Effects of exercise training and cardiorespiratory fitness upon cardiac surgery incidence and outcomes

Abstract

Most cardiac surgical procedures involve temporary arrest of the heart and its blood and oxygen supply (ischemia). This leads to ischemia-reperfusion injury (I/R-injury) of the heart. Animal studies have implicated that as little as one bout of exercise performed 24 hours prior to ischemia can protect the heart against I/R-injury, but this has up to now not been investigated in humans. We therefore wanted to investigate whether one single bout of exercise 24 hours before open heart surgery was sufficient to protect the heart against I/R-injury. Furthermore, we investigated whether physical activity and cardiorespiratory fitness (CRF) earlier in life could influence the results after heart surgery, but also how these factors influence the risk of developing surgerydemanding heart disease in the first place. Altogether, this resulted in three papers, which lay the foundation of this thesis. The first study included 20 patients referred to coronary bypass surgery. Patients were randomized to perform a 30-minute bout of treadmill exercise 24 hours before surgery or to prepare for surgery according to standard protocols. Myocardial biopsies were analyzed for mitochondrial function and transcription levels of genes involved in cell death. Results revealed that the patients who had exercised prior to surgery had a higher transcription level of the pro-apoptotic protein caspase-3 at the beginning of surgery and impaired mitochondrial function in the heart tissue at the end of surgery. The data suggest that acute exercise before heart surgery is insufficient to protect the heart during surgery and that the heart might be more susceptible to damage after this type of intervention. The next two studies were based on data from the Trøndelag Health Study (HUNT), where participants from HUNT2 (1995-1997) and HUNT3 (2006-2008) formed the foundation for our analyses. We categorized physical activity and estimated CRF (eCRF) in the participants based on self-reported and measured data from HUNT. eCRF data was cross-linked with the local heart surgery register of St. Olavs hospital, Trondheim University Hospital to identify those who had undergone coronary bypass surgery, or aortic valve replacement due to aortic valve stenosis. We also cross-linked the data with the Cause of Death Registry to assess mortality after surgery. eCRF was inversely associated with the risk of undergoing coronary bypass surgery, or aortic valve replacement due to aortic valve stenosis. The association between physical activity and surgery was not as strong. We also found that higher eCRF was associated with significantly lower mortality risk after both types of surgery. Altogether, our results imply that physical activity and high eCRF could influence not only mortality risk after surgery but also the risk of even developing heart disease requiring open heart surgery. Exercise 24 hours prior to surgery does not appear to be as favorable and could potentially do more harm than good.