Uncertainty and psychologic stress after coronary angioplasty and coronary bypass surgery

Uncertainty and psychologic stress after coronary angioplasty and coronary bypass surgery

R o s e m a r y E. White, BN, MSc,* and N a n c y F r a s u r e - S m i t h , PhD, Montreal, Quebec, Canada Objective: To examine the trajectory of uncertainty and symptoms of psychologic stress during the first 3 months after coronary angioplasty and coronary bypass surgery and to study the impact of social support on uncertainty and psychologic stress in these patient populations. Design: Descriptive, correlative. Setting: Urban community, at-home interviews. Patients: Male patients with angioplasty (n = 22) and bypass (n = 25) at 1 and 3 months after treatment. Age range was 39 to 75 years (mean 58 years). Outcome Measures: Mishel Uncertainty in Illness scores, General Health Questionnaire scores, and Perceived Social Support Scale scores. Intervention: Patients underwent either percutaneous transluminal coronary angioplasty or coronary artery bypass grafting as treatment for coronary artery disease. Results: Data were analyzed with repeated measures analysis of variance and Pearson correlation coefficients. Results showed that at both time periods angioplasty patients were more uncertain than bypass patients (p < 0.05), and that regardless of procedure, patients reported fewer symptoms of psychologic stress at 3 months than at 1 month (p < 0.01). Patients with high social support had less uncertainty and psychologic stress than patients with low support (p < 0.05). Analysis of the social support and treatment group interaction showed that angioplasty patients with low perceived social support had significantly more psychologic stress than angioplasty patients with high support (p < 0.01). Analysis of the correlations between uncertainty and psychologic stress in the angioplasty and bypass grafting procedure groups after control for social support revealed that social support was a significant mediator of the relationship between uncertainty and stress only among patients undergoing percutaneous transluminal coronary angioplasty. There was little evidence of a mediating role for social support in the coronary artery bypass grafting group. Conclusions: These results suggest that angioplasty patients may be in particular need of interventions aimed at reducing uncertainty, and that interventions that increase social support could be important in achieving this reduction. (HEARTLUNG| 1995;24: 19-27)

During the last decade percutaneous transluminal coronary angioplasty (PTCA) has become increasingly more common as a treatment for coronary artery disease (CAD). Approximately

From the Department of Psychiatry and School of Nursing, McGill University, and the Montreal Heart Institute, Montreal, Quebec. This study was supported by a Heart and Stroke Foundation of Canada Nursing Research Fellowship, and by a McGill University Faculty of Graduate Studies, Social Sciences Research Grant. Reprint requests: Rosemary E. White, BN MSc, PEI Heart Health Program, P.O. Box 2000, Charlottetown, PEI, Canada C1A 7N8. * R E W is currently at the Department of Health and Social Services in Charlottetown, Prince Edward Island. She was an MSc candidate at McGill University at the time this study was carried out. This article is based on the first author's thesis, completed in partial fulfillment of requirements for the Master of Science degree at the School of Nursing, McGill University, Montreal. The second author served as her advisor. Copyright 9 1995 by Mosby-Year Book, Inc. 0147-9563/95 $3.00 + 0 2/1/58299

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240,000 P T C A procedures were carried out in the United States in 1988,1 and it is estimated that nearly 50~ of patients requiring surgical treatment for CAD are suitable candidates for PTCA. 2 Despite the large numbers of patients involved and the many reasons to expect differences in psychosocial outcomes associated with the type of revascularization procedure, few studies have examined post-PTCA psychosocial outcomes. Fewer still have compared coronary artery bypass graft (CABG) patients with P T C A patients. 3"6 In this context, we sought to explore possible psychosocial differences between P T C A patients and CABG patients in the hope of developing more appropriate treatment strategies. Uncertainty is common in patients with chronic illness 7 and is especially likely tO be prominent during periods of active treatment intervention, when it may vary in relation to the type of treatment involved. A number of factors are associated 19

