Use of assumed versus measured oxygen consumption for the determination of cardiac output using the Fick principle

Assumed oxygen consumption (VO₂) is increasingly used as a convenient surrogate for measured VO₂ for calculation of cardiac output. This substitution is often based on empirical formulae, previously validated only in relatively young patients. To assess the inaccuracy introduced by extrapolating these formulae to older patients, we compared measured VO₂ with assumed VO₂ in 57 patients. VO₂ was measured using an open circuit analyzer. Assumed VO₂ was calculated according to the LaFarge or Bergstra formulae. Agreement between both methods was assessed according to the method of Bland and Altman. The mean difference of measured VO₂ minus assumed VO₂ was 7.9 ml/min/m² (P < 0.02) using the LaFarge formula, and −15.6 ml/min/m² (P < 0.0002) using the Bergstra formula across a range of measured VO₂ from 70 to 176 ml/min/m². A systematic error was introduced by assumed VO₂ from both formulae of underestimating higher and overestimating lower values of VO₂, resulting in poor overall agreement with measured VO₂. The same error and poor agreement was found when analyzing subgroups of patients ≥60 or <70 years of age. In summary, use of assumed VO₂ introduces large, unpredictable errors in adult patients, suggesting requirement for measurement of VO₂ when calculating cardiac output. Cathet. Cardiovasc. Diagn. 43:372–380, 1998. © 1998 Wiley-Liss, Inc.     

Baixa Concordância entre a Classificação da NYHA e as Variáveis do Teste de Exercício Cardiopulmonar em Pacientes com Insuficiência Cardíaca e Fração de Ejeção Reduzida

BackgroundThe New York Heart Association (NYHA) functional classification is the most commonly used classification system for heart failure (HF), whereas cardiopulmonary exercise testing (CPET) is the gold standard for functional status evaluation in HF.ObjectiveThis study aimed to analyze correlation and concordance between NYHA classes and CPET variables.MethodsHF patients with clinical indication for CPET and ejection fraction (EF) < 50% were selected. Correlation (Spearman coefficient) and concordance (kappa) between NYHA classification and CPET-based classifications were analyzed. A p < 0.05 was accepted as significant.ResultsIn total, 244 patients were included. Mean age was 56 ± 14 years, and mean EF was 35.5% ± 10%. Distribution of patients according to NYHA classification was 31.2%% class I, 48.3% class II, 19.2% class III, and 1.3% class IV. Correlation (r) between NYHA and Weber classes was 0.489 (p < 0.001), and concordance was 0.231 (p < 0.001). Correlation (r) between NYHA and ventilatory classes (minute ventilation/carbon dioxide production [VE/VCO₂] slope) was 0.218 (p < 0.001), and concordance was 0.002 (p = 0.959). Spearman correlation between NYHA and CPET score classes was 0.223 (p = 0.004), and kappa concordance was 0.027 (p = 0.606).ConclusionThere was a moderate association between NYHA and Weber classes, although concordance was low. Ventilatory (VE/VCO₂slope) and CPET score classes had a weak association and a low concordance with NYHA classes.     

