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Arch Gen Intern Med 2017 | Volume 1 Issue 3
allied
academies
International Conference on
FAMILY MEDICINE AND FAMILY PHYSICIANS
October 16-17, 2017 | Toronto, Canada
I
recently attended on the cardiology consult service of an
academic medical center. It involved working with a talented
team of medicine interns, residents, and cardiology fellows
in assisting colleagues caring for patients with a variety of
cardiovascular issues. These consults were for patients not
admitted to a cardiovascular service and came from essentially
every medical and surgical specialty. At the presentation of
each new patient, it was helpful to know the reason for the
consult. For approximately 20% of the consults the reason
was that the patient had an elevated troponin level. Most
of these patients did not have an acute coronary syndrome.
The focus of this commentary is appropriate use of current
generation troponin tests. Acute coronary syndromes due
to coronary plaque rupture and thrombotic occlusion are a
major cause of morbidity and mortality and troponin assays
are helpful in detecting them.1 Troponin is a protein in striated
muscle that regulates excitation and contraction, and consists
of three molecules (C, I, and T.) Troponin I and T are specific
to cardiac tissue, and when released in the bloodstream are
markers for myocardial injury or stress.1-3 For patients with
signs and symptoms of myocardial ischemia, a troponin assay
aids in early detection of acute coronary syndromes and saves
lives.1-3 Per the Third Universal Definition of Myocardial
Infarction global task force, troponin is now the biomarker of
choice when evaluating for classic myocardial infarction (type
1) that is due to acute occlusion (partial or full) of a coronary
artery.2 First generation troponin assays were highly predictive
of acute coronary syndromes and clinicians were conditioned
to make that diagnosis with any troponin elevation. This no
longer holds true. Now in their fourth or fifth generation,
troponin assays yield elevated levels for a number of conditions
besides acute coronary syndrome.2-5 In a series of 12,553
hospitalized patients using a current assay, over 40% with an
elevated troponin did not have a thrombotic coronary event,
and the positive predictive value for diagnosing acute coronary
syndrome was 56%; with a troponin level of 1.0 ng/ml or
lower it was 48% or less.4 When not due to decreased renal
clearance, troponin elevations may be an indication of cardiac
myocyte strain or injurywithout thrombotic coronary occlusion,
when the heart is an “innocent bystander” during a severe non-
cardiac condition.3,5 This type of acute injury to themyocardial
cells is designated as a type 2 myocardial infarction (myocardial
necrosis where a condition other than coronary artery disease
contributes to an imbalance betweenmyocardial oxygen supply
and/or demand 2); it is anticipated that type 2 myocardial
infarction will be added as an ICD-10 code in October, 2017.
Proposed mechanisms of cardiac injury in these patients
include circulating inflammatory cytokines and elevated
catecholamines.5Conditions thatmay cause troponindetection
with current assays include tachycardia (from essentially any
cause), hypotension, hypertension, strenuous exercise (e.g.
marathon runners), sepsis, renal failure, pulmonary embolus,
heart failure, pericarditis, polymyositis, rhabdomyolysis, burns,
cardiac trauma, respiratory failure, ventricular hypertrophy, drug
toxicity (including cancer chemotherapy) andneurally-mediated
sympathetic activation.2-5 Advanced age may be added to this
list; one recent study found that 41% of patients over age 70
presenting to the ED in whom both acute coronary syndrome
and other known non-thrombotic coronary syndrome causes
were ruled out had troponin elevations.6
This relatively new phenomenon of elevated troponin levels in
patients not having an acute coronary syndrome may lead to
overlooking the appropriate diagnosis and thus inappropriate
treatments, increased costs of tests and services, increased
length of stay, and unindicated procedures.7 For example,
when patients with gastrointestinal bleeding or intracranial
hemorrhage have elevated troponin results, treatment for
acute coronary syndrome with antiplatelet or anticoagulant
medication is antithetical to their primary diagnosis. Likewise,
giving a beta blocker for a positive troponin to a hypotensive
Gregory D Chapman
University of Alabama, USA
Occam, Hickam, troponin and appropriate use - A commentary on the clinical efficacy
of a frequently requested and useful lab test