Preconditioning with 15-minute ischemia extends myocardial infarct size after subsequent 30-minute ischemia in rabbits

Human Tissue-Engineered Model of Myocardial Ischemia-Reperfusion Injury

IMPACT STATEMENT

Reducing ischemia-reperfusion injury would significantly improve patient survival. Current preclinical models are inadequate because they rely on animals, which do not emulate human physiology and the clinical setting. We developed a human tissue platform that allowed us to assess the human cardiac response, and demonstrated the platform's utility by measuring injury during ischemia-reperfusion and the effects of cardioprotective strategies. The model provides a foundation for future studies on how patient-specific backgrounds may affect response to therapeutic strategies. These steps will be necessary to help translate therapies into the clinical setting.

Reduction of myocardial infarct size with ischemic "conditioning": physiologic and technical considerations

A wealth of evidence has revealed that the heart can be "conditioned" and rendered less vulnerable to ischemia-reperfusion injury via the upregulation of endogenous protective signaling pathways. Three distinct conditioning strategies have been identified: (1) preconditioning, the phenomenon where brief episodes of myocardial ischemia (too brief to cause cardiomyocyte death) limit necrosis caused by a subsequent sustained ischemic insult; (2) postconditioning, the concept that relief of myocardial ischemia in a staged or stuttered manner attenuates lethal ischemia-reperfusion injury; and (3) remote conditioning, or upregulation of a cardioprotective phenotype initiated by ischemia in a remote organ or tissue and "transported" to the heart. Progress has been made in defining the technical requirements and limitations of each of the 3 ischemic conditioning models (including the timing and severity of the protective stimulus), as well as elucidating the molecular mechanisms (in particular, the receptor-mediated signaling pathways) responsible for conditioning-induced myocardial protection. Moreover, phase III clinical trials are in progress, seeking to capitalize on the protection that can be achieved by postconditioning and remote conditioning, and applying these strategies in patients undergoing cardiac surgery or angioplasty for the treatment of acute myocardial infarction. There is, however, a potentially important caveat to the clinical translation of myocardial conditioning: emerging data suggest that the efficacy of ischemic conditioning is compromised in aging, diabetic, and hypertensive cohorts, the specific populations in which myocardial protection is most relevant. Successful clinical application of myocardial conditioning will therefore require an understanding of the potential confounding consequences of these comorbidities on the "conditioned" phenotype.

Effect of Ischemic Preconditioning Based on Different Epicardial Branching Patterns of the Left Coronary Artery in the Rabbit Heart

The aim of this study was to characterize the effect of increasing numbers of preconditioning cycles on the different branching patterns (bifurcation/trifurcation) of the coronary artery in the rabbit heart. Fifty-six NZW rabbits were assigned to a bifurcation group and subjected to 0, 1, 3, 5, or 7 (B0, B1, B3, B5, or B7 subgroup, respectively) cycles of preconditioning (PC) (5 min of regional ischemia plus 10 min of reperfusion/cycle) and this was followed by 45 min of sustained ischemia and 72 h of reperfusion; 16 rabbits were assigned to a trifurcation group and subjected to 0, 1, 3, or 5 (T0, T1, T3, or T5 subgroup, respectively) cycles of PC. The ratio of necrotic zone (NZ) to ischemic zone (IZ) was calculated. The bifurcation group showed higher mortality (28.6%) than the trifurcation group (0%). The volume of the ischemic zone (expressed as a percentage of volume of the left ventricle) and the volume of the necrotic zone were larger in the bifurcation group than in the trifurcation group. The ratio of the necrotic zone to the ischemic zone was significantly lower in the B5 and B7 subgroups than in the B0, B1, and B3 subgroups. In the trifurcation group, the ratio of the necrotic zone to the ischemic zone showed a diminishing tendency in the subgroups as the PC cycle number increased, but without statistical significance. Thus, in the trifurcation pattern of the rabbit coronary artery there could be little effect on preconditioning, but in the bifurcation pattern the number of preconditioning is recommended to be 5 to 7 cycles. In this regard, different branching patterns of the epicardial branching of the rabbit coronary artery should be considered when interpreting experimental results on ischemic preconditioning.

[The role of ischemic preconditioning in acute myocardial infarction]

INTRODUCTION

Ischemic preconditioning is a phenomenon in which brief episodes of ischemia and reperfusion increase myocardial tolerance and substantially reduce the infarction size.