Association of functional and health status measures in heart failure

BackgroundA wide variety of instruments have been used to assess the functional capabilities and health status of patients with chronic heart failure (HF), but it is not known how well these tests are correlated with one another, nor which one has the best association with measured exercise capacity.Methods and ResultsForty-one patients with HF were assessed with commonly used functional, health status, and quality of life measures, including maximal cardiopulmonary exercise testing, the Duke Activity Status Index (DASI), the Veterans Specific Activity Questionnaire (VSAQ), the Kansas City Cardiomyopathy Questionnaire (KCCQ), and 6-minute walk distance. Pretest clinical variables, including age, resting pulmonary function tests (forced expiratory volume in 1 s and forced vital capacity), and ejection fraction (EF) were also considered. The association between performance on these functional tools, clinical variables, and exercise test responses including peak VO₂ and the VO₂ at the ventilatory threshold, was determined. Peak oxygen uptake (VO₂) was significantly related to VO₂ at the ventilatory threshold (r = 0.76, P < .001) and estimated METs from treadmill speed and grade (r = 0.72, P < .001), but had only a modest association with 6-minute walk performance (r = 0.49, P < .01). The functional questionnaires had modest associations with peak VO₂ (r = 0.37, P < .05 and r = 0.26, NS for the VSAQ and DASI, respectively). Of the components of the KCCQ, peak VO₂ was significantly related only to quality of life score (r = 0.46, P < .05). Six-minute walk performance was significantly related to KCCQ physical limitation (r = 0.53, P < .01) and clinical summary (r = 0.44, P < .05) scores. Among pretest variables, only age and EF were significantly related to peak VO₂ (r = −0.58, and 0.46, respectively, P < .01). Multivariately, age and KCCQ quality of life score were the only significant predictors of peak VO₂, accounting for 72% of the variance in peak VO₂.ConclusionCommonly used functional measures, symptom tools, and quality of life assessments for patients with HF are poorly correlated with one another and are only modestly associated with exercise test responses. These findings suggest that exercise test responses, non-exercise test estimates of physical function, and quality of life indices reflect different facets of health status in HF and one should not be considered a surrogate for another.     

Meta-analyzing the factors affecting the efficacy of gliflozins in patients with heart failure based on heart failure trials

Background:The factors affecting the efficacy of gliflozins in patients with heart failure (HF) are not clear. We aimed to evaluate the effects of 11 important factors on the efficacy of gliflozins in HF patients.Methods:Randomized trials assessing gliflozins in HF patients were included. The outcome of interest was composite HF outcome, a composite of cardiovascular death, or hospitalization for HF. Meta-analysis was done according to 11 factors: status of type 2 diabetes, sex, use of angiotensin receptor-neprilysin inhibitor, age, history of hospitalization for HF, estimated glomerular filtration rate, body mass index, New York Heart Association (NYHA) class, race, region, and left ventricular ejection fraction.Results:Compared with placebo, gliflozins reduced the risk of composite HF outcome by 14% in the subgroup of patients with NYHA class III or IV (hazard ratios [HR] 0.86, 95% confidence intervals [CI] 0.75–0.99), by 34% in the subgroup of patients with NYHA class II (HR 0.66, 95% CI 0.59–0.74), and by 85% in the subgroup of patients with NYHA class I (HR 0.15, 95% CI 0.03–0.73). This between-group difference was approximate to statistical significance (P_subgroup = .06). The benefit of gliflozins in HF patients was not affected by the other 10 factors (P_subgroup ≥ .123).Conclusions:Gliflozins are applicable for a broad population of HF patients as for preventing HF events, while gliflozins may lead to greater benefits in patients with mild HF than in those with moderate to severe HF.     

NYHA Functional Classification and Outcomes After Transcatheter Mitral Valve Repair in Heart Failure: The COAPT Trial

ObjectivesThe aim of this study was to evaluate the outcomes of MitraClip implantation versus guideline-directed medical therapy (GDMT) in patients with secondary mitral regurgitation (SMR) according to baseline functional status as assessed by the widely used New York Heart Association (NYHA) functional classification.BackgroundPatients with heart failure (HF) and impaired functional status at baseline have poor prognosis. Whether the effects of transcatheter repair of secondary SMR in patients with HF are influenced by baseline functional status is unknown.MethodsIn the COAPT (Cardiovascular Outcomes Assessment of the MitraClip Percutaneous Therapy for Heart Failure Patients with Functional Mitral Regurgitation) trial, patients with HF with moderate to severe or severe SMR who remained symptomatic despite maximally tolerated GDMT were randomized to MitraClip implantation versus GDMT alone. Outcomes were evaluated according to baseline functional status as assessed using the NYHA functional classification. The primary endpoint of interest was the rate of death or HF-related hospitalization (HFH) at 2 years in time-to-first-event analyses.ResultsAmong 613 randomized patients, 240 were in NYHA functional class II (39.2%), 322 were in NYHA functional class III (52.5%), and 51 were in ambulatory NYHA functional class IV (8.3%). Rates of death or HFH were progressively higher with increasing NYHA functional class. Compared with GDMT alone, MitraClip implantation resulted in lower 2-year rates of death or HFH consistently in patients in NYHA functional class II (39.7% vs. 63.7%; hazard ratio [HR]: 0.54; 95% confidence interval [CI]: 0.37 to 0.77), NYHA functional class III (46.6% vs. 65.5%; HR: 0.60; 95% CI: 0.45 to 0.82), and NYHA functional class IV (66.7% vs. 85.2%; HR: 0.55; 95% CI: 0.28 to 1.10; p_interaction = 0.86). Greater improvements in quality of life at 2 years were observed in patients treated with the MitraClip compared with GDMT irrespective of baseline functional status.ConclusionsThe NYHA functional classification provides prognostic utility in patients with HF and moderate to severe or severe SMR. In the COAPT trial, the benefits of MitraClip implantation were consistent in patients with better or worse functional status as assessed by NYHA functional class. (Cardiovascular Outcomes Assessment of the MitraClip Percutaneous Therapy for Heart Failure Patients With Functional Mitral Regurgitation [The COAPT Trial] [COAPT]; NCT01626079)     

