Time course of "warm-up" in stable angina

Exercise-induced ischemic preconditioning and the potential application to cardiac rehabilitation: a systematic review

Exercise-induced ischemic preconditioning (IPC) can be assessed by the results of the second of sequential exercise tests. Exercise-induced IPC is quantified by using the time to 1-mm ST-segment depression, the rate-pressure product at 1-mm ST-segment depression, the maximal ST-segment depression, and the rate-pressure product at the peak of exercise. Few studies reported whether exercise-induced IPC could be used in cardiovascular rehabilitation. A systematic review of the literature limited to human studies was performed using electronic databases, and the main key words were ischemic preconditioning, warm-up phenomenon, and exercise. After careful review, 38 articles were included in the systematic review. This review summarizes the molecular pathways of IPC and describes the first window of protection induced by sequential exercise tests, as well as the effect of medication on exercise-induced IPC. A section on the exercise protocol, mode of exercise, and intensity provides understanding as to what is needed for clinicians to induce IPC with sequential stress tests. The final section of the review is a discussion of the potential use of exercise-induced IPC in a cardiovascular rehabilitation setting. Even if exercise-induced IPC is a well-documented phenomenon, additional studies are needed in order to more fully understand its use in rehabilitation.

Role of Trimetazidine in Ischemic Preconditioning in Patients With Symptomatic Coronary Artery Disease

Ischemic preconditioning (IP) is a powerful cardioprotective cellular mechanism that has been related to the "warm-up phenomenon" or "walk-through" angina, and has been documented through the use of sequential exercise tests (ETs). It is known that several drugs, for example, cromokalim, pinacidil, adenosine, and nicorandil, can interfere with the cellular pathways of IP. The purpose of this article is to report the effect of the anti-ischemic agent trimetazidine (TMZ) on IP in symptomatic coronary artery disease (CAD) patients.We conducted a prospective study evaluating IP by the analysis of ischemic parameters in 2 sequential ETs. In phase I, without TMZ, patients underwent ET1 and ET2 with a 30-minute interval between them. In phase II, after 1 week of TMZ 35 mg twice daily, all patients underwent 2 consecutive ETs (ET3 and ET4). IP was considered present when the time to 1.0-mm segment ST on electrocardiogram deviation (T-1.0 mm) and rate pressure product (RPP) were greater in the second of 2 tests. The improvement in T-1.0 mm and RPP were compared in the 2 phases: without TMZ and after 1-week TMZ to assess the action of such drug in myocardial protective mechanisms. ETs were analyzed by 2 independent cardiologists.From 135 CAD patients screened, 96 met inclusion criteria and 62 completed the study protocol. Forty patients manifested IP by demonstrating an improvement in T-1.0 mm in ET2 compared with ET1, without the use of any drugs (phase I). In phase II, after 1-week TMZ, 26 patients (65%) did not show any incremental result in ischemic parameters in ET4 compared with ET3. Furthermore, of these patients, 8 (20%) had IP blockage.In this study, TMZ did not add any benefit to IP in patients with stable symptomatic CAD.

Effect of hypoglycemic agents on ischemic preconditioning in patients with type 2 diabetes and symptomatic coronary artery disease

OBJECTIVE

To assess the effect of two hypoglycemic drugs on ischemic preconditioning (IPC) patients with type 2 diabetes and coronary artery disease (CAD).

RESEARCH DESIGN AND METHODS

We performed a prospective study of 96 consecutive patients allocated into two groups: 42 to group repaglinide (R) and 54 to group vildagliptin (V). All patients underwent two consecutive exercise tests (ET1 and ET2) in phase 1 without drugs. In phase 2, 1 day after ET1 and -2, 2 mg repaglinide three times daily or 50 mg vildagliptin twice daily was given orally to patients in the respective group for 6 days. On the seventh day, 60 min after 6 mg repaglinide or 100 mg vildagliptin, all patients underwent two consecutive exercise tests (ET3 and ET4).

