Lectura

days if possible, and preferably for 7, unless the urgency for revascularization outweighs the risks of

bleeding. (Level of Evidence: B)

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emanate from a series of randomized clinical trials per- formed before the reperfusion era. A systematic overview of these studies demonstrated a reduction in mortality (3.5% ARD; 23% RRR) and a reduction in risk of reinfarction (1.5% ARD; 18% RRR) with UFH (537). The control groups in these trials were not treated with other therapies, particu- larly aspirin, that are now considered routine. Not- withstanding this, it is primarily these randomized data from an earlier era that support the recommendation to use UFH in patients not treated with fibrinolytic therapy.

The occurrence of a large anterior infarction, documenta- tion of thrombus in the LV by echocardiography, history of a previous embolic event, and AF have been associated with a high risk of embolic stroke. Although no randomized trial evidence exists to demonstrate a definite benefit specific to this group, some empirical evidence exists that the risk of systemic emboli in the general population of MI patients can be reduced by early initiation of UFH (744). In the SCATI trial (Studio sulla Calciparina nell’Angina e nella Trombosi Ventricolare nell’Infarto), patients were randomly assigned to a 2000-IU bolus of UFH followed by 12 500 U subcuta- neously twice per day or to placebo. In the subgroup also treated with streptokinase, aspirin was withheld. In-hospital mortality was 4.6% in the UFH group and 8.8% in the con- trol group, and a reduction in stroke was observed. Therefore, UFH is recommended for these patients at high risk for systemic arterial emboli, regardless of the fibrinolyt- ic agent given. A LMWH may be used in place of UFH. Initial anticoagulation with UFH or a LMWH should be fol- lowed by warfarin in patients at high risk for systemic emboli (see Section 7.12.11 for additional discussion).

The previous ACC/AHA guidelines on acute MI (744) and the American College of Chest Physicians’ guidelines (746) recommended 7500 U of subcutaneous UFH twice per day. The empirical basis for this recommendation was the demon- stration that DVT was reduced from 12% to 4% in an overview of 3 randomized controlled trials (747). Continued adherence to this practice may be useful, although routine earlier mobilization and use of aspirin may make this treat- ment unnecessary.

7.4.6. Oxygen

Supplemental oxygen therapy should be continued beyond the first 6 hours in STEMI patients with arte-

rial oxygen desaturation (SaO2 less than 90%) or

overt pulmonary congestion.(Level of Evidence: C)

The use of oxygen in patients presenting with STEMI is discussed in Section 6.3.1.1. In view of its expense (approx- imately $70 per day), there is little justification for continu- ing its routine use beyond 6 hours in uncomplicated cases.

Pulse oximetry is now routine for continuous monitoring of oxygen saturation and is helpful for providing early warning of hypoxemia. In patients with oxygen saturation less than 90%, supplemental oxygen by nasal prongs is usually admin- mg) should be administered as soon as possible (within 24

hours) after CABG unless contraindicated (see Section 7.10.7).

Use of the thienopyridines ticlopidine and clopidogrel in the early management of STEMI is discussed above (Section 6.3.1.6.8.2.2). Clopidogrel 75 mg daily is generally preferred to ticlopidine 250 mg twice daily because of fewer side effects and once-daily dosing (740,741).

In the Clopidogrel vs. Aspirin in Patients at Risk of Ischemic Events (CAPRIE) trial of patients with UA/NSTE- MI, there was a statistically significant risk reduction in vas- cular death, MI, or stroke in favor of clopidogrel (0.51% ARD; RRR 8.7%) (742). Clopidogrel has also demonstrated efficacy in addition to aspirin versus aspirin alone in patients with acute coronary syndrome (728). Therefore, a thienopy- ridine (preferably clopidogrel) should be substituted for aspirin in patients with STEMI for whom aspirin is con- traindicated because of hypersensitivity or major gastroin- testinal intolerance. On the basis of several randomized trials of combination antiplatelet therapy (577,741,743), clopido- grel, in combination with low-dose aspirin (75 to 162 mg, to minimize the risk of bleeding), is recommended for all patients after stent implantation (432).

7.4.5. Antithrombotics

Intravenous UFH (bolus of 60 U/kg, maximum 4000-U

IV bolus; initial infusion of 12 U/kg

_/

U/h) or LMWH should be used in patients after STEMI who are at high risk for systemic emboli (large or anterior MI, AF, previous embolus, known LV

thrombus, or cardiogenic shock). (Level of Evidence:

C)

Class IIa

It is reasonable that STEMI patients not undergoing reperfusion therapy who do not have a contraindica- tion to anticoagulation be treated with intravenous or subcutaneous UFH or with subcutaneous LMWH for at least 48 hours. In patients whose clinical condition necessitates prolonged bedrest and/or minimized activities, it is reasonable that treatment be continued

until the patient is ambulatory. (Level of Evidence: C)

Class IIb

Prophylaxis for DVT with subcutaneous LMWH (dosed appropriately for specific agent) or with sub- cutaneous UFH, 7500 to 12 500 U twice per day until completely ambulatory, may be useful, but the effec- tiveness of such a strategy is not well established in the contemporary era of routine aspirin use and early

mobilization. (Level of Evidence: C)

In patients treated with fibrinolytic therapy, there is little evidence of the benefit of UFH in the modern era, during which aspirin, beta-blockers, nitrates, and ACE inhibitors are routinely available. Nevertheless, the best available data

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rate, it is possible to estimate the quantity of myocardium infarcted (751). Reasonable correlations have been estab- lished with anatomic estimates derived from postmortem human studies (752). Whereas other biomarkers of myocar- dial necrosis exist, such as myoglobin and lactate dehydro- genase, the highly sensitive cardiac troponins (I or T) have greater myocardial tissue specificity and higher sensitivity than conventional biomarkers. Measurement of cardiac tro- ponin T at 72 hours provides an estimate of infarct size in patients with STEMI who do and do not receive reperfusion therapy (753,754). In a consensus document of the Joint European Society of Cardiology and the ACC, the use of car- diac troponins was supported for the assessment of MI. The Joint Committee has emphasized that high-sensitivity car- diac biomarkers, such as troponins, can identify patients with small areas of myocardial necrosis weighing less than 1.0 g (755).

7.5.3. Radionuclide Imaging

The most comprehensive assessment of STEMI with radionuclide imaging was developed with the Technetium sestamibi SPECT approach (756). This technique has been validated extensively and offers the opportunity for both early and late imaging to initially assess the area of ischemic risk as opposed to the ultimate infarct size. This approach is well delineated in the ACC/AHA/ASNC Guidelines on Car- diac Radionuclide Imaging (239). Radionuclide angiography with a variety of radiolabeled isotopes can also provide an estimate of regional and global LV function.

7.5.4. Echocardiography

Global and regional LV function provides an assessment of the functional consequences of STEMI and ischemia. Such measures may be enhanced by an assessment of the extent of regional systolic wall thickening. Readers are referred Section 7.11.1.2 and to the ACC/AHA/ASE 2003 Guideline Update for the Clinical Application of Echocardiography (226).

7.5.5. Magnetic Resonance Imaging

Measurement of infarct size with magnetic resonance imag- ing is a promising new technique that affords enhanced spa- tial resolution, thereby permitting more accurate assessment of both the transmural and circumferential extent of infarc- tion (757). However, additional experience and comparison with other methods of assessing infarct size are required before any clinical recommendations can be provided.

7.6. Hemodynamic Disturbances

7.6.1. Hemodynamic Assessment

1. Pulmonary artery catheter monitoring should be per-