Submaximal oxygen uptake kinetics, functional mobility, and physical activity in older adults with heart failure and reduced ejection fraction

Background Submaximal oxygen uptake measures are more feasible and may better predict clinical cardiac outcomes than maximal tests in older adults with heart failure (HF). We examined relationships between maximal oxygen uptake, submaximal oxygen kinetics, functional mobility, and physical activity in older adults with HF and reduced ejection fraction. Methods Older adults with HF and reduced ejection fraction (n = 25, age 75 ± 7 years) were compared to 25 healthy age- and gender-matched controls. Assessments included a maximal treadmill test for peak oxygen uptake (VO_2peak), oxygen uptake kinetics at onset of and on recovery from a submaximal treadmill test, functional mobility testing [Get Up and Go (GUG), Comfortable Gait Speed (CGS), Unipedal Stance (US)], and self-reported physical activity (PA). Results Compared to controls, HF had worse performance on GUG, CGS, and US, greater delays in submaximal oxygen uptake kinetics, and lower PA. In controls, VO_2peak was more strongly associated with functional mobility and PA than submaximal oxygen uptake kinetics. In HF patients, submaximal oxygen uptake kinetics were similarly associated with GUG and CGS as VO_2peak, but weakly associated with PA. Conclusions Based on their mobility performance, older HF patients with reduced ejection fraction are at risk for adverse functional outcomes. In this population, submaximal oxygen uptake measures may be equivalent to VO_2peak in predicting functional mobility, and in addition to being more feasible, may provide better insight into how aerobic function relates to mobility in older adults with HF.     

The Effects of Race on Peak Oxygen Consumption and Survival in Patients With Systolic Dysfunction

BackgroundThe relationship of peak exercise oxygen consumption (VO₂) to survival in black heart failure (HF) patients is not well established. We examined the effects of race on peak VO₂ values and survival in HF patients with systolic dysfunction.Methods and ResultsThis study evaluated consecutive ambulatory HF patients who underwent symptom-limited stress tests with breath-by-breath expired gas analyses using ramped treadmill protocols. The relationship between cardiopulmonary exercise parameters and patient transplant-free survival was assessed by race. This study included 580 HF patients (mean age 52 ± 12 years; 28% females; 22% blacks; mean left ventricular ejection fraction 26 ± 12%; mean body mass index 28.7 ± 5.4; 73% on β-blocker). Black patients had a significantly lower peak VO₂ than white patients (14.2 ± 5.2 versus 16.4 ± 7.0; P < .0001), despite adjusting for identified covariates. However, there was no significant difference in the 1-year transplant-free survival between black and white HF patients (87% versus 85%; P = NS). Peak VO₂ was significantly associated with survival in both racial groups.ConclusionsBlack HF patients had significantly lower peak VO₂, but yet had equivalent survival rates at 1 year. Further study is warranted to clarify the impact of these racial differences on the timing of cardiac transplantation black HF patients.     

High-intensity Interval Training Dosage for Heart Failure and Coronary Artery Disease Cardiac Rehabilitation. A Systematic Review and Meta-analysis

Introduction and objectives

High-interval intensity training (HIT) has been suggested to improve peak VO₂ in cardiac rehabilitation programs. However, the optimal HIT protocol is unknown. The objective of this study was to identify the most effective doses of HIT to optimize peak VO₂ in coronary artery disease (CAD) and heart failure (HF) patients.

