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Acoustic and afterload evaluation of left ventricular assist devices
Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Cardiology in Linköping. Medicin- och geriatrikkliniken, Höglandssjukhuset, Eksjö.ORCID iD: 0000-0001-5485-1052
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background: Heart Failure is a serious condition with consequences not only for the individual patient but also for the society with a 5-year mortality rate of 45-60%, and a substantial economic burden. The estimated prevalence in Sweden is 2.2% and the age adjusted prevalence increases with higher age. The fundamental treatment for heart failure is pharmaceutical in combination with life-style changes, and physiotherapy. For patients with advanced heart failure, the use of long-term circulatory support can be an option as a bridge to transplantation, or as destination therapy. However, this treatment entails a risk of multiple adverse events. The incidence of pump thrombosis increased as a clinical problem in 2012 and the need for diagnostic methods were desired. The aim of this thesis was to develop and to evaluate the use of a mock loop circuit to study the acoustics of left ventricular assist devices, to evaluate different recording devices and to study the effect of afterload on pump function.

Methods: Two different mock loops, with the possibility to insert artificial thrombus and to adjust preload and afterload were created to facilitate recording of the left ventricular assist devices. An iPhone/iPodTM was used as recording device since remote monitoring is desirable. The sounds from HeartMate IITM during different conditions were studied. The iPhone/iPod was evaluated in comparison to dedicated recording equipment, and the mock loop recordings to clinical situation. The sound from HeartMate 3TM was studied, compared between in vivo and in vitro recordings, and the use of an electronic stethoscope was evaluated. The impact of afterload on left ventricular assist devices was studied in a mock loop circuit with different changes in preload and afterload.

Results: Mock loop circuit is a promising method to safely change the surrounding conditions as the pump is working. The sound from both HeartMate IITM and HeartMate 3TM can be recorded and analyzed in frequency and time domain. When inserting artificial thrombus in a HeartMate IITM the frequency spectrum is altered. The use of dedicated recording devices is superior to both electronic stethoscope and iPhone/iPodTM, but these handheld devices can be used in clinical settings. The recordings from mock loop circuit and patients appear similar for both HeartMate IITM and HeartMate 3TM. The flow of the devices is affected by the afterload. The HeartMate 3TM is more resistant to increased clot analogs within the pump. For both pumps, best efficacy is seen for clean circuits. The flow rate from the monitor might be misleading since the measured flow rate and the flow rate from monitor can differ due to surrounding conditions. The estimated flow might be adjusted by fitting a parabolic curve.

Conclusion: The use of mock loop circuit to study both flow and sound under different conditions is valid. It is possible to record and study the sound from both HeartMate IITM and HeartMate 3TM. The sound holds information of pump function and appears similar in vivo and in vitro. All recording devices can be used, but dedicated equipment is superior to the more handheld devices, although these might have a function as a screening device. The flow measurement on the monitor might not be valid and optimization of fluid status and afterload can further increase pump efficiency.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2019. , p. 86
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1707
Keywords [en]
Afterload, Electronic stethoscope, Flow, HeartMate II, HeartMate 3, iOS-devices, Sound Analysis
National Category
Medical Equipment Engineering
Identifiers
URN: urn:nbn:se:liu:diva-161902DOI: 10.3384/diss.diva-161902ISBN: 9789179299880 (print)OAI: oai:DiVA.org:liu-161902DiVA, id: diva2:1369502
Public defence
2019-12-11, Granitsalen, Hus 448, Campus US, Linköping, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2019-11-12 Created: 2019-11-12 Last updated: 2019-11-18Bibliographically approved
List of papers
1. Acoustic Analysis of a Mechanical Circulatory Support
Open this publication in new window or tab >>Acoustic Analysis of a Mechanical Circulatory Support
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2014 (English)In: Artificial Organs, ISSN 0160-564X, E-ISSN 1525-1594, Vol. 38, no 7, p. 593-598Article in journal (Refereed) Published
Abstract [en]

Mechanical circulatory support technology is continually improving. However, adverse complications do occur with devastating consequences, for example, pump thrombosis that may develop in several parts of the pump system. The aim of this study was to design an experimental clot/thrombosis model to register and analyze acoustic signals from the left ventricular assist device (LVAD) HeartMate II (HMII) (Thoratec Corporation, Inc., Pleasanton, CA, USA) and detect changes in sound signals correlating to clots in the inflow, outflow, and pump housing. Using modern telecom techniques, it was possible to register and analyze the HMII pump-specific acoustic fingerprint in an experimental model of LVAD support using a mock loop. Increase in pump speed significantly (P less than 0.005) changed the acoustic fingerprint at certain frequency (0-23 000 Hz) intervals (regions: R1-3 and peaks: P1,3-4). When the ball valves connected to the tubing were narrowed sequentially by similar to 50% of the inner diameter (to mimic clot in the out-and inflow tubing), the frequency spectrum changed significantly (P less than 0.005) in P1 and P2 and R1 when the outflow tubing was narrowed. This change was not seen to the same extent when the lumen of the ball valve connected to the inflow tube was narrowed by similar to 50%. More significant (P less than 0.005) acoustic changes were detected in P1 and P2 and R1 and R3, with the largest dB figs. in the lower frequency ranges in R1 and P2, when artificial clots and blood clots passed through the pump system. At higher frequencies, a significant change in dB figs. in R3 and P4 was detected when clots passed through the pump system. Acoustic monitoring of pump sounds may become a valuable tool in LVAD surveillance.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2014
Keywords
Mechanical circulatory support; Frequency analysis; Thrombosis
National Category
Cardiac and Cardiovascular Systems
Identifiers
urn:nbn:se:liu:diva-112071 (URN)10.1111/aor.12244 (DOI)000343223400001 ()24372095 (PubMedID)
Available from: 2014-11-14 Created: 2014-11-13 Last updated: 2019-11-12Bibliographically approved
2. Sound analysis of a left ventricular assist device: A technical evaluation of iOS devices
Open this publication in new window or tab >>Sound analysis of a left ventricular assist device: A technical evaluation of iOS devices
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2018 (English)In: International Journal of Artificial Organs, ISSN 0391-3988, E-ISSN 1724-6040, Vol. 41, no 5, p. 254-260Article in journal (Refereed) Published
Abstract [en]

