Heart rate reactivity and antisocial behaviour: Table 1.

We were very interested to read Dr Palatini’s thoughtful letter1 about our study of heart rate and violence in a Brazilian birth cohort. The key finding of our study was that males with a low resting heart rate were at increased risk for participation in violence in late adolescence.2 In his letter, Dr Palatini considers the possible role of cardiovascular reactivity in relation to antisocial behaviour. He points to the interesting phenomenon whereby some people show increased heart rate and blood pressure when undergoing medical examination, a phenomenon known as the ‘white coat effect’. The white coat effect was first described in the late 19th century, and is thought to reflect a temporary alerting reaction when undergoing assessment by a physician. Recent studies show that even physical assessment by a nurse or by the patient themselves in a doctor’s office can induce a white coat effect.3 This is a major problem for accurate clinical assessment of hypertension but, as Dr Palatini points out, could offer an opportunity to study heart rate reactivity in relation to antisocial behaviour in our Brazilian study. The gold standard for identifying the white coat effect uses continual assessment of heart rate and blood pressure before, during and after consultation with a physician.4 However, surrogate methods include assessing the difference between clinic and home readings, or calculating the difference between repeated measures during a medical assessment. After an initial rise in heart rate and blood pressure, people may become accustomed to the medical environment and show lower readings on subsequent measures. Given that we measured heart rate twice at each assessment phase in our study, Dr Palatini suggests that we might investigate the relationship between heart rate reactivity and antisocial behaviour–using the difference in heart rate readings as an indicator of the white coat effect. The first heart rate measures available in our birth cohort study were taken during a home visit assessment when participants were aged 11 years. The first clinic-based heart rate measures come from an assessment at age 18 years. We calculated the difference between the first and second heart rate readings taken during each of these assessments, and examined whether these differences were associated with violent or non-violent crime measured at age 18 (see the online supplement for descriptive statistics, available as Supplementary data at IJE online). The table below shows the odds of crime across quartiles of the heart rate differences. Individuals in the upper quartile–with higher heart rates at the first reading than the second–are assumed to manifest a white coat effect. Individuals in the bottom quartile–with higher heart rates at the second reading–represent a group with possible so-called ‘masked’ effects.5 In both unadjusted and adjusted analyses, there was no association between either violent or non-violent crime and quartiles of heart rate difference at ages 11 or 18 years, either for males or females. For example, at age 18 years, comparing males in the 4th quartile (males with an apparent white coat effect) with males in the 2nd and 3rd quartiles (males with relatively stable heart rates), adjusted odds ratios were 1.18 [95% confidence interval (CI) = 0.88–1.57) for violent crime and 1.03 (95% CI = 0.71–1.50) for non-violent crime. These null results might be caused by inaccurate assessment of the white coat effect in the current study. Calculating the difference between two heart rate measures is not a gold-standard measure of the white coat effect, and there are other context-specific reasons why this indicator might have low accuracy in our study. At age 11, the study assessments were completed in the adolescent’s home by research assistants. Although this was the first time that study participants had been examined since age 4 years, and their first and second heart rate measures were some 60 min apart, it is possible that the white coat effect would not manifest under these conditions. At age 18, although the assessment was conducted in a clinic setting, the first and second measures of heart rate occurred closer together, at the beginning and end of anthropometric assessments that lasted about 10 min. Although a white coat effect has been observed over such a short time period in other studies,5 in the current study these procedures often took place after other assessments in the clinic, such that participants might already have become accustomed to the clinic environment. Given these considerations, differences between the first and second heart rate measures may reflect measurement error in this study, rather than the white coat effect. It is also possible that the current indicator of the white coat effect is valid, but that cardiovascular reactivity indicated by the white coat effect is not associated with violent or non-violent crime. Considering other research on stress reactivity and antisocial behaviour, the experience of a medical assessment represents a relatively minor form of stress. For example, other studies have examined antisocial behaviour in relation to heart rate reactivity during exposure to very loud noises, electric shocks or pictures of mutilated body parts.6 Studies examining whether the white coat effect correlates with reactivity to other forms of stress, such as performing mental arithmetic or a mirror drawing test, have shown mixed results.3 Hence, levels of cardiovascular reactivity may be inconsistent across different types of stress, and reactivity to minor stress in a medical visit may not be relevant to crime. Previous antisocial behaviour research has been informative in this regard. Meta-analyses suggest that antisocial behaviour is positively associated with heart rate reactivity following negative stimuli, but inversely associated with reactivity following non-negative stimuli.6 Hence, although heart rate reactivity may be important for antisocial behaviour, the specific type of stimulus that causes reactivity seems to be important, and a ‘white coat experience’ may not be a relevant type of stimulus in relation to antisocial behaviour. Dr Palatini also points out that a literature showing a weaker relationship between cardiovascular events and mortality for women than men is consistent with our finding weaker evidence for women regarding associations between resting heart rate and crime. Clearly, there is much to be learned from a cross-disciplinary exchange between antisocial behaviour research and cardiovascular research. We are grateful to Dr Palatini for making useful suggestions in this regard, and hope that other studies may perform additional tests to see whether cardiovascular reactivity represented by the white coat effect is relevant to antisocial behaviour. Odds ratio (OR) for violent and non-violent crime at age 18 according to quartiles of heart rate difference at ages 11 and 18 years in the 1993 Pelotas Birth Cohort Covariates included in adjusted model: unplanned pregnancy, mother smoked in pregnancy, maternal alcohol use in pregnancy, maternal age, number of siblings, maternal education, and family income in perinatal period; child skin colour, smoking, drinking, physical activity, height, weight, blood pressure, maternal mental health at age 11 years. For details see reference 2. aWald test for heterogeneity. Odds ratio (OR) for violent and non-violent crime at age 18 according to quartiles of heart rate difference at ages 11 and 18 years in the 1993 Pelotas Birth Cohort Covariates included in adjusted model: unplanned pregnancy, mother smoked in pregnancy, maternal alcohol use in pregnancy, maternal age, number of siblings, maternal education, and family income in perinatal period; child skin colour, smoking, drinking, physical activity, height, weight, blood pressure, maternal mental health at age 11 years. For details see reference 2. aWald test for heterogeneity.