Chapter 21 Marini Acute Coronary Syndromes

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CHAPTER 21 • Acute Coronary Syndromes

Reducing Myocardial Oxygen Consumption The principal measures to decrease myocardial oxy- gen consumption are to limit heart rate and after- load. These goals are immediately accomplished by curtailing physical activity with bed rest. Exercise stress tests are contraindicated in unstable patients because frank infarction may ensue. Arrhythmias like atrial fibrillation (AF) and sinus tachycardia should be controlled, both to reduce O 2 consump- tion and to optimize diastolic filling time, thereby maximizing the sufficiency of coronary perfusion. Controlling hypertension and CHF decreases myo- cardial wall tension and therefore facilitates per- fusion (see Chapter 22). Situations that increase heart rate (anxiety, use of short-acting nifedipine) or both heart rate and total body oxygen consump- tion (e.g., thyrotoxicosis, alcohol withdrawal, stimu- lant drug intoxication, anxiety, agitation, infections, etc.) should be promptly recognized and corrected. β -Blockers effectively reduce myocardial oxygen consumption by decreasing heart rate and cardiac contractility and improve O 2 supply by lengthening diastolic filling time. β -Blocking drugs are particu- larly useful in reducing oxygen consumption in the tachycardic and hypertensive patient with UA and

antiplatelet, and antianginal treatments (Fig. 21-2). Most patients with UA can be stabilized with appro- priate medical therapy. Although the immediate urgency of STEMI-ACS is attenuated, coronary angiography and revascularization procedures have become increasingly popular in the treatment of these patients over the course of the last decades. Emergent coronary angiography and revasculariza- tion procedures are uncommon for NSTE-ACS patients, but most are advised to undergo coronary angiography and possible revascularization within a few days of admission to the hospital. Coronary revascularization procedures include either percu- taneous coronary interventions (PCIs) (PTCA and stenting) (Fig. 21-3) or coronary artery bypass graft (CABG) surgery. Essentially, only patients with con- traindications for invasive cardiac procedures are treated by noninvasive medical management alone. Thrombolytics are not advisable in most (nonoc- clusive) NSTE-ACS because “red thrombus” is not present and because thrombolytics have proco- agulant properties. Apart from considerations relat- ing to coronary patency, the two basic principles in the treatment of UA are to reduce myocardial O 2 demand and improve O 2 supply.

Chest Pain

Targeted H&P 12 Lead ECG O 2 , Morphine, ASA, TNG

Low-Mod Risk Pain Relieved Quickly Negative Troponin

Mod-High Risk Prolonged Pain, Dynamic ST Pos. Troponin, Prior PCI or CABG

Enoxaparin or Heparin Eptifibatide / Tirofiban (Clopidogrel if No CABG Planned)

R/O AMI With ECG & Serial Troponins

Consider Cath in 1–2 Days

Stress Imaging Study

Early Cath / PCI or CABG

Mod-Large Reversible Defect

No Reversible Ischemia or Small Region Only

Continue Med Rx

NSTEMI Algorithm

FIGURE 21-2. Non–ST elevation MI (NSTEMI) management algorithm. ECG, electrocardiogram.