PhD Dissertation Abstract

Monitoring of myocardial function byultrasonic transducers

doi: 10.1111/aas.12339

Andreas W. Espinoza

The Intervention Centre and Department of Cardiology,Rikhospitalet, Institute for Clinical Medicine, University of Oslo,N-0424 Oslo, Norway

Background: The aim of this PhD thesis was to provide a con-tinuous method to monitor myocardial function during cardiacsurgery with the superior sensitivity of ultrasonic technique andthe continuity of electrocardiographic (ECG) monitoring.Methods: An ultrasound system with epicardial transducerswas provided, presenting real-time M-mode LV wall images. Intwo experimental studies the transducers were tested. Their sen-sitivity in myocardial function assessment was compared toECG and hemodynamics during ischemia and hypothermia. Inone patient study during off-pump coronary artery bypasssurgery the transducers were used to monitor myocardial func-tion, and an automated analysis algorithm was tested.Results: In the experimental studies the ultrasound systemcould detect myocardial dysfunction during ischemia, and dias-tolic dysfunction during hypothermia. In the patient study theultrasound signal detected ischemia without concomitant ECGST-segment abnormalities or hemodynamic changes. The auto-mated algorithm had equal sensitivity for detection of ischemicmyocardial dysfunction as manual off-line analysis.Conclusions: The provided ultrasound system could give con-tinuous real-time monitoring of myocardial function, and detectmyocardial dysfunction with superior sensitivity than ECG orhemodynamic monitoring. This could be used for improvedmonitoring of myocardial function during cardiac surgery.

In this work, we have developed an ultrasonic system for attach-ment on the heart for continuous assessment of myocardial func-

tion during cardiac surgery. As the patients undergoing cardiacsurgery are getting older, and the surgical treatment is gettingincrementally more complex, the risk for complications increase.Perioperative ischemia is an important predictor for adversepatient outcome, and it is crucial to detect this early.Echocardiographic assessment for early detection of myocardialischaemia is superior to electrocardiography (ECG) orhaemodynamic monitoring, but it is performed intermittently inthe perioperative setting and continuous ECG monitoring haspoor sensitivity in detecting ischemia, which could trigger anechocardiographic exam.

To provide continuous myocardial motion monitoring a newsystem for ultrasonic assessment of myocardial function wasdeveloped. The miniaturised transducers can be fixated directlyon the epicardial surface of the heart. In an experimental study,the signals from the epicardial transducers could detect myocar-dial ischaemia with good sensitivity compared with the refer-ence two-dimensional (2D) echocardiography1 and couldseparate ischaemia from other variations in myocardial function.During graded coronary occlusion, the transmural velocitysignals were gradually reduced and allowed discrimination ofsubtle changes in coronary flow. In a model on moderate hypo-thermia as used during cardiac surgery or in cardiac arrest sur-vivors, the signals from the ultrasound system coulddemonstrate changes in both systolic and diastolic function.2 Therelative shortening of diastole with shift from early to late dias-tolic filling could have impact on the interpretation ofechocardiographic findings in patients during hypothermia.

In a study on patients undergoing off-pump coronary bypasssurgery, the epicardial sensors could detect ischaemia similar tothe reference method 2D echocardiography.3 Importantly, thesignal could also be analysed automatically and detect ischaemiaequally good as manual offline analysis. The proposed ultra-sound system enables improved myocardial monitoring duringcardiac surgery. This continuous technique can, together withthe automated interpretation, facilitate early bedside diagnosticsin a clinical setting.

List of published papers1. Espinoza A, Halvorsen PS, Hoff L, Skulstad H, Fosse E, Ihlen

H, Edvardsen T. Detecting myocardial ischaemia using min-iature ultrasonic transducers – a feasibility study in a porcinemodel. Eur J Cardiothorac Surg 2010; 37: 119–26.

2. Espinoza A, Kerans V, Opdahl A, Skulstad H, Halvorsen PS,Bugge JF, Fosse E, Edvardsen T. Effects of therapeutic hypo-thermia on left ventricular function assessed by ultrasoundimaging. J Am Soc Echocardiogr 2013; 26: 1353–63.

3. Espinoza A, Halvorsen PS, Skulstad H, Lundblad R, Bugge JF,Hoff L, Fosse E, Edvardsen T. Automated detection of myo-cardial ischaemia by epicardial miniature ultrasound trans-ducers – a novel tool for patient monitoring during cardiacsurgery. Eur J Cardiothorac Surg 2011; 39: 53–9.

Principal supervisors: Professor Thor Edvardsen, Department ofCardiology, Rikshospitalet, University of Oslo, Norway; ProfessorErik Fosse, The Intervention Centre, Rikshospitalet, University ofOslo, Norway.Opponents: Professor Erik Sloth, Institute for Clinical Medicine,Department of Anaesthesiology, SKS, University of Aarhusuniversitet, Denmark; Research fellow Charlotte Björk Ingul, Depart-ment of Circulation and Medical Imaging, Norwegian University ofScience and Technology, Trondheim, Norway; Professor Harald L.Lindberg, Department of Cardiothoracic Surgery, Institute for clinicalmedicine, University of Oslo, Norway.Thesis defended: 24 October 2013.

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Acta Anaesthesiol Scand 2014; 58: 908Printed in Singapore. All rights reserved

© 2014 The Acta Anaesthesiologica Scandinavica Foundation.Published by John Wiley & Sons Ltd

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