With respect to the cardiac risk factors on which the FAA routinely collects data, the
RBBB cases and controls were very similar. A summary of the risk factors of the case and
control groups is shown in Table 3. Data on study subjects’ smoking behavior and serum
cholesterol levels were not available for analysis

Table 3

Summary of Baseline Characteristics of RBBB Cases and Controls

RBBB Cases Controls
Mean Age 47.5 years 46.9 years
Body Mass Index 25.43 25.59
Percent Obese 27% 27%
Mean Blood Pressure 125/78 125/78
Percent with Other Known | 13% 0%
Cardiovascular Conditions

The follow-up of the cases began with the first visit at which the RBBB was noted
during or prior to 1970. Controls were followed from their latest 1970 exam. Beginning the
control group follow-up later than cases dilutes somewhat the benefit of age matching and,
therefore, the person years contributed by this group.

To address this issue, the person-years of experience contributed by each control was
increased by 2.5 years. The 2.5 years represent the mean number of years between the date
on which the RBBB is first noted in the case group and the last examination in 1970.

For the cases and controls, the response rates to the mailed questionnaire were 56%
and 50% respectively. Of the completed questionnaires, 73% were completed by the airman,
22% by the airman's spouse, 2% by the airman's offspring and 3% by others. With the
information from the questionnaire, complete data for the study period were available for
85% of the cases and 83% of the controls.

Among the pilots not responding to the questionnaires, 49% were returned by the
postal system because the pilot was no longer at the most current address of which the FAA
had knowledge. Forty-eight percent of the mailed questionnaires were not returned by
either the airman, his next-of-kin or the postal system. Three percent were found to have
new information on the FAA database; therefore, this information was used in lieu of
questionnaire data.

Of the cases who were sent a questionnaire and did not respond, 88% had only the
RBBB at baseline, while 12% had other cardiovascular conditions, in addition to the RBBB.
The mean age at baseline of the non-respondents was 47.6 years and they were followed a
mean of 5.8 years before they were lost to follow-up. Among the non-respondents in the
RBBB case group, six had cardiac events that occurred before they were lost to follow-up. In
these cases, information from the questionnaire, if completed, would have added little to the
study. In the control group, no cardiac events were experienced before they were lost to
follow-up. At baseline, the subgroup of the airmen who did not have complete information
on the airman history file and did not respond to the “questionnaire were similar to those
for which complete information was available.

A “cardiac event” was defined as pathology codes on the airman history file indicating
the diagnosis of myocardial infarction, atherosclerotic heart disease, or coronary heart
disease. For those airmen with incomplete data for the study period on the history file,



stored on computer tape as part of the airman history file. The computerized airman history
file was the major source of data for this study.

Twenty-nine percent of the case group and 28 percent of the control group identified in
1970 did not maintain medical certification through the end of 1985 although they were less
than 60 years of age at the end of the follow-up period. If cardiac event experience was
related to this failure to apply for recertification, a significant bias in the results would
occur. To address this issue, a questionnaire was sent to this subgroup to determine their
cardiac event experience through the end of 1985. In the event of a deceased or incapacitated
study subject, the next of kin were instructed to complete the questionnaire to the best of
their ability.

The cases and controls were compared at the beginning of the study period to
cardiovascular disease risk factors on which information is routinely collected. These
factors were blood pressure, weight, and cardiac abnormalities. Age, an important
cardiovascular risk factor in itself, was the only variable on which the cases and controls
were matched. The mean age of the RBBB cases was 47.5 years while the mean age of the
control group was 46.9 years.

Height and weight were used to calculate body mass index (BMI) at the beginning of the
study period for each of the study subjects. The mean BMI for the case group was 25.43 and
25.59 for the control group. West (10) has proposed an ideal BMI for males measured with
light clothing and no shoes of 22.4. Using the definition of obesity as 20% above the ideal
BMI, 27% of both case and control groups were obese.

