Naval Submarine Medical Research Laboratory

NSMRL Report 1162 7 December 1990

A CLINICAL TRIAL OF A COMPUTER DIAGNOSIS

PROGRAM FOR CHEST PAIN

S. M. Luria

David G. Southerland

Douglas M. Stetson

Released by:

R. G. Walter, CAPT, DC, USN

Commanding Officer

Naval Submarine Medical Research Laboratory

Approved for public release; distribution unlimited
A CLINICAL TRIAL OF A COMPUTER DIAGNOSIS

PROGRAM FOR CHEST PAIN

S. M. Luria

David G. Southerland

Douglas M. Stetson

NAVAL SUBMARINE MEDICAL RESEARCH LABORATORY

NSMRL REPORT 1162

Naval Medical Research and Development Command

Research Work Unit 3706N-M0095.005-5010

Approved and released by

R. G. WALTER CAPT, DC, USN

Commanding Officer

NavSubMedRschLab

Approved for public release; distribution unlimited
Summary Page

THE PROBLEM

To determine whether NSMRL computer program to diagnose chest

pain is suitable for use by corpsmen at sea.

THE FINDINGS

132 patients with confirmed diagnoses of chest pain

(myocardial infarction, angina, chest infection, or other)

presenting at Naval Hospitals at Portsmouth, Charleston, and San

Diego were diagnosed by the emergency room physicians and the NSMRL

computer program. The percentage of correct diagnoses by the

computer (72%) was not significantly different from the percentage

of correct diagnoses by the ER physicians (79%). The physicians

were significantly better than the computer program at

distinguishing myocardial infarction from angina. However, the

computer program was equally successful at determining whether a

patient was suffering from myocardial infarction.

APPLICATION

The computer program for diagnosing chest pain should be of

assistance to the independent duty corpsman in the diagnosis and

management of patients aboard submarines presenting with chest

pain.

Administrative Information

This investigation was conducted under Naval Medical Research

and Development Command Research Work Unit 63706N - M0095.005-5010,

"Sea trials for computer-based medical diagnostic/patient

management system for use aboard SSN/SSBN submarines." It was

submitted for review on 25 July 1990, approved for publication on

7 December 1990, and has been designated as Navl Submarine Medical

Research Laboratory Report No. 1162.

ii
Abstract

We evaluated the performance of a computer program designed to

assist corpsmen in managing patients who present at sea with chest

pain. The diagnostic accuracy of the program for three common and

serious causes of chest pain -- myocardial infarction (MI), angina,

chest infection -- as well as its accuracy for nonspecific chest

pain, was compared with that of emergency room physicians at three

Naval hospitals for 132 patients. The percentage of correct

diagnoses by the computer program (72%) was not significantly

different from that of the physicians (79%), although the accuracy

of the physicians was better. The computer program was able to

distinguish MI from the other diseases as well as the physicians

(i.e. was as sensitive, 83% vs. 84%) and at the same time made

fewer false diagnoses of MI (i.e. was more specific). The

computer's ability to distinguish among cardiac illnesses was not

as good as that of the physicians and it misdiagnosed more cases of

angina. The computer program is suitable for use by medical

personnel practicing in isolated locations and may help improve

diagnostic accuracy in cases of MI. Its failures emphasize that it

cannot substitute for medical personnel, but can be helpful to

medical personnel when a patient's diagnosis is uncertain.

iii
Introduction

There has in recent years been much interest in using the

computer as an aid in medical diagnosis (Rogers, Ryack, and

Moeller, 1979). This interest is greatest in the submarine fleet.

Physicians are assigned only to newly commissioned Trident

submarines; complete responsibility for medical care otherwise

rests with the ship's independent duty hospital corpsman. With

neither the training nor experience of a practicing physician, the

corpsman must decide whether or not to recommend a medical

evacuation. To ensure that his patients receive all needed care,

particularly when a patient's condition is puzzling, corpsmen find

evacuation to a physician's care an attractive option. But

evacuations are costly, dangerous to both the patient and the deck

crew, and operationally undesirable. Reducing unnecessary

evacuations is a desirable goal. Submariners, therefore, would

find it useful to have a tool with a demonstrated ability to assist

the corpsman in making a good decision and reducing the number of

inappropriate -- that is, premature or delayed -- medical

evacuations.

