Chapter 21 Marini Acute Coronary Syndromes

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SECTION II • Medical and Surgical Crises

guiding the nature and urgency of therapeutic inter- vention. During episodes of ischemic chest pain, elec- trocardiogram (ECG) features may include (1) ST segment elevation or depression, (2) T wave flattening or inversion, (3) premature ventricular contractions (PVCs), or (4) conduction disturbances, including bundle-branch block (Fig. 21-1). Q waves often but not invariably indicate completed infarction. ST seg- ment elevation strongly correlates with fresh coronary occlusion (STEMI), whereas ST depression in asso- ciation with or without T wave inversion indicates ischemia without acute coronary luminal occlusion (non-STEMI or NSTEMI). Perhaps only 20% to 25% of ACS syndromes are STEMIs. Reversible ST depression or T wave inversion is detectable in most affected patients if continu- ous ECG monitoring is used, a finding that may not emerge during a single 12-lead ECG. Even with intensive monitoring, ECG findings are absent in up to 15% of symptomatic patients with UA. Therefore, a normal ECG does not exclude a diagnosis of UA or MI. Conversely, it has been estimated that up to 70% of all ECG-documented episodes of ischemia are clinically silent. Cardiac Enzyme Markers Elevated total CK (including the CK–MB fraction) and cardiac troponins (I and T) are markers of myo- cardial necrosis and indicate an MI, even in the absence of convincing ST segment–T wave changes. Troponins (I/T) are more sensitive and specific in making the diagnosis of an AMI than is CK-MB. Their rise may be delayed 1 to 3 hours after onset, so that their absence at a very early stage does not exclude an ongoing AMI. Once present, elevations are often detected for 10 days or longer, especially in patients with renal insufficiency. Troponin eleva- tion in NSTE-ACS correlates with adverse progno- sis. These are also patients who are likely to benefit from aggressive antiplatelet regimens and from early coronary angiography and revascularization. Highly sensitive C-reactive protein (hs-CRP) levels are also

increased in patients with ACS. ACS patients with the highest levels of hs-CRP and troponins have the worst prognosis. Prognostic Factors Patients with UA have a lower short-term mortality rate (2% to 3% at 30 days) compared to those with acute NSTEMI (5% to 7% at 30 days). The in-hos- pital or short-term mortality of patients with STEMI is higher compared with those with NSTEMI (6% to 9% vs. 5% to 7% at 30 days). However, the long- term mortality in NSTEMI (10% to 12%) is similar to or greater than that associated with STEMI (9% to 11%), likely because of their greater incidence of multivessel CAD. Thrombolysis in Myocardial Infarction Risk Score Several risk variables have been identified in patients with NSTE-ACS. A value of 1 has been assigned to each risk variable, and the total score has been shown to bear a linear relationship with risk of adverse events (death, MI, recurrent isch- emia, and need for urgent revascularization) in the short term. The variables are (1) age greater than or equal to 65 years, (2) prior coronary stenosis greater than or equal to 50%, (3) presence of greater than or equal to three coronary risk factors, (4) ST segment deviation on admission ECG, (5) elevated cardiac biomarkers, (6) greater than or equal to two anginal episodes in the last 24 hours, and (7) prior use of aspirin (marker for vascular disease). The adverse event rate is 4% to 5% for thrombolysis in myocardial infarction (TIMI) risk score of 0 to 1 but approaches 40% for those with score of 6 to 7. Elevated levels of hs-CRP indicate a worse prognosis in each TIMI scoring category. Management of NSTE-ACS Patients with NSTE-ACS should be monitored closely and should receive aggressive antithrombotic,

FIGURE 21-1. Electrocardiographic evolution of AMI. SEMI, subendocar­ dial (nontransmural) MI.