Use of cardiopulmonary exercise testing with hemodynamic monitoring in the prognostic assessment of ambulatory patients with chronic heart failure

Association between early central venous pressure measurement and all-cause mortality in critically ill patients with heart failure: A cohort of 11,241 patients

Background

The timing of central venous pressure (CVP) measurement may play a crucial role in heart failure management, yet no studies have explored this aspect.

Methods

Clinical information pertaining to patients in critical condition with a diagnosis of heart failure was retrieved from the MIMIC-IV database. The association between initial measurements of central venous pressure (CVP) and the incidence of mortality from all causes was analyzed using the Cox proportional hazards approach. Subgroup analysis and propensity score matching were conducted for sensitivity analyses.

Results

This study included 11,241 participants (median age, 75 years; 44.70 % female). Utilizing restricted cubic spline and Kaplan-Meier survival analyses, it was determined that prognostic outcomes were better when CVP was measured within the initial 5-h window. Multivariate-adjusted 1-year (HR: 0.69; 95 % CI: 0.61-0.77), 90-day (HR: 0.70; 95 % CI: 0.62-0.80), and 30-day (HR: 0.67; 95 % CI: 0.57-0.78) all-cause mortalities were significantly lower in patients with early CVP measurement, which was proved robustly in subgroup analysis. Subsequent to the application of propensity score matching, a cohort of 1536 matched pairs was established, with the observed mortality rates continuing to be significantly lower among participants who underwent early CVP assessment.

Conclusions

Early CVP measurement (within 5 h) demonstrated an independent correlation with a decrease in both immediate and extended all-cause mortality rates among patients in critical condition suffering from heart failure.

Lean body mass and the cardiorespiratory phenotype: An ethnic-specific relationship in Hans Chinese women and men

BACKGROUND

Lean body mass (LBM) and the functional capacity of cardiovascular (CV) and respiratory systems constitute a female-specific relationship in European-American individuals. Whether this recent finding be extrapolated to the world's largest ethnic group, that is, Hans Chinese (HC, a population characterized by low LBM), is unknown.

METHODS

Healthy HC adults (n = 144, 50% ♀) closely matched by sex, age and physical activity were included. Total and regional (leg, arm and trunk) LBM and body composition were measured via dual-energy X-ray absorptiometry. Cardiac structure, stiffness, central/peripheral haemodynamics and peak O2 consumption (VO2peak) were assessed via transthoracic echocardiography and pulmonary gas analyses at rest and during exercise up to peak effort. Regression analyses determined the sex-specific relationship of LBM with cardiac and aerobic phenotypes.

RESULTS

Total and regional LBM were lower and body fat percentage higher in women compared with men (P < 0.001). In both sexes, total LBM positively associated with left ventricular (LV) mass and peak volumes (r ≥ 0.33, P ≤ 0.005) and negatively with LV end-systolic and central arterial stiffness (r ≥ -0.34, P ≤ 0.004). Total LBM strongly associated with VO2peak (r ≥ 0.60, P < 0.001) and peak cardiac output (r ≥ 0.40, P < 0.001) in women and men. Among regional LBM, leg LBM prominently associated with the arterio-venous O2 difference at peak exercise in both sexes (r ≥ 0.43, P < 0.001). Adjustment by adiposity or CV risk factors did not modify the results.

CONCLUSIONS

LBM independently determines internal cardiac dimensions, ventricular mass, distensibility and the capacity to deliver and consume O2 in HC adults irrespective of sex.

Predicting heart failure outcomes by integrating breath-by-breath measurements from cardiopulmonary exercise testing and clinical data through a deep learning survival neural network

Aims

Mathematical models previously developed to predict outcomes in patients with heart failure (HF) generally have limited performance and have yet to integrate complex data derived from cardiopulmonary exercise testing (CPET), including breath-by-breath data. We aimed to develop and validate a time-to-event prediction model using a deep learning framework using the DeepSurv algorithm to predict outcomes of HF.

Methods and results

Inception cohort of 2490 adult patients with high-risk cardiac conditions or HF underwent CPET with breath-by-breath measurements. Potential predictive features included known clinical indicators, standard summary statistics from CPETs, and mathematical features extracted from the breath-by-breath time series of 13 measurements. The primary outcome was a composite of death, heart transplant, or mechanical circulatory support treated as a time-to-event outcomes. Predictive features ranked as most important included many of the features engineered from the breath-by-breath data in addition to traditional clinical risk factors. The prediction model showed excellent performance in predicting the composite outcome with an area under the curve of 0.93 in the training and 0.87 in the validation data sets. Both the predicted vs. actual freedom from the composite outcome and the calibration of the prediction model were excellent. Model performance remained stable in multiple subgroups of patients.

Conclusion

Using a combined deep learning and survival algorithm, integrating breath-by-breath data from CPETs resulted in improved predictive accuracy for long-term (up to 10 years) outcomes in HF. DeepSurv opens the door for future prediction models that are both highly performing and can more fully use the large and complex quantity of data generated during the care of patients with HF.

The Chinese cardiorespiratory and circulatory system at work in women and men: a case-control study

Background

The physiology of prominent prognostic factors in the cardiorespiratory system remains unchartered in the world's largest ethnic group: Hans Chinese (HC). This study assessed and contrasted the fundamental variables in HC and European-American (EA) individuals.

Methods

Healthy HC and EA adults (n = 140, 43% ♀) closely matched by age, sex and physical activity were included. Body composition (DXA) and haematological variables (haemoglobin mass, blood volume (BV)) were measured at rest. Pulmonary O2 uptake (VO2) measurements along with cycle ergometry designed for accurate transthoracic echocardiography were implemented to assess cardiorespiratory structure/function up to peak effort.

Findings

HC presented with higher body fat and lower lean body mass (LBM) percentage than EA irrespective of sex (P ≤ 0.014). BV did not differ whereas blood haemoglobin concentration was lower in HC compared with EA, particularly in females (P = 0.009). Myocardial diastolic and overall function at rest was enhanced in HC versus EA (P < 0.001). During exercise, heart volumes and output per unit of body size did not differ between ethnicities, whereas larger heart volumes per unit of LBM were found in HC versus EA in females (P ≤ 0.003). At high exercise intensities, VO2 (-16%) and the arteriovenous O2 difference (-28%) were markedly reduced in HC compared with EA in females (P ≤ 0.024). In males, no physiological difference between HC and EA was observed during exercise.

Interpretation

Notwithstanding lower LBM, HC are characterised by similar BV and cardiac capacity but reduced peak VO2 than EA in females, partly explained by low ethnic-specific blood O2 carrying capacity.

Funding

Early Career Scheme (106210224, to D.M.) and Seed Fund (104006024, to D.M.).

Sex-specific improvement in cardiac phenotype in older females combining blood withdrawal and exercise training

This study determined whether an intervention combining hematological and exercise stimuli may overcome the prevailing limitations to improve the cardiac phenotype and orthostatic tolerance (OT) of females with advanced age. Healthy females (n = 15) and males (n = 14) matched by age (63.7 ± 7.0 vs. 63.6 ± 8.7 yr) and moderate physical activity were recruited. OT, transthoracic echocardiography, and central hemodynamics were assessed during incremental lower body negative pressure (LBNP) levels (up to -50 mmHg) for 1 h or until presyncope, prior to and after an intervention comprising standard (10%) blood withdrawal and an 8-wk exercise training program designed to maximize central hemodynamic adaptations. OT time was lower in females compared with males (48.1 ± 10.6 vs. 57.0 ± 4.8 min, P = 0.008) before the intervention. Improved OT time (+11%) in females (48.1 ± 10.6 vs. 53.5 ± 6.1 min, P = 0.021) but not in males (57.0 ± 4.8 vs. 56.7 ± 5.6 min, P = 0.868) was found following the intervention, resulting in similar OT time between females and males (P = 0.156). The intervention induced improvements in left ventricular (LV) diastolic function (+13% for myocardial e') along with increased LV mass (+13%) in females (P ≤ 0.039) but not in males (P ≥ 0.257). During the initial LBNP stages (0 to -20 mmHg), LV stroke volume and cardiac output were exclusively increased in females after the intervention (P ≤ 0.034). In conclusion, the cardiac phenotype of females with advanced age can be structurally and functionally modified in parallel to improved OT via short-term hematological and central hemodynamic stimuli.NEW & NOTEWORTHY Based on previous studies, main features of the cardiac phenotype in females with advanced age are generally unresponsive to lifestyle interventions. The present findings reveals that the cardiac phenotype of middle-age and older females is amenable to large modification in a short-term period when hematological stimuli are combined with those induced by exercise training. The same intervention only induced minor adaptations in males matched by age and potential confounding factors.

