Emergency medical technologists (EMT) arrive in a quarter of an
hour. Based on hospital protocol, an intravenous line is inserted in
patient’s right arm; he is administered morphine sulphate 10 mg,
aspirin, beta blocker, supplemental oxygen by mask; an electrocardiogram
(ECG) tracing is radioed to the local emergency room while he is in the
ambulance. Sublingual nitroglycerin was given with minimal relief of
pain. He receives nasal 100% oxygen but is not intubated. His
respirations are more than 30 per minute and shallow. His skin is cool
and clammy. Blood pressure: 110/78. The substernal pain is slightly
relieved with medications and rest. EMT calls emergency triage nurse at
nearest community hospital regarding middle-aged white male complaining
of severe chest pain. He is breathing rapidly and perspiring.
The patient arrives in the emergency room and is seen immediately
by a triage nurse. He complains of severe chest pain when descending the
stairs to the kitchen; the pain persists . Nurse inquires if he
has had a previous a history of chest pain. “No,” the patient answers.
She assesses his vital signs: heart tracing on electrocardiogram,
respiratory rate, and temperature. She searches for any previous medical
record in the computerized system to share with a physician. She is
following protocol for chest pain and patient estimates pain at 7/10. He
receives an additional 10 mg morphine sulphate that eases his pain. On
auscultation a soft, decrescendo diastolic murmur is heard over the
precordium.9 Respirations are labored. Tachycardia is
evident, 110 bpm.
Initial diagnosis: Physician arrives in the acute side of
the emergency room. She decides that the likeliest diagnosis is acute
coronary syndrome (ACS), i.e. a sudden restriction of blood flow from
the coronary arteries into the heart, leading to cardiac ischemia
(oxygen deprivation to the heart) and subsequent myocardial injury
(death of heart cells). Based on the history and physical examination
she orders two laboratory tests: ECG and serum cardiac enzymes.
Commentary: How does the clinician reach her initial diagnosis?
The first step is to generate one or more diagnoses capable of
explaining the most salient signs and symptoms. She knows that shortness
of breath and sweating are common symptoms of ACS, so following
something like Peirce’s schema, she concludes that there is reason to
suspect this diagnosis: if ACS were the case, it would explain the chest
pain and most other symptoms. She also knows (from prevalence studies
and clinical experience) that ACS is the most common cause of chest pain
in men in their fifties in this part of the country.
At this stage, rather than systematically generating a wider list of
potential diagnoses, she immediately orders two tests. Her reasons can
be reconstructed as follows: (i) ACS is the most common cause of the
chief symptom (chest pain); (ii) it can cause severe damage and is
life-threatening if left untreated; (iii) the ordered tests are a rapid
and effective way of confirming the hypothesis: if the ECG shows
patterns characteristic of myocardial damage and the blood test shows
elevated levels of the enzymes an ischemic heart muscle would release,
this would be very strong evidence in favor of the hypothesis. The
decision not to generate further hypotheses before taking action
is based on the same kind of reasons as would justify selecting
already generated hypotheses for further consideration.
Negative results: The laboratory and ECG results are
negative: the cardiac enzymes test did not show elevated levels of the
relevant enzymes (c-troponin). The electrocardiogram shows a rapid heart
rate (120 bpm) but none of the characteristics of heart disease (no
elevation in the S-T segment, neither T wave inversion nor new Q wave
occurrence). Both results rule against cardiac ischemia and thus against
the diagnosis of ACS.