We compared the clinical features, laboratory and coronary angiographic findings, treatments, and outcomes among patients with ST-segment elevation myocardial infarction (MI) with and without left bundle branch block (LBBB). We examined 5,742 patients with ST-segment elevation MI with and without LBBB treated with primary percutaneous coronary intervention in the Assessment of Pexelizumab in Acute Myocardial Infarction trial. The main outcome measures were obstructive coronary disease, MI, positive cardiac biomarkers, angiographic Thrombolysis In Myocardial Infarction flow, and death, MI, or congestive heart failure at 90 days. LBBB was present in 98 patients (1.7%). According to the protocol, patients with LBBB were eligible only if they had ≥1 mm concordant ST-segment elevation. Obstructive coronary artery disease was present in >87% of the patients with LBBB. Documented MI (elevated biomarkers) with an initially occluded infarct artery was more common in patients with LBBB with concordant ST-segment elevation (71.4%) than in patients without (44.1%; p = 0.027). The use of ST-segment elevation concordance criteria in the presence of LBBB was more often associated with documented MI with an identifiable culprit vessel with an initially occluded infarct-related artery. In conclusion, because a substantial proportion of patients with LBBB have acute MI with a culprit lesion and positive biomarkers, these data support immediate catheterization with the intent for primary percutaneous coronary intervention for all patients presenting with suspected ST-segment elevation myocardial infarction, ischemic symptoms, and presumed new LBBB, particularly if concordant ST-segment elevation is present.
We studied patients with presumed new left bundle branch block (LBBB) and suspected myocardial infarction (MI) who were undergoing primary percutaneous coronary intervention (PCI) to evaluate the clinical features, laboratory and angiographic findings, and 90-day outcomes. Additionally, we evaluated how the clinical and angiographic characteristics and 90-day outcomes differed in patients with LBBB with and without ST-segment elevation concordant with the QRS complex.
Methods
We conducted these analyses using data from patients enrolled in the Assessment of Pexelizumab in Acute Myocardial Infarction (APEX-AMI) trial. The rationale and design of the APEX-AMI trial has been previously published. In brief, APEX-AMI was a randomized, double-blind, placebo-controlled trial comparing the effect of pexelizumab (an inhibitor of complement) with placebo. The multicenter trial involved 17 countries and 296 sites and enrolled 5,745 patients from 2004 to 2006. Patients were deemed eligible for the study if they were ≥18 years old, presented for primary PCI with ischemic symptom onset within 6 hours, and had electrocardiographic findings indicative of acute ST-segment elevation myocardial infarction (STEMI) showing the following: ≥2 mm ST-segment elevation in 2 anterior or lateral leads, or ≥2 mm ST-segment elevation in 2 inferior leads and ST-segment depression in 2 contiguous anterior leads for a total ST-segment deviation of ≥8 mm, or new LBBB with ≥1 mm concordant ST-segment elevation. The exclusion criteria included previous treatment with fibrinolytic therapy, isolated inferior MI, pregnancy or breastfeeding, complement deficiency or active serious infection, or other serious medical conditions limiting survival. The institutional review boards of the participating medical centers approved the APEX-AMI protocol, and all patients gave written informed consent.
All electrocardiographic data in the APEX-AMI trial were independently interpreted by 2 experienced electrocardiographic readers at the ECG Core Laboratories (Canadian VIGOUR Centre, Edmonton, Alberta, Canada and Duke Clinical Research Institute, Durham, North Carolina) who were unaware of the clinical, laboratory, and angiographic data and the outcomes. The 12-lead electrocardiograms were recorded at a paper speed of 25 mm/s and were properly calibrated. The LBBB was defined as a QRS duration of ≥0.130 seconds in the presence of a sinus or supraventricular rhythm; a QS or rS complex in lead V 1 ; and an R-wave peak time of ≥0.06 seconds in lead I, V 5 , or V 6 associated with the absence of a Q wave in the same lead. Electrocardiography was performed at presentation and at hospital discharge.
For inclusion in APEX-AMI trial, the patients with LBBB were to have ≥1 mm of concordant ST-segment elevation. The concordant 1-mm ST-segment elevation, 1 of the 3 Sgarbossa criteria, is the most reliable predictor of STEMI in the presence of LBBB. Although not as powerful as the first, the other 2 Sgarbossa criteria (1-mm ST-segment depression in V 1 , V 2 , or V 3 lead; 5-mm ST-segment elevation with discordant QRS complex) are also useful in predicting acute MI in the presence of LBBB. Despite the concordant 1-mm ST-segment elevation being an inclusion criterion of the APEX-AMI trial, 46 patients were entered into the trial who did not meet this criterion. This was possible because a considerable discrepancy was found between the electrocardiographic reading in the context of emergency clinical care and the core laboratory reading. Moreover, we performed a sensitivity analysis to evaluate 16 of the 46 patients who did not meet the concordant ST-segment elevation criterion but met ≥1 of the other 2 criteria. These patients were classified as having LBBB meeting the Sgarbossa criteria.