Lean body mass and the cardiovascular system constitute a female-specific relationship

Recent evidence points toward a link between lean body mass (LBM) and cardiovascular capacity in women. This study aimed at determining the sex-specific relationship of LBM with central and peripheral circulatory variables in healthy women and men (n=70) matched by age (60±12 years versus 58±15 years), physical activity, and cardiovascular risk factors. Regional (legs, arms, and trunk) and whole-body (total) body composition were assessed via dual-energy x-ray absorptiometry. Cardiac structure, function, and central/peripheral hemodynamics were measured via transthoracic echocardiography and the volume-clamp method at rest and peak incremental exercise. Regression analyses determined sex-specific relationships between LBM and cardiovascular variables. Regional and total LBM were lower in women than men (P<0.001), with little overlap between sexes. Leg and arm LBM positively associated with left ventricular (LV) internal resting dimensions in women (r≥0.53, P≤0.002) but not men (P≥0.156). Leg, arm, and total LBM only associated with LV relaxation in women (r≥0.43, P≤0.013). All LBM variables strongly associated with LV volumes at peak exercise in women (r≥0.54, P≤0.001) but not men and negatively associated with total peripheral resistance at peak exercise in women (r≥0.43, P≤0.023). Adjustment by adiposity-related or cardiovascular risk factors did not alter results. In conclusion, leg and arm LBM independently associate with internal cardiac dimensions, ventricular relaxation, and systemic vascular resistance in a sex-specific manner, with these relationships exclusively present in women.

Transvenous Right Greater Splanchnic Nerve Ablation in Heart Failure and Preserved Ejection Fraction: First-in-Human Study

BACKGROUND

Ablation of the right-sided greater splanchnic nerve (GSN) can reduce excessive splanchnic vasoconstriction, potentially improving the handling of volume shifts in patients with heart failure with preserved ejection fraction (HFpEF).

OBJECTIVES

The purpose of this study was to assess a novel catheter procedure of right-sided GSN ablation to treat HFpEF: splanchnic ablation for volume management.

METHODS

This trial included 11 HFpEF patients (8 women, age 70 ± 8 years) with New York Heart Association functional class II or III symptoms, ejection fraction ≥50%, and elevated pulmonary capillary wedge pressure at rest or with exercise. After splanchnic ablation for volume management, follow-up at 1, 3, 6, and 12 months included 6-minute walk test, Kansas City Cardiomyopathy Questionnaire (KCCQ), and echocardiography.

RESULTS

There were no device-related adverse cardiac events or clinical sequelae following right GSN ablation through 12 months. Patients experienced clinical improvements by 1 month that were sustained through 12 months. KCCQ score improved from baseline median 48 (IQR: 35-52) to 65 (IQR: 58-77) at 1 month and 80 (IQR: 77-88) at 12 months (P &lt; 0.05). The 6-minute walk test distance increased from baseline 292 ± 82 m to 341 ± 88 m at 1 month and 359 ± 75 m at 12 months (P &lt; 0.05). The NT-proBNP decreased from a baseline mean of 1,292 ± 1,186 pg/mL to 1,202 ± 797 pg/mL (P = 0.585) at 1 month, to 472 ± 226 pg/mL (P = 0.028) at 6 months, and to 379 ± 165 pg/mL (P = 0.039) at 12 months.

CONCLUSIONS

In this open-label, single-arm feasibility study, right-sided GSN ablation was safe and improved mostly subjective clinical metrics in patients with HFpEF over 12 months. (Endovascular GSN Ablation in Subjects With HFpEF; NCT04287946).

LVAD as a Bridge to Remission from Advanced Heart Failure: Current Data and Opportunities for Improvement

Left ventricular assist devices (LVADs) are an established treatment modality for advanced heart failure (HF). It has been shown that through volume and pressure unloading they can lead to significant functional and structural cardiac improvement, allowing LVAD support withdrawal in a subset of patients. In the first part of this review, we discuss the historical background, current evidence on the incidence and assessment of LVAD-mediated cardiac recovery, and out-comes including quality of life after LVAD support withdrawal. In the second part, we discuss current and future opportunities to promote LVAD-mediated reverse remodeling and improve our pathophysiological understanding of HF and recovery for the benefit of the greater HF population.

Lung Fluid Volume during Cardiopulmonary Exercise Testing

Background and Objectives: Cardiopulmonary exercise testing can be used to quantify exercise capacity in patients with heart failure with reduced ejection fraction (HfrEF). Lung fluid levels as measured non-invasively by remote dielectric sensing (ReDSTM), often correlate with intracardiac filling pressures. The change in lung fluid levels in patients with HfrEF during cardiopulmonary exercise testing is unknown. Materials and Methods: Patients with chronic HfrEF who underwent cardiopulmonary exercise testing between October 2021 and March 2022 were prospectively included in this proof-of-concept study, with ReDS values measured before and after testing. Results: Thirteen patients (median age 41 (37, 52) years, 69% men, plasma B-type natriuretic peptide 141 (57, 368) pg/mL) were included. Median peak oxygen consumption was 11.4 (10.7, 14.0) mL/kg/min. During the test, ReDS values increased from 25% to 32% only in one patient on inotropic support, whereas ReDS values remained unchanged in the other 12 patients. The former patient remained hospitalized, whereas the other patients were dischargeable without any new incidence of clinical events during the observational period (median duration 69 (33, 112] days). Conclusions: The ReDS system may be a feasible complementary tool to noninvasively assess the changes in lung fluid levels during cardiopulmonary exercise testing. The clinical implications of ReDS values during exercise needs further investigation.

Correlation of Hemodynamic and Respiratory Parameters in Invasive Cardiopulmonary Exercise Testing (iCPET)

Background: Invasive cardiopulmonary exercise testing (iCPET) is an integral part in the advanced diagnostic workup of pulmonary hypertension (PH). Our study evaluated the relation between hemodynamic and respiratory parameters at two different resting conditions and two defined low exercise levels with a close synchronization of measurements in a broad variety of dyspnea patients. Subjects and methods: We included 146 patients (median age 69 years, range 22 to 85 years, n = 72 female) with dyspnea of uncertain origin. Invasive hemodynamic and gas exchange parameters were measured at rest, 45° upright position, unloaded cycling, 25 and 50 W exercise. All measurements were performed in a single RHC procedure. Results: Oxygen uptake (VO2/body mass) correlated significantly with cardiac index (all p ≤ 0.002) at every resting and exercise level and with every method of cardiac output measurement (thermodilution, method of Fick). Mean pulmonary arterial pressure (PAPmean) correlated with all respiratory parameters (respiratory rate, partial end-tidal pressures of oxygen and carbon dioxide [petCO2 and petO2], ventilation/carbon dioxide resp. oxygen ratio [VE/VCO2, VE/VO2], and minute ventilation [VE], all p < 0.05). These correlations improved with increasing exercise levels from rest via unloaded cycling to 25 W. There was no correlation with right atrial or pulmonary arterial wedge pressure. Summary: In dyspnea patients of different etiologies, the cardiac index is closely linked to VO2 at every level of rest and submaximal exercise. PAPmean is the only pressure that correlates with different respiratory parameters, but this correlation is highly significant and stable at rest, unloaded cycling and at 25 W.