“Definite hypertension” is defined by the FAA as a blood pressure exceeding 160/98.
The mean blood pressure for both the case and control groups was 125/78. Neither case nor
control group had any members who fell into the hypertensive category, a finding which is
not surprising, given the several medications approved by FAA for blood pressure control
and the fact that this group is a highly-screened occupational population.

At baseline, the cases were characterized as to their cardiac risk profile using their ECG
abnormalities and the pathology codes assigned them by the AMCD. The distribution of
baseline cardiac risk factor profiles among the cases is shown in Table 2. Thirteen percent
of the cases of RBBB also had other conditions such as ischemic electrocardiographic
changes, arrhythmias, changes in cardiac chamber size and axis deviation, which may
affect cardiac outcome experience. Eighty-seven percent of the cases had only RBBB with no
known other electrocardiographic abnormalities or conditions that would affect their
outcome. The control group had no known electrocardiographic abnormality or
cardiovascular conditions that would alter their risk.

Table 2

Baseline Risk Factor Profile Categories

RISK CATEGORIES No. Percent
Uncomplicated RBBB 377 87
RBBB with evidence of ischemia 8 2
RBBB with arrhythmia 5 1
RBBB with chamber size changes 17 4
RBBB with axis deviation 16 4
RBBB with other conduction defects 3 1
RBBB with diabetes mellitus 3 1
RBBB with other conditions 4 1



responses on the questionnaire were used to determine their cardiac outcome experience. A
cardiac event, which was ascertained from the questionnaire, was defined as reported
history of myocardial infarction, coronary heart disease, angina or atherosclerotic heart
disease.

Followup of the cases and controls was accomplished using the computerized airman
history file and the follow-up questionnaire sent to pilots with incomplete data on the
history file. The mean length of follow-up for the case group was 14.2 years with a range of 1
month to 21.6 years, compared to a mean of 14.3 years for the control group. Length of
follow-up in the control group ranged from 1 month to 16 years.

RESULTS AND DISCUSSION

Twenty-four cardiac events were experienced by the 433 cases with RBBB (6%), while the
control group of 338 pilots experienced 9 events (3%). This increased proportion of cardiac
events in RBBB cases compared to the controls was of borderline statistical significance
with a ChiSquare = 3.85, 1 df, p<.05. Of the 24 events occurring in the case group, 10 (42%)
were myocardial infarction, and 14 (58%) were coronary heart disease and/or
atherosclerotic heart disease with or without angina pectoris. Among the cases who had
myocardial infarction, one had coronary artery bypass surgery. Two of the cases with
coronary artery disease had bypass surgery. Of the nine events occurring in the control
group, five (56%) were myocardial infarction and four (44%) were coronary heart disease
and/or atherosclerotic heart disease, with or without angina. Among those controls with
coronary artery disease, one pilot had coronary artery bypass surgery.

Owing to the unequal length of follow-up for the cases and controls, person-years of
observation were used as the denominators for the calculation of incidence rates. The
incidence rate of cardiac events in the case group was 3.93 per 1,000 person-years of
observation, compared with an incidence rate of 1.87 per 1,000 person-years of observation
in the control group. The relative risk was 2.012 (95% confidence limits: .994-4.484) (3).

Current literature on cardiac outcomes among aviators with RBBB does not support a
role for RBBB as a risk factor for subsequent cardiac outcomes. Among those studies (2,6,8)
that examined the risk of cardiac outcomes in military aviator populations, RBBB was not
found to be a significant predictor of cardiovascular events in an asymptomatic population.
In Rabkin's study (4) of sudden death among Royal Canadian Air Force pilots and pilots
licensed by the Canadian Department of Transportation, no increased risk of sudden death
was noted among the 65 pilots with an RBBB. In the study of civilian aviators in Argentina
by Canaveris (1), no excess risk of adverse cardiac outcomes was demonstrated.

The findings of the present study of cardiovascular outcomes in the Class I airmen are
not inconsistent with the findings of the previous studies. Although our risk ratio is
elevated, the 95% confidence interval includes the value 1.

