The aim of this study was to investigate the prognosis associated with bundle branch block (BBB) depending on location, time of appearance, and duration in patients with myocardial infarction (MI). From January 1998 to January 2008, we recruited 5,570 patients with acute MI. Thirty-day and 7-year all-cause mortality, according to BBB location, time of appearance, and duration were analyzed by multivariable analyses. BBB was present in 964 patients (17.3%); right BBB (RBBB) 10.6% and left BBB (LBBB) 6.7%. Overall mortality rate at 30 days was 13.2% (n = 738) and 7 years was 6.34 deaths per 100 patient-year. Both RBBB and LBBB were more frequently previous, 42.9% and 58.8%. Compared with non-BBB, all BBB groups showed higher prevalence of co-morbidities, especially rates of diabetes (49.0% vs 34.3%, p <0.001) and more often heart failure during hospitalization (54.5% vs 26.6%, p <0.001). Compared with RBBB, patients with LBBB had a higher prevalence of co-morbidities and a higher mortality, especially the new BBB, 30 days: 52.5% versus 31.6% and 7 years (incident rate): 27.2 versus 13.3 per 100 patient-year. New transient BBB had lower heart failure on admission (42.6% vs 58.3%, p = 0.008) and 30-day mortality (20.3% vs 69.6%, p <0.001) compared with permanent in both locations. New permanent RBBB was independently associated with 30-day (hazard ratio [HR] 2.01, 95% confidence interval [CI] 1.45 to 2.79) and 7-year mortality (HR 3.12, 95% CI 2.38 to 4.09). New-permanent LBBB was independently associated with 30-day (HR 2.15, 95% CI 1.47 to 3.15) and 7-year mortality (HR 2.91, 95% CI 2.08 to 4.08). In conclusion, in patients with acute MI, the appearance of a new BBB was independently associated with a higher 30-day and 7-year all-cause mortality.
Bundle branch block (BBB) in acute myocardial infarction (MI) is often associated with high mortality. Right BBB (RBBB) is often associated with large infarctions, whereas the poor prognosis associated with left BBB (LBBB) may be because of co-morbidity. The time of appearance and duration of BBB have different prognostic significances ; however, studies have not always distinguished between new and preexisting, and the time of appearance has been documented using heterogeneous criteria. Moreover, the most recent data on BBB in MI have been obtained in post hoc analyses. Additionally, patients presenting with presumed new LBBB and suspected MI do not always have the latter confirmed, and this may lead to the recommendation of reperfusion based on a stepwise alternative to that of current guidelines. We hypothesized that prognosis associated with BBB might be different depending on the location (right or left), time of appearance (preexisting, unknown or new), and duration (transient or persistent) in a population of patients admitted with an acute MI.
Methods
We recruited prospectively consecutive patients with acute MI admitted to the coronary care unit of 2 hospitals in the Murcia region (Spain) from January 1998 to January 2008. Inclusion criteria were (1) patients aged ≥18 years with confirmed acute MI, (2) admitted within 24 hours to the coronary care unit, and (3) agreed to participate. The exclusion criteria were (1) MIs occurring during bypass surgery or coronary angioplasty and (2) MI diagnosis later invalidated in favor of another diagnosis. The diagnosis was established using at least 2 of the following criteria: typical precordial pain lasting >30 minutes, a deviation of >0.1 mV in ST segment in >2 leads, and an increase in the creatine kinase muscle-brain fraction (CK-MB) to a minimum of twice the normal level. Acute MI was classified into ST-segment or non–ST-segment elevation MI. In the case of LBBB, this classification was not used, and the MI location was identified, when possible, according to leads with concordant or discordant ST-segment deviation and/or evidence of T-wave inversion in serial electrocardiograms (ECGs) with further corroboration by echocardiography. Previous electrocardiographic records were obtained when possible. Electrocardiographic records were obtained on admission, post-reperfusion therapy, every 6 hours on day 1, twice daily on day 2, and daily thereafter. In the absence of reperfusion, ECGs were obtained on admission, every 8 hours in the first 24 hours after admission, and thereafter daily until discharge. Additional electrocardiographic