The warm-up effect protects against ischemic left ventricular dysfunction in patients with 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.

Cardioprotection acquired through exercise: the role of ischemic preconditioning

A great bulk of evidence supports the concept that regular exercise training can reduce the incidence of coronary events and increase survival chances after myocardial infarction. These exercise-induced beneficial effects on the myocardium are reached by means of the reduction of several risk factors relating to cardiovascular disease, such as high cholesterol, hypertension, obesity etc. Furthermore, it has been demonstrated that exercise can reproduce the "ischemic preconditioning" (IP), which refers to the capacity of short periods of ischemia to render the myocardium more resistant to subsequent ischemic insult and to limit infarct size during prolonged ischemia. However, IP is a complex phenomenon which, along with infarct size reduction, can also provide protection against arrhythmia and myocardial stunning due to ischemia-reperfusion. Several clues demonstrate that preconditioning may be directly induced by exercise, thus inducing a protective phenotype at the heart level without the necessity of causing ischemia. Exercise appears to act as a physiological stress that induces beneficial myocardial adaptive responses at cellular level. The purpose of the present paper is to review the latest data on the role played by exercise in triggering myocardial preconditioning.

Aerobic exercise intensity assessment and prescription in cardiac rehabilitation: a joint position statement of the European Association for Cardiovascular Prevention and Rehabilitation, the American Association of Cardiovascular and Pulmonary Rehabilitation, and the Canadian Association of Cardiac Rehabilitation

Aerobic exercise intensity prescription is a key issue in cardiac rehabilitation, being directly linked to both the amount of improvement in exercise capacity and the risk of adverse events during exercise. This joint position statement aims to provide professionals with up-to-date information regarding the identification of different exercise intensity domains, the methods of direct and indirect determination of exercise intensity for both continuous and interval aerobic training, the effects of the use of different exercise protocols on exercise intensity prescription and the indications for recommended exercise training prescription in specific cardiac patients' groups. The importance of functional evaluation through exercise testing prior to starting an aerobic training program is strongly emphasized, and ramp incremental cardiopulmonary exercise test, when available, is proposed as the gold standard for a physiologically comprehensive exercise intensity assessment and prescription. This may allow a shift from a 'range-based' to a 'threshold-based' aerobic exercise intensity prescription, which, combined with thorough clinical evaluation and exercise-related risk assessment, could maximize the benefits obtainable by the use of aerobic exercise training in cardiac rehabilitation.

Aerobic exercise intensity assessment and prescription in cardiac rehabilitation: a joint position statement of the European Association for Cardiovascular Prevention and Rehabilitation, the American Association of Cardiovascular and Pulmonary Rehabilitation and the Canadian Association of Cardiac Rehabilitation

Aerobic exercise intensity prescription is a key issue in cardiac rehabilitation, being directly linked to both the amount of improvement in exercise capacity and the risk of adverse events during exercise. This joint position statement aims to provide professionals with up-to-date information regarding the identification of different exercise intensity domains, the methods of direct and indirect determination of exercise intensity for both continuous and interval aerobic training, the effects of the use of different exercise protocols on exercise intensity prescription and the indications for recommended exercise training prescription in specific cardiac patients' groups. The importance of functional evaluation through exercise testing prior to starting an aerobic training program is strongly emphasized, and ramp incremental cardiopulmonary exercise test, when available, is proposed as the gold standard for a physiologically comprehensive exercise intensity assessment and prescription. This may allow a shift from a 'range-based' to a 'threshold-based' aerobic exercise intensity prescription, which, combined with thorough clinical evaluation and exercise-related risk assessment, could maximize the benefits obtainable by the use of aerobic exercise training in cardiac rehabilitation.

Stress test with dual isotope studies for the documentation of classical ischemic preconditioning

OBJECTIVES

We investigated whether myocardial perfusion imaging (MPI) can demonstrate the effect of classical preconditioning.

METHODS

21 patients with documented coronary artery disease (stenosis>or=70%) underwent two exercise stress tests (EST) with concomitant MPI, using TL-201 for the first and tetrofosmin-Tc-99m for the second. A third MPI was performed at rest, using Tc-99m. Total defect score was derived by summing tracer uptake in a 17 segments left ventricle model, graded on a 5-point scale. Tomographic images were also analyzed quantitatively, to derive the total defect size.