NSMRL has developed microcomputer-based medical support

systems to aid the corpsmen in treating a variety of maladies.

Some of the systems are based on one devised by de Dombal (1973;

1979), but they have been specifically tailored for the submarine

population (Osborne, 1984; Ryack, 1987). One provides information

to aid the corpsmen in the diagnosis and management of chest pain

(Southerland and Fisherkeller, 1987; Fisherkeller, Southerland, and

Moeller, 1987). The corpsman, using a data collection form to

guide his examination, records findings for 27 history and 20

physical exam categories. The program then provides the user with

probabilities that the patient is suffering from each of four

illnesses: myocardial infarction, angina, chest infection, and

non-specific chest pain.

Although the program produces the probabilities for four

separate diagnoses, it can be argued that it is more important for

the corpsman to determine which patients are suffering from an MI

(and must receive specialized care) than it is to distinguish among

various other medical diagnoses. The reason is that the corpsman

is trying to decide whether or not a patient must be evacuated. It

would be most useful if the program would help to identify patients

with MI.

Although a new program may appear to be similar to another

which has been validated (de Dombal, 1973), it still requires independent validation. There have been previous field trials of

such programs in the Navy (Henderson, et al., 1981), but these have

sought only to determine how easily the corpsmen can use the

program and how well they accept it; they have not attempted to

validate the programs themselves.

1
This prospective validation of the chest pain program was

begun to assess its reliability and consequent usefulness to

independent duty corpsmen. This report compares the diagnostic

accuracy of the NSMRL chest pain program with that of emergency

room physicians for patients who were reasonably representative of

an active duty Navy population.

METHOD

Subjects

The subjects were 132 male or female active duty or retired

Navy personnel or their dependents between the ages of 15 and 50.

They presented with chest pain in the emergency rooms of the Naval

Hospitals at Portsmouth, VA, Charleston, SC, and San Diego, CA,

from May 31, 1988 to September 30, 1988 and volunteered to

participate in the study. The patients also met the requirement

that they not have a prior history of myocardial infarction,

angina, or such chronic illness as diabetes, since these conditions

are grounds for exclusion from submarine service.

Technicians

Six research technicians -- two at each hospital -- collected

the data. They were trained in the use of the chest pain data

sheet by a Navy medical officer over a two-day period. The

technicians worked consecutive 8-hour shifts between 8:00 a.m. and

midnight, five days a week, for the four month period.

Procedure

Patients who presented at the emergency room with a complaint

of chest pain were interviewed by a research technician who

described the study and solicited their participation. Patients

who agreed to participate in the study signed consent forms and

then the technician recorded case history details wiile waiting for

the examining physician. This included such things as the

patient's sex and age, the history of smokinc°, previous surgery,

history of MI, angina, bronchitis, previous illnesses, etc. While

the patient was being examined by the physician, the technician

listened to the examination and recorded the answers to the

questions asked by the computer program on the data sheet shown in

Figure 1. For example, the chest pain program asks the site of the

pain, the presence of radiation, duration and severity of the pain,

and so on. The required information could be obtained by watching

the examination. The physician was asked to verbalize his findings

as he conducted the examination so that the technician, listening,

could complete the data sheet. Sometimes the physician was too

busy to provide a complete report; in these cases the technician

obtained the missing information from the patient's emergency

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UN
treatment record. The technician was not allowed to interview the

patient without the permission of the physician and was asked to

leave the examining room if the patient was uncomfortable. The

collected information was later entered into the computer program

to obtain the computer's diagnosis.

The computer program for chest pain was written to assign the

probabilities that a given patient's symptoms indicated angina,

chest infection, myocardial infarction, and non-specific chest

pain. The category "Angina" included both stable and unstable

angina. Chest infection was defined as any infection of the

pleural cavity (including pleuritis and pericorditis) which would

require medical intervention, such as pneumonia or bronchitis.

Cases of pneumothorax are also included in this chest pain category

because they exhibit symptoms of pleuritic pain. Non-specific

chest pain was defined as chest pain that is not serious, not lifethreatening, and does not require urgent medical intervention.

Mechanical chest discomfort and GI tract pain fall in this

category.

