High-risk and some intermediate-risk unstable angina patients will be moved to the nonintensive phase after 1 or more days of intensive management and stabilization. Some of these latter patients will have undergone cardiac catheterization, and some also will have had one or more revascularization procedures. Other intermediate-risk unstable angina patients may be admitted initially to a monitored intermediate care unit until the diagnosis of MI can be excluded and it is clear that the patient's symptoms are adequately controlled on medical therapy. These patients then enter the nonintensive phase of management. Still other intermediate-risk and some low-risk patients may be admitted directly to a regular hospital bed with telemetry capabilities, thereby proceeding directly to the nonintensive phase. Management of the nonintensive phase is described in this chapter (see Figure 8).
Transfer out of the intensive care phase is an important indicator that the patient has progressed to a lower risk state. At this point, emphasis shifts from acute stabilization to design of a maintenance medical regimen that will suppress reactivation of acute disease activity. In addition, a major focus is placed on risk stratification with primary goals of assessing the future risk of adverse cardiac events, the sufficiency of medical therapy in controlling symptoms, and the need for diagnostic cardiac catheterization and revascularization. Use of noninvasive testing is detailed in Chapter 6, and indications for catheterization and revascularization are described in Chapter 7. This chapter will describe the general care of patients who have reached the nonintensive phase of care. By this point in the hospital course, most patients with acute MI have been identified; their subsequent management is outside the scope of this guideline.
Once patients reach the nonintensive phase of management, reasons for continued hospitalization include optimization of medical therapy, evaluation of the propensity for recurrent ischemia or ischemic complications, and risk stratification to determine the need for catheterization and revascularization. Continuous monitoring of the ECG at this phase is generally unnecessary. All patients should be instructed to notify nursing personnel immediately if chest discomfort recurs. Recurrent ischemic episodes should prompt a brief nursing assessment and an emergent ECG and generally should be brought to the attention of a physician. The patient's medical regimen should be reevaluated and doses of anti-ischemic agents should be increased as tolerated. Patients who have pain or ECG evidence of ischemia increasing in severity for > 20 minutes and unresponsive to NTG should be transferred to the intensive management phase protocol. Patients who respond to sublingual NTG do not need to be transferred. However, a second recurrence of chest pain of at least 20 minutes duration in the setting of appropriate medical therapy should prompt return of the patient to a monitored environment and the management steps outlined in the intensive management phase.
In general, patients reaching this phase would be referred within 1 to 2 days either for noninvasive functional testing or for cardiac catheterization. Selection of the appropriate strategy of risk stratification is discussed in Chapters 6 and 7. Patients can be considered ready for discharge from the hospital when their evaluation is complete and an appropriate outpatient therapeutic regimen is established.
Steps to move the patient towards readiness for hospital discharge should be initiated during this phase. These steps include instruction on home diet and exercise, physical activity, resumption of sexual relations, return to work, and resumption of driving and other usual activities. In addition, detailed discussions should be conducted with the patient, his or her family, and the patient's advocate to review the events since presentation and their significance, current status, diagnostic and therapeutic options, and general prognosis.
The slower pace of this phase of the patient's hospitalization, in contrast to early stabilization and intensive care, offers the most appropriate time for CAD education. During the initial phase of the hospitalization, the patient may be in much pain, under sedation, or generally too anxious to retain the information. Likewise, immediately before discharge the patient may be distracted by preparations for going home.
The following information should be added to the medical record during this phase of care:
The nonintensive phase of management begins with ICU or intermediate care unit transfer and extends until hospital discharge. During this phase, risk stratification will be completed, and many patients will undergo cardiac catheterization and revascularization procedures. Thus, low-risk patients not requiring further intervention may be discharged in 1 to 2 days, but patients with complicated cases or those requiring CABG may require an additional week or more of hospitalization.
The entire process of managing patients with unstable angina requires ongoing risk stratification. Much prognostic information of value derives from the initial assessment and the patient's subsequent course over the first few days of management, as described in Chapters 3 and 4. In many cases, noninvasive stress testing provides a useful supplement to these clinically based risk assessments.
