The Impact of Event Scale—Revised: evaluation of the subscales and correlations to psychophysiological startle response patterns in survivors of a life-threatening cardiac event

Journal of Affective Disorders 82 (2004) 29 – 41 www.elsevier.com/locate/jad

Research report

The Impact of Event Scale—Revised: evaluation of the subscales and correlations to psychophysiological startle response patterns in survivors of a life-threatening cardiac event An analysis of 129 patients with an implanted cardioverter defibrillator Jens Baumert a,b, Heidi Simon a, Harald Gu¨ndel a, Claus Schmitt c, Karl-Heinz Ladwig a,b,* a

Institut und Poliklinik fu¨r Psychosomatische Medizin, Psychotherapie und Med. Psychologie Universita¨tsklinikum rechts der Isar der Technischen Universita¨t Mu¨nchen, Langerstraße 3-81675, Munich, Germany b National Research Center for Environment and Health (GSF), Institute of Epidemiology, Germany c Deutsches Herzzentrum Mu¨nchen, Klinik an der Technischen Universita¨t Mu¨nchen, Munich, Germany Received 24 January 2003; received in revised form 17 September 2003; accepted 22 September 2003

Abstract Background: The aim of the present study was to examine the reliability and validity of the Impact of Event Scale— Revised (IES-R) with special emphasis on the evaluation of the hyperarousal subscale against a standardized psychophysiological measurement. Methods: A total of 129 survivors of a life-threatening cardiac event underwent a psychodiagnostic evaluation and a psychophysiological acoustic startle reflex (ASR) paradigm. The ASR assessed the magnitude and habituation of electromyogram (EMG) and skin conductance responses (SCR) in response to the delivery of 15 acoustic startle trials. Pearson correlation and factor analysis was used to measure reliability and construct validity. The hyperarousal subscale was validated against the ASR in terms of sensitivity and specificity mainly using receiver operating characteristic (ROC) curve analysis. Results: A high reliability was found for the intrusion and avoidance subscale (a > 0.8); however, the hyperarousal subscale showed a weaker reliability (a = 0.66). No avoidance item, one intrusion item but four hyperarousal items revealed higher correlations to another than its assigned subscale. The hyperarousal subscale was not able to discriminate sufficiently between patients with and without exaggerated startle reactions as indicated by ROC curves running near the diagonal line. Limitations: The scores in all three subscales are lower compared to subjects traumatized by non-cardiac events. Conclusions: Reliability and construct validity for the intrusion and avoidance subscale proved to be high but was only sufficient for the hyperarousal subscale. Moreover, the criterion validity of the

* Corresponding author. Institut und Poliklinik fu¨r Psychosomatische Medizin, Psychotherapie und Med. Psychologie Universita¨tsklinikum rechts der Isar der Technischen Universita¨t Mu¨nchen, Langerstraße 3-81675, Munich, Germany. Tel.: +49-89-4140-4399; fax: +49-89-4140-4845. E-mail address: [email protected] (K.-H. Ladwig). 0165-0327/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jad.2003.09.006

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hyperarousal subscale regarding psychophysiological measurements is arguable and indicates further investigations in this area. D 2003 Elsevier B.V. All rights reserved. Keywords: Posttraumatic stress disorders; Hyperarousal; Startle reactions; Psychophysiological assessment; Sensitivity and specificity

1. Introduction After the experience of a traumatic event, subjects may suffer from multiple psychological symptoms. The Impact of Event Scale (IES) is a self-report inventory developed by Horowitz et al. (1979) to assess the frequency of intrusive and avoidant symptoms associated with the experience of a traumatic event. Subsequently, the IES evolved to one of the most widely used self-report instruments in trauma research and thus has proven its usefulness in the assessment of psychological stress after traumatic events (Weiss and Marmar, 1997; Briere and Elliott, 1998; Joseph, 2000; Sundin and Horowitz, 2002). As the IES consists of only two of the three core criteria to diagnose a posttraumatic stress disorder (PTSD), a modified version of the IES was introduced to additionally record hyperarousal symptoms (Weiss and Marmar, 1997). The modified version called Impact of Event Scale—Revised (IES-R) comprises 22 items in three subscales indexing symptoms of intrusion, avoidance, and hyperarousal. Since its introduction, it has been applied in various study groups (Maercker and Schu¨tzwohl, 1998; Marmar et al., 1999; Schu¨tzwohl and Maercker, 2000; Asukai et al., 2002; Feinstein et al., 2002). Nevertheless, knowledge about psychometric properties is still limited (Joseph, 2000). So far, the criterion validity of the newly introduced hyperarousal subscale has not been examined against an established psychophysiological gold standard. Such a validation is urgently needed as self-reported startle or hyperarousal reactions may correspond only poorly with physiological measurable parameters (Orr and Kaloupek, 1997; Hoehn-Saric and McLeod, 2000; Orr and Roth, 2000). In the present study, we employed the acoustic startle reflex (ASR) paradigm to assess an objective measurement of hyperarousability in patients traumatized by a cardiac arrest or an acute myocardial infarction. Exaggerated startle responses have been

