Evidence-Based Coronary Care

Since Herrick's classic description of acute myocardial infarction was published in 1912, the management of this condition has gone through four phases. The first, which may be called the “clinical observation phase” of coronary care, lasted about half a century and consisted of the simple assessments that were possible at that time. Vital signs were recorded frequently, especially on the first day after infarction; clinical examinations were done and electrocardiograms were obtained daily for the first few days; and chest roentgenograms were obtained once or twice a week. The infarcted heart was considered to be a wounded organ, the repair of which required the equivalent of the immobilization of a fractured bone. Treatment therefore consisted of strict bed rest and sedation. Digitalis was administered for heart failure, and quinidine was given for frequent premature ventricular contractions. Patients were usually hospitalized for 5 to 6 weeks. The major debates during this phase revolved around whether ambulation could be started early (1 week) or late (2 to 3 weeks) after admission. There was also considerable controversy about the indications for anticoagulant agents, which were administered primarily to prevent pulmonary thromboembolism, a major complication of bed rest. The in-hospital mortality rate approached 30%; after discharge, patients usually led restricted lives, and 15% died during the remainder of the first year.

The situation changed radically during the early 1960s in the so-called “coronary care unit phase” [1]. This phase was marked by the refinement of techniques for closed-chest cardiac resuscitation and the gathering in a single location in the hospital of equipment for continuous electrocardiographic monitoring and teams of trained physicians and nurses who could efficiently use the newly available antiarrhythmic agents (such as lidocaine) and could use direct-current defibrillators and pacemakers to treat life-threatening arrhythmias. During this period, patients enjoyed the benefit of a halving of the in-hospital mortality rate for acute myocardial infarction but remained susceptible to the late consequences of large infarctions: heart failure and malignant ventricular arrhythmias. This resulted in a continued high incidence of late deaths and serious disability.

The third phase of coronary care, the “high-technology phase,” began in the 1970s and was characterized by the appearance of several new diagnostic and therapeutic methods driven by advances in instrumentation and pharmaceuticals. Notable among these advances was the introduction of the Swan-Ganz catheter for bedside assessment of hemodynamics, which was done to define subsequent management [2]. A battery of tests that sometimes provided overlapping information was often carried out before hospital discharge; these tests included 24-hour ambulatory (Holter) electrocardiography, which was occasionally followed by electrophysiologic testing. Exercise electrocardiography, radionuclide ventriculography, and myocardial perfusion scintigraphy were often performed, both at rest and during exercise, and they were often followed by coronary arteriography and myocardial revascularization. It was during this era that the concept of protecting the ischemic myocardium was developed [3]; this led first to the use of β-blockers and then to early myocardial reperfusion-thrombolytic therapy and primary coronary angioplasty. Coronary care was based primarily on the rational application of pathophysiologic principles. The clinical outcome of patients with acute myocardial infarction improved further, and the in-hospital mortality rate was reduced to less than 10%. The patients' postdischarge prognosis also improved. Because early reperfusion often limited the infarction size, patients were left with more viable myocardium, which reduced the risk for subsequent heart failure and fatal arrhythmias [4].

Because of the perception that all or most of the aforementioned diagnostic and therapeutic measures had to be applied to a large fraction of patients with acute myocardial infarction, a veritable army of subspecialists-clinical cardiologists, interventional cardiologists, nuclear cardiologists, cardiac electrophysiologists, cardiac radiologists, and surgeons-all participated in the care (and billing) of patients with acute myocardial infarction. The costs of care skyrocketed, even though the hospital stay was shortened. As concern about costs mounted, questions were raised. Had the pendulum swung too far? Were too many expensive diagnostic procedures performed, resulting in overly aggressive, expensive, and unnecessary therapy?

The stage was set for the commencement of a new phase, which might appropriately be termed the “evidence-based coronary care phase.” The analysis of coronary care by Peterson and colleagues in this issue [5] is an excellent starting point for an understanding of this phase. These authors argue persuasively that the performance of a specialized test in a patient with acute myocardial infarction is only justified if the test can provide incremental information that will change the clinician's practice so as to favorably affect clinical outcome. It now seems that the tests (such as Holter electrocardiography) that were developed and widely applied in the high-technology phase of coronary care fail to provide information that influences care in many patients. Other tests, such as nuclear imaging techniques, frequently offer only redundant information [6]. Coronary angiography after acute infarction leads to management decisions that improve outcome in only a minority of patients [7]. The reasons why many of the tests in the high-technology phase of coronary care had limited clinical value are complex. Chief among these reasons is a progressively lower pretest likelihood of adverse outcome (largely due to improvements in the care of patients with acute myocardial infarction), which produced low positive predictive values for many tests.