records were obtained in the case of recurrence of chest pain, arrhythmia, changes in QRS complex monitoring, or after invasive procedures. The study protocol was approved by the Clinical Investigation Committees of both hospitals. Conduction disturbances were defined using standard electrocardiographic criteria. BBB was classified according to the time of appearance: Pre-existing, when it had been documented previously; unknown, if it was present on admission and no previous ECG was available; and new, if it appeared after admission or was present on admission but was not recorded on an ECG performed within the previous 6 months. New was further classified as transient when it was not present at the time of hospital discharge and permanent either when the patient died or was discharged with BBB still present. Chronic obstructive pulmonary disease was defined by a history of chronic obstructive pulmonary disease, chronic bronchitis, or emphysema. Previous peripheral arterial disease was defined as a documented history of peripheral arterial disease, claudication, and amputation because of arterial failure, aortoiliac occlusive disease, surgical or percutaneous peripheral arterial revascularization, or positive results on noninvasive testing. Previous stroke was established with a documented history of sudden-onset loss of neurologic function that persisted in time. The primary end points were the occurrence of short (30 days) and long-term all-cause mortality. This was confirmed either by a review of medical records, local electronic registries, or telephone information.
Relative risk of short- and long-term all-cause death was calculated as a hazard ratio (HR) with a 95% confidence interval (CI) derived from Cox proportional hazard regression with multivariable adjustment. Variables considered as covariates were those that have shown a potential impact on mortality in previous studies and were independently associated with mortality (p <0.05) in our study. For this purpose, we used all baseline variables (age, gender, hypertension, diabetes mellitus, current smoker, dyslipidemia, preexisting MI, heart failure, stroke, peripheral arterial disease, atrial fibrillation, cancer, chronic renal disease, chronic obstructive pulmonary disease, type of MI, ST-segment vs non–ST-segment elevation, and anterior location), additional procedural variables (reperfusion, including coronary revascularization), and Killip class at admission, heart rate, systolic blood pressure, glycemia on admission, peak CK-MB, and left ventricular ejection fraction (LVEF). Because all the earlier mentioned variables were considered relevant, they were all forced with an enter method in the model. Proportional hazards and linear assumptions were tested and appeared valid for all analyses. Kaplan-Meier curves were constructed to estimate survival rates, and comparisons were performed using the log-rank test. To test the robustness of the data, we performed a cross-validation by randomly dividing the sample into 2 subgroups (50% to 50%) and estimated the hazard ratio corresponding to each of the new BBB subgroups. Analyses were performed using SPSS, version 20.0 (IBM, Armonk, NY).
Results
Of the 5,570 patients, 964 (17.3%) had BBB: RBBB 590 (10.6%) and LBBB 374 (6.7%). RBBB and LBBB were most frequently classified as preexisting ( Table 1 ). Information during follow-up, median 7.2 years (interquartile range 1.8 to 9.9), was obtained in 99.5% of patients.
| Variable | RBBB [n= 590] | LBBB [n=374] | Total [n=964] |
|---|---|---|---|
| Preexisting | 253 (42.9%) | 220 (58.8%) | 473 (49.0%) |
| Unknown | 125 (21.2%) | 53 (14.2%) | 178 (18.5%) |
| New | 212 (35.9%) | 101 (27.0%) | 313 (32.5%) |
Compared with patients without BBB, those with RBBB or LBBB of any type were older and had greater co-morbidity, except for those with unknown and new RBBB ( Table 2 ). Also, compared with non-BBB, all BBB groups presented more often with heart failure except in new and unknown RBBB. Except when RBBB was unknown or new and unknown LBBB, all other BBB were less frequently associated with anterior MI, these patients received less reperfusion therapy and had multivessel coronary disease more frequently. Comparison within each time of appearance group showed that patients with LBBB had greater co-morbidity and less frequent anterior location MI than RBBB (data not shown).
