Validity, prognostic value and optimal cutoff of respiratory muscle strength in patients with chronic heart failure changes with beta-blocker treatment.

BACKGROUND: Training studies frequently use maximum inspiratory mouth occlusion pressure (PImax) as a therapeutic target and surrogate marker. For patients on beta-blocker (BBL), prognostic data allowing this extrapolation do not exist. Furthermore, the effects of BBL, mainstay of modern chronic heart failure therapy, on respiratory muscle function remain controversial. Finally, no proper separate cutoff according to treatment exists.
DESIGN: Prospective, observational inclusion of patients with stable systolic chronic heart failure and recording of 1 year and all-time mortality for endpoint analysis.
METHODS: In 686 patients, 81% men, 494 patients on BBL, PImax was measured along with clinical evaluation. The median follow-up was 50 months (interquartile range: 26-75 months).
RESULTS: Patients with or without BBL did not differ significantly for PImax, percentage of predicted PImax or other marker of disease severity. PImax was a significant (hazard ratio: 0.925; 95% confidence interval: 0.879-0.975; chi(2): 8.62) marker of adverse outcome, independent of BBL-status or aetiology. Percentage of predicted PImax was not independent of PImax. The cutoff identified through receiver-operated characteristics for 1-year mortality was 4.14 kPa for patients on BBL and 7.29 kPa for patients not on BBL. When separated accordingly, 1-year mortality was 8.5 versus 21.4%, P=0.02, for patients not on BBL and 4.3 versus 16.2%, P<0.001, for patients on BBL.
CONCLUSION: This study fills the gap between trials targeting respiratory muscle on a functional basis and the resultant prognostic information with regard to BBL. BBL lowered the optimal PImax cutoff values for risk stratification without changing the measured values of PImax. This should be considered at inclusion and evaluation of trials and interpretation of exercise parameters.