demonstrated to be a valid criterion for persistent presence of increased arousal in subjects in the aftermath of psychotraumatic events (Pitman et al., 1987; Butler et al., 1990; Blanchard et al., 1991; Shalev et al., 1992, 2000; Orr et al., 1997; Orr et al., 2002; Griffin et al., 1997; Ladwig et al., 2002; Ladwig et al., 2003). The main study aims of the present investigation were the assessment of reliability and construct validity of the subscales of IES-R and the evaluation of criterion validity of the hyperarousal subscale against an established physiological standard measurement to assess hyperarousability in PTSD sufferers.

2. Methods 2.1. Patients Patients were recruited consecutively from the LICAD (living with an implanted cardioverter defibrillator) study including initially 213 patients treated with an implanted cardioverter defibrillator (ICD). These patients attended the cardiology outpatient clinic of the Deutsches Herzzentrum Mu¨nchen (German Heart Center Munich) for routine ICD checkup between January and May 1998 (first wave) or between April and June 2002 (second wave). Patients were not included if the first implantation of the ICD was less than 3 months ago or age was V 16 years. Among these 213 patients, 7 refused to participate. Three patients who suffered from severe cognitive impairment and eight patients who had a defined hearing loss (>40 dB in five distinct frequency bands) were excluded from the analysis. Nine patients had insufficient physiological data. From the remaining 186 patients, 155 patients met the A criterion of a PTSD because they experienced a singular life-threatening cardiac event. Among these, we had complete data regarding all 22 items of the IES-R from 129 patients. Thus, 129 patients were included in the present analysis. Written informed consent was

J. Baumert et al. / Journal of Affective Disorders 82 (2004) 29–41

obtained from all patients. The study was approved by the ethic committee of the medical faculty of the Technical University of Munich (TUM).

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(anger-control) (Spielberger, 1988; Schwenkmezger and Hodapp, 1991). The Somatosensoric Amplification Scale (SSAS) with 10 items was used to measure symptoms of hypochondria (Barsky et al., 1990).

2.2. The impact of event scale 2.4. Psychophysiological parameters The original version of the IES had two subscales, intrusion (seven items) and avoidance (eight items), with symptom frequencies evaluated on four-point non-equidistant levels: 0, 1, 3, and 5 indicating a range from ‘‘not at all’’ to ‘‘often’’ (Horowitz et al, 1979). Weiss and Marmar (1997) introduced five new items describing hyperarousal symptoms and dividing one item (‘‘I have trouble falling asleep or staying asleep’’) into two new items. The IES-R scored on five-point levels instead of the original four-point levels. It has to be remarked that the IES-R hyperarousal subscale has seven items instead of the five items comprising DSM-IV PTSD Category D. In various studies, different weightings to score the IES-R and different assignments of the items to the subscales were used (Joseph, 2000). In the present study, the 22 items were assigned to three subscales according to Weiss and Marmar (1997) using weighted scores due to Horowitz et al. (1979). These assignments led to the IES-R subscales intrusion (seven items, range 0 – 35), avoidance (eight items, range 0– 40), and hyperarousal (seven items, range 0– 35). 2.3. Other psychometric measurements A rater-administered version of the Peritraumatic Dissociative Experiences Questionnaire (PDEQ) was used to assess peritraumatic dissociation at the time of the occurrence of the traumatic event (Marmar et al., 1997). Anxiety and depression symptoms were measured using the German version of the 14-item Hospital Anxiety and Depression Scale (HADS) (Zigmond and Snaith, 1983; Herrmann et al., 1994) and the German version of SCL-90 with an additional measure of phobic anxiety (Franke, 1995). To evaluate sleep disturbance as an indicator for psychic distress, a fouritem scale adapted from form A of the Maastricht questionnaire were used (Appels and Mulder, 1988). Anger symptoms were determined using the 24-item State-Trait Anger Expression Inventory (STAXI) assessing overt or direct anger (anger-in), inside or suppressed anger (anger-out), and controlled anger

