(Circulation. 2000;102:2204.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
From the University of Texas-Houston Health Science Center, School of Public Health.
Correspondence to Lyn Steffen-Batey, PhD, MPH, University of Minnesota School of Public Health, Division of Epidemiology, 1300 South Second Street, Suite 300, Minneapolis, MN 55454. E-mail steffen{at}epi.umn.edu
| Abstract |
|---|
|
|
|---|
Methods and ResultsMI patients were interviewed at baseline and annually thereafter about PA, medical history, and risk factors of coronary heart disease. Change in level of PA after the index MI was categorized as (1) sedentary, no change (referent group), (2) decreased activity, (3) increased activity, and (4) active, no change. Over a 7-year period, the relative risk (95% CI) of death was as follows: 0.21 (0.10 to 0.44) for the active, no change group; 0.11 (0.03 to 0.46) for the increased activity group; and 0.49 (0.26 to 0.90) for the decreased activity group. The relative risk of reinfarction was as follows: 0.40 (0.24 to 0.66) for the active, no change group; 0.22 (0.09 to 0.50) for the increased activity group; and 0.93 (0.59 to 1.42) for the decreased activity group.
ConclusionsThese findings are consistent with a beneficial role of PA for Mexican American and non-Hispanic white women and men who survive a first MI and have practical implications for the management of MI survivors.
Key Words: myocardial infarction epidemiology prevention
| Introduction |
|---|
|
|
|---|
Known CHD risk factors continue to have relevance in persons who have recovered from an MI, particularly elevated blood pressure and serum cholesterol levels, smoking, and diabetes.2 3 4 Among other risk factors, regular leisure-time physical activity (PA) has been associated with a reduced risk of incident CHD and all-cause mortality in some studies.5 6 7 In 1992, the American Heart Association identified physical inactivity as an important risk factor for heart disease.8
Since the 1950s, exercise has been an integral part of cardiac rehabilitation. Seventeen clinical trials have been conducted to determine the effectiveness of cardiac rehabilitation with an exercise component in improving survival among mostly white male CHD patients.9 However, in only 3 of these studies was there significantly longer survival in patients enrolled in the intervention group than among those in the control group.10 11 12 One meta-analysis of many of these trials showed a 20% reduction in mortality among those who received the cardiac rehabilitation intervention compared with the control group.13 It should be noted that the numbers of female MI patients included in these studies were inadequate for meaningful analysis and that no data at all were available for Mexican American (MA) MI patients.
The role of leisure-time PA in improving survival and decreasing the probability of reinfarction after an initial MI remains unresolved. We assessed the relationship between the risk of all-cause mortality or the occurrence of a second MI and change in the level of PA among MA and non-Hispanic white (NHW) survivors of a first MI. Because PA habits can change during follow-up, inference based on a single measure of PA at baseline could lead to erroneous conclusions.14 The Corpus Christi Heart Project (CCHP) included several data points for characterizing change in the level of PA.15
| Methods |
|---|
|
|
|---|
The follow-up study included only those patients who were interviewed
during the hospital stay. The participation rate among eligible
patients was 79%. Reasons for nonparticipation were physician or nurse
refusal (n=5), patient refusal (n=37), illness of patient (too ill to
participate, n=19), discharge of the patient before the interview could
be obtained (n=38), or incompetence of the patient (n=17). Of the 453
patients with a first MI who were interviewed, 47 were excluded from
further analysis because they were not of MA or NHW ethnicity
(n=33), they did not survive beyond 30 days after MI (n=10), or data
for
1 variable of interest were unavailable (n=4). The final
study population included 406 MA and NHW women and men.
Data Collection
The Committee for the Protection of Human Subjects at the
University of Texas-Houston Health Science Center reviewed and approved
the present study. With the use of standardized procedures, data
were collected by trained CCHP personnel by means of medical record
abstraction, in-person baseline interview, and telephone follow-up
interviews.
Baseline data on medical history and sociodemographic characteristics
were abstracted from the medical record after discharge. Age at
first MI was determined by subtracting the birth date from the date of
onset. Ethnicity was obtained from the medical record and also by
self-report during the interview, according to the procedure of the
1980 US Census.18 The agreement between the 2 sources of
information was 95% (
=0.91,
P<0.001).15 When the 2 sources disagreed,
ethnicity was assigned as per the interview.
Clinical data abstracted from the medical record included ECG and laboratory findings obtained within 72 hours after arrival at the hospital or after having an in-hospital MI. ECG findings were used to classify type and location of the MI according to the Minnesota Code.19 A modified Norris Index for predicting long-term survival was developed and used to classify the severity of the MI as mild or severe.20 This index included age, the presence of pulmonary edema or congestive heart failure, and previous history of ischemia. Heart size, which is included in the original Norris Index, was not available.