RESULTS

Maximum ST depression did not differ significantly between the two EST (2.2+/-1 vs 2.2+/-1 mm, p=NS), however in the second EST longer times for onset of ischemic changes (228+/-94 vs 265+/-103 s, p=0.01) and appearance of angina (282+/-153 vs 328+/-177 s, p=0.04) were observed. Exercise perfusion abnormalities were significantly lower in the second MPI, in terms of both total defect score (19.2+/-11.5 vs 10+/-10.4, p<0.0001) and total defect size (28.3+/-16.9 vs 13.8+/-15.8, p<0.0001).

CONCLUSION

Significant improvement in perfusion pattern was demonstrated in the second MPI, accompanied by delayed appearance of ischemic manifestations. The improvement in myocardial perfusion extends far beyond the changes that can be attributed to differences in myocardial uptake between tracers, reflecting the effect of classical preconditioning.

Myocardial protection in man--from research concept to clinical practice

Myocardial protection aims at preventing myocardial tissue loss: (a) In the acute stage, i.e., during primary angioplasty in acute myocardial infarction. In this setup, the attenuation of reperfusion injury is the main target. As a "mechanical" means, post-conditioning has already been tried in man with encouraging results. Pharmacologic interventions that could be of promise are statins, insulin, peptide hormones, including erythropoietin, fibroblast growth factor, and many others. (b) The patient with chronic coronary artery disease offers another paradigm, with the target of avoidance of further myocyte loss through apoptosis and inflammation. Various pharmacologic agents may prove useful in this context, together with exercise and "mechanical" improvement of cardiac function with attenuation of myocardial stretch, which by itself is a noxious influence. A continuous effort toward acute and chronically preserving myocardial integrity is a concept concerning both the researcher and the clinician.

Effects of pharmacological modulation of the ATP-sensitive potassium channels on the development of warm-up angina pectoris

The aim of this study was to examine the effect of pharmacological modulation of the ATP-sensitive potassium channels in the development of warm-up angina pectoris. Thirty-one patients with stable angina pectoris, a positive exercise test and angiographically documented coronary artery disease underwent three exercise tests 90 min after receiving either glibenclamide 10.5 mg (an ATP-sensitive potassium channel blocker), pinacidil 25 mg (an ATP-sensitive potassium channel opener) or placebo in a blinded fashion. There was a 30-min recovery period between the first and the second test and 60 min between the second and the third test. The rate-pressure product at 1-mm ST-segment depression (ischemic threshold) and the maximum ST-segment depression (STD) adjusted to the highest rate-pressure product common to the three tests were analyzed. In the placebo group, there was a significant increase in the ischemic threshold during the second and third test and a significant decrease in the maximum adjusted STD during the second test which was lost during the third test. This apparent adaptation to exercise-induced ischemia was not seen in the glibenclamide-treated patients. In the pinacidil-treated patients, there was a paradoxical decrease in ischemic threshold during the second test with no change in maximum adjusted STD which tended to be lower than in the placebo-treated patients on each exercise test. This study confirms that the warm-up phenomenon can be induced during repeated exercise testing. The blockade of this phenomenon by glibenclamide suggests that the ATP-sensitive potassium channels may be involved in this potential protective mechanism. At the same time, the paradoxical response in the pinacidil-treated patients flags a warning that drugs acting on the sarcolemmal ATP-sensitive potassium channels may have a direct effect on the ST-segment that may interfere with the interpretation of the electrocardiogram.

[The role of ischemic preconditioning in acute myocardial infarction]

INTRODUCTION

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

CASE REPORT

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

CONCLUSION

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

[Ischemic preconditioning]

BACKGROUND

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

CASE REPORT

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

CONCLUSION

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

Degree of activity at the onset of myocardial infarction and thrombolysis outcome

BACKGROUND

The aim of this study was to evaluate the possible relationship between the degree of physical activity at the onset of myocardial infarction and thrombolysis outcome.

METHODS

A total of 351 consecutive patients, who underwent thrombolysis due to ST elevation acute myocardial infarction, were prospectively studied. Patients were classified into three groups according to a generally accepted scale: group I patients had experienced symptoms during exertion, group II when sitting and group III during sleep or when reclining.

RESULTS

There was a significantly increased chance of either intravenous thrombolysis effectiveness or cardiac survival probability with increasing physical activity at the onset of myocardial infarction. In particular, group I patients had a significantly higher incidence of complete ST-segment resolution (P<0.001 for both II vs. I and III vs. I groups) or TIMI 3 flow in the infarct-related artery (II vs. I: P=0.002, and III vs. I: P<0.001) and less compromised left ventricular function (P<0.001 for both II vs. I and III vs. I) by both univariate and multivariate analysis. Moreover, although the degree of physical activity was associated with lower in-hospital (II vs. I: P=0.048, and III vs. I: P=0.01), and cardiac mortality at 39 months (II vs. I: P=0.002, and III vs. I: P<0.001) by univariate analysis, this did not hold true by multivariate analysis.