WHITE AND FRASURE.-SMITH

with P T C A that could potentially increase patient uncertainty in relation to the uncertainty experienced after CABG. For example, despite the increased use of PTCA, there is no consensus as to whether the long-term outcome will be better or worse than for bypass surgery) In addition, restenosis of the dilated lesion occurs in approximately 30% of P T C A cases, most often within the first 6 months. 9 Finally, because the hospital stay for uncomplicated P T C A is usually 1 to 2 days, 1~ there is limited time for in-hospital patient and family education. 11 Thus unknown long-term outcome, a restenosis rate of 30%, and limited patient and family education could conceivably combine to create a situation of high uncertainty for angioplasty patients. In contrast, CABG has a history of successful outcomes with large numbers of patients. 12 Graft-patency rates are high, and blockage is a relatively minor problem over the first 5 years after C A B G ) 3 In addition, patient education programs are well established in the majority of centers where bypass surgery is performed) 4 Against this background, it seems likely that P T C A patients may perceive greater uncertainty than CABG patients, at least during the first 6 months after treatment. An uncertain illness trajectory may well challenge patient and familial coping resources7' 15 and result in psychologic stress. Mishel's Model of Perceived Uncertainty in Illness predicts that a situation appraised as uncertain will mobilize individuals to use their resources to adapt to that situation.16 On the basis of the definition of stress as a combination of the individual's appraisal of the environment and perceived ability to cop@ 7 it would seem likely that psychologic stress could result if individuals appraise an uncertain situation as taxing or exceeding their resources and endangering their well-being. Thus in addition to experiencing higher uncertainty levels than CABG patients, P T C A patients may experience more psychologic stress. Although CABG is major surgery, P T C A is a relatively minor procedure. Because of this, it seems probable that family and friends may perCeive P T C A and CABG patients' needs during the rehabilitation period differently. Mishel's Model of Perceived Uncertainty in Illness predicts that social support will have both a direct and indirect influence on uncertainty. 16 Social support will reduce uncertainty by modifying, (1) ambiguity concerning the state of the illness, (2) the complexity perceived in treatment, and (3) the unpredictability of the future. The indirect influence of social support is on strengthening the clarity of the 20

symptom pattern. CABG patients may be given more social support because their treatment is better known and more visible. In contrast, P T C A patients may not be given as much support because their treatment may not be well understood or may be perceived as relatively simple. In addition to differences in uncertainty and psychologic stress, there may be procedure-related differences in social support. Thus the present study focused on the following questions: 1. Are P T C A patients more uncertain than CABG patients at 1 and 3 months after treatment? 2. Do P T C A patients have more symptoms of psychologic stress than CABG patients at 1 and 3 months after treatment? 3. Are there procedure-related differences in perceived social support? 4. Is the relationship between uncertainty and stress different for P T C A and CABG patients? METHODS

Procedures. All patients were treated at the Royal Victoria Hospital (a teaching hospital affiliated with McGill University) during the first 6 months of 1989. They were initially approached about participating in the study by nursing staff during hospitalization after PTCA or CABG. The researcher then approached the patient to explain the purpose of the study and to describe what would be involved. After consent was obtained an appointment was made for a home interview approximately 1 month after discharge. Written consent was obtained before beginning the first home interviewl All patients were interviewed at home a second time at approximately 3 months after P T C A or CABG. Sample. Eligibility requirements included (1) being male, (2) being first-time recipients of elective P T C A or CABG, (3) having no concomitant major illness (such as renal failure, severe uncontrolled diabetes, cancer, liver disease, or cerebral vascular accident), and (4) having the ability to speak and read English. Women were excluded because of the relatively small number of women who undergo revascularization procedures and the possibility that psychosocial outcomes may well vary according to gender: Patients who had undergone previous revascularization procedures were excluded because of the possible impact of previous experience on uncertainty. Of the 28 eligible P T C A patients asked to participate in the study, three refused because they were not feeling well enough to complete the questionnaires. One-month interviews were completed with 25 PTCA patients. Three of these patients HEART & LUNG@ JANUARY/FEBRUARY 1995

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were unwilling to complete the second interview at 3 months. Thus 78.6% of the 28 eligible P T C A patients took part in both interviews, and 88.0% of the patients who completed the first interview also completed the second. A total of 39 CABG patients were approached to participate in the study. Of this number, a total of 11 (28.2%) declined to become involved in the project. Most of the CABG patients who declined said they were not feeling well enough to be interviewed. Of the 28 patients who were interviewed at 1 month, three were not available for the 3-month interview. Thus 64.1% of the 39 eligible CABG patients took part in both interviews, and 89.3% of the patients who completed the first interview also completed the second. Although a greater number of CABG patients than P T C A patients refused to participate in the study, the difference was not statistically significant (p = 0.17). There was no statistical difference between groups in relation to the number of patients who were lost to the second interview, and those patients who were lost did not differ in baseline characteristics from those who completed both interviews. Power statistics 18 were used to calculate that a target sample size of 20 to 26 per group would be required to achieve a power of 0.80 for detecting large differences between means at the p = 0.05 level of significance for a one-tailed t test. The convenience sample of 22 P T C A patients and 25 CABG patients resulted in an achieved power of 0.85 for detecting large differences between means = 0.05).