Eligible patients were asked to enroll in the study, sign an informed consent, and complete a baseline interview that occurred on or about the fourth hospital day. Data included demographic characteristics, family history of CHD, medical and health history, use of medical services, cigarette smoking, and PA before the first MI.
A telephone follow-up interview was conducted annually for up to 5 years for each participant. The interviewer obtained information about vital status, recurrent MI, general health status, and PA since discharge or the previous interview.
Outcome variables were all causes of death, recurrent MI, and survival time. Deaths were identified from obituaries, next of kin or other contact persons, hospital charts, and death certificates. Information about a nonfatal second MI was ascertained from the study participant during the telephone interview and verified through the ongoing community surveillance. Survival since the first MI was defined as the number of days from the date of hospital admission to the date of death, the occurrence of a second MI, or December 31, 1996, whichever occurred first.
The primary exposure variable was change from baseline to follow-up
levels of PA after the index MI. The participant was asked the
following at baseline and at each follow-up visit: "During the past
year, what physical activities do you usually do outside of your
working hours?" For each reported activity, the interviewer prompted
the participant for frequency, level of exertion, and duration of
performance and inquired about additional activities. A
standardized scheme was used by the interviewer to classify the
participants baseline and follow-up visit PA level as sedentary,
minimally active, moderately active, active, or vigorously active (see
Table 1
). The field center director reviewed the accuracy of the
coding.
|
For analysis, baseline PA levels classified as sedentary (n=75) or minimally active (n=181) were collapsed into a single sedentary group. Those classified as moderately active (n=127), active (n=22), or very active (n=1) were collapsed into a single active group.
The number of follow-up visits for study participants before any recurrent MI ranged from 1 to 5. A composite variable representing PA level during follow-up was developed for each participant. Study participants who were classified as sedentary or minimally active for the majority of their follow-up visits were categorized as sedentary. Those who were classified as moderately active, active, or very active for the majority of follow-up visits were coded as active. Participants were categorized as sedentary or active during follow-up according to their activity level at their last visit if half of the visits were reported as active or sedentary. Change in level of PA was determined for each participant on the basis of his/her categorization at baseline and at follow-up as (1) sedentary, no change from baseline, (2) decreased activity, (3) increased activity, or (4) active, no change.
Statistical Analysis
The statistical package STATA, release 4.0, was used for data
analysis.21 Two-tailed t tests were
used to determine variation in the distributions of continuous
variables. The Mantel-Haenszel
2 statistic
was used to test for variation in the distributions of categorical
variables. Unadjusted mortality and reinfarction rates were
estimated for each group defined by change in level of PA. The
Kaplan-Meier product-limit method was used to estimate survival or
reinfarction-free survival by category of PA.22
Survival curves were compared among PA groups by the log-rank
statistic.23 Cox proportional hazards regression
analyses were used to assess the relationships between change
in level of PA and risk of all-cause mortality or fatal and nonfatal
reinfarction.24
| Results |
|---|
|
|
|---|
|
Unadjusted rates for reinfarction and all-cause mortality were lowest
in those who were active or had increased activity (Table 3
). All-cause death rate, but not the
rate of reinfarction, was lower in those who were initially active and
had decreased activity than in those who were sedentary (Table 3
). Kaplan-Meier survival curves of reinfarction and all-cause
mortality by change in level of PA show the consistency of
these patterns during study follow-up (Figures 1
and 2
).
Similar results were observed when the data were stratified by sex,
ethnicity, or severity of first MI (data not shown).
|
|
|
Multivariate-adjusted hazard ratios for reinfarction
and all-cause mortality are presented in Table 4
. After adjusting for age, sex,
ethnicity, severity of MI, family history of CHD, hypertension,
diabetes, high serum cholesterol, and smoking, patients who
remained active after a first MI had a 60% lower risk of fatal or
nonfatal reinfarction than those who remained sedentary (relative risk
[RR] 0.40, 95% CI 0.24 to 0.66). Patients who increased their
activity after their first MI had a 78% lower risk of reinfarction (RR
0.22, 95% CI 0.09 to 0.50), whereas patients who decreased their PA
had a nonsignificant 7% lower risk of reinfarction (RR 0.93, 95% CI
0.59 to 1.42) than patients who remained sedentary.
|
Similarly, MI patients who remained active or increased their activity had a 79% (RR 0.21, 95% CI 0.10 to 0.44) and 89% (RR 0.11, 95% CI 0.03 to 0.46), respectively, lower risk of death due to all causes than did patients who remained sedentary. Patients who decreased their PA after their first MI had 51% lower risk of all-cause mortality (RR 0.49, 95% CI 0.26 to 0.90) than did sedentary MI patients. No interaction was observed between change in PA level and sex, ethnicity, or severity of first MI.