However, some patients, such as those with rest angina and ECG-documented ischemia, have such a high likelihood of CAD and risk of adverse events that noninvasive risk stratification would not be likely to identify a subgroup with sufficiently low risk to merit noninterventional strategies. Other patients are not willing to consider interventional treatment or have severe complicating illnesses or advanced age so that referral for revascularization would not be reasonable. Still other patients may be felt to have a very low likelihood of CAD after their initial complete clinical evaluation with an associated risk of cardiac events so low that no positive test finding would prompt consideration of catheterization and myocardial revascularization. All patients who do not fall into one of the above exception categories are reasonable candidates for risk stratification by noninvasive testing (see Figure 9).
The goals of noninvasive testing in a patient with unstable angina who has recently been stabilized are to estimate the subsequent prognosis, especially for the next 3 to 6 months, to decide what additional tests and adjustments in therapy are required based on this prognosis, and to provide the patient with the information and reassurances necessary to return to a lifestyle as full and productive as possible.
Noninvasive functional or stress testing refers to a series of provocative tests that use either exercise or pharmacologic means to detect ischemia or inhomogeneity in myocardial blood flow due to obstructive CAD. The exercise tests are based on the principle of using a progressive physiologic stress (usually treadmill or bicycle exercise) to increase myocardial work and oxygen demand while using some method (ECG, function, perfusion) to document objective evidence of ischemia. Provocation of ischemia at a low workload (e.g., >e;5 to 6 metabolic equivalents [METs]) signifies a high-risk patient who would generally merit referral to cardiac catheterization. On the other hand, attainment of a higher workload (e.g., >e;5 to 6 METs) without ischemia is associated with a better prognosis, and many such patients can be safely managed conservatively. Other patients, including those who tolerate only a low workload but have no evident ischemia or those who develop ischemia at a high workload, represent an intermediate-risk group for whom several reasonable strategies can be proposed.
Pharmacologic stress testing provides an important complement to exercise testing, particularly for the subset of patients who are unable to exercise ( Zhu, Chung, Botvinick et al., 1991). The IV-administered coronary vasodilators such as dipyridamole decrease coronary vascular resistance and thus substantially increase coronary flow. Where significant epicardial coronary stenosis exists, the increase in flow is limited relative to myocardial segments supplied by nonobstructed coronary arteries. This flow discrepancy is routinely evaluated with perfusion scintigraphy. Occasionally, these agents produce ischemia by provoking an endocardial to epicardial steal and consequent diminished endocardial blood flow in the territory of a critical coronary stenosis. In contrast, dobutamine stress testing with measurement of cardiac function or perfusion acts by increasing myocardial oxygen demand in a fashion similar to exercise.
The greatest experience with these agents is in patients who are unable to exercise. In general, their prognostic value appears equivalent to exercise testing with imaging although there are few direct comparison studies of prognostic stratification with the two approaches. However, the known prognostic information derived from maximal exercise level attained argues for use of pharmacologic stress testing as an alternative to exercise testing only for specific indications.
No empirical data or theoretical arguments have yet established that LV function during exercise or pharmacologic stress provides more valuable prognostic information than a perfusion scan or vice versa. Both the extent of CAD and the degree of LV dysfunction are important for selection of appropriate therapy. Studies directly comparing prognostic information from multiple noninvasive tests for ischemia in patients after stabilization of unstable angina are hampered by small sample size ( Amanullah, Bevegard, Lindvall et al., 1992; Marmur, Freeman, Langer et al., 1990).
Two relatively large studies addressed the prognostic value of exercise testing in unstable angina to predict death and MI. The Multicenter Myocardial Ischemia Research Group recently reported the results of a 23-month followup study of the prognostic value of noninvasive testing in 936 stable CAD patients who had an MI (70%) or unstable angina (30%) hospitalization within the 6-month period prior to testing ( Moss, Goldstein, Hall et al., 1993). Noninvasive testing involved rest, ambulatory, and exercise ECG and stress thallium-201 scintigraphy. The outcome event tested was a composite of death (n=22), nonfatal MI (n=53), or unstable angina (n=125). In the primary analysis, only ST depression on the resting ECG was an independent prognostic factor. Both exercise ECG ST-depression (p=0.29) and reversible thallium defects (p=0.05) showed univariate trends towards a worse prognosis. Ambulatory ECG changes were not significant predictors of outcome in this population (p=0.93). Additional prespecified analyses revealed that the combination of exercise ST depression >0.10 mV and an exercise duration <9 minutes (modified Bruce protocol) identified patients at a 3.4-fold (<6 minutes) to 1.9-fold (6-9 minutes) increase in risk of cardiac events. With the exercise thallium, a reversible defect and increased lung thallium uptake indicated a 2.8-fold increase in risk; a reversible defect alone signified a 1.2-fold increase in risk.
