Risk Stratification in Patients With Unstable Angina
Unstable angina (UA) and non-ST elevation myocardial infarction (NSTEMI) are closely related clinical syndromes; they are often undistinguishable at presentation, and often entail similar early diagnostic and therapeutic approach. Unstable angina is defined as: 1) angina that occurs at rest or with minimal exertion; 2) new onset angina (within one month) with Canadian Cardiovascular Society Classification III or IV in severity; or 3) worsening previously stable angina. First attempts in evaluating UA were directed toward ruling out myocardial infarction (MI). More modern approaches consider NSTEMI (or non-Q wave MI) to be a more severe state of the same clinical syndrome. This syndrome is often referred to as non-ST elevation acute coronary syndrome (ACS). Risk stratification is of crucial importance for the practice of contemporary medicine, especially when dealing with patients presenting with UA/NSTEMI, due to the wide range of acuity and risk of untoward outcome. The frequency of hospital admissions and the cost of diagnosis and management of suspected UA/NSTEMI make this an important health care issue. It is estimated that more than 1.4 million patients are admitted to American hospitals every year with suspected UA. The value of risk stratification is apparent, since a substantial portion of these patients are at low risk for cardiac events and can be treated as outpatients with huge cost savings, and higher risk patients can be effectively managed with aggressive medical and interventional therapy, resulting in lower event rates and costs. On the other hand, identifying patients at increased risk for cardiac events is crucial from the therapeutic point of view. As a general principle, patients at increased risk for unfavorable outcome have incremental benefit from therapeutic interventions. This principle is especially applicable to patients presenting with UA/NSTEMI.
Early risk stratification attempts used electrocardiogram (ECG) changes as indicators of increased risk. ST-segment deviation ≥ 1 mm (ST depression or transient elevation) and dynamic T-wave inversion ≥ 3 mm were found to be important markers of adverse outcome (death, MI) and anatomic severity of coronary artery disease (CAD). More recent data from the TIMI-III registry have found left bundle branch block and ST deviation (≥ 0.5 mm) to be independent predictors of death in 1 year. Other investigators found incremental risk with increasing ST-segment depression on admission ECG. GUSTO-IIb data showed that ST-segment depression carries worse prognosis than T-wave inversion.
Braunwald was the first to establish a comprehensive classification scheme for patients presenting with UA ( Table 1 ). He classified UA based on the acuity of the pain syndrome (progressive exertional angina, rest pain within 2 weeks but none in the past 48 hours, and rest pain within the past 48 hours) and certain clinical circumstances (extracardiac exacerbation, primary, and after MI within the past 14 days). Theses classes can be further subdivided based on the intensity of antianginal treatment at presentation, and the presence or absence of ST-segment depression during chest pain. The ability of this classification to predict risk of cardiac events has been validated in several studies. In the TIMI-III registry, the Braunwald classification was found to be an important predictor of death or MI after 1 year, both by the severity of chest pain syndrome and by the clinical circumstances in which it occurred.
Unstable angina (UA) and non-ST elevation myocardial infarction (NSTEMI) are closely related clinical syndromes; they are often undistinguishable at presentation, and often entail similar early diagnostic and therapeutic approach. Unstable angina is defined as: 1) angina that occurs at rest or with minimal exertion; 2) new onset angina (within one month) with Canadian Cardiovascular Society Classification III or IV in severity; or 3) worsening previously stable angina. First attempts in evaluating UA were directed toward ruling out myocardial infarction (MI). More modern approaches consider NSTEMI (or non-Q wave MI) to be a more severe state of the same clinical syndrome. This syndrome is often referred to as non-ST elevation acute coronary syndrome (ACS). Risk stratification is of crucial importance for the practice of contemporary medicine, especially when dealing with patients presenting with UA/NSTEMI, due to the wide range of acuity and risk of untoward outcome. The frequency of hospital admissions and the cost of diagnosis and management of suspected UA/NSTEMI make this an important health care issue. It is estimated that more than 1.4 million patients are admitted to American hospitals every year with suspected UA. The value of risk stratification is apparent, since a substantial portion of these patients are at low risk for cardiac events and can be treated as outpatients with huge cost savings, and higher risk patients can be effectively managed with aggressive medical and interventional therapy, resulting in lower event rates and costs. On the other hand, identifying patients at increased risk for cardiac events is crucial from the therapeutic point of view. As a general principle, patients at increased risk for unfavorable outcome have incremental benefit from therapeutic interventions. This principle is especially applicable to patients presenting with UA/NSTEMI.
Early risk stratification attempts used electrocardiogram (ECG) changes as indicators of increased risk. ST-segment deviation ≥ 1 mm (ST depression or transient elevation) and dynamic T-wave inversion ≥ 3 mm were found to be important markers of adverse outcome (death, MI) and anatomic severity of coronary artery disease (CAD). More recent data from the TIMI-III registry have found left bundle branch block and ST deviation (≥ 0.5 mm) to be independent predictors of death in 1 year. Other investigators found incremental risk with increasing ST-segment depression on admission ECG. GUSTO-IIb data showed that ST-segment depression carries worse prognosis than T-wave inversion.
Braunwald was the first to establish a comprehensive classification scheme for patients presenting with UA ( Table 1 ). He classified UA based on the acuity of the pain syndrome (progressive exertional angina, rest pain within 2 weeks but none in the past 48 hours, and rest pain within the past 48 hours) and certain clinical circumstances (extracardiac exacerbation, primary, and after MI within the past 14 days). Theses classes can be further subdivided based on the intensity of antianginal treatment at presentation, and the presence or absence of ST-segment depression during chest pain. The ability of this classification to predict risk of cardiac events has been validated in several studies. In the TIMI-III registry, the Braunwald classification was found to be an important predictor of death or MI after 1 year, both by the severity of chest pain syndrome and by the clinical circumstances in which it occurred.