RESULTS

In phase 1, IPC was demonstrated by improvement in the time to 1.0 mm ST-segment depression and rate pressure product (RPP). All patients developed ischemia in ET3; however, 83.3% of patients in group R experienced ischemia earlier in ET4, without significant improvement in RPP, indicating the cessation of IPC (P < 0.0001). In group V, only 28% of patients demonstrated IPC cessation, with 72% still having the protective effect (P < 0.0069).

CONCLUSIONS

Repaglinide eliminated myocardial IPC, probably by its effect on the KATP channel. Vildagliptin did not damage this protective mechanism in a relevant way in patients with type 2 diabetes and CAD, suggesting a good alternative treatment in this population.

Effect of low doses of alcohol on the warm-up phenomenon in patients with stable angina pectoris

Experimental studies suggest that alcohol may have protective effects similar to that of ischemic preconditioning (IPC). The acute effects of alcohol on IPC in humans, however, are poorly known. In this study, we assessed the effect of alcohol administration on the warm-up phenomenon, as an expression of IPC, in patients with stable coronary artery disease (CAD). We randomized 45 stable CAD patients with positive (ST-segment depression > or =1 mm) exercise stress test to 1 of 3 groups of 15 patients each: (1) group 1 = 60 cc of gin (18.5 g of ethanol); (2) group 2 = 180 cc of red wine (18.9 g of ethanol); and (3) group 3 = placebo (120 cc of water). A first exercise test was performed 15 minutes after beverage administration. In those with a positive exercise test (13, 14, and 14 patients in the gin, wine, and placebo groups, respectively), a second exercise test was performed 15 minutes after the end of the first one. On the first test, there were no differences among groups in rate pressure product and time of exercise at 1-mm ST-segment depression, as well as in maximal ST segment depression. Furthermore, an improvement of the ischemic exercise variables was observed in each group, without any statistically significant differences among them. In conclusion, our data show that, in stable CAD patients, the acute intake of low doses of alcohol does not significantly influence IPC, as expressed by the warm-up phenomenon on exercise stress testing.

The effects of glibenclamide, a K(ATP) channel blocker, on the warm-up phenomenon

BACKGROUND

The warm-up phenomenon observed after the second of two sequential exercise tests is characterized by an increased time to ischemia and ischemic threshold, and the latter is related to ischemic preconditioning. Previous studies have demonstrated that a single dose of glibenclamide, a cardiac ATP-sensitive K (K(ATP)) channel blocker, prevents ischemic preconditioning. This study aimed to investigate the effects of chronic treatment with glibenclamide during two sequential exercise tests.

METHODS

Forty patients with angina pectoris were divided into three groups: 20 nondiabetics (NDM), 10 patients with diabetes in treatment with glibenclamide (DMG) and 10 diabetic patients with other treatments (DMO). All patients underwent two consecutive exercise tests.

RESULTS

Heart rate and rate-pressure product at 1.0 mm ST-segment depression significantly increased during the second exercise test in NDM group (121.3+/-16.5 vs 127.3+/-15.3 beats/min, P<0.001, and 216.7+43.1 vs 232.1+/-43.0 beats.min-1.mmHg.10(2), P<0.001), and in DMO group (114.1+/-19.6 vs 119.6+/-18.1 beats/min, P=0.001, and 199.8+/-36.6 vs 222.2+/-29.2 beats.min-1.mmHg.10(2), P=0.019), but it did not change in patients in DMG group (130.7+/-14.5 vs 132.1+/-4.7 beats/min, P=ns, and 251.7+/-47.2 vs 250.3+/-42.8 beats.min-1.mmHg.10(2), P=ns). In the three groups, NDM, DMO, and DMG, the time to 1.0 mm ST-segment depression during the second exercise test was greater than during the first (225.0+/-112.5 vs 267.0+/-122.3 seconds, P=0.006; 187.5+/-54.0 vs 226.5+/-74.6 seconds, P=0.029 and 150.0+/-78.7 vs 186.0+/-81.9 seconds, P<0.001).

CONCLUSION

The chronic use of glibenclamide may have mediated the loss of preconditioning benefits in the warm-up phenomenon, probably through its KATP channel-blocker activity, but without acting upon the tolerance to exercise.

Effects of warm-up on exercise capacity, platelet activation and platelet-leucocyte aggregation in patients with claudication

BACKGROUND

The effects of exercise and warm-up were investigated in patients with claudication.

