Can ischemic preconditioning ensure optimal myocardial protection when delivery of cardioplegia is impaired?

BACKGROUND

Ischemic preconditioning is a potent protective intervention that is effective in all species studied. We have previously shown it to be as effective as cardioplegia; however, we have also shown that their combined use does not afford greater protection than the use of either alone. In the present study we investigated whether coincident ischemic preconditioning could compensate for inadequate cardioplegic protection when the delivery of cardioplegia was impaired, such as occurs in the presence of severe coronary stenosis or occlusion.

METHODS AND RESULTS

Isolated rat hearts were subjected to 30 minutes of global ischemia followed by 40 minutes of reperfusion. Four groups of hearts (n = 12 per group) were studied: group 1, controls (no intervention); group 2, cardioplegia administered to hearts with a proximally occluded coronary artery; group 3, ischemic preconditioning applied before ischemia; and group 4, ischemic preconditioning and cardioplegia given in combination to hearts with a proximally occluded coronary artery. The postischemic recovery of left ventricular (LV) developed pressure (LVDP), expressed as a percentage of preischemic values, was significantly greater (P < .05) in preconditioned hearts (64 +/- 3%) than in control hearts (24 +/- 4%) or hearts treated with suboptimal cardioplegia (43 +/- 5%). Hearts with preconditioning plus cardioplegia recovered to an extent similar to that seen with preconditioning alone (59 +/- 2%). LV end-diastolic pressure was greater in control hearts (58 +/- 4 mm Hg) than in hearts with cardioplegia (41 +/- 4 mm Hg; P < .05 versus group 1) despite the incomplete delivery of the cardioplegia; the best protection was observed in preconditioned hearts and hearts with preconditioning plus cardioplegia (24 +/- 1 and 26 +/- 2 mm Hg, respectively; P < .05 versus groups 1 and 2).

CONCLUSIONS

When the delivery of cardioplegia was impaired, myocardial protection (postischemic LVDP) was better served by ischemic preconditioning. Under the same conditions, the combination of cardioplegia plus preconditioning afforded superior protection compared with cardioplegia alone. These results may be of clinical interest since most patients who undergo surgery for ischemic heart disease suffer from severe coronary artery lesions that can prevent the adequate delivery of cardioplegia.