The computer diagnoses were compared with diagnoses from two

other sources. The first was the diagnosis arrived at by the

examining physician in the emergency room. If the patient was

admitted to the hospital, there would, of course, be further

observations and tests leading to a "discharge diagnosis" entered

in the patient's records. The discharge diagnosis was presumably

more accurate and was accepted as the "final" diagnosis. If a

patient was not admitted, there was a follow-up telephone call to

the patient by a physician or nurse at least three weeks after the

visit to the emergency room to determine if subsequent events cast

doubt on the emergency room discharge diagnosis. If a subject had

had further medical care related to the same illness, the results

of that care were considered in establishing a "final" diagnosis.

In comparing the diagnosis reached by the computer program

with those reached by physicians after evaluating a patient during

an ER visit or a hospitalization, it is important to remember that

the computer program is designed for use in isolated situations

where X-rays, electrocardiograms (EKG), laboratory procedures such

as creatine phosphokinase (CPK) and serum glutamate oxaloacetic

acid transferase (SGOT) assays and consultations with specialists

are generally not available. The diagnosis of the computer program

must, therefore, be based on only a fraction of the information to

which the ER physician has access.

RESULTS

Table 1 compares the final diagnoses with the diagnoses made

by the emergency room physicians and with those made by the

computer program. There are 132 computer diagnoses but only 130

emergency room diagnoses because two of the emergency treatment

records were not available.

4
Table 1 shows, for example, that of the 132 cases, 9 were

finally diagnosed as MI, 6 as angina, 9 as chest infection, and 108

as cases of non-specific chest pain. Overall, 79% of the diagnoses

made by the emergency room physicians and 72% of the computer

diagnoses agreed with the final diagnoses. These percentages are

not significantly different (t = 1.35, df = 129, p < .50).

Table 1. Comparison of the diagnoses by the computer program and

the emergency room physicians with the final diagnoses for

myocardial infarction (MI), angina (AN), chest infection (CI), and

non-specific chest pain (NS).

FINAL DIAGNOSES

MI AN CI NS MI AN CI NS

C MI 3 P 6 2 15

0 H

M AN 5 1 1 15 Y 1 4 5

P S

U CI 2 4 I 8 1

T C

E NS 1 5 6 89 I 1 1 86

R A

N

Of the 9 cases of MI, the computer program accurately

diagnosed 3; it misdiagnosed 5 as angina and one as non-specific

chest pain. Each computer diagnosis of MI was confirmed on

admission. Of 8 cases of MI, the physicians accurately diagnosed

6; they misdiagnosed one as angina and one as non-specific chest

pain. (We did not have the physicians' emergency room diagnoses

for the remaining MI patient.) Seventeen physician diagnoses of MI

were not confirmed on admission; 15 patients were diagnosed with

non-specific chest pain and 2 with angina.

The set of diagnoses established by the emergency room

physicians was not significantly different from the final

diagnoses, according to a Chi Square test (X2 = 16.95, df = 3, p <

.001).

Cardiac Event vs. Myocardial Infarction

Among patients with MI, the computer program did not

accurately discriminate between MI and angina. It was

predominantly this factor and several misdiagnoses of angina which

produced the difference in the Chi Square results for the computer

and physicians.

However, the program correctly identified all but one of the

5
MI patients as having either an MI or angina. If we combine MI and

angina as a diagnosis of "cardiac event," the performance of the

computer program and the ER physicians is much more similar (Table

2). Both the computer program and the ER physicians correctly

identified all but one of the patients with MI; the computer

correctly identified 106 of the 123 patients who did not have MI,

and the physicians correctly identified 96 of them (the emergency

room diagnosis of one of the non-MI patients is also missing). The

Chi Square test now shows that the computer program diagnoses were

not significantly different from the final diagnoses (X?= 2.46, df

= 1, p < .15), whereas the ER diagnoses were significantly

different from the final diagnoses (X2 = 5.67, df = 1, p < .02).

Table 2. Comparison of computer program and emergency room

physicians for final diagnosis of myocardial infarction (MI) when

initial diagnosis of cardiac event (CE, i.e. MI or angina) is made.

Computer Physicians

Final Diagnosis Final Diagnosis

MI Not MI MI Not MI

CE 8 17 CE 7 26

Not CE 1 106 Not CE 1 96

6
DISCUSSION

Physicians evaluating a patient with chest pain err on the

side of conservatism and admit to hospitals, often with a "rule out

MI" diagnosis, three or more patients who actually turn out to have

non-cardiac causes of pain for every patient who turns out to have

suffered a heart attack. This approach is entirely appropriate as

the risk of imminent death associated with a missed diagnosis of MI

is far less acceptable than the inconvenience of a period of

observation necessary to ensure that no heart damage has occurred.