CASE REPORT

Two patients with acute left anterior descending artery occlusion received fibrinolytic therapy within 6 hours of symptom onset, but nevertheless developed myocardial infarctions of different size. The first patient, without a history of preinfarction angina, developed a large anterior infarction, because there was no time for ischemic preconditioning or development of coronary collateral vessels. The second patient, with a 4-day history of preinfarction angina, had a more favorable outcome - he developed apical necrosis, with greater myocardial viability in the infarct-related area.

CONCLUSION

The beneficial effects of angina occurring 24-48h before infarction are resulting from ischemic preconditioning, which reduces cardiac mortality, infarct size and occurrence of life-threatening ventricular arrhythmias.

[Ischemic preconditioning]

BACKGROUND

Ischemic preconditioning is a phenomenon during which myocardium, subjected to brief episodes of ischemia followed by reperfusion, tolerates better the subsequent, more prolonged episode of this ischemia, thus reducing the infarction size substantially.

CASE REPORT

Two patients with acute left anterior descendent artery occlusion received fibrinolytic therapy (alteplase) within 6 hours of the onset of chest pain, but developed myocardial infarctions of different sizes. The first patient, without the history of preinfarction angina, developed large anterior infarct, because there was no time either for ischemic preconditioning or for the coronary collateral vessels development. In the second patient, with 4-day history of preinfarction angina, the more favorable outcome was seen he developed smaller apical necrosis, with the great degree of myocardial viability in the infarct-related area.

CONCLUSION

Ischemic preconditioning in patients with acute myocardal infarction results in the reduction of mortality, infarction size, as well as in the frequency of malignant arrhythmias.

Pharmacological modulation of the ATP sensitive potassium channels during repeated coronary occlusions: no effect on myocardial ischaemia or function

BACKGROUND

Repeated episodes of myocardial ischaemia may lead to ischaemic preconditioning. This is believed to be mediated by the ATP sensitive potassium channels.

OBJECTIVE

To examine the effect of pharmacological modulation of the ATP sensitive potassium channels during repeated coronary occlusions.

DESIGN

Double blind, double dummy study.

METHODS

38 patients with a proximal stenosis of the left anterior descending coronary artery and no visible coronary collateral vessels underwent three identical 90 second balloon occlusions, each followed by five minutes of reperfusion. The patients were randomised to pinacidil 25 mg, glibenclamide 10.5 mg, or matching placebo 90 minutes before the start of the procedure. Myocardial ischaemia was measured by continuous monitoring of ECG ST segment changes. Changes in left ventricular function were recorded with a miniature radionuclide detector, and angina was scored on the Borg scale.

RESULTS

In all patients the first balloon occlusion led to significant ST segment elevation, a clear decrease in left ventricular ejection fraction, and angina pectoris. This response was not attenuated at the second or third balloon occlusion, either in the placebo group or in the patients pretreated with pinacidil or glibenclamide.

CONCLUSIONS

Under the given experimental conditions, this randomised and double blind study did not support the view that the human myocardium has an intrinsic protective mechanism that is activated by short lasting episodes of ischaemia.

Evidence of ischemic preconditioning in patients experiencing first non-ST-segment elevation myocardial infarction (NSTEMI)

BACKGROUND

Several studies have demonstrated the protective effects of preinfarction angina in Q wave myocardial infarction, implicating the role of ischemic preconditioning but this role remains uncertain in patients with a NSTEMI. Subendocardial viability in NSTEMI patients, is thought to be less dependent on collateral circulation and thus more likely to be protected by other mechanisms such as preconditioning.

METHODS

We have studied prospectively 40 patients with first NSTEMI and with angiographically proven poor or no collateral development and compared two groups; those with versus those without preinfarction angina. All in-hospital events, such as recurrent angina, congestive heart failure, arrhythmias and reinfarction were recorded. Serum markers of myocardial necrosis (CPK, CPK-MB, AST) and discharge QTc values were estimated.

RESULTS

Preconditioned patients suffered less recurrent angina (18 vs. 55% P=0.014), congestive heart failure (0 vs. 22%, P=0.02), arrhythmic events (0 vs. 27%, P=0.008) and had significant smaller values of mean peak CPK (381 +/- 152 vs. 859 +/- 496 I.U./l, P=0.0008), mean peak CPK-MB (45.5 +/- 24.6 vs. 105.2 +/- 87 I.U./l, P=0.01), mean peak AST (59.8 +/- 23.1 vs. 112.4 +/- 64.3 I.U./l, P=0.003) and QTc value at discharge (0.42 +/- 0.03 vs. 0.46 +/- 0.05 s, P=0.005) than patients without preconditioning. Multiple logistic regression analysis confirmed that the absence of preinfarction angina (relative risk 9.10, 95% CI 2.08-40.00, P=0.003) was a significant predictor of in-hospital complications.