Sex and age interaction in fundamental circulatory volumetric variables at peak working capacity

Background

Whether the fundamental hematological and cardiac variables determining cardiorespiratory fitness and their intrinsic relationships are modulated by major constitutional factors, such as sex and age remains unresolved.

Methods

Transthoracic echocardiography, central hemodynamics and pulmonary oxygen (O₂) uptake were assessed in controlled conditions during submaximal and peak exercise (cycle ergometry) in 85 healthy young (20–44 year) and older (50–77) women and men matched by age-status and moderate-to-vigorous physical activity (MVPA) levels. Main outcomes such as peak left ventricular end-diastolic volume (LVEDV_peak), stroke volume (SV_peak), cardiac output (Q_peak) and O₂ uptake (VO_2peak), as well as blood volume (BV), BV–LVEDV_peak and LVEDV_peak–SV_peak relationships were determined with established methods.

Results

All individuals were non-smokers and non-obese, and MVPA levels were similar between sex and age groups (P ≥ 0.140). BV per kg of body weight did not differ between sexes (P ≥ 0.118), but was reduced with older age in men (P = 0.018). Key cardiac parameters normalized by body size (LVEDV_peak, SV_peak, Q_peak) were decreased in women compared with men irrespective of age (P ≤ 0.046). Older age per se curtailed Q_peak (P ≤ 0.022) due to lower heart rate (P < 0.001). In parallel, VO_2peak was reduced with older age in both sexes (P < 0.001). The analysis of fundamental circulatory relationships revealed that older women require a higher BV for a given LVEDV_peak than older men (P = 0.024).

Conclusions

Sex and age interact on the crucial circulatory relationship between total circulating BV and peak cardiac filling, with older women necessitating more BV to fill the exercising heart than age- and physical activity-matched men.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13293-021-00409-9.

[Invasive Cardiopulmonary Exercise Testing: A Review]

Right heart catheterization (RHC) is the internationally standardized reference method for measuring pulmonary hemodynamics under resting conditions. In recent years, increasing efforts have been made to establish the reliable assessment of exercise hemodynamics as well, in order to obtain additional diagnostic and prognostic data. Furthermore, cardiopulmonary exercise testing (CPET), as the most comprehensive non-invasive exercise test, is increasingly performed in combination with RHC providing detailed pathophysiological insights into the exercise response, so-called invasive cardiopulmonary exercise testing (iCPET).In this review, the accumulated experience with iCPET is presented and methodological details are discussed. This complex examination is especially helpful in differentiating the underlying causes of unexplained dyspnea. In particular, early forms of cardiac or pulmonary vascular dysfunction can be detected by integrated analysis of hemodynamic as well as ventilatory and gas exchange data. It is expected that with increasing validation of iCPET parameters, a more reliable differentiation of normal from pathological stress reactions will be possible.

Sex dimorphism in cardiac and aerobic capacities: The influence of body composition

OBJECTIVE

The contribution of body composition to sex differences in strong prognostic cardiorespiratory variables remains unresolved. This study aimed to elucidate whether body composition determines sex differences in cardiac and oxygen (O₂ ) uptake responses to incremental exercise.

METHODS

Healthy, moderately active women and men (n = 60, age = 60.7 [12.3] years) matched by age and cardiorespiratory fitness were included. Body composition was determined via dual-energy x-ray absorptiometry. Transthoracic echocardiography and O₂ uptake were assessed at rest and throughout incremental exercise with established methods. Major cardiac and pulmonary outcomes were normalized by body surface area (BSA), total lean body mass (LBM), or leg LBM.

RESULTS

Women presented with smaller anthropometrical indices (height, weight, BSA) and LBM compared with men (p < 0.001). Peak exercise cardiac dimensions and output (i.e., peak cardiac outout [Q_peak ]), commonly normalized by BSA, were reduced in women relative to men (p ≤ 0.019). Cardiac sex differences were abolished after normalization by total or leg LBM (p ≥ 0.115). Strong linear relationships of total and leg LBM with Q_peak and peak oxygen uptake were detected exclusively in women (r ≥ 0.53, p ≤ 0.003), independent of body fat percentage.

CONCLUSIONS

Total and leg LBM stand out as strong independent determinants of cardiac and aerobic capacities in women, regardless of body fat percentage, relationships that are not present in age- and fitness-matched men.

Exercise Cardiac Magnetic Resonance Imaging in Boys With Duchenne Muscular Dystrophy Without Cardiac Disease

BACKGROUND

Duchenne muscular dystrophy is caused by mutations in the DMD gene, resulting in cardiomyopathy in all affected children by 18 years. Although cardiomyopathy is now the leading cause of mortality in these children, there is ongoing debate regarding timely diagnosis, secondary prevention, and treatment of this condition. The purpose of this study was to use exercise cardiac magnetic resonance imaging in asymptomatic young boys with Duchenne muscular dystrophy to describe their heart function and compare this with healthy controls.

METHODS

We studied 11 boys with Duchenne muscular dystrophy aged 8.6 to 13.9 years and 11 healthy age- and sex-matched controls.

RESULTS

Compared with the controls, boys with Duchenne muscular dystrophy had lower ejection fraction at rest (57% versus 63%; P = 0.004). During submaximal exercise, they reached similar peak tachycardia but increased their heart rate and cardiac output only half as much as controls (P = 0.003 and P = 0.014, respectively). End-systolic volume remained higher in boys with Duchenne muscular dystrophy both at rest and during exercise. When transthoracic echocardiography was compared with cardiac magnetic resonance imaging, 45% of the echocardiograms had suboptimal or poor views in the Duchenne muscular dystrophy group.

CONCLUSIONS

Boys with Duchenne muscular dystrophy had abnormalities in left ventricular systolic function that were exaggerated by exercise stress. Exercise cardiac magnetic resonance imaging is feasible in a select population of children with Duchenne muscular dystrophy, and it has the potential to unmask early signs of cardiomyopathy.

Weaning from ventricular assist device support after recovery from left ventricular failure with or without secondary right ventricular failure

Although complete myocardial recovery after ventricular assist device (VAD) implantation is rather seldom, systematic search for recovery is worthwhile because for recovered patients weaning from VADs is feasible and can provide survival benefits with long-term freedom from heart failure (HF) recurrence, even if a chronic cardiomyopathy was the primary cause for the drug-refractory HF necessitating left ventricular (LVAD) or biventricular support (as bridge-to-transplantation or definitive therapy) and even if recovery remains incomplete. LVAD patients explanted for myoacardial recovery compared to those transplanted from LVAD support showed similar survival rates and a significant proportion of explanted patients can achieve cardiac and physical functional capacities that are within the normal range of healthy controls. In apparently sufficiently recovered patients, a major challenge remains still the pre-explant prediction of the weaning success which is meanwhile reliably possible for experienced clinicians. In weaning candidates, the combined use of certain echocardiography and right heart catheterization parameters recorded before VAD explantation can predict post-weaning cardiac stability with good accuracy. However, in the absence of standardization or binding recommendations, the protocols for assessment of native cardiac improvement and also the weaning criteria differ widely among centers. Currently there are still only few larger studies on myocardial recovery assessment after VAD implantation. Therefore, the weaning practice relies mostly on small case series, local practice patterns, and case reports, and the existing knowledge, as well as the partially differing recommendations which are based mainly on expert opinions, need to be periodically systematised. Addressing these shortcomings, our review aims to summarize the evidence and expert opinion on the evaluation of cardiac recovery during mechanical ventricular support by paying special attention to the reliability of the methods and parameters used for assessment of myocardial recovery and the challenges met in both evaluation of recovery and weaning decision making.