The psychophysiological parameters were measured according to the acoustic startle reflex (ASR) paradigm from Shalev et al. (1992). It comprised the delivery of 15 loud tones as independent stimuli. The acoustic startle stimulus was a 500-ms burst of 1000 Hz with a near-instantaneous rise time presented binaurally through headphones (Panasonic). The intensity of the acoustic stimulus was 95 dB (sound pressure level). Intertrial intervals were randomly selected and ranged from 17 to 32 s. The room temperature and humidity were maintained at 20 –25 jC and at 32 – 45%, respectively. The electromyogram (EMG) response was used to assess sensimotor responses, and the skin conductance response (SCR) was used to assess autonomic reactivity. Signals were amplified and filtered by a bioamplifier (B-scopeR, Regensburg, Germany). The EMG signal was recorded through 4-mm (sensor diameter) surface electrodes (Biopac Beckman type Ag/AgCl) laminated with a isoton paste and filtered so as to retain a 90 – 500-Hz-frequency range. Skin conductance response (SCR) was measured directly by a coupler using a constant 0.5 V through 9-mm (sensor diameter) electrodes (Beckman-type Ag/AgCl) placed on the subject’s nondominant palm. SCR was analysed in a spectrum from 15.9 mHz to 10 Hz and digitalized at 50 Hz. SC values were measured in microsiemens. Sampling frequency was 1000 Hz for the EMG and 50 Hz for the SCR. The patient investigation was carried out between 9:00 a.m. and 1:00 p.m. Study subjects underwent a hearing test and received instructions while the electrodes were attached according to published recommendations. We measured magnitude and habituation of the autonomic responses. To assess the magnitude of the startle responses, an EMG score for each trial was calculated by substracting the mean EMG level during the 2 s immediately preceding tone onset from the highest EMG response measured within 40– 200 ms after tone onset. The response window for skin conductance was 1 – 4 s after tone onset. Square root

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transformations were performed on the EMG and SCR. Habituation for each patient was defined as response slope of the regression equation Y=(bX + a)/a for trial 2– 15, where Y equals the magnitude of the response and X the log trial number calculated for each patient (for more details, see Ladwig et al., 2002). Thus, four different psychophysiological parameters were available: the magnitude and habituation for SCR and EMG, respectively. The mean values were 0.42 (S.D. 0.30) for SCR magnitude and 0.25 (S.D. 0.11) for SCR habituation. In the case of EMG, a mean of 5.38 (S.D. 3.02) for magnitude and 0.18 (S.D. 0.11) for habituation were observed. For each psychophysiological parameter, we dichotomized the ‘‘startle reaction’’ in patients with low and high startle reactions. As cutoff points, we chose the median, the 25%, and 75% quantile of the distribution of each psychophysiological parameter. 2.5. Statistical methods The reliability assessing the internal consistency of the three subscales was measured by Cronbach’s a. We analyzed the construct validity as an assessment for discovering substructures of the 22 items by two methods. First, we computed the item-to-subscale correlation determining the Pearson correlation coefficient of the item and the three subscales using corrected correlations due to Weiss and Marmar (1997): as being part of a subscale, the correlation between an item with its assigned subscale would be overestimated. Therefore, in the case of the assessment of the relationship of an item with its assigned subscale, the correlation coefficient was corrected removing the item from its assigned subscale. Moreover, as a second way to evaluate the construct validity, factor analysis with principal components and varimax rotation was performed with a maximal number of three and four predetermined factors. The convergent validity assessing the relationship of the three subscales to various other psychometric instruments and the associations of the three subscales to the psychophysiological parameters described above were measured by Pearson correlation coefficients. To evaluate the ability of the hyperarousal subscale to discriminate patients with and without exaggerated startle reactions in terms of sensitivity and specificity, we used a receiver operating characteristic (ROC)

curve analysis according to Hanley and McNeil (1982, 1983) and De Long et al. 1988. In this study, sensitivity and specificity were always stated in percent. A receiver operating characteristic (ROC) curve is a plot of sensitivity versus (100 specificity) of all possible classifications of the measurement due to a varying cutoff point. The area under the ROC curve usually marked as ‘‘the c statistic’’ is useful to quantify the ability of a measurement to discriminate and also a possibility to compare different measurements. A ROC curve of a diagonal line from point (0,0) to point (100,100) represents ‘‘no discrimination’’ with a c statistic of 0.5. In contrast, a ROC curve from point (0,0) to point (0,100) and from point (0,100) to point (100,100) would represent a ‘‘perfect discrimination’’ with a c statistic of 1. Moreover, to give an insight about the extent of sensitivity and specificity, 2  2 cross-tables between the hyperarousal subscale and the physiological parameters (classified with 25%-quantile, median- or 75%-quantile split) were calculated according to the p minimum value approach: a ‘‘best’’ discrimination was defined as the dichotomization of the hyperarousal subscale with a cutoff point, for which the p value of the chi-square test of association with the psychophysiological parameter reached the minimum value. Only tests satisfying the Cochran criterion were considered. A further measure for assessing the ability to discriminate is Youden’s index calculated by ((Sensitivity + Specificity 100)/100), which summarized test accuracy into a single numeric value (Hilden and Glasziou, 1996). A perfect test would have a Youden index of + 1; a score of >0.6 indicates a sufficient ability to discriminate. For all statistical analysis, a P value less than 0.05 was considered to be statistically significant. The evaluations were performed with the statistical software packages SAS (Version 6.12, SAS Institute, Cary, NC, USA) and SPSS (Version 10, SPSS, Chicago, IL, USA).

