Safety and feasibility of adjunctive regadenoson injection at peak exercise during exercise myocardial perfusion imaging: The Both Exercise and Regadenoson Stress Test (BERST) trial.

BACKGROUND: The data existing in the literature regarding the safety of using regadenoson with symptom-limited exercise are limited, which motivated the authors to undertake this randomized study. METHODS: We offered patients scheduled to undergo vasodilator stress nuclear myocardial perfusion imaging the opportunity to exercise instead. Patients who failed to reach target heart rate (THR) were randomized to (1) receive regadenoson at peak exercise or (2) stop exercise and receive regadenoson at rest. Patients who reached THR received a standard Tc-99m sestamibi injection with no regadenoson. RESULTS: 200 patients were included (66% male, mean age 52.5 ± 13.6). 125 patients (62%) reached THR with exercise alone. All stress protocols were well tolerated, and there were no significant adverse events. There were no statistically significant differences in the extent of perfusion abnormalities, image quality, or rate of referral to cardiac catheterization within 60 days between the groups. In fully adjusted logistic regression models, beta-blocker use and diabetes remained significant univariate predictors of failure to reach THR (OR 0.21, 95% CI 0.1-0.5, P < .0001, OR 0.34, 95% CI 0.2-0.7, P = .004, respectively). CONCLUSIONS: A protocol combining regadenoson at peak exercise in patients unable to reach THR with exercise is feasible, well-tolerated, and yields comparable imaging results to a standard regadenoson injection at rest. In addition, pharmacologic stress testing may be over-ordered in current clinical practice, as patients referred for such testing were often able to exercise.

Contractile properties of adjacent segments of single human muscle fibers.

A comparison of the contractile properties of adjacent segments of single human muscle fibers may help to explain the interaction among nuclear domains within the myofiber. Biopsy samples were obtained from the vastus lateralis muscle of 20 healthy untrained women (age 18-79 years). Single fibers (n = 38) were dissected and cut into halves (segments A and B). Segment diameter and depth were measured using an image analysis system. Maximal force (Po) was recorded during activation with calcium (pCa 4.5). Maximal unloaded shortening velocity (Vo) was calculated using the slack test. Myosin heavy chain (MyHC) expression was determined using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). A significant difference ( approximately 7%) in Po was seen between adjacent segments expressing type I MyHC that could not be attributed to differences in fiber size. Significant differences were observed in Vo even after adjusting for fiber type. A positive correlation was seen in Po (concordance coefficient Rho_C = 0.803) and Vo (Rho_C = 0.690) between segments, but concordance was less than perfect in both cases. Possible explanations for nonuniformity of contractile properties include random variations in physiological systems or variability of protein expression among nuclear domains.