[Intracoronary thrombus in patients with unstable angina pectoris]

[Therapy of acute coronary syndrome. Aspirin, heparin, low-molecular-weight heparin, hirudin and GP-IIb/IIIa blockers]

Plaque rupture with consecutive formation of an intraluminal, platelet-rich thrombus is the central mechanism leading to critical reduction of coronary perfusion in the acute coronary syndrome. Current therapeutic strategies aim at the inhibition of activation of platelets and the coagulation cascade and the suppression of platelet aggregation and fibrin formation. The use of acetylsalicylic acid (ASA) is well established in the therapy of the acute coronary syndrome and its efficacy is documented in several large clinical studies. The results of a respective metaanalysis by the Antiplatelet Trialists' Collaboration are shown in Table 1. Further risk reduction has been achieved with the additional application of heparin during the early phase of treatment. Table 2 shows the results of the Montreal Heart Study of combined vs single drug treatment, and Figure 1 a metaanalysis by Oler et al. of combination therapy with heparin plus ASA compared to monotherapy with ASA. In the past, hirudin and analogues were not superior to heparin as adjunctive treatments to lysis in acute myocardial infarction, but bleeding complications were more frequent. In contrast, in the recently published OASIS-2 study, outcome in patients with unstable angina pectoris was significantly better with hirudin than with heparin. Several large studies have demonstrated at least equivalent efficacy of LMWHs compared to standard heparin. For the early phase of the acute coronary syndrome, the FRIC and ESSENCE studies have even demonstrated improved clinical outcome without increase in bleeding complications. However, in TIMI 11 and FRAXIS, long-term application of LMWH resulted in more bleeding complications and, in FRAXIS, in a trend to a worse clinical outcome. The use of GP-IIb/IIIa blockers, especially the chimeric antibody fragment abciximab, is well established in interventional cardiology. Figure 2 shows the mechanism of action of the GP-IIb/IIIa blockers on platelet aggregation. In addition, their use in conjunction with ASA and heparin in the acute coronary syndrome led to further significant reduction of cardiovascular events in several studies. For example, the reduction of events by abciximab in the CAPTURE-study is delineated in Table 3. The results obtained with several of the new competitive GP-IIb/IIIa receptor antagonists are shown in Table 4.

The prognostic value of serum troponin T in unstable angina

BACKGROUND

Cardiac troponin T is a regulatory contractile protein not normally found in blood. Its detection in the circulation has been shown to be a sensitive and specific marker for myocardial cell damage. We used a newly developed enzyme immunoassay for troponin T to determine whether its presence in the serum of patients with unstable angina was a prognostic indicator.

METHODS

We screened 72 patients with unstable angina (Class III, acute unstable angina) for serum creatine kinase activity, creatine kinase myocardial band (isoenzyme M) activity, and troponin T, every 8 h for 2 days after admission to the hospital. The outcomes of interest during the hospitalization were death and myocardial infarction.

RESULTS

Troponin T was detected in the serum of 24 of the 72 patients (34%) with acute angina at rest. Only four of these patients had elevated creatine kinase M activity. Of the 24 patients who were positive for troponin T, 12 had myocardial infarction, and 6 of these died during hospitalization. In contrast, only 2 of the 48 patients with angina at rest who were negative for troponin T had an acute myocardial infarction, and these patients died. Thus, 12 of the 14 patients with myocardial infarctions had detectable levels of troponin T; only 2 had elevated creatine kinase M activity.

CONCLUSIONS

Cardiac troponin T in serum appears to be a more sensitive indicator of myocardial-cell injury than serum creatine kinase MB activity, and its detection in the circulation may be a useful prognostic indicator in patients with unstable angina.

The prognostic value of serum troponin T in unstable angina

BACKGROUND

Cardiac troponin T is a regulatory contractile protein not normally found in blood. Its detection in the circulation has been shown to be a sensitive and specific marker for myocardial cell damage. We used a newly developed enzyme immunoassay for troponin T to determine whether its presence in the serum of patients with unstable angina was a prognostic indicator.

METHODS

We screened 109 patients with unstable angina (25 with accelerated or subacute angina and 84 with acute angina at rest) for serum creatine kinase activity, creatine kinase isoenzyme MB activity, and troponin T every eight hours for two days after admission to the hospital. The outcomes of interest during the hospitalization were death and myocardial infarction.

RESULTS

Troponin T was detected (range, 0.20 to 3.64 micrograms per liter; mean, 0.78; median, 0.50) in the serum of 33 of the 84 patients (39 percent) with acute angina at rest. Only three of these patients had elevated creatine kinase MB activity (two were positive for troponin T, and one was negative). Of the 33 patients who were positive for troponin T, 10 (30 percent) had myocardial infarction (3 after coronary-artery bypass surgery), and 5 of these died during hospitalization. In contrast, only 1 of the 51 patients with angina at rest who were negative for troponin T had an acute myocardial infarction (P less than 0.001), and this patient died (P = 0.03). Thus, 10 of the 11 patients with myocardial infarctions had detectable levels of troponin T; only 1 had elevated creatine kinase MB activity. Troponin T was not detected in any of the 25 patients with accelerated or subacute angina, and none of these patients died.

CONCLUSIONS

Cardiac troponin T in serum appears to be a more sensitive indicator of myocardial-cell injury than serum creatine kinase MB activity, and its detection in the circulation may be a useful prognostic indicator in patients with unstable angina.

Unstable angina: pathophysiology and drug therapy

Unstable angina is a clinical syndrome characterized by increased rate and severity of angina pectoris attacks and, sometimes but not always, accompanied by ECG changes similar to those seen in coronary insufficiency. According to the present conception of the pathogenesis, ruptures at points of high-grade stenosis in the epicardial coronary arteries with simultaneous apposition of thrombi and vasoconstriction cause critical narrowing of the vascular lumen, which means that with the same level of oxygen consumption, coronary blood flow might be inadequate even at rest. In this way the development of severe ischemia, sudden cardiac death or myocardial infarction is programmed. Therapy must accordingly aim at avoiding or eliminating the progression of thrombosis and at increasing the reduced coronary blood flow. The prognosis is unequivocally improved by aspirin. In addition, heparin, 400 units/kg body weight, should be given. Thrombolysis may be possible after mechanical recanalization, depending on the individual results of coronary angiography. Providing the adverse reactions are monitored, nitroglycerin given intravenously is the basic drug therapy, although comparative studies against other drugs are not available and some data show the development of tolerance during prolonged use. Therefore, an early change to sustained-release nitrates or mononitrates can be justified. beta-receptor blockers reduce the frequency of silent ischemia and of myocardial infarction. By these means, in 80% of the patients affected, unstable angina will be converted to the stable form of the disease. If symptoms persist coronary angiography is urgently indicated, to allow the selection of PTCA or aortocoronary bypass surgery according to the findings.

Unstable angina: current concepts of medical management

Unstable angina describes a clinical syndrome bridging the gap between stable angina and acute myocardial infarction. By definition, patients with angina of new onset, of a crescendo pattern, and with angina at rest are included in this high-risk group. The underlying pathogenetic mechanisms are complex and include initial atherosclerotic plaque rupture, release of vasoactive substances, and intracoronary thrombus formation. The currently established medical approach of the acute phase consists of heparin for anticoagulation and nitrates combined with beta-blockers for the relief of pain. Calcium antagonists are indicated, if anginal symptoms persist. The effect of thrombolytic therapy is still under investigation. Angina refractory to medical treatment and angina at rest are associated with a particularly unfavorable prognosis and prompt early catheterization. The long-term prognosis of the patient is markedly improved by chronic platelet inhibitory treatment with aspirin.