Pharmacologic myocardial protection during percutaneous transluminal coronary angioplasty by intracoronary application of dipyridamole: impact on hemodynamic function and left ventricular performance

Adenosine as a Marker and Mediator of Cardiovascular Homeostasis: A Translational Perspective

Adenosine, a purine nucleoside, is produced broadly and implicated in the homeostasis of many cells and tissues. It signals predominantly via 4 purinergic adenosine receptors (ADORs) - ADORA1, ADORA2A, ADORA2B and ADOosine signaling, both through design as specific ADOR agonists and antagonists and as offtarget effects of existing anti-platelet medications. Despite this, adenosine has yet to be firmly established as either a therapeutic or a prognostic tool in clinical medicine to date. Herein, we provide a bench-to-bedside review of adenosine biology, highlighting the key considerations for further translational development of this proRA3 in addition to non-ADOR mediated effects. Through these signaling mechanisms, adenosine exerts effects on numerous cell types crucial to maintaining vascular homeostasis, especially following vascular injury. Both in vitro and in vivo models have provided considerable insights into adenosine signaling and identified targets for therapeutic intervention. Numerous pharmacologic agents have been developed that modulate adenmising molecule.

Myocardial Preconditioning: Characteristics, Mechanisms, and Clinical Applications

Perioperative myocardial ischemia and dysfunction re main prevalent after cardiac surgery despite the use of conventional measures to provide myocardial protec tion. Myocardial preconditioning is a powerful, endog enously regulated means of myocardial protection that may also have some clinical usage for patients undergo ing cardiac surgical procedures. The paradoxical con cept of using ischemia as a stimulus for myocardial protection has been studied extensively in animals and humans. The specific characteristics and constituents of preconditioning have been well identified. The mecha nism remains to be completely elucidated due to differ ences among species and experimental models. Some pharmacologic agents are capable of mimicking the classic mechanism of ischemic preconditioning. Pharma cologic and ischemic preconditioning may have signifi cant clinical use and therapeutic efficacy as a means of providing myocardial protection during cardiac surgery, especially in procedures that do not use cardioplegia and cardiopulmonary bypass, such as minimally inva sive coronary artery bypass grafting. This article re views the characteristics, mechanisms, potential clini cal applications, and therapeutic efficacy of myocardial preconditioning.

Adenosine-mediated effects of ticagrelor: evidence and potential clinical relevance

This review constitutes a critical evaluation of recent publications that have described an additional mode of action of the P2Y12 receptor antagonist ticagrelor. The effect is mediated by inhibition of the adenosine transporter ENT1 (type 1 equilibrative nucleoside transporter), which provides protection for adenosine from intracellular metabolism, thus increasing its concentration and biological activity, particularly at sites of ischemia and tissue injury where it is formed. Understanding the mode of action of ticagrelor is of particular interest given that its clinical profile, both in terms of efficacy and adverse events, differs from that of thienopyridine P2Y12 antagonists.

Treatment with dipyridamole improves cardiac function and prevent injury in a rat model of hemorrhage

Hemorrhagic shock is a leading cause of death despite the improvement in emergency services. One reason is that the resuscitation policies are designed to reestablish tissue perfusion, but not to prevent the inflammatory response to shock that cause myocardial dysfunction and injury. Dipyridamole is a platelet inhibitor that promotes anti-inflammatory effects. The present study investigated the therapeutic value of treatment with dipyridamole before resuscitation from hemorrhagic shock on myocardial injury and protection. Male Sprague-Dawley rats were assigned to 3 experimental groups (n=6 per group): 1) hemorrhage, 2) hemorrhage treated with dipyridamole, and 3) sham hemorrhage. Rats were hemorrhaged over 60min to reach a mean arterial blood pressure of 40mmHg. After 60min hemorrhagic shock, rats were treated or not by injection of 1mL of (20μg/L) dipyridamole intra-arterially. Resuscitation was made in vivo by reinfusion of the shed blood to restore norm tension for 30min. Arterial blood samples were collected for measurements of TNF-α. Left ventricular generated pressure and +dP/dtmax was significantly higher in dipyridamole treated rats compared to the untreated group. Myocardial biopsy samples were taken for light and electron microscopy. Dipyridamole decreased the number of inflammatory cells and mitochondrial swollen. Dipyridamole also decreased the plasma levels of TNF-α. Our results demonstrate that treatment with dipyridamole before in vivo resuscitation of hemorrhagic shock protect the myocardium against post-resuscitation myocardial dysfunction by decreasing the inflammatory response to shock.

Cell therapy in dilated cardiomyopathy: from animal models to clinical trials

Dilated cardiomyopathy can be the end-stage form and common denominator of several cardiac disorders of known cause, such as hypertensive, ischemic, diabetic and Chagasic diseases. However, some individuals have clinical findings, such as an increase in ventricular chamber size and impaired contractility (classical manifestations of dilated cardiomyopathy) even in the absence of a diagnosed primary disease. In these patients, dilated cardiomyopathy is classified as idiopathic since its etiology is obscure. Nevertheless, regardless of all of the advances in medical, pharmacological and surgical procedures, the fate of patients with dilated cardiomyopathy (of idiopathic or of any other known cause) is linked to arrhythmic episodes, severe congestive heart failure and an increased risk of sudden cardiac death. In this review, we will summarize present data on the use of cell therapies in animal models of dilated cardiomyopathies and will discuss the few clinical trials that have been published so far involving patients affected by this disease. The animal models discussed here include those in which the cardiomyopathy is produced by genetic manipulation and those in which disease is induced by chemical or infectious agents. The specific model used clearly creates restrictions to translation of the proposed cell therapy to clinical practice, insofar as most of the clinical trials performed to date with cell therapy have used autologous cells. Thus, translation of genetic models of dilated cardiomyopathy may have to wait until the use of allogeneic cells becomes more widespread in clinical trials of cell therapies for cardiac diseases.

Nucleoside transport inhibitor, dipyridamole, induced myocardial protection following hemorrhagic shock in ex vivo perfused rat hearts

INTRODUCTION

Successful protection against post-resuscitation myocardial injury is not available for trauma patients. Whereas intensive improvement in resuscitation strategies reduce myocardial injury, death among trauma patients are among the highest in the world due to myocardial dysfunction and multiple organ failure. Dipyridamole is a nucleoside transport inhibitor. Recent studies have shown that elevation of serum adenosine caused by dipyridamole improve cardiac function. The purpose of the present study was to examine the myocardial protective effects of dipyridamole therapy following 1 h of hemorrhagic shock.

