Abstract
People with schizophrenia die on average 15–20 years earlier than age and gender matched controls in the general population. An essential part of this excess mortality in people with schizophrenia is caused by physical illnesses. Among the physical illnesses, cardiovascular disease (CVD) has been identified as the most common natural cause of death in up to 40–45% of the cases. Chronotropic incompetence (CI) is defined as the inability of the heart to increase its beating frequency in proportion to increased physical activity or higher metabolic demand. It is an established independent cardiovascular risk factor for major cardiac events and overall mortality and might explain adaptation intolerance of the cardiovascular system to even minor exercise courses. CI needs objective exercise testing for definitive diagnosis and therefore represents a biological marker indicating the integrity of the cardiovascular system. It was recently described in patients with schizophrenia and might help explain the reduced physical fitness in these patients and the inability of a subgroup of patients to benefit from exercise interventions. In this study, we tried to replicate the occurrence of CI in an independent sample of patients with schizophrenia and evaluated whether CI can be influenced by a continuous endurance training of 12 weeks. Therefore, we re-analyzed the fitness testing data of 43 patients with schizophrenia and 22 aged and gender matched healthy controls. Parameters of aerobic fitness and chronotropic response to exercise were calculated. Patients with schizophrenia were less physically fit than the healthy controls and displayed a significantly higher heart rate at rest. 10 of 43 patients with schizophrenia and no healthy control subject were classified as chronotropically incompetent. Chronotropic response to exercise did not change significantly after 12 weeks of continuous aerobic exercise training. No differences were observed for baseline heart rate and peak heart rate in both subgroups of schizophrenia patients. Aerobic fitness did not improve significantly in the patients with schizophrenia classified as chronotropically incompetent. Our results confirm the occurrence of CI in patients with multi-episode schizophrenia. This should be taken into account when planning an exercise or lifestyle intervention studies in this population. Schizophrenia patients with CI do not seem to benefit as well as schizophrenia patients without CI from aerobic exercise training interventions. Larger, prospective randomized controlled clinical trials with different training interventions are urgently needed to address the topic of schizophrenia patients not responding to exercise and the relationship to the illness itself.
Highlights
There is a solid body of evidence underpinning the notion that people with schizophrenia die on average 15–20 years earlier than age and gender matched controls in the general population [1,2,3]
The second MANOVA for heart rate parameters revealed a significant effect for the factor GROUP [F(3, 61) = 6.45; P < 0.01]
Had an impaired heart rate response to exercise and were classified as chronotropically incompetent, whereas no healthy control subject was below the cut-off value
Summary
There is a solid body of evidence underpinning the notion that people with schizophrenia die on average 15–20 years earlier than age and gender matched controls in the general population [1,2,3] This mortality gap between the general population and patients with schizophrenia seems to increase instead of converge over the last decades [4,5,6]. It has been shown that young unmedicated patients with schizophrenia show increased heart rates at rest caused by severe autonomic dysfunction [19]. Increased resting heart rate has been shown to be a risk factor for reduced life expectancy in both the general population [22, 23] and in populations with cardiovascular diseases [24, 25]. More research is needed to better explain cardiovascular dysregulation in schizophrenia because in contrast to patients suffering from severe CAD the cardiac autonomic dysfunction in schizophrenia is not caused by structural or functional alterations of the heart itself but by abnormalities in the brain— heart interaction [33]
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