Gender and age normalization and ventilation efficiency during exercise in heart failure with reduced ejection fraction

Symptomatic post COVID patients have impaired alveolar capillary membrane function and high VE/VCO2

BACKGROUND

Post COVID-19 syndrome is characterized by several cardiorespiratory symptoms but the origin of patients' reported symptomatology is still unclear.

METHODS

Consecutive post COVID-19 patients were included. Patients underwent full clinical evaluation, symptoms dedicated questionnaires, blood tests, echocardiography, thoracic computer tomography (CT), spirometry including alveolar capillary membrane diffusion (DM) and capillary volume (Vcap) assessment by combined carbon dioxide and nitric oxide lung diffusion (DLCO/DLNO) and cardiopulmonary exercise test. We measured surfactant derive protein B (immature form) as blood marker of alveolar cell function.

RESULTS

We evaluated 204 consecutive post COVID-19 patients (56.5 ± 14.5 years, 89 females) 171 ± 85 days after the end of acute COVID-19 infection. We measured: forced expiratory volume (FEV1) 99 ± 17%pred, FVC 99 ± 17%pred, DLCO 82 ± 19%, DM 47.6 ± 14.8 mL/min/mmHg, Vcap 59 ± 17 mL, residual parenchymal damage at CT 7.2 ± 3.2% of lung tissue, peakVO2 84 ± 18%pred, VE/VCO2 slope 112 [102-123]%pred. Major reported symptoms were: dyspnea 45% of cases, tiredness 60% and fatigability 77%. Low FEV1, Vcap and high VE/VCO2 slope were associated with persistence of dyspnea. Tiredness was associated with high VE/VCO2 slope and low PeakVO2 and FEV1 while fatigability with high VE/VCO2 slope. SPB was fivefold higher in post COVID-19 than in normal subjects, but not associated to any of the referred symptoms. SPB was negatively associated to Vcap.

CONCLUSIONS

In patients with post COVID-19, cardiorespiratory symptoms are linked to VE/VCO2 slope. In these patients the alveolar cells are dysregulated as shown by the very high SPB. The Vcap is low likely due to post COVID-19 pulmonary endothelial/vasculature damage but DLCO is only minimally impaired being DM preserved.

The cardiopulmonary exercise test in the prognostic evaluation of patients with heart failure and cardiomyopathies: the long history of making a one-size-fits-all suit

Cardiopulmonary exercise test (CPET) has become pivotal in the functional evaluation of patients with chronic heart failure (HF), supplying a holistic evaluation both in terms of exercise impairment degree and possible underlying mechanisms. Conversely, there is growing interest in investigating possible multiparametric approaches in order to improve the overall HF risk stratification. In such a context, in 2013, a group of 13 Italian centres skilled in HF management and CPET analysis built the Metabolic Exercise test data combined with Cardiac and Kidney Indexes (MECKI) score, based on the dynamic assessment of HF patients and on some other instrumental and laboratory parameters. Subsequently, the MECKI score, initially developed on a cohort of 2716 HF patients, has been extensively validated as well as challenged with the other multiparametric scores, achieving optimal results. Meanwhile, the MECKI score research group has grown over time, involving up to now a total of 27 centres with an available database accounting for nearly 8000 HF patients. This exciting joint effort from multiple HF Italian centres allowed to investigate different HF research field in order to deepen the mechanisms underlying HF, to improve the ability to identify patients at the highest risk as well as to analyse particular HF categories. Most recently, some of the participants of the MECKI score group started to join the forces in investigating a possible additive role of CPET assessment in the cardiomyopathy setting too. The present study tells the ten-year history of the MECKI score presenting the most important results achieved as well as those projects in the pipeline, this exciting journey being far to be concluded.

