Clinical effects of ischemic preconditioning

The bitter fate of the sweet heart: impairment of iron homeostasis in diabetic heart leads to failure in myocardial protection by preconditioning

Cardiovascular dysfunction is a major complication of diabetes. Examining mechanistic aspects underlying the incapacity of the diabetic heart to respond to ischemic preconditioning (IPC), we could show that the alterations in iron homeostasis can explain this phenomenon. Correlating the hemodynamic parameters with levels of ferritin, the main iron storage and detoxifying protein, without and with inhibitors of protein degradation, substantiated this explanation. Diabetic hearts were less sensitive to ischemia-reperfusion stress, as indicated by functional parameters and histology. Mechanistically, since ferritin has been shown to provide cellular protection against insults, including ischemia-reperfusion stress and as the basal ferritin level in diabetic heart was 2-fold higher than in controls, these are in accord with the greater resistance of the diabetic heart to ischemia-reperfusion. Additionally, during ischemia-reperfusion, preceded by IPC, a rapid and extensive loss in ferritin levels, during the prolonged ischemia, in diabetic heart but not in non-diabetic controls, provide additional substantiation to the explanation for loss of respond to IPC. Current research is shedding light on the mechanism behind ferritin degradation as well, suggesting a novel explanation for diabetes-induced loss of cardioprotection.

The potential for clinical use of cannabinoids in treatment of cardiovascular diseases

Cannabinoids, the constituents of the marijuana plant and their analogs, have not only neurobehavioral but also cardiovascular effects. Great advances in the last couple of decades have led to better understanding of the physiological effects of the cannabinoids and of their role in various cardiovascular pathologies. The potential therapeutic use of cannabinoids in various cardiac diseases, such as ischemic injury, heart failure, and cardiac arrhythmias, has been studied in animal models. The purpose of this article is to review the physiological cardiovascular properties of cannabinoids and to summarize the knowledge related to their potential therapeutic use.

Stem cell therapy for the treatment of acute myocardial infarction

The last decade has been accompanied by great optimism and interest in the concept of cell or tissue regeneration in the postinfarction myocardium. However, despite the promise, progress was slow. Data derived from multiple controlled studies in hundreds of patients postmyocardial infarction have shown hints of potential benefit but not of the magnitude anticipated. The complexity and hurdles to repair the damaged myocardium have been more daunting than originally estimated. In the end analysis, progress will be made incrementally. The promise for cell therapy continues to be significant, but so are the challenges ahead. This article takes a fresh look at the progress in myocardial regeneration. The authors look at the postmyocardial environment for cues that may guide repair and they look closely at the clinical data for evidence of cardiac regeneration. This evidence is used for suggestions on how to best proceed with future work.

Exercise above the ischemic threshold and serum markers of myocardial injury

BACKGROUND

Current guidelines for exercise training in coronary patients state that in the presence of exercise-induced ischemia, the heart rate during exercise should be at least 10 beats/min below the heart rate associated with an ST segment depression of 1 mm or greater. For patients with a relatively low ischemic threshold, this recommendation does not allow for a sufficient training stimulus.

OBJECTIVE

To document the effects of a single session of exercise above the ischemic threshold on biochemical markers of myocardial injury in stable coronary patients with exercise-induced ischemia. Because creatine kinase (CK) and its MB isoenzyme (CK-MB) can both increase after exercise because of skeletal muscle injury, troponin T was also measured.

METHODS

Twenty-one patients with documented coronary artery disease underwent two 20 min exercise sessions. The intensity of the first exercise training session was fixed at a heart rate below the ischemic threshold (ie, approximately 10 beats/min lower than the heart rate associated with the appearance of an ST segment depression of 1 mm or greater). The intensity of the second exercise session was fixed at a heart rate above the ischemic threshold.

RESULTS

Blood test measurements at baseline, 6 h after and 24 h after the exercise sessions did not show any increase in total CK, CK-MB or troponin. The value of all measurements remained well below the lower limits associated with myocardial damage.