Calcium Upregulation by Percutaneous Administration of Gene Therapy in Cardiac Disease (CUPID Trial), a First-in-Human Phase 1/2 Clinical Trial

BackgroundSERCA2a deficiency is commonly seen in advanced heart failure (HF). This study is designed to investigate safety and biological effects of enzyme replacement using gene transfer in patients with advanced HF.Methods and ResultsA total of 9 patients with advanced HF (New York Heart Association [NYHA] Class III/IV, ejection fraction [EF] ≤30%, maximal oxygen uptake [VO₂ max] <16 mL·kg·min, with maximal pharmacological and device therapy) received a single intracoronary infusion of AAV1/SERCA2a in the open-label portion of this ongoing study. Doses administered ranged from 1.4 × 10¹¹ to 3 × 10¹² DNase resistant particles per patient. We present 6- to 12-month follow-up data for these patients. AAV1/SERCA2a demonstrated an acceptable safety profile in this advanced HF population. Of the 9 patients treated, several demonstrated improvements from baseline to month 6 across a number of parameters important in HF, including symptomatic (NYHA and Minnesota Living with Heart Failure Questionnaire, 5 patients), functional (6-minute walk test and VO₂ max, 4 patients), biomarker (NT-ProBNP, 2 patients), and LV function/remodeling (EF and end-systolic volume, 5 patients). Of note, 2 patients who failed to improve had preexisting anti-AAV1 neutralizing antibodies.ConclusionsQuantitative evidence of biological activity across a number of parameters important for assessing HF status could be detected in several patients without preexisting neutralizing antibodies in this open-label study, although the number of patients in each cohort is too small to conduct statistical analyses. These findings support the initiation of the Phase 2 double-blind, placebo-controlled portion of this study.     

Assumed oxygen consumption based on calculation from dye dilution cardiac output: an improved formula

This study was performed because of observed differences betweendye dilution cardiac output and the Fick cardiac output, calculatedfrom estimated oxygen consumption according to LaFarge and Miettinen,and to find a better formula for assumed oxygen consumption.In 250 patients who underwent left and right heart catheterization,the oxygen consumption VO₂ (ml. min^–1) was calculatedusing Fick's principle. Either pulmonary or systemic flow, asmeasured by dye dilution, was used in combination with the concordantarteriovenous oxygen concentration difference. In 130 patients,who matched the age of the LaFarge and Miettinen population,the obtained values of oxygen consumption VO₂(dd) were comparedwith the estimated oxygen consumption values VO₂(lfm), foundusing the LaFarge and Miettinen formulae. The VO₂(lfm) was significantlylower than VO₂(dd); – 21.8 ±29.3 ml. min^–1(mean±SD),P<0.001, 95% confidence interval (95% CI) –26.9 to–16.7, limits of agreement (LA) –80.4 to 36.9. Anew regression formula for the assumed oxygen consumption VO₂(ass)was derived in 250 patients by stepwise multiple regressionanalysis. The VO₂(dd) was used as a dependent variable, andbody surface area BSA (m²), Sex (0 for female, 1 for male),Age (years), Heart rate (min^–1) and the presence of aleft to right shunt as independent variables. The best fittingformula is expressed as: VO₂(ass)=(157.3 x BSA+10.0 x Sex –10.5 x In Age+4.8) ml.min^–1, where In Age=the natural logarithm of the age.This formula was validated prospectively in 60 patients. A non-significantdifference between VO₂(ass) and VO₂(dd) was found; mean 20±23.4ml.min^–1,P=0.771, 95% CI= –4.0 to +8.0, LA –44.7 to +48.7.In conclusion, assumed oxygen consumption values, using ournew formula, are in better agreement with the actual valuesthan those found according to LaFarge and Miettinen's formulae.     