The biomarkers of myocardial necrosis used in the present study were creatine kinase, its fraction MB (creatine kinase-MB), and troponin (either T or I). The creatine kinase-MB and troponin levels were considered elevated if they were 2 and 3 times the upper limit of normal, respectively.
The angiographic information included the maximum stenosis in each main coronary artery and culprit artery and the pre- and post-PCI Thrombolysis In Myocardial Infarction flow was assessed by the local site investigator. Significant coronary artery disease was defined as ≥50% stenosis in any coronary artery.
“False activation” of the cardiac catheterization laboratory was defined according to the following 3 criteria: (1) the absence of significant coronary disease; (2) negative biomarkers; and/or (3) the absence of a culprit lesion.
The primary outcome of the trial was all-cause 30-day mortality in patients with STEMI treated with primary PCI. In the present study, the main outcomes were mortality at 90 days and the composite of death, congestive heart failure, and shock at 90 days.
Death was defined as all-cause mortality. Congestive heart failure and cardiogenic shock were centrally adjudicated by a clinical events committee that was unaware of the treatment assignment. Congestive heart failure was defined on the basis of the physician’s decision to treat congestive heart failure with an intravenous diuretic, inotropic agent, or vasodilator and ≥1 of the following: the presence of pulmonary edema or pulmonary vascular congestion on the chest radiograph believed to be of cardiac cause; rales reaching ≥1/3 up the lung fields believed to be due to congestive heart failure; pulmonary capillary wedge pressure or left ventricular end-diastolic pressure >18 mm Hg; or dyspnea, with documented oxygen pressure <80 mm Hg on room air or oxygen saturation <90% on room air, without significant lung disease.
Cardiogenic shock was defined as hypotension of <90 mm Hg systolic blood pressure lasting for ≥1 hour that was not responsive to fluid resuscitation and/or heart rate correction, believed to be secondary to cardiac dysfunction, and associated with ≥1 of the following signs of hypoperfusion: cool, clammy skin; oliguria; altered sensorium; or cardiac index ≤2.2 L/min/m 2 .
The results are reported as percentages for discrete variables and median with 25th and 75th percentiles for continuous variables. For the comparisons between groups, the chi-square or Fisher exact test was used for discrete variables and Mann-Whitney U test for continuous variables. All tests were 2-sided, with a 5% level of significance. All analyses were performed with the Statistical Package for Social Sciences software, version 17 (SPSS, Chicago, Illinois).
Results
Of the 5,742 patients included in the APEX-AMI trial, LBBB was present in 98 (1.7%). Although the protocol required that patients with LBBB were eligible only if LBBB was “not known to be old” and was accompanied by concordant ≥1 mm ST-segment elevation, 47% of patients with LBBB (46 of 98) did not meet this criterion, as previously described. The baseline characteristics according to the presence of LBBB and concordant ST-segment elevation are listed in Table 1 . The patients with LBBB without concordant ST-segment elevation were less often noted by the investigators to have inferior MI (2.4%) compared to those with concordant ST-segment elevation (31.4%).
| Parameter | No LBBB (n = 5,644) | LBBB (n = 98) | p Value | LBBB With Concordant ST-Segment Elevation (n = 52) | LBBB Without Concordant ST-Segment Elevation (n = 46) | p Value |
|---|---|---|---|---|---|---|
| Age (years) | 61 (52, 71) | 70 (60, 76) | <0.001 | 71 (61, 76) | 69 (60, 77) | 0.997 |
| Women | 22.9% | 30.6% | 0.073 | 32.7% | 28.3% | 0.635 |
| Race | 0.294 | 1.000 | ||||
| White | 94.2% | 96.9% | 96.2% | 97.8% | ||
| Black | 2.4% | 0.0% | 0.0% | 0.0% | ||
| Other | 3.4% | 3.1% | 3.8% | 2.2% | ||
| United States patients | 30.5% | 29.6% | 0.845 | 38.5% | 19.6% | 0.041 |