CONCLUSION

A 20 min period of exercise above the ischemic threshold did not result in myocardial necrosis.

Cardiovascular manifestations of sedatives and analgesics in the critical care unit

There are numerous sedatives and analgesics used in critical care medicine today; these medications are used on critically ill patients, many of whom have heart disease, including coronary artery disease or congestive heart failure. The purpose of this review is to recognize the effects of these medications on the heart. Studies that evaluated the effects of sedatives and analgesics on normal individuals or on those with heart disease were reviewed. Current choices for sustained sedation in the critically ill include the benzodiazepines, morphine, propofol, and etomidate. Each of these medications has their particular advantages and disadvantages. Benzodiazepines provide the greatest amnesia and cardiovascular safety but they can cause significant hypotension in the hemodynamically unstable patient. Morphine provides analgesia and cardioprotective activity after ischemia, although the large observational study CRUSADE showed increased mortality rate in those patients with non-ST segment elevation myocardial infarction who received morphine. Propofol is the most easily titratable drug with cardioprotective features, but its use must be accompanied with great attention to possible development of propofol infusion syndrome, which is a deadly disease, especially in patients with head injury and those with septic shock receiving vasopressors. Etomidate has a rapid onset effect and short period of action with great hemodynamic stability even in patients with shock and hypovolemia, but the incidence of adrenal insufficiency during infusion, not bolus doses, may cause deterioration in the circulatory stability. In conclusion, the sedatives and analgesics mentioned here have characteristics that give them a cardiovascular safety profile useful in critically ill patients. However, use of these drugs on an individual basis is dependent on each agent's safety and efficacy.

Diabetes and the heart: could the diabetic myocardium be protected by preconditioning?

Both type 1 and type 2 diabetes (insulin-dependent and non-insulin dependent diabetes, respectively) are associated with increased risk for microvascular and macrovascular complications including retinopathy, neuropathy, nephropathy and atherosclerosis. Type 2 diabetes markedly increases the risk for cardiovascular morbidity and mortality, which has major public health implications. In this review, molecular mechanisms pertaining to diabetes-induced heart pathology are addressed.

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.

Post-stenotic coronary blood flow at rest is not altered by therapeutic doses of the oral antidiabetic drug glibenclamide in patients with coronary artery disease

OBJECTIVE

To investigate whether blood flow in normal and post-stenotic coronary arteries is altered by therapeutic doses of the sulfonylurea agent glibenclamide.

PATIENTS

12 patients with a high grade stenosis of the left anterior descending coronary artery (n = 10) or left circumflex coronary artery (n = 2), and an angiographically normal corresponding left circumflex artery or left anterior descending artery, respectively.

DESIGN

Two Doppler ultrasound wires were positioned in the "normal" and post-stenotic artery for simultaneous measurements of coronary blood flow velocity under baseline conditions and after intravenous glibenclamide, 0.05 mg/kg body weight. Local coronary blood flow was calculated from the average peak velocity and the cross sectional area derived from quantitative coronary angiographic analysis. Coronary flow reserve was determined after intracoronary injection of 30 microg adenosine and 12 mg papaverine.

RESULTS

One hour after glibenclamide, serum insulin increased from (mean (SD)) 7.4 (2.0) to 44.8 (25.5) mU/l (p < 0.005), and C peptide from 1.4 (0.4) to 3.4 (1.2) ng/l (p = 0.005). In normal coronary arteries coronary flow reserve was 2.6 (0.4) after adenosine and 3.0 (0.4) after papaverine, while in post-stenotic arterial segments it was 1.2 (0.3) after adenosine (p = 0.005) and 1.3 (0.3) after papaverine (p = 0.005). There was no significant difference after glibenclamide. In non-stenotic arteries, average peak velocity (18.8 (5.2) cm/s) and calculated coronary blood flow (23.8 (10.7) ml/min) were not altered by glibenclamide (18.3 (5.2) cm/s and 22.8 (10.4) ml/min, respectively). In post-stenotic arteries, baseline average peak velocity was 13.3 (4.9) ml/min and coronary blood flow was 9.1 (3.0) ml/min, without significant change after glibenclamide (13.3 (5.2) cm/s, 9.0 (3.2) ml/min).