3. Results 3.1. Patient characteristics The majority of the study population was male (n = 113, 88%); the mean age was 60.5 years (S.D.

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12.7). The life-threatening cardiac event was defined as a sudden cardiac arrest or an acute myocardial infarction (MI) with subsequent reanimation (93 patients, 72%) or without subsequent reanimation (36 patients, 28%). Mean time period since the acute cardiac event was 27.7 months (S.D. 23.9). The mean score for intrusion was 4.0 (S.D. 6.1), for avoidance 3.9 (S.D. 6.7), and for hyperarousal 4.2 (S.D. 5.2). Patients with an age < 50 years or with the history of a cardioversion had higher scores in each of the three subscales than the entire study population (Table 1). 3.2. Reliability The reliability was high for the intrusion and avoidance subscale with values for Cronbach’s a of >0.8 (Table 2). A considerably weaker a value came out for the hyperarousal subscale (Cronbach’s a = 0.66). Additionally, Table 2 displays for each item the mean, the standard deviation (S.D.), and Cronbach’s a for a subscale without the item (a*). For the intrusion subscale, the removal of item 2

Table 1 Distribution of patient characteristics and mean values with standard deviation (S.D.) of the IES-R subscales Factor

N

Total

129 100.0 4.0 (6.1) 3.9 (6.7)

Gender M F Age group V 49 years 50 – 69 years V 70 years Occupation Yes No

%

Intrusion Avoidance Hyperarousal 4.2 (5.2)

113 16

87.6 4.2 (6.2) 3.7 (6.6) 12.4 3.3 (5.5) 5.9 (7.4)

4.1 (5.0) 5.0 (6.6)

24 70 35

18.6 6.1 (8.1) 5.5 (7.8) 54.3 3.9 (5.6) 3.8 (6.6) 27.1 3.0 (5.0) 3.0 (6.1)

6.4 (6.3) 3.9 (5.1) 3.5 (4.2)

34 94

26.6 4.5 (7.8) 3.5 (5.5) 73.4 3.9 (5.4) 4.1 (7.1)

4.9 (6.0) 4.0 (4.9)

Cardiac diagnoses CAD/MI 98 Other 31

75.0 3.3 (5.0) 3.4 (6.6) 25.0 6.3 (8.4) 5.7 (6.7)

3.6 (4.3) 6.2 (7.1)

Traumatic event Reanimation No reanimation

72.1 4.9 (6.8) 4.7 (7.3) 27.9 1.9 (2.9) 2.0 (4.4)

5.0 (5.7) 2.4 (3.0)

93 36

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Table 2 Single items of the IES-R subscales with mean and standard deviation (S.D.) and reliability measured by Cronbach’s a for a subscale without item (a*) and for the whole subscale (a) Item Intrusion (1) Any reminder brought back feelings about it (2) I had trouble staying asleep (3) Other things kept making me think about it (6) I thought about it when I didn’t mean to (9) Pictures about it popped into my mind (16) I had waves of strong feelings about it (20) I had dreams about it

Mean

S.D.

a*

0.54

1.29

0.75

1.34 0.64

1.83 1.35

0.85 0.76

0.59

1.38

0.73

0.54

1.33

0.76

0.23

0.75

0.80

0.16

0.66

0.79

a

0.80 Avoidance (5) I avoided letting myself get upset when I thought about it or was reminded of it (7) I felt as if it hadn’t happened or wasn’t real (8) I stayed away from reminders about it (11) I tried not to think about it (12) I was aware that I still had a lot of feelings about it, but I didn’t deal with them (13) My feelings about it were kind of numb (17) I tried to remove it from my memory (22) I tried not to talk about it

0.71

1.50

0.77

0.42

1.21

0.83

0.47

1.34

0.77

0.67 0.27

1.51 0.86

0.77 0.78

0.22

0.86

0.81

0.69

1.56

0.74

0.50

1.25

0.79 0.81

Hyperarousal (4) I felt irritable and angry (10) I was jumpy and easily startled (14) I found myself acting or feeling as though I was back at that time (15) I had trouble falling asleep (18) I had trouble concentrating (19) Reminders of it caused me to have physical reactions, such as sweating, trouble breathing, nausea, or a pounding heart (21) I felt watchful or on-guard

0.85 0.84

1.39 1.52

0.64 0.55

0.14

0.56

0.66

0.17 0.94 0.32

0.66 1.59 1.09

0.65 0.63 0.59

1.00

1.76

0.60 0.66

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Table 3 Intercorrelations between the seven hyperarousal subscale items measured by Pearson correlation coefficient Item 4 (4) Irritable (10) Startled (14) Back at time (15) Falling asleep (18) concentrating (19) Physical (21) Watchful

. 0.28 0.02 0.01 0.20 0.19 0.23

Item 10

Item 14

Item 15

Item 18

Item 19

Item 21

. 0.19 0.24 0.35 0.43 0.40

. 0.13 0.11 0.29 0.08

. 0.06 0.50 0.16

. 0.18 0.27

. 0.31

.

