Electromechanical changes during load manipulation of the mammalian heart
Electromechanical changes during load manipulation of the mammalian heart
There is increasing evidence that mechano-electric feedback, defined as a change in mechanical state or load that precedes and alters transmembrane potential, is a ubiquitous phenomenon operating in a wide variety of preparations and species including man. This thesis examines the effect of changes in cardiac load on the in situ heart of the anaesthetised pig. Monophasic action potentials, electrocardiograms and segment length changes were recorded from up to three regions of the left ventricular epicardium simultaneously using suction operated devices. Cardiac load was reduced by infusion of sodium nitroprusside and increased by aortic clamping. A reduction in load resulted in a rise in action potential duration which was linearly related to the fall in systolic left ventricular pressure and minimum systolic length. However, these changes were inhomogeneous, there being a greater change at the base compared to the apex and were reflected by changes in the epicardial ECG viz, a prolongation of the QT interval and an increase in amplitude of the T-wave. There was also inhomogeneity of regional mechanical response to load change, but there was no clear relationship between mechanical and electrophysiological indices. Myocardia excitability assessed by measurement of the absolute refractory period showed similar changes to the action potential in response to load manipulation, but in addition there was a regional variation in change leading to a dispersion of refractoriness across the left ventricle. Since inhomogeneity of ventricular recovery is known to favour the development of re-entrant arrhythmias, and in clinical practice, patients with conditions associated with an increased afterload have an increased incidence of arrhythmias and sudden death, the findings of this thesis may have therapeutic implications for such arrhythmias. (DX88265)
University of Southampton
1988
Dean, John William
(1988)
Electromechanical changes during load manipulation of the mammalian heart.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
There is increasing evidence that mechano-electric feedback, defined as a change in mechanical state or load that precedes and alters transmembrane potential, is a ubiquitous phenomenon operating in a wide variety of preparations and species including man. This thesis examines the effect of changes in cardiac load on the in situ heart of the anaesthetised pig. Monophasic action potentials, electrocardiograms and segment length changes were recorded from up to three regions of the left ventricular epicardium simultaneously using suction operated devices. Cardiac load was reduced by infusion of sodium nitroprusside and increased by aortic clamping. A reduction in load resulted in a rise in action potential duration which was linearly related to the fall in systolic left ventricular pressure and minimum systolic length. However, these changes were inhomogeneous, there being a greater change at the base compared to the apex and were reflected by changes in the epicardial ECG viz, a prolongation of the QT interval and an increase in amplitude of the T-wave. There was also inhomogeneity of regional mechanical response to load change, but there was no clear relationship between mechanical and electrophysiological indices. Myocardia excitability assessed by measurement of the absolute refractory period showed similar changes to the action potential in response to load manipulation, but in addition there was a regional variation in change leading to a dispersion of refractoriness across the left ventricle. Since inhomogeneity of ventricular recovery is known to favour the development of re-entrant arrhythmias, and in clinical practice, patients with conditions associated with an increased afterload have an increased incidence of arrhythmias and sudden death, the findings of this thesis may have therapeutic implications for such arrhythmias. (DX88265)
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Published date: 1988
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Local EPrints ID: 461360
URI: http://eprints.soton.ac.uk/id/eprint/461360
PURE UUID: 268f715a-522c-44bf-b7a0-baacd7717334
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Date deposited: 04 Jul 2022 18:43
Last modified: 04 Jul 2022 18:43
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Author:
John William Dean
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