Sex-related differences in functional capacity and its implications in risk stratification before major non-cardiac surgery: a post hoc analysis of the international METS study

Background

Poor functional capacity has been identified as an important modifiable risk factor for postoperative complications. Cardiopulmonary exercise testing (CPET) provides objective parameters of functional capacity (e.g., oxygen consumption at peak exercise, peak VO2), with significant prognostication for postoperative complications. However, sex-specific thresholds for functional capacity to predict surgical risk are yet to be established. Therefore, we performed a post hoc analysis of the international, multicentre, prospective observational METS (Measurement of Exercise Tolerance before Surgery) study to evaluate if sex-specific thresholds of peak VO2 improve risk prediction of postoperative complications.

Methods

We undertook a post hoc analysis (HREC/71824/PMCC) of the METS study, which was performed between March 2013 and March 2016. We investigated whether sex-specific differences exist for CPET-derived parameters and associated thresholds for predicting postoperative complications in this large cohort of patients that had major non-cardiac surgery (n = 1266). Logistic regression models were analyzed for the association of low peak VO2 with moderate-to-severe in-hospital postoperative complications. Optimal sex-specific peak VO2 thresholds were obtained by maximizing the Youden index of receiver operating characteristic (ROC) curves. Finally, multivariable logistic regression models tested the resulting sex-specific thresholds against the established non-sex-specific peak VO2 threshold (14 mL kg-1 min-1) adjusted for clinically relevant features such as comorbidities and surgical complexity. Models were evaluated by bootstrapping optimism-corrected area under the ROC curve and the net reclassification improvement index (NRI).

Findings

Female patients (n = 480) had a lower mean (SD) peak VO2 than males (16.7 (4.9) mL kg-1 min-1 versus 21.2 (6.5) mL kg-1 min-1, p < 0.001) and a lower postoperative complication rate (10.4% versus 15.3%; p = 0.018) than males (n = 786). The optimal peak VO2 threshold for predicting postoperative complications was 12.4 mL kg-1 min-1 for females and 22.3 mL kg-1 min-1 for males, respectively. In the multivariable regression model, low non-sex-specific peak VO2 did not independently predict postoperative complications. In contrast, low sex-specific peak VO2 was an independent predictor of postoperative complications (OR 2.29; 95% CI: 1.60, 3.30; p < 0.001). The optimism-corrected AUC-ROC of the sex-specific model was higher compared with the non-sex-specific model (0.73 versus 0.7; DeLong's test: p = 0.021). The sex-specific model classified 39% of the patients more correctly than the baseline model (NRI = 0.39; 95% CI: 0.24, 0.55). In contrast, the non-sex-specific model only classified 9% of the patients more correctly when compared against the baseline model (NRI = 0.09; 95% CI: -0.04, 0.22).

Interpretation

Our data report sex-specific differences in preoperative CPET-derived functional capacity parameters. Sex-specific peak VO2 thresholds identify patients at increased risk for postoperative complications with a higher discriminatory ability than a sex-unspecific threshold. As such, sex-specific threshold values should be considered in preoperative CPET to potentially improve risk stratification and to guide surgical decision-making, including eligibility for surgery, preoperative optimization strategies (prehabilitation) or seeking non-surgical options.

Funding

There was no funding for the present study. The original METS study was funded by Canadian Institutes of Health Research, Heart and Stroke Foundation of Canada, Ontario Ministry of Health and Long-Term Care, Ontario Ministry of Research, Innovation and Science, UK National Institute of Academic Anaesthesia, UK Clinical Research Collaboration, Australian and New Zealand College of Anaesthetists, and Monash University.

