Ischemic Preconditioning In Patients Research Articles

Inhibitors of ischemic preconditioning do not attenuate Na+/H+ exchange inhibitor mediated cardioprotection.

Pharmacologic inhibition of the K(ATP) channel with sulfonylureas or the adenosine receptor with methylxanthines has been shown to attenuate ischemic preconditioning (IPC). Both classes of compounds are widely used clinically, and several reports have demonstrated adverse outcomes in patients taking sulfonylureas. Recently inhibition of the sodium/hydrogen exchanger isozyme-1 (NHE-1) has been shown to be equal to IPC at providing myocardial protection in dogs and may be an alternative to IPC in patients taking sulfonylureas or methylxanthines. However, no experiments have examined the pharmacologic overlap between IPC and NHE-1 inhibitor-mediated cardioprotection in dogs. With an in vivo canine infarct model in which the left anterior descending coronary artery was occluded for 60 min and reperfused for 3 h, neither the K(ATP) channel antagonist glibenclamide nor the adenosine-receptor antagonist PD 115199 attenuated NHE-1 inhibitor-mediated reduction in infarct size expressed as a percentage of the area at risk produced by EMD 85131 (Control, 24.2 +/- 3.6%; EMD 85131, 6.4 +/- 2.3%; PD 115199 + EMD 85131, 6.6 +/- 2.4%; glibenclamide + EMD 85131, 3.5 +/- 1.2%). NHE-1 inhibition and IPC do not overlap pharmacologically, and NHE-1 inhibition may be an alternative for cardioprotection in patients taking sulfonylureas or methylxanthines.

Calcium Preconditioning, but Not Ischemic Preconditioning, Bypasses the Adenosine Triphosphate-Dependent Potassium (KATP) Channel

Background. Recent evidence has implicated the KATP channel as an important mediator of ischemic preconditioning (IPC). Indeed, patients taking oral sulfonylurea hypoglycemic agents (i.e., KATP channel inhibitors) for treatment of diabetes mellitus are resistant to the otherwise profoundly protective effects of IPC. Unfortunately, many cardiopulmonary bypass patients, who may benefit from IPC, are chronically exposed to these agents. Calcium preconditioning (CPC) is a potent form of similar myocardial protection which may or may not utilize the KATP channel in its mechanism of protection. The purpose of this study was to determine whether CPC may bypass the KATP channel in its mechanism of action. If so, CPC may offer an alternative to IPC in patients chronically exposed to these agents.Methods. Isolated rat hearts (n = 6–8/group) were perfused (Langendorff) and received KATP channel inhibition (glibenclamide) or saline vehicle 10 min prior to either a CPC or IPC preconditioning stimulus or neither (ischemia and reperfusion, I/R). Hearts were subjected to global warm I/R (20 min/40 min). Postischemic myocardial functional recovery was determined by measuring developed pressure (DP), coronary flow (CF), and compliance (end diastolic pressure, EDP) with a MacLab pressure digitizer.Results. Both CPC and IPC stimuli protected myocardium against postischemic dysfunction (P < 0.05 vs I/R; ANOVA with Bonferroni/Dunn): DP increased from 52 ± 4 (I/R) to 79 ± 2 and 83 ± 4 mmHg; CF increased from 11 ± 0.7 to 17 ± 2 and 16 ± 1 ml/min; and EDP decreased (compliance improved) from 50 ± 7 to 27 ± 5 and 31 ± 7 mmHg. However, KATP channel inhibition abolished protection in hearts preconditioned with IPC (P < 0.05 vs IPC alone), but not in those preconditioned with CPC (P > 0.05 vs CPC alone).Conclusions. (1) Both IPC and CPC provide similar myocardial protection; (2) IPC and CPC operate via different mechanisms; i.e., IPC utilizes the KATP channel whereas CPC does not; and (3) CPC may offer a means of bypassing the deleterious effects of KATP channel inhibition in diabetic patients chronically exposed to oral sulfonylurea hypoglycemic agents.

Transient Ischemia Does Not Limit Subsequent Ischemic Regional Dysfunction in Humans: A Transesophageal Echocardiographic Study During Minimally Invasive Coronary Artery Bypass Surgery

Objectives. This study sought to assess the effects of sequential coronary artery occlusion during minimally invasive coronary artery bypass graft surgery (CABG) on hemodynamic variables and left ventricular systolic function by means of transesophageal echocardiography (TEE).Background. Clinical and experimental studies suggest a protective effect of ischemic preconditioning in patients with acute coronary syndromes. However, the effect of repetitive myocardial ischemia on myocardial mechanical function in humans is not completely understood.Methods. Seventeen patients with left anterior descending coronary artery (LAD) stenosis ≥70% and normal rest left ventricular systolic function referred for minimally invasive CABG underwent intraoperative TEE for assessment of regional left ventricular wall motion and measurement of hemodynamic variables at baseline (baseline 1), during a 5-min coronary occlusion (occlusion 1), after a 5-min reperfusion period (baseline 2) and a during a second coronary occlusion during bypass anastomosis (occlusion 2).Results. Left ventricular wall motion score (LVWMS) increased significantly from baseline (16.0) to occlusion 1 (21.4 ± 3.1 [mean ± SD], p < 0.05) and occlusion 2 (21.8 ± 3.1, p < 0.05). No difference in LVWMS was noted between occlusions 1 and 2. Pulmonary artery systolic pressure increased significantly from baseline (25 ± 6 mm Hg) to occlusion 1 (32 ± 7 mm Hg, p < 0.05) and occlusion 2 (33 ± 6 mm Hg, p < 0.05). Pulmonary artery diastolic pressure also increased significantly from baseline (12 ± 4 mm Hg) to occlusion 1 (16 ± 4 mm Hg, p < 0.05) and occlusion 2 (16 ± 4 mm Hg, p < 0.05). No significant differences in pulmonary artery pressures were noted between occlusions 1 and 2.Conclusions. Ischemic dysfunction was precipitated by the 5-min LAD occlusion, as shown by the increase in LVWMS and pulmonary artery pressure. However, a 5-min coronary occlusion and the resulting ischemia do not alter regional left ventricular systolic function during subsequent ischemia in humans.

Angina: who needs it? Cardioprotection in the preconditioning era.

Over the past two decades, it has been demonstrated in various animal species that the myocardium possesses innate adaptive mechanisms that may render it more resistant to ischemic injury. Ischemic preconditioning, defined as the protection conferred to ischemic myocardium by prior episodes of brief sublethal ischemia, is one of the most potent of such adaptive phenomena. Extensive research over the past decade has alluded to the cellular mechanisms underlying this powerful means of reducing myocardial ischemia-reperfusion injury. Moreover, the possibility that such adaptive mechanisms might be inducible in the human heart has generated considerable excitement and enthusiastic research, which has significantly enhanced our understanding of the pathogenesis of ischemia-reperfusion injury. An insight into the mechanisms underlying the cardioprotective properties of ischemic preconditioning has, on the one hand, directed research aimed at identification of novel therapeutic agents for the treatment of ischemic heart disease, and on the other, questioned the use of potentially deleterious agents that may abolish the cardioprotective actions of ischemic preconditioning in patients with angina. Current studies are under way to evaluate the potential protection afforded by these "preconditioning" agents in patients with acute coronary syndromes, and some early reports provide some basis for optimism that a beneficial and clinically detectable improvement in myocardial protection may be possible. This article reviews our current knowledge of the cellular mechanisms responsible for mediation of ischemic preconditioning, the evidence for the existence of this phenomenon in humans, and its potential therapeutic applications.