Instruments. The first structured home interview included questions on demographic variables and the amount of cardiac teaching received, as well as the following instruments: the Mishel Uncertainty in Illness Scal0 9 (MUIS); the General Health Questionnaire 2~ (GHQ); and the Perceived Social Support Scale21 (PSSS). The second interview included items concerning confidence in treatment and care givers, perceived seriousness of illness, recurrence of symptoms, and the MUIS, G H Q , and PSSS. In addition to the interviews, each patient's hospital medical chart was reviewed for physiologic indicators of seriousness of illness (i.e., previous myocardial infarction, cardiac arrhythmias, number of arteries treated, and Canadian Cardiovascular Society angina class). MUIS. The M U I S was constructed to measure uncertainty experienced by hospitalized patients. The tool is composed of 34 items representing four subscales: ambiguity, lack of information, unpredictability, and complexity. 15 Each item is scored HEART & LUNG @ VOL.

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on a five-point basis, with weights of one to five for each response choice. Validity and reliability of the scale are well documented.a9 Although developed for the general patient population, the MUIS has performed adequately in other studies involving CAD patients. 22, 23 Because the scale was developed for use with hospitalized patients, four items not appropriate for community populations were deleted for the home interviews (e.g., "It is vague to me how I will manage my care after I leave the hospital"). In addition, to make the questionnaire more applicable to CAD patients each occurrence of the word "illness" was replaced with the phrase "heart condition." The Cronbach's alpha reliability coefficient for the M U I S in the PTCA sample was 0.90, and 0.89 for the CABG sample. GHQ. Although the G H Q was originally developed to help general medical practitioners screen patients for nonpsychotic psychiatric disorders, it has been commonly used as a measure of the symptoms of psychologic distress that may vary with life stresses. 24, 25 The G H Q includes 20 cognitive-behavioral symptoms of psychologic stress such as loss of sleep over worry, loss of confidence, and inability to concentrate. The 20-item version of the G H Q includes no overtly physiologic symptoms that could be manifestations of CAD. For each item patients are asked to think about the past week, and to compare present status with what is normal for them using a four-point Likert scale (e.g., not at all, no more than usual, rather more than usual, much more than usual): This widely used index has shown good validity and reliability in numerous studies involving a broad range of patient populations. 2~ 26-30 Likert scoring of the G H Q with weights of 0 to 3 for each response choice yielded an alpha of 0.84 for the PTCA group and 0.82 for the CABG sample. PSSS. The PSSS was developed as a measure of social support for patients with heart disease. 21 It includes 12 items on seven-point response scales ranging from "very strongly disagree" to "very strongly agree," tapping the perceived availability of social support from family, friends, and significant others. The scale has demonstrated adequate reliability. 21 Criterion-related validity of the scale was demonstrated in a study that examined the degree of CAD severity in patients with Type A and Type B behavior. 21 Social support appeared to protect Type A patients, but not Type B, from CAD. The Cronbach's alpha coefficient for the PSSS in the P T C A sample was 0.86 and 0.92 for the CABG sample. Data analysis. The first step in data analysis was to compare the PTCA and CABG groups on

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Table I. Background characteristics of P T C A and CABG Groups Variable Age Mean Range Married (%) High school graduate (%) Blue collar worker

PTCA (N = 22)

CABG (N = 25)

55.6 39-68 100.0 77.3

61.5 40-75 92.0 88.0

0.53 0.56

9.1

12.0

1.00

36.4

60.0

O, 19

18.2

100.0

9,0

26.1

0,0 86,4

27.3 100.0

p*

0,041t

(%) Previous myocardial infarction (%) More than two arteries treated

<.001~,w

(%) Preprocedural angina class _< 1 (%) Arrhythmias (%)82 Confident in treatment 3 months after treatment (%) Self-rated seriousness o f illness > 5 at 3 months after treatment (%) Mean social support score with less than 1 hour cardiac teaching