Introduction: The use of left ventricular assist device (LVAD) has grown rapidly. Adverse events do continue to occur. In recent years, analysis of LVAD sound recordings emerged as a means to monitor pump function and detect pump thrombosis. The aim of this study was to characterize the sounds from HeartMate II and to evaluate the use of handheld iOS devices for sound recordings. Method: Signal analysis of LVAD sound recordings, with dedicated recording equipment and iOS devices, was performed. Two LVADs running in mock loop circuits were compared to an implanted LVAD. Spectral analysis and parametric signal models were explored to quantify the sound and potentially detect changes in it. Results: The sound recordings of two LVADs in individual mock loop circuits and a third one implanted in a patient appeared to be similar. Qualitatively, sound characteristics were preserved following changes in pump speed. Recordings using dedicated equipment showed that HeartMate II sound comprises low-frequency components corresponding to pump impeller rotation, as well as high-frequency components due to a pulse width modulation of the electric power to the pump. These different signal components interact and result in a complicated frequency spectrum. The iPhone and iPod recordings could not reproduce the sounds as well as the dedicated equipment. In particular, lower frequencies were affected by outside disturbances. Discussion: This article outlines a systematic approach to LVAD sound analysis using signal processing methods to quantify and potentially detect changes, and describes some of the challenges, for example, with the use of inexpensive recording devices.

Place, publisher, year, edition, pages
SAGE PUBLICATIONS LTD, 2018
Keywords
HeartMate II; left ventricular assist device; sound; spectral analysis
National Category
Biomedical Laboratory Science/Technology
Identifiers
urn:nbn:se:liu:diva-148111 (URN)10.1177/0391398818762352 (DOI)000432135400004 ()29519192 (PubMedID)
Available from: 2018-05-30 Created: 2018-05-30 Last updated: 2019-11-12
3. Sound analysis of the magnetically levitated left ventricular assist device HeartMate 3
Open this publication in new window or tab >>Sound analysis of the magnetically levitated left ventricular assist device HeartMate 3
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2019 (English)In: International Journal of Artificial Organs, ISSN 0391-3988, E-ISSN 1724-6040, Vol. 42, no 12, p. 717-724Article in journal (Refereed) Published
Abstract [en]

INTRODUCTION: The HeartMate 3 has shown lower rates of adverse events compared to previous devices due to the design and absence of mechanical bearings. For previous devices, sound analysis emerged as a way to assess pump function. The aims of this study were to determine if sound analysis can be applied to the HeartMate 3 in vivo and in vitro and to evaluate an electronic stethoscope.

METHOD: Sound recordings were performed with microphones and clinical accessible electronic stethoscope. The recordings were studied in both the time and the frequency domains. Recordings from four patients were performed to determine if in vivo and in vitro recordings are comparable.

RESULTS: The results show that it is possible to detect sound from HeartMate 3 and the sound spectrum is clear. Pump frequency and frequency of the pulsatile mode are easily determined. Frequency spectra from in vitro and in vivo recordings have the same pattern, and the major proportion (96.7%) of signal power is located at the pump speed frequency ±40 Hz. The recordings from the patients show low inter-individual differences except from location of peaks originating from pump speed and harmonics. Electronic stethoscopes could be used for sound recordings, but the dedicated equipment showed a clearer sound spectrum.

DISCUSSION: The results show that acoustic analysis can also be performed with the HeartMate 3 and that in vivo and in vitro sound spectrum is similar. The frequency spectra are different from previous devices, and methods for assessing pump function or thrombosis need further evaluation.

Place, publisher, year, edition, pages
Sagamore Publishing, 2019
Keywords
HeartMate 3, Spectral analysis, left ventricular assist device, sound
National Category
Biomedical Laboratory Science/Technology
Identifiers
urn:nbn:se:liu:diva-161898 (URN)10.1177/0391398819857443 (DOI)000493895600006 ()31250690 (PubMedID)2-s2.0-85068309681 (Scopus ID)
Available from: 2019-11-12 Created: 2019-11-12 Last updated: 2019-11-25Bibliographically approved

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