Digital frequency analysis of valve sound phenomena in patients after prosthetic valve surgery: its capability as a true home monitoring of valve function.

ABSTRACT

BACKGROUND AND AIM OF THE STUDY Depending on the individual risk profile of a patient, disturbances of the functional integrity of mechanical heart valve prostheses occur in up to 2.5% of patients each year. The early phase of prosthetic dysfunction (due to thrombus formation, tissue ingrowth or endocarditis) usually remains undiagnosed, as patients do not present with symptoms in this situation, and imaging techniques (echocardiography, fluoroscopy) demonstrate normal occluder motion. The delay between the onset of prosthetic valve dysfunction and its clinical manifestation may result in complications (e.g. thromboembolism) or extended therapeutic options (e.g. reoperation rather than more intensive anticoagulation). METHODS: A total of 291 patients with mechanical heart valves was allocated to four different sub-groups, and each measured their valve sounds regularly with the 'ThromboCheck' device. Depending on the subgroup, the signals were compared with different reference signals. Patients in whom a suspicious signal was detected were immediately contacted and examined meticulously. RESULTS: Fourteen patients were found to have suspicious signals. In 13 patients, valve dysfunction was confirmed by fluoroscopy, but in four cases neither transthoracic nor transesophageal echocardiography detected abnormal occluder motion or 'musses' adjacent to the prosthesis. Normal valve sounds returned in four patients who underwent thrombolytic therapy. All patients regularly recorded and passed on their signals. Surveys revealed high acceptance and easy handling of the Thrombocheck device. CONCLUSION: Home monitoring of sound pressure measurements of prosthetic valves by digital frequency analysis via a Fast Fourier transformation may detect even very mild alterations of prosthetic valve function. The next evolution of control systems, allowing for registration of flow, frequency spectrum and electrocardiography, opens potential applications for Internet-based, remote monitoring of cardiac patients.