to rule out false negative results in patients with asymptomatic valve dysfunction.
It is true that only patients with altered frequency spectra or clinically suspected valve dysfunction, or both, were subject to extended imaging studies, such as transesophageal (TEE) and transthoracic echocardiography (TTE), as well as cine-fluoroscopy (CF). Unfortunately, Hettich and associates’ [1] notion does not translate into a feasible clinical study, considering that TTE, TEE, and CF do not necessarily reveal concordant results due to specific limitations in each [1]. Thus, all three imaging studies would need to be performed in conjunction so as to not miss a single case that remained undetected in any of the studies. Furthermore, the three imaging studies would have to be done at the same time of the ThromboCheck analysis in each patient, because valve dysfunction could theoretically be only transiently present. This in turn would neutralize one of the major strengths of the ThromboCheck device (ie, its frequent usage by the patient). Although our patients used the device for as much as twice a week, the three imaging studies could obviously be done only at a far lower rate.
For two reasons, we are confident that the sensitivity is as high as we report in our article. First, the results of the current clinical study are in very close agreement with our previous experimental work [2]. In the latter we show that any experimentally induced valve dysfunction did alter the frequency spectra, even if the dysfunction was only mild. Second, there was not a single case of clinically overt valve dysfunction that went undetected by the ThromboCheck device during follow-up. None of the patients found with normal sound spectra at the time the manuscript was submitted became clinically symptomatic in the subsequent 2 years. In our ongoing clinical study, we have currently enrolled 724 patients up until July 2007. All of these patients were found to be asymptomatic in our report in The Annals of Thoracic Surgery and continue to be in excellent clinical status with no signs of valve dysfunction and with normal sound frequency spectra. Thus, the sensitivity of the ThromboCheck device for clinically relevant valve dysfunction is indeed 100%.
In their second critique, Hettich and associates [1] asked why some patients did not show any sign of valve dysfunction by TTE, although it was demonstrated by CF or upon valve replacement, or both. Despite considerable improvements in the quality of imaging studies, the correct diagnosis of valve dysfunction remains challenging in several cases. In particular, the "gold standard" of diagnostic imaging studies remains controversially discussed. In a recent report by Montorsi and colleagues [3], CF was still found to be the most useful technique because leaflet dynamics are correctly evaluated in only a minority of patients by echocardiography. The report also confirms our clinical experience of several instances of "unremarkable" echocardiography studies of malfunctioning valve prostheses referred to the operating room.
Additional studies will be performed by our group to further elucidate the usefulness of sound spectra analyses in the diagnosis of valve dysfunction. Potential advantages of the ThromboCheck device are its versatile usage and very favorable predictive capabilities as to valve dysfunction. "Online" monitoring of heart valve prostheses at a low cost may predispose the device as a valuable screening tool in an outpatient setting. The device may even be used to evaluate treatment success of thrombolysis, because sound spectra commonly return to baseline with effective restoration of valve function. Therefore, we expect this methodology to be introduced into the standard care of heart valve recipients [4, 5].
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