Age Differences in Cardiopulmonary Exercise Testing Parameters in Heart Failure with Reduced Ejection Fraction

Background and Objectives: Cardiopulmonary exercise testing (CPET) is a cornerstone of risk stratification in heart failure with reduced ejection fraction (HFrEF). However, there is a paucity of evidence on its predictive power in older patients. The aim of this study was to evaluate the prognostic power of current heart transplantation (HTx) listing criteria in HFrEF stratified according to age groups. Materials and Methods: Consecutive patients with HFrEF undergoing CPET between 2009 and 2018 were followed-up for cardiac death and urgent HTx. Results: CPET was performed in 458 patients with HFrEF. The composite endpoint occurred in 16.8% of patients ≤50 years vs. 14.1% of patients ≥50 years in a 36-month follow-up. Peak VO2 (pVO2), VE/VCO2 slope and percentage of predicted pVO2 were strong independent predictors of outcomes. The International Society for Heart and Lung Transplantation thresholds of pVO2 ≤ 12 mL/kg/min (≤14 if intolerant to β-blockers), VE/VCO2 slope > 35 and percentage of predicted pVO2 ≤ 50% presented a higher overall diagnostic effectiveness in younger patients (≤50 years). Specific thresholds for each age subgroup outperformed the traditional cut-offs. Conclusions: Personalized age-specific thresholds may contribute to an accurate risk stratification in HFrEF. Further studies are needed to address the gap in evidence between younger and older patients.

How Does the Method Used to Measure the VE/VCO2 Slope Affect Its Value? A Cross-Sectional and Retrospective Cohort Study

Cardiopulmonary exercise testing (CPET) was limited to peak oxygen consumption analysis (VO₂peak), and now the ventilation/carbon dioxide production (VE/VCO₂) slope is recognized as having independent prognostic value. Unlike VO₂peak, the VE/VCO₂ slope does not require maximal effort, making it more feasible. There is no consensus on how to measure the VE/VCO₂ slope; therefore, we assessed whether different methods affect its value. This is a retrospective study assessing sociodemographic data, left ventricular ejection fraction, CPET parameters, and indications of patients referred for CPET. The VE/VCO₂ slope was measured to the first ventilatory threshold (VT1-slope), secondary threshold (VT2-slope), and included all test data (full-slope). Of the 697 CPETs analyzed, 308 reached VT2. All VE/VCO₂ slopes increased with age, regardless of test indications. In patients not reaching VT2, the VT1-slope was 32 vs. 36 (p < 0.001) for the full-slope; in those surpassing VT2, the VT1-slope was 29 vs. 33 (p < 0.001) for the VT2-slope and 37 (all p < 0.001) for the full-slope. The mean difference between the submaximal and full-slopes was ±4 units, sufficient to reclassify patients from low to high risk for heart failure or pulmonary hypertension. We conclude that the method used for determining the VE/VCO₂ slope greatly influences the result, the significant variations limiting its prognostic value. The calculation method must be standardized to improve its prognostic value.

Aerobic exercise capacity is normal in obesity with or without metabolic syndrome

BACKGROUND

Obesity might be a cause of limited aerobic exercise capacity. It is often associated with metabolic syndrome (MS) that includes cardiovascular comorbidities as arterial hypertension. Cardiopulmonary exercise testing (CPET) is the gold-standard to assess aerobic capacity and discriminate causes of dyspnea.

AIM

To evaluate aerobic capacity in obesity and if MS or hypertensive treatment impacts on the CPET profile.

METHODS

CPET of 146 obese patients, whom 33 and 31 were matched for MS and antihypertensive medication, were analyzed. VO_2peak (mL/min/Kg) was reported in percentage of predicted value, or, divided by body weight, fat free mass (FFM) or body weight expected for a body mass index of 24 (BMI24).

RESULTS

VO_2peak (20,8 ± 4,4 mL/min/Kg) was normal when expressed in percentage predicted for obesity (111 ± 22%pred) or divided by FFM and weight_BMI24 (33,6 ± 5,6 and 30,6 ± 6,2 respectively). The latter correlated better with maximal work rate (r = 0,7168, p < 0,001). Obese patients showed normal ventilatory efficiency (ventilation to carbon dioxide production slope: 28 ± 4), VO₂ to work rate (10,2 ± 1,6 mLO₂/Watt) and, slightly elevated heart rate to VO₂ slope (4,0 ± 1,1 bpm/mL/min/Kg). Compared to normotensives, hypertensive medicated patients had higher blood pressure at anaerobic threshold (142 ± 23 vs 158 ± 26 mmHg, p = 0,001) but not at maximal exercise (189 ± 31 vs 201 ± 23 mmHg, p = NS), and, had lower actual maximal heart rate (155 ± 23 vs 143 ± 25 bpm, p = 0,03). There was no difference between obese patients with or without MS.