METHODS

Sprague-Dawley rats were used. The study consisted of three phases: Phase I to examine the direct effects of dipyridamole on myocardial function by perfusion of the isolated hearts with Krebs Henseleit buffer (KHB) + dipyridamole on the Langendorff apparatus. Phase II examined the protective effects of dipyridamole following 60 min of hemorrhagic shock (HS) by ex vivo treatment with dipyridimole 20 μg/L for 5 min followed by resuscitation with KHB for 55 min. Phase III: 60 min HS followed by in vivo treatment by injecting 1 ml of (20 μg/L) dipyridamole intra-arterially, and resuscitation for 30 min. Myocardial protection was assessed by measuring left ventricular generated pressure (LVGP) and end diastolic pressures (LVEDP).

RESULTS

During ex vivo resuscitation, hearts from dipyridamole treated animals had significantly higher LVGP, and significantly lower LVEDP versus controls.

CONCLUSION

Dipyridamole therapy produces protection against post-resuscitation myocardial injury in rats.

Dipyridamole therapy improves long-term survival after complete revascularization in patients with impaired cardiac function: a propensity analysis

BACKGROUND

Although dipyridamole is no longer used as a mainstream medication for coronary artery disease because of the coronary steal phenomenon, recent studies have shown that the elevation of serum adenosine levels caused by dipyridamole improves cardiac function in heart failure patients. In the present study it was investigated whether use of dipyridamole at the time of complete revascularization affects long-term mortality in patients with impaired left ventricular (LV) function.

METHODS AND RESULTS

The 1,836 consecutive patients who underwent complete revascularization between 1984 and 1992 were assessed; 254 patients with impaired LV function (ejection fraction < 50%) were enrolled. Cox proportional hazards regression adjusted for baseline covariates and the propensity score were used to compare the risks for mortality between patients who did and did not take dipyridamole. The mean follow-up period was 12 years; 178 patients (70.1%) took dipyridamole and there were 66 (37.1%) all-cause and 22 (12.4%) cardiac deaths in that group. In the multivariate analysis, the dipyridamole group had a lower risk for both all-cause (hazard ratio (HR) 0.54; p = 0.005) and cardiac mortality (HR 0.42; p = 0.010).

CONCLUSION

The use of dipyridamole reduced both all-cause and cardiac mortality in patients with impaired LV function.

The diagnostic accuracy of pharmacological stress echocardiography for the assessment of coronary artery disease: a meta-analysis

BACKGROUND

Recent American Heart Association/American College of Cardiology guidelines state that "dobutamine stress echo has substantially higher sensitivity than vasodilator stress echo for detection of coronary artery stenosis" while the European Society of Cardiology guidelines and the European Association of Echocardiography recommendations conclude that "the two tests have very similar applications". Who is right?

AIM

To evaluate the diagnostic accuracy of dobutamine versus dipyridamole stress echocardiography through an evidence-based approach.

METHODS

From PubMed search, we identified all papers with coronary angiographic verification and head-to-head comparison of dobutamine stress echo (40 mcg/kg/min +/- atropine) versus dipyridamole stress echo performed with state-of-the art protocols (either 0.84 mg/kg in 10' plus atropine, or 0.84 mg/kg in 6' without atropine). A total of 5 papers have been found. Pooled weight meta-analysis was performed.

RESULTS

the 5 analyzed papers recruited 435 patients, 299 with and 136 without angiographically assessed coronary artery disease (quantitatively assessed stenosis > 50%). Dipyridamole and dobutamine showed similar accuracy (87%, 95% confidence intervals, CI, 83-90, vs. 84%, CI, 80-88, p = 0.48), sensitivity (85%, CI 80-89, vs. 86%, CI 78-91, p = 0.81) and specificity (89%, CI 82-94 vs. 86%, CI 75-89, p = 0.15).

CONCLUSION

When state-of-the art protocols are considered, dipyridamole and dobutamine stress echo have similar accuracy, specificity and - most importantly - sensitivity for detection of CAD. European recommendations concluding that "dobutamine and vasodilators (at appropriately high doses) are equally potent ischemic stressors for inducing wall motion abnormalities in presence of a critical coronary artery stenosis" are evidence-based.

Dipyridamole enhances ischaemia-induced reactive hyperaemia by increased adenosine receptor stimulation

BACKGROUND AND PURPOSE

Dipyridamole enhances post-occlusive reactive hyperaemia (PORH) in the human forearm vascular bed. We hypothesize that this effect is completely mediated by increased adenosine receptor stimulation. To test this hypothesis, the effect of caffeine (an adenosine receptor antagonist) on dipyridamole-induced augmentation of PORH was explored.

EXPERIMENTAL APPROACH

The forearm vasodilator responses to three increasing periods of forearm ischaemia (2, 5 and 13 min) were determined during placebo infusion. Forty minutes after the last reperfusion period, this procedure was repeated during intra-arterial infusion of dipyridamole (7.4 nmol min(-1) per 100 ml forearm). At least 2 weeks later, this whole procedure was repeated, but now in the presence of caffeine (90 microg min(-1) per 100 ml volume).

KEY RESULTS

After 2, 5 and 13 min of ischaemia, the average forearm blood flow increased to 5.6+/-0.7, 9.7+/-1.3 and 34.5+/-2.1 ml min(-1) per 100 ml. After infusion of dipyridamole into the brachial artery, these numbers were significantly increased to 7.7+/-0.8, 12.5+/-1.5 and 41.6+/-3.1 ml min(-1) per 100 ml. This response was abolished by the concomitant infusion of caffeine (6.6+/-0.5, 10.2+/-0.6, 35.1+/-2.2 (caffeine) versus 7.4+/-0.4, 10.5+/-0.6, 33.7+/-2.2 ml min(-1)per 100 ml (caffeine/dipyridamole)).

CONCLUSIONS AND IMPLICATIONS

Caffeine prevented the augmenting effect of dipyridamole on PORH. This indicates that dipyridamole-induced augmentation of PORH is mediated via increased adenosine receptor stimulation as a result of elevated extracellular formation of adenosine during ischaemia.