The Effect of Vitamin D on Aldosterone and Health Status in Patients With Heart Failure

BackgroundVitamin D deficiency is associated with heart failure (HF) events, and in animal models vitamin D down-regulates renin-angiotensin-aldosterone system hormones.MethodsPatients with New York Heart Association (NYHA) functional class II–IV HF and a 25OH-D level ≤37.5 ng/mL received 50,000 IU vitamin D₃ weekly (n = 31) or placebo (n = 33) for 6 months. Serum aldosterone, renin, echocardiography, and health status were determined at baseline and 6 months.ResultsMean age of participants was 65.9 ± 10.4 years, 48% were women, 64% were African American, mean ejection fraction was 37.6 ± 13.9%, 36% were in NYHA functional class III, and 64% were in class II. The vitamin D group increased serum 25OH-D (19.1 ± 9.3 to 61.7 ± 20.3 ng/mL) and the placebo group did not (17.8 ± 9.0 to 17.4 ± 9.8 ng/mL). Aldosterone decreased in the vitamin D group (10.0 ± 11.9 to 6.2 ± 11.6 ng/dL) and not in the placebo group (8.9 ± 8.6 to 9.0 ± 12.4 ng/dL; P = .02). There was no difference between groups in renin, echocardiographic measures, or health status from baseline to 6 months. Modeling indicated that variables which predicted change in aldosterone included receiving vitamin D, increasing age, African American race, and lower glomerular filtration rate.ConclusionsVitamin D₃ repletion decreases aldosterone in patients with HF and low serum vitamin D. Vitamin D may be an important adjunct to standard HF therapy. Further study will assess if vitamin D provides long-term benefit for patients with HF.     

Association of muscular fitness with rehospitalization for heart failure with reduced ejection fraction

BackgroundLimited information is available regarding the prognostic potential of muscular fitness parameters in heart failure (HF) with reduced ejection fraction (HFrEF).HypothesisWe aimed to investigate the predictive potential of knee extensor muscle strength and power on rehospitalization and evaluate the correlation between exercise capacity and muscular fitness in patients newly diagnosed with HFrEF.MethodsNinety nine patients hospitalized with a new diagnosis of HF were recruited (64 men; aged 58.7 years [standard deviation (SD), 13.2 years]; 32.3% ischemic; ejection fraction, 28% [SD, 8%]). The inclusion criteria were left ventricular ejection fraction <40% and sufficient clinical stability to undergo exercise testing. Aerobic exercise capacity was measured with cardiopulmonary exercise testing. Knee extensor maximal voluntary isometric contraction (MVIC) and muscle power (MP) were measured using the Baltimore therapeutic equipment system. The clinical outcome was HF rehospitalization.ResultsOver a mean follow‐up period of 1709 ± 502 days, 39 patients were rehospitalized due to HF exacerbation. HF rehospitalization was more probable for patients with diabetes and lower oxygen uptake at peak exercise (peak VO₂), knee extensor MVIC, and MP. The Kaplan–Meier survival analysis revealed significantly different cumulative HF rehospitalization rates according to the tertiles of peak VO₂ (P = 0.005) and MP (P = 0.002). Multivariable Cox proportional hazard model showed that the lowest tertiles of peak VO₂ (hazard ratio (HR), 6.26; 95% confidence interval (CI), 1.93–20.27); and MP (HR, 5.29; 95% CI, 1.05–26.53) were associated with HF rehospitalization. Knee extensor muscle power was an independent predictor for rehospitalization in patients with HFrEF.ConclusionKnee extensor muscle power was an independent predictor for rehospitalization in patients with HFrEF.     