CONCLUSIONS

Preinfarction angina constitutes a strong clinical correlate to ischemic preconditioning in patients with first NSTEMI, offering serious protection, by improving in-hospital outcome and reducing infarct size.

Relation Between the Timing of the Last Preinfarction Angina and Microvascular Reperfusion in Patients With Recanalized Acute Myocardial Infarction

In patients with recanalized acute myocardial infarction (AMI), the relation between the timing of preinfarction angina (PA) and microvascular reperfusion remains unclear. A total of 186 patients (114 with anterior and 72 with inferior AMI) who had total occlusion and TIMI 3 recanalization < or = 6 hours from the onset of AMI were divided into 4 groups according to the time interval between the last episode of PA and the onset of AMI: < or = 2 hours (group A, n = 52); 2 to 48 hours (group B, n = 43), > or = 48 hours (group C, n = 33), and no PA (group D, n = 58). The angiographic myocardial blush grade, a marker of microvascular reperfusion, was retrospectively assessed immediately after recanalization. There were no differences in baseline characteristics, except for sex among the 4 groups. Myocardial blush grade 3 was more frequent (42% vs 21%, 9%, and 14%) and peak creatine kinase was lower (2659 vs 3455, 4422, and 4622 mU/mL) in group A than in groups B, C, and D (all P < 0.05). Multivariate analysis showed that PA occurring < or = 2 hours before AMI (OR 3.88, P < 0.05), a smaller summed ST-segment elevation before recanalization (OR 0.84, P < 0.01), earlier time to recanalization (OR 0.52, P < 0.05), and interior AMI (OR 4.87, P < 0.05) were independently associated with adequate microvascular reperfusion. We conclude that PA < or = 2 hours before the onset of AMI is independently associated with adequate microvascular reperfusion after recanalization in patients with AMI.

Cardioprotective effects of nicorandil in rabbits anaesthetized with halothane: potentiation of ischaemic preconditioning via KATP channels

1. The roles of ATP-sensitive K+ channels (KATP channels) in ischaemic or pharmacological preconditioning in the rabbit heart remain unclear. Infarct limitation by ischaemic preconditioning was abolished by the KATP channel blocker glibenclamide under ketamine/xylazine anaesthesia, but not under anaesthesia induced by pentobarbital. Infarct limitation by the KATP channel opener pinacidil was detected under ketamine/xylazine anaesthesia, but not under pentobarbital anaesthesia. Thus, these effects appear to be anaesthetic dependent. 2. In the present study, we examined whether nicorandil (a KATP channel opener nitrate) exhibits cardioprotective actions under halothane anaesthesia, another commonly used volatile anaesthetic. Control animals were subjected to 40 min coronary occlusion and 120 min reperfusion. Before 40 min ischaemia, the nicorandil group received nicorandil (100 microg/kg per min, i.v., for 10 min), the 5' preconditioning (PC) group received 5 min ischaemia/20 min reperfusion, the 2.5'PC group received 2.5 min preconditioning ischaemia/20 min reperfusion, the nicorandil +2.5'PC group received both nicorandil and 2.5 min ischaemia/20 min reperfusion, the nicorandil +2.5'PC + 5-hydroxydecanoate (5HD) group received both nicorandil and 2.5 min ischaemia/20 min reperfusion in the presence of 5-hydroxydecanoate (5HD; a KATP blocker) and the 5HD group received 5 mg/kg, i.v., 5HD alone. Myocardial infarct size in control (n = 7), nicorandil (n = 5), 5'PC (n = 8), 2.5'PC (n = 5), nicorandil + 2.5'PC (n = 5), nicorandil + 2.5'PC + 5HD (n = 5) and 5HD (n = 4) groups averaged 44.4 +/- 3.6, 41.7 +/- 5.7, 17.8 +/- 3.2,* 34.1 +/- 4.8, 21.3 +/- 4.2,* 39.1 +/- 5.6 and 38.9 +/- 5.0% of the area at risk, respectively (*P <0.05 vs control). 3. Thus, nicorandil alone did not have an infarct size-limiting effect in halothane-anaesthetized rabbits. However, the results suggest that even when nicorandil alone does not demonstrate a direct cardioprotective effect, it may enhance ischaemic preconditioning via KATP channels. Key words: ATP-sensitive K+ (KATP) channel, ischaemic preconditioning, myocardial infarction, nicorandil, rabbit.