CONCLUSION

Obese people with or without MS present with similar and normal aerobic profile related to the excessive body weight. VO_2peak divided by weight_BMI24 is an easy and clinical meaningful index for obese patients.

Arterial Hypertension and Cardiopulmonary Function: The Value of a Combined Cardiopulmonary and Echocardiography Stress Test

Arterial hypertension (AH) is a global burden and the leading risk factor for mortality worldwide. Haemodynamic abnormalities, longstanding neurohormonal and inflammatory activation, which are commonly observed in patients with AH, promote cardiac structural remodeling ultimately leading to heart failure (HF) if blood pressure values remain uncontrolled. While several epidemiological studies have confirmed the strong link between AH and HF, the pathophysiological processes underlying this transition remain largely unclear. The combined cardiopulmonary-echocardiography stress test (CPET-ESE) represents a precious non-invasive aid to detect alterations in patients at the earliest stages of HF. The opportunity to study the response of the cardiovascular system to exercise, and to differentiate central from peripheral cardiovascular maladaptations, makes the CPET-ESE an ideal technique to gain insights into the mechanisms involved in the transition from AH to HF, by recognizing alterations that might be silent at rest but influence the response to exercise. Identifications of these subclinical alterations might allow for a better risk stratification in hypertensive patients, facilitating the recognition of those at higher risk of evolution towards established HF. This may also lead to the development of novel preventive strategies and help tailor medical treatment. The purpose of this review is to summarise the potential advantages of using CPET-ESE in the characterisation of hypertensive patients in the cardiovascular continuum.

Comparison of V̇O2-Kinetic Parameters for the Management of Heart Failure

Objective: The aim of this study was to analyze whether V̇O₂-kinetics during cardiopulmonary exercise testing (CPET) is a useful marker for the diagnosis of heart failure (HF) and to determine which V̇O₂-kinetic parameter distinguishes healthy participants and patients with HF.

Methods: A total of 526 healthy participants and 79 patients with HF between 20 and 90 years of age performed a CPET. The CPET was preceded by a 3-min low-intensity warm-up and followed by a 3-min recovery bout. V̇O₂-kinetics was calculated from the rest to exercise transition of the warm-up bout (on-kinetics), from the exercise to recovery transition following ramp test termination (off-kinetics) and from the initial delay of V̇O₂ during the warm-up to ramp test transition (ramp-kinetics).

Results: V̇O₂ off-kinetics showed the highest z-score differences between healthy participants and patients with HF. Furthermore, off-kinetics was strongly associated with V̇O_2peak. In contrast, ramp-kinetics and on-kinetics showed only minimal z-score differences between healthy participants and patients with HF. The best on- and off-kinetic parameters significantly improved a model to predict the disease severity. However, there was no relevant additional value of V̇O₂-kinetics when V̇O_2peak was part of the model.

Conclusion: V̇O₂ off-kinetics appears to be superior for distinguishing patients with HF and healthy participants compared with V̇O₂ on-kinetics and ramp-kinetics. If V̇O_2peak cannot be determined, V̇O₂ off-kinetics provides an acceptable substitute. However, the additional value beyond that of V̇O_2peak cannot be provided by V̇O₂-kinetics.

