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Purpose: This study aims to compare transcatheter aortic valve replacement (TAVR) planning on 16 cm wide-detector computed tomography (CT) to TAVR planning on 4 cm detector CT., Materials and Methods: A total of 36 patients who had TAVR planning axial CT on a wide-detector scanner (protocol 1) were compared to 36 patients who had helical 4 cm detector CT (protocol 2)., Results: Vascular attenuation was greater for protocol 1, but image noise, contrast-to-noise ratio, and signal-to-noise ratio were the same. Radiation dose was lower and iodine dose was less for protocol 1., Conclusion: Protocol 1 had greater vascular attenuation and similar image quality but lower radiation and less iodine compared to protocol 2., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Introduction: Resting heart rate (RHR) declines with exercise training. Possible mechanisms include: 1) increased parasympathetic tone, 2) decreased responsiveness to beta-adrenergic stimulation, 3) decreased intrinsic heart rate or 4) combination of these factors., Objective: To determine whether an increase in resting parasympathetic tone or decrease in response to beta-adrenergic stimulation contributes to the decrease in RHR with training., Methods: 51 screened healthy subjects aged 18-32 (n=20, mean age 26, 11 female) or 65-80 (n=31, mean age 69, 16 female) were tested before and after 6months of supervised exercise training. Heart rate response to parasympathetic withdrawal was assessed using atropine and beta-adrenergic responsiveness during parasympathetic withdrawal using isoproterenol., Results: Training increased VO2 max by 17% (28.7±7.7 to 33.6±9.20ml/kg/min, P<0.001). RHR decreased from 62.8±6.6 to 57.6±7.2 beats per minute (P<0.0001). The increase in heart rate in response to parasympathetic withdrawal was unchanged after training (+37.3±12.8 pre vs. +36.4±12.2 beats per min post, P=0.41). There was no change in the heart rate response to isoproterenol after parasympathetic blockade with training (+31.9±10.9 pre vs. +31.0±12.0 post beats per min, P=0.56). The findings were similar in all four subgroups., Conclusions: We did not find evidence that an increase in parasympathetic tone or a decrease in responsiveness to beta-adrenergic activity accounts for the reduction in resting heart rate with exercise training. We suggest that a decline in heart rate with training is most likely due to decrease in the intrinsic heart rate., Competing Interests: There are no conflict interests for this study. The results of the present study do constitute endorsement by ACSM., (Published by Elsevier Ireland Ltd.)