The double anaerobic threshold in heart failure: MECKI score database overview

In heart failure (HF), anaerobic threshold (AT) may be indeterminable but its value held a relevant prognostic role. AT is evaluated joining three methods: V-slope, ventilatory equivalent, and end-tidal methods. The possible non-concordance between the V-slope (met AT) and the other two methods (vent AT) has been highlighted in healthy individuals and named double threshold (DT).

We reanalysed 1075 cardiopulmonary exercise tests of HF patients recruited in the Metabolic Exercise test data combined with Cardiac and Kidney Indexes (MECKI) score database. We identified DT in 43% of cases. Met AT precedes vent AT being met-ventΔVO₂ 221 (interquartile range: 129-319) mL/min. Peak VO₂ , 1307 ± 485 vs. 1343 ± 446 mL/min (63 ± 17 vs. 63 ± 17 percentage of predicted), was similar between DT+ and DT- patients. Differently, DT+ showed a lower ventilatory vs. carbon dioxide production (VE/VCO₂ ) slope (29.6 ± 6.1 vs. 31.0 ± 6.3), a lower peak exercise end-tidal oxygen tension (PetO₂ ) 115.3 (111.5-118.9) vs. 116.4 (112.4-120.2) mmHg, and a higher carbon dioxide tension (PetCO₂ ) 34.2 (30.9-37.1) vs. 32.4 (28.7-35.5) mmHg. Vent AT showed a significant higher VO₂ , 957 ± 318 vs. 719 ± 252 mL/min, VCO₂ , 939 ± 319 vs. 627 ± 226 mL/min, ventilation, 31.0 ± 8.3 vs. 22.5 ± 6.3 L/min, respiratory exchange ratio, 0.98 ± 0.08 vs. 0.87 ± 0.07, PetO₂ , 108 (104-112) vs. 105 (101-109) mmHg, PetCO₂ , 37 (34-40) vs. 36 (33-39) mmHg, and VE/VO₂ ratio, 33.5 ± 6.7 vs. 32.6 ± 6.9, but lower VE/VCO₂ ratio, 33 (30-37) vs. 36 (32-41), compared with met AT. At 2 year survival by Kaplan-Meier analysis, even adjusted for confounders, DT resulted not associated with survival.

Double threshold is frequently observed in HF patients. DT+ is associated to a decreased ventilatory response during exercise.