This study investigated the relationship between LMS at the time of discharge and rehospitalization and physical functioning in VAD patients in the early to mid-term phase after discharge. The results showed that the rate of rehospitalization over 1 year was higher in patients in group L than in those in group H. The 1-year rehospitalization rate was 64.3% in group L, nearly the same rate (64%) as in a previous study [11]. The relationship between LMS at the time of discharge and the rehospitalization rate within 1 year was a novel finding of this study. Although previous studies have not reported an association between rehospitalization and LMS, rehospitalization events have been associated with measures of nutritional status such as BMI before VAD surgery and with serum albumin and BMI at discharge [5, 12]. In addition, previous studies using perioperative grip strength as an index have shown an increase in the long-term mortality rate in patients with low grip strength after VAD use [13]. These reports suggest that the prolongation of perioperative cardiac cahexia is a risk factor. The confounding factors of LMS were BNP, T-Bill, and AR in multiple regression analysis. LMS at discharge is a surrogate marker of the degree of recovery of general condition at the time of discharge, and it seems that preoperational heart failure management may affect it. Previous studies have reported a connection between frailty and event onset [5, 14]. Although this subject is not as frail as previous studies, the degree of recovery from the general wasting state may have been affected by the control of heart failure. Changes in LMS and BMI from before surgery to the time of discharge did not differ between groups. Several studies have shown that a combination of exercise therapy and nutritional therapy was helpful for improving cardiac cahexia, as recovery from muscle wasting mediated by protein synthesis is required [15–17]. The reason for many rehospitalization events is that patients were considered to be at risk for perioperative muscle assimilation due to lack of muscle contraction.
Grip strength is an indicator of whether muscle strength level is frail or not. However, in the case of cardiac surgery, training interventions for the upper limb muscles such as grip strength have not been introduced in daily clinical practice in order to avoid adverse effects on bone adhesion. On the other hand, since the lower limb skeletal muscle can intervene in exercise, it is considered to be an indicator of recovery effect determination in accordance with clinical practice.
The LMS did not change in the mid-term period. The patients' body surface area reportedly affects outcomes after VAD implantation [18, 19]. The rate of change in BMI from before surgery to discharge was a lower tendency than before surgery for group L. BMI at the time of discharge in this study was about the same as that reported for the J-MACS study [18], but it was much lower than that reported for VAD patients in Europe and the United States [7]. Differences in BMI have been found to affect recovery from frailty [20]. Therefore, the absence of any increase in LMS among patients in this study is considered to be a result of a long term bedridden accompanied by low physical activity and malnutrition.
In addition, in the early to mid-term phase, grip strength and exercise tolerance were observed to increase relative to values at the time of discharge. However, the LMS exhibited no change at the time of discharge. BMI at the time of discharge and at admission for educational hospitalization were compared with values for patients who were not rehospitalized, and BMI was observed to increase at the time of educational hospitalization. It is considered that LMS did not change in the mid-term period because the output of muscle strength as measured by LMS did not change, although weight might have increased. This is similar to the results of a previous study in which BMI increased at 2 years after surgery [21]. In order to further increase muscle strength in the preoperative BMI, it is necessary to give the muscle a strong contraction. Since this study is a retrospective observational study, the obvious mechanism is unknown. Daily life without pulses during VAD wearing periods has been shown to have a physical impact [22]. Resistance training has been reported to prevent events in patients with cardiovascular disease [23]. Muscle weakness is insufficient in protein synthesis, so the low muscle strength group lacked aggressive resistance training and lack of protein synthesis, so there may be many readmission events.on using strength training.
Reports from other countries have indicated that grip strength increases over time [13]. The present study found similar improvement over time. The results for Peak VO2 were also similar to those from previous studies [10, 24, 25]. Heart transplantation treatment, which typically involves a long period of wearing mechanical assistance devices before transplantation, requires a strategy for maintaining the patient's quality of life (QOL) [26]. Patients with severe heart failure commonly have dysfunction of skeletal muscle [27]; thus, preserving skeletal muscle function in daily life under long-term mechanical circulation support is difficult. Previous research found that the LMS increased in heart failure patients due to cardiac rehabilitation during the recovery phase [28]. It is necessary in the future to observe patients’ physical functioning from the perspective of long-term mechanical support and to establish management strategies at home [29]. To maintain patients’ QOL, it is necessary to maintain physical function. Therefore, we suggest that it is important to be attentive to patients’ physical function during the hospitalization period. Our facility does not provide outpatient rehabilitation under supervised. Previous studies have reported the usefulness of cardiac rehabilitation for LVAD patients [30]. However, the low implementation rate of outpatient cardiac rehabilitation is a problem in Japan [31]. In particular, continuous medical care for VAD patients is limited to VAD management facilities, and I think that inpatient training is important because there are high hurdles to outpatient cardiac rehabilitation. We believe that LMS should be recognized as a target for rehabilitation interventions, but it is not clear in this study whether the low leg strength group in this study becomes the high strength group after intervention. We think that future research is necessary. There are reports that lower limb muscle strength is a prognostic indicator in frail cases with non-VAD heart failure [32]. However, non-LVAD patients may experience worsening heart failure due to strong exercise loads and cannot introduce aggressive resistance training. VAD patients managed for discharge are said to be most likely to benefit from exercise therapy because they can introduce to strong resistance training [33]. We believe that lower limb muscle strength is an indicator of improvement potential in VAD patients. In this study, we hope that the results that the leg muscle strength was associated with readmission could be a target for future hospitalization rehabilitation.
In this study, only the early to mid-term stage was considered. The leg extensor muscles are prone to atrophy in severe heart failure, and the recovery course of leg muscle strength in the medium to long term is not clear. In the future, it is necessary to investigate recovery over a medium- to long-term course.