Enhanced cardioprotection against ischemia-reperfusion injury with a dipyridamole and low-dose atorvastatin combination

Atorvastatin (ATV) limits infarct size (IS) by activating Akt and ecto-5-nucleotidase, which generates adenosine. Activated Akt and adenosine activate endothelial nitric oxide synthase (eNOS). When given orally, high doses (10 mg/kg) are needed to achieve full protection. We determined whether dipyridamole (DIP), by preventing the reuptake of adenosine, has a synergistic effect with ATV in reducing myocardial IS. In this study, rats received 3-days of the following: water, ATV (2 mg·kg−1·day−1), DIP (6 mg·kg−1·day−1), or ATV + DIP. In addition, rats received 3-days of the following: aminophylline (Ami; 10 mg·kg−1·day−1) or Ami + ATV + DIP. Rats underwent 30 min of myocardial ischemia followed by 4 h of reperfusion (IS protocol), or hearts were explanted for immunoblotting. As a result, IS in the controls was 34.0 ± 2.8% of the area at risk. ATV (33.1 ± 2.1%) and DIP (30.5 ± 1.5%) did not affect IS, whereas ATV + DIP reduced IS (12.2 ± 0.5%; P < 0.001 vs. each of the other groups). There was no difference in IS between the Ami alone (48.1 ± 0.8%) and the Ami + ATV + DIP (45.8 ± 2.9%) group ( P = 0.422), suggesting that Ami completely blocked the protective effect. Myocardial adenosine level in the controls was 30.6 ± 3.6 pg/μl. ATV (51.0 ± 4.9 pg/μl) and DIP (51.5 ± 6.8 pg/μl) caused a small increase in adenosine levels, whereas ATV + DIP caused a greater increase in adenosine levels (66.4 ± 3.1 pg/μl). ATV and DIP alone did not affect myocardial Ser473 phosphorylated-Akt and Ser1177 phosphorylated-eNOS levels, whereas ATV + DIP significantly increased them. In conclusion, low-dose ATV and DIP had synergistic effects in reducing myocardial IS and activation of Akt and eNOS. This combination may have a potential benefit in augmenting the eNOS-mediated pleiotropic effects of statins.

Delayed preconditioning via Angiotensin-converting enzyme inhibition: pros and cons from an experimental study

1. Bradykinin B(2) receptor activation confers preconditioning from ischaemic injury. In the present study, we tested whether an angiotensin-converting enzyme (ACE) inhibitor (captopril) could mediate delayed preconditioning and, thus, cardioprotection. 2. New Zealand white rabbits received 15 mL infusion of either saline (control group; n = 7) or drugs (0.3 mg/kg captopril (CAP group; n = 7) or 0.3 mg/kg captopril + 0.1 mg/kg HOE 140 (CAPHOE group; n = 7)) via a marginal ear vein over 30 min. After 24 h, hearts were connected to a Langendorff apparatus and buffer perfused. The experimental protocol consisted of 20 min global normothermic hypoxia, followed by 120 min reperfusion. 3. Compared with baseline, the mean (SEM) contractile state (= dP/dt(max)) at 120 min reperfusion was decreased to 42 +/- ;23, 72 +/- ;16 (*P < 0.05 vs control) and 49 +/- ;22% in the control, CAP and CAPHOE groups, respectively. Early relaxation (= dP/dt(min)) was reduced to 55 +/- ;28, 73 +/- ;15 (*P < 0.05 vs control) and 52 +/- ;19% in the control, CAP and CAPHOE groups, respectively. The estimate for myocardial oxygen consumption (MVO(2)= rate-pressure product) was decreased to 52 +/- ;15, 69 +/- ;24 (*P < 0.05 vs control) and 56 +/- ;15% in the control, CAP and CAPHOE groups, respectively. Similarly, coronary flow was decreased in the control, CAP and CAPHOE groups to 49 +/- ;20, 67 +/- ;18 and 46 +/- ;19%, respectively. In contrast, ventricular extrasystoles during reperfusion were significantly elevated in both the CAP and CAPHOE groups (1.3 +/- ;0.2 and 1.1 +/- ;0.3 /min, respectively) compared with control (0.4 +/- ;0.2 /min). 4. Captopril confers delayed preconditioning against stunning via a B(2) receptor-mediated pathway. This pharmacological preconditioning protects against systolic and diastolic stunning, against vascular stunning and preserves cardiac metabolism. In addition to its accepted cardioprotective effects in early preconditioning, captopril should induce delayed preconditioning (e.g. for routine interventional cardiology or in elective cardiac surgery).

Effects of Long-Term Oral Dipyridamole Treatment on Coronary Microcirculatory Function in Patients With Chronic Stable Angina: A Substudy of the Persantine In Stable Angina (PISA) Study

AIMS

A meta-analysis of 13 randomized placebo-controlled trials demonstrated a benefit for dipyridamole therapy, particularly with longer duration of treatment. Although the mechanism of this effect is not well understood, dipyridamole increases endogenous tissue adenosine, which may have a beneficial effect on myocardial perfusion. Therefore, we measured the effects of dipyridamole on myocardial blood flow (MBF) and coronary flow reserve (CFR) by using positron emission tomography and H2O in patients with coronary artery disease.

METHODS

Forty-four patients with angiographically documented coronary artery disease were double-blind randomized to either oral dipyridamole [200 milligrams (mg) twice daily (bd)] or placebo as add-on to conventional antianginal treatment for 24 weeks. MBF was measured at rest and during dobutamine stress at baseline and study completion for the region subtended by the most severe coronary artery stenosis (Isc) and remote myocardium subtended by arteries with minimal or no disease (Rem). CFR was calculated as MBF-peak/MBF-rest.

RESULTS

Thirty-five patients completed the study. Isc MBF-rest decreased in patients receiving dipyridamole (0.10 mL/minute/g; P = 0.03) and increased in the placebo group (0.16 mL/minute/g; P = 0.01) during the 24-week study. No significant change in MBF-peak was demonstrated in either group. Consequently, Isc-CFR increased significantly in patients receiving dipyridamole (1.65 +/- 0.47 vs 1.83 +/- 0.67; P < 0.05). By contrast, Isc-CFR decreased significantly in those receiving placebo (1.74 +/- 0.44 versus 1.38 +/- 0.46; P < 0.03). No change was seen in Rem-CFR territories.

CONCLUSIONS

At the end of treatment, a reduction in baseline MBF but no significant changes in hyperemic MBF were observed in ischemic myocardial territories, and therefore the significance of the observed improvement in CFR remains unclear.