Cardiac output changes during exercise in heart failure patients: focus on mid-exercise

Aims

Peak exercise oxygen uptake (VO₂) and cardiac output (CO) are strong prognostic indexes in heart failure (HF) but unrelated to real‐life physical activity, which is associated to submaximal effort.

Methods and results

We analysed maximal cardiopulmonary exercise test with rest, mid‐exercise, and peak exercise non‐invasive CO measurements (inert gas rebreathing) of 231 HF patients and 265 healthy volunteers. HF patients were grouped according to exercise capacity (peak VO₂ < 50% and ≥50% pred, Groups 1 and 2). To account for observed differences, data regarding VO₂, CO, stroke volume (SV), and artero‐venous O₂ content difference [ΔC(a‐v)O₂] were adjusted by age, gender, and body mass index. A multiple regression analysis was performed to predict peak VO₂ from mid‐exercise cardiopulmonary exercise test and CO parameters among HF patients. Rest VO₂ was lower in HF compared with healthy subjects; meanwhile, Group 1 patients had the lowest CO and highest ΔC(a‐v)O₂. At mid‐exercise, Group 1 patients achieved a lower VO₂, CO, and SV [0.69 (interquartile range 0.57–0.80) L/min; 5.59 (4.83–6.67) L/min; 62 (51–73) mL] than Group 2 [0.94 (0.83–1.1) L/min; 7.6 (6.56–9.01) L/min; 77 (66–92) mL] and healthy subjects [1.15 (0.93–1.30) L/min; 9.33 (8.07–10.81) L/min; 87 (77–102) mL]. Rest to mid‐exercise SV increase was lower in Group 1 than Group 2 (P = 0.001) and healthy subjects (P < 0.001). At mid‐exercise, ΔC(a‐v)O₂ was higher in Group 2 [13.6 (11.8–15.4) mL/100 mL] vs. healthy patients [11.6 (10.4–13.2) mL/100 mL] (P = 0.002) but not different from Group 1 [13.6 (12.0–14.9) mL/100 mL]. At peak exercise, Group 1 patients achieved a lower VO₂, CO, and SV than Group 2 and healthy subjects. ΔC(a‐v)O₂ was the highest in Group 2. At multivariate analysis, a model comprising mid‐exercise VO₂, carbon dioxide production (VCO₂), CO, haemoglobin, and weight predicted peak VO₂, P < 0.001. Mid‐exercise VO₂ and CO, haemoglobin, and weight added statistically significantly to the prediction, P < 0.050.

Conclusions

Mid‐exercise VO₂ and CO portend peak exercise values and identify severe HF patients. Their evaluation could be clinically useful.

Echo-derived peak cardiac power output-to-left ventricular mass with cardiopulmonary exercise testing predicts outcome in patients with heart failure and depressed systolic function

AIMS

Peak cardiac power output-to-mass (CPOM) represents a measure of the rate at which cardiac work is delivered respect to the potential energy stored in left ventricular (LV) mass. We studied the value of CPOM and cardiopulmonary exercise test (CPET) in risk stratification of patients with heart failure (HF).

MATERIALS AND RESULTS

We studied 159 patients with chronic HF (mean rest LV ejection fraction 30%) undergoing CPET and exercise stress echocardiography. CPOM was calculated as the product of a constant (K = 2.22 × 10-1) with cardiac output (CO) and the mean blood pressure (MBP), divided by LV mass (M), and expressed in the unit of W/100 g: CPOM = [K × CO (L/min) × MBP (mmHg)]/LVM(g). Patients were followed-up for the primary endpoint, including all-cause death, ventricular assist device implantation, and heart transplantation, and the secondary endpoint that comprised hospitalization for HF. In multivariate Cox regression analyses, peak CPOM was selected as the most powerful independent predictor of both primary and secondary endpoint [hazard ratio (HR) 0.004, 95% confidence interval (CI) 0.004-0.3; P = 0.002 and HR 0.09, 95% CI 0.02-0.55; P = 0.009]. Sixty-month survival free from the combined endpoint was 85% in those exhibiting oxygen consumption (VO2) > 14 mL/min/kg and peak CPOM > 0.6 W/100 g. Peak VO2 ≤ 14 mL/min/kg provided incremental prognostic value over demographic and clinical variables, brain natriuretic peptide, and resting echocardiographic parameters (χ2 from 58 to 64; P = 0.04), that was further increased by peak CPOM ≤ 0.6 W/100 g (χ2 77; P < 0.001).

CONCLUSION

Peak CPOM and peak VO2 showed independent and incremental prognostic values in patients with chronic HF.

The utility of the oxygen pulse recovery as a marker of the cardiac output response to exercise in patients with chronic heart failure

PURPOSE

The cardiac output (CO) response to exercise is a useful marker to grade the prognosis and severity of chronic heart failure (CHF). The recovery of the oxygen pulse (OP) is a non-invasive parameter, which is related to exercise capacity in cardiac patients. However, the relation between OP recovery and the central haemodynamic response to exercise remains to be determined. We hypothesized that an impaired OP recovery is associated with a reduced CO response to exercise in CHF patients.

METHODS

Sixty one CHF patients performed cardiopulmonary exercise test with simultaneous measurement of CO. Impaired OP recovery was defined as an overshoot during the first minute of recovery or OP at 1-min recovery as a percentage of peak OP (OP_RR ).

RESULTS

An OP overshoot was observed in 9% (n = 5) of patients. In these patients, peak CO and VO₂ were significantly lower (peak CO 7.9 ± 0.8 versus 11.2 ± 4.3 L/min and peak VO₂ 14.1 ± 4.7 versus 19.6 ± 5.8 ml min^-1  kg^-1 ). Mean relative recovery of OP was 78 ± 20%. Slow OP recovery (negative OP_RR ) was seen in 13% (n = 8). Peak CO and VO₂ were significantly lower in the negative OP_RR group (11 ± 4 versus 8 ± 0.7 L/min and 19.7 ± 5.9 versus 14.6 ± 3.7 ml kg min^-1 ). There was a significant relation between OP_RR and stroke volume (SV) _RR (r = .57), as well as between OP_RR and a-v O₂ diff _RR (r_s  = .4).

CONCLUSION

An impaired OP recovery is associated with a reduced CO response to exercise and worse functional status. Therefore, the OP recovery can be used to grade the severity of CHF.

Non-invasive estimation of stroke volume during exercise from oxygen in heart failure patients

AIMS

In heart failure, oxygen uptake and cardiac output measurements at peak and during exercise are important in defining heart failure severity and prognosis. Several cardiopulmonary exercise test-derived parameters have been proposed to estimate stroke volume during exercise, including the oxygen pulse (oxygen uptake/heart rate). Data comparing measured stroke volume and the oxygen pulse or stroke volume estimates from the oxygen pulse at different stages of exercise in a sizeable population of healthy individuals and heart failure patients are lacking.

METHODS

We analysed 1007 subjects, including 500 healthy and 507 heart failure patients, who underwent cardiopulmonary exercise testing with stroke volume determination by the inert gas rebreathing technique. Stroke volume measurements were made at rest, submaximal (∼50% of exercise) and peak exercise. At each stage of exercise, stroke volume estimates were obtained considering measured haemoglobin at rest, predicted exercise-induced haemoconcentration and peripheral oxygen extraction according to heart failure severity.

RESULTS

A strong relationship between oxygen pulse and measured stroke volume was observed in healthy and heart failure subjects at submaximal (R2 = 0.6437 and R2 = 0.6723, respectively), and peak exercise (R2 = 0.6614 and R2 = 0.5662) but not at rest. In healthy and heart failure subjects, agreement between estimated and measured stroke volume was observed at submaximal (-3 ± 37 and -11 ± 72 ml, respectively) and peak exercise (1 ± 31 and 6 ± 29 ml, respectively) but not at rest.

