Evaluation of Medical Care: Effectiveness of Interventions for Myocardial Infarctions on Hospital Case-Fatality

In this exercise, you will consider data related to the management of myocardial infarction, one of the leading causes of hospitalization and death throughout the world. Myocardial infarction occurs when oxygen delivered to the heart muscle is inadequate due to narrowing of the coronary arteries and the formation of blood clots within the arteries. Some consequences of myocardial infarction include death of the heart muscle and an inability of the heart to deliver enough blood to the tissues and maintain blood pressure (cardiogenic shock). The rhythm of the injured heart may also be abnormal (referred to as arrhythmia) and some of the arrhythmias may lead to cardiac arrest. As myocardial infarction became increasingly common, and therapeutic measures were developed, the treatment of myocardial infarctions moved within hospitals from general medical floors to specialized units called coronary care units (CCU). At the time of this transition, about 30 years ago, questions were raised concerning the benefits of treating patients in CCUs. The units were expensive to operate and some questioned whether outcomes were, in fact, improved.

This exercise presents studies carried out some years ago to evaluate CCUs. These studies have been selected because they exemplify important concepts and approaches in using epidemiology to evaluate health services. They are not intended to present a complete review of this area of investigation. Many other studies have been carried out in recent years, but are not included in this exercise.

Epidemiologic methods can be used to evaluate health services. Epidemiologic studies may evaluate a new modality of prevention, diagnosis, or therapy. Evaluation may also focus on organizational characteristics of the health care delivery system. such as comprehensive care clinics in place of categorical clinics or outreach programs in place of traditional programs.

Evaluation studies may be of two types:

1. Studies of Process

Studies of process examine the extent to which the care of patients meets current accepted standards of medical care. The underlying rationale for process studies is the assumption that "correct" process will favorably affect outcome. However, even if the process of care is judged to be good there may not necessarily be any relationship between the process of care and the desirable outcome.

2. Studies of Outcome

Epidemiologic methods are particularly useful for measuring outcome. Specifically, does a new form of medical care benefit the patients who receive this care? Are mortality and morbidity rates lower in patients receiving a new type of care than in comparable patients receiving "traditional" care?

This exercise deals with studies of outcome. Different study designs are compared for evaluating the effectiveness of health services and methodologic issues involved in applying epidemiologic techniques to this type of evaluation are explored.

In this exercise, you will review some of the initial studies carried out to determine if coronary care units improved outcome of myocardial infarction. These units aim to reduce the case-fatality rate (CFR) from myocardial infarction by prompt detection, effective prevention, and appropriate treatment of life-threatening cardiac arrhythmias using specific drugs, defibrillation, and pacemakers.

While the original debate is long resolved in favor of CCUs, the application of epidemiologic methods to evaluate the CCU remains relevant today. We repeatedly face the same types of evaluation questions as new approaches to diagnosis and treatment are introduced without being tested in clinical trials. Observational studies remain the foundation for health services research, although as seen in this exercise, clinical trials may also be performed.

Short extracts are presented from two observational studies that have attempted to evaluate the effect of CCUs on in-hospital CFR (Case-Fatality Rates) from myocardial infarction. These studies are of two types:

A. "Before-After" Study

In this study the CFRs in Ml patients prior to the establishment of the CCU are compared with rates in patients admitted to CCUs after they were established. This is also called a "historical control" study.

B. "Simultaneous Comparison" Studies

In this study, MI patients admitted to hospitals having CCUs are compared with MI patients admitted to hospitals that did not have CCUs during the same time period.

(The language used in describing these studies is that of the original authors, and only minor changes have been made in the parts that were reproduced. Most of the tables are copies of the originals.)

SECTION 1

STUDY A: "BEFORE-AFTER" STUDY (Robinson JS: Israel J Med Sci 5:772, 1969)

The first 200 patients with acute MI admitted to the CCU at Royal Perth Hospital were studied. The CCU was large enough to treat all patients admitted to the hospital with a suspected MI. The hospital records of 200 consecutive patients with acute Ml who were treated in the hospital immediately prior to opening the CCU were also reviewed; these patients were defined as the control group. In both groups the diagnosis of acute MI was confirmed based on clinical history and relevant tests, and severity of the infarctions was classified using the same criteria.