Short surrogates for each item were used to facilitate the reading of the table. The full text of the item is given in Table 2.

(‘‘I had trouble staying asleep’’) would increase Cronbach’s a to 0.85. The intercorrelations between the seven items of the hyperarousal subscale were low and confirmed rather weak associations as measured by Pearson correlation coefficients (Table 3).

3.3. Construct validity Item-to-subscale correlation and factor analysis was applied to determine construct validity as a measurement for evaluating substructures (Table 4). The itemto-subscale correlation was found to be highest with

Table 4 Construct validity of the IES-R subscales using item-to-subscale correlation with correction for the item and factor analysis with principal components and varimax rotation and four factors predetermined Item

Item-to-subscale correlation

Factor analysis

I

A

H

Factor 1

Factor 2

Factor 3

Intrusion (1) Reminder (2) Staying asleep (3) Other things (6) Thought about (9) Pictures (16) Strong feelings (20) Dreams

0.70 0.30 0.66 0.77 0.64 0.41 0.55

0.52 0.27 0.48 0.48 0.45 0.46 0.34

0.48 0.27 0.51 0.58 0.50 0.53 0.52

0.34 0.26 0.24 0.14 0.21 0.58 0.15

0.69 0.06 0.79 0.73 0.44 0.27 0.78

0.21 0.39 0.13 0.42 0.51 0.32 0.16

0.08 0.04 0.16 0.19 0.28 0.23 0.10

Avoidance (5) Get upset (7) Not real (8) Stayed away (11) Not think (12) Not deal (13) Kind of numb (17) Remove it (22) Not talk

0.59 0.09 0.31 0.57 0.43 0.26 0.47 0.34

0.61 0.21 0.58 0.62 0.58 0.33 0.75 0.51

0.54 0.10 0.30 0.51 0.36 0.26 0.35 0.21

0.68 0.03 0.68 0.66 0.75 0.16 0.66 0.56

0.22 0.01 0.07 0.37 0.24 0.12 0.28 0.07

0.42 0.06 0.03 0.25 0.04 0.14 0.05 0.05

0.05 0.78 0.34 0.08 0.08 0.73 0.34 0.30

Hyperarousal (4) Irritable (10) Startled (14) Back at time (15) Falling asleep (18) Concentrating (19) Physical (21) Watchful

0.26 0.46 0.19 0.46 0.36 0.61 0.40

0.11 0.39 0.30 0.49 0.22 0.50 0.32

0.30 0.57 0.19 0.28 0.36 0.49 0.44

0.08 0.26 0.48 0.59 0.05 0.54 0.06

0.13 0.13 0.20 0.41 0.22 0.53 0.39

0.58 0.70 0.34 0.08 0.55 0.28 0.44

0.01 0.06 0.09 0.01 0.27 0.33 0.11

Short surrogates for each item were used to facilitate the reading of the table. The full text of the item is given in Table 2.

Factor 4

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their assigned subscale for all avoidance items and for all intrusion items except for item 16 (‘‘I had waves of strong feelings about it’’) which revealed a stronger relationship with the hyperarousal subscale. For the items of the hyperarousal subscale, four items showed a stronger or an equal association to different subscales, indicating a low construct validity. The results of the factor analysis for four predetermined factors are displayed in Table 4. The first factor consisted of six of eight items of the avoidance subscale. The other two items, item 7 (‘‘I felt as if it hadn’t happened or wasn’t real’’) and item 13 (‘‘My feelings about it were kind of numb’’), loaded to a fourth ‘‘numbing’’ factor. The intrusion items loaded to the second factor except for item 16. The reliabilities of the four factors measured by Cronbach’s a were 0.86 (factor 1), 0.84 (factor 2), 0.67 (factor 3), and 0.57 (factor 4). In a factor analysis with only three predetermined factors, the items of factor 2 and 3 of the fourth-factor solution loaded to one factor. 3.4. Convergent validity To determine the convergent validity, the association between the IES-R subscales to other psychometric instruments was evaluated. Correlations of the three subscales to a variety of psychometric instruments were found to be significant in different strengths and thus suggested to be sufficient (Table 5A). Remarkably, a significant association with anger could be determined only for the hyperarousal subscale. 3.5. Correlation with psychophysiological parameters As for the validation of the hyperarousal subscale against exaggerated startle reactions using the ASR, a significant association emerged only for EMG habituation with a Pearson correlation coefficient of 0.29 ( p = 0.03). For the SCR magnitude and habituation as well as for the EMG magnitude, no significant correlations were determined with Pearson correlation coefficients varying from 0.09 to 0.13 (Table 5B). The ability of the hyperarousal subscale to discriminate patients with and without exaggerated startle reactions in terms of sensitivity and specificity using an ROC curve analysis is performed for SCR in Fig. 1 and for EMG in Fig. 2. The ROC curve for each