Hypertension in Obesity

ABSTRACT. To compare maximal exercise testing with the NYHA functional criteria in grading symptomatic severity in mitral valve disease, a symptom-limited bicycle exercise test was performed by 40 patients undergoing right and left heart catheterization. In the group as a whole (r=-0.50) and in patients with combined valvular lesion (r=? 0.72), peak O₂ uptake (VO₂) correlated with the NYHA criteria, whereas exercise duration failed to demonstrate such a relationship. In each hemodynamic subgroup large individual variations in peak VO₂ were seen, particularly in NYHA class II and if the lesion was less severe. Unusually high O₂ cost at peak work load was observed in almost half the patients. However, assuming that patients with an aerobic capacity of ≤ 16 ml/kg per min were severely symptomatic (NYHA class III or IV), an agreement between VO₂ and the NYHA criteria was seen in 30 patients (75%). In the remaining 10 patients the NYHA criteria were more often predictive of the severity of the lesion. In “pure” mitral stenosis, however, a total VO₂ of <1.11/min was more likely (r=0.62) to reveal significant valvular narrowing (≤1.5 cm²). Neither peak VO₂ nor the NYHA criteria revealed impaired left ventricular performance or the degree of mitral regurgitation at rest. Rather then being superior, maximal exercise testing seemed to be complementary to the symptom-rated appraisal. Recognizing the potential limitations of exercise testing, which mainly appeared to be attributable to variations in the threshold of perceived exertion and in the non-cardiac component of VO₂, measurement of peak VO₂ is likely to provide a basic estimate of the degree of impairment, particularly in the presence of mitral valve obstruction.     

Frequency and Predictors of Falls Among Adults With Heart Failure: A Prospective Study

ObjectiveAdults with heart failure (HF) may be at high risk for falling due to age, comorbidities and frailty; however, few studies have examined falls in HF. The purpose of this study was to quantify the frequency and predictors of falls over 1 year among adults with HF.MethodsWe conducted a prospective study of adults with New York Heart Association (NYHA) functional class I–IV HF. After baseline assessment of physical frailty and clinical characteristics, participants self-reported falls every 3 months during 1 year. Comparative statistics were used to identify baseline differences between those who fell vs those who did not. A stepwise negative binomial regression model was used to identify predictors of fall rate over 1 year.ResultsThe sample (n = 111) was 63.4 ± 15.7 years old, 48% were women, 28% had HF with preserved ejection fraction, and 41% were frail. Over 1 year, 43 (39%) of participants reported at least 1 fall and 28 (25%) of participants reported 2+ falls. Among those who fell, 29 (67%) reported injurious falls. Those who fell had significantly higher body mass indexes and were more likely to have NYHA class III/IV, type 2 diabetes and HF with preserved ejection fraction and to meet slowness and physical exhaustion criteria than those who did not fall. The fall rate was elevated among those with type 2 diabetes and those meeting the slowness and physical exhaustion criteria for physical frailty.ConclusionsNearly 40% of adults with HF experienced a fall within 1 year. Screening for comorbidities, slowness and exhaustion may help to identify those at risk for a fall.     

Relação da Função Pulmonar e da Força Inspiratória com Capacidade Aeróbica e com Prognóstico na Insuficiência Cardíaca

Background Spirometry is underused in heart failure (HF) and the extent to which each defect associates with exercise capacity and prognosis is unclear.Objective To determine the distinct relationship of continuous %predicted FVC (ppFVC) and FEV₁/FVC with: 1) maximal inspiratory pressure (MIP), left ventricular ejection fraction (LVEF), exercise performance; and 2) prognosis for the composite of cardiovascular death, heart transplantation or left ventricular assist device implant.Methods A cohort of 111 HF participants (AHA stages C/D) without diagnosed pneumopathy, spirometry, manovacuometry and maximum cardiopulmonary test. The association magnitudes were verified by linear and Cox (HR; 95% CI) regressions, age/sex adjusted. A p<0.05 was considered significant.Results Age was 57±12 years, 60% men, 64% in NYHA III. Every 10%-point increase in FEV₁/FVC [β 7% (95% CI: 3–10)] and ppFVC [4% (2-6)] associated with ventilatory reserve (VRes), however only ppFVC associated with MIP [3.8 cmH₂O (0.3-7.3)], LVEF [2.1% (0.5-3.8)] and VO₂peak [0.5 mL/kg/min (0.1–1.0)], accounting for age/sex. In 2.2 years (mean), 22 events occurred, and neither FEV₁/FVC (HR 1.44; 95% CI: 0.97–2.13) nor ppFVC (HR 1.13; 0.89–1.43) was significantly associated with the outcome. Only in the LVEF ≤50% subgroup (n=87, 20 events), FEV₁/FVC (HR 1.50; 1.01–2.23), but not ppFVC, was associated with greater risk.Conclusions In chronic HF, reduced ppFVC associated with lower MIP, LVEF, VRes and VO₂peak, but no distinct poorer prognosis over 2.2 years of follow-up. Distinctively, FEV₁/FVC was associated only with VRes, and, in participants with LVEF ≤50%, FEV₁/FVC reduction proportionally worsened prognosis. Therefore, FEV₁/FVC and ppFVC add supplementary information regarding HF phenotyping.     

