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Acute coronary syndrome Part
1
Interpreting chest pain to pinpoint
an accurate diagnosis
BY Matthew Bennett, MD and Andrew
Ignaszewski, MD
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What are the challenges with acute
coronary syndrome?
Every day numerous patients present to
emergency departments (ED) throughout Canada with complaints of
chest pain. Each year, this results in approximately 60,000 admissions
to hospital for acute coronary syndrome (ACS).1
Since the incidence of coronary artery disease (CAD) increases with
age, it's anticipated that more patients will present with myocardial
infarctions (MIs) as baby boomers move into this high-risk demographic.
The diagnosis of ACS can be a simple one to
make. For example, a man with multiple risk factors for vascular
disease, who complains of retrosternal chest pressure that radiates
to the left arm, is diagnosed with ACS until proven otherwise. Unfortunately,
individuals diagnosed with ACS don't always present this way. In
fact, certain groups of patients have atypical symptoms of ACS more
often than others. Moreover, not everyone who presents with chest
pain has ACS, so it's important to consider the differential diagnosis
of life-threatening and non-life-threatening diseases when faced
with this situation.
What is ACS?
Acute coronary syndrome encompasses unstable angina, non-ST segment
elevation myocardial infarction (NSTEMI) and ST segment elevation
myocardial infarction (STEMI). These three diseases represent a
spectrum of coronary artery occlusion: unstable angina represents
a partial occlusion with no cardiac myocyte damage; non-STEMI characterizes
partial occlusion of a coronary artery with cardiac myocyte damage;
and STEMI, which corresponds to cardiac myocyte damage secondary
to complete occlusion of a coronary artery.
These three diseases may present similarly
in terms of the history and physical exam. The factors that differentiate
them clinically, however, are the serum cardiac biomarkers and electrocardiogram
(ECG). In unstable angina, the biomarkers will remain negative.
To differentiate NSTEMI from STEMI, use the ECG, which, in STEMI,
will show ST segment elevation or a new left bundle branch block
(LBBB).2
What is the
initial assessment of ACS?
When a patient presents with suspected ACS, it's essential to immediately
differentiate the cause of the patient's symptoms. According to
the American College of Cardiology (ACC) and American Heart Association
(AHA) guidelines, an ECG should be performed within the first 10
minutes of arrival to the ED.3,4
The patient should have a large bore intravenous inserted and immediately
be placed on oxygen and a cardiac monitor. After screening vitals
are obtained to assess the patient's stability, proceed with a focused
history, physical exam, screening blood work and a chest x-ray.
The history will reveal any past cardiac history
(prior chest pain, MI or known CAD), in addition to the presence
of chest pain and other symptoms, risk factors for the etiologies
of chest pain, past medical history, current medications, drug use
(specifically cocaine) or allergies.
If the individual had coronary artery bypass
grafting in the past, prior angiograms or angioplasty, when and
which epicardial vessels were bypassed or stented is important information.
The results of any cardiac testing (recent exercise treadmill tests
or myocardial perfusion imaging) will be essential for future risk
stratification.
The keystone of the chest pain history, however,
is the quality of the pain, its duration, severity, radiation and
whether there are any precipitating, relieving or worsening factors.
This history is crucial to differentiating chest pain associated
with MI from other causes.
Does the
presence of vascular risk factors help diagnose ACS?
A key component of any cardiac history is the presence or absence
of risk factors. The classic risk factors for vascular disease include
diabetes, hypertension, hyperlipidemia, a history of smoking, or
a family history of premature CAD (as defined by a first-degree
male relative younger than 55 years and first-degree female relative
younger than age 65). It was previously thought that as many as
50% of individuals presenting with acute MI would have no vascular
risk factors. This has been shown to be false. Khot et al observed
122,458 patients presenting with STEMI, NSTEMI, unstable angina
or having percutaneous coronary intervention. Of these, 112,243
presented with STEMI, NSTEMI, or unstable angina. Of the men and
women included in this trial, 85.6% and 80.6%, respectively, presented
with at least one of the classic risk factors for vascular disease.5
 Matthew
Bennett, MD, is a cardiology fellow in the Division of Cardiology
at the University of British Columbia.
Andrew Ignaszewski, MD, FRCPC is Medical Director of
the Healthy Heart Program at St. Paul's Hospital in Vancouver and
a clinical associate professor in the Division of Cardiology at
the University of British Columbia.
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