ELECTROCARDIOGRAPHIC
DIAGNOSIS OF MYOCARDIAL INFARCTION IN PATIENTS WITH LEFT BUNDLE BRANCH BLOCK.
Li SF,
et al. Ann Emerg Med 2000 Dec;36(6):561-5.
STUDY
OBJECTIVE: To validate ECG criteria previously proposed by Sgarbossa et al for
the detection of myocardial infarction (MI) in patients with left bundle branch
block (LBBB) and suspected ischemia.
METHODS:
A retrospective cohort study was performed at an urban teaching hospital. All
patients admitted with suspected ischemia and LBBB were eligible. MI was
defined as an elevated creatine kinase (CK) isoenzyme MB (>14 IU/L) that was
at least 5% of total CK level. ECGs were interpreted by 2 physicians blinded to
patient outcome. Interpreters were asked to rate ECGs for the presence of each
of the 3 criteria proposed by Sgarbossa et al: (1) ST-segment elevation greater
than or equal to 1 mm concordant with the QRS complex; (2) ST-segment elevation
greater than or equal to 5 mm discordant with the QRS complex; and (3)
ST-segment depression in leads V(1) through V(3). Interobserver agreement was
assessed.
RESULTS:
Of 190 eligible patients, 25 (13%) had MI. Sensitivities of the 3 criteria
varied from 0 to 16%, with specificities of 93% to 100%. Only the first
criterion demonstrated a clinically useful likelihood ratio (positive
likelihood ratio=16 [95% confidence interval 4 to >100]). Patients with new
LBBB were more likely to have MI (relative risk=5. 1 [95% confidence interval
2.6 to 10]). Interobserver agreement among ECG interpreters ranged from 93% to
98%.
CONCLUSION:
The criteria of Sgarbossa et al cannot be used to exclude MI in patients with
LBBB because of low sensitivities and poor negative likelihood ratios.
ST-segment elevation concordant with the QRS complex had a high positive
likelihood ratio for identification of MI. Patients with new LBBB and suspected
ischemia are 5 times more likely to have MI than patients with LBBB of chronic
or unknown duration.
SHOULD
THE ELECTROCARDIOGRAM BE USED TO GUIDE THERAPY FOR PATIENTS WITH LEFT BUNDLE-BRANCH
BLOCK AND SUSPECTED MYOCARDIAL INFARCTION?
Shlipak
MG, et al. JAMA 1999 Feb 24;281(8):714-9.
CONTEXT:
Recently, an algorithm based on the electrocardiogram (ECG) was reported to
predict myocardial infarction (MI) in patients with left bundle-branch block
(LBBB), but the clinical impact of this testing strategy is unknown.
OBJECTIVE:
To determine the diagnostic test characteristics and clinical utility of this
ECG algorithm for patients with suspected MI. DESIGN: Retrospective cohort study
to which an algorithm was applied, followed by decision analysis regarding
thrombolysis made with or without the algorithm.
SETTING:
University emergency department, 1994 through 1997.
PATIENTS:
Eighty-three patients with LBBB who presented 103 times with symptoms
suggestive of MI.
MAIN
OUTCOME MEASURES: Myocardial infarction determined by serial cardiac enzyme
analyses and stroke-free survival.
RESULTS:
Of 9 ECG findings assessed, none effectively distinguished the 30% of patients
with MI from those with other diagnoses. The ECG algorithm indicated positive
findings in only 3% of presentations and had a sensitivity of 10% (95%
confidence interval, 2%-26%). The decision analysis showed that among 1000
patients with LBBB and chest pain, 929 would survive without major stroke if
all received thrombolysis compared with 918 if the ECG algorithm was used as a
screening test.
CONCLUSIONS:
The ECG is a poor predictor of MI in a community-based cohort of patients with
LBBB and acute cardiopulmonary symptoms. Acute thrombolytic therapy should be
considered for all patients with LBBB who have symptoms consistent with MI.
ELECTROCARDIOGRAPHIC
DIAGNOSIS OF EVOLVING ACUTE MYOCARDIAL INFARCTION IN THE PRESENCE OF LEFT
BUNDLE-BRANCH BLOCK. GUSTO-1 (GLOBAL UTILIZATION OF STREPTOKINASE AND TISSUE
PLASMINOGEN ACTIVATOR FOR OCCLUDED CORONARY ARTERIES) INVESTIGATORS.
Sgarbossa
EB, et al. N Engl J Med 1996 Feb 22;334(8):481-7.
BACKGROUND.
The presence of left bundle-branch block on the electrocardiogram may conceal
the changes of acute myocardial infarction, which can delay both its
recognition and treatment. We tested electrocardiographic criteria for the
diagnosis of acute infarction in the presence of left bundle-branch block.
METHODS.
The base-line electrocardiograms of patients enrolled in the GUSTO-1 (Global
Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded
Coronary Arteries) trial who had left bundle-branch block and acute myocardial
infarction confirmed by enzyme studies were blindly compared with the
electrocardiograms of control patients who had chronic coronary artery disease
and left bundle-branch block. The electrocardiographic criteria for the
diagnosis of infarction were then tested in an independent sample of patients
presenting with acute chest pain and left bundle-branch block.
RESULTS.
Of 26,003 North American patients, 131 (0.5 percent) with acute myocardial
infarction had left bundle-branch block. The three electrocardiographic
criteria with independent value in the diagnosis of acute infarction in these
patients were an ST-segment elevation of 1 mm or more that was concordant with
(in the same direction as) the QRS complex; ST-segment depression of 1 mm or
more in lead V1, V2, or V3; and ST-segment elevation of 5 mm or more that was
disconcordant with (in the opposite direction from) the QRS complex. We used
these three criteria in a multivariate model to develop a scoring system (0 to
10), which allowed a highly specific diagnosis of acute myocardial infarction
to be made.
CONCLUSIONS.
We developed and validated a clinical prediction rule based on a set of
electrocardiographic criteria for the diagnosis of acute myocardial infarction
in patients with chest pain and left bundle-branch block. The use of these
criteria, which are based on simple ST-segment changes, may help identify
patients with acute myocardial infarction, who can then receive appropriate
treatment.