Intravenous adenosine protects the myocardium primarily by activation of a neurogenic pathway

Endogenous adenosine is a trigger for ischemic myocardial preconditioning (IPC). Although intravascular administration of adenosine has been used to further unravel the mechanism of protection by IPC, it is questionable whether adenosine and IPC employ the same signaling pathways to exert cardioprotection. We therefore investigated whether the active metabolic barrier of the endothelium prevents an increase in myocardial interstitial adenosine concentrations by intravenous adenosine, using microdialysis, and also the role of NO and activation of a neurogenic pathway in the cardioprotection by adenosine. In pentobarbital-anesthetized rats, area at risk and infarct size (IS) were determined 120 min after a 60-min coronary artery occlusion (CAO), using trypan blue and nitro-blue-tetrazolium staining, respectively. IPC with a single 15-min CAO and a 15-min adenosine infusion (ADO, 200 microg min(-1) i.v.) limited IS to the same extent (IS = 41 +/- 6% and IS = 40 +/- 4%, respectively) compared to control rats (IS = 63 +/- 3%, both P < 0.05). However, IPC increased myocardial interstitial adenosine levels seven-fold from 4.3 +/- 0.7 to 27.1 +/- 10.0 microM (P < 0.05), while ADO had no effect on interstitial adenosine (4.1 +/- 1.2 microM), or any of the other purines. The NO synthase inhibitor N(omega)-nitro-L-arginine (LNNA), which did not affect IS (IS = 62 +/- 3%), attenuated the protection by ADO (IS = 56 +/- 3%; P < 0.05 vs ADO, P = NS vs LNNA). The ganglion blocker hexamethonium, which had also no effect on IS (IS = 66 +/- 3%), blunted the protection by ADO (IS = 55 +/- 4%; P < 0.05 vs ADO and vs hexamethonium). These observations demonstrate that cardioprotection by ADO is dependent on NO, and is primarily mediated by activation of a neurogenic pathway.

Cardiac Preconditioning during Percutaneous Coronary Interventions

Ischemic preconditioning (PC) is a polygenic defensive cellular adaptive phenomenon of the heart to ischemic stress, whereby the heart changes its phenotype to become more resistant to subsequent ischemia. Early and late of PC represent two chronologically and pathophysiologically distinct phases of this phenomenon, which can be recruited pharmacologically. We represent a post hoc analysis examining the late PC-mimetic effects of nitroglycerin (NTG) on peri-procedural myocardial necrosis during percutaneous coronary intervention (PCI). A group of 66 patients presenting with angina were randomized, 24 h prior to a scheduled PCI for single obstructive CAD, to a 4 h pretreatment with intravenous NTG or saline. Measurements of electrocardiographic ST-segment shifts, echocardiographic regional wall motion and angina scores demonstrated that NTG pre-treatment preconditioned the heart by rendering it resistant to ischemia during balloon inflations. NTG-pretreated patients exhibited trends towards lower average peak CK (131.1 vs. 188.6 U/L, P = 0.38) and CK-MB levels (7.1 vs. 12.6 ng/ml, P = 0.40). NTG, however, had no significant impact on the incidence of post-procedural MI or any cardiac enzyme elevation. The exploitation of ischemic and pharmacological PC may prove a useful strategy to confer cardioprotection during high-risk PCI and is worth exploring.

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.

Blockade of nucleoside transport is required for delivery of intraarterial adenosine into the interstitium: relevance to therapeutic preconditioning in humans

BACKGROUND

Adenosine, a known mediator of preconditioning, has been infused into the coronary circulation to induce therapeutic preconditioning, eg, in preparation for angioplasty. However, results have been disappointing. We tested the hypothesis that endothelial nucleoside transporter acts as a barrier impeding the delivery of intravascular adenosine into the underlying myocardium and that this can be overcome with dipyridamole, a nucleoside transporter blocker.

METHODS AND RESULTS

We infused saline or adenosine (0.125 and 0.5 mg/min) into the brachial artery while monitoring forearm blood flow (FBF) and interstitial adenosine levels with microdialysis probes implanted in the flexor digitorum superficialis of the forearm in 7 healthy volunteers during intravenous administration of saline or dipyridamole (loading dose, 0.142 mg/kg per min for 5 minutes followed by 0.004 mg/kg per min). Adenosine produced near maximal forearm vasodilation, increasing FBF from 4.0+/-0.7 to 10.4+/-1.9 and 13.1+/-1.6 mL/100 mL per min for the low and high doses, respectively, but did not increase muscle dialysate adenosine concentration (from 88+/-21 to 65+/-23 and 85+/-26 nmol/L). Intravenous dipyridamole enhanced resting muscle dialysate adenosine (from 77+/-25 to 147+/-50 nmol/L), adenosine-induced increase in FBF (from 4.1+/-0.8 to 12.6+/-3 and 15.1+/-3 mL/100 mL per min for the low and high dose, respectively), and the delivery of adenosine into the interstitium (to 290+/-80 and 299+/-143 nmol/L for the low and high dose, respectively, P=0.04).

CONCLUSIONS

Intravascular adenosine is likely ineffective in inducing myocardial preconditioning because of poor interstitial delivery. This can be overcome by blocking the nucleoside transporter with dipyridamole.

Frequency and clinical significance of ischemic preconditioning during percutaneous coronary intervention

OBJECTIVES

We sought to examine the short- and long-term clinical consequences of ischemic preconditioning (IP) during percutaneous coronary intervention (PCI).

BACKGROUND

Ischemic preconditioning has been demonstrated in animal models to significantly diminish the extent of myocardial necrosis consequent to coronary occlusion. Surrogate markers of ischemic injury (ST segment shift, lactate release, creatine kinase release) in humans have been shown to be similarly diminished with IP elicited during PCI. There are no studies of the frequency of inducibility of IP during PCI, nor are there longer-term data on the clinical relevance of IP.

METHODS

A total of 382 patients underwent elective PCI employing a previously validated protocol to elicit IP. Procedural, in-hospital, and one-year outcomes were recorded.

