ACC/AHA guidelines for the early management of patients with acute myocardial infarction. A report of the American College of Cardiology/American Heart Association Task Force on Assessment of Diagnostic and Therapeutic Cardiovascular Procedures (subcommittee to develop guidelines for the early management of patients with acute myocardial infarction)

Use of nitroglycerin for the treatment of acute myocardial infarction

After a decade of warnings against the use of nitrates in acute myocardial infarction (MI), they are becoming recognized for their potential to salvage left ventricular (LV) myocardium, geometry and function. Low-dose intravenous (IV) nitroglycerin (NTG) infusion for the first 48 h after acute MI, titrated to lower mean blood pressure by 10% to 30%, but not below 80 mmHg, has been shown to be safe, to improve hemodynamics, and to decrease infarct size, infarct expansion, complications, and deaths in a prospective, randomized, single-blind study of 310 patients. In addition, low-dose NTG infusion for the first 48 h, followed by prolonged buccal NTG given during healing after acute MI in an eccentric dose schedule to minimize tolerance, was found to limit further progressive remodeling and preserve LV function. Meta-analysis of nitrate studies in acute MI indicate that they improve survival. Preliminary and ongoing studies suggest that prolonged NTG therapy post MI can produce further benefit.

Effects of nitrate therapy on ventricular remodeling and function

The hypothesis that nitrates might effectively limit left ventricular remodeling and improve function after acute myocardial infarction has been tested in experimental and clinical models, with special attention to the pathophysiologic evolution of remodeling. In 1 clinical study, before the thrombolytic era, the effects of low-dose intravenous nitroglycerin infusion for the first 48 hours during acute myocardial infarction was evaluated in a prospective, randomized, single-blinded, placebo-controlled study of 310 patients (154 nitroglycerin; 156 placebo). Nitroglycerin proved to be safe and produced several benefits compared with placebo: (1) smaller infarct size; (2) less left ventricular dysfunction; (3) less infarct expansion and thinning; (4) better functional status; (5) fewer in-hospital complications such as left ventricular failure, left ventricular thrombus, cardiogenic shock, and infarct extension; and (6) fewer deaths up to 1 year. Two subsequent clinical studies in the thrombolytic era, with low-dose intravenous nitroglycerin infusion during infarction over the first 48 hours followed by buccal nitrate (eccentric dose regimen) or placebo during healing over 6 weeks postinfarction, indicated that prolonged nitrate therapy effectively limited left ventricular remodeling and improved function further compared with placebo.

Early detection of myocardial infarction with magnetic resonance imaging in a canine model

STUDY OBJECTIVE

To determine the effectiveness of magnetic resonance imaging in detecting early myocardial infarction in vivo after coronary artery occlusion.

DESIGN

A prospective, controlled canine study using a left anterior descending coronary artery ligation model.

INTERVENTIONS

After thiopental anesthesia, nine mongrel dogs underwent cardiac-gated magnetic resonance imaging with a 2.35-T magnet with a 40-cm bore before and four hours after ligation of the left anterior descending coronary artery.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic and left ventricular blood flow changes were determined. The mean image intensity ratio of the suspected infarct region to the normal myocardium was determined in the four-hour postocclusion images and compared with the ratio from the same anatomic region obtained at baseline. The area of necrotic and ischemic myocardium was determined using fluorescein and triphenyl tetrazolium chloride staining immediately after four-hour images. All animals were noted to have necrotic (range, 1.8% to 20.4% of ventricles) and ischemic (range, 9.2% to 36.6% of ventricles) myocardium with histochemical staining. The mean intensity ratio of infarcted myocardium four hours after left anterior descending coronary artery occlusion was significantly higher than baseline (four hours, 2.31 +/- 0.82; baseline, 1.02 +/- 0.09; P < .002).

CONCLUSION

Magnetic resonance imaging can distinguish myocardial edema associated with acute infarcting myocardium in vivo as early as four hours after left anterior descending coronary artery occlusion. Magnetic resonance imaging may be clinically useful in identifying thrombolytic therapy candidates among acute myocardial infarction patients presenting with atypical symptoms.

The role of antiplatelet therapy in acute coronary syndromes and for secondary prevention following a myocardial infarction