CONCLUSIONS

In conclusion, the degree of physical activity at the onset of myocardial infarction may be positively associated with acute success of intravenous thrombolysis and this may favorably influence short- and long-term cardiac survival.

Ischemic preconditioning is not cardioprotective in senescent human myocardium

BACKGROUND

Cellular and functional changes secondary to aging could impair myocardial tolerance to ischemia and affect the heart's response to ischemic preconditioning.

METHODS

We investigated the impact of cardiac aging on preconditioning in right atrial trabeculae of adult patients (< or = 55 years) and senescent patients (> or = 70 years) with coronary artery disease. Specimens were subjected to 30 minutes of simulated ischemia (hypoxic substrate-free superfusion) with and without 5 minutes of ischemic pretreatment. Postischemic contractile recovery was measured and expressed as percentage of base line force values.

RESULTS

During the reoxygenation period, trabeculae of adult patients but not those of senescent patients improved after ischemic preconditioning. After 40 minutes of reoxygenation, preconditioned adult trabeculae developed 57% +/- 5% of their preischemic force (nonpreconditioned control 44% +/- 5%, p < 0.01), senescent trabeculae recovered to 44% +/- 4% (control 45% +/- 3%). Especially myocardium from adult patients with Canadian Cardiovascular Society (CCS) stage III angina pectoris treated with ACE inhibitors recovered well (70% +/- 7%; control 50% +/- 8%, p < 0.01), contrasting with trabeculae from patients with CCS stage II angina (44% +/- 5%; control 40% +/- 10%). Ischemia-inducible Hsp70 (human heat shock protein) was additionally measured after reoxygenation. Total Hsp70 mRNA was elevated in preconditioned myocardium along with its contractile recovery (r = 0.33, p = 0.07). Because the control transcription, analyzing 18S rRNA and beta-actin, was reduced by ischemia but recovered in preconditioned trabeculae, relative Hsp70 mRNA was not altered.

CONCLUSIONS

Our data indicate that ischemic preconditioning has no beneficial effect on the postischemic functional recovery of senescent human myocardium.

Cardiac rehabilitation secondary prevention programs

Contemporary cardiac rehabilitation programs are more accurately described as "secondary prevention centers." They offer comprehensive care for the patient with cardiovascular disease, resulting in decreased mortality, improvement of most cardiac risk factors, and an enhanced quality of life. Although overall participation has increased with enhanced recognition of the importance of secondary prevention, 80% of eligible patients still do not participate, in part due to lack of insurance reimbursement. This rate can be significantly increased by specific endorsement from the physician.

Does a selective adenosine A(1) receptor agonist protect against exercise induced ischaemia in patients with coronary artery disease?

BACKGROUND

The "warm up" effect in angina may represent ischaemic preconditioning, which is mediated by adenosine A(1) receptors in most models.

OBJECTIVE

To investigate the effect of a selective A(1) agonist, GR79236 (GlaxoSmithKline), on exercise induced angina and ischaemic left ventricular dysfunction in patients with coronary artery disease.

DESIGN

A double blind crossover study.

PATIENTS

25 patients with multivessel coronary artery disease.

INTERVENTIONS

On mornings one week apart, patients received intravenous GR79236 10 microgram/kg or placebo, and then carried out two supine bicycle exercise tests separated by 30 minutes. Equilibrium radionuclide angiography was done before and during exercise.

RESULTS

The onset of chest pain or 1 mm ST depression was delayed and occurred at a higher rate-pressure product during the second exercise test following either placebo or GR79236. Compared with placebo, GR79236 did not affect these indices during equivalent tests. GR79236 reduced resting global ejection fraction from (mean (SD)) 63 (7)% to 61 (5)% (p < 0.05) by a selective reduction in the regional ejection fraction of "ischaemic" left ventricular sectors (those where the ejection fraction fell during the first exercise test following placebo). Ischaemic sectors showed increased function during the second test following placebo (72 (21)% v 66 (20)%; p = 0.0001), or during the first test following GR79236 (69 (21)% v 66 (20)%; p = 0.0001). Sequential exercise further increased the function of ischaemic sectors even after drug administration.

CONCLUSIONS

GR79236 failed to mimic the warm up effect, and warm up occurred even in the presence of this agent. This suggests that ischaemic preconditioning is not an important component of this type of protection. The complex actions of the drug on regional left ventricular function at rest and during exercise suggest several competing A(1) mediated actions.