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Exercise-induced ischemia initiates the second window of protection in humans independent of collateral recruitment

^* Department of Cardiology, King’s College London, The Rayne Institute, St. Thomas’ Hospital, London, United Kingdom

View larger version (18K): [in a new window]   Figure 1 Study protocol. Patients were divided into two groups: isolated early preconditioning (IEP) and second window of protection (SWOP). In the IEP group, serial exercise tests were performed at least 14 days before elective percutaneous coronary intervention for single-vessel left anterior descending coronary artery disease. In the SWOP group, exercise was 24 h and 4 h before PCI. Solid rectangle = treadmill exercise tolerance test. Cross-hatched rectangle = 180-s intracoronary balloon inflation.

View larger version (70K): [in a new window]   Figure 2 Pattern of ST-segment deviation in the second window of protection (SWOP). Panels A and B are representative electrocardiograms (ECGs) taken from a patient in the SWOP group with a collateral flow index of 0.2. Panel A shows the appearance of precordial ECG leads V4 and V5 at 5 min of exercise on efforts 1 to 4 (see Fig. 1). In this particular example, the attenuation of ST depression seen on exercise treadmill test (ETT) 2 versus ETT 1 is less marked, though still apparent, on ETT 3. A similar trend was seen in the group data (Table 2). However, on ETT 4, performed 24 h after ETT 1, the attenuation of ST depression is at least as marked as on ETT 2. Panel B is from the surface 12-lead ECG recorded after 180 s of the first and second intracoronary balloon occlusions. In contrast to patients in the IEP group, there is no attenuation of ST elevation on the second balloon occlusion. Furthermore, in the grouped data (Table 2) the magnitude of ST elevation on first inflation is less than in the IEP group.

View larger version (24K): [in a new window]   Figure 3 ST-segment elevation during the first and second intracoronary balloon occlusions of the left anterior descending coronary artery in early and late preconditioning groups. With increasing duration of ischemia, the attenuation of ST elevation seen on the second compared with the first occlusion is apparent only in the early preconditioning group. In addition, the absolute magnitude of ST elevation on occlusion 1 is less in the SWOP than in the IEP group (see Table 2). Two-way repeated-measures analysis of variance was performed with post-hypothesis testing to compare the degree of ST elevation between inflations 1 and 2 at 30-s intervals, having examined the effects of time, treatment, and group. *p < 0.05, p < 0.01 for occlusion 1 versus occlusion 2.

View larger version (16K): [in a new window]   Figure 4 The relationship between maximal ST elevation and collateral flow index (CFI) during the first intracoronary balloon occlusion. ST elevation is negatively related to collateral flow in the isolated early preconditioning (IEP) group (p < 0.01). However, this dependence is less marked in the second window of protection (SWOP) group. Moreover, when collateral support is poor (CFI < 0.25), ST elevation is less marked in the SWOP group (Table 2).