RESULTS

Ischemic preconditioning was elicited in 80% of patients and was associated with a significant reduction in the likelihood of in-hospital adverse cardiac events (IP group, 12.1%; non-IP group, 44.1%; p < 0.0001). Women and diabetic patients were less likely to exhibit IP. By one year, patients failing to manifest IP were at significantly greater risk of post-discharge death or non-fatal myocardial infarction (MI) (non-IP group, 25.9%; IP group, 11.1%; p < 0.002). Failure to manifest IP was significantly and independently associated with an increased risk of death or non-fatal MI by one year.

CONCLUSIONS

Clinically relevant short- and long-term cardioprotection can be found in association with IP during PCI. In-hospital adverse ischemic events are significantly diminished in patients with IP, as are the risks of death or non-fatal MI at one year. Failure to elicit IP during PCI serves as an independent marker of increased risk of future ischemic events.

Hibernation, Stunning, and Preconditioning: Historical Perspective, Current Concepts, Clinical Applications, and Future Implications

Despite considerable advances, coronary artery disease is the leading cause of morbidity and mortality in the Western world. The development of effective therapeutic strategies for protecting the myocardium from ischemia would have major impact on patients with coronary artery disease. It is now accepted that patients with coronary artery disease can experience prolonged regional ischemic dysfunction that does not necessarily arise from irreversible tissue damage, and to some extent, can be reversed by restoration of blood flow. The initial stages of dysfunction are probably caused by chronic stunning that can be reversed after revascularization, resulting in rapid and complete functional recovery. On the other hand, the more advanced stages of dysfunction likely correspond to chronic hibernation. After revascularization, functional recovery will probably be quite delayed and mostly incomplete. Over the past decade, the possibility that an innate mechanism of myocardial protection might be inducible in the human heart has generated considerable excitement. In the last two decades, there was phenomenal growth in the understanding of the mechanism known as ischemic preconditioning that is responsible for the innate myocardial protection. Continued research and progress in this area may soon lead to the availability of preconditioning-mimetic treatments. The current concepts, mechanisms, and potential clinical applications of myocardial hibernation, stunning, and ischemic preconditioning are reviewed.

Adenosine in myocardial protection in on-pump and off-pump cardiac surgery

Adenosine is most well known for its potent vasodilation of the vasculature. However, it also promotes glycolysis, and activates potassium-sensitive adenosine triphosphate (K(ATP)) channels. Adenosine also strongly inhibits neutrophil function such as superoxide anion production, protease release, and adherence to coronary endothelial cells. Hence adenosine attenuates ischemic injury as well as neutrophil-mediated reperfusion injury. Adenosine has also been implicated in the cardioprotective phenomenon of ischemic preconditioning. Accordingly experimental evidence shows that adenosine reduces postischemic injury when administered before ischemia and at the onset of reperfusion. Clinical studies in cardiology and cardiac surgery show cardioprotective trends with adenosine treatment but the effects are not as dramatic as those reported by experimental studies.

Nicorandil-induced preconditioning as evidenced by troponin T measurements after coronary angioplasty in patients with stable angina pectoris

Nicorandil has been reported to have a preconditioning effect which suppresses the ST-segment shift or lactate production during coronary angioplasty in patients with stable angina pectoris. The present study investigated whether the preconditioning effect of nicorandil affects troponin T (TnT) levels after coronary angioplasty. Twenty-four patients with stable angina pectoris were randomized to receive a 1-minute intravenous infusion of nicorandil (100 microg/kg) or normal saline. Five minutes later they underwent three 2-minute balloon inflations 5 minutes apart. The sum of ST-segment elevation in all leads (Sum-ST) was determined at the end of each balloon inflation. Serum levels of TnT were measured 6 and 18 hours after the procedure, and the higher value of the two measurements was compared between the groups. SumST decreased progressively during the three sequential balloon inflations in both groups and was less in the nicorandil group than in the control group. The TnT level after the procedure was significantly lower in the nicorandil group than in the control group (0.05+/-0.05 vs 0.11+/-0.10 ng/mL). In conclusion, pretreatment with intravenous nicorandil suppresses TnT release after coronary angioplasty as well as ST-segment elevation during coronary angioplasty, suggesting pharmacological preconditioning by nicorandil.

Nicorandil enhances myocardial tolerance to ischemia without progressive collateral recruitment during coronary angioplasty

Nicorandil, a hybrid nitrate and ATP-sensitive potassium channel opener, has had a preconditioning effect in some coronary angioplasty studies. The present study investigated whether the cardioprotective effects of nicorandil involve coronary collateral function. Thirty-two patients with stable angina pectoris were randomized to receive a 1-min intravenous infusion of nicorandil (100 microg/kg) or normal saline. Five minutes later they underwent three 2-min balloon inflations 5-min apart. The maximum ST-segment elevation (deltaSTmax), the sum of ST-segment elevations in all leads (sigmaST), and the chest pain score were determined at the end of each balloon inflation. The collateral flow index (CFI) was derived from simultaneous measurement of the mean aortic pressure and the coronary wedge pressure obtained from a pressure guidewire during balloon inflation. The deltaSTmax, sigmaST, and chest pain score decreased progressively during the 3 sequential balloon inflations in both groups, and the deltaSTmax and sigmaST were less in the nicorandil group than in the control group during each inflation. The CFI did not change during the 3 inflations in either group and was similar in the 2 groups during each inflation. In conclusion, pretreatment with intravenous nicorandil enhances myocardial tolerance to ischemia without progressive collateral recruitment during coronary angioplasty.

Pharmacological modulation, preclinical studies, and new clinical features of myocardial ischemic preconditioning

The term "ischemic preconditioning (PC)" was first applied to canine myocardium subjected to brief episodes of ischemia and reperfusion that tolerated a more prolonged episode of ischemia better than myocardium not previously exposed to ischemia. Protective effect of myocardial ischemic PC was demonstrated in several animal species, resulting in the strongest endogenous form of protection against myocardial injury, jeopardized myocardium, infarct size, and arrhythmias other than early reperfusion. New onset angina before acute myocardial infarction, episodes of myocardial ischemia during coronary angioplasty or bypass surgery, and the "warm-up" phenomenon may represent clinical counterparts of the PC phenomenon in humans. Here, we have attempted to summarize pharmacological modulation, preclinical studies, and new clinical features of ischemic PC. To date, the pathophysiological basis of the "chemical PC" is still not well established, and "putting PC in a bottle" for clinical applications still remains a new pharmacological venture.

