Abnormally high exertional breathlessness predicts mortality in people referred for incremental cycle exercise testing

BackgroundExertional breathlessness is a key symptom in cardiorespiratory disease and can be quantified using incremental exercise testing (IET), but its prognostic significance is unknown. Research questionWe evaluated the ability of abnormally high breathlessness intensity during IET to predict all-cause, respiratory, and cardiac mortality. Study Design and MethodsLongitudinal cohort study of adults referred for cycle IET followed prospectively for mortality assessed using the Swedish National Causes of Death Registry. Abnormally high exertional breathlessness was defined as a breathlessness intensity response (Borg 0-10 scale) > the upper limit of normal (ULN) using published reference equations. Mortality was analyzed using multivariable Cox regression, unadjusted and adjusted for age, sex, and body mass index. ResultsOf the 13,506 people included (46% female, age 59{+/-}15 years), 2,867 (21%) had abnormally high breathlessness during IET. Over a median follow up of 8.0 years, 1,687 (12%) people died. No participant was lost to follow-up. Compared to those within normal predicted ranges, people with abnormally high exertional breathlessness had higher mortality from all causes (adjusted hazard ratio [aHR] 2.3, [95% confidence interval] 2.1-2.6), respiratory causes (aHR 5.2 [3.4-8.0]) and cardiac causes (aHR 3.0 [2.5-3.6]). Even among people with normal exercise capacity (defined as peak Watt [≥]75% of predicted exercise capacity, n=10,284) those with abnormally high exertional breathlessness were at greater risk of all-cause mortality than people with exertional breathlessness within the normal predicted range (aHR 1.5 [1.2-1.8]). InterpretationAmong people referred for cycle IET, abnormally high exertional breathlessness, quantified using healthy reference values, independently predicted all-cause, respiratory and cardiac mortality.