Exercise training in patients with ischemic heart disease works but more high‐quality studies are wanted …

Cardiorespiratory fitness is an important prognostic factor in healthy individuals as well as in patients with ischemic heart disease (IHD). One study even indicated that having a very low exercise capacity (VO2maxo21mL/kg/min) rules out the importance of other traditional risk factors as smoking, hypertension and overweight (Laukkanen et al., 2004). Exercise training in IHD patients has numerous beneficial effects including reduced myocardial work indirectly by improved adaption of the peripheral circulation and directly by increasing myocardial perfusion (Lee et al., 2008) and is associated with improved survival (Taylor et al., 2004). Furthermore, exercise training has been shown to be safe even in patients with reduced left ventricular function (O’Connor et al., 2009). Consequently, guidelines recommend that exercise training should be an integrated component of cardiac rehabilitation, but how the training should be prescribed is not well defined. To address the important question: to what extent did VO2max increase in relation to the exercise training in patients with coronary artery disease and what characteristics of the exercise intervention determine the effectiveness, Valkeinen and colleagues in this issue of the journal present a literature search and meta-analysis that includes randomized controlled trials published in 1966–2009. Surprisingly, only 18 trials including 922 participants met the inclusion criteria and even in those studies the methodological quality was not deemed to be high. Most studies applied aerobic training but there was great variation in exercise intensity, frequency and duration. The mean increase in VO2max was approximately 14%, which is surprisingly low, although even this effect has been shown to have beneficial effects in these patients (Lee et al., 2008). Results seemed to point at longer training periods having a greater effect than training o6 months and a greater effect of exercise training intervention if initiated within the first 3 months after the cardiac event. Although the limited number of studies included prohibits to draw firm conclusions, these results do point to a few important points. Firstly, the variation in exercise training offered in these studies is so great – what is deemed intervention in one study can be control in another – that conclusions on which type of exercise regarding intensity, frequency and duration cannot be drawn. Second, there is a lack of studies that document longterm effect of training intervention. Essentially, much of the effects of exercise training offered presently in various cardiac rehabilitation programs are likely to be lost after the supervised intervention is discontinued and studies of how training effects should be maintained are lacking. Finally, as pointed out by Valkeinen and colleagues, the study population in the meta-analysis comprises males age 60 and thus is not at all representative of patients with IHD, who are older, have comorbidity and include a large proportion of women. A few years ago, meta-analyses of randomized controlled trials of exercise training in patients with systolic heart failure gave similar results: exercise training led to approximately 15% increase in VO2peak, improved 6-min walking test, quality of life and reduced morbidity and mortality (Rees et al., 2004). This prompted initiation of the large HFaction study, in which approximately 2300 patients with systolic heart failure were randomized to longterm exercise intervention or usual care. The study, which was published last year, was disappointing: the effect of training on VO2peak was smaller and there was only approximately 10% reduction in a composite end-point and no reduction in mortality (O’Connor et al., 2009). The discrepancy between the meta-analysis in this field and the results of a large, well-conducted study, are thought provoking, but rather than lead us to discredit exercise training they should prompt us to conduct larger, high-quality studies that address the issues raised in the paper by Valkeinen and colleagues. In conclusion, exercise training is safe and continues to be important in cardiac patients but we need more knowledge on how to prescribe exercise training in cardiac patients.