Intracoronary administration of dipyridamole prior to percutaneous transluminal coronary angioplasty provides a protective effect exceeding that of ischemic preconditioning

BACKGROUND

Ischemic preconditioning renders hearts more resistant to the deleterious consequences of ischemia. Adenosine is an important mediator in the induction and maintenance of ischemic preconditioning. Percutaneous transluminal coronary angioplasty (PTCA) allows the investigation of the consequences of ischemia in humans. The severity of myocardial ischemia decreases with subsequent balloon inflations during the course of PTCA.

OBJECTIVE

To compare the effect of intracoronary administration of dipyridamole with the effect of consecutive balloon inflations.

METHODS

We investigated 30 patients undergoing PTCA of the left anterior descending coronary artery in the setting of stable angina pectoris. Patients were randomly allocated to be administered either 0.5 mg/kg body weight dipyridamole intracoronarily or an equal amount of saline. Patients administered saline served as a control group. All patients were subjected to three consecutive balloon inflations. Severity of myocardial ischemia was assessed in terms of severity of chest pain, electrocardiographic signs of ischemia, and duration of balloon inflation tolerated.

RESULTS

Patients administered dipyridamole intracoronarily tolerated significantly longer durations of balloon inflation than did patients in the control group. Severity of anginal pain and extent of electrocardiographic signs of ischemia were significantly lower after intracoronary administration of dipyridamole. The reductions in anginal pain and ST-segment shift caused by intracoronary administration of dipyridamole during the first balloon inflation were even more pronounced than the protection that was afforded by the third balloon inflation for patients in the control group.

CONCLUSIONS

Intracoronary administration of dipyridamole prior to PTCA is associated with a significant gain in tolerance of ischemia. The protection afforded by intracoronary administration of dipyridamole is even more pronounced than the effect of ischemic preconditioning.

Preconditioning during percutaneous transluminal coronary angioplasty by endogenous and exogenous adenosine

BACKGROUND

The purpose of this study was to assess whether pharmacologic preconditioning by exogenous or endogenous adenosine prevents the deterioration of hemodynamic function and left ventricular performance during percutaneous transluminal coronary angioplasty (PTCA). Ischemic preconditioning renders the heart more resistant to subsequent ischemia. Adenosine plays a key role in its pathogenesis. Coronary angioplasty is a suitable model for the induction of myocardial ischemia.

METHODS AND RESULTS

We investigated 30 patients receiving PTCA of the left anterior descending coronary. Patients were randomly allocated to either dipyridamole, leading to the liberation of endogenous adenosine (0.5 mg/kg body weight, intracoronary), exogenous adenosine (20 mg intracoronary), or an equal amount of saline. Chest pain, tolerated inflation time, and ST-segment shift were registered. Left ventricular hemodynamics, isovolumetric phase indexes, indexes of volume, ejection fraction, and indexes of diastolic dysfunction were analyzed. Patients receiving endogenous or exogenous adenosine tolerated longer balloon inflation times (dipyridamole, 208 +/- 23 seconds; adenosine, 188 +/- 41 seconds; control, 153 +/- 36 seconds; P <.05). Deterioration of left ventricular ejection fraction was less severe after adenosine (72% +/- 5% before PTCA vs 64% +/- 6% during angioplasty; P =.11) and could be prevented by intracoronary dipyridamole (69% +/- 12% before PTCA vs 68% +/- 11% after PTCA; P <. 01) compared with the control group (71% +/- 7% before PTCA vs 60% +/- 7% during angioplasty).

CONCLUSIONS

Intracoronary application of exogenous adenosine and liberation of endogenous adenosine increase the tolerance to ischemia and prevent deterioration of left ventricular function during ischemia. These findings can be attributed to ischemic preconditioning. However, endogenous adenosine exceeds the protective effects of exogenous adenosine.

Effect of adjunctive intracoronary adenosine on myocardial ischemia, hemodynamic function and left ventricular performance during percutaneous transluminal coronary angioplasty: clinical access to ischemic preconditioning?

BACKGROUND

Ischemic preconditioning has been defined as a mechanism that renders the heart more resistant to subsequent ischemia. Adenosine plays an important role in the pathogenesis of ischemic preconditioning.

OBJECTIVE

To assess whether intracoronary administration of adenosine prevents the deterioration of left ventricular performance and hemodynamic function by allowing adaptation to myocardial ischemia in the setting of percutaneous transluminal coronary angioplasty (PTCA).

DESIGN

This was a prospectively randomized doubly blinded trial.

METHODS

We investigated 20 patients undergoing PTCA of the left anterior descending coronary artery supplying myocardium with normal left ventricular function in the setting of stable angina pectoris. Patients were randomly allocated to be administered adenosine intracoronarily (20 mg/10 min) or an equal amount of saline, providing a control population. Results of standardized chest pain questionnaires, tolerated inflation times, ST-segment shifts, left ventricular and aortic pressures, isovolumetric phase indexes, and indexes of volume and ejection fraction during the course of PTCA between the two groups were compared.

RESULTS

Patients administered adenosine tolerated significantly longer balloon-inflation times (188 +/- 41 versus 153 +/- 36 s; P = 0.03), which were associated with less pronounced signs of ischemia, and exhibited less deterioration of isovolumetric phase indexes during PTCA. Deterioration of left ventricular ejection fraction was slightly less severe with adenosine (72 +/- 5% before PTCA versus 64 +/- 6% during angioplasty) than it was for the control group (71 +/- 7% before PTCA versus 60 +/- 7% during angioplasty; P = 0.11).

CONCLUSIONS

Intracoronary application of adenosine prior to coronary angioplasty increases tolerance of ischemia and prevents deterioration of left ventricular hemodynamics during ischemia. One potential explanation of these results is that induction of ischemic preconditioning took place.

Adjunctive intracoronary dipyridamole in the interventional treatment of small coronary arteries: a prospectively randomized trial

BACKGROUND

Patients undergoing intracoronary stent placement or balloon angioplasty for the treatment of small coronary arteries are at an increased risk of an adverse outcome from a higher incidence of abrupt closure and restenosis. Intracoronary thrombus formation plays a key role in the pathogenesis of abrupt vessel closure and of restenosis. Dipyridamole prevents platelet aggregation by a mechanism that differs from aspirin. The purpose of this study was to investigate the effect of intracoronary dipyridamole on acute complications and restenosis after percutaneous transluminal coronary angioplasty.