| Height (cm) | 173 (166, 178) | 170 (163, 176) | 0.014 | 170 (164, 175) | 170 (160, 178) | 0.929 |
| Weight (kg) | 80 (70, 91) | 80 (70, 92) | 0.743 | 77 (68.5, 93) | 80 (71.5, 92) | 0.474 |
| Body mass index (kg/m 2 ) | 27.0 (24.4, 30.0) | 27.7 (24.7, 31.7) | 0.216 | 27.7 (24.2, 32.0) | 27.8 (24.9, 31.4) | 0.591 |
| Blood pressure (mm Hg) | ||||||
| Systolic | 133 (117, 150) | 134 (120, 151) | 0.561 | 132 (119, 149) | 140 (120, 157) | 0.399 |
| Diastolic | 80 (70, 90) | 80 (70, 85) | 0.246 | 78 (70, 86) | 80 (70, 85) | 0.929 |
| Heart rate (beats/min) | 75 (65, 86) | 80 (69, 93) | 0.005 | 78 (68, 89) | 80 (69, 100) | 0.308 |
| Killip class | 0.066 | 0.789 | ||||
| I | 89.5% | 83.7% | 82.6% | 84.6% | ||
| II/III | 9.5% | 16.3% | 17.4% | 15.4% | ||
| IV | 1% | 0% | 0% | 0% | ||
| Inferior myocardial infarction location | 40.6% | 18.5% | <0.001 | 31.4% | 2.4% | <0.001 |
| Interval from symptoms to PCI (hours) | 3.3 (2.5, 4.5) | 3.7 (2.7, 5.3) | 0.086 | 3.5 (2.5, 4.7) | 4.1 (3.2, 5.7) | 0.171 |
| Previous myocardial infarction | 11.9% | 20.4% | 0.011 | 23.1% | 17.4% | 0.486 |
| History of coronary artery disease ⁎ | 16.2% | 25.5% | 0.014 | 28.8% | 21.7% | 0.421 |
| Angina pectoris | 23.9% | 30.6% | 0.124 | 26.9% | 34.8% | 0.400 |
| Previous heart failure | 3.5% | 11.2% | <0.001 | 15.4% | 6.5% | 0.165 |
| Diabetes mellitus | 15.7% | 25.5% | 0.009 | 30.8% | 19.6% | 0.204 |
| Hypertension (by history) | 49.3% | 60.2% | 0.032 | 59.6% | 60.9% | 0.899 |
| Previous stroke | 3.7% | 5.1% | 0.475 | 5.8% | 4.3% | 1.000 |
| Previous transient ischemic attack | 1.5% | 3.1% | 0.194 | 1.9% | 4.3% | 0.599 |
| Previous percutaneous coronary intervention | 9.7% | 13.3% | 0.243 | 17.3% | 8.7% | 0.246 |
| Previous coronary bypass | 2.2% | 4.1% | 0.174 | 1.9% | 6.5% | 0.339 |
| Smoker | <0.001 | 0.422 | ||||
| Never | 33.1% | 40.2% | 35.3% | 45.7% | ||
| Current | 43.6% | 22.7% | 27.5% | 17.4% | ||
| Past | 23.3% | 37.1% | 37.3% | 37.0% | ||
| Creatine clearance (ml/min) | 83 (64, 107) | 69 (51, 92) | <0.001 | 64 (50, 88) | 81 (55, 97) | 0.205 |
⁎ Defined as previous myocardial infarction or previous coronary bypass surgery or previous percutaneous coronary intervention.
Of the 98 patients with LBBB, 65 (66.3%) still had LBBB on the discharge electrocardiogram. There were 32 (61%) of 52 patients from the group with concordant ST-segment elevation and 33 (72%) of 46 patients from the group without concordant ST-segment elevation.
Biomarker information according to the presence or absence of LBBB is listed in Table 2 . Although the elevation of biomarkers consistent with the definition of MI and identification of a culprit lesion on the angiogram were more common in patients who did not have LBBB (>97%), most patients with LBBB (>87%) had enzyme elevation and an identifiable culprit lesion. An initial Thrombolysis In Myocardial Infarction flow of 0 to 1 in the infarct-related artery combined with positive biomarkers was more common in patients with LBBB and concordant ST-segment elevation (71.4%) than in patients with LBBB without concordant ST-segment elevation (44.1%). In 5 patients without concordant ST-segment change and negative biomarkers, no subsequent evolutionary changes were noted on their electrocardiograms, suggesting they had “infarct masquerade,” in accordance with our previous observations. Additionally, a pre-Thrombolysis In Myocardial Infarction flow of 2 to 3 plus negative biomarkers was more common in patients without concordant ST-segment elevation (17.6%) than in those with concordant ST-segment elevation (2.0%; Table 2 ). Furthermore, acute coronary syndrome, as identified by elevated biomarkers and identifiable culprit lesion, was observed in >99% of patients without LBBB, but also in >95% of patients with LBBB, regardless the presence of concordant ST-segment elevation ( Figure 1 ). Most notably, coronary artery disease was present in >97% of patients with or without LBBB and, when LBBB was present, regardless of the presence of concordant ST-segment elevation.
