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Fibrin-selective agents have a high
    velocity of clot lysis, whereas the nonselective agents have a slower clot
    lysis and more prolonged systemic lyric state.
    The indication for thrombolytic therapy includes chest pain that is
    suggestive of myocardial ischemia and is associated with acute ST segment elevation on a 1 2-lead ECG or a presumed new left ventricular bundle branch block. Hospital protocol regarding the time period to perform thrombolyric therapy usually varies, as clinical trials have led to some controversy.12 Some studies show benefits only if treaanent is conducted within 6 hours of symptoms, whereas others have demonstrated improvement with treatment up to 24 hours after onset of symptoms. 12
    The contra indications to thrombolytic therapy generally include
    patients who are at risk for excessive bleeding. Because of the variability that can occur among patients, many contraindications ate considered relative caurions, and the potential benefits of therapy are
    weighed against the potential risks. Thtombolytic therapy is used in
    conjunction with other medical treatments such as aspirin, intravenous heparin, intravenous nitroglycerin, lidocaine, atropine, and a beta-blocker. As previously discussed, early peaking of CK-MB is
    associated with reperfusion.'2
    Percutaneous Revascularization Procedures
    Percutaneous revascularization procedures are used to return blood
    flow through coronary arteries that have become occlusive secondary

    CARDIAC SYSTEM
    5 1
    to atherosclerotic plaques. The following list briefly describes three
    percutaneous revascularization proceduresl2:
    1 . PerClltalleOllS translumillal corollary allgioplasty (PTCA)
    is performed on small atherosclerotic lesions that do not completely occlude the vessel. PTCA can be performed at the time of an initial diagnostic catheterization, electively at some time after a
    catheterization, or urgently in the setting of an acute Ml.
    A sheath is inserted into the femoral, radial, or brachial artery,
    and a catheter is guided through the sheath into the coronary
    artery. A balloon system is then passed through the catheter to the
    lesion site. Inflations of variable pressure and duration may be
    arrempted to reduce the lesion by at least 20% diameter with a
    residual narrowing of less than 50% in the vessel lumen 12 Owing
    to some mild ischemia that can occur during the procedure,
    patients occasionally require temporary transvenous pacing, intraaortic ballon counterpulsation, or femorofemoral cardiopulmonary bypass circulatory suppOrt during PTCA.
    The use of coronary laser angioplasty, directional coronary
    atherectomy, and endoluminal stents was developed in response to
    the major limitations of PTCA, which include abrupt closure (in
    up to 7.3% of patients), restenosis, anatomically unsuitable
    lesions, chronic total occlusions, unsatisfactory results in patients
    with prior coronary arrery bypass graft (CABG) surgery '·
    2.
    Coronary laser angioplasty uses laser energy to create precise
    ablation of plaques without thermal injury to the vessel. The laser treatment results in a more pliable lesion that responds better to balloon expansion. The use of laser angioplasty is limited owing to the expense
    of the equipment and a high restenosis rate (>40%).·5
    3.
    Directional coro/wry atherectomy can be performed by
    inserting a catheter with a currer housed at the distal end on one
    side of the catheter and a balloon on the other side.12 The balloon
    inflates and presses the cutter against the atheroma (plaque). The
    cutter can then cut the atheroma and remove it from the arterial
    wall. This can also be performed with a laser on the tip of the
    catheter. Rotational ablation uses a high-speed rotating bur coated
    with diamond chips, creating an abrasive surface. This selectively
    removes atheroma due to its inelastic properties as opposed to the
    normal elastic tissue. 12 The debris emitted from this procedure is
    passed into the coronary circulation and