Acute Coronary Syndromes: Therapy with aspirin is recommended for all patients with acute myocardial ischemic syndromes unless contraindications for its use is present. None of the studies thus far have conclusively established evidence for a selective dose of aspirin. Until conclusive evidence exists, aspirin in doses of 81 mg (children's tablet) to 325 mg (adult tablet) are recommended. Ticlopidine may prove to be an attractive alternate choice in those who cannot take aspirin. According to the ACC/AHA task force recommendations, patients with acute myocardial infarction receiving thrombolytic therapy should receive both heparin and aspirin. Aspirin is to be administered in a dose of 160 mg daily. Heparin can be discontinued after 2 days if the patient's clinical course remains uncomplicated. Aspirin should be continued indefinitely. An alternative strategy in those who cannot take aspirin is to switch to warfarin before hospital discharge with a view toward long-term anticoagulant therapy. Secondary Prevention: Aspirin in a dose of 325 mg daily is recommended for all survivors of an acute myocardial infarction. No benefit derives from the addition of dipyridamole. The role of sulfinpyrazone remains undefined. Warfarin is an effective antithrombotic alternative to aspirin for secondary prevention after a myocardial infarction. However, aspirin is cheaper to administer and follow up when compared with warfarin. From available information, aspirin appears to be an adequate antithrombotic agent in patients who have near-normal left-ventricular function, the elderly, patients with coexisting cerebrovascular or peripheral vascular disease, and those with contraindications for anticoagulants. Warfarin should be preferred in high-risk patients with anterior or apical myocardial infarction, left-ventricular dysfunction with or without a mural thrombus, and those with associated atrial fibrillation. A randomized study assessing aspirin versus warfarin for secondary prevention after myocardial infarction is being initiated to determine the relative efficacy and safety of these drugs in secondary prevention after myocardial infarction.

Role of nitrates after acute myocardial infarction

Apart from their ability to relieve myocardial ischemia, nitrates have an important role to play on preservation of left ventricular (LV) geometry and function after acute myocardial infarction (MI). In the first 48 hours after acute MI, intravenous nitroglycerin infusion titrated to a low-dose regimen produces multiple benefits, including smaller infarct size, better regional and global LV function, less remodeling, fewer in-hospital complications, and fewer deaths in-hospital and up to 1 year. This regimen might be an effective adjunct during reperfusion therapy for salvaging ischemic myocardium, LV geometry, and function. Recent studies indicate that prolonged therapy with nitrates during the healing phase after acute MI can effectively further limit progressive LV remodeling (less LV dilation, expansion, thinning, and aneurysm formation) and preserve LV function. Tolerance with chronic therapy is avoided by an eccentric dose regimen to provide a nitrate-free interval.

Association of patency of the infarct-related coronary artery with plasma levels of plasminogen activator inhibitor activity in acute myocardial infarction

To examine the fibrinolytic capacity in patients with acute myocardial infarction (AMI), baseline levels of plasma plasminogen activator inhibitor (PAI) activity and tissue-type plasminogen activator (t-PA) antigen were measured in 47 patients with Q-wave AMI who underwent emergent coronary angiography 3.0 +/- 0.2 hours after the symptom onset. They received intracoronary injection of urokinase if their infarct-related arteries were occluded. They were classified into 3 groups according to the patency of the infarct-related artery before and after thrombolytic therapy: the patent group (13 patients), the recanalized group (23 patients) and the occluded group (11 patients). The mean level of plasma PAI activity (IU/ml) was higher in patients with AMI as a whole than in the control group (12.8 +/- 1.6 vs 5.4 +/- 0.5, p less than 0.01). The level was lower in the patent group (3.0 +/- 1.1) and higher in the recanalized (18.6 +/- 2.2) and occluded (10.8 +/- 2.5) groups than in the control group (each p less than 0.01). The level was lower in the occluded than in the recanalized group (p less than 0.01) and 62% of the patients in the occluded group had levels within range of the control group. The mean level of plasma t-PA antigen (ng/ml) was higher in patients with AMI as a whole than in the control group (10.3 +/- 0.8 vs 5.8 +/- 0.3, p less than 0.01). There was no difference in the level among the 3 groups with AMI.(ABSTRACT TRUNCATED AT 250 WORDS)

Medical and Neuropsychiatric Complications Associated with Use of the Intraaortic Balloon Pump

We conducted a retrospective chart review of 195 consecutive patients who had an intraaortic balloon pump (IABP) placed at the Massachusetts General Hospital during the calendar year 1988 to determine the incidence of complications associated with IABP treatment. Demographics, medical and psychiatric history, hospital course, medical and neuropsychiatric complications observed while on the IABP, pharmacological management, and outcome were recorded. Patients ranged in age from 26 to 81 years, with a mean of 62 years. Women comprised only 25% of the sample but had a mortality (40%) twice that of men (20%; p = 0.008). An IABP was inserted for cardiogenic shock in 52% of patients, for refractory angina in 36%, and intraoperatively in 12%. Patients were treated with an IABP for a mean of 4.4 days (range, several hours to 36 days). Complications included delirium (34%), mortality (25%), peripheral vascular insufficiency (17%), bleeding (14%), acute renal failure (14%), infection (8%), and stroke (4.6%). Delirium was associated only with a history of seizures and with development of a residual organic brain syndrome. Mortality was associated with female sex, cardiogenic shock, and number of complications present per patient. Vascular insufficiency was associated with female sex, history of peripheral vascular disease, valve replacement surgery, and mortality. Residual organic brain syndromes were more common in patients in whom delirium developed. A review of the literature on complications associated with IABP therapy is provided. This study highlights the common but previously unrecognized complication of delirium in IABP patients.