| Biomarkers | No LBBB (n = 5,644) | LBBB (n = 98) | p Value | LBBB With Concordant ST-Segment Elevation (n = 52) | LBBB Without Concordant ST-Segment Elevation (n = 46) | p Value |
|---|---|---|---|---|---|---|
| Peak creatine kinase, ratio of upper limit of normal [valid n] | 9 (4, 18) [4,294] | 7 (2, 17) [64] | 0.050 | 7 (3, 18) [39] | 4 (1, 15) [25] | 0.218 |
| Peak creatine-MB, ratio of upper limit of normal [valid n] | 28 (12, 53) [2,224] | 19 (2, 41) [29] | 0.023 | 19 (3, 48) [17] | 19 (0, 41) [12] | 0.394 |
| Peak troponin T, ratio of upper limit of normal [valid n] | 84 (30, 187) [1,430] | 112 (9, 257) [30] | 0.642 | 110 (30, 415) [15] | 114 (4, 256) [15] | 0.539 |
| Peak troponin I, ratio of upper limit of normal [valid n] | 230 (74, 667) [2,987] | 206 (33, 663) [38] | 0.561 | 251 (69, 818) [25] | 142 (16, 661) [13] | 0.564 |
| Positive biomarkers | 96.7% | 86.7% | <0.001 | 92.3% | 80.4% | 0.003 |
| Culprit artery | 97.8% | 87.8% | <0.001 | 94.2% | 80.4% | 0.038 |
| Culprit artery with pre-Thrombolysis In Myocardial Infarction flow 2–3 | 24.6% | 28.6% | 0.365 | 15.4% | 43.5% | 0.002 |
| Culprit artery and positive biomarkers | 99.5% | 95.9% | <0.001 | 96.2% | 95.7% | 0.900 |
| Presence of coronary artery disease | 99.2% | 99% | 0.548 | 97.8% | 100% | 0.469 |
| Coronary narrowing (>75%) | 41.2% | 39.8% | 0.786 | 32.6% | 46.2% | 0.172 |
| Left anterior descending | 63.4% | 57.9% | 0.268 | 57.1% | 58.7% | 0.878 |
| Left circumflex | 29.9% | 30.4% | 0.912 | 37.5% | 22.7% | 0.124 |
| Right coronary | 51.0% | 41.3% | 0.066 | 46.8% | 35.6% | 0.273 |
| Multivessel narrowing | 33.6% | 33.7% | 0.984 | 36.5% | 30.4% | 0.523 |
| Percutaneous coronary intervention or coronary artery bypass grafting within 24 hours | 94.2% | 78.6% | <0.001 | 84.6% | 71.7% | 0.121 |
| Primary percutaneous coronary intervention or in-hospital Coronary artery bypass grafting | 95.7% | 80.6% | <0.001 | 88.5% | 71.7% | 0.037 |
| Primary percutaneous coronary intervention not done | 6.2% | 21.4% | <0.001 | 15.4% | 28.3% | 0.121 |
| Primary reason not done | 0.176 | 0.314 | ||||
| No culprit lesion identified | 31.0% | 57.1% | 50.0% | 61.5% | ||
| Culprit lesion is patent | 7.8% | 9.5% | 12.5% | 7.7% | ||
| Technical limitations | 11.8% | 9.5% | 0.0% | 15.4% | ||
| Need for coronary artery bypass grafting | 27.3% | 9.5% | 25.0% | 0.0% | ||
| Catheterization not performed | 3.7% | 0.0% | 0.0% | 0.0% | ||
| Others | 18.4% | 14.3% | 12.5% | 15.4% | ||
| Pre-Thrombolysis In Myocardial Infarction flow | 0.004 | 0.005 | ||||
| 2–3 | 26.1% | 38.8% | 23.1% | 56.5% | ||
| 0–1 | 73.9% | 61.3% | 76.9% | 43.5% | ||
| Post-Thrombolysis In Myocardial Infarction flow | 0.673 | 0.748 | ||||
| 2–3 | 97.9% | 97.4% | 90.9% | 94.0% | ||
| 0–1 | 2.1% | 2.6% | 9.1% | 6.0% | ||
| Pre-Thrombolysis In Myocardial Infarction flow and biomarker | <0.001 | 0.027 | ||||
| Thrombolysis In Myocardial Infarction 0–1 and positive biomarker | 72.9% | 60.2% | 71.4% | 44.1% | ||
| Thrombolysis In Myocardial Infarction 2–3 and negative biomarkers | 2.3% | 8.4% | 2.0% | 17.6% | ||
| 90-Day outcomes | ||||||
| Death | 4.7% | 5.1% | 0.861 | 1.9% | 8.7% | 0.128 |
| Death/congestive heart failure/shock | 10.1% | 14.3% | 0.179 | 13.5% | 15.2% | 0.804 |
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