Among the descriptive studies that examined RBBB in aviators, the prevalence rates in
the study population varied. Hickman (2) found a prevalence of RBBB in USAF pilots under
the age of 50 years to be six per 1,000 pilots. Canaveris (1) reported a prevalence rate of
5.9/1,000 pilots. In the present FAA study, the point prevalence rate was 12.16 per 1,000
Class I pilots. The differences in the prevalence rates are likely to be a function of the
different populations studied and certification or eligibility criteria.

The computerized medical history and ECG file maintained by the FAA provided a
unique opportunity to examine the role of RBBB in the subsequent development of selected
cardiac outcomes in a large civilian aviator population. Unfortunately, information on two
of the most important cardiovascular risk factors, serum cholesterol level and smoking, is
not available from the airman history file. While the case and contro] groups are
comparable with respect to the covariates on which we have data, it cannot be determined




from this study if any excess risk of cardiac events experienced by the case group is a result
of the RBBB, or is in fact related to one of the risk factors on which we have no data.

CONCLUSIONS

The data suggest an increased risk for the subsequent development of cardiac event in
the RBBB cases, compared to the age-matched controls. This apparent elevated risk is an
interesting finding, although inconclusive. The borderline significance of the test of
independence of the RBBB and the cardiac events, as well as the interval estimates for the
relative risk which are inclusive of one, suggest further in-depth examination is necessary.
A portion of the cohort of RBBB cases and controls that has been identified could possibly
be evaluated in terms of serum cholesterol levels and smoking behavior. An analysis that
adjusts for the influence of these covariates would more clearly determine the role of RBBB
as a risk factor for subsequent cardiac events.

REFERENCES

1 Canaveris G. Intraventricular conduction disturbances in flying personnel: right
bundle branch block. Av Space Environ Med. 1986;57:591-6.

2 Hickman JR. Disposition of electrocardiographic abnormalities in aviators. AGARD
Sixth Advanced Operational Aviation Medicine Course. Report #681. Brussels, Belgium.
March 24-28, 1980 (NATO).

3 Kahn H. An Introduction to Epidemiologic Methods. New York Oxford: Oxford
University Press, 1983.

4 Rabkin SW. Electrocardiographic abnormalities in apparently healthy men and the
risk of sudden death. Drugs. 1984;28(Oct)(Suppl 1):28-45.

5 Reusch CS. Vival JR. Clinical analysis of right bundle branch block. American Heart
Journal. 1959; 58(Oct):543-6.

6 Rotman M, Triebwasser JH. A clinical and follow-up study of right and left bundle
branch block. Circulation. 1975;51(Mar):477-84.

7 Rowland DJ. Left and right bundle branch block, left anterior and left posterior
hemiblock. Eur Heart J. 1970;80{(Dec):746-51.

8 Smith RF, Jackson DH, Harthorne JW, et al. Acquired bundle branch block in a
healthy population. Am Heart J. 970; 80((Dec):746-51.

9  Tunstall-Pedoe H. Risk of coronary heart attack in the normal population and how it
might be modified in flyers. Eur Heart J. 1984;5(Suppl A): 43-9

10 West K. Computing and expressing degree of fatness. JAMA. 1980;(Apr):1421.

*US GOVERNMENT PRINTING OFFICE:1990-761-020/20249


Technical Repert Documentation Pege

T. Report Ne. 3. Recipient's Catalog Ne.

DOT/FAA/AM-90/7

42 Title end Subtitle .

RIGHT BUNDLE BRANCH BLOCK AS A RISK FACTOR
FOR SUBSEQUENT CARDIAC EVENTS

5, Report Date
August 1990

6. Performing Orgenizetion Code

[€- Partorming Orgonization Report Ne,

7. author'sILeslie S. Hudson, M.P.H., Charles F. Booze, Ph.D
and Audie W. Davis, M.D.