0.2711 0.028?, # O. 19

RESULTS

18.2

16.0

! .00

74.4

78.4

0,032t

54.5

80.0

0.12

19.7 92.5 40.9

29.7 93.7 16.0

<0.001:!: 0.68 O. 11

(%1 Mean days after treatment at 1st Interview 2nd Interview Experienced recurrent symptoms (%)

*Based on chi-squares with Yates' correction for continuity for catagoric variables and t tests for independent samples for continuous variables. All Ps are two-sided. fp < 0.05. :~p < 0.001. w missing for two bypass subjects. IJData missing for two bypass subjects. 82 treated medically in hospital post-procedure. #Data missing for three bypass subjects.

background variables using chi-square tests with Yates' correction for continuity for categoric variables and independent t tests for continuous measures. Correlations among the major psychosociai outcome variables were also examined. To test the hypotheses that P T C A patients have more uncertainty and psychologic stress than CABG patients at 1 and 3 months after treatment and to examine the potential role of social support, separate repeated measures analyses of variance were carried out for uncertainty and psychologic stress. The in22

dependent variables included procedural group and social support, with social support dichotomized at the overall mean value for the two procedural groups. To ensure that the P T C A and CABG patients within each support group were comparable in terms of social support, the mean social support scores for the high-support angioplasty and high-support bypass patients, as well as for the low-support angioplasty and low-support bypass patients, were compared by use of t tests. Results showed no significant differences. Significant interactions emerging from the analyses of variance for multiple comparisons were explored using Bonferoni t tests. 31 Finally, partial correlations were calculated to examine the potential mediating impact of social support on the relationships between uncertainty and psychologic stress in the separate P T C A and CABG procedural groups.

Background variables. Table I compares the background characteristics of the 22 P T C A and 25 CABG patients who completed both interviews. Patients ranged in age from 34 to 74 years, with a mean of 55.6 years for the angioplasty group and 61.5 years for the bypass group. Over 90% were married, and the majority had at least a high school education. Significant differences existed between the P T C A and CABG groups for five of the 14 variables. P T C A patients were younger, had fewer arteries treated, were less likely to have been treated for arrhythmias, had their first interview earlier, and perceived less social support than bypass patients. There were no differences in education, marital status, occupation, previous myocardial infarction, preprocedural angina class, rehospitalizations, confidence in treatment, self-rated seriousness of illness, or the reported amount of cardiac teaching received. Correlations among outcome variables. Because of the potential for a high degree of overlap between uncertainty, symptoms of psychologic stress, and social support, we examined the Pearson correlations among these variables. All correlations, although significant, were less than 0.60, indicating at most 36% shared variance and some independence of the concepts involved. Procedural group and psychosocial outcomes. As Table II shows, results of the analysis of variance (ANOVA) for uncertainty revealed a main effect of procedural group (p < 0.05), and a main effect of social support (p < 0.01). A procedural group by social support interaction did not reach statistical significance. Time had no signifHEART & LUNG |

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icant impact, indicating that uncertainty did not change over the two interviews. P T C A patients were more uncertain than bypass patients at both 1 and 3 months after treatment. Irrespective of procedure, patients with lower social support were more uncertain than those with higher social support. The ANOVA for GHQ scores, the measure of symptoms of psychologic stress, revealed significant main effects for social support (p < 0.01) and time (p < 0.01), as well as a significant procedural group by social support interaction (p < 0.05) (Table III). To better understand the relationships among procedural group, social support, and psychologic stress that were demonstrated by the significant procedural group by social support interaction, cell means were compared by use of Bonferoni t tests. 31 Although angioplasty patients were more uncertain than bypass patients, they did not report higher overall levels of psychologic stress. Further, although uncertainty remained fairly stable over time, symptoms of psychologic stress decreased between the two interviews. Although patients with high social support reported fewer symptoms of psychologic stress than patients with low social support, regardless of procedural group, the difference was far more marked for angioplasty patients (Fig. 1). In fact, multiple-comparisons tests showed that the social support-related difference in psychologic stress was significant only for angioplasty patients. Although the main effect of social support was apparent for both angioplasty and bypass patients, the relationship between social support and psychologic stress was more pronounced among angioplasty patients. Control for baseline differences. Before drawing conclusions on the basis of these analyses, we need to consider that the P T C A and CABG patients differed significantly in age, number of arteries treated, whether or not they received treatment for arrhythmias, and the timing of the first interview. Because the number of arteries requiring treatment is a fundamental factor in candidates for either angioplasty or bypass surgery, controlling for the number of treated arteries was judged to be both impossible with the sample obtained and of no clinical importance. However, control for the other differing background variables was needed to rule out the possibility that apparent treatment-related differences in psychosocial outcomes were due to baseline differences between P T C A and CABG patients. To control for the effects of age and posttreatment days at the first interview, all analyses of H E A R T & L U N G @ VOL.