O Teste do Degrau de Seis Minutos como Preditor de Capacidade Funcional de Acordo com o Consumo de Oxigênio de Pico em Pacientes Cardíacos

Background:Six-minute step test (6MST) is a simple way to evaluate functional capacity, although it has not been well studied in patients with coronary artery disease (CAD) or heart failure (HF).Objective:Analyze the association between the 6MST and peak oxygen uptake (VO_2peak) and develop an equation for estimating VO_2peak based on the 6MST, as well as to determine a cutoff point for the 6MST that predicts a VO_2peak ≥20 mL.Kg^-1.min^-1Methods:In 171 patients who underwent the 6MST and a cardiopulmonary exercise test, correlation, regression, and ROC analysis were used and a p < 0.05 was admitted as significant.Results:mean age was 60±14 years and 74% were male. Mean left ventricle ejection fraction was 57±16%, 74% had CAD and 28% had HF. Mean VO_2peak was 19±6 mL.Kg^-1.min^-1 and mean 6MST performance was 87±45 steps. Association between 6MST and VO_2peak was r 0.69 (p <0.001). The model VO_2peak =19.6 + (0.075 x 6MST) – (0.10 x age) for men and VO_2peak =19.6 + (0.075 x 6MST) – (0.10 x age) – 2 for women could predict VO_2peak based on 6MST results (adjusted R 0.72; adjusted R² 0.53). The most accurate cutoff point for 6MST to predict a VO_2peak ≥20 mL.Kg^-1.min^-1 was >105 steps (AUC 0.85; 95% CI 0.79 -0.90; p <0.001).Conclusion:An equation for predicting VO_2peak based on 6MST results was derived, and a significant association was found between 6MST and VO_2peak. The cutoff point for 6MST, which predicts a VO_2peak ≥20 mL.Kg^-1.min^-1, was >105 steps. (Arq Bras Cardiol. 2021; 116(5):889-895)     

Cardiac output and cardiopulmonary responses to exercise in heart failure: application of a new bio-reactance device

BackgroundCardiopulmonary exercise testing (CPX) is widely used to evaluate heart failure (HF) patients, but lacks information about ventricular performance. There is a need for a noninvasive cardiac output (CO) measurement.Methods and ResultsTwenty-three HF patients and 13 normals underwent CPX and CO measurements with a new, noninvasive, bioreactance technology based on assessment of relative phase shifts (dΦ/dt) of electric currents injected across the thorax, heart rate, and ventricular ejection time. CO and oxygen uptake (VO₂) closely paralleled each another during exercise, and peak CO was strongly correlated with peak VO₂ (r = 0.73, P < .001). The relationships between peak VO₂ and peak cardiac index (CI) were similar for directly measured CI (r = 0.61) and noninvasive CI (r = 0.61). The CO-VO₂ relationship was also similar between the current study and previous studies from the literature, as evidenced by a similar line of best fit and 95% confidence limits. Maximal CO was significantly related to indices of ventilatory efficiency, including the VE/VCO₂ slope (r = −0.47, P < .01), and the oxygen uptake efficiency slope (r = 0.67, P < .01).ConclusionNoninvasive measurement of CO during exercise using a novel bioreactance-based device has potentially important applications as a simple, inexpensive tool to supplement the clinical evaluation of patients with HF.     