If being sedentary were a reflection of a generally debilitated state, even before the first MI, the mortality differential according to PA change category would be restricted to the period soon after the occurrence of MI. To examine this possibility, the data were reanalyzed after excluding patients who died or had a recurrent MI within 2 years after their first event. Results were similar to those of the analysis in which all study participants were included (data not shown).
| Discussion |
|---|
|
|
|---|
Although there are some exceptions,7 14 in most studies the association between a single measure of the exposure of interest at baseline and subsequent outcomes has been investigated. Because PA habits can change substantially, analyses of observational data can be subject to misclassification, leading to erroneous estimation of the RR and misleading interpretations of the results.14 A more representative measure of PA, especially for the patient recovering from an MI, is one that reflects change in PA behavior after the index MI.
Although the observed inverse association between level of PA and risk of all-cause mortality and reinfarction supports the hypothesis that PA reduces risk, there may be alternate explanations. One explanation may be selection bias. Among those who had a hospitalized MI in the target population, 95% of MI patients were identified through surveillance methods of the CCHP, and among these patients, 79% agreed to be interviewed at the baseline and follow-up visits. Several patients did not agree to be interviewed because they were too ill or the physician or nurse refused patient participation in the study. This would produce an undersampling of patients who were very ill or who had more severe first MIs. However, had these patients enrolled in the study, they would most likely be physically inactive in the post-MI period and at higher risk of death because of their more severe conditions and not because of physical inactivity. This would lead to a spurious beneficial association between PA and risk of a second event. However, we did account for severity of MI in the analysis, making it unlikely that the absence of these patients seriously affected the results. Another potential source of bias is the possibility that study participants reduced or did not increase their PA levels after a first MI and during follow-up because of deterioration in their ventricular function. We did not collect quality-of-life information or obtain information about clinical status that would allow us to address this issue. However, we did reanalyze the data after first excluding those patients who died within 2 years after their MIs to determine whether severe disease caused both a sedentary condition and early reinfarction, and we observed results similar to those in the original analysis.
Misclassification of disease as a possible explanation of the association also seems unlikely. Vital status was determined for all interviewed participants. For classification of suspected MI, hospital records of patients were reviewed and classified by the CCHP review committee according to study criteria.16 17 If misclassification of reinfarction had occurred, it would likely be nondifferential with respect to PA level, inasmuch as the outcome was obtained without the knowledge of any other information about the participants and would lead to an attenuation of the true association.
Misclassification of level of PA as a possible explanation of the association also seems unlikely. Because the interviewers obtained the self-reported PA information before the occurrence of the second CHD event or death, misclassification of activity level would likely be nondifferential with respect to outcome.
The possible role of confounding factors and effect modification must also be considered. The association between change in level of PA and risk of reinfarction or death persisted after adjustment for the major factors known to be related to the occurrence of a second CHD event, although an unknown confounder is always a possibility. As expected, no effect modification by ethnicity or sex was observed.
There are few published data with which to directly compare the results of this investigation. Wannamethee et al5 observed beneficial effects of PA among men who had a history of cardiovascular disease, including stroke, CHD, or other heart trouble. Compared with men who remained sedentary during follow-up, men who remained active, became active, or became sedentary had RRs (95% CIs) of 0.62 (0.39 to 1.00), 0.44 (0.23 to 1.82), and 1.41 (0.89 to 2.24), respectively. The study population is different from the first-MI patients in the present study. However, the results clearly indicate the benefits of PA for men with a history of cardiovascular disease.
Most studies of the association between PA and survival among MI patients were randomized clinical trials of cardiac rehabilitation programs that included an exercise component and were usually conducted exclusively among white male MI patients.9 Our results are consistent with the meta-analysis in which OConnor et al13 reported significantly lower total mortality, CHD mortality, and fatal reinfarction in the cardiac rehabilitation group than in the comparison group.
The major strengths of the present study include its population-based surveillance study design and the completeness of follow-up. Data on all end points were available for all participants at the end of follow-up. Approximately 95% of all hospitalized MI cases were ascertained; 79% of these patients participated in the baseline interviews, and 95% completed most of their follow-up interviews. Another strength is the frequency with which PA data were updated so that change in PA patterns was captured. Finally, substantial numbers of women and MAs were included.