| Non-BBB (n=4606) | PREEXISTING (n = 473) | UNKNOWN (n = 178) | NEW (n= 313) | ||||
|---|---|---|---|---|---|---|---|
| RBBB (n=253) | LBBB (n=220) | RBBB (n=125) | LBBB (n=53) | RBBB (n=212) | LBBB (n = 101) | ||
| Age (years) median (IQR) | 66.5 (56.5-74.5) | 73.5 (67.7-78.5) ∗ | 74.5 (68.5-79.5) ∗ | 72.5 (65.5-77.5) p<.001 | 72.5 (66.0-77.5) ∗ | 69.5 (60.5-76.7) | 72.5 (64.2-78.7) |
| Women | 26.2% | 17.4% ∗ | 35.0% ∗ † | 21.6% | 34.0% | 24.8% | 40.6% ∗ † |
| Antecedents | |||||||
| Hypertension | 54.0% | 63.7% ∗ | 68.6% ∗ | 52.4% | 47.2% | 47.1% | 59.8% ∗ † |
| Diabetes mellitus | 34.3% | 48.8% ∗ | 58.2% ∗ † | 37.6% | 52.8% ∗ † | 39.5% | 59.8% ∗ † |
| Current smoker | 37.1% | 25.8% ∗ | 15.9% ∗ † | 30.4% | 20.8% ∗ | 39.5% | 22.8% ∗ † |
| Previous Myocardial Infarction | 17.4% | 31.3% ∗ | 41.4% ∗ † | 13.6% | 13.2% | 12.9% | 28.7% ∗ † |
| Heart failure | 22.2% | 34.8% ∗ | 58.2% ∗ † | 23.2% | 35.8% ∗ † | 23.8% | 42.6% ∗ † |
| Stroke | 8.6% | 11.7% ∗ | 15.0% ∗ | 8.0% | 5.7% | 9.5% | 13.9% ∗ |
| Peripheral arteriopathy | 6.8% | 11.7% | 16.0% ∗ | 4.8% | 7.5% | 10.0% | 12.7% ∗ |
| Percutaneous Coronary Intervention | 8.7% | 19.5% ∗ | 18.6% ∗ | 4.0% | 7.5% | 7.1% | 7.9% |
| Cardiovascular treatment | 47.3% | 64.1% ∗ | 75.9% ∗ † | 51.6% | 62.3% ∗ | 45.7% | 64.4% ∗ † |
| Chronic renal failure | 4.3% | 11.3% ∗ | 10.5% ∗ | 7.2% | 11.3% ∗ | 4.8% | 13.7% ∗ † |
| Chronic Obstructive Pulmonary Disease | 8.3% | 16.8% ∗ | 11.4% ∗ | 12.8% | 11.3% | 7.6% | 13.7% ∗ |
| Cancer | 3.5% | 7.8% | 1.4% † | 4% | 5.7% | 5.2% | 3.9% |
∗ Statistical significance compared with non-BBB.
† Significant difference between Right and Left within each group. Cardiovascular treatment includes calcium-channel blockers, β-blockers, digoxin, diuretics, and/or anti-arrhythmic drugs. Chronic renal failure was defined as creatinine level ≥2 mg/dL.
Compared with patients without BBB, all BBB types were more frequently diagnosed with heart failure during hospitalization and within each location group. Atrial fibrillation was more often seen in all categories of BBB (except in unknown RBBB), complete auriculoventricular block in new RBBB and LBBB, and ventricular fibrillation in unknown and new RBBB (data not shown).
Overall 30-day mortality rate was 13.2% (n = 738). The incidence rate of mortality at 7 years was 6.3 (95% CI 6.1 to 6.6) deaths per 100 patient-year (n = 2,268). Mortality was significantly greater in BBB compared with non-BBB. Within each group of BBB, 30-day mortality was numerically higher in LBBB compared with RBBB. However, the differences in 1-year mortality were statistically significant within all the 3 groups. New LBBB showed the greatest 1-year and long-term mortality.