METHODS

This case-control crossover study involved two treadmill exercise tests, one preceded by a warm-up. Exercise continued until maximal leg pain (patients with claudication) or exhaustion (controls). Blood was taken before, and 5 and 60 min after exercise for flow cytometric analysis of platelet activation and platelet-leucocyte aggregation.

RESULTS

Both cohorts (eight patients with claudication of median age 63 years and eight healthy controls of median age 63.5 years) demonstrated improvement in exercise capacity after warm-up (13.1 per cent, P = 0.012 and 15.6 per cent, P = 0.008 respectively). Platelet activation increased after exercise in patients with claudication (fibrinogen binding: 1.11 per cent before exercise versus 2.63 per cent after exercise, P = 0.008; P-selectin: 0.68 versus 1.11 per cent, P = 0.028). Neither agonist stimulation nor warm-up altered this trend. Platelet-leucocyte (PLA) and platelet-neutrophil (PNA) aggregation were similarly increased immediately after exercise in patients with claudication (PLA: 7.6 versus 13.0 per cent, P = 0.004; PNA: 6.8 versus 10.2 per cent, P = 0.012). These remained high 60 min after exercise only in patients with claudication, but recovered to baseline levels when preceded by warm-up. Warm-up significantly desensitized PNA after stimulation with 10 micromol/l adenosine 5'-diphosphate at all time points.

CONCLUSION

Warm-up increased the exercise capacity of patients with claudication. Exercise induced a thromboinflammatory response, with PLA and PNA persistently increased after 60 min in patients with claudication, an effect diminished after warm-up.

Preconditioning the Myocardium: From Cellular Physiology to Clinical Cardiology

Yellon, Derek M., and James M. Downey. Preconditioning the Myocardium: From Cellular Physiology to Clinical Cardiology. Physiol Rev 83: 1113-1151, 2003; 10.1152/physrev.00009.2003.—The phenomenon of ischemic preconditioning, in which a period of sublethal ischemia can profoundly protect the cell from infarction during a subsequent ischemic insult, has been responsible for an enormous amount of research over the last 15 years. Ischemic preconditioning is associated with two forms of protection: a classical form lasting ∼2 h after the preconditioning ischemia followed a day later by a second window of protection lasting ∼3 days. Both types of preconditioning share similarities in that the preconditioning ischemia provokes the release of several autacoids that trigger protection by occupying cell surface receptors. Receptor occupancy activates complex signaling cascades which during the lethal ischemia converge on one or more end-effectors to mediate the protection. The end-effectors so far have eluded identification, although a number have been proposed. A range of different pharmacological agents that activate the signaling cascades at the various levels can mimic ischemic preconditioning leading to the hope that specific therapeutic agents can be designed to exploit the profound protection seen with ischemic preconditioning. This review examines, in detail, the complex mechanisms associated with both forms of preconditioning as well as discusses the possibility to exploit this phenomenon in the clinical setting. As our understanding of the mechanisms associated with preconditioning are unravelled, we believe we can look forward to the development of new therapeutic agents with novel mechanisms of action that can supplement current treatment options for patients threatened with acute myocardial infarction.

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.

What induces the warm-up ischemia/angina phenomenon: exercise or myocardial ischemia?

BACKGROUND

The relation of the warm-up ischemia phenomenon to the presence and intensity of initial myocardial ischemia is unclear. We sought to determine whether the warm-up ischemia phenomenon requires initial myocardial ischemia or can be induced by exercise without ischemia and whether there is a relation between the intensity of initial ischemia and the attenuation of ischemia on reexercise.