The "bias" toward overdiagnosis of MI is magnified when the

person providing medical care has less experience with MI patients

as occurs when hospital corpsmen are caring for ship's crews alone

at sea. In this context, a computer program which is about as

reliable as an emergency room physician in detecting cases of MI,

but which does not miss cases more frequently than physicians did,

might be a useful tool to corpsmen at sea.

In terms of the overall percentage of correct diagnoses, the

performance of the computer program was not significantly different

from that of the emergency room physicians. This finding rests

largely on the overwhelming percentage of non-specific chest pain

diagnoses in the sample populations. The physicians were better at

distinguishing among specific illnesses. The program did not do

well at diagnosing angina, for example.

But in evaluating the performance of the computer program

designed for use on submarines and in comparing its accuracy with

that of physicians, it is necessary to remember that the physicians

had access to a variety of other diagnostic information not

available to the program: detailed interpretation of EKGs, CPK

assays, chest X-rays, and consultations with specialists. It is

also necessary to remember that the primary purpose of the computer

program is to help the independent duty corpsman faced with a

puzzling case to distinguish between chest pain stemming from an MI

and other causes of chest pain. The program's ability to specify

precisely what illness the patient actually has is aot as critical

as its ability to correctly categorize the illness as an MI or some

other condition. In this restricted sense, thr performance of the

program is about the same as that of the ER physicians.

Other computer programs have been reported to diagnose MI

quite accurately. Goldman and his colleagues (1982, 1988) have

reported that their program was significantly more specific than

were ER physicians. In an earlier study (Goldman, Weinberg,

Weisberg, et al., 1982), they identified nine critical questions

which bear on the presence or absence of MI. One of them, however,

is not appropriate to submariners; it is whether or not this same

pain was previously diagnosed as MI. If this had been the case,

the man would not be serving on submarines. Further, it is

important to note that in their recent report (Goldman, Cook,

7
Brand, et al., 1988) we see that the information requested by their

very first question -- "ST elevation or Q waves in 2 or more leads,

not known to be old?" -- is not available on submarines.

Independent duty corpsmen are not routinely trained to make

detailed evaluations of EKGs, and most do not have EKG equipment

available. Similarly, another question in Goldman's algorithm asks

about EKG changes associated with ischemia or strain. This

information, too, is not available to most independent duty

corpsmen. Thus, a program which may work very well in a typical

hospital may be ineffective at sea. 1

We hasten to emphasize that this study shows that the computer

program makes errors. It erroneously categorizes the source of the

pain in about one quarter of the patients. In about one percent of

the cases, it incorrectly suggested that a person suffering from MI

had some other problem. In 13% of the cases, it suggested

inaccurately that a person was suffering from cardiac chest pain.

The magnitude of these errors is similar for physicians and

underlines the need for the user to make an independent and careful

evaluation of the advice provided by the program.

Like the emergency room physicians, independent duty hospital

corpsmen have much more information available to them in treating

an individual case than is collected by the computer program. The

program gathers only 47 responses; most of them are either "yes" or

"no." The corpsman at sea generally has a detailed knowledge of

the patient, his past history and behavior, and an acute awareness

of the degree that the patient's present condition deviates from

the norm. In every case, the corpsman, particularly when aided by

additional information as is provided by the computer program,

might be expected to be a more capable diagnostician than the

computer program by itself. The corpsman's insight and judgment

remain indispensable at sea.

A final point should be stressed. Rogers, Ryack, and Moeller

(1979) pointed out that the usefulness of these programs depends

not simply on their being reasonably accurate but on being more

accurate than the diagnostician for whom the program is intended.

Since the purpose of the computer program is to serve as a

diagnostic aid to the independent duty submarine corpsmen, its

performance should be compared with that of a corpsmen practicing

at sea. Information bearing on the accuracy of corpsmen diagnoses

is being collected. The present comparison with physicians serves

only to illustrate that the program is not wildly inaccurate when

compared with a generally acceptable standard.

Work is in progress to adapt Goldman's program to

isolated Navy situations.