BBB was classified as new in a higher proportion of patients with RBBB compared with LBBB ( Table 1 ), and it was transient in a similar proportion. Compared with patients with permanent BBB, those with transient shared a number of clinical characteristics: they were less frequently women, they presented with shorter delay to admission, although this did not reach statistical significance, and they had a greater LVEF. Heart failure on admission was less frequent in transient RBBB compared with permanent, whereas LBBB showed similar rates. Among the former, despite a similarly depressed LVEF, heart failure was present in a significantly greater number of patients with LBBB. Ventricular fibrillation occurred more frequently in transient RBBB than in LBBB ( Table 3 ).
| Variable | New RBBB (n = 212) | New LBBB (n = 101) | ||
|---|---|---|---|---|
| Transient (n = 137) | Permanent (n = 75) | Transient (n = 61) | Permanent (n = 40) | |
| Age (years) median (IQR) | 67.0 (58.7-73.5) | 72.5 (63.5-78.5) | 72.5 (63.5-78.5) | 72.5 (64.5-79.5) |
| Women | 19.0% | 36.0% ∗ | 34.4% † | 50.0% ∗ |
| Hypertension | 48.5% | 44.6% | 57.4% | 63.4% ∗ |
| Diabetes mellitus | 35.3% | 47.3% | 59.0% † | 61.0% |
| Current smoker | 40.4% | 37.8% | 29.5% † | 12.5% ∗ ‡ |
| Previous MI | 13.2% | 12.2% | 21.3% † | 40.0% ∗ ‡ |
| Heart failure | 18.4% | 33.8% ∗ | 39.3% † | 47.5% ‡ |
| Stroke | 10.3% | 8.1% | 13.1% | 15.0% |
| Chronic renal failure | 5.9% | 2.7% | 9.8% | 19.5% ∗ ‡ |
| Admission delay, median (IQR) (IQR) | 90 (55-169) | 120 (60-210) | 76 (40-180) | 120 (60-281) ∗ |
| Killip > I at admission | 37.0% | 57.0% ∗ | 56.0% † | 63.0% |
| Killip IV | 14.7% | 64.9% ∗ | 39.3% † | 61.0% ∗ |
| Heart rate ± SD | 86 ± 27 | 88 ± 25 | 90 ± 31 | 90 ± 28 |
| Systolic blood pressure (mm Hg) | 125 ± 32 | 112 ± 28 ∗ | 129 ± 38 | 114 ± 33 ∗ |
| Glycemia (mmol/dl) | 11.1 ± 5.7 | 12.0 ± 6.0 ∗ | 16.0 ± 7.8 † | 15.0 ± 5.6 ‡ |
| CK-MB peak median (IQR) | 230 (104-465) | 306 (119-500) ∗ | 116 (58-238) † | 159 (59-287) ‡ |
| STEMI | 91.2% | 92.6% | – | – |
| Anterior location | 73.0% | 78.7% | 34.4% † | 50.0% ‡ |
| LVEF | 43 ± 10 | 34 ± 11 ∗ | 41 ± 13 | 34 ± 10 ∗ |
| PCI | 62.8% | 63.0% | 45.9% † | 52.5% ‡ |
| Acute reperfusion | 79.4% | 74.3% | 49.2% † | 53.7% ‡ |
| 3 or more vessels narrowed | 19.8% | 34.9% ∗ | 27.6% | 61.1% ∗ ‡ |
| LADA culprit lesion | 75.9% | 76.7% | 64.3% | 61.1% |
| Ventricular fibrillation | 21.3% | 13.5% | 4.9% † | 9.8% |
| Mechanical complications | 2.2% | 9.5% ∗ | 3.3% | 12.2% |
| 30-day mortality | 14.6% | 62.7% ∗ | 32.8% † | 82.5% ∗ ‡ |
| 1-year mortality | 23.5% | 72.0% ∗ | 37.7% † | 90.0% ∗ ‡ |
| Total follow-up mortality, incidence rate per 100 patients-year, 95% CI | 8.2 (6.4-10.5) | 16.1 (11.7-21.7) ∗ | 40.3 (30.8-51.8) † | 10.1 (7.1-13.9) ∗ ‡ § |
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