METHODS AND RESULTS

Twelve subjects with exertional myocardial ischemia performed 2 exercise ECG tests (1 and 2) at a +/-10-minute interval on 3 occasions (A, B, C) 1 month apart. A1 and A2 were symptom-limited. B1 was kept as long as A1, but its intensity was held under the ischemic threshold (heart ratexsystolic pressure at 1-mm ST depression [STD]) noted at A1. B2 was symptom-limited. C1 was also kept as long as A1 but with an intensity adjusted to maintain one-half maximum STD of A1. C2 was symptom-limited. Exercise duration of A2, B2, and C2 increased similarly compared with A1 (P=0.009). However, the ischemic threshold (x10-3) increased at A2 (23.5+/-6.0) compared with A1 (20.3+/-4.8; P<0.0001) but not at B2 (19.8+/-5.0) or C2 (21.5+/-5.8). Similarly, maximum STD adjusted to the highest heart rate-systolic pressure product common to A1, A2, B2, and C2 decreased at A2 (1.4+/-0.7 mm) compared with A1 (2.5+/-0.9 mm; P<0.0001) but not at B2 (2.7+/-0.9 mm) or C2 (2.3+/-0.9 mm).

CONCLUSIONS

Exercises under the ischemic threshold and of intermediate ischemic intensity increase short-term exercise capacity, but myocardial ischemia of more than moderate intensity is needed to induce the warm-up ischemia phenomenon.

Evidence that stunning can be cumulative in man

Myocardial stunning and hibernation are two entities that have become increasingly recognised as clinically important causes of reversible left ventricular (LV) dysfunction. Their occurrence is important as resting myocardial dysfunction, which was once thought to be irreversible, may recover if ischaemia is lessened or abolished. Recent evidence has suggested that cumulative stunning can occur in man and may in fact be responsible for the phenomenon of hibernation. In this chapter we will review the evidence supporting the occurrence of cumulative stunning in man.

Characterization of the warm-up phenomenon in patients with coronary artery disease

BACKGROUND

The warm-up phenomenon, that is, attenuation of myocardial ischemia during repeated physical exercise, has been demonstrated in numerous studies. However, its duration and underlying factors have not been properly studied in patients with coronary artery disease.

METHODS

Fifty-two patients with stable angina pectoris and previous positive stress testing underwent cardiac catheterization and 2 successive exercise tests randomly separated by resting periods of 15, 30, 60, or 120 minutes (groups 1-4).

RESULTS

The percentage of patients demonstrating the warm-up phenomenon was 85%, 31%, 31%, and 46% in groups 1 through 4, respectively (P =.018). The differences in the parameters (test 2 to test 1) registered during exercise tests were 28.1 +/- 7.1, 3.5 +/- 5.8, -4.9 +/- 4.8, and 4.9 +/- 5.1 (P =.003) for the double product (beats/min x mm Hg. 100) at 0.1 mV ST depression; 1.1 +/- 0.2, 0.2 +/- 0.2, 0.2 +/- 0.2, and 0.2 +/- 0.2 (P =.004) for the time (min) to 0.1 mV ST depression; -3.4 +/- 1.2, 0.5 +/- 0.7, -0.3 +/- 0.8, and -0.3 +/- 0.3 (P =.032) for the ST/HR-slope (microV/beats/min); and -0.3 +/- 0.2, 0.1 +/- 0.1, -0.1 +/- 0.1, and -0.7 +/- 0.4 (P =.047) for the ischemic burden (mV x min) in groups 1 through 4, respectively. The patients having angiographically less severe disease showed significantly better ischemia adaptation (P =.012), but there was no correlation between the extent of adaptation and other clinical or angiographic findings.

CONCLUSIONS

The warm-up phenomenon is commonly encountered in patients with coronary artery disease, although the protection appears to wane relatively quickly. The adaptation appears to be markedly better in patients with less severe disease.