8
Acknowledgments

We are indebted to the staffs of the Portsmouth, Charleston,

and San Diego Naval Hospitals for their unstinting cooperation. We

also thank the research technicians Julie Ann Carroll, Dawn Marie

Emigh, Ann Marie Engfelt, Abigail Flondarina, Danette E. Fralix,

and Manisha N. Trivedi for their indispensable assistance.

9
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Proc. Roy. Soc. B. (London) 184: 433.

F. T. de Dombal (1979). Computers and the surgeon -- a matter of

decision. Surg. Ann. 11: 33.

L. Goldman, E. F. Cook, D. A. Brand, T. H. Lee, G. W. Rouan, M. C.

Weisberg, D. Acampora, C. Stasiulewicz, J. Walshon, G.

Terranova, L. Gottlieb, M. Kobernick, B. Goldstein-Wayne, D.

Copen, K. Daley, A. A. Brandt, D. Jones, J. Mellors, and R.

Jakubowski (1988). A computer protocol to predict myocardial

infarction in emergency department patients with chest pain.

New England J. Med. 318: 797-803.

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Sargent, G. A. Lamas, C. Dennis, C. Wilson, L. Deckelbaum, H.

Fineberg, R. Stiratelli, and the Medical House Staffs at YaleNew Haven Hospital and Brigham and Women's Hospital (1982).

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room patients with acute chest pain. New England J. Med. 307:

588-596.

K. D. Fisherkeller, D. G. Southerland, and G. Moeller (1987). CPDX

-- A decision support system for the management of acute chest

pain. User's Manual. NSMRL Report 1144.

J. V. Henderson, B. L. Ryack, G. Moeller, R. Post, and K. D.

Robinson (1981). Use of a computer-aided diagnosis system

aboard patrolling FBM submarines: Initial at-sea trials.

NSMRL Report 939.

S. F. Osborne (1984). Medical diagnosis aboard submarines: Use of

a computer based Bayesian method of analysis in an abdominal

pain diagnostic program. J. Occup. Med. 26: 110-114.

W. Rogers, B. Ryack, and G. Moeller (1979). Computer-aided medical

diagnosis: Literature review. Int. J. Biomed. Computing 10:

267-289.

B. L. Ryack (1987). A computer-based diagnostic/information

patient management system for isolated environments: MEDIC

ten years later. NSMRL Report 1089.

D. G. Southerland and K. D. Fisherkeller (1987). ABDX -- A

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pain. User's Manual. NSMRL Report 1146.

10
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S. M. TLmrin, David G. Southerland, & Douglas M. Stetson

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Interim IFROM -TO ___I1990 December 7 I 10

16 SUPPLEMENTARY NOTATION

17 COSATI CODES 18 SUBJECT TERMS (Continue on reverse if necessary and identify by block number)

FIELD GROUP SUB-GROUP Computer-aided diagnosis; Chest pain; Diagnosis:

Angina; M~yocardial infarction (MI)

19 ABSTRACT (Continue on reverse if necessary and identify by block number)

We evaluated the performance of a computer program designed to assist corpsmen in

managing patients who present at sea with chest pain. The diagnostic accuracy of the

programi for three common and serious causes of chest pain -- myocardial infarction (MI),

angina, and chest infection -- as well as its accuracy for nonspecific chest pain, was

compared with that of emergency room physicians at three Naval hospitals for 132

patients. The percentage of correct diagnoses by the computer program (72%) was not

significantly different from that of the physicians (79%), although the accuracy of the

physicians was better. The computer program was able to distinguish MI from the other

diseases as well as the physicians (i.e. was as sensitive, 83% vs. 84%) and at the same

time made fewer false diagnoses of MI (i.e. was more specific). The computer's ability

to distinguish among cardiac illnesses was not as good as that of the physicians and

it misdiagnosed more cases of angina. The computer program is suitable for use by 1

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"22a NAME OF RESPONSIBLE INDIVIDUAL 22b TELEPHONE (Include Area Code) 22c OFFICE SYMBOL

Susan D. Monty, Publications Office (203) 449-3967 421

DD Form 1473, JUN 86 Previous editions are obsolete.

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medical personnel practicing in isolated locations and may help improve diagnostic

accuracy in cases of MI. Its failures emphasize that it cannot substitute for medical

personnel, but can be helpful to medical personnel when a patient's diagnosis is

uncertain.

DID Form 1473, JUN 86 (Re', rse) SECURITY CLASSIFICATION OF THIS PAGE

UNCLASSIFIED