The basic strategy described by Peterson and colleagues is 1) to assess risk continuously during the patients' course, especially at the initial presentation, at 24 hours, during the late hospital phase, and before discharge and 2) to drive management at each point according to the results of these assessments. Notably, the simple demographic characteristics (such as age) and clinical findings (such as pulse and blood pressure) that so preoccupied clinicians during the clinical observation phase of coronary care have now been shown to be the most important descriptors of risk [8, 9]. Quantitative assessment of left ventricular function should be obtained during hospitalization. Clinicians should select one of the following on the basis of clinical circumstances and local institutional expertise: echocardiography, radionuclide angiography, or left ventriculography. Stress electrocardiography, sometimes supplemented by two-dimensional transthoracic echocardiography, can be used to select the subset of patients in whom coronary arteriography is likely to provide the most useful information. As suggested by Table 4 of the paper by Peterson and colleagues, the routine use of exercise myocardial perfusion imaging is not indicated because of reduced specificity and lack of improvement in positive predictive value for adverse outcome compared with conventional exercise electrocardiography. Coronary revascularization done using surgical or catheter-based techniques is not ordinarily performed simply because coronary obstruction is present. Rather, its use is limited to subgroups of patients in whom it has clearly been shown to prolong life or improve quality of life. Risk factors for recurrent coronary events are assessed at the time of admission, and secondary prevention using diet; optimization of blood pressure, serum lipid levels, and glucose levels; and smoking cessation is begun early in the hospital course and continued aggressively after discharge.

Two major forces have converged to bring us into the evidence-based coronary care phase. The first is the widespread agreement that it is no longer acceptable to base the use of diagnostic tests and therapeutic measures on anecdotal experience or on the results of retrospective cohort studies, especially for a condition such as acute myocardial infarction, which is so common and has been studied so intensively. The second is the advent of managed, particularly capitated, care, which places such a high priority on reducing costs by using only those diagnostic tests and therapeutic interventions that have a proven effect on clinical outcome. During this phase of evidence-based coronary care, we can look forward to maintaining and even improving on the excellent results developed during the high-technology phase, with the additional benefit of returning patients to work and to a normal lifestyle much more rapidly than before. Early attention to secondary prevention is likely to result in substantial further improvement in long-term outcome. It should be possible to accomplish this while preventing further escalation of costs; in many instances, the costs of care may even be reduced.

Many challenges remain in the care of patients with acute myocardial infarction. Even though in-hospital mortality rates have been reduced by approximately two thirds since the end of the clinical observation phase 35 years ago, about 500 000 patients in the United States still die of acute myocardial infarction each year [10]. What causes these fatal outcomes? Most of the deaths are sudden and occur before the patient reaches the hospital. Most of the remainder result from massive infarctions that cause cardiogenic shock or internal or external cardiac rupture. Although reperfusion therapy (thrombolysis or primary percutaneous transluminal coronary angioplasty) has enormously improved the care of patients with acute myocardial infarction and ST-segment elevations who present to the hospital soon after the onset of symptoms, patients with large infarctions and ST-segment depression present a continuing challenge. In the future, an increasing focus on patient behavior will be required. For example, we will have to learn how to identify persons who delay seeking medical assistance after the development of symptoms and how to modify the behavior of these persons so that these delays are shortened [11].

The new generation of antiplatelet agents will be of increasing interest. The potent direct glycoprotein IIb/IIIa inhibitors, when used in conjunction with thrombolytic agents, have the potential to establish patency of occluded vessels more rapidly, thereby reducing myocardial damage, enhancing myocardial function, and improving both short- and long-term outcomes. Oral forms of these inhibitors have been developed, and large-scale testing of these agents in patients who have had acute myocardial infarction is about to begin.

Whatever the direction of future research, the incorporation of the results of that research into clinical practice will be based on rigorous analysis of evidence. It is likely, therefore, that evidence-based coronary care will be more than just another phase in the evolution of coronary care; we believe that it is here to stay.

• Copyright ©2004 by the American College of Physicians