Preconditioning - endogenous defence mechanisms of the heart

The term 'preconditioning' refers to the paradoxical phenomenon that pretreatment with a potential noxious stress-stimulus can increase cellular tolerance to subsequent noxious stress-stimuli. This was first described in an experimental model in dogs in which short-lasting periods of myocardial ischemia resulted in reduced infarction during a subsequent long-lasting coronary artery occlusion. Similar observations have also been made in other species and in other organs. During the last few years, the term preconditioning has been expanded to include pretreatment with other physical stress-stimuli or pharmacological agents that can increase cellular resistance to injury. The phenomenon probably represents a general adaptive response to cellular stress, but mechanisms involved are not fully clarified. This review focuses on preconditioning in the heart. Firstly, we want to address the observation that activation of endogenous defence mechanisms can increase cellular tolerance to several potentially noxious stimuli. Based on results from experimental research, we will give an overview of intracellular mechanisms that is currently in focus. Secondly, we want to address the potential role of preconditioning in clinical practice. We will present results from studies in patients with coronary artery disease and discuss possible clinical implications. Results show that the phenomenon probably exists in the human myocardium. In the future, this might be exploited in patients with acute coronary syndromes, especially since advanced techniques are now available for acute revascularization. Additionally, identification of possible mechanisms involved may influence the choice of medical treatment in high-risk patients with stable coronary artery disease. Preconditioning can also be exploited during elective surgical procedures. This should be of great interest, as the extent of elective surgery in patients at high-risk for coronary events is increasing. In this respect it is important to note that opioid-receptors are probably involved in preconditioning in humans. The last part of this review will address the possible relation between preconditioning and different anesthetic agents and sedatives.

Myocardial perfusion imaging findings and the role of adenosine in the warm-up angina phenomenon

OBJECTIVES

This study examined the roles of myocardial perfusion and adenosine in warm-up angina.

BACKGROUND

In warm-up angina, neither the role of an adenosine-mediated mechanism, as is found in experimental ischemic preconditioning, nor of increased myocardial perfusion is well defined.

METHODS

In substudy A, a single-photon emission computed tomography (SPECT)-thallium-201 exercise test was performed by 12 subjects with ischemic heart disease on three occasions one week apart. The third test was preceded by a warm-up test. The extent of the thallium deficit and its intensity on the third test were compared with the baseline tests controlling for the heart rate-systolic blood pressure product (RPP) at thallium injection. In substudy B, 12 similar subjects did two successive exercise tests at two separate sessions and received the adenosine antagonist, aminophylline (intravenous 5 mg/kg bolus and 0.9 mg/kg/h infusion) at one session, and equivalent saline at the other session. Change in ischemic threshold (RPP at 1 mm ST segment depression) and in maximum ST depression adjusted for RPP were analyzed.

RESULTS

In substudy A, despite a significant attenuation of electrocardiogram indexes of myocardial ischemia between the baseline and third (warmed-up) tests, the thallium extent deficits (20.8 +/- 15.1% and 16.8 +/- 12.4%) and intensity deficits (41.2 +/- 12.6% and 39.3 +/- 12.6%) did not differ significantly. In substudy B, the increase in ischemic threshold on re-exercise was unaffected by aminophylline. Adjusted maximum ST depression even decreased to a greater extent on re-exercise with aminophylline (by 51 +/- 21%) than with saline (by 32 +/- 19%) (p = 0.012).

CONCLUSIONS

While warm-up angina is associated with a significant attenuation of exercise electrocardiogram indexes of ischemia, it is unaccompanied by significant changes in SPECT perfusion and does not appear to be mediated by an adenosine-dependent mechanism since it is not blocked by aminophylline. Thus, its mechanism, which appears distinct from experimental ischemic preconditioning, remains unidentified.

The preconditioning phenomenon: A tool for the scientist or a clinical reality?

The possibility that an innate mechanism of myocardial protection might be inducible in the human heart has generated considerable excitement and enthusiastic research. The potential to enhance myocardial resistance to ischemic injury in patients suffering the consequences of coronary artery disease has led to studies with more direct clinical relevance. However, in common with many other areas of clinical interest based on advances in basic scientific understanding, early enthusiasm may be disproportionate to ultimate therapeutic significance. There can be little doubt that our understanding of the mechanisms underlying the pathogenesis of ischemia-reperfusion injury has been enhanced significantly by the plethora of research stimulated by interest in endogenous myocardial protection. Direct extrapolation of observations in the laboratory to the cardiology clinic or operating theater is tempting but should be avoided. The results of recent clinical experiments that suggest that preconditioning can protect against ischemia, although encouraging, should be interpreted cautiously, with particular attention to the limitations of the end points available. A reasoned evaluation of recent research should prevent unrealistic expectations and allow improved design of future trials so that this potent adaptive phenomenon can be exploited to its maximum potential.