The RISC study group evaluated the use of predischarge symptom-limited, bicycle exercise testing in 740 men admitted with unstable angina (51%) or non-Q-wave MI (49%) ( Nyman, Larsson, Areskog et al., 1992). Multivariate analysis showed that the extent of ischemic ST depression (number of positive leads) and low maximal workload were independent predictors of 1-year, infarct-free survival.
In addition to these two large studies, six studies of patients with unstable angina report at least 10 cardiac deaths and/or MIs during followup (see Table 10). These studies permit comparison of the effectiveness of exercise electrocardiogram and exercise or dipyridamole thallium-201 for risk stratification. The total annualized risk of cardiac events in each study is depicted in Figure 10, with the individual studies arranged from left to right in ascending order of risk. This arrangement places studies in populations at lower risk on the left and at higher risk of subsequent event on the right. The annualized percentage risk in the high- and low-risk groups stratified by a positive or negative noninvasive test is plotted using criteria defined as optimal for each study. All three studies show similar accuracy in dichotomizing the total population into low- and high-risk subgroups.
In low-risk patients, it is unclear that an imaging modality adds importantly to a standard treadmill test. Thus, selection of the test to use with an individual patient should rest primarily on patient characteristics, knowledge of local availability, and interpretation expertise. Because of simplicity, lower cost, and widespread familiarity with performance and interpretation, the standard ECG treadmill is the most reasonable test to select in patients able to exercise who have a normal resting ECG. Patients with an abnormal baseline ECG that would interfere with interpretation of the exercise results should have an imaging modality added to their test. Patients unable to exercise should have a pharmacologic stress test. The optimal testing strategy in women remains less well defined than in men. All major forms of exercise testing have been reported as less accurate for diagnosis in women. At least a portion of the lower reported accuracy derives from a lower pretest likelihood of CAD in populations of women compared with men. The relative accuracy of noninvasive testing for prognosis in women and men has not been adequately studied. Until data are reported to clarify this issue, it is reasonable to use noninvasive testing for prognosis in women as freely as in men with proper consideration of the influence of sex on the pretest likelihood of CAD.
The stress test using a standard protocol can be performed as soon as appropriate indications are present and the patient has stabilized clinically. In 1991, Larsson, Areskog, Areskog and colleagues compared the results of a symptom-limited exercise test performed before discharge at 3 to 7 days after an episode of unstable angina or non-Q-wave infarction with the results of a similar test 1 month later in 189 patients. The diagnostic and prognostic value of both tests was similar, but the earlier test identified events occurring over the first month which represented one-half of all events during the first year. This study illustrates the importance of early noninvasive testing for risk stratification of patients with unstable angina.
Noninvasive tests are most useful in patient management decisions when risk can be stated in terms of events over time. A large population of patients must be studied to derive and test equations needed to accurately predict risk for individual patients. No noninvasive study has been reported in a sufficient number of patients after stabilization of unstable angina to develop and test the accuracy of a multivariable equation to report test results in terms of absolute risk. Therefore, data borrowed from studies of patients with stable angina must be used if risk is to be reported as events/time. Although the pathologic process evoking ischemia may be different in the two subgroups, it is likely that use of prognostic nomograms derived on groups of patients with stable angina would also be predictive of risk in patients with recent unstable angina after stabilization. Using this untested assumption, the much larger literature derived from populations that include patients with both stable and unstable angina provides equations for risk stratification which convert physiologic changes observed during noninvasive testing into statements of risk expressed as events over time.
An exercise treadmill is the most commonly used stress test and has the largest reported experience for use in patients with unstable angina. A nomogram useful to convert results from this test into a statement of mortality has been derived on a large sample of patients with CAD (Figure 11). Even though use of this nomogram to quantitate risk from results of treadmill examinations may understate risk in patients with unstable angina, this approach provides more clinically useful information than a simple normal/abnormal reading ( Mark, Shaw, Harrell et al., 1991).
Results of a noninvasive test should be reported to the patient, his or her family, and advocate in language they can understand, and the test results should be used by the patient and the doctor to determine the advisability of cardiac catheterization and the need for adjustments in the patient's medical regimen.
The medical record should include:
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