Evidence for the delayed effect in human ischemic preconditioning: prospective multicenter study for preconditioning in acute myocardial infarction

OBJECTIVES

This study aimed to investigate prospectively the protective effect of a first preinfarction angina attack against acute myocardial infarction (AMI) in human hearts without significant collaterals.

BACKGROUND

Several retrospective studies and the prospective studies have demonstrated the existence of the preconditioning (PC) effect in humans. However, collaterals were not examined in the prospective studies. In animal models, the PC effect on myocardial infarct size appears soon after PC reperfusion (classic) but disappears within 1 to 2 h. It then reappears 24 to 48 h after reperfusion (the delayed PC effect). Meanwhile, the PC effect on stunning appears 12 h after PC reperfusion (the delayed PC effect). The concept of the classic and delayed PC effects has not been investigated in human AMI studies. If the above concept is also correct in humans, the infarct size and/or impairment of the left ventricular function should be inversely correlated with the time interval between the first preinfarction angina attack and the onset of AMI when that time interval is limited to between 2 and 48 h.

METHODS

The subjects were 25 patients with first AMI of the proximal left anterior descending artery who underwent successful direct percutaneous transluminal coronary angioplasty (PTCA) 2 to 6 h after the onset and with no (or poor) collateral circulation (grade 0 or 1). They were divided into two groups: preinfarction angina (PA)(+) group: 11 patients with new onset preinfarction angina from 2 to 48 h before the onset, PA(-) group: 14 patients without angina before infarction. Peak creatine kinase (CK) and cumulative CK were examined, and the left ventricular ejection fraction (LVEF) and the regional wall motion (RWM) were determined from the left ventriculograms during the acute (immediately after the coronary reperfusion) and chronic (four weeks after the onset of AMI) phases. The RWM index (RWMI) was then calculated as the mean motion of chords (standard deviation [SD]/chord) lying in the area of chords of RWM < or = -2 SD in the acute phase (ischemic risk area). RESULTS The increase in the RWMI between the acute and chronic phases was significantly larger in the PA(+) group than in the PA(-) group (1.55 +/- 1.32 and 0.69 +/- 0.75, p < 0.05, respectively) although no significant difference in the enzymatic infarct size was seen between the two groups. The increases in the LVEF and the RWMI were significantly correlated with the time interval from the first preinfarction angina attack to the onset of AMI (r = 0.622, p < 0.05 and r = 0.646, p < 0.05, respectively), but the enzymatic infarct size was not.

CONCLUSIONS

The beneficial effect of preinfarction angina on left ventricular wall motion, independently of collateral flows, indicates the existence of the PC effect in humans. The greater protective effect of a longer time interval between angina pectoris and AMI suggests that the protection is due to a delayed PC effect.

Ischemic preconditioning and myocardial hypothermia in rabbits with prolonged coronary artery occlusion

This study tests whether combining regional hypothermia and ischemic preconditioning (IP) provides greater myocardial protection during prolonged coronary artery occlusion (CAO) than either intervention alone, and whether increasing the duration of IP from 5 to 7 min extends the window of protection to include a 2-h CAO. Anesthetized rabbits were randomized to four groups (n = 8 rabbits/group): control (C), hypothermia alone (H), IP alone for two 7-min episodes (IP7), and IP plus hypothermia (H + IP7). To compare differences in IP for 5 versus 7 min, additional rabbits (n = 6) received one 5-min episode of ischemia (IP5). All rabbits got 2 h of CAO and 3 h of reperfusion. In comparison with the infarct size in the control group (72 +/- 4% of the risk zone), infarct size was significantly reduced in H (50 +/- 7%), IP7 (49 +/- 5%), and H + IP7 (42 +/- 6%) (all P < 0.05 vs. control group). IP5 failed to confer protection (67 +/- 5% of the risk zone). Therefore, IP can protect against a 2-h CAO if the IP regimen is increased from 5 to 7 min. The combination therapy significantly improved regional myocardial blood flow in the previously ischemic region to a greater extent than either treatment alone.