Importance of reperfusion on thromboxane A2 metabolite excretion after thrombolysis

Fibrinolytic therapy is a major advance in the treatment of coronary artery disease. A marked elevation in plasma and urinary metabolites of thromboxane A2 (TXA2) after administration of thrombolytic therapy has been observed and has been related to a direct effect of thrombolytic drugs on platelets. To test this hypothesis we evaluated the 11-dehydro-thromboxane B2 (11-d-TXB2) level, as an index of platelet activation, in 20 healthy subjects and in 30 patients with acute myocardial infarction (AMI). Patients with infarction received streptokinase (n = 8), recombinant tissue-type plasminogen activator (rt-PA) (n = 8), or thrombolytic therapy preceded by acetylsalicylic acid (n = 7) or were treated without thrombolytic therapy (n = 7). The urinary 11-d-TXB2 level in healthy control subjects was 327 +/- 126 pg/mg creatinine. A significant increase was observed in patients with AMI with no difference between those who received no thrombolytic therapy (673 +/- 283 pg/mg creatinine in the first 12 hours) and those who received streptokinase (833 +/- 613 pg/mg creatinine) or rt-PA (836 +/- 653 pg/mg creatinine). Patients pretreated with acetylsalicylic acid had urinary 11-d-TXB2 values ranging between 361 and 155 pg/mg creatinine. A significant difference in 11-d-TXB2 values was observed only when patients who were reperfused were separated from those who remained occluded according to angiographic criteria (1085 +/- 498 vs 391 +/- 227 pg/mg creatinine in the first 12 hours, p less than 0.001). We conclude that reperfusion and not thrombolytic agents per se appears to be the factor that induces platelet activation and consequently facilitates reocclusion.

Cardiac troponin T in the diagnosis of myocardial injury

In the last several decades serum levels of cardiac enzymes and isoenzymes have become the final arbiters by which myocardial damage is diagnosed or excluded. Because conventionally used enzymes are neither perfectly sensitive nor specific, there is need for a new sensitive and cardiospecific marker of myocardial damage. Cardiac troponin T (TnT) is a contractile protein unique to cardiac muscle and can be differentiated by immunologic methods from its skeletal-muscle isoform. An enzyme immunoassay specific for cardiac TnT is now available in a commercial kit for routine use. The biggest advantage of this assay is its cardiospecificity. TnT measurements, however, are also highly sensitive in diagnosis of myocardial injury and accurately discern even small amounts of myocardial necrosis. TnT measurements are, therefore, particularly useful in patients with borderline CK-MB and in clinical settings in which traditional enzymes fail to diagnose myocardial damage efficiently because of lack of specificity--for example, perioperative myocardial infarction or blunt heart trauma. TnT release kinetics reveal characteristics of both soluble, cytoplasmic, and structurally bound molecules. It starts to increase a few hours after the onset of myocardial damage and remains increased for several days. TnT allows late diagnosis of myocardial infarction. The diagnostic efficiency remains at 98% until 6 d after the onset of infarct-related symptoms. TnT is also useful in monitoring the effectiveness of thrombolytic therapy in myocardial infarction patients. The ratio of peak TnT concentration on day 1 to TnT concentration at day 4 discriminates between patients with successful (greater than 1) and failed (less than or equal to 1) reperfusion. TnT measurements are very sensitive and specific for the early and late diagnosis of myocardial damage and could, therefore, provide a new criterion in laboratory diagnosis of the occurrence of myocardial damage.

Intravenous nitroglycerin unloading in acute myocardial infarction

Low-dose intravenous nitroglycerin infusion can be safely administered during acute myocardial infarction to unload the left ventricle and salvage ischemic myocardium and left ventricular geometry and function. In an experimental conscious dog model, low-dose infusion titrated to decrease mean blood pressure by 10% over the first 6 hours after coronary artery ligation resulted in 51% decrease in infarct size, 54% decrease in preload, and more than 50% increase in collateral blood flow. The same benefits were seen when methoxamine was given to counteract that 10% decrease in blood pressure. Similar short-term nitroglycerin infusion also limited remodeling in the dog model. More important, no myocardial salvage was seen with excessive nitroglycerin-induced hypotension to levels less than 80 mm Hg. Clinically, prolonged low-dose nitroglycerin infusion was evaluated in a prospective, randomized, single-blinded, placebo-controlled study of 310 patients with acute infarction: 154 received nitroglycerin and 156 received placebo. Nitroglycerin was titrated to reduce mean blood pressure by 10% in normotensive patients and up to 30% in hypertensive (blood pressure greater than 140/90 mm Hg) patients, but not to less than 80 mm Hg. Nitroglycerin produced several benefits compared with placebo: (1) smaller creatine kinase infarct size; (2) less regional left ventricular dysfunction, better global ejection fraction, and less infarct expansion and thinning; (3) better clinical functional status and hemodynamics; (4) fewer inhospital complications such as acute left ventricular failure and dilation due to marked infarct expansion, left ventricular thrombus, cardiogenic shock, and infarct extension; and (5) fewer deaths up to 1 year in patients with anterior Q-wave infarction.