METHODS

In a prospectively randomized study including 491 dilatations of coronary arteries with a diameter <2.75 mm, additional intracoronary application of dipyridamole was compared with conventional pretreatment consisting of heparin and aspirin. Study end points were defined as incidence of abrupt vessel closure, myocardial infarction, angiographic restenosis, and target vessel revascularization rate.

RESULTS

Intracoronary dipyridamole was associated with a significant reduction of abrupt vessel closure (2.8% vs 8.6%; P =.005) and a nonsignificant reduction of myocardial infarction (1.6% vs 4.5%; P =.07) after percutaneous transluminal coronary angioplasty. Net gain 6 months after angioplasty was significantly higher in the dipyridamole group (0.60 +/- 0.35 mm vs 0.42 +/- 0.34 mm; P <.001). However, dipyridamole failed to reduce the incidence of angiographic restenosis (41.6% vs 49.1%; P =.11) and target vessel revascularization rate (20.6% vs 269%; P =.12).

CONCLUSIONS

Intracoronary dipyridamole reduces the incidence of adverse cardiovascular events in the first 48 hours after balloon angioplasty of small coronary arteries. Reduction of restenosis rates failed to reach statistical significance. However, a significant increase in net gain was observed. Thus intracoronary application of dipyridamole should be considered in the treatment of small coronary arteries when intracoronary stenting is not appropriate.

Intracoronary dipyridamole reduces the incidence of abrupt vessel closure following PTCA: a prospective randomised trial

OBJECTIVES

To investigate the effect of intracoronary dipyridamole on the incidence of abrupt vessel closure, myocardial infarction, necessity for bypass grafting, and death following percutaneous transluminal coronary angioplasty (PTCA).

PATIENTS

Patients were randomly allocated to receive either conventional pretreatment (heparin 15 000 IU and aspirin 500 mg intravenously) or additional intracoronary dipyridamole (0.5 mg/kg bodyweight). Dipyridamole was administered in 550 PTCA procedures (455 interventions in men, mean (SD) age 59.2 (8.4) years; 74 acute coronary syndromes), while conventional pretreatment was administered in 544 interventions (444 interventions in men 58.3 (7.9) years old; 81 acute coronary syndromes). In 53 interventions bail out stenting was performed for threatened abrupt vessel closure.

RESULTS

Intracoronary dipyridamole significantly reduced the incidence of abrupt vessel closure (odds ratio 0.42. 95% confidence interval (CI) 0.22 to 0.79). While abrupt vessel closure occurred in 6.1% of interventions following conventional pretreatment, dipyridamole reduced the incidence to 2.5%. Restricting the analysis to balloon angioplasty, this reduction was observed in patients with stable angina (odds ratio 0.49, 95% CI 0.23 to 0.96) as well as in those with acute coronary syndromes (odds ratio 0.29, 95% CI 0.09 to 0.87). Reduction of secondary end points in the dipyridamole treated patients failed to reach significance in the PTCA group.

CONCLUSIONS

Intracoronary dipyridamole before PTCA reduces the incidence of abrupt vessel closure following PTCA for stable angina and acute coronary syndromes.

Antiarrhythmic efficacy of dipyridamole in treatment of reperfusion arrhythmias : evidence for cAMP-mediated triggered activity as a mechanism responsible for reperfusion arrhythmias

BACKGROUND

Intracellular calcium overload is believed to play an important role in development of reperfusion arrhythmias. Dipyridamole, an inhibitor of cellular uptake of adenosine, may prevent or terminate reperfusion arrhythmias by reducing intracellular calcium overload.

METHODS AND RESULTS

First, we tested for a preventive effect of dipyridamole. Sixty-one patients who underwent primary PTCA for treatment of acute anterior wall myocardial infarction were enrolled in this prospective study. Patients were divided into dipyridamole (DP) and nondipyridamole (non-DP) groups. The 2 groups had similar baseline characteristics. In the DP group, dipyridamole 0.5 mg/kg was infused intravenously for 3 minutes immediately before reperfusion during primary PTCA. Arrhythmias after reperfusion were analyzed from continuous ECG recordings. None of the patients in the DP group (n=23) had accelerated idioventricular rhythms (AIVR) or ventricular tachycardia (VT). In contrast, 7 (18.4%) had AIVR and 3 (7.9%) had VT in the non-DP group (n=38; P<0.01). Second, we tested for a termination effect of dipyridamole. Dipyridamole 0.5 mg/kg was infused intravenously while continuous ECG recordings were obtained in 9 patients who had either sustained AIVR (n=7) or sustained VT (n=2) after reperfusion of occluded coronary artery. Arrhythmias were terminated in all patients.

CONCLUSIONS

These results indicate that administration of dipyridamole can prevent and terminate reperfusion arrhythmias such as AIVR and VT. cAMP-mediated triggered activity may, at least in part, be responsible for reperfusion-induced AIVR and VT.

Low-dose dipyridamole infusion acutely increases exercise capacity in angina pectoris: a double-blind, placebo controlled crossover stress echocardiographic study

OBJECTIVES

The aim of this study was to assess whether endogenous accumulation of adenosine, induced by low-dose dipyridamole infusion, protects from exercise-induced ischemia.

BACKGROUND

Adenosine is a recognized mediator of ischemic preconditioning in experimental settings.

METHODS

Ten patients (all men: mean age 63.4 +/- 7.3 years) with chronic stable angina, angiographically assessed coronary artery disease (n = 7) or previous myocardial infarction (n = 3) and exercise-induced ischemia underwent on different days two exercise-stress echo tests after premedication with placebo or dipyridamole (15 mg in 30 min, stopped 5 min before testing) in a double-blind, placebo controlled, randomized crossover design.

RESULTS

In comparison with placebo, dipyridamole less frequently induced chest pain (20% vs. 100%, p = 0.001) and >0.1 mV ST segment depression (50% vs. 100%, p < 0.05). Wall motion abnormalities during exercise-stress test were less frequent (placebo = 100% vs. dipyridamole = 70%, p = ns) and significantly less severe (wall motion score index at peak stress: placebo = 1.55 +/- 0.17 vs. dipyridamole = 1.27 +/- 0.2, p < 0.01) following dipyridamole, which also determined an increase in exercise time up to echocardiographic positivity (placebo = 385.9 +/- 51.4 vs. dipyridamole = 594.4 +/- 156.9 s, p < 0.01).

