ABC | Volume 114, Nº2, February 2020

Original Article Gonçalves et al. Prediction of CPET in HF patients with AF Arq Bras Cardiol. 2020; 114(2):209-218 In regard to SR patients, the lower risks associated are responsible for a lower value of PPV above the pVO 2 cutoff. The PPV was raised from 38,5% to 75% when the analysis excluded patients not doing BB. The NPV remains high in this group (94,3%). During exercise, both CO 2 output and ventilation increase steadily, but in patients with HF, the slope of the relationship is increased. 31 Previous studies have confirmed the prognostic impact of VE/VCO 2 in patients with HF, with higher values being associated with worse outcomes. 32-35 However, the value of VE/VCO 2 in AF patients with HF is not so well established, with differences in results in some trials. 36,37 In our study, with a VE/VCO 2 slope > 35, lower values of PPV were reported (33.3% and 29.8% for AF and SR groups, respectively), with similar NPV compared to pVO 2 results (92.3% and 98.3% for AF and SR groups, respectively, figure 1). The power to predict the primary outcome by the VE/VCO 2 slope, revealed an AUC of 0.906 for the SR group (the highest of all the CPET parameters analysed) and 0.844 in the AF group, with no statistically significant difference found when comparing the different AUC values of the CPET parameters. These differences in PPV may suggest that despite the fact that VE/VCO 2 slope could be at least as good for prognostic assessment in HF patients as pVO 2 , the cut-off to use with the VE/VCO 2 slope is not so well established as the cut-off for pVO 2 in AF patients. One previous study has shown that in a multivariate Cox analysis, pVO 2 was identified as a sole significant predictor of cardiac events in HF patients in SR and the VE/VCO 2 slope in AF patients. 38 Our results, however, do not concur with the previous results. In fact, our multivariate Cox analysis (Table 5) showed that when pVO 2 and the VE/VCO 2 slope are analysed together, pVO 2 lost its predictive power (p = 0.280) while the VE/VCO 2 slope remained predictive of the primary outcome (p = 0.001) in the SR group. In the AF group, the VE/VCO 2 slope lost its predictive power (p = 0.398) while pVO 2 showed a trend for the prediction of the primary outcome (p = 0.091). Figure 1 – Positive (PPV) and negative predictive value (NPV) of pVO 2 and VE/VCO 2 slope. The predicted pVO 2 (%) has been demonstrated as a useful prognostic marker in previous HF studies. 39 In the multivariate Cox analysis of predicted pVO 2 (%) and the VE/VCO 2 slope, predicted pVO 2 (%) kept his predictive power in the SR group (p = 0.006) in contrast to pVO 2 , while in the AF group, it showed a trend towards prediction of the primary outcome (p = 0.094) and had the highest AUC predictive value (0.878). OUES is derived by plotting VO 2 as a function of log10VE, which is an approximately linear relation, indicating how effectively O 2 is extracted and taken into the body. 40 In HF patients, OUES is reduced in proportion to disease severity and linked to outcome. 41,42 In our population, OUES had the numerically lower AUC for predicting the primary outcome in both AF and SR groups and lost its predictive power in the multivariate Cox analysis when compared with pVO 2 and when compared with the VE/VCO 2 slope, which is in accordance with other previous study. 43 Study limitations There are limitations to our study that should be referenced. Even though data was obtained from the outpatient clinic visits, medical charts were reviewed and complemented with a standardized telephone interview to all patients at 12 months of follow-up to collect data for the primary and secondary outcomes. Information pertaining to the selection or not of rhythm control for the treatment of AF was not gathered. Despite this, the goal of the trial was to define, during the initial evaluation, which patients needed early indication for HT or mechanical circulatory support, reducing the importance of the aforementioned information. Despite being a seven-year follow-up of patients evaluated for HT in one advanced HF centre, the analysed cohort was not larger than other studies of the relation between HF and AF. 2,36,38 However, the sample size is similar to other studies that highlighted the value of CPET parameters, including for the selection of patients for HT. 8,32,35,44,45 Since patients were referred for a tertiary hospital for the purpose of evaluation with HF team and possible indication 215