Collateral recruitment and "warm-up" after first exercise in ischemic heart disease

BACKGROUND

Proposed mechanisms for "warm-up" after angina on first exercise include ischemic preconditioning and collateral recruitment. The aim of this study was to determine whether patients with ischemic heart disease and well-developed coronary collateral vessels have a greater warm-up response than those with no visible collateral vessels.

METHODS AND RESULTS

Fifteen patients with a total coronary occlusion and collateral vessels and 18 patients with a single coronary artery stenosis and no angiographically visible collateral vessels were studied. Warm-up was measured as the difference in ST depression on the second compared with the first of 2 sequential treadmill exercise tests separated by 10 minutes of rest. There was a trend for the duration of second exercise to increase more in patients with occlusion than in those with stenosis (+1.3 vs +0.54 minutes, respectively, P =.087). In both groups, ST depression was less on second exercise than on first exercise. The size of this decrease was greater in the occlusion group than in the stenosis group. ST depression at equivalent submaximal exercise decreased by 0.52 vs 0.19 mm, respectively (P =.049). The rate of increase in ST depression during exercise decreased by 1.08 versus 0. 55 mm/min, respectively (P =.034). These differences were less after adjustment for ST depression on first exercise (P =.11 and P =.063, respectively).

CONCLUSIONS

The trend for a greater decrease in ST depression on second compared with first exercise in the patients with total coronary occlusion suggests that an increase in collateral flow is a mechanism for warm-up after first exercise in ischemic heart disease.

Relation between duration and intensity of first exercise and "warm up" in ischaemic heart disease

OBJECTIVE

To determine the importance of the duration and intensity of "warm up" exercise for reducing ischaemia during second exercise in patients with exertional angina.

DESIGN

Randomised crossover comparison of three warm up exercise protocols.

PATIENTS

18 subjects with stable ischaemic heart disease and > 0.1 mV ST segment depression on treadmill exercise testing.

INTERVENTIONS

The warm up protocols were 20 minutes of slow exercise at 2.7 km/h, symptom limited graded exercise for a mean of 7.4 (range 5.0 to 10.5) minutes, and three minutes of symptom limited fast exercise of similar maximum intensity.

MAIN OUTCOME MEASURES

ST segment depression during graded treadmill exercise undertaken 10 minutes after each warm up protocol or no warm up exercise.

RESULTS

Compared with exercise with no warm up, the duration of graded exercise after earlier slow warm up increased by 4.9% (95% confidence interval (CI), -3.3% to 13.7%), after graded warm up by 10.3% (95% CI, 5.6% to 15.2%), and after fast warm up by 16% (95% CI, 6.2% to 26.7%). ST segment depression at equivalent submaximal exercise decreased after slow warm up by 27% (95% CI, 5% to 44%), after graded warm up by 31% (95% CI, 17% to 44%), and after fast warm up by 47% (95% CI, 27% to 61%). Compared with slow warm up exercise, the more intense graded and fast warm up protocols significantly increased the duration of second exercise (p = 0.0072) and reduced both peak ST depression (p = 0.0026) and the rate of increase of ST depression (p = 0.0069).

CONCLUSIONS

In patients with exertional angina the size of the warm up response is related to the maximum intensity rather than the duration of first exercise.

Effect of repetitive episodes of exercise induced myocardial ischaemia on left ventricular function in patients with chronic stable angina: evidence for cumulative stunning or ischaemic preconditioning?

BACKGROUND

Myocardial stunning is known to occur following a single episode of effort angina in patients with coronary artery disease. The effect on left ventricular (LV) function of repeated episodes of ischaemia is unknown.

OBJECTIVES

To investigate the effects of repeated episodes of exercise induced ischaemia on LV function in patients with chronic stable angina.

METHODS

Patients with significant coronary artery disease and normal LV function underwent two episodes of symptom limited treadmill exercise separated by three different time intervals: either 30 minutes (group A, n = 14); 60 minutes (group B, n = 14); or 240 minutes (group C, n = 14). Quantitative stress echocardiography was performed at repeated intervals between the two exercises and for 240 minutes following the second test.