CONCLUSIONS

Low-dose dipyridamole infusion increases exercise tolerance in chronic stable angina, possibly by endogenous adenosine accumulation acting on high affinity A1 myocardial receptors involved in preconditioning or positively modulating coronary flow through collaterals.

Chronic dipyridamole therapy produces sustained protection against cardiac ischemia-reperfusion injury

Sustained protection against ischemia-reperfusion injury is not available for patients at risk for myocardial infarction who may require emergent reperfusion therapy. Whereas ischemic preconditioning and adenosinergic agents reduce myocardial injury, they are only effective when given immediately before ischemia or reperfusion. We recently found chronic ethanol exposure, an adenosine uptake inhibitor, produced sustained cardioprotection against ischemia-reperfusion injury. We now ask whether chronic dipyridamole therapy, a clinically usable nucleoside transport inhibitor, induces similar cardioprotection. Perfused hearts from guinea pigs, given dipyridamole (4 mg. kg(-1). day(-1)) in their water for 2-6 wk (n = 10 for each group), underwent ischemia-reperfusion. Injury was assessed by recovery of left ventricular developed (LVDP) and end-diastolic (LVEDP) pressures and creatine kinase release. During reperfusion, hearts from dipyridamole-treated animals (6 wk) had 74% higher LVDP, 28% lower LVEDP, and 61% lower creatine kinase release versus controls. Adenosine A(1)-receptor antagonism (8-cyclopentyl-1, 3-dipropylxanthine; 200 nM) abolished the protection of dipyridamole but A(2) antagonism (3,7-dimethyl-1-propargylxanthine; 10 mM) did not. Dipyridamole therapy produces sustained protection against ischemia-reperfusion injury in guinea pigs. This cardioprotection requires adenosine A(1) receptor signaling at the time of ischemia.

Clinical effects of ischemic preconditioning

A variety of experimental studies have confirmed that preconditioning the myocardium by brief periods of ischemia represents a powerful cardioprotective effect resulting in a reduction of infarct size. After 15 years of research in the experimental laboratory, some evidence shows the existence of preconditioning in human patients with coronary artery disease: repeated balloon inflations before coronary angioplasty induce preconditioning-like effects; moreover, some studies demonstrate better clinical outcome in patients with angina before acute myocardial infarction, resembling a preconditioning effect. So far, a few drugs have been identified as potential mediators of preconditioning, e.g., adenosine, adenosine receptor agonists, and adenosine triphosphate-sensitive potassium channel openers. Before coronary angioplasty and heart surgery, these preconditioning mimetics might be used to protect myocardial tissue by means of preconditioning. Further research is required before preconditioning mimetics could be used for therapy in patients with chronic myocardial ischemia. Possible antipreconditioning effects of several drugs, e.g., sulfonylurea drugs have to be considered in the treatment of patients with coronary artery disease.

Beneficial impact of preconditioning during PTCA on creatine kinase release

BACKGROUND

Previous studies in humans have indicated that there is less ischemic dysfunction during PTCA when ischemic preconditioning is elicited. However, the clinical relevance of these observations remains unclear. The present study design tests the hypothesis that PTCA performed to elicit the preconditioning response would result in less myocardial necrosis as assessed by postprocedure creatine kinase (CK) levels.

METHODS AND RESULTS

Patients (n=150) undergoing PTCA for unstable ischemic syndromes were randomly assigned to receive a previously validated approach to PTCA-mediated preconditioning (PC) or an unrestricted approach to balloon angioplasty (UC). CK levels were determined at 8, 12, and, if necessary, 24 hours. Clinical success rates were equivalent for the 2 groups. However, the frequency of any CK elevation was significantly higher in the UC group (25%) than in the PC group (7. 1%) (P<0.005). Multivariable analysis confirmed a significant effect of preconditioning on CK release.

CONCLUSIONS

A standardized protocol to elicit preconditioning during PTCA results in a significant reduction in the rate of CK elevation in a high-risk population. These observations support the clinical relevance of ischemic preconditioning in humans.

Ischemic preconditioning: exploring the paradox

Brief transient episodes of nonlethal myocardial ischemia protect or "precondition" the heart and render the myocardium resistant to a subsequent more sustained ischemic insult. The hallmark of this phenomenon--documented in virtually all species and experimental models evaluated to date in countless laboratories worldwide--is the profound reduction in infarct size seen in preconditioned groups versus time-matched controls. Efforts to identify the cellular mechanisms responsible for this paradoxical ischemia-induced cardioprotection, to expand the definition of ischemic preconditioning beyond infarct size reduction, and, perhaps most importantly, to evaluate the efficacy of preconditioning in disease models and in the clinical setting, are all topics of intensive ongoing investigation.

Ischemic preconditioning in unstable coronary syndromes: evidence for time dependence

OBJECTIVES

We hypothesized a time-dependent relation between angina occurring spontaneously before percutaneous transluminal coronary angioplasty (PTCA) and the likelihood of an ischemic response during initial balloon occlusion. We further hypothesized that the ability to elicit the "classic" mode of PTCA-related preconditioning would vary with the interval from clinical angina to PTCA.

BACKGROUND

Antecedent angina represents a potential for myocardial preconditioning in unstable ischemic coronary syndromes.

METHODS

We studied 67 patients with Braunwald class III unstable coronary syndromes undergoing PTCA. The interval between the last spontaneous episode of angina preceding PTCA and initial balloon inflation was categorized as follows: 0 to 6 h; 6 to 12 h; 12 to 24 h; and >24 h.

RESULTS

Across the various intervals, there was a significant difference (p = 0.004) in the proportion of patients with an absent ischemic response during the first balloon inflation (0 to 6 h, 50%; 6 to 12 h, 35%; 12 to 24 h, 23%; and >24 h, 4%). There was, however, no difference between the first and second inflations in the proportion of patients with a diminished ischemic response until 6 to 12 h (p = 0.017) had elapsed since the last spontaneous episode of angina. Patients whose angina last occurred >24 h before the first inflation showed the greatest inducibility of PTCA-related preconditioning.

CONCLUSIONS

Strong evidence exists for the occurrence of ischemic preconditioning in unstable coronary syndromes. Although the protective effect of spontaneous angina appears to wane beyond 6 h, recovery of preconditioning occurs from 6 to 12 h. Thus, preconditioning can be reinduced during PTCA with a marked potentiation of the effect at 24 h. This suggests an underlying time-dependent mechanism with a physiologic "half-life" of 6 to 12 h.