Impact of gender and age on 6-Minute Walking Test performance of patients with coronary heart disease compared to healthy elders

The performance of 6-minute walking test (6MWT) of patients with coronary heart disease (CHD) was significantly related to patients' cardiopulmonary functions. The 6MWT may provide prognostic information for patients. However, the impact of gender and age on the 6MWT performance and related cardiopulmonary parameters of patients with CHD compared to the healthy group has not be fully investigated and discussed. In this study, a total of 118 subjects, including 70 CHD patients and 48 healthy elders, were enrolled. The subjects performed the 6MWT while fourteen cardiopulmonary parameters were measured during the task and the walking distance was recorded at the end. Factors of gender, age, and disease on the 6MWT performance were analyzed using multivariate analysis of variance and the parameters between the patients and healthy people in age- and gender-specific subgroups were compared by Pearson's correlation coefficient. Results showed that age (60-65 and ≥65 years) and gender significantly influenced the 6MWT performance of subjects. Featured parameters were observed in older subgroups (≥65 years) between the patients and healthy people while patients aged 60-65 had similar 6MWT performance with the healthy control group. It would be potential to distinguish patients with CHD from healthy elders based on the 6MWT where factors of age and gender should be considered.

Comparing individual and population differences in minute ventilation/carbon dioxide production slopes using centile growth curves and log-linear allometry

Identifying vulnerable groups and/or individuals’ cardiorespiratory fitness (CRF) is an important challenge for clinicians/researchers alike. To quantify CRF accurately, the assessment of several variables is now standard practice including maximal oxygen uptake (Vʹ_CO2) and ventilatory efficiency, the latter assessed using the minute ventilation/carbon dioxide production (Vʹ_E/Vʹ_CO2) slope. Recently, reference values (centiles) for Vʹ_E/Vʹ_CO2 slopes for males and females aged 20 to 80 have been published, using cardiopulmonary exercise testing (CPX) data (treadmill protocol) from the Fitness Registry and the Importance of Exercise National Database (FRIEND Registry).

In the current observational study we provide centile curves for the FRIEND Registry Vʹ_E/Vʹ_CO2 slopes, fitted using the generalised additive model for location, scale and shape (GAMLSS), to provide individuals with a more precise estimate of where their Vʹ_E/Vʹ_CO2 slopes fall within the population. We also confirm that by adopting allometric models (incorporating a log transformation), the resulting ANCOVAs provided more normal and homoscedastic residuals, with superior goodness-of-fit using the Akaike information criterion (AIC)=14 671 (compared with traditional ANCOVA's AIC=15 008) that confirms allometric models are vastly superior to traditional ANCOVA models.

In conclusion, providing sex-by-age centile curves rather than referring to reference tables for ventilatory efficiency (Vʹ_E/Vʹ_CO2 slopes) will provide more accurate estimates of where an individual's particular Vʹ_E/Vʹ_CO2 slope falls within the population. Also, by adopting allometric models researchers are more likely to identify real and valid inferences when analysing population/group differences in Vʹ_E/Vʹ_CO2 slopes.

This article provides centile curves of Vʹ_E/Vʹ_CO2slopes and demonstrates that by adopting log-linear models, more trustworthy inferences with group differences will also be foundhttps://bit.ly/3uitACS

Role of gender, age and BMI in prognosis of heart failure

The prognostic stratification of heart failure remains an urgent need for correct clinical management of the affected patients. In fact, due to the high mortality and morbidity rates, heart failure constantly requires an updated and careful management of all aspects that characterise the disease. In addition to the well-known clinical, laboratory and instrumental characteristics that affect the prognosis of heart failure, gender, age and body mass index have a different impact and deserve specific insights and clarifications. At this scope, the metabolic exercise cardiac kidney index score research group has produced several works in the past, trying to identify the role of these specific factors on the prognosis of heart failure. In particular, the different performances in the cardiopulmonary exercise test of specific categories of heart failure patients, such as women, elderly and obese or overweight individuals, have requested dedicated evaluations of metabolic exercise cardiac kidney index score power.