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Table II. Results of repeated measures analysis of variance examining the impact of treatment group and social support on uncertainty Source of variance

Mean square

Between-subjects factors Group 1059.12 Social support 2580.34 Group X social 674.73 support Within-subject factors Time 6.87 Group • time 8.89 Social support • 0.45 time Group X social 0.56 support X time

F (df 1,43)

p

5,10 12.43 3.25

0.029" 0.001 * 0.078t"

0.10 0.13 O.O1

0.75 0.72 0.94

0.01

0.93

*P < 0.05. tp < 0.10.

Table III. Results of repeated measures analysis of variance examining the impact of treatment group and social support on symptoms of psychologic stress Source of variance

Between-subjects factors Group Social support Group X social support Within-subject factors Time Group X time Social support X time Group X social support X time

Mean square

F (df 1,43)

p

21.50 127.49 53.73

1.71 10.17 4.28

0.20 0.003 * 0.045t

110.78 36.34 0.07

10.30 3.38 O.01

0.003* 0.078~ 0.94

0.00

0.00

0.99

*P < 0.01. 4rP < 0.(~5. ~p < O.lO.

variance were repeated with these variables entered as covariates. The potential impact of treatment for arrhythmias was assessed by running the analysis with the data on the full sample (n = 47), and then comparing these results with the results of analyses omitting the data for the six patients treated for arrhythmias. The results of the Analysis of Covariance (ANCOVA) showed that neither age nor time to first interview had a significant impact on either psychologic stress or uncertainty. In addition when the analyses were repeated with data from the arrhythmia patients deleted, the results remained essentially unchanged. In short, the observed differ-

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\ ~

x Lo,,,So .. Suppo. ~

0 High Social Support

5

mcarl

4

GHQ Score

2

0

o

!

Angioplasty Patients (N=22)

I

Bypass Patients (N=25)

Figure 1. Mean psychological stress scores (GHQ) for angioplasty and bypass patients with high and low social support (*p < 0.05; **p < 0.01; A p < 0.10; ns, not significant).

ences in psychosocial outcomes between P T C A and CABG patients were not caused by measured baseline differences between the groups. T h e relationships among social support, uncertainty, and psychologic stress. We were interested in examining the potential mediating effect of social support on the relationship between uncertainty and psychologic stress in each procedural group. According to Mishel et al, 32 to consider a variable as a potential mediator several conditions must hold. T h e independent variable (in this case uncertainty) must be significantly related to the potential mediator (social support), as well as to the dependent variable (psychologic stress). In addition, the mediator (social support) must be related to the dependent variable (psychologic stress). In other words, significant relationships must exist among all three variables. When this is the case, the role of the mediating variable can be tested by examining the relationship between the independent and dependent variables after control for the mediator. If the strength of the relationship between the independent and dependent variables decreases, there is evidence that the relationship between them is dependant on the mediating variable. As a first step in examining the mediating role of social support, we calculated the correlations among uncertainty, psychologic stress, and social support at each time period separately for each procedural group. T h e results appear in Table IV. 24

All three of the correlations among psychologic stress, uncertainty, and social support were significant at each time period for the P T C A group, suggesting a mediating role for social support. In the CABG group psychologic stress and uncertainty were also significantly related at each time period. However, social support was not significantly related to either variable, indicating little potential mediating role for social support in patients who had undergone CABG. To further evaluate the role of social support in the P T C A patients, we calculated the partial correlations between uncertainty and psychologic stress at each time period, controlling for social support. At time 1 (1 month after treatment), the raw correlation between uncertainty and psychologic stress was 0.57 (p = 0.006). After controlling for social support, the partial correlation between uncertainty and psychologic stress declined to 0.41 (p -- 0.064). This reduction in the strength of the relationship indicates some mediating role for social support in the link between uncertainty and psychologic stress at 1 month after PTCA. At time 2 the raw correlation between uncertainty and psychologic stress was 0.53 (p = 0.012). Control for social support resulted in a greatly reduced partial correlation of 0.13 (p = 0.58). This suggests that social support plays an important role in the link between uncertainty and psychologic stress at 3 months after treatment in the P T C A group. HEART & LUNG@ JANUARY/FEBRUARY 1995