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Table 5 Convergent validity evaluating correlations between IES-R subscales intrusion, avoidance, hyperarousal, and other psychometric measures (A) and correlations to the psychophysiological parameters (B) measured by Pearson correlation coefficient Questionnaire Completing Intrusion Avoidance Hyperarousal questionnaire (A) Intrusion Avoidance Hyperarousal Peritraumatic Dissociation (PDEQ) Sleep disturbance Anxiety (HADS) Anxiety (SCL-90) Phobic anxiety (SCL-90) Depression (HADS) Depression (SCL-90) Anger (STAXI) Hypochondria (SSAS) (B) SCR magnitudea SCR habituationb EMG magnitudea EMG habituationb

129 129 129

– 0.60** 0.66**

– – 0.51**

– – –

128

0.28*

0.29**

0.27*

128

0.39**

0.22*

0.40**

124

0.45**

0.28*

0.55**

118

0.47**

0.30*

0.54**

120

0.33**

0.20*

0.42**

124

0.35**

0.21*

0.35**

113

0.37**

0.28*

0.49**

115

0.13

0.15

0.20*

118

0.32**

0.17

0.47**

127

0.05

0.08

0.10

127

0.04

0.09

0.04

127

0.13

0.02

0.05

127

0.07

0.07

0.29*

a Magnitude was measured as the mean of square root transformations of the responses of 15 trials. b Habituation was measured as the response slope of the regression equation Y=(bX + a)/a for trial 2 – 15 ( Y = magnitude, X = log trial number) for each patient. * P < 0.05. ** P < 0.001.

psychophysiological parameter and each split run near the diagonal line indicating a low ability to discriminate in two different groups. The area under the curve measured by the c statistic was not significantly different to the diagonal line with values for the c statistic varying from 0.4 to 0.6.

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Fig. 1. ROC curve of SCR magnitude and habituation using 25%-quantile, median, and 75%-quantile splits.

Fig. 2. ROC curve of EMG magnitude and habituation using 25%-quantile, median, and 75%-quantile splits.

J. Baumert et al. / Journal of Affective Disorders 82 (2004) 29–41

The ‘‘best’’ discrimination was reached for SCR magnitude in the case of a 25%-quantile split and a cutoff point score of 4, resulting in a sensitivity of 28.4% and a specificity of 50.0% ( p = 0.03). For SCR habituation, the lowest p value was 0.06, resulting in a sensitivity of 64.1% and specificity of 52.4% (median split, cutoff point score 1). In the case of EMG, a p value of 0.06 resulted in a discrimination of 54.8% sensitivity and 64.6% specificity (75%-quantile split, a cutoff point score 3) for magnitude and a p value of 0.001 revealed a discrimination of 31.3% sensitivity and 92.1% specificity (median split, cutoff point score 7) for habituation. Regarding Youden’s index as a measure to summarize sensitivity and specificity, no value of higher than 0.23 was determined, demonstrating again a very weak ability of the hyperarousal subscale to discriminate between patients with and without exaggerated startle reactions. We repeated the ROC analysis with two modified assignments: one new assignment followed the fourfactor solution drawn from the factor analysis described above with the items of the third factor as a ‘‘new hyperarousal subscale.’’ The second modified assignment excluded item 14 and 19 from the hyperarousal subscale as the remaining five items corresponds to the DSM-IV PTSD definition. In both modified assignments, similar results were determined as with the original IES-R subscales assignments: The Youden’s indices were not higher than 0.24. Moreover, an independent analysis of item 10 (‘‘I was jumpy and easily startled’’) which reflects self-reported startle revealed no significant discrimination between patients with and without exaggerated startle reactions. The ‘‘best’’ discrimination was reached for EMG habituation in the case of a 75%-quantile split and a cutoff point score of 1 resulting in a sensitivity of 32.3% and a specificity of 87.5% ( p = 0.01). The Youden’s indices were not above 0.2, revealing an insufficient ability of item 10 to discriminate between patients with and without exaggerated startle reactions.