CONCLUSION

In heart failure patients, stroke volume estimation and oxygen pulse during exercise represent stroke volume, albeit with a relevant individual data dispersion so that both can be used for population studies but cannot be reliably applied to a single subject. Accordingly, whenever needed stroke volume must be measured directly.

Comparison of Hemodynamic Factors Predicting Prognosis in Heart Failure: A Systematic Review

Objectives: We systematically reviewed the literature to address the question of which of the three hemodynamic factors predicts prognosis best in heart failure patients when directly compared to each other: cardiac output, preload or afterload. Methods: Prognostic studies in heart failure (HF) were searched that included at least two of the three hemodynamic variables: (1) cardiac output or cardiac index (CI), (2) preload represented by pulmonary capillary wedge pressure (PCWP) and (3) afterload simplified to systolic blood pressure (SBP). Critical appraisal was done according to the QUIPS format for prognostic studies. The main endpoint was all-cause mortality, which could be combined with other endpoints. We report the number of studies in which CI, PCWP and SBP remained significant prognostic predictors in multivariate analysis. We also assessed whether hemodynamic predictors of prognosis varied in four different HF-populations. Results: Included were 18 studies containing a multivariate analysis. PCWP was an independent predictor of prognosis in 10 of 18 studies, SBP in 3 of 14 studies and CI in none of 18 studies. Results were not specific for any of the HF-populations. Conclusions: A higher PCWP and lower SBP are independent predictors of poor prognosis in HF. In spite of the frequently used concept behind HF, this review demonstrates that CI is not an independent predictor of prognosis in HF.

Neural Networks for Prognostication of Patients With Heart Failure

Background Prognostication of heart failure patients from cardiopulmonary exercise test (CPET) currently involves simplification of complex time-series data into summary indices. We hypothesized that prognostication could be improved by considering the totality of the data generated during a CPET, instead of using summary indices alone. Methods and Results Complete data from 1156 CPETs were used to predict clinical deterioration (characterized by initiation of mechanical circulatory support, listing for heart transplantation or mortality) 1 year post-CPET. We compared the prognostic value (area under the receiver operating characteristic curve) of (1) the most predictive summary indices, (2) staged data collected at discrete intervals using multivariable regression models, and (3) breath-by-breath data using a feedforward neural network. The top-performing models were compared with the commonly used CPET risk score, using absolute net reclassification index. All models were trained and assessed using a 100-iteration Monte Carlo cross-validation. A total of 190 (16.4%) patients experienced clinical deterioration. The summary indices demonstrated subpar discriminative value (area under the receiver operating characteristic curve ≤0.800). Each multivariable model outperformed the summary indices, with the neural network incorporating breath-by-breath data achieving the best performance (area under the receiver operating characteristic curve =0.842). When compared with the CPET risk score (area under the receiver operating characteristic curve =0.759), the top-performing model obtained a net reclassification index of 4.9%. Conclusions The current practice of considering summary indices in isolation fails to realize the full value of CPET data. This may lead to less accurate prognostication of patients and in consequence, inaccurate selection of patients for advanced therapy. Clinical practices, like CPET prognostication, must be continuously reevaluated to ensure optimal usage of valuable (and oft-underutilized) data sources.

Identifying a low-flow phenotype in heart failure with preserved ejection fraction: a secondary analysis of the RELAX trial

AIMS

The relationship between resting stroke volume (SV) and prognostic markers in heart failure with preserved ejection fraction (HFpEF) is not well established. We evaluated the association of SV index (SVI) at rest with exercise capacity and N-terminal pro-B-type natriuretic peptide (NT-proBNP) in stable patients with HFpEF.

METHODS AND RESULTS

Participants enrolled in the Phosphodiesterase-5 Inhibition to Improve Clinical Status and Exercise Capacity in Diastolic Heart Failure (RELAX) trial with available data on SVI by the Doppler method were included in this analysis (n = 185). A low-flow state defined by resting SVI < 35 mL/m2 was present in 37% of study participants. Multivariable adjusted linear regression analysis suggested that higher resting heart rate, higher body weight, prevalent atrial fibrillation, and smaller left ventricular (LV) end-diastolic dimension were each independently associated with lower SVI. Patients with low-flow HFpEF had lower systolic blood pressure and smaller LV end-diastolic dimension. In multivariable adjusted linear regression models, lower SVI was significantly associated with lower peak oxygen consumption (peak VO2 ) and higher NT-proBNP levels at baseline, and greater decline in peak VO2 at 6 month follow-up independent of other confounders. Resting LV ejection fraction was not associated with peak VO2 and NT-proBNP levels.

CONCLUSIONS

There is heterogeneity in the resting SVI distribution among patients with stable HFpEF, with more than one-third of patients identified with the low-flow HFpEF phenotype (SVI < 35 mL/m2 ). Lower SVI was independently associated with lower peak VO2 , higher NT-proBNP levels, and greater decline in peak VO2 . These findings highlight the potential prognostic utility of SVI assessment in the management of patients with HFpEF.

Test-Retest Reliability of Non-Invasive Cardiac Output Measurement during Exercise in Healthy Volunteers in Daily Clinical Routine

Background

Thoracic bioreactance (TB), a noninvasive method for the measurement of cardiac output (CO), shows good test-retest reliability in healthy adults examined under research and resting conditions.

Objective

In this study, we evaluate the test-retest reliability of CO and cardiac power (CPO) output assessment during exercise assessed by TB in healthy adults under routine clinical conditions.

Methods

25 test persons performed a symptom-limited graded cycling test in an outpatient office on two different days separated by one week. Cardiorespiratory (power output, VO_2peak) and hemodynamic parameters (heart rate, stroke volume, CO, mean arterial pressure, CPO) were measured at rest and continuously under exercise using a spiroergometric system and bioreactance cardiograph (NICOM, Cheetah Medical).

Results

After 8 participants were excluded due to measurement errors (outliers), there was no systematic bias in all parameters under all conditions (effect size: 0.2-0.6). We found that all noninvasively measured CO showed acceptable test-retest-reliability (intraclass correlation coefficient: 0.59-0.98; typical error: 0.3-1.8). Moreover, peak CPO showed better reliability (intraclass correlation coefficient: 0.80-0.85; effect size: 0.9-1.1) then the TB CO, thanks only to the superior reliability of MAP (intraclass correlation coefficient: 0.59-0.98; effect size: 0.3-1.8).

Conclusion

Our findings preclude the clinical use of TB in healthy subject population when outliers are not identified.

The Added Value of Exercise Stress Echocardiography in Patients With Heart Failure

Doppler echocardiography can provide reliable and repeatable measures of cardiac index (CI), whereas lung ultrasound (LUS) represents a quantitative approach to assess pulmonary congestion. We tested the hypothesis that simultaneous assessment of CI and LUS during exercise stress echocardiography (ESE) may define heart failure (HF) outpatients with different risk of adverse outcome. Standard transthoracic echocardiography and LUS (B-lines) evaluation were assessed during semisupine ESE. CI and B-lines were measured at baseline and peak exercise. Resting plasma B-type natriuretic peptide levels were also evaluated. We enrolled 105 HF patients (87 males; age 62 ± 11 years; New York Heart Association class I to III) with reduced left ventricular ejection fraction (30 ± 7%). Patients were classified into 4 profiles: (1) peak CI ≥4.0 l/min/m² and peak B-lines <15 (no evidence of congestion or hypoperfusion, n = 47); (2) peak CI ≥4.0 l/min/m² and peak B-lines ≥15 (congestion with adequate perfusion, n = 23); (3) peak CI <4.0 l/min/m² and peak B-lines <15 (hypoperfusion without congestion, n = 13); and (4) peak CI <4.0 l/min/m² and peak B-lines ≥15 (congestion and hypoperfusion, n = 22). There were 21 cardiovascular deaths and 18 hospitalizations for worsening HF during a median follow-up of 29 months. Multivariate predictors of the combined end point were peak hemodynamic profiles (hazard ratio [HR] 1.62, 95% confidence interval [CI] 1.19 to 2.21; p = 0.002), B-type natriuretic peptide (HR 1.00, 95% CI 1.00 to 1.01; p = 0.001), and rest E/e' (HR 1.09, 95% CI 1.03 to 1.15; p = 0.002). Survival analysis showed a worse survival in patients with ESE-derived D profile, followed by patients with C, B, and A profile (log-rank: chi-square = 40.5; p <0.0001). In conclusion, dual evaluation of CI and LUS during ESE is useful for risk stratification of HF patients with reduced ejection fraction. Evidence of pulmonary congestion and low CI at peak ESE identifies a subgroup with a very high risk of adverse outcome.

