The double anaerobic threshold in heart failure

Background: Cardiopulmonary exercise test (CPET) has an important role in assessing heart failure (HF) patients. Among CPET parameters, a pivotal role is attributed to the anaerobic threshold (AT), normally determined by V-slope, ventilatory equivalent and end-tidal methods. In about 10% of healthy subjects, a lack of concordance between these methods has been reported. This event was named double AT (DT). We hypothesized that DT was due to a delay in chemoreflex response.

Methods: We reanalyzed CPET data of two cross-over studies in which we compared CPET in stable HF patients treated for two months with bisoprolol and carvedilol. In chronic HF, carvedilol has a greater sympathetic inhibition than bisoprolol, as shown by a lower chemoreflex response.

Results: In 87 patients, we identified DT in 46% and 66% of cases during bisoprolol and carvedilol treatment, respectively (p < 0.01). Compared with bisoprolol, carvedilol treatment was associated to a lower peak oxygen uptake (from 17.4 ± 4.3 to 16.4 ± 4.1 mL/min/kg) and oxygen pulse (from 11.8 ± 2.9 to 11.1 ± 2.9 mL/min/kg) suggestive of lower peak cardiac output.

Conclusions: DT is frequent in HF and more often with carvedilol than bisoprolol treatment, may be due to a greater inhibition of sympathetic tone and prolonged circulatory time. These findings open an unexplored research field.