The limitations of the present study include some aspects of exposure assessment and the numbers of outcome events in some categories of exposure. First, the instrument used to measure level of PA was not validated within the present study population. However, our PA instrument used the core elements of the validated Paffenbarger questionnaire,6 including frequency, duration, and intensity of usual PAs performed during the previous year. Our results were consistent with those of other CHD studies that compared sedentary with active individuals.5 25 Second, because we lack data about quality of life and reasons why participants were not physically active, we are limited in our ability to interpret the persistence of sedentary status or decreased activity after MI. However, first-MI patients who were active survived longer than those who were sedentary for patients with either a mild or severe first MI. Because the mortality differential between active and sedentary patients was similar throughout follow-up and not restricted to the period soon after the occurrence of MI, we conclude that the disease was not causing physical inactivity. Third, the small number of events in some exposure categories limited the precision of some of the estimates of RR.
With better medical care, increased primary prevention efforts, and improved therapies, the number of MI survivors is increasing. As a result, more MI patients are at risk of a second CHD event or death. Our findings suggest that increased PA or a continuation of a physically active lifestyle is independently and inversely associated with all-cause mortality and reinfarction among patients surviving a first MI.
The present study supports the hypothesis that survivors of a first MI who are physically active have a lower risk of a recurrent MI or death from all causes or CHD than do those who are sedentary. Most important, these results support the current recommendation that PA be an integral component of regimens for the secondary prevention of CHD in all ethnic populations.26
| Acknowledgments |
|---|
| Footnotes |
|---|
Received August 17, 1999; revision received June 9, 2000; accepted June 14, 2000.
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
A. L.P. Markou, M. Evers, H. A. van Swieten, and L. Noyez Gender and physical activity one year after myocardial revascularization for stable angina Interactive CardioVascular and Thoracic Surgery, February 1, 2008; 7(1): 96 - 101. [Abstract] [Full Text] [PDF] |
||||
![]() |
N. Thengchaisri, R. Shipley, Y. Ren, J. Parker, and L. Kuo Exercise Training Restores Coronary Arteriolar Dilation to NOS Activation Distal to Coronary Artery Occlusion: Role of Hydrogen Peroxide Arterioscler. Thromb. Vasc. Biol., April 1, 2007; 27(4): 791 - 798. [Abstract] [Full Text] [PDF] |
||||
![]() |
H. L. Collins, A. M. Loka, and S. E. DiCarlo Daily exercise-induced cardioprotection is associated with changes in calcium regulatory proteins in hypertensive rats Am J Physiol Heart Circ Physiol, February 1, 2005; 288(2): H532 - H540. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. S. Church, Y. J. Cheng, C. P. Earnest, C. E. Barlow, L. W. Gibbons, E. L. Priest, and S. N. Blair Exercise Capacity and Body Composition as Predictors of Mortality Among Men With Diabetes Diabetes Care, January 1, 2004; 27(1): 83 - 88. [Abstract] [Full Text] [PDF] |
||||
![]() |
G. D. Batty, M. J. Shipley, M. G. Marmot, and G. Davey Smith Leisure Time Physical Activity and Disease-Specific Mortality Among Men With Chronic Bronchitis: Evidence From the Whitehall Study Am J Public Health, May 1, 2003; 93(5): 817 - 821. [Abstract] [Full Text] [PDF] |
||||
![]() |
F. Lubin, A. Lusky, A. Chetrit, and R. Dankner Lifestyle and Ethnicity Play a Role in All-Cause Mortality J. Nutr., April 1, 2003; 133(4): 1180 - 1185. [Abstract] [Full Text] [PDF] |
||||
![]() |
G. E. Billman Aerobic exercise conditioning: a nonpharmacological antiarrhythmic intervention J Appl Physiol, February 1, 2002; 92(2): 446 - 454. [Abstract] [Full Text] [PDF] |
||||
![]() |
Other Articles Noted Evid. Based Nurs., October 1, 2001; 4(4): E1 - 11. [Full Text] [PDF] |
||||
![]() |
K. L. Griffin, C. R. Woodman, E. M. Price, M. H. Laughlin, and J. L. Parker Endothelium-Mediated Relaxation of Porcine Collateral-Dependent Arterioles Is Improved by Exercise Training Circulation, September 18, 2001; 104(12): 1393 - 1398. [Abstract] [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Circulation Home | Subscriptions | Archives | Feedback | Authors | Help | AHA Journals Home | Search Copyright © 2000 American Heart Association, Inc. All rights reserved. Unauthorized use prohibited. |