Accurate measurement of oxygen consumption in children undergoing cardiac catheterization

Oxygen consumption (VO₂) is an important part of hemodynamics using the direct Fick principle in children undergoing cardiac catheterization. Accurate measurement of VO₂ is vital. Obviously, any error in the measurement of VO₂ will translate directly into an equivalent percentage under‐ or overestimation of blood flows and vascular resistances. It remains common practice to estimate VO₂ values from published predictive equations. Among these, the LaFarge equation is the most commonly used equation and gives the closest estimation with the least bias and limits of agreement. However, considerable errors are introduced by the LaFarge equation, particularly in children younger than 3 years of age. Respiratory mass spectrometry remains the “state‐of‐the‐art” method, allowing highly sensitive, rapid and simultaneous measurement of multiple gas fractions. The AMIS 2000 quadrupole respiratory mass spectrometer system has been adapted to measure VO₂ in children under mechanical ventilation with pediatric ventilators during cardiac catheterization. The small sampling rate, fast response time and long tubes make the equipment a unique and powerful tool for bedside continuous measurement of VO₂ in cardiac catheterization for both clinical and research purposes. © 2012 Wiley Periodicals, Inc.     

Circuit resistance training in chronic heart failure improves skeletal muscle mitochondrial ATP production rate--a randomized controlled trial

BackgroundWe aimed to determine the role of skeletal muscle mitochondrial ATP production rate (MAPR) in relation to exercise tolerance after resistance training (RT) in chronic heart failure (CHF).Methods and ResultsThirteen CHF patients (New York Heart Association functional class 2.3 ± 0.5; Left ventricular ejection fraction 26 ± 8%; age 70 ± 8 years) underwent testing for peak total body oxygen consumption (VO_2peak), and resting vastus lateralis muscle biopsy. Patients were then randomly allocated to 11 weeks of RT (n = 7), or continuance of usual care (C; n = 6), after which testing was repeated. Muscle samples were analyzed for MAPR, metabolic enzyme activity, and capillary density. VO_2peak and MAPR in the presence of the pyruvate and malate (P+M) substrate combination, representing carbohydrate metabolism, increased in RT (P < .05) and decreased in C (P < .05), with a significant difference between groups (VO_2peak, P = .005; MAPR, P = .03). There was a strong correlation between the change in MAPR and the change in peak total body oxygen consumption (VO_2peak) over the study (r = 0.875; P < .0001), the change in MAPR accounting for 70% of the change in VO_2peak.ConclusionsThese findings suggest that mitochondrial ATP production is a major determinant of aerobic capacity in CHF patients and can be favorably altered by muscle strengthening exercise.     

A flattening oxygen consumption trajectory phenotypes disease severity and poor prognosis in patients with heart failure with reduced,mid‐range,and preserved ejection fraction

Background

In heart failure (HF), a flattening oxygen consumption (VO₂) trajectory during cardiopulmonary exercise test (CPET) reflects an acutely compromised cardiac output. We hypothesized that a flattening VO₂ trajectory is helpful in phenotyping disease severity and prognosis in HF with either reduced (HFrEF), mid‐range (HFmrEF), or preserved (HFpEF) ejection fraction.

Methods and results

Overall, 319 HF patients (198 HFrEF, 80 HFmrEF, and 41 HFpEF) underwent CPET. A flattening VO₂ trajectory was tracked and defined as an inflection of VO₂ linearity as a function of work rate with a second slope downward inflection >35% extent of the first one. Peak VO₂, the minute ventilation/carbon dioxide production (VE/VCO₂) slope, and the presence of exercise oscillatory ventilation (EOV) were also determined. Pulmonary artery systolic pressure (PASP) and tricuspid annular plane systolic excursion (TAPSE) were measured by echocardiography. A flattening VO₂ occurred in 92 patients (28.8%). PASP and TAPSE at rest were significantly higher and lower (P < 0.001), respectively. The primary outcome was the combination of all‐cause death, heart transplantation and left ventricular assist device implantation. The secondary outcome was the primary outcome plus hospitalization for cardiac reasons. In the multivariate model including peak VO₂, VE/VCO₂ slope, EOV and VO₂ trajectory, a flattening VO₂ trajectory and EOV were retained in the regression for primary (X² = 35.78, and 36.36, respectively; P < 0.001) and secondary (X² = 12.45 and 47.91, respectively; P < 0.001) outcomes.

Conclusions

Results point to a flattening VO₂ trajectory as a likely new and strong predictor of events in HF with any ejection fraction. Given the relation of right‐sided cardiac dysfunction to pulmonary hypertension, this oxygen pattern might suggest a real‐time decrease in pulmonary blood flow to the left heart.