RESULTS

For all groups there was no difference between the degree of ischaemia judged by maximal ST depression during the two tests. All episodes of exercise induced ischaemia produced prolonged abnormalities of LV systolic and diastolic function despite rapid normalisation of haemodynamic and ECG changes. In group A (30 minutes) these abnormalities were less pronounced after the second test than after the first, while in group B (60 minutes) they were more severe and long lasting. In group C (240 minutes) the two tests produced similar abnormalities of LV function.

CONCLUSIONS

Prolonged abnormalities of LV function occurred following exercise induced ischaemia with a time course consistent with myocardial stunning. The severity and degree of LV dysfunction caused by a further episode of ischaemia appear to be dependent on the time interval between ischaemic episodes.

Exercise-induced myocardial ischemia triggers the early phase of preconditioning but not the late phase

The aim of the present study was to establish whether exercise-induced ischemia triggers the second window of protection in 15 patients with coronary artery disease undergoing 2 consecutive treadmill exercise tests and a third test 24 hours later. Our findings confirm that a first exercise-induced ischemic challenge induces the early phase of preconditioning but not the late phase, thus suggesting that either a late protective effect of preconditioning does not exist in the setting of demand ischemia or, if it exists, it must be weaker than the early protective effect.

Attenuation of myocardial ischemia with repeated exercise in subjects with chronic stable angina: relation to myocardial contractility, intensity of exercise and the adenosine triphosphate-sensitive potassium channel

OBJECTIVES

This study characterized the attenuation of myocardial ischemia observed with re-exercise to determine whether: 1) a differing exercise intensity modifies this attenuation; 2) it could be explained by contractile down-regulation or stunning; 3) it is mediated by activation of ATP-sensitive potassium channels (K+-ATP).

BACKGROUND

Subjects with ischemic heart disease (IHD) frequently note less angina with re-exercise after a brief rest. Potential mechanisms of this 'warm-up' phenomenon have been little explored.

METHODS

IHD subjects with a positive exercise test were studied. Groups I and II (12 subjects each) underwent 2 successive Naughton protocol exercise echocardiography tests (with 1 min instead of 2 min stages for Group II). Group D (10 subjects) had type II diabetes, were on > or =10 mg daily of the K+-ATP blocker, glibenclamide, and underwent the group I exercise protocol. The ischemic threshold or rate-pressure product at 1 mm ST segment depression, ST depression corresponding to the peak rate-pressure product of the first exercise (maximum ST depression equivalent), and left ventricular wall motion indexes before and immediately after each exercise were analyzed.

RESULTS

Exercise-induced myocardial ischemia with re-exercise was similarly attenuated in groups I, II, and D. The ischemic threshold was raised by nearly 20% with re-exercise (p=0.001, p=0.02, and p=0.02, respectively) and the maximum ST depression equivalent was nearly halved on re-exercise (p=0.005, p=0.006, and p=0.001, respectively). Exercise-induced wall motion dysfunction was attenuated with re-exercise. In group I, wall motion returned to the initial baseline score prior to exercise 2, whereas in the more intense protocol of group II, wall motion dysfunction persisted prior to exercise 2.

CONCLUSIONS

Thus, the attenuation of myocardial ischemia observed with re-exercise appears to be independent of the intensity of the exercise protocol and is not explained by down-regulation of myocardial contractility induced by the initial ischemic stimulus. Since results were similar in diabetic subjects on robust doses of glibenclamide, this phenomenon does not appear to be mediated by K+-ATP activation.

The "warm-up" phenomenon occurs in patients with chronic stable angina but not in patients with syndrome X

