Cardiovascular medicine
Repolarisation and refractoriness during early ischaemia in
humans
P M I Suttona, P Taggarta, T Opthofb, R Coronelc, R Trimletta, W Pugsleya, P Kallisa
a The Hatter
Institute, Department of Cardiology, Department of Cardiothoracic
Surgery, University College London Hospitals, Grafton Way, London
WC1E 6DB, UK, b Department of Medical Physiology, University
Medical Centre Utrecht, Netherlands, c Experimental and Molecular Cardiology Group,
Academic Medical Centre, Amsterdam, Netherlands
Correspondence to: Dr Sutton peter.sutton{at}ucl.ac.uk
Accepted 24 May 2000
OBJECTIVES
To determine whether
effective refractory period (ERP) shortens or lengthens in the first
minutes of ischaemia in humans, and the relation between ERP changes
and action potential duration (APD).
METHODSERP and monophasic action
potential duration (MAPD) were measured from a single left ventricular
epicardial site in 26 patients undergoing coronary artery surgery.
Cardiopulmonary bypass was instituted and normothermia maintained.
Refractory period was determined by the extrastimulus technique at a
basic cycle length of 500 ms, at four times (group 1, 15 patients) or
two times (group 2, 11 patients) the preischaemic diastolic threshold.
A three minute period of ischaemia was instituted by aortic cross
clamping between the input from the pump oxygenator and the heart.
RESULTSAfter three minutes of
ischaemia, mean (SEM) ERP lengthened from 232 (5) ms (control) to 246 (7) ms (p < 0.005) in group 1, and from 256 (10) ms (control) to
348 (25) ms (p < 0.005) in group 2. In the same time MAPD shortened
from 256 (5) ms (control) to 189 (9) ms (p < 0.001) with no
difference between groups. Thus postrepolarisation refractoriness
developed during ischaemia. Before ischaemia, ERP showed a good
correlation with APD
(R2 = 0.64) but by one minute
of ischaemia the correlation was poor (R2 = 0.29).
CONCLUSIONSThese results show that
during the first three minutes of global ischaemia in patients with
coronary artery disease: (1) ERP lengthened in response to both a low
and a high stimulus strength; and (2) there was a good correlation
between ERP and APD before ischaemia, which was lost by one minute as
APD decreased and ERP increased. These findings may have important
implications in arrhythmogenesis.
Keywords: refractoriness; ischaemia; repolarisation
© 2000 by Heart
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