Exercise-induced (EI) right bundle branch block (RBBB) is an infrequent electrocardiographic phenomenon, and controversy exists regarding its association with cardiovascular disease. We compared the prevalence and prognostic significance of RBBB, abnormal ST depression, and normal electrocardiographic findings in response to exercise testing in 9,623 consecutive veterans who underwent exercise testing from 1987 to 2007. EI RBBB, EI ST depression, and a normal exercise electrocardiographic response occurred in 0.24%, 15.2%, and 71.9% veterans, respectively. After appropriate exclusions, of the 8,047 patients analyzed, 6 patients in the EI RBBB subgroup died. Of these 6 deaths, 3 were cardiovascular deaths during the 9 years of follow-up. The annual death rate was 7.3% (1.4% cardiac deaths), 2.6% (1.2% cardiac deaths), and 1.8% (0.6% cardiac death) among those with EI RBBB, EI ST depression, and a normal ST response, respectively (p <0.0001). The patients with EI RBBB were significantly older, more overweight, and had a greater prevalence of coronary artery disease, heart failure, and hypertension compared to the 2 other subgroups. Patients with EI RBBB had an age-adjusted Cox proportional hazard ratio of 1.13 (p = 0.75, 95% confidence interval 0.51 to 2.5) for all-cause mortality and 1.57 (p = 0.43, 95% confidence interval 0.51 to 4.8) for cardiovascular mortality, respectively. In conclusion, EI RBBB is a rare occurrence during routine clinical exercise testing that appears to be benign.
Exercise-induced (EI) right bundle branch block (RBBB) is an infrequent electrocardiographic phenomenon, and controversy exists regarding its association with coronary artery disease (CAD) and heart failure. Although information about EI left BBB (LBBB) is available, fewer studies of EI RBBB have been published. Therefore, in a large series of EI RBBB, we prospectively evaluated its prognostic significance compared to EI ST depression and a normal electrocardiographic response to exercise testing.
Methods
Consecutive adult patients who underwent clinically indicated exercise treadmill testing from 1987 to 2007 at the Long Beach and Palo Alto Veteran Affairs Medical Centers were evaluated (n = 9,623). Standard criteria were used to define RBBB, including the presence of (1) sinus rhythm; (2) QRS duration of ≥120 ms; (3) terminal R wave in lead V 1 (eg, R, rR′, rsR′, rSR′, or qR); (4) slurred S wave in leads I and V 6 ; and (5) T waves opposite in direction to the major QRS amplitude.
Only the first test performed was considered. A total of 338 women (3.5%) were excluded. We also excluded patients with the following electrocardiographic patterns that interfered with the analysis of the exercise electrocardiogram: (1) resting ST depression and/or left ventricular hypertrophy, paced rhythm, and pre-excitation syndromes (n = 675, 7%); (2) atrial fibrillation (n = 109, 1.1%); (3) RBBB at rest (n = 348, 3.6%); (4) LBBB at rest (n = 68, 0.7%); and (4) EI LBBB (n = 38, 0.39%). The final cohort for analysis consisted of 8,047 male veterans. The institutional review board approved the research protocol. All patients provided informed consent.
The subjects underwent symptom-limited treadmill testing using an individualized ramp treadmill protocol and exercised to maximum exertion. Twelve-lead electrocardiographic data were recorded during exercise and for 5 minutes during recovery. Visual ST-segment depression and ST slopes were measured and read by 2 board-certified cardiologists. ST-segment depression was measured at the J junction, and the ST slope was measured during the following 60 ms of the ST segment. The exercise response was considered abnormal if the patient had ≥1 mm of horizontal or downsloping ST-segment depression in leads V 5 or V 6 measured at the J point using the PQ segment as the baseline, even in patients with early repolarization. Standard criteria for stopping were used, including serious arrhythmias, a decrease in systolic blood pressure to less than that at rest, >3 mm ST-segment depression or elevation, severe angina pectoris, or central nervous system complaints. When the end point had been reached, the treadmill was stopped abruptly, and the patient was placed in the supine position within 1 minute. The baseline and maximum exercise variables, EI hypotension or angina, and exercise capacity, estimated in metabolic equivalents from the final treadmill speed and grade were recorded.
The outcomes and demographics were compared among the patients with EI BBB, those with ≥1.0 mm horizontal or downsloping ST-segment depression (EI ST depression), and those with normal electrocardiographic responses. None of the patients with EI RBBB exhibited concomitant ST depression. The primary outcome variables were all-cause and cardiovascular mortality. The California Death Index (from the California Department of Health Services) and the Social Security Death Index were used to ascertain the vital status of each patient as of December 31, 2007. The California Death Index provided the cause of death, which was confirmed by reviewing the Veteran Affairs Clinical Database.
The differences among the subjects with EI RBBB, EI ST segment depression, and normal ST responses to exercise testing were compared. Analysis of variance with Bonferroni post hoc adjustment for multiple comparisons and chi-square tests were used for continuous and dichotomous variables, respectively. All continuous variables exhibited a normal distribution and are presented as the mean ± SD. Categorical variables are expressed as the absolute and relative (percentage) frequencies. p Values <0.05 were considered statistically significant. All-cause and cardiovascular mortality were used as the primary end points for the Kaplan-Meier survival analysis. Cox proportional hazards analysis was used to determine which variables were independently and significantly associated with the time to death in multivariate models. The analyses were adjusted for age in years as a continuous variable. The Number Cruncher Statistical System (NCSS, Kaysville, Utah) was used for all statistical analyses.