4. Discussion Despite the usefulness of the IES scale to measure psychological reactions in response to traumatic stressors, Weiss and Marmar (1997) revised the instru-

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ment, arguing that—in line with current diagnostic criteria—complete assessment of the response to traumatic events requires tracking of responses in the domain of hyperarousal symptoms. Undoubtedly, the psychophysiological arousal concept with a lowered threshold for sensory stimulation and decreased autonomic inhibitory control is a key concept in PTSD research with far reaching consequences concerning the clinical appearance of PTSD patients and subsequent treatment considerations (Pitman et al., 1987; Butler et al., 1990; Blanchard et al., 1991; Shalev et al., 1992; Orr et al., 1997; Griffin et al., 1997). Van der Kolk and Ducey (1989) summarized findings concerning the clinical consequences of exaggerated arousal to apparently mild stimuli in the description of ‘‘typical’’ PTSD patients: ‘‘. . .they tend to go immediately from stimulus to response without first being able to figure out the meaning of what is going on; they respond with fight-or-flight reactions. This causes them to freeze or, alternatively, to overreact and intimidate others in response to minor provocations’’. The study presented here is, to the best of our knowledge, the first one to evaluate the content validity of the IES-R hyperarousal subscale against the gold standard of an established psychophysiological measurement of hyperarousability. 4.1. Validity of the hyperarousal subscale A significant association between the hyperarousal subscale and the psychophysiological parameters measured by Pearson correlation was only found in the case of EMG habituation. However, as Pearson correlation measures simply the strength of an association between two variables, it does not assess the diagnostic value of an instrument regarding the ability of the instrument to discriminate patients with and without a specific event. This is usually expressed in terms of sensitivity and specificity. The ROC curves in Figs. 1 and 2 describe a considerably weak ability of the hyperarousal subscale to discriminate patients with or without exaggerated startle reactions. Therefore, the major result of the present study is to suggest a weak content validation of the IES-R hyperarousal subscale shown by insufficient sensitivity and specificity of its scores against physiological magnitude and habituation measures of the acoustic

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startle paradigm. Multiple reasons may account for this finding: (1) The concept of autonomic hyperarousability might not be adequately captured in the assessment of seven items which are considered as a crucial hyperarousal component of a PTSD according the current international classification systems which have been adopted by Weiss and Marmar (1997) to define the hyperarousal subscale: ‘‘difficulty in falling or staying asleep, irritability or outbursts of anger, difficulty in concentrating, hypervigilance and exaggerated startle responses.’’ These items seem to represent nonspecific stress symptoms which are weakly intercorrelated as was shown in the present analysis. Thus, it remains unclear to what extent the single items of the subscale contribute to the syndrome of hyperarousal. It may also be that some of the items are surrogate measures for negative affective states apart from PTSD. Difficulties in falling or staying asleep, for example, are markers for insomnia which is a core symptom for depression (Van der Kolk, 1996) and is not necessarily accompanied by autonomic hyperexcitability. Recently, it was shown that insomnia is the key symptom in the identification of depressed patients in the context of general hospitals (Balestrieri et al., 2002). Moreover, it may be that the patient’s perception of his inner state does not correspond to the ‘‘true’’ physiological state. In a study regarding anxiety, Hoehn-Saric and McLeod (2000) assumed that the inconsistency between self-reports of physiological states and actual physiological activity results from alterations of bodily sensations through psychological factors leading to perceptual distortions. (2) It may be that the gold standard defined with the psychophysiological measurement ASR is not a valid instrument to assess physiological aspects of hyperarousal. However, in various studies, this concept demonstrated to be a valid criterion for persistent presence of increased arousal in subjects in the aftermath of psychotraumatic events (Pitman et al., 1987; Butler et al., 1990; Shalev et al., 1992, 2000; Orr et al., 1997; Griffin et al., 1997; Ladwig et al., 2002, Ladwig et al., 2003). It is assumed that traumatized persons have difficulty in evaluating sensory stimuli and mobilizing appropriate levels of physiological arousal (Shalev and Rogel-Fuchs, 1993; Van der Kolk, 1996). Moreover, Bremner et al. (1996) stated the

failure of extinction of startle responses as a characteristic of individuals exposed to extreme stressors. Exaggerated startle may also be brought about by the stress of an environment perceived as threatening as Grillon et al. (1998) have shown in PTSD patients who only showed abnormal startle reactions in a threatening context. (3) It may be argued that the study group of cardiac arrest survivors does not represent a feasible population of trauma patients and thus yields results which may not be generalized. A growing body of evidence, however, proves that patients with a life-threatening acute myocardial infarction and, even more, survivors of a cardiac arrest meet the A criterion of the PTSD classification in DSM-4 and ICD-10 (American Psychiatric Association, 1994; World Health Organisation, 1992). Therefore, it has been shown that this patient population is at risk to develop PTSD and may develop co-morbid states with truly subsequent PTSD criteria (Ladwig and Dammann, 1997; Alonzo, 1999; Hamner et al., 1999; Ladwig et al., 1999; Bennett et al., 2001; Buckley and Kaloupek, 2001; Pedersen, 2001). However, we could show with the data of the present analysis that the general level of involvement—as measured with IES scores—may be somewhat lower for cardiac patients than for other PTSD populations. 4.2. Reliability and construct validity of the subscales The data of the present study confirm and substantiate earlier findings of high reliabilities regarding the ‘‘original’’ intrusion and avoidance subscales. Values of Cronbach’s a of >0.8 correspond with results found in earlier studies stating alphas ranging from 0.80 to 0.92 (Weiss and Marmar, 1997; Maercker and Schu¨tzwohl, 1998; Asukai et al., 2002). These results are consistent regardless of the version applied by either Weiss and Marmar (1997) or the German-adapted version of Maercker and Schu¨tzwohl (1998). An exchange of item 2 with the hyperarousal subscale item 14 (‘‘I found myself acting or feeling as though I was back at that time’’) according to the German-adapted version (Maercker and Schu¨tzwohl, 1998) increases Cronbach’s a for the intrusion subscale from 0.80 to 0.83, whereas for the hyperarousal subscale, this exchange reveals hardly a difference (from 0.66 versus 0.65). Therefore, the intrusion and avoidance subscales represent a homogeneous and