Evaluation of Cardiac Recovery in Ventricular Assist Device Recipients: Particularities, Reliability, and Practical Challenges

In carefully selected patients with ventricular assist devices (VADs), good long-term results after device weaning and explantation can be achieved when reverse remodelling and improvement of native cardiac function occur. Monitoring of cardiac size, geometry, and function after initial VAD implantation is necessary to identify such patients. Formal guidelines for recovery assessment in patients with VADs do not exist, and protocols for recovery assessment and criteria for device weaning and explantation vary among centres. Barriers to evaluation of cardiac recovery include technical problems in obtaining echo images in patients with VADs, time restrictions for necessary VAD reductions/interruptions during assessment, and regurgitant flow patterns that occur with interruption of continuous flow VADs. The few larger studies addressing cardiac recovery after VAD implantation employed varied study designs, limiting interpretation. Current clinical practice is guided largely by local practice patterns, case reports, and small case series, and the available body of research-consisting mostly of expert opinions-has not been systematically addressed. This summary reviews evidence and expert opinion on VAD-promoted cardiac recovery assessment, its reliability, and associated challenges.

An Analog Front End ASIC for Cardiac Electrical Impedance Tomography

In this paper, an end-to-end CMOS application specific integrated circuit (ASIC) for readout channel in a cardiac electrical impedance tomography system is presented. The ASIC consists of an integrated current driver for current injection, an instrumentation amplifier, variable gain amplifier at the analog front end for voltage readout from electrodes, and an on-chip 10-bit successive approximation register analog to digital converter with serial peripheral interface. The ASIC is fabricated in the CMOS 0.18 $\mu$ m process with a supply voltage of 3.3 V. Amplitude and phase extraction of the voltages is performed in the digital domain with a matched filter. A fully integrated solution for use in multiple electrode system is demonstrated. The readout chain in the ASIC achieves a minimum signal-to-noise ratio of 71 dB over the frequency range of 500 Hz-700 kHz, while maintaining an average accuracy of 99.7 $\%$. Frame rates of 21 frames per second for a 32 electrode system is feasible, and the ASIC has an overall power consumption of 11.8 mW.

Relationship Between Post-exercise Heart Rate Recovery and Changing Ratio of Cardiopulmonary Exercise Capacity

Objective

To determine whether heart rate recovery (HRR) following an exercise tolerance test (ETT) is correlated with a changing ratio of peak oxygen consumption (VO₂) and maximal metabolic equivalents (MET_max).

Methods

A total of 60 acute myocardial infarction (AMI) patients who underwent ETT at both assessment points - 3 weeks (T0) after the AMI attack and 3 months after T0 (T1) were included. After achieving a peak workload, the treadmill was stopped with a 5-minute cooldown period, and the patients recovered in a comfortable and relaxed seated position. HRR was defined as the difference between the maximal heart rate (HR_max) and the HR measured at specific time intervals - immediately after the cool down period (HRR-0) and 3 minutes after the completion of the ETT (HRR-3).

Results

HRR-0 and HRR-3 increased over time, whereas VO_2max and MET_max did not show significant changes. There was a positive correlation between HRR at T0 and the exercise capacity at T0. HRR at T0 also showed a positive correlation with the exercise capacity at T1. There was no significant correlation between HRR measured at T0 and the change in the ratio of VO_2max and MET_max, as calculated by subtracting VO_2max and MET_max obtained at T0 from those obtained at T1, divided by VO_2max at T0 and multiplied by 100.

Conclusion

Post-exercise HRR measured at 3 weeks after the AMI onset can reflect the exercise capacity 3 months after the first ETT. However, it may be difficult to correlate post-exercise HRR at T0 with the degree of increase in cardiopulmonary exercise capacity in patients with AMI.

Evaluation of Resting Cardiac Power Output as a Prognostic Factor in Patients with Advanced Heart Failure

If the heart is represented by a hydraulic pump, cardiac power represents the hydraulic function of the heart. Cardiac pump function is frequently determined through left ventricular ejection fraction using imaging. This study aims to validate resting cardiac power output (CPO) as a predictive biomarker in patients with advanced heart failure (HF). One hundred and seventy-two patients with HF severe enough to warrant cardiac transplantation were retrospectively reviewed at a single tertiary care institution between September 2010 and July 2013. Patients were initially evaluated with simultaneous right-sided and left-sided cardiac catheter-based hemodynamic measurements, followed by longitudinal follow-up (median of 52 months) for adverse events (cardiac mortality, cardiac transplantation, or ventricular assist device placement). Median resting CPO was 0.54 W (long rank chi-square = 33.6; p < 0.0001). Decreased resting CPO (<0.54 W) predicted increased risk for adverse outcomes. Fifty cardiac deaths, 10 cardiac transplants, and 12 ventricular assist device placements were documented. The prognostic relevance of resting CPO remained significant after adjustment for age, gender, left ventricular ejection fraction, mean arterial pressure, pulmonary vascular resistance, right atrial pressure, and estimated glomerular filtration rate (HR, 3.53; 95% confidence interval, 1.66 to 6.77; p = 0.0007). In conclusion, lower resting CPO supplies independent prediction of adverse outcomes. Thus, it could be effectively used for risk stratification in patients with advanced HF.

Clinical Classification of Heart Failure Patients Using Cardiac Function during Exercise

An effective approach for determining the clinical classification of heart failure (HF) patients is to estimate cardiac hemodynamics during exercise. This approach is strengthened further when measurements including cardiac power are used to describe cardiac hemodynamics. We hypothesize that cardiac power quantifies the hemodynamic and pressure-generating capability of the heart, relating with exercise tolerance better than traditional measurements in HF.

Cardiopulmonary Exercise Testing in Heart Failure

Exercise intolerance, indicated by dyspnea and fatigue during exertion, is a cardinal manifestation of heart failure (HF). Cardiopulmonary exercise testing (CPET) precisely defines maximum exercise capacity through measurement of peak oxygen uptake (VO2). Peak VO2 values have a critical role in informing patient selection for advanced HF interventions such as heart transplantation and ventricular assist devices. Oxygen uptake and ventilatory patterns obtained during the submaximal portion of CPET are also valuable to recognize because of their ease of ascertainment during low-level exercise, relevance to ability to perform activities of daily living, independence from volitional effort, and strong relationship to prognosis in HF. The ability of peak VO2 and other CPET variables to be measured reproducibly and to accurately reflect HF severity is increasingly recognized and endorsed by scientific statements. Integration of CPET with invasive hemodynamic monitoring and cardiac imaging during exercise provides comprehensive characterization of multisystem reserve capacity that can inform prognosis and the need for cardiac interventions. Here, we review both practical aspects of conducting CPETs in patients with HF for clinical and research purposes as well as interpretation of gas exchange patterns across the spectrum of preclinical HF to advanced HF.

