Cardiac rehabilitation (CR) is a fundamental component for successful long-term CHD treatment [30–32]. Data from almost 100,000 CHD patients enrolled in about 150 randomized trials have demonstrated the benefit of CR on both cardiovascular and total mortality [33, 34]. Moreover, many studies established that CR improves quality of life as well [35, 36]. In Germany, standard of care for CHD patients after ACS or CABG surgery comprises a multimodal 3-week CR at specialized rehabilitation centers [29, 35, 37–39]).
The multicenter LLT-R registry provided a representative cross-section of CHD patients and the treatment situation during and after CR in Germany. The registry data are based on only one exclusion criterion (i.e., the lack of informed consent) and the overall characteristics of the patient cohort, such as an average age of 63 years and less than 25 % females [29, 37–39].
Multimodal rehabilitation in Germany attempts to optimize drug therapy and to educate patients on the impact and the possible adverse effects of drugs in order to increase compliance with drug treatment [29, 37–39]. Further, CR commonly implements intensive programs on five days a week, including psychosocial support, physical exercise, and nutrition counseling [29]. Examples of improvements during start and end of rehabilitation include decreases in systolic blood pressure, heart rate, and waist circumference, but not in BMI [29, 37]. These findings are in excellent agreement with our observation regarding the unchanged body weight during follow-up after discharge from CR. Furthermore, effective CR could also account for the observed decline in insulin therapy during the course of LLT in the registry.
In agreement with the literature, this registry showed that total and LDL cholesterol levels changed within the first 3 months after CR, and then remained at that level, irrespective of prevalent diabetes mellitus. By contrast, the HDL levels in nondiabetic patients remained constant 3 months after CR, whereas HDL levels in diabetic patients continued to increase in the same period. In addition, our analysis indicated a faster decline in LDL cholesterol levels below 55 mg/dL in diabetes mellitus patients than in patients without diabetes. It should be stated, however, that the few measurement time points in the follow-up period provide only a low resolution of the kinetics of these adjustments.
In the cohort of this CR registry, 33.9 % of patients had received a diagnosis of diabetes mellitus (Table 1), whereas the overall rate of diabetic patients among all cardiac events in the German population varies between only 10 % and 16 % [40]. The overrepresentation of patients with diabetes mellitus in the CR registry cohort can very likely be attributed to the higher number of high-risk patients, such as elderly people who have suffered myocardial infarction and who are admitted more frequently to CR than younger diabetic patients with less severe cardiac events. Nonetheless, this discrepancy between the general population and the registry is a coincidental observation that requires thorough statistical assessment. In any case, the findings presented here have implications for CR patients or patients with recurrent cardiac events. This is particularly important in light of the continuously increasing magnitude of this patient group due to the growing number of multimorbid and older patients.
There are several limitations of this registry. First of all, it is difficult to interpret the data set due to the observational and nonrandomized design of the patient cohort. Changing the design of this study by introducing a control group is almost impossible as every patient in Germany has the litigable right to participate in CR after ACS or CABG [29, 37–39]. Nonetheless, this study aimed for the highest possible data quality. The Coordination Center for Clinical Studies, Martin Luther-University Halle Wittenberg, Germany (KKS Halle), enrolled patients consecutively on a prospective basis in order to provide adequate monitoring and to record all relevant patient information.
In addition, there may be potential incoherencies in LLT medication in this registry. In general, the study showed no differences in treatment of diabetic and nondiabetic patients during LTT. Nonetheless, patients received different drugs during the course of CR in order to address clinical needs, such as duration and severity of disease as well as comorbidities. Consequently, these changes in medication confound the association between treatment and outcome, thus introducing channeling or allocation biases. However, rehabilitation centers and patients enrolled in prospective studies are more likely to adhere to guideline-oriented therapy than patients outside of such centers or studies.
Moreover, different types of diabetes mellitus could not be addressed separately in this registry as data on the specific types were limited and inconclusive.
Lastly, a follow-up period of 12 months is rather short for monitoring lifelong chronic diseases. Hence, a longer follow-up period might have shown further differences between patients with and without diabetes mellitus.