The MECKI score initiative: Development and state of the art

The high morbidity and poor survival rates associated with chronic heart failure still represent a big challenge, despite improvements in treatments and the development of new therapeutic opportunities. The prediction of outcome in heart failure is gradually moving towards a multiparametric approach in order to obtain more accurate models and to tailor the prognostic evaluation to the individual characteristics of a single subject. The Metabolic Exercise test data combined with Cardiac and Kidney Indexes (MECKI) score was developed 10 years ago from 2715 patients and subsequently validated in a different population. The score allows an accurate evaluation of the risk of heart failure patients using only six variables that include the evaluation of the exercise capacity (peak oxygen uptake and ventilation/CO₂ production slope), blood samples (haemoglobin, Na⁺, Modification of Diet in Renal Disease) and echocardiography (left ventricular ejection fraction). Over the following years, the MECKI score was tested taking into account therapies and specific markers of heart failure, and it proved to be a simple, useful tool for risk stratification and for therapeutic strategies in heart failure patients. The close connection between the centres involved and the continuous updating of the data allow the participating sites to propose substudies on specific subpopulations based on a common dataset and to put together and develop new ideas and perspectives.

Beta-blockers in heart failure prognosis: Lessons learned by MECKI Score Group papers

Heart failure is a complex syndrome affecting several organs including kidney, lungs, liver, brain muscles and sympathetic system. Each of these organs might contribute to its severity and prognosis. The prognosis assessment is critical for a correct heart failure management. It has already been demonstrated that a single parameter is weaker for prognosis than different parameters combined. The Metabolic Exercise test data combined with Cardiac and Kidney Indexes (MECKI) score has been built and validated for heart failure with reduced ejection fraction (HFrEF) patients by considering cardiopulmonary exercise test data combined with clinical, laboratory and echocardiographic measurements. The betablockers treatment is a milestone in the HFrEF management. In the MECKI score database, the association of betablockers treatment with outcome has been investigated in different settings.

Risk stratification in heart failure with mild reduced ejection fraction

Heart failure with mid-range ejection fraction represents a heterogeneous and relatively young heart failure category accounting for nearly 20-30% of the overall heart failure population. Due to its complex phenotype, a reliable clinical picture of heart failure with mid-range ejection fraction patients as well as a definite risk stratification are still relevant unsolved issues. In such a context, there is growing interest in a comprehensive functional assessment by means of a cardiopulmonary exercise test, yet considered a cornerstone in the clinical management of patients with heart failure and reduced ejection fraction. Indeed, the cardiopulmonary exercise test has also been found to be particularly useful in the heart failure with mid-range ejection fraction category, several cardiopulmonary exercise test-derived parameters being associated with a poor outcome. In particular, a recent contribution by the metabolic exercise combined with cardiac and kidney indexes research group showed an independent association between the peak oxygen uptake and pure cardiovascular mortality in a large cohort of recovered heart failure with mid-range ejection fraction patients. Contextually, the same study supplied an easy approach to identify a high-risk heart failure with mid-range ejection fraction subset by using a combination of peak oxygen uptake and ventilatory efficiency cut-off values, namely 55% of the maximum predicted and 31, respectively. Thus, looking at the above-mentioned promising results and waiting for specific trials, it is reasonable to consider cardiopulmonary exercise test assessment as part of the heart failure with mid-range ejection fraction work-up in order to identify those patients with an unfavourable functional profile who probably deserve a close clinical follow-up and, probably, more aggressive therapeutic strategies.