Unexplained exertional dyspnea caused by low ventricular filling pressures: results from clinical invasive cardiopulmonary exercise testing

To determine whether low ventricular filling pressures are a clinically relevant etiology of unexplained dyspnea on exertion, a database of 619 consecutive, clinically indicated invasive cardiopulmonary exercise tests (iCPETs) was reviewed to identify patients with low maximum aerobic capacity (V̇o2max) due to inadequate peak cardiac output (Qtmax) with normal biventricular ejection fractions and without pulmonary hypertension (impaired: n = 49, V̇o2max = 53% predicted [interquartile range (IQR): 47%-64%], Qtmax = 72% predicted [62%-76%]). These were compared to patients with a normal exercise response (normal: n = 28, V̇o2max = 86% predicted [84%-97%], Qtmax = 108% predicted [97%-115%]). Before exercise, all patients received up to 2 L of intravenous normal saline to target an upright pulmonary capillary wedge pressure (PCWP) of ≥5 mmHg. Despite this treatment, biventricular filling pressures at peak exercise were lower in the impaired group than in the normal group (right atrial pressure [RAP]: 6 [IQR: 5-8] vs. 9 [7-10] mmHg, P = 0.004; PCWP: 12 [10-16] vs. 17 [14-19] mmHg, P < 0.001), associated with decreased stroke volume (SV) augmentation with exercise (+13 ± 10 [standard deviation (SD)] vs. +18 ± 10 mL/m(2), P = 0.014). A review of hemodynamic data from 23 patients with low RAP on an initial iCPET who underwent a second iCPET after saline infusion (2.0 ± 0.5 L) demonstrated that 16 of 23 patients responded with increases in Qtmax ([+24% predicted [IQR: 14%-34%]), V̇o2max (+10% predicted [7%-12%]), and maximum SV (+26% ± 17% [SD]). These data suggest that inadequate ventricular filling related to low venous pressure is a clinically relevant cause of exercise intolerance.

The value of novel invasive hemodynamic parameters added to the TIMI risk score for short-term prognosis assessment in patients with ST segment elevation myocardial infarction

BACKGROUND

We compared the prognostic capacity of conventional and novel invasive parameters derived from the slope of the preload recruitable stroke work relationship (PRSW) in STEMI patients and assessed their contribution to the TIMI risk score.

METHODS

Left ventricular end-diastolic pressure (EDP), ejection fraction (EF), pressure adjusted maximum rate of pressure change in the left ventricle (dP/dt/P), aortic systolic pressure to EDP ratio (SBP/EDP) and end-diastolic volume adjusted stroke work (EW), derived from the slope of the PRSW relationship, were obtained during the emergency cardiac catheterization in 523 STEMI patients. The predictive power of the analyzed parameters for 30-day and 1-year mortality was evaluated using C-statistics and reclassification analysis was adopted to assess the improvement in TIMI score.

RESULTS

The highest area under the curve (AUC) values for 30-day mortality were observed for EW (0.872(95% confidence interval 0.801-0.943)), SBP/EDP (0.843(0.758-0.928)) and EF (0.833(0.735-0.931)); p<0.001 for all values. For 1-year mortality the best predictive value was found for EW (0.806(0.724-0.887) and EF (0.793(0.703-0.883)); p<0.001 for both. The addition of EDP, SBP/EDP ratio and EW to TIMI score significantly increased the AUC according to De Long's test. For 30-day mortality, increased discriminative power following addition to the TIMI score was observed for EW and SBP/EDP (Integrated Discrimination Improvement was 0.086(0.033-0.140), p=0.002 and 0.078(0.028-0.128), p=0.002, respectively).

CONCLUSIONS

EW and SBP/EDP are prognostic markers with high predictive value for 30-day and 1-year mortality. Both parameters, easily obtained during emergency catheterization, improve the discriminatory capacity of the TIMI score for 30-day mortality.

Skeletal Muscle Changes in Chronic Cardiac Disease and Failure

Peak exercise performance in healthy man is limited not only by pulmonary or skeletal muscle function but also by cardiac function. Thus, abnormalities in cardiac function will have a major impact on exercise performance. Many cardiac diseases affect exercise performance and indeed for some cardiac conditions such as atherosclerotic heart disease, exercise testing is frequently used not only to measure functional capacity but also to make a diagnosis of heart disease, evaluate the efficacy of treatment, and predict prognosis. Early in the course of cardiac diseases, exercise performance will be minimally affected but with disease progression impairment in exercise capacity will become apparent. Ejection fraction, that is, the percent of blood volume ejected with each cardiac cycle is often used as a measure of cardiac performance but frequently there is a dissociation between the ejection fraction and exercise capacity in patients with heart disease. How abnormalities in cardiac function impacts the muscles, vasculature, and lungs to impact exercise performance will here be reviewed. The focus of this work will be on patients with systolic heart failure as the incidence and prevalence of heart failure is reaching epidemic proportions and heart failure is the end result of many other chronic cardiac diseases. The prognostic role of exercise and benefits of exercise training will also be discussed.

Pulmonary congestion at rest and abnormal ventilation during exercise in chronic systolic heart failure

BACKGROUND

In patients with chronic heart failure, abnormal ventilation at cardiopulmonary testing (expressed by minute ventilation-to-carbon dioxide production, or VE/VCO2 slope, and resting end-tidal CO2 pressure) may derive either from abnormal autonomic or chemoreflex regulation or from lung dysfunction induced by pulmonary congestion. The latter hypothesis is supported by measurement of pulmonary capillary wedge pressure, which cannot be obtained routinely but may be estimated noninvasively by measuring transthoracic conductance (thoracic fluid content 1/kΩ) with impedance cardiography.

METHODS AND RESULTS

Preliminarily, in 9 patients undergoing invasive hemodynamics during cardiopulmonary testing, we demonstrated a significant relationship between VE/VCO2 slope and resting end-tidal CO2 pressure with baseline and peak pulmonary capillary wedge pressure. Later, noninvasive hemodynamic evaluation by impedance cardiography was performed before cardiopulmonary testing in 190 patients with chronic systolic heart failure and normal lung function (aged 67±3 years, 71% with ischemia, ejection fraction 32±7%, 69% with implantable cardioverter-defibrillator or cardiac resynchronization therapy). In this group, we determined the relationship between abnormal ventilation (VE/VCO2 slope and resting end-tidal CO2 pressure) and transthoracic conductance. In the whole population, thoracic fluid content values were significantly related to VE/VCO2 slope (R=0.63, P<0.0001) and to resting end-tidal CO2 pressure (R=-0.44, P<0.001).

CONCLUSIONS

In patients with chronic heart failure, abnormal ventilation during exercise may be related in part to pulmonary congestion, as detected by resting baseline impedance cardiography.

Assessment of cardiac output with transpulmonary thermodilution during exercise in humans

The accuracy and reproducibility of transpulmonary thermodilution (TPTd) to assess cardiac output (Q̇) in exercising men was determined using indocyanine green (ICG) dilution as a reference method. TPTd has been utilized for the assessment of Q̇ and preload indexes of global end-diastolic volume and intrathoracic blood volume, as well as extravascular lung water (EVLW) in resting humans. It remains unknown if this technique is also accurate and reproducible during exercise. Sixteen healthy men underwent catheterization of the right femoral vein (for iced saline injection), an antecubital vein (ICG injection), and femoral artery (thermistor) to determine their Q̇ by TPTd and ICG concentration during incremental one- and two-legged pedaling on a cycle ergometer and combined arm cranking with leg pedaling to exhaustion. There was a close relationship between TPTd-Q̇ and ICG-Q̇ ( r = 0.95, n = 151, standard error of the estimate: 1.452 l/min, P < 0.001; mean difference of 0.06 l/min; limits of agreement −2.98 to 2.86 l/min), and TPTd-Q̇ and ICG-Q̇ increased linearly with oxygen uptake with similar intercepts and slopes. Both methods had mean coefficients of variation close to 5% for Q̇, global end-diastolic volume, and intrathoracic blood volume. The mean coefficient of variation of EVLW, assessed with both indicators (ICG and thermal) was 17% and was sensitive enough to detect a reduction in EVLW of 107 ml when changing from resting supine to upright exercise. In summary, TPTd with bolus injection into the femoral vein is an accurate and reproducible method to assess Q̇ during exercise in humans.

