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C HAPTER 22 / Acute Coronary Syndromes 513
Table 22-2 ■ APPLYING CLASSIFICATION OF RECOMMENDATIONS AND LEVEL OF EVIDENCE
Size of Treatment Effect
Class I Class IIa Class IIb Class III
Benefit Risk Benefit Risk Benefit Risk Risk Benefit
Additional studies with Additional studies with broad No additional studies needed
focused objectives needed objectives needed; Additional
registry data would be helpful
ESTIMATE OF CERTAINTY (PRECISION) OF TREATMENT EFFECT
Procedure/Treatment IT IS REASONABLE to Procedure/Treatment MAY Procedure/Treatment should
SHOULD be performed/ perform procedure/ BE CONSIDERED NOT be performed/
administered administer treatment administered SINCE IT IS
NOT HELPFUL, AND IT
MAY BE HARMFUL
Level A • Recommendation that pro- • Recommendation in favor • Recommendation’s useful- • Recommendation that pro-
cedure or treatment is of treatment or procedure ness/efficacy less well cedure or treatment is not
Multiple (3–5) useful/effective being useful/effective established useful/effective and may be
population risk strata • Sufficient evidence from • Some conflicting evidence • Greater conflicting harmful
d
d
evaluated* multiple randomized trials from multiple randomized evidence from multiple • Sufficient evidence from
General consistency of direc- or meta-analyses trials or meta-analyses randomized trials or multiple randomized trials
tion and magnitude of effect meta-analyses or meta-analyses
Level B • Recommendation that pro- • Recommendation in favor • Recommendation’s useful- • Recommendation that pro-
cedure or treatment is of treatment or procedure ness/efficacy less well estab- cedure or treatment is not
Limited (2–3) population risk useful/effective being useful/effective lished useful/effective and may be
d
strata evaluated* • Limited evidence from sin- • Some conflicting evidence • Greater conflicting harmful
d
gle randomized trials or from single randomized evidence from single • Limited evidence from sin-
non-randomized studies trial or non-randomized randomized trial or gle randomized trial or
studies non-randomized studies non-randomized studies
Level C • Recommendation that pro- • Recommendation in favor • Recommendation’s useful- • Recommendation that pro-
cedure or treatment is of treatment or procedure ness/efficacy less well estab- cedure or treatment is not
Very limited (1–2) population useful/effective being useful/effective lished useful/effective and may be
d
d
risk strata evaluated* • Only expert opinion, case • Only diverging expert • Only diverging expert harmful
studies, or standard-of-care opinion, case studies, or opinion, case studies, or • Only expert opinion, case
standard-of-care standard-of-care studies, or standard-of-care
Suggested phrases for writ- Should Is reasonable May/might be considered Is not recommended
ing recommendations † Is recommended Can be useful/effective/ May/might be reasonable Is not indicated
Is indicated beneficial Usefulness/effectiveness is Should not
Is useful/effective/beneficial Is probably recommended or unknown/unclear/uncer- Is not useful/effective/
indicated tain or not well established beneficial
May be harmful
†
In 2003, the ACC/AHA Task Force on Practice Guidelines developed a list of suggested phrases to use when writing recommendations. All guideline recommendations have been
written in full sentences that express a complete thought, such that a recommendation, even if separated and presented apart from the rest of the document (including headings
above sets of recommendations), would still convey the full intent of the recommendation. It is hoped that this will increase readers’ comprehension of the guidelines and will allow
queries at the individual recommendation level.
*Data available from clinical trials or registries about the usefulness/efficacy in different subpopulations, such as gender, age, history of diabetes, history of prior myocardial infarction,
history of heart failure, and prior aspirin use. A recommendation with Level of Evidence B or C does not imply that the recommendation is weak. Many important clinical
questions addressed in the guidelines do not lend themselves to clinical trials. Even though randomized trials are not available, there may be very clear clinical consensus that a par-
ticular test or therapy is useful or effective.
Anderson, L. J, Bennett, S. J., Brooks, N. H., et al. (2006). ACC/AHA clinical performance measures for adults with ST-elevation and non-ST-elevation myocardial infarction: A re-
port of the American College of Cardiology/American Heart Association task force on performance measures. JACC, 47, 236–65.
Early Risk Stratification litus and extracardiac disease are major risk factors for poor out-
4
comes in patients with ACS. The ECG is central to the diagnos-
An estimation of risk is useful in selection of the initial medical tic and triage pathway for ACS. Figure 22-1 illustrates practice
and interventional therapies. Generally, risk is highest at the time guidelines recommended for ACS and demonstrates the pivotal
of presentation and declines subsequently but remains elevated role the 12-lead ECG plays in treatment course selection. Transient
even beyond the acute phase. In patients with symptoms sugges- ST-segment changes greater than or equal to 0.05 mV or 0.5 mm
tive of ACS, the initial medical history, physical examination, that develop during the time the patient is symptomatic at rest is
ECG, and assessment of renal function and cardiac biomarker can strongly suggestive of myocardial ischemia due to severe CAD.
be integrated into an estimation of the risk of mortality or a non- Patients who present with ST-segment depression could have
fatal cardiac event. either UA or NSTEMI. The distinction is made by the later de-
The five most important factors on the initial history are the tection of biomarkers of myocardial necrosis. Inverted T waves,
nature of the anginal symptoms, a prior history of CAD, sex, age, particularly if greater than or equal to 2 mm, can also be indica-
and the number of risk factors present. In patients without preex- tive of UA/NSTEMI. Q waves are suggestive of prior MI and in-
isting clinical CHD, older age is the most important factor. 4 dicate high likelihood of CAD. A normal ECG does not com-
A history of MI increases the risk of obstructive and multives- pletely exclude ACS; 1% to 6% of patients with documented
sel CAD. Traditional risk factors are only weakly predictive of the NSTEMI and 4% of patients with documented UA will have a
likelihood of acute ischemia, and they are less important than normal ECG. Serial ECGs increase diagnostic sensitivity and are
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symptoms, ECG findings, and cardiac biomarkers. Diabetes mel- recommended because ST-segment elevation on the 12-lead ECG