CONCLUSIONS

Glibenclamide, 0.05 mg/kg intravenously, is effective in increasing serum insulin, suggesting a K(ATP) channel blocking effect in pancreatic beta cells. It does not compromise coronary blood flow and vasodilatation in response to adenosine and papaverine in post-stenotic and angiographically normal coronary arteries at rest.

The role and regulation of adenosine in the central nervous system

Adenosine is a modulator that has a pervasive and generally inhibitory effect on neuronal activity. Tonic activation of adenosine receptors by adenosine that is normally present in the extracellular space in brain tissue leads to inhibitory effects that appear to be mediated by both adenosine A1 and A2A receptors. Relief from this tonic inhibition by receptor antagonists such as caffeine accounts for the excitatory actions of these agents. Characterization of the effects of adenosine receptor agonists and antagonists has led to numerous hypotheses concerning the role of this nucleoside. Previous work has established a role for adenosine in a diverse array of neural phenomena, which include regulation of sleep and the level of arousal, neuroprotection, regulation of seizure susceptibility, locomotor effects, analgesia, mediation of the effects of ethanol, and chronic drug use.

Activation of ATP-sensitive potassium channels in hypoxic cardiac failure is not mediated by adenosine-1 receptors in the isolated rat heart

BACKGROUND

Hypoxic cardiac failure is accompanied by action potential shortening, which in part might be a consequence of opening of cardiac ATP-sensitive potassium channels (K(ATP) channels). Coupling of the adenosine-1 receptor (A-1 receptor) to these channels has been described; however, the interaction of A-1-receptors and K(ATP) channels in different models of ischemia is still under debate. The hypothesis as to whether A-1 receptors are involved in hypoxic K(ATP) channel-activation in the saline-perfused rat heart was tested.

METHODS AND RESULTS

Pharmacologic modulation of the K(ATP) channel by Glibenclamide (inhibitor) and Rimalkalim (activator) and of the A-1 receptor by R(-)-N6-(1-methyl-2-phenylethyl)-adenosine (R(-)-PIA, agonist) and 1,3-diethyl-3,7-dihydro-8-phenyl-purine-2,6-dione (DPX, antagonist) at different oxygen tensions (95% O2 and 20% O2) was performed in isolated Langendorff-rat hearts. Peak systolic pressure (PSP, intraventricular balloon), duration of monophasic action potential (epicardial suction electrode, time to 67% of repolarization: MAP(67%)), coronary flow, and heart rate (HR) were registered. Hypoxic perfusion resulted in a significant reduction of PSP (from 106 +/-11 to 56 +/-8 mmHg, P < 0.005) and shortening of MAP(67%) (from 37 +/-3 to 25 +/-4 ms, P < 0.005). With application of 1 microM Glibenclamide, MAP(67%) returned to normoxic values and PSP increased to 78 +/-9 mmHg (P < 0.005 vs hypoxia). In normoxia, 2 microM Rimalkalin resulted in reduction of MAP(67%) and PSP, which was reversed by Glibenclamide. Application of 0.1 microM R(-)-PIA in normoxia resulted in a decrease of HR (from 235 +/-36/min to 75 +/-41/min, P < 0.005), which was accompanied by an increase of PSP from 96 +/-7 to 126 +/-9 mmHg (P < 0.05) without changes in MAP(67%). These effects were reversible by 1 microM DPX and remained unaffected by application of 1 microM Glibenclamide. Application of 1 microM DPX in hypoxia had no effect on the measured parameters.

CONCLUSION

In isolated rat hearts, the K(ATP) channel-system is activated in hypoxic cardiac failure and contributes to action potential shortening and reduced contractile performance. These effects seem to be independent of the A-1 receptor in this model.

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.