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reliable formation as stated recently by Sundin and Horowitz (2002). The weaker reliability of the hyperarousal subscale is not due to misplacement of some items. The exclusion of one item would not increase the reliability above 0.66. Even removing the ‘‘wrong’’ items 14 and 19 would not improve the reliability. The construct validity measured by the item-tosubscale correlation with all except one intrusion items and all of the avoidance items correctly assigned to the ‘‘right’’ subscale confirms a high degree of accordance to the assignments for these two subscales. In contrast, the hyperarousal items proved to have only a weak association to their assigned subscale. The factor analysis with the limitation of at most three possible factors as another method for evaluating the construct validity determined three factors with the avoidance subscale items assigned to one factor except for item 7 (‘‘I felt as if it hadn’t happened or wasn’t real’’) and item 13 (‘‘My feelings about it were kind of numb’’) which loaded to a separate factor. This finding is in accordance with Maercker and Schu¨tzwohl (1998) and Asukai et al. (2002), who proposed further evaluations about a possible introduction of a fourth factor ‘‘numbing.’’ In the present study, the intrusion and hyperarousal items loaded mainly to the same factor using a three-factor solution which is in line with the results of a cluster analysis done by Asukai et al. (2002) revealing intrusion and hyperarousal items mixed mainly in the same cluster. Maercker and Schu¨tzwohl (1998) revealed that the items of the intrusion and hyperarousal subscales loaded mainly to different factors which is different from our four-factor solution. In this study, avoidance symptoms were assumed to be a relatively independent dimension as compared with intrusion and hyperarousal symptoms which are highly correlated. Therefore, both methods for discovering substructures of the single items proved the avoidance subscale to be a homogenous and stable construct, whereas the intrusion and hyperarousal subscale items could not be sufficiently separated in different substructures. 4.3. Conclusion The original IES belongs to the most widely used self-rating scales worldwide to assess traumatic stress symptoms. Therefore, this instrument allows compar-

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isons to be made with findings from older PTSD studies. Because the IES is limited in its assessment of PTSD phenomena as it does not contain items tapping hyperarousal (criterion D), a revised version of the IES has been proposed which includes items based on this criterion to test for symptoms of hyperarousal. The present study failed to confirm concordance between psychophysiological measures of exaggerated startle as a valid criterion of hyperarousability and the IES-R subscale score of hyperarousal. The IES-R has the disadvantage of including multiple items for some PTSD symptoms and also an arrangement of items that does not agree with the PTSD symptom categories of DSM IV. Other brief instruments especially to assess PTSD symptoms are already available and in widespread use. Nevertheless, the present study also confirms the usefulness of IES-R as a short self-report measure in the assessment of psychological stress after traumatic events as it was shown in psychometric validation studies recently conducted in different cultural contexts (Maercker and Schu¨tzwohl, 1998; Joseph, 2000; Asukai et al., 2002; Sundin and Horowitz, 2002). It confirmed former assumptions of the possibility of emotional numbing (with two items) to be a distinct factor. Further investigations are urgently needed to translate psychophysiological arousal states into clinical symptoms. Acknowledgements This study was supported by a grant from the Medical Faculty of the Technical University of Munich (KKF-H 18-97), by a nonrestricted grant from Guidant Medical devices, and a research grant from the Deutsche Forschungs-Gesellschaft (DFG). We are indebted to Anja Grethlein, Birgit Hofmann, Johannes Schapperer, Janin Schroth, and Claudia Wirsching (Institut und Poliklinik fu¨r Psychosomatische Medizin, Psychotherapie und Med. Psychologie des Klinikums rechts der Isar der Technischen Universita¨t Mu¨nchen) for their precise activity in collecting the data. References Alonzo, A.A., 1999. Acute myocardial infarction and posttraumatic stress disorder: the consequences of cumulative adversity. J. Cardiovasc. Nurs. 13 (3), 33 – 45.

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