Differential associations of emotional and physical domains of the MacNew Heart with changes in 6-min walking test

Cardiovascular diseases (CVD) are the leading cause of global disease burden, requiring increasing health care expenditures [1]. Cardiac rehabilitation (CR) is strongly recommended by international guidelines [2], contributing to improved cardiovascular health outcomes by reducing cardiovascular mortality, morbidity and hospitalization [3]. CR comprises three-phases including the acute inpatient phase (phase I), the subacute and reconditioning phase (phase II), and the long term maintenance period (phase III). In Switzerland, phase II inpatient CR programs last three weeks and encompass a set of core components defined by the Swiss Working Group for Cardiovascular Prevention, Rehabilitation, and Sports Cardiology (www.​scprs.​ch). These components include exercise-based training, smoking, and nutritional counseling, as well as psychosocial and psychoeducational interventions. Quality measurements of cardiac rehabilitation clinics are implemented and monitored by the Swiss National Association for the Development of Quality in Hospitals and Clinics (ANQ; https://​www.​anq.​ch/​en).

Considering the major impact of psychosocial factors on the development and course of CVD—ranking third among the modifiable risk factors for CVD, after hyperlipidemia and smoking [4]—the importance of integrated psychosocial interventions is highly emphasized. A widely employed screening tool and outcome measure of therapeutic interventions in cardiac patients is health-related quality of life (HRQOL) [5], a multidimensional construct of the patients’ perceived health. Poor HRQOL has previously been identified as an independent predictor of survival, (re-)hospitalization [6], mortality [7], and cardiovascular morbidity in cardiac patients [8]. Although evidence on the relationship between HRQOL and exercise capacity is emerging, until now, HRQOL has primarily been recognized as an outcome variable in CR [9, 10]. To date, and only recently, two smaller studies have examined the predictive potential of non-disease specific HRQOL on improvement of metabolic equivalents of tasks (METs) as a marker of exercise capacity in CR. While one found no significant association [11], the second one detected a positive association between physical HRQOL and improvement in exercise capacity [12].

The aim of our study was to investigate the association between HRQOL at admission to CR and exercise capacity change during CR with a disease-specific and thus more suitable HRQOL questionnaire in a large sample from 6 Swiss rehabilitation clinics. We first aimed to explore the association between global HRQOL at admission to CR and CR outcome, assessed by a change in exercise capacity during CR using the six minutes walking test (6MWT) as a proxy of CR effectiveness. The second aim was to explore the predictive value of individual HRQOL domains on CR outcome. We hypothesized that better global HRQOL and its individual domains at admission to CR would be associated with greater improvement in exercise capacity from admission to discharge from CR. Covering the relevant domains of HRQOL- emotional, physical, and social indices- we applied the MacNew Heart (MNH) questionnaire as a well-known, disease-specific and validated outcome measure of HRQOL in cardiac patients [13].

To the best of our knowledge, to date there are only two studies, which recently investigated the predictive potential of baseline HRQOL on change in exercise capacity in CR using metabolic equivalents (METs) as a measure of exercise capacity [11, 12]. While METs and 6MWT have a strong positive correlation and are both valid measures of exercise capacity [25], the much smaller sample of these studies and the use of a non-disease specific HRQOL questionnaire (short form-36 (SF-36)) limits their explanatory power.