Do optimal prognostic thresholds in continuous physiological variables really exist? Analysis of origin of apparent thresholds, with systematic review for peak oxygen consumption, ejection fraction and BNP

Background

Clinicians are sometimes advised to make decisions using thresholds in measured variables, derived from prognostic studies.

Objectives

We studied why there are conflicting apparently-optimal prognostic thresholds, for example in exercise peak oxygen uptake (pVO₂), ejection fraction (EF), and Brain Natriuretic Peptide (BNP) in heart failure (HF).

Data Sources and Eligibility Criteria

Studies testing pVO₂, EF or BNP prognostic thresholds in heart failure, published between 1990 and 2010, listed on Pubmed.

Methods

First, we examined studies testing pVO₂, EF or BNP prognostic thresholds. Second, we created repeated simulations of 1500 patients to identify whether an apparently-optimal prognostic threshold indicates step change in risk.

Results

33 studies (8946 patients) tested a pVO₂ threshold. 18 found it prognostically significant: the actual reported threshold ranged widely (10–18 ml/kg/min) but was overwhelmingly controlled by the individual study population's mean pVO₂ (r = 0.86, p<0.00001). In contrast, the 15 negative publications were testing thresholds 199% further from their means (p = 0.0001). Likewise, of 35 EF studies (10220 patients), the thresholds in the 22 positive reports were strongly determined by study means (r = 0.90, p<0.0001). Similarly, in the 19 positives of 20 BNP studies (9725 patients): r = 0.86 (p<0.0001).

Second, survival simulations always discovered a “most significant” threshold, even when there was definitely no step change in mortality. With linear increase in risk, the apparently-optimal threshold was always near the sample mean (r = 0.99, p<0.001).

Limitations

This study cannot report the best threshold for any of these variables; instead it explains how common clinical research procedures routinely produce false thresholds.

Key Findings

First, shifting (and/or disappearance) of an apparently-optimal prognostic threshold is strongly determined by studies' average pVO₂, EF or BNP. Second, apparently-optimal thresholds always appear, even with no step in prognosis.

Conclusions

Emphatic therapeutic guidance based on thresholds from observational studies may be ill-founded. We should not assume that optimal thresholds, or any thresholds, exist.

Functional and hemodynamic cardiac determinants of exercise capacity in patients with systolic heart failure

Decreased exercise capacity is the main symptom in patients with heart failure (HF). We assessed the association among noninvasively determined maximal cardiac output at exercise, systolic and diastolic cardiac functions at rest, and peak oxygen uptake (pVo(2)) exercise capacity in patients with congestive HF. We studied 102 patients 62 ± 11 years of age with New York Heart Association class II to IV stable HF and left ventricular (LV) ejection fraction <45%. All patients underwent echocardiography and a treadmill cardiopulmonary exercise test for evaluation of pVo(2) corrected for fat-free mass. During the cardiopulmonary exercise test, cardiac output was estimated noninvasively and continuously using Nexfin HD. Fat-free mass-corrected pVo(2) was associated in an univariate linear regression analysis with peak exercise cardiac index (CI) (beta 0.511, p <0.001), LV end-diastolic pressure estimates (peak early diastolic filling velocity/early diastolic tissue velocity [E/e'], beta -0.363, p = 0.001), and right ventricular function (tricuspid annular plane systolic excursion, beta 0.393, p <0.001). In multivariate analysis peak exercise CI (beta 0.380, p = 0.001), but not cardiac output or LV ejection fraction at rest, was an independent predictor of pVo(2). Other independent predictors of pVo(2) were E/e' (beta -0.276, p = 0.009) and tricuspid annular plane systolic excursion (beta 0.392, p <0.001), also when adjusted for age and gender. In conclusion, peak CI is an independent predictor of fat-free mass-corrected pVo(2) in patients with systolic HF. Of all echocardiographic parameters at rest, right ventricular function and E/e' were independently and significantly associated with pVo(2), whereas LV ejection fraction at rest was not.

Estimation of cardiac output in patients with congestive heart failure by analysis of right ventricular pressure waveforms

Background

Cardiac output (CO) is an important determinant of the hemodynamic state in patients with congestive heart failure (CHF). We tested the hypothesis that CO can be estimated from the right ventricular (RV) pressure waveform in CHF patients using a pulse contour cardiac output algorithm that considers constant but patient specific RV outflow tract characteristic impedance.

Method

In 12 patients with CHF, breath-by-breath Fick CO and RV pressure waveforms were recorded utilizing an implantable hemodynamic monitor during a bicycle exercise protocol. These data were analyzed retrospectively to assess changes in characteristic impedance of the RV outflow tract during exercise. Four patients that were implanted with an implantable cardiac defibrillator (ICD) implementing the algorithm were studied prospectively. During a two staged sub-maximal bicycle exercise test conducted at 4 and 16 weeks of implant, COs measured by direct Fick technique and estimated by the ICD were recorded and compared.

Results

At rest the total pulmonary arterial resistance and the characteristic impedance were 675 ± 345 and 48 ± 18 dyn.s.cm^-5, respectively. During sub-maximal exercise, the total pulmonary arterial resistance decreased (Δ 91 ± 159 dyn.s.cm^-5, p < 0.05) but the characteristic impedance was unaffected (Δ 3 ± 9 dyn.s.cm^-5, NS). The algorithm derived cardiac output estimates correlated with Fick CO (7.6 ± 2.5 L/min, R² = 0.92) with a limit of agreement of 1.7 L/min and tracked changes in Fick CO (R² = 0.73).

Conclusions

The analysis of right ventricular pressure waveforms continuously recorded by an implantable hemodynamic monitor provides an estimate of CO and may prove useful in guiding treatment in patients with CHF.

Assessment of cardiac dynamics during stress echocardiography by the peak power output-to-left ventricular mass ratio

Peak cardiac power-to-mass and peak mass-to-power are variables that couple cardiac power output with left ventricular (LV) mass at peak exercise or during maximal inotropic stimulation. Quantitative stress echocardiography enables the calculation of power output according to the formula: 133 × 10–6 × stroke volume per second (ml) × mean blood pressure (BP; mmHg) × heart rate. Power-to-mass may be calculated as LV power output per 100 g of LV mass: 100 g × LV power output divided by LV mass (W/100 g). Conversely, mass-to-power may be estimated by dividing LV mass index by LV power output (g/m2/W). With a little rearrangement of the formulas we can write: power-to-mass (W/100 g) = 0.222 × cardiac output (l/min) × mean BP (mmHg)/LV mass (g) and mass-to-power (g/m2/W) = LV mass index/0.00222 × cardiac output (l/min) × mean BP (mmHg). These parameters reflect the energy delivery of ventricular myocardium with respect to potential energy that is stored in LV mass. The assessment of peak power-to-mass and peak mass-to-power indices may be useful to distinguish compensatory versus maladaptive remodeling in patients with LV dysfunction. When the integrity of myocardial structure is compromised, a disproportion becomes apparent between maximal cardiac power output and LV mass and this leads to either a reduction of peak power-to-mass or an increase of peak mass-to-power. Preliminary reports have demonstrated the usefulness and the prognostic value of peak power-to-mass and peak mass-to-power in patients with LV systolic dysfunction and coronary artery disease.