Results
The demographic, clinical, baseline electrocardiographic, and exercise test data, and outcomes of the population of veterans screened (n = 9,623) and those meeting the inclusion and exclusion criteria (n = 8,047 male subjects) are listed in Tables 1 and 2 , respectively. Most patients had a normal exercise electrocardiographic response. The patients with EI RBBB were significantly older, more overweight, and had a greater prevalence of CAD, heart failure, and hypertension than those with EI ST depression and a normal exercise electrocardiographic response ( Table 2 ). The annual death rates for all-cause and cardiovascular mortality were greatest for the patients with EI RBBB and were lower for those with EI ST depression and those with normal exercise test results. Figure 1 shows the Kaplan-Meier plots. During an average follow-up of 8.8 ± 5.4 years, 6 patients in the EI RBBB subgroup died (all-cause), of which 3 were cardiovascular in origin. Table 3 lists the characteristics of those with RBBB who survived and those who died.
| Variable | Total Population (n = 9,623) |
|---|---|
| Age (years) | 58.8 ± 11.3 |
| Height (inches) | 69.2 ± 3.5 |
| Weight (pounds) | 193.3 ± 38.8 |
| Body mass index (kg/m 2 ) | 28.4 ± 5.3 |
| Women | 338 (3.5%) |
| Coronary artery disease ⁎ | 22.3% |
| Ischemic heart failure | 3.7% |
| Nonischemic heart failure | 3.4% |
| Hypertension | 50.6% |
| Smoker | 58.2% |
| Diabetes mellitus | 13.5% |
| Obesity † | 32.1% |
| Pulmonary disease | 6.0% |
| At rest left bundle branch block | 0.7% |
| At rest right bundle branch block | 3.6% |
| Atrial fibrillation | 1.1% |
| Left ventricle hypertrophy (strain) or paced rhythm | 1.3% |
| At rest ST depression or pre-excitation | 5.7% |
| Any diagnostic electrocardiographic Q wave | 15.9% |
| At rest heart rate (beats/min) | 77 ± 21 |
| Maximum heart rate (beats/min) | 138 ± 24 |
| Peak systolic blood pressure (mm Hg) | 177 ± 29 |
| Metabolic equivalent | 8 ± 3 |
| Borg scale | 17 ± 3 |
| Exercise-induced ST-segment depression | 8.0% |
| Exercise-induced left bundle branch block | 0.4% |
| Exercise-induced right bundle branch block | 0.24% |
| Annual all-cause mortality | 1.8% |
| Annual cardiovascular mortality | 0.6% |
| Survivors | 7,929 (82.4%) |
| Deaths | 1,694 (17.6%) |
⁎ Defined as presence of ≥50% coronary obstruction in any major epicardial artery as evaluated on coronary angiograms or evidence of myocardial ischemia on stress echocardiogram or nuclear stress test imaging.
| Variable | Normal Electrocardiographic Exercise Response (n = 6,569) | EI ST Depression (n = 1,458) | EI RBBB (n = 23) |
|---|---|---|---|
| Age (years) | 58 ± 11 | 62 ± 10 | 65 ± 10 ⁎ |
| Height (inches) | 69 ± 3 | 69 ± 4 | 69 ± 3 |
| Weight (pounds) | 196 ± 39 | 190 ± 35 | 201 ± 56 ⁎ |
| Body mass index (kg/m 2 ) | 28.6 ± 5 | 27.9 ± 5 | 29.6 ± 8 ⁎ |
| Coronary artery disease | 19.3% | 30.4% | 39.1% ⁎ |
| Ischemic heart failure | 2.1% | 3.4% | 4.3% ⁎ |
| Nonischemic heart failure | 2.6% | 2.7% | 8.7% ⁎ |
| Hypertension | 49.4% | 52.8% | 52.2% |
| Smoker | 60.7% | 54.6% | 52.2% ⁎ |
| Diabetes mellitus | 13.45% | 14.7% | 14.2% |
| Obesity | 33.8% | 27.2% | 34.8% † |
| Pulmonary disease | 6.6% | 3.8% | 4.3% ‡ |
| Any diagnostic Q wave | 14.5 | 18.9 | 8.7 ⁎ |
| Heart rate at rest (beats/min) | 77 ± 23 | 75 ± 14 | 75 ± 15 ‡ |
| Maximum heart rate (beats/min) | 139 ± 24 | 138 ± 23 | 134 ± 25 |
| Peak systolic blood pressure (mm Hg) | 177 ± 28 | 178 ± 28 | 181 ± 27 |
| Metabolic equivalents | 9 ± 4 | 8 ± 3 | 8 ± 3 |
| Borg scale | 17 ± 3 | 17 ± 3 | 18 ± 2 |
| Annual all-cause mortality | 1.7% | 2.4% | 7.3% ⁎ |
| Annual cardiovascular mortality | 0.6% | 1.2% | 1.4% ⁎ |
| Survivors | 5,449 (82.9%) | 1,105 (75.8%) | 17 (73.9%) |
| Deaths | 1,120 (17.1%) | 353 (24.2%) | 6 (26.1%) |
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