Oxygen uptake kinetics and cardiopulmonary performance in lone atrial fibrillation and the effects of sotalol

Exercise Ventricular Rates, Cardiopulmonary Exercise Performance, and Mortality in Patients With Heart Failure With Atrial Fibrillation

BACKGROUND

In heart failure (HF) with sinus rhythm, resting and exercise heart rates correlate with exercise capacity and mortality. However, in HF with atrial fibrillation (AF), this correlation is unknown. Our aim is to investigate the association of resting and exercise ventricular rates (VRs) with exercise capacity and mortality in HF with AF.

METHODS

We identified 903 patients with HF and AF referred for cardiopulmonary stress testing. AF was defined as history of AF and AF during cardiopulmonary stress testing. We constructed multivariable models to evaluate the association of resting VR, peak exercise VR, VR reserve (peak VR-resting VR), and chronotropic index with (1) peak oxygen consumption (PVO₂) ≤18 mL/kg per minute, (2) continuous PVO₂, and (3) 10-year all-cause mortality.

RESULTS

Median (25th-75th percentile) age was 60 (52-67) years, left ventricular ejection fraction was 25 (15-50)%, and 76.1% were males. Patients with lower (quartile 1) compared with higher (quartile 4) peak VR, VR reserve, and chronotropic index were more likely to have PVO₂ ≤18 mL/kg per min (adjusted odds ratio [95% CI]: 14.92 [8.07-27.58], 24.60 [12.36-48.98], and 22.31 [11.24-44.27], respectively), and higher all-cause mortality (adjusted hazard ratio [95% CI]: 2.56 [1.62-4.04], 2.29 [1.47-3.59], and 2.30 [1.51-3.49], respectively). For every 10 beats per minute increase in VR reserve, PVO₂ increased by 1.05 mL/kg per minute (B-coefficient [95% CI]: 1.05 [0.94-1.15]) and mortality decreased by 12% (adjusted hazard ratio [95% CI]: 0.88 [0.83-0.94]). Resting VR was associated with PVO₂ (B-coefficient [95% CI]: -0.46 [-0.70 to -0.23]) but not mortality (adjusted hazard ratio [95% CI]: 0.97 [0.88-1.06]).

CONCLUSIONS

In patients with HF and AF, higher resting VR and lower peak exercise VR, VR reserve, and chronotropic index were all associated with worse peak exercise capacity, but only lower exercise VR parameters were associated with higher mortality. Dedicated studies are needed to gauge whether modulating exercise VR enhances exercise performance and outcomes.

Physiological and Perceived Exertion Responses during Exercise: Effect of β-blockade

PURPOSE

This study investigated the effect of β-blockade on physiological and perceived exertion (RPE) responses during incremental treadmill exercise.

METHODS

Sixteen healthy participants (n = 8 men; age, 25.3 ± 4.6 yr) performed a maximal treadmill exercise test after ingestion of 100 mg metoprolol or placebo, with a double-blind, randomized, and counterbalanced design. Heart rate (HR), ventilatory, and gas exchange variables were measured continuously, and participants reported RPE at the end of each minute. Physiological and RPE responses during each condition were compared at the ventilatory threshold (VT), respiratory compensation point, and at maximal exercise using repeated-measures ANOVA. Linear regression modeled relationships between perceived exertion and physiological variables.

RESULTS

The HR and V˙O2 at the VT, respiratory compensation point, and maximal exercise were all significantly lower after β-blockade (P < 0.05). However, when standardized to within condition peak values, differences were no longer significant. The RPE associated with VT was higher after β-blockade (12.9 ± 1.0 vs 12.3 ± 1.2, P < 0.05) but lower at maximal exercise (19.1 ± 0.6 vs 19.4 ± 0.5, P < 0.05). Increases in RPE relative to HR were greater after β-blockade and remained significant when expressed relative to peak HR. There was no difference in the growth of the relationship between RPE and V˙O2 across conditions, although the origin of the relationship was higher with β-blockade.

CONCLUSIONS

Although β-blockade resulted in a significant reduction in exercising HR and V˙O2, the RPE for a given relative intensity remained unchanged. The relationship between RPE and V˙O2 was not affected by β-blockade. The results provide evidence that RPE is a useful and reliable measure for exercise testing and prescription in patients prescribed β-blockade therapy.

Influence of atrial fibrillation on oxygen uptake and exercise tolerance in cardiovascular patients; close association with heart rate response

To investigate the effect of atrial fibrillation (AF) on the oxygen uptake and exercise tolerance, we evaluated cardiopulmonary exercise test (CPET) data in AF patients and heart rate-matched controls with sinus rhythm (cSR) who received ambulatory cardiac rehabilitation. We compared CPET data between AF (N = 27) and cSR patients (N = 106) who had similar HRs at rest and the peak points. Oxygen uptake (VO₂)/kg and relative O₂ pulse (ml/bpm/kg) at rest and the anaerobic threshold (AT) level was not different between AF and cSR patients, but these parameters above the AT level were significantly lower in AF than in cSR patients. Concisely the parallel increase of relative O₂ pulse during exercise was blunted above the respiratory compensation level (Rc) in the AF group. In addition, the HR change during exercise was inversely correlated with the increase of the O₂ pulse above the AT level and this inverse correlation was more prominent in AF patients than in cSR patients. In conclusion, the value of VO₂ was significantly lower above the AT level in AF patients. The trend of O₂ pulse above the AT level was strongly associated with the detrimental response of HR increase and the response was markedly exaggerated in the AF patients.

Impact of Atrial Fibrillation on Exercise Capacity and Mortality in Heart Failure With Preserved Ejection Fraction: Insights From Cardiopulmonary Stress Testing

Background

Atrial fibrillation (AF) has been objectively associated with exercise intolerance in patients with heart failure with reduced ejection fraction; however, its impact in patients with heart failure with preserved ejection fraction has not been fully scrutinized.

Methods and Results

We identified 1744 patients with heart failure and ejection fraction ≥50% referred for cardiopulmonary stress testing at the Cleveland Clinic (Cleveland, OH), 239 of whom had AF. We used inverse probability of treatment weighting to balance clinical characteristics between patients with and without AF. A weighted linear regression model, adjusted for unbalanced variables (age, sex, diagnosis, hypertension, and β‐blocker use), was used to compare metabolic stress parameters and 8‐year total mortality (social security index) between both groups. Weighted mean ejection fraction was 58±5.9% in the entire population. After adjusting for unbalanced weighted variables, patients with AF versus those without AF had lower mean peak oxygen consumption (18.5±6.2 versus 20.3±7.1 mL/kg per minute), oxygen pulse (12.4±4.3 versus 12.9±4.7 mL/beat), and circulatory power (2877±1402 versus 3351±1788 mm Hg·mL/kg per minute) (P<0.001 for all comparisons) but similar submaximal exercise capacity (oxygen consumption at anaerobic threshold, 12.0±5.1 versus 12.4±6.0mL/kg per minute; P =0.3). Both groups had similar peak heart rate, whereas mean peak systolic blood pressure was lower in the AF group (150±35 versus 160±51 mm Hg; P<0.001). Moreover, AF was associated with higher total mortality.

Conclusions

In the largest study of its kind, we demonstrate that AF is associated with peak exercise intolerance, impaired contractile reserve, and increased