9. Performing Organizetion Nome ond Address 10. Work Unit No. (TRAIS)
FAA Civil Aeromedical Institute

P.O. Box 25082

TI. Contract or Grent Ne.
Oklahoma City, Oklahoma 73125

13. Type of Report ond Period Covered

12. Sponsoring Agency Name ond Address
Office of Aviation Medicine

Federal Aviation Administration

800 Independence Avenue, S.W. T4, Sponsoring Agency Code
Washington, D.C. 20591 . AAM-330

TS. Supplementary Notes

16. Abstract

The identification of risk factors for adverse cardiac events is valuable to
the certification of airmen. This study examines the importance of right
bundle branch block (RBBB) as a risk factor for myocardial infarction (MI),
atherosclerotic heart disease (ASHD) and coronary heart disease (CHD).

Using a non-concurrent prospective design, 433 Class I airmen between the ages
of 35 and 60 years who had an RBBB on their electrocardiogram (ECG) in 1970
were matched to 338 control Class I airmen who had no abnormalities on their
1970 ECG. Using the longitudinal database maintained by the Federal Aviation
Administration (FAA), the medical records of these airmen were screened for
MI, ASHD, and CHD through the end of 1985. Questionnaires were sent to airmen
with incomplete data on the computerized database.

The first occurrence of any of these outcomes was considered an adverse cardiac
event. In the case group, 24 cardiac events occurred (3.93/1,000 person-years)
compared with 9 events in the control group (1.87/1,000 person-years). The
relative risk was 2.012 with 95% confidence intervals of .994 to 4.484. The
ChiSquare for independence was 3.85 1 df, p<0.05.

The findings suggest an increased risk of adverse cardiac events but are of
borderline statistical significance.

17, Key Words 18. Distribution Statement

Aeromedical certification Document is available to the public

Right bundle branch block through the National Technical

Myocardial infarction Information Service, Springfield, VA

Coronary heart disease 22161

19. Security Classil. (of thi y WH. Security Classif. (of this poge) Zl. No. of Peges | 22, Price
UNCLASSIFIED UNCLASSIFIED 8 ‘

Form DOT F 1700.7 (8-72) Reproduction of completed page cuthorized

|



RIGHT BUNDLE BRANCH BLOCK AS A RISK FACTOR
FOR SUBSEQUENT CARDIAC EVENTS

INTRODUCTION

The Federal Aviation Administration (FAA) grants pilots Class I medical certificates
for flight based on the results of medical examinations conducted by one of the 2,700
physicians designated as Class I aviation medical examiners (AMEs). After teaching the age
of 35 years, in addition to the routine medical examination, pilots applying for Class I
certification are required to have a resting 12-lead electrocardiogram (ECG). This
longitudinal assessment of electrocardiographic findings makes it possible to identify
airmen who should receive intensive cardiovascular evaluations before medical certificates
are granted.

Right bundle branch block (RBBB), a ventricular conduction defect, is defined as a QRS

interval (ventricular depolarization) of greater than or equal to 0.12 seconds in Lead V1
(right chest lead). This conduction defect is considered by the FAA to be an

diagnosis of myocardial infarction (MI), atherosclerotic heart disease (ASHD) or coronary
heart disease (CHD) in airmen holding Class I medical certificates with complete RBBB on
routine resting ECG to the risk experienced by Class I airmen without this ECG abnormality.

Methods

Table 1

Point Prevalence Rates of RBBB Among Class I Airmen By Age
December 31, 1970

Class I Airman | No. of Airmen Point Prevalence

Age Group Population with RBBB per 1,000 Airmen
35 - 39 11,481 61 5.40
40 - 44 7,134 92 12.90
45 - 49 8,957 146 16.30
50-54 6,079 103 16.90
55 - 59 1,966 31 15.80
Total 35,617 433 12.16

These cases were matched within 5 years of age to 338 male Class I airmen without an
RBBB. These study subjects were followed for the occurrence of a cardiac event through
December 31, 1985.

As a result of the ongoing medical examination Process required for certification of
pilots, the FAA has a large, relatively complete, longitudinal database on Class I airmen.
This database, known as the airman history file, contains results of all medical
certification examinations and ECGs. These Tesults are forwarded from AME offices to the
FAA's Aeromedical Certification Division (AMCD), where they are coded, compiled and