Chapter 21 Marini Acute Coronary Syndromes

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SECTION II • Medical and Surgical Crises

Whenever possible, central venous catheters and arte- rial punctures should be avoided during antithrombo- lytic therapy. If the ECG is suggestive and the history is compatible with MI, aspirin and nitrates (if toler- ated) should be administered to almost all patients while the intervention strategy is actuated. Opiates (classically morphine) and/or benzodiazepines should be considered for control of pain and anxiety. Unless contraindications exist, β -blockers should be admin- istered to most patients with rapid tachycardia, but their use should otherwise be deferred until cardiac performance is assessed and stability is assured. Aspirin Because it is safe, fast, and effective at prevent- ing recurrent thrombosis, aspirin (160 to 325 mg) should be given promptly to all patients with AMI without contraindications (e.g., history of aspirin allergy) and should be continued on a daily basis. Aspirin alone achieves an average 20% reduction in mortality, and when combined with other antiplate- let agents, an amazing 40% reduction in death rate is observed. For patients who are allergic to aspirin, clopidogrel used alone is less desirable but effec- tive fall back option. Regardless of the suitability of the patient for thrombolytic therapy or angioplasty, an aspirin tablet once or twice daily reduces mor- tality risk and reinfarction rates for essentially all subgroups of patients with MI. Aspirin can be con- tinued safely for years while providing continued benefit. Aspirin alone is as effective as preparations that combine it with sulfinpyrazone or dipyridamole. Nitrates Unless contraindicated, NTG should be tried in nearly every patient having acute ischemic symp- toms and an ECG suggesting MI. If a portion of the affected coronary artery remains patent, nitrates can promote flow through the narrowed segment. If the coronary occlusion is complete, however, nitrate therapy is unlikely to offer much, if any, boost in flow. Nitrates improve myocardial oxygen supply by reducing preload (and to a limited extent afterload) as well as by directly dilating coronary arteries. Intravenous nitrates may reduce infarct size and probably reduce mortality of AMI substan- tially. Except for hypotension or profound tachycar- dia, few contraindications to nitrate therapy exist. Nitrates should be used cautiously in inferior MI because of the potential to aggravate bradycardia and with great caution for patients with coexisting

RV infarction, in whom small reductions in venous return can produce profound hypotension. Initially, sublingual or intranasal dosing makes sense because it is fast, is titrated easily, and can help alleviate symptoms while definitive reperfusion therapy is executed. If pain relief is achieved temporarily with sublingual or intranasal NTG, administration by continuous intravenous infusion often proves useful for longer relief. Long-acting oral nitrates should be avoided because of the inability to easily reverse or titrate their effects. Headache is common but easily treated with acetaminophen. Alcohol intoxication (from the intravenous vehicle) and methemoglo- binemia are uncommon complications of prolonged intravenous infusion therapy. Analgesia and Anxiolysis Relief of pain and anxiety is important in the treat- ment of AMI. Ideally, ischemic pain is reversed by achieving reperfusion of the hypoxic cardiac mus- cle; however, direct analgesia may be necessary. Morphine, given in carefully measured doses, is the drug of choice. In addition to providing direct pain relief, morphine serves to reduce preload and, to a lesser degree, afterload—both potentially improving the balance in myocardial oxygen supply/ demand. Furthermore, morphine inhibits anxiety- induced catecholamine release, further reducing myocardial oxygen consumption. Despite the fears of physicians, morphine-induced bradycardia and hypotension occur rarely; when they do occur, they usually respond promptly to fluids and/or low-dose atropine. Nausea is a more frequent problem that may warrant an opiate alternative such as carefully administered fentanyl. When analgesic range doses of morphine (2 to 10 mg) are given slowly, the risk of respiratory depression or any other complication is minimized. For the extremely anxious patient, especially one experiencing MI from cocaine use, benzodiazepines are very useful anxiolytic agents. β- Blockade Intravenous β -blockade given soon after the onset of MI may reduce infarct size and lower the risks of cardiac arrest, reinfarction, and death. These ben- efits are achieved predominantly by lowering myo- cardial oxygen consumption through reductions in heart rate, blood pressure, and contractility; how- ever, β -blockers also provide independent antiar- rhythmic effects. In addition to the early protective effects, continued therapy also lowers the long-term