Table 1 DISTRIBUTION OF MILD INFARCTION, SEVERE INFARCTION,
AND CARD1OGENIC SHOCK IN NON-CCU AND CCU PATIENTS

Grade                       Non-CCU Patients                Coronary Care Unit Patients

                                 N                    (%)                N                    (%)

Mild                          121                    (60)            56                    (28)

Severe                       72                   (36)             119                    (59)

Shock                       7                     (4)                 25                    (13)

Total                        200                 (100)             200                 (100)

Table 2 NUMBER OF CASES AND DEATHS FOR NON-CCU PATIENTS AND CCU-TREATED PATIENTS WITHIN THE THREE CLINICAL GRADES OF INFARCTION

Grade                             Non-CCU Patients                                    Coronary Care Unit Patients

                                      N              Died                 CFR                   N             Died             CFR

Mild

                                      121               25              _____                56              1               ___

Severe                            72                36               _____               119           32

Shock                              7                   7                                        25               22

Total                              200              68                                         200             55

Question 1: What is the Case-Fatality Rate (CFR) for each group of MI patients? What is the combined CFR for Mild and Severe Non-CCU patients? What is the combined CFR for Mild and Severe CCU patients?

Question 2: Do you consider the comparison of Non-CCU patients and CCU patients in Tables I and 2 valid? Why? What statistical test can be performed to evaluate the comparison? What is the result of these tests?

The author concludes that: "This study demonstrates that compared with conventional medical ward treatment, the coronary care unit does lead to a reduction in the mortality of acute myocardial infarction".

Question 3: Discuss the author's conclusion. How could bias and changes in medical treatment affect the results of this study? Do limitations of the study design affect the conclusions that can be drawn?

STUDY B: "SIMULTANEOUS COMPARISON" (Gordis et al., Johns Hopkins Med J, 141:287, 1977).

In 1960, the Regional Medical Program of Maryland carried out a statewide study of hospital discharges with several objectives. The study aimed to develop an epidemiologic profile of the major chronic disease problems in the Maryland region, including heart disease, cancer, stroke, and chronic respiratory disease, so that guidelines for planning activities and policies of the Maryland Regional Medical Program could be rationally developed.

For a one-year period (1967) a sample of all hospitalizations in Maryland was selected and the hospital records of the patients sampled were abstracted in detail. The final sample included only cases that were acute myocardial infarctions, defined by history and clinical and laboratory findings. Table 3 presents data on all patients with myocardial infarctions in the sample, regardless of whether admitted to a CCU or general ward.

Table 3 MYOCARDIAL INFARCTION IN MARYLAND: IN HOSPITAL DEATHS BY RACE, SEX, AGE AND SEVERITY FACTORS

Question 4: Race, sex, and age have sometimes been found to affect the immediate prognosis of myocardial infarction, Based on the data in Table 3, would you agree with this statement? Why?

Question 5: Complete the table below. For each calculation you must specify a reference group. What are some considerations for this determination. Which OR estimates are statistically significant?

Question 6: Does severity on admission appear to affect outcome? Would you expect these categories to be correctly identified for all hospital admissions? Are there other complications affecting prognosis that should be analyzed?

Commenting on the results of the study, the authors stated: "A surprising finding in this study is that case-fatality rates for patients in CCUs were higher than for those treated in regular hospital beds, even when patients with differing gradations of severity were examined separately. When the data were simultaneously adjusted for race, sex, age, and severity, the differences in case fatality rate persisted."

Question 7: Calculate the adjusted relative risk for death due to use of the CCU. Interpret this estimate. How does it compare with the results from the "before-after" study?

Question 8: Can you suggest an explanation for the differences between the two studies?