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Table IV. Intercorrelations among uncertainty, psychologic stress, and social support in P T C A patients (n = 22) and CABG patients (n = 24) Uncertainty Time I PTCA patients Stress, time 1

0.57" (p = 0.006)

Uncertainty, time 1

Social Support Time 1

-0.51 t (p = 0.016) -0.54t (p = 0.010)

Social support, time 1

Stress Time 2

Uncertainty Time 2

Social Support Time 2

0.35 (p = 0.11) -0.40 (p = 0.068) -0.52t (p = 0.013)

0.45t (p = .036) 0.76* (p ---%.0001) --0.55* (p -- 0.008) 0.53t (p = 0.012)

--0.52t (p = 0.012) --0.49t (p = .020) 0.84* (p _< 0.0001) --0.72* (p <_ 0.0001) -0.64t

Stress, time 2 Uncertainty, time 2

(p = 0.001) CABG patients Stress, time 1

0.43 t (p = 0.030)

Uncertainty, time 1

--0.11 (p -- 0.61) --0.18 (p -- 0.39)

Social support, time 1 Stress, time 2 Uncertainty, time 2

0.23 (p = 0.27) 0.34 (p = 0.095) --0.11 (p = 0.61)

0.26 (p = 0.21) 0.32 (p = 0.12) --0.17 (p = 0.42) 0.61" (p = 0.001)

0.16 (p = 0.59) --0.063 (p = 0.77) 0.54* (p = 0.007) --0.17 (p = 0.41) --0.33 (p = 0.12)

,p < 0.01. tp_< 0.05.

We also examined the relationship between uncertainty and psychologic stress at time 2 controlling for social support at time 1. Here, the raw correlation of 0.53 (p = 0.012) was reduced to 0.34 (p = 0.13) when the impact of social support was partialled out. Thus although social support at time 2 plays more of a role in the link between uncertainty and psychologic stress at this time period than does the level of social support sooner after the procedure, the mediating effects of social support a r e apparent at both time periods for the PTCA group. This is not the case among CABG patients for whom social support appears to play little role in mediating the relationship between uncertainty and psychologic stress. DISCUSSION

Although the review of the literature did not reveal any studies that compared uncertainty and psychologic stress in angioplasty and bypass patients (which made it impossible to examine the present results in the context of previous results), the findings of this study do raise a number of points for discussion. As hypothesized, angioplasty patients experienced more uncertainty than bypass patients at both 1 and 3 months after treatment. However, the HEART & LUNG @ VOL.

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difference was most marked for patients with low social support. Uncertainty in illness occurs when patients have difficulty giving meaning to the events surrounding their illness, or when they perceive the situation as unpredictable. Such perceptions may also arise when patients find themselves in unfamiliar circumstances or faced with treatments that seem too complex to understand) 9 Our hypothesis, that angioplasty patients would experience greater uncertainty than bypass patients, was based primarily on the fact that restenosis is fairly common within 6 months of dilatation. All angioplasty patients in our study had been informed by their treating physicians that restenosis occurs in approximately 30% of dilated vessels within 6 months after treatment. Other possible sources of heightened uncertainty for the angioplasty patients may have been lack of information on the long-term success of P T C A and the limited time available for patient and family education due to short hospitalizations. However, almost half the P T C A patients reported receiving more than 1 hour of cardiac teaching in the hospital in contrast to only 20% of the CABG patients (none of whom were enrolled in a formal cardiac rehabilitation program), suggesting that differences in information were not responsible for the difference in un-