Adenosine and preconditioning revisited

1. Myocardial tolerance against infarction is substantially increased by exposing myocytes to 3-10 min transient ischaemia. In this phenomenon, termed 'preconditioning', the adenosine receptor is one of the redundant triggers and the best characterized factor in the cardioprotective mechanism. 2. An increase in interstitial adenosine during preconditioning is thought to be derived primarily from hydrolysis of 5'-AMP in the myocyte by cytosolic 5'-nucleotidase, although a contribution of ectosolic 5'-nucleotidase remains controversial. Adenosine production during ischaemia is substantially suppressed in the preconditioned myocardium, probably due to a decrease in ATP utilization. 3. The adenosine receptor needs to be activated not only at the time of preconditioning ischemia, but also during ischaemic insult for the preconditioning to be cardioprotective. However, the extent of cardioprotection afforded by preconditioning is primarily determined by the interstitial adenosine level achieved during preconditioning ischaemia, not by the level during sustained ischaemia. These data suggest that a post-receptor mechanism downstream of the adenosine receptor may be up-regulated after preconditioning. 4. Studies in vitro suggest that the subtypes of adenosine receptor relevant to preconditioning against infarction are A1 and A3, the activation of which appears to provide additive protection. The functional interrelationship between these subtypes in vivo remains unknown. 5. An important step downstream of adenosine receptor activation is protein kinase C (PKC), which facilitates opening of ATP-sensitive potassium (KATP) channels, probably leading to enhancement of myocardial tolerance. However, activation of other protein kinases, such as tyrosine kinase, may also be important in preconditioning, depending on the animal species and preconditioning protocols. The PKC isoform and location of KATP channels (i.e. sarcolemmal vs mitochondrial KATP) that induce anti-infarct tolerance in myocytes remain to be identified.

Effectiveness of ischemic preconditioning on long-term myocardial preservation

BACKGROUND

This study was designed to assess whether the protective effect of ischemic preconditioning can be adapted for myocardium undergoing 6 hr of ischemia.

METHODS

Eighteen isolated rat hearts were perfused with oxygen-bicarbonated Krebs-Henseleit buffer in the Langendorff mode for 35 min (group A, controls) or perfused in the Langendorff apparatus for 20 min, followed by 5 min of global normothermic ischemia and 10 min of buffer perfusion (group B, preconditioning) or followed by two cycles of 2.5 min of global normothermic ischemia plus 5 min of buffer perfusion (group C, preconditioning). The hearts were then arrested and preserved for 6 hr with Bretschneider's histidine-tryptophan-potassium cardioplegic solution at 4 degrees C, followed by 30 min of reperfusion. Recovery of cardiac function, postischemic enzyme leakage, and intracellular calcium concentration were compared.

RESULTS

After 6 hr of ischemia, the hearts that underwent preconditioning in groups B and C showed better recovery of left ventricular developed pressure (P<0.05), a lower end-diastolic pressure level (P<0.05), less leakage of creatine kinase, and a lower intracellular calcium concentration than those in group A. There were no statistical differences in the rate of recovery of coronary flow.

CONCLUSIONS

Our study demonstrated that ischemic preconditioning improves myocardial functional recovery after 6 hr of hypothermic preservation in the isolated rat heart. Preconditioning might be useful for preserving the heart against long-term ischemia/reperfusion injury.

Cardioprotective efficacy of ischemic preconditioning on long-term myocardial ischemia

This study was designed to assess whether the protective effect of ischemic preconditioning can be adapted for myocardium undergoing 6 h of no-flow ischemia. Twelve isolated rat hearts were either perfused with oxygen-bicarbonated Krebs-Henseleit buffer in the Langendorff mode for 35 min (n=6), or perfused in the same way for 20 min, following 5 min of global normothermic ischemia and 100 min of buffer-perfusion (n=6). The 12 hearts were then preserved for 6 h in HTK solution at 4 degrees C, followed by 30 min of reperfusion. Recovery of cardiac function, metabolic activity and intracellular free calcium concentration were compared between the two groups. After 6 h ischemia, the hearts that underwent preconditioning showed better recovery of left ventricular developed pressure (P<0.01), a lower end-diastolic pressure level (P<0.05), less creatine kinase leakage and a lower calcium concentration. There was no statistical difference in the recovery rate of coronary flow and leakage rate of LDH between the two groups. In conclusion, this experiment demonstrates that ischemic preconditioning improved myocardial functional recovery after 6 h of hypothermic ischemic preservation in the isolated rat heart. Preconditioning might be a potential mechanism for preserving the heart against long-term ischemia/reperfusion injury.