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(a treadmill test) the following morning. Mr. Johnson performed well on the stress test; he exercised for 12 minutes without any type of abnormality, either in the ST-segment or in his vital signs. On the basis of this "negative" stress test, the defendant advised Mr. and Mrs. Johnson that the test result was negative and explained that nothing in the test indicated ischemia. He said whatever caused the chest pain was not related to Darrel Johnson's heart.
Dr. Truong discharged Mr. Johnson from the hospital on January 25, gave him a note to return to work the next day without restrictions, and advised him to see his family physician within the next two weeks. Mr. Johnson made an appointment to see his family doctor the following Tuesday, February 2, 1993. He returned to work the next day, which was a Wednesday, and on Friday evening told his wife that he had experienced the "same problem"again on Wednesday and Thursday. The Johnsons were concerned about the recurring symptoms, but, having been assured the cause was not cardiac, decided to wait for the doctor's appointment. The following Monday, February 1, while at work, Mr. Johnson collapsed and died. On autopsy, all three major coronary arteries were obstructed about 80 percent, with evidence that a small myocardial infarction had occurred most likely 3 to 4 days before death. The mechanism of death was arrhythmia caused by infarction, which was in turn caused by the undiagnosed coronary artery disease.
At trial, the defendant's position, which had support in the literature, was that the hospital evaluation was appropriate and complete, and a negative treadmill test after 12 minutes of exercise justified discharging the
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patient back to normal activity with confidence. The doctor also claimed that the decedent was negligent for failing to come back in with the recurring symptoms.
Plaintiffs' strongest theories of liability were as follows:
- Failure to recognize the limitations of the exercise stress test in ruling out coronary disease as the cause of the symptoms.
- Improperly reassuring the decedent and creating a false sense of security that his symptoms were noncardiac, when, in fact, cardiac causes had not been ruled out.
- Failure to provide decedent with adequate discharge and follow-up instructions, specifically that cardiac causes had not been ruled out, and to get prompt medical attention if the symptoms reoccurred.
Plaintiffs' position was that, while the defendant went through all of the proper motions, collected most of the important information, and did an acceptable test, he had a fundamental and dangerous lack of understanding in two important areas: First, he did not recognize or appreciate that Mr. Johnson's symptoms were "typical angina"; he called the presentation "atypical." Second, he did not understand the limitations of the stress electrocardiogram, based on the "sensitivity"of the test.
Sensitivity indicates the frequency of a positive test result in a population of patients who have a particular disease. In the case of the treadmill test, the sensitivity is about 70 percent. This means that for every 100 patients who have coronary artery disease as the explanation for their chest symptoms, the treadmill will be negative for 30, resulting in 30 false-negative results. Particularly for patients with "typical angina,"
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who have a high "pretest likelihood"of coronary artery disease, physicians must be skeptical of negative treadmill results. Clearly, a negative treadmill test cannot rule out coronary artery disease as the cause of chest symptoms in patients like Mr. Johnson, whose "typical angina"carries a very high pretest risk of coronary artery disease. The defendant did not understand this principle.
This brings us back to the good Rev. Thomas Bayes, an 18th Century mathematician whose probability calculations were published in 1763. His work is now known as Bayes Theorem, and is widely used and accepted by clinicians to assess the probability of the existence of disease in the face of conflicting clinical and laboratory data. Understanding the principle (if not the source) of Bayes Theorem is part of the medical standard of care. Bayes Theorem states that the predictive value of a test result is predetermined by the incidence of disease in the population being evaluated.
Applying these principles to our case, defendant's expert witnesses admitted that Mr. Johnson presented with "typical angina." Tables published in the major cardiology textbooks indicate that, with this presentation, the "pretest probability"that such symptoms are caused by underlying coronary artery disease is in the 80-90 percent range. Since the treadmill test has only a 70 percent sensitivity, the clinical question for Dr. Truong became: "What is the likelihood that this patient has coronary artery disease as the cause of his symptoms notwithstanding a negative stress test result?" Stated another way: "Am I justified in telling Mr. Johnson that his symptoms are not attributable to cardiac causes, or do I have an obligation to advise him
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