Mechanically induced changes in action potential duration and left ventricular segment length in acute regional ischaemia in the in situ porcine heart.
OBJECTIVE
The electrophysiological events accompanying early ischaemia are important. The aim of this study was to investigate mechano-electric feedback in acute regional myocardial ischaemia in the intact heart in situ by measuring the change in action potential duration in response to increased ventricular loading imposed by transient aortic occlusion.


METHODS
11 landrace pigs were anaesthetised and their hearts exposed. A pneumatically operated blood pressure clamp was placed around the aorta. Monophasic action potentials and an index of segment motion were recorded from the epicardium in and around the ischaemic area produced by a snare placed around a coronary artery. Ventricular and systemic arterial pressures were measured. An initial aortic clamp was performed during which control recordings were taken. The coronary artery was then tied and the aorta clamped for 5-10 s every 5 min for the duration of the 30 min tie. Recordings were taken from the ischaemic area and non-ischaemic areas.


RESULTS
Aortic clamp before ischaemia increased intraventricular diastolic and systolic pressure and reduced action potential duration in all the areas studied (p < 0.001). During acute regional myocardial ischaemia aortic clamping resulted in significantly more shortening of the action potential in the ischaemic area after 10 min of ischaemia than in the control area (5 ms v 10 ms, p = 0.008). Over the following 20 min the degree of shortening decreased. The greater shortening at 10 min could not be attributed to changes in the end diastolic segment length or peak ventricular pressure and could thus represent a change in the expression of mechano-electric feedback by ischaemic myocardium rather than a change in loading conditions.


CONCLUSIONS
During the first 30 min following a coronary artery occlusion mechano-electric feedback in the ischaemic myocardium varies with time.
Horner
S M
SM
Department of Physiology, Charing Cross and Westminster Medical School, London, United Kingdom.
Lab
M J
MJ
Murphy
C F
CF
Dick
D J
DJ
Zhou
B
B
Harrison
F G
FG
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000503:physiopathology; D005246:Feedback; D005260:Female; D006321:Heart / Q000503:physiopathology*; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D017202:Myocardial Ischemia / Q000503:physiopathology*; D013552:Swine