25

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certainty. Therefore, it seems possible that the 30% chance of restenosis may be a major source of uncertainty after PTCA. If this is the case, uncertainty may not drop off until 6 months after angioplasty, when patients feel that their period of greatest risk is over. Unfortunately, we were able to observe patients for only 3 months after revascularization, and additional study would be needed to assess the long-term trajectory of uncertainty in these patients. Mishel's Model of Uncertainty in Illness predicts that unresolved uncertainty will lead to stress) 9 On the basis of this assumption it was expected that if angioplasty patients had greater uncertainty, they would also report more symptoms of psychologic stress than bypass patients at both 1 and 3 months after revascularization. This hypothesis was not supported. We found no significant difference between P T C A and CABG patients in terms of psychologic stress. Symptoms of psychologic stress declined with time regardless of revascularization procedure. Therefore, although angioplasty patients were significantly more uncertain than bypass patients at both 1 and 3 months, the groups did not differ in symptoms of psychologic stress. This implies that the psychologic stress experienced by the bypass group may have been the result of something other than uncertainty. One possible explanation may be that much of the stress experienced by the patients in the bypass group was related to their physical condition after surgery. Differences in the P T C A and CABG groups in terms of physical functioning after treatment were revealed in a study that compared the quality of life between 32 angioplasty and 44 bypass patients at 3 weeks after hospital discharge. 6 T h e study showed that physical functioning improved for both CABG and P T C A groups after the procedure, but there was significantly greater improvement in the P T C A group. Unfortunately, no measures of physical condition were collected for the present study; therefore, it is not possible to further explore this hypothesis. As expected, patients with high social support had less uncertainty than patients with low social support. Analysis also revealed that patients with high social support had fewer symptoms of psychologic stress. However, the impact of social support on psychologic stress was most marked after angioplasty. In addition, results of analyses examining the potential mediating role of social support on the relationship between uncertainty and psychologic stress revealed that uncertainty was significantly related to psychologic stress for both an26

gioplasty patients and bypass patients. However, only within the P T C A group was there evidence that social support influenced the relationship between uncertainty and psychologic stress: Social support did not appear to influence the link between uncertainty and psychologic stress after CABG. Reasons for this procedure-related difference in the mediating role of social support are unclear. It is possible that the nature of the support involved (solicited versus unsolicited) may be a factor. Recipients of social support do not always view the support that they are offered as helpful 33 or appropriate to meet their individual contextspecific needs. 34 Because P T C A patients recover rapidly and lack visible exterior signs of treatment, families and friends of these patients may not perceive that they need support. T h u s P T C A patients may get support primarily in response to their own requests. P T C A patients with high social support may benefit from individually tailored support. For example, angioplasty patients may have to explain that their treatment could fail and that they need help to formulate a plan of action to cope with this eventuality. T h e support received in response to this kind of specific request may be particularly effective in helping them cope with uncertainty and stress because it is tailored to their specific needs. In contrast, because the bypass procedure is much more common and better understood by the public, bypass patients may receive considerable unsolicited support that is deemed as appropriate or useful by support-givers. Such unsolicited, nonspecific support may not function as effectively as support directed to specific needs. Thus patients with high levels of social support after CABG and P T C A may receive very different sorts of support that differ in their impact. Unfortunately, we have no supplementary information about the nature of the support received by the patients in our study to further explore this issue. Additional research is clearly warranted. Limitations. A major weakness of descriptive, comparative research of this kind is the inability to randomly assign individuals to procedural groups 35 and the consequent inability to draw cause and effect conclusions. Although for this study potentially important background variables were measured and imbalanced variables statistically controlled, it is possible that an imbalance on some unmeasured variable may have accounted for the observed group differences. A second potential study limitation is the fact that most of the measures used in this study were based on self-report. A prominent source of bias in many studies is the subject's knowledge that he is participating in a study, 36 and HEART & LUNG@ JANUARY/FEBRUARY 1995

WHITE AND FRASURE-SMITH

social desirability response bias is always a potential problem with self-report data. 37 Finally, an additional limitation of the study is the small sample size. Although the group sizes of 22 and 25 resulted in an achieved power of 0.85 for detecting large differences at the p < 0.05 level of significance, medium and small differences may have been left undetected. In conclusion, the findings of this study suggest that interventions aimed at increasing social support may be particularly important in reducing uncertainty and psychologic stress in P T C A patients during the early rehabilitation phase of recovery. The high uncertainty levels for the angioplasty group also suggest that follow-up monitoring of P T C A patients to the 3-month point and beyond may be required. Clearly, further longitudinal study is needed to investigate whether uncertainty and psychologic stress decline once the 6-month period of high risk for restenosis is over, or whether there are other treatment-related factors besides fear of restenosis that influence psychosocial outcomes after revascularization.

13.

14.

15. 16. 17. 18. 19. 20. 21.

22.

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