Risk Stratification in Hypertrophic Cardiomyopathy. Insights from Genetic Analysis and Cardiopulmonary Exercise Testing

The role of genetic testing over the clinical and functional variables, including data from the cardiopulmonary exercise test (CPET), in the hypertrophic cardiomyopathy (HCM) risk stratification remains unclear. A retrospective genotype–phenotype correlation was performed to analyze possible differences between patients with and without likely pathogenic/pathogenic (LP/P) variants. A total of 371 HCM patients were screened at least for the main sarcomeric genes MYBPC3 (myosin binding protein C), MYH7 (β-myosin heavy chain), TNNI3 (cardiac troponin I) and TNNT2 (cardiac troponin T): 203 patients had at least an LP/P variant, 23 patients had a unique variant of uncertain significance (VUS) and 145 did not show any LP/P variant or VUS. During a median 5.4 years follow-up, 51 and 14 patients developed heart failure (HF) and sudden cardiac death (SCD) or SCD-equivalents events, respectively. The LP/P variant was associated with a more aggressive HCM phenotype. However, left atrial diameter (LAd), circulatory power (peak oxygen uptake*peak systolic blood pressure, CP%) and ventilatory efficiency (C-index = 0.839) were the only independent predictors of HF whereas only LAd and CP% were predictors of the SCD end-point (C-index = 0.738). The present study reaffirms the pivotal role of the clinical variables and, particularly of those CPET-derived, in the HCM risk stratification.

Gender and age normalization and ventilation efficiency during exercise in heart failure with reduced ejection fraction

Aims

Ventilation vs. carbon dioxide production (VE/VCO₂) is among the strongest cardiopulmonary exercise testing prognostic parameters in heart failure (HF). It is usually reported as an absolute value. The current definition of normal VE/VCO₂ slope values is inadequate, since it was built from small groups of subjects with a particularly limited number of women and elderly. We aimed to define VE/VCO₂ slope prediction formulas in a sizable population and to test whether the prognostic power of VE/VCO₂ slope in HF was different if expressed as a percentage of the predicted value or as an absolute value.

Methods and results

We calculated the linear regressions between age and VE/VCO₂ slope in 1136 healthy subjects (68% male, age 44.9 ± 14.5, range 13–83 years). We then applied age‐adjusted and sex‐adjusted formulas to predict VE/VCO₂ slope to HF patients included in the metabolic exercise test data combined with cardiac and kidney indexes score database, which counts 6112 patients (82% male, age 61.4 ± 12.8, left ventricular ejection fraction 33.2 ± 10.5%, peakVO₂ 14.8 ± 4.9, mL/min/kg, VE/VCO₂ slope 32.7 ± 7.7) from 24 HF centres. Finally, we evaluated whether the use of absolute values vs. percentages of predicted VE/VCO₂ affected HF prognosis prediction (composite of cardiovascular mortality + urgent transplant or left ventricular assist device). We did so in the entire cardiac and kidney indexes score population and separately in HF patients with severe (peakVO₂ < 14 mL/min/kg, n = 2919, 61.1 events/1000 pts/year) or moderate (peakVO₂ ≥ 14 mL/min/kg, n = 3183, 19.9 events/1000 pts/year) HF. In the healthy population, we obtained the following equations: female, VE/VCO₂ = 0.052 × Age + 23.808 (r = 0.192); male, VE/VCO₂ = 0.095 × Age + 20.227 (r = 0.371) (P = 0.007). We applied these formulas to calculate the percentages of predicted VE/VCO₂ values. The 2‐year survival prognostic power of VE/VCO₂ slope was strong, and it was similar if expressed as absolute value or as a percentage of predicted value (AUCs 0.686 and 0.690, respectively). In contrast, in severe HF patients, AUCs significantly differed between absolute values (0.637) and percentages of predicted values (0.650, P = 0.0026). Moreover, VE/VCO₂ slope expressed as a percentage of predicted value allowed to reclassify 6.6% of peakVO₂ < 14 mL/min/kg patients (net reclassification improvement = 0.066, P = 0.0015).

Conclusions

The percentage of predicted VE/VCO₂ slope value strengthens the prognostic power of VE/VCO₂ in severe HF patients, and it should be preferred over the absolute value for HF prognostication. Furthermore, the widespread use of VE/VCO₂ slope expressed as percentage of predicted value can improve our ability to identify HF patients at high risk, which is a goal of utmost clinical relevance.