ischaemic preconditioning of the human heart. - Leicester Research ...

have shown worse log-term prognosis in these patients 1671. Most of the studies showing
a negative effect of prodromal angina on outcome are from the period prior to the use of
thrombolytic therapy, however, as reperfuslon is necessary for the preconditioning
phenomenon, these findings should be considered with caution. However, there are recent
studies from the thrombolytic era which fail to show
C. 'Warm-Up'Angina
benefit [231.
This situation describes acute tolerance to angina developing following repeated
anginal episodes. In this model an initial effort induces angina, followed by a subsequent,
equivalent efTort which produces no angina with increased exercise tolerance [ 1571. It has
been suggested that this could be due to an increase in collateral blood flow, although
Okaszaki and colleagues [2331 found no evidence for this. Wayne and colleagues [328]
also found that the second effort reproducibly exceeded the first effort provided that these
two were separated by a rest of at least 2-5 minutes but not more than 30-60 minutes.
These time intervals are consistent with the well established biological nature of
ischaernic preconditioning in animals [3191. Small collateral vessels which cannot be
visualised by coronary angiography might 'open-up' between the two exercise periods
and cannot be totally eliminated as a possible reason for the improvement of symptoms.
D. Cardiac Surgery
The first in vivo study using a model of global ischaernia, thereby eliminating the
possible influence of collateral blood flow, was performed by Yellon's group
[3461. They
examined whether a preconditioning protocol prior to cross clamp fibrillation protects the
myocardium from prolonged ischaemia during coronary artery bypass surgery Twenty
31