Most patients with chronic stable angina show an improvement in ischemic threshold when a second exercise test is performed a few minutes after a first positive test. In this study we evaluated whether this "warm-up" phenomenon also occurs in patients with syndrome X. We performed 2 consecutive exercise tests in 14 patients with chronic stable angina and 11 patients with syndrome X. The second exercise test was performed after 10 minutes from the end of the first one, always after complete recovery to baseline of ST segment. In patients with stable angina, heart rate (108+/-18 vs 99+/-16 beats/min, p = 0.005), rate-pressure product (17,020+/-4,541 vs 15,215+/-3,734 beats/min x mm Hg, p = 0.028), and exercise time (587+/-297 vs 444+/-244 seconds, p = 0.002) at 1-mm ST depression were higher in the second test than in the first one and a significant improvement in these parameters during the second test was also observed at peak exercise. Conversely, in patients with syndrome X, there were no significant differences between the 2 tests in heart rate (128+/-18 vs 131+/-23 beats/min), rate-pressure product (19,922+/-5,153 vs 19,390+/-5,654 beats/min x mm Hg), and exercise time (592+/-243 vs 566+/-228 seconds) at 1-mm ST-segment depression. Similarly, in this group of patients, no significant differences in exercise variables between the 2 tests were observed at peak exercise. Thus, unlike patients with chronic stable angina, patients with syndrome X have no evidence of warm-up in response to repeated exercise testing.

Association between activity at onset of symptoms and outcome of acute myocardial infarction

OBJECTIVES

This study sought to compare the clinical features and outcome of a first myocardial infarction with onset of symptoms during or within 30 min of exercise, at rest and in bed.

BACKGROUND

It is not known whether activity at onset influences outcome of acute myocardial infarction.

METHODS

Information collected using a standard questionnaire was used to relate activity at the onset of symptoms to in-hospital outcome in 2,468 consecutive patients admitted to a coronary care unit with a first myocardial infarction between 1975 and 1993.

RESULTS

Patients with exercise-related onset were more likely to be younger and male. Those with onset in bed were more likely to be older and have a history of stable or unstable angina. Compared with patients whose symptoms began at rest, those with exercise-related onset had a lower in-hospital mortality rate after adjusting for age, gender and year of admission (odds ratio [OR] 0.60, 95% confidence interval [CI] 0.40 to 0.89), and patients with onset in bed had a higher mortality rate (OR 1.38, 95% CI 1.03 to 1.85). The incidence of cardiac failure requiring diuretic therapy was also lower for exercise-related onset (OR 0.83, 95% CI 0.67 to 1.04) and higher when onset was in bed (OR 1.36, 95% CI 1.11 to 1.66).

CONCLUSIONS

There is an association between activity at onset and outcome of acute myocardial infarction. Differences in pathophysiology or in the population at risk could explain this observation.

Preconditioning by transient myocardial ischemia confers protection against ischemia-induced ventricular arrhythmias in variant angina

BACKGROUND

In experimental models, ischemic preconditioning of the heart protects against ischemic damage and ventricular arrhythmias during subsequent coronary occlusion. In this study, we investigated whether protection against ischemic suffering and ischemia-induced arrhythmias may occur after spontaneous transmural ischemia in humans.

METHODS AND RESULTS

We performed 24-hour Holter monitoring in 10 patients with variant angina who developed complex ventricular arrhythmias (CVAs, more than five premature ventricular beats per minute or repetitive ventricular arrhythmias) during episodes of ST-segment elevation. A total of 150 episodes of ST-segment elevation were detected on Holter monitoring, 21 (14%) of which showed CVAs. Episodes separated from the previous one by a time interval of < or = 30 minutes or by a time interval of > 30 minutes did not differ in either magnitude or duration of ST-segment elevation, but CVAs occurred more frequently in the second group (3% versus 29%, P < .0001). The time interval from the preceding ischemic episode was longer for the episodes with compared with those without CVAs (197 +/- 275 versus 57 +/- 87 minutes, P < .001), but these two groups of episodes also had similar severities and durations of ST-segment elevation. Finally, when we analyzed 13 clusters of two to six ischemic episodes, CVAs were found much more frequently in the first (92%) than in the last (23%, P = .009) episode of the clusters, while ST-segment elevations were similar (2.1 +/- 1.6 versus 2.2 +/- 1.1 mm) and ischemia durations shorter in the first than in the last episode (3.9 +/- 3.6 versus 6.1 +/- 1.7 minutes, P = .03).

CONCLUSIONS

Our data indicate that preconditioning by transient ischemia induces a significant protection against ischemia-induced CVAs in patients with variant angina. This beneficial effect was not related to a reduction in either severity or duration of ischemia, suggesting that arrhythmic protection was a direct consequence of preconditioning rather than an epiphenomenon of ischemic protection.