Our findings confirm the initial assumption of a positive association of emotional HRQOL with greater improvement in the 6MWT during CR. In turn, this means that lower emotional HRQOL might be a potential risk factor for less improvement of exercise capacity throughout CR. As such, the construct of emotional HRQOL might represent an important determinant of CR outcome. Encompassing items on feeling ‘frustrated,’ ‘worthless,’ ‘tearful,’ ‘frightened,’ emotional HRQOL has been linked to affective disorders due to partial conceptual overlap (e.g., anxiety and depression) [26]. Affective symptoms (e.g., anxiety and depression) have similarly been identified as relevant determinants of worse CR outcome [27]. Further, the perception of lower emotional health [28] and negative affectivity [29] have previously been linked to adherence as a relevant psychosocial risk factor for poor CR outcome, increasing the risk of non-completion and non-adherence. These mental conditions on admission to CR could thus potentially translate into worse adherence throughout CR and consequently contribute to a poorer CR outcome. Considering this, an early and thorough identification of vulnerable patients directly after (or even before) admission to CR may enable an optimized support to patients in need and could substantially contribute to an improved CR outcome. Not only do CR patients themselves value psychosocial support as an integral component of the CR program [30], but psychologically based interventions have been advocated in improving CR outcome. Enhanced psychological care [31] and integrated stepped-care programs embedded within CR [32], targeted to improve care for CR patients with depression and anxiety have correspondingly received increased attention in recent years. While significant effects in the reduction of affective symptoms were achieved compared to usual care [32], limitations became evident in the integration of these specialized psychological services into the clinical context of CR [31]. However, patients in the subsyndromal range of affective symptomatology, as captured by emotional HRQOL, could be easily overlooked in the allocation to specialized care. Thus, by focusing solely on individuals with affective disorders on CR entry, opportunities may be missed to identify and support emotionally impaired individuals at risk for less improvement in exercise capacity. Utilizing lower threshold assessments might thus help to identify patients already with subsyndromal emotional impairments. These patients could particularly benefit from closer supervision of their exercise program or individually tailored high intensity interval training during CR by physical therapists. Clearly, before firm recommendations can be made, such interventions should be tested in randomized controlled trials for their efficacy and safety in the subgroup of patients with low emotional HRQOL. Also, it has to be confirmed in future studies, whether the effect of low emotional wellbeing on adherence truly mediates the effect on CR outcome.

Since evidence indicates patients to be especially motivated and determined to make behavioral and lifestyle changes during inpatient setting [33], intensive psychosocial care in this crucial phase is particularly relevant. Yet, psychological care within CR is often provided by nurses, who consider it essential for patient recovery, but often enough encounter barriers in providing support sufficiently due to time and resource constraints [30]. Multidisciplinary approaches integrating psychological interventions provided by mental healthcare professionals may thus better address patients’ needs [32] and help to mitigate frequent organizational constraints in providing optimal support in the future. As mental health outcome is also predicted by CR waiting time and a delay in commencing CR significantly impacts anxiety and depression [34] and possibly emotional HRQOL, keeping the wait time to CR as short as possible is also highly important to promote better emotional HRQOL at CR entry and consecutively the best possible CR outcome.

Contrary to the initial assumption, our findings indicate a negative association of physical HRQOL and change in exercise capacity during CR: Higher physical HRQOL at admission to CR was linked to a lower improvement in exercise capacity. While from a clinical perspective it is encouraging that inversely patients with low physical QoL benefit more from CR, patients who feel only mildly physically burdened by the symptoms of their disease on entering CR, reflected in higher values of physical HRQOL, may possibly be less motivated to participate in CR. An alternative explanation may be a ceiling effect in that people who already experience relatively good physical health may benefit less from the CR measures and thus improve less in the 6MWT as a physical outcome variable. Moreover, prior findings have linked physical QOL to the construct of illness perception, defined as expectations and beliefs about ones illness- a negative illness perception being correlated with lower physical QOL [35]. In turn, a positive illness perception has been demonstrated to predict lower adherence to CR procedures [36]. Consequently, in patients with higher physical HRQOL, resultant poorer adherence could thus ultimately contribute to the poorer improvement in exercise capacity.

We found no impact of social HRQOL on improvement in exercise capacity during CR. Evidence on the benefit of social support in the framework of CR is contradictory. While our results are in line with findings by Husak et al. [37], they contradict earlier evidence of a positive correlation between perceived social support (as a construct of social HRQOL) and effectiveness of CR [37, 38]. Previous validity analyses on the German version of the MNHs factor structure have already pointed to a difficulty of interpreting the social domain due to poor construct validity [39]. Also, the inpatient survey context of this study may account for some of the differences in findings. Questions on social HRQOL might be less relevant in inpatient treatment and answers might rather reflect the perceived support by the treatment team than by personal caregivers. This assumed, a different construct of social HRQOL may have been covered by the underlying design of our study; the anticipated positive correlations between social HRQOL and change in exercise capacity may be more evident in an outpatient setting.

Whereas abundant evidence links higher global HRQOL to a positive course of cardiac diseases [6‐8], global HRQOL did not predict CR outcome in terms of exercise capacity in our study. This might be related to the internal structure of the MNH (with a cross-dimensional global index based on the average of the emotional, social, and physical MNH scores). Since the physical and emotional domain of HRQOL showed opposite effects on exercise capacity in our results, their individual effect might mutually neutralize each another, thus amounting to the missing effect of global HRQOL on exercise capacity. In line with this and given the complex and multidimensional concept of HRQOL, arguments have also been raised against the use of a global HRQOL score, favoring to consider individual HRQOL dimensions separately [40].

Our investigation of multidimensional HRQOL as a possible determinant for the effectiveness of CR fills an important gap in the existing literature. Although it is well known that psychosocial factors play a crucial role in the effectiveness of CR [41], evidence on the prognostic properties of HRQOL on exercise capacity has so far been missing. The thorough factor-analytical approach to the MNH items prior to the main analysis allowed the theory and data-driven identification of the most appropriate definition of the HRQOL domains for the present data set, which formed a solid basis for the subsequent main analyses.

Further major strengths of the present study are the large sample size, the multi-center approach, and the inclusion of a wide spectrum of cardiac diagnoses, which substantiate the representativeness of the sample.

Yet, some limitations have to be acknowledged. Our large sample size enabled us to thoroughly investigate the predictive properties of HRQOL on exercise capacity, however, the effects found were small. Moreover, given the multidimensionality of the quality of life concept, many different HRQOL survey instruments have been applied in the past, also in cardiovascular patients. This wide range of available instruments represents a challenge in research on this topic in general and can also contribute to the divergent findings across studies. Moreover, the factor structure of the MNH may affect the generalizability of existing evidence, especially, since score composition also varies by language [39].

Further, due to the correlational design, no causal effect of CR can be inferred. The observed changes in exercise capacity may also be driven by factors other than HRQOL. Training intensity, for instance, was identified as the most critical predictor of exercise capacity at discharge of CR [42], a variable we could not deduce from the present data set. While in several European countries, inpatient phase II CR services are provided, this is not the case on a global level, where phase II CR is often only provided in an outpatient setting. This might limit generalizability of our results. In light of this, replication of our results in outpatient settings would be desirable in future studies.

The results of our study highlight a need for an adequate and reliable assessment of HRQOL that is not limited to an evaluation of the global HRQOL. Rather, the imperative of focusing on specific domains of HRQOL must be emphasized. In our study, emotional and physical HRQOL emerged as potentially valuable determinants of CR outcome. Particular focus should be directed toward patients with lower emotional HRQOL, who are at risk for lower gain in exercise capacity during CR. As a broad and dimensional construct, emotional HRQOL allows for a particularly applicable assessment of vulnerable patients even with subsyndromal emotional impairments being at risk for worse CR outcome. Efforts should therefore be directed at early identification of these patients in the CR admission assessment. Only then, early and targeted interventions might allow to modulate CR outcome and to mitigate unfavorable impacts of poor emotional HRQOL. Future research efforts should be aimed at developing such interventions for an early support of patients with poorer emotional HRQOL and examine their impact on CR outcome. Also, the potential influence of individual domains of HRQOL on adherence as an overarching determinant of CR outcome should be considered.