Start early, start strong: physical activity for avoiding and surviving coronary surgery

Amidst mountains and fjords of Mid-Norway rests a true goldmine for population-based research: Nord Trøndelag. Since the 1980s, the Trøndelag Health Study (HUNT) has regularly investigated the health of the region’s inhabitants using, e.g. questionnaires, blood tests and clinical examinations. Despite the relatively small population of around 130 000, the contribution of Nord Trøndelag to the medical- and health-related research is irrefutable: >1000 research projects have been started [1] and hundreds of articles published based on HUNT data [2]. Now also cardiac surgeons have taken an interest in this valuable databank. During the past 4 decades, the HUNT study has provided important findings to the field of cardiovascular disease. For example, Mørkedal et al. showed that obesity, regardless of linked metabolic abnormalities, is associated with an increased risk of developing heart failure [3]. In addition, long-term obesity but also changes in BMI, when compared with stable normal weight, were linked to an increased risk of atrial fibrillation [4]. A special focus has been on physical activity, with positive effects demonstrated in multiple studies: higher physical activity has shown an association with a lower risk of cardiovascular disease and death in patients with atrial fibrillation [5], as well as with a lower risk of death from stroke in women [6]. Coronary artery disease (CAD) continues to be a significant cause of mortality and morbidity worldwide. As the incidence of acute myocardial infarction attacks decreases [7], epidemiological studies need another useful surrogate end point reflecting the severity of the disease. Given that coronary bypass surgery (CABG) is recommended for patients with the most anatomically and functionally advanced CAD, it serves as a natural alternative marker for severe disease. In the current issue of the journal, Smenes et al. [8] investigate the association between physical activity and risk of undergoing CABG, as well as mortality after CABG. For this, they took advantage of the second wave of the HUNT study (HUNT2) dating back to 1995–1997 with a praiseworthy participation rate (69.5%) and a noteworthy cohort size (45 491 participants). Physical activity was assessed using a previously validated questionnaire in which participants reported the average number of hours of light and high-intensity physical activity performed weekly. In addition, an indirect measurement of estimated cardiorespiratory fitness was used: this parameter was calculated based on sex, age, waist circumference, reported physical activity hours and resting heart rate. To obtain data on CABG, the HUNT database was cross-linked with the database in the local university hospital, which, given the structure of the public health care system in Norway, provides all cardiac surgery services to the whole region of Nord Trøndelag. The unique personal identification number of each citizen in Norway, universally used in a large number of national services and registries, facilitates any cross-linking between different databases for more comprehensive data analyses. The results seem logical and rather expected. Those reporting high levels (hours and intensity) of physical activity at baseline had a lower risk of undergoing CABG during the follow-up. In addition, high estimated cardiorespiratory fitness seemed to protect from death after CABG. The results were supportive of earlier studies, again raising the question if assessing previous physical activity should have a more prominent role in risk stratification tools for CAD [8]. It should be noted that the level of physical activity was only recorded at the start of the follow-up. On one hand, this reflects its far-reaching effects: on average, CABG was performed 11 years later. On the other hand, the effects of continuous physical activity versus changing physical activity over the years cannot be assessed with this study and may dilute the results. As the authors point out, this was an observational study with its natural limitations. Results from population-based cohort studies cannot be used to prove causation as they only observe association. However, they have an important role in generating hypotheses for more targetted future trials. Large prospective population-based cohort studies require patience before bearing fruit, and the waitful watching needed has not been a traditional virtue of surgeons. Databases similar to the HUNT study can provide enormous data resources, including interesting possibilities for registry cross-linking, and the study by Smenes et al. will hopefully encourage fresh approaches to research in cardiothoracic surgery. And instead of studying why the sick get sick, we could focus more on how the healthy stay healthy.