Dr Carolyn Lam:                Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to The Journal and it's editors. We're your co-hosts. I'm Carolyn Lam, Associate Editor from the National Heart Center and Duke National University of Singapore. Dr Greg Hundley:             And I'm Greg Hundley, also Associate Editor from the Pauley Heart Center in Richmond, Virginia, VCU Health Sciences. Dr Carolyn Lam:                How well are we doing with guideline-directed stroke prevention therapy in atrial fibrillation? Well, there are going to be very important results that you need to hear about from Get With the Guidelines Atrial Fibrillation. That's our feature paper coming right up in a future discussion. But first, you've got Greg and I discussing really important papers that we've spotted in The Journal. Greg. Dr Greg Hundley:             Absolutely, Carolyn. And my favorite kind of follows from that 'cause it's really about left atrial electromechanical remodeling following two years of high intensity exercise training in sedentary middle-aged adults, kind of like me. The studies from Ben Levine at University of Texas Southwestern Medical Center in Dallas. So, what he's driving at here are moderate-intensity exercises associated with a decrease in incidents of atrial fibrillation. However, extensive training in competitive athletes is associated with an increased atrial fibrillation risk.                                                 So, in this study, they're looking at the effects of 24 months of high-intensity exercise training on left atrial mechanical as well as electrical remodeling in sedentary, healthy, middle-aged adults. So, he had 61 individuals, their average age was 53.5 years, quite young, who were randomized to 10 months of exercise training followed by 14 months of maintenance exercise and some stretching or stretching and balance control. He also had another group of 14 master's athletes that were added for a comparison and he looked at three of the echocardiograms to assess left atrial and left ventricular volumes and also had signal average EKG's for filtered P-wave durations and atrial light potentials. He made assessments at baseline, so before everyone started, and 10 and 24 months. Dr Carolyn Lam:                Hold on, hold on. Let's really understand here how much exercise were these sedentary middle-aged adults subjected to. Dr Greg Hundley:             So, let's talk about that because that was very interesting because a lot of us are out there exercising. So briefly the way he started this, there was an initial phase that was comprised of six months of regressive training during which an increase in the frequency, the duration, and the intensity of exercise, including two high-intensity aerobic interval sessions per week that were prescribed to peak training load. The peak training load included five to six hours of exercise per week that included two interval sessions, at least one being an hour-long session, and then two 30-minute sessions.                                                 Once you got that peak training load, that was sustained for four months and then he made these 10-month measurements as part of his study design. Now following that phase, a 14-month sort of a continuation, all of the 24 months, a 14-month period of maintenance exercise was completed where the frequency of high-intensity intervals was reduced to once per week plus continuous training all the way to that 24-month time point. And during the maintenance phase, participants performed a total of about three hours a week of aerobic exercise. Dr Carolyn Lam:                Well, don't keep us in suspense now. What did the study show? Dr Greg Hundley:             So at the 24 month time point of high-intensity exercise, it led to a disproportionate dilation of the left atrium compared to the left ventricle. So, mechanical changes, but no electrical remodeling was seen. And interesting,