Effect of nitrates on myocardial remodeling after acute myocardial infarction

Postconditioning with Nitrates Protects Against Myocardial Reperfusion Injury: A New Use for an Old Pharmacological Agent

Early reperfusion remains the key therapy to salvage viable myocardium and must be applied as soon as possible following an acute myocardial infarction (AMI) to attenuate the ischemic insult. However, reperfusion injury may develop following reintroduction of blood and oxygen to vulnerable myocytes, which results in more severe cell death than in the preceding ischemic episode. Ischemic postconditioning (I-PostC) provides a cardioprotective effect in combination with pharmacological agents. Although nitrates have been tested in many experimental and clinical studies of acute AMI to evaluate the cardioprotective effect, few investigations have been focused on nitrates postconditioning in patients undergoing percutaneous coronary intervention (PCI). This review presents the manifestations of myocardial reperfusion injury (RI) and potential mechanisms underlying it, and provides the mechanisms involved in the cardioprotection of I-PostC. We also present a new therapeutic approach to attenuate RI by use of an ‘old’ agent – nitrates – in AMI patients.

Therapeutic effects of continuous infusion of brain natriuretic peptides on postmyocardial infarction ventricular remodelling in rats

BACKGROUND

Previous studies have shown protective effects of brain natriuretic peptide (BNP) against the postmyocardial infarction (MI) remodelling process. The transcription factor NF-κB is known to play an important role after MI.

AIMS

To investigate if NF-κB is involved in the protective effects of BNP against adverse post-MI remodelling.

METHODS

Rats were randomly assigned to five groups: sham-operation; MI by coronary ligation; MI treated with chronic BNP infusion; MI treated with enalapril; MI treated with BNP+enalapril. Rats were closely monitored for survival rate analysis. Rats from each group were sacrificed on days 3, 7 and 28 postoperation.

RESULTS

The results showed that chronic continuous BNP infusion achieved similar effects to enalapril therapy, as evidenced by improved survival rate within the 28-day observation period compared with MI group rats; this effect was closely associated with preserved cardiac geometry and performance. The treatment combination did not offer extra benefits in terms of survival rate. Both BNP and enalapril therapy produced higher heart tissue concentrations of cyclic guanosine monophosphate and lower expression levels of inflammatory cytokines, including tumour necrosis factor-α, interleukin-1 and interleukin-6. These benefits were associated with lower phosphorylation levels of NF-κB subunits IκBα, p50 and p65. While enalapril significantly inhibited extracellular matrix remodelling via regulation of the protein expression ratio of matrix metalloproteinase/tissue inhibitor of metalloproteinase and the activity of matrix metalloproteinase, these variables were not affected by BNP, indicating that the two therapies involve different mechanisms.

CONCLUSION

Chronic BNP infusion can provide beneficial effects against adverse post-MI remodelling.

Reverse remodeling in heart failure with intensification of vasodilator therapy

BACKGROUND

Heart failure therapy with beta-receptor blockade has been shown to effect a partial reversal of left ventricular (LV) remodeling in heart failure.

HYPOTHESIS

We tested the hypothesis that, in the absence of beta blockade, uptitration of angiotensin-converting enzyme (ACE) inhibitor and nitrate therapy over conventional dosages would improve symptoms as well as LV function in patients with severe heart failure.

METHODS

For patients with nonischemic or ischemic cardiomyopathy, intensive high-dose angiotensin-converting enzyme inhibitor and nitrate therapy was uptitrated. Echocardiograms were obtained semiannually and evaluated in a blinded fashion. Of 99 patients in the study, aged 55 +/- 13 years, with heart failure for 5.2 +/- 3.1 years, 74 were men, 69 were Caucasian, and 34 had ischemic cardiomyopathy. The final dosage of enalapril was 40 +/- 23 mg/day of isosorbide dinitrate it was 153 +/- 127 mg/day.

RESULTS

Initial New York Heart Association classification improved from 2.8 +/- 0.9 to 1.7 +/- 0.9 (p < 0.001) in 2.7 years of follow-up. Of the 99 patients, 72 further improved their ejection fraction. For the whole group, ejection fraction increased from 21 +/- 9% to 30 +/- 13% in 6 months (p < 0.001), with a reduction in LV end-diastolic size from 6.6 +/- 0.9 to 6.3 +/- 1.0 cm (p = 0.002), a decrease in the severity of mitral regurgitation from mild/moderate to only mild. Resting heart rate declined with no change over time in systemic systolic blood pressure. Final ejection fraction for nonischemic patients (n = 65) was 36 +/- 16% versus 23 +/- 9% for the ischemic population.

CONCLUSIONS

Uptitration of high-dose ACE inhibitor and nitrate therapy to higher doses is well tolerated in severe heart failure, further improves both clinical status and LV systolic function, and is more effective in nonischemic than in ischemic cardiomyopathy.

Effects of long-term transdermal nitrate treatment on left ventricular function in patients following myocardial infarction

BACKGROUND

[corrected] Nitrates are widely used for the treatment of myocardial infarction (MI). The large megatrials (GISSI-3 and ISIS-4) did not in fact demonstrate a significant decrease in mortality in the nitrate-treated group. However, examination of the number of postinfarction angina episodes and the occurrence of cardiogenic shock in the GISSI-3 study did reveal significant decreases.

HYPOTHESIS

It was hypothesized that chronic nitrate treatment after an MI preserves left ventricular systolic and/or diastolic functions.

METHODS

Patients were divided into two groups: those receiving chronic nitrate treatment for 6 months after an MI (n = 30), and those without such treatment (n = 29). Echocardiography was performed 3, 14, 42, and 180 days after the infarction. The changes in early diastolic and atrial contraction-related mitral valve inflow pattern and deceleration time were assayed. Alterations in systolic, diastolic, and atrial reverse flow velocities in the pulmonary vein were measured, as were ejection fraction (EF), the number of registered angina episodes, and the maximal ST-segment depression in response to the stress test.

RESULTS

During the 6-month study period, the increase in systolic pulmonary venous flow velocity was significantly larger in the nitrate group than in the controls. The decreases in the velocities of the diastolic and the atrial reverse flow were also more pronounced in the nitrate group than in the controls. The EF was improved only in the nitrate group. Examination of the maximal ST-segment depression in response to the stress test revealed a significant decrease in the nitrate group only. There were no significant differences between the two groups in the number of registered angina episodes or mitral inflow pattern.

CONCLUSIONS

The study showed that prolonged nitrate treatment after an MI may help preserve diastolic left ventricular function.

Myocardial contractile effects of nitric oxide

Recent experimental and clinical research solved some of the controversies surrounding the myocardial contractile effects of NO. These controversies were: (1) does NO exert a contractile effect at baseline? (2) is NO a positive or a negative inotrope? (3) Are the contractile effects of NO similar when NO is derived from NO-donors or from the different isoforms of NO synthases (NOS)? (4) Does NO exert the same effects in hypertrophied, failing or ischemic myocardium? Transgenic mice with cardioselective overexpression of NOS revealed NO to produce a small reduction in basal developed LV pressure and a LV relaxation-hastening effect mainly through myofilamentary desensitization. Similar findings had previously been reported during intracoronary infusions of NO-donors in isolated rodent hearts and in humans. The LV relaxation hastening effect was accompanied by increased diastolic LV distensibility, which augmented LV preload reserve especially in heart failure patients. This beneficial effect on diastolic LV function always overrode the small NO-induced attenuation in LV developed pressure in terms of overall LV performance. In most experimental and clinical conditions, contractile effects of NO were similar when NO was derived from NO-donors or produced by the different isoforms of NOS. Because expression of inducible NOS (NOS2) is frequently accompanied by elevated oxidative stress, NO produced by NOS2 can lead to peroxynitrite-induced contractile impairment as observed in ischemic or septic myocardium. Finally, shifts in isoforms or in concentrations of myofilaments can affect NO-mediated myofilamentary desensitization and alter the myocardial contractile effects of NO in hypertrophied or failing myocardium.

The reperfusion era. Strategies for establishing or maintaining coronary patency

Only 3 decades ago, controversy existed over the origin of the thrombus that occluded coronary arteries during myocardial infarction (MI). Then, the acute clinical angiographic studies of DeWood butterssed new pathological and experimental evidence that the thrombus was the proximate cause of MI and unstable angina. The remaining years of the 20th century saw an explosion of knowledge delineating a spectrum of related disorders now collectively called acute coronary syndromes (ACS). The clinician managing patients is confronted with an array of evidence as more than 75,000 patients worldwide have been randomized to clinical trials in ACS. This article reviews key pathophysiological concepts, presents an initial strategy for triage of patients, and summarizes evidence-based medicine guiding therapy for acute coronary lesions.

GENERAL PHARMACOLOGIC TREATMENT OF ACUTE MYOCARDIAL INFARCTION

The general pharmacotherapeutic issues surrounding AMI are complex and expanding, especially with regard to treatment aimed at the [table: see text] culprit, coronary atherosclerotic thrombus. Basic, well-established therapy includes the routine administration of oxygen, nitroglycerin, aspirin, and at times morphine, with selected cases invoking caution with respect to these agents (e.g., nitroglycerin and the risk of hypotension in right ventricular infarction; contraindication to nitrolycerin in patients on sildenafil). Cardioprotective agents, especially beta-adrenergic antagonists, should be considered early in light of their demonstrated benefit; others, such as ACE inhibitors, need not be administered in the ED. Heparin, both UFH and the newer LMWHs, have well-established roles in acute coronary syndromes. The GP IIb/IIIa inhibitors are the most recent addition to the pharmacologic armamentarium; their role is evolving rapidly as research on this frontier continues. Table 2 reviews recommended dosing of selected agents in acute coronary syndromes.

[Left ventricular diastolic function: physiology, physiopathology, evaluation, therapy, consequences of anesthesia]

With the exception of cardiac surgery, the acute disturbance of the left ventricular diastole occurs mainly in the elderly. Today it represents 30 to 40% of congestive cardiac failures, however with a lower mortality than for acute systolic disturbances. Generally indicated are relaxation anomalies, proto-mesodiastolic mechanism and problems with compliance, an indicator of the pressure/volume diastolic relationship. Invasive techniques remain the standard method. Doppler echocardiography is becoming increasingly important for the assessment of diastolic function. In most cardiopathies, relaxation anomalies occur early, whereas compliance disturbances are mainly associated with advanced cardiac diseases. During anaesthesia, adverse events (auricular fibrillation, hypovolaemia) may worsen a fragile situation. Anaesthetic agents, in particular volatile agents, act on the ventricular diastole. Long-term therapy of diastolic anomalies includes agents amending left ventricular hypertrophy. Emergency therapy has not yet been systematised.