Schlitt et al. report an enormous reduction of the overall mortality of 93% in patients with coronary heart disease who participated in cardiac rehabilitation (1). A meta-analysis cited by the authors found only a decline in overall mortality among cardiac rehabilitation participants of 13%.
The value of Schlitt et al.’s study is that it highlights the variation in cardiac rehabilitation participation rates among the various German Federal States and thus points towards another potential cause of regional differences in cardiac mortality. However, we think that the number needed to treat of 4.6, which can be estimated from the study data, is unrealistic. We suspect that the authors have overestimated the actual impact of cardiac rehabilitation on overall mortality:
1. Immortal time bias may have had an impact. All patients who underwent cardiac rehabilitation had at least survived until the start of the rehabilitation program. One reason for an overestimate of the effect of cardiac rehabilitation could be that in the rehab group waiting times until the start of the rehabilitation were included in the effect estimates even though no deaths could be observed during these times.
2. In the rehab group, 0.2% of the patients with coronary heart disease died of non-cardiac causes compared with 7.3% in the non-rehab group which indicates that the patient groups differed by health status right from the start. While data were adjusted above all for cardiovascular factors, no adjustment was made for pre-existing diseases and for indicators of health status relevant to the approval of cardiac rehabilitation, such as the Barthel index and nursing care level.
3. For two subgroups of the patient population, there is reason to assume that patients did either not start with the rehabilitation program or that the rehab group application processing was stopped because of a particularly poor health status. If, based on the intention-to-treat principle, these two subgroups were assigned to the rehab group, the effect estimate would move closer to 1.
Dr. rer. nat. Dr. rer. san. Bernd Kowall
Prof. Dr. med. Andreas Stang, MPH
Institute of Medical Informatics, Biometry and Epidemiology,
University Hospital of Essen, Germany
Conflict of interest statement
The authors declare that no conflict of interest exists.
|1.||Schlitt A, Wischmann P, Wienke A, Hoepfner F, Noack F, Silber RE, Werdan K: Rehabilitation in patients with coronary heart disease— participation and its effect on prognosis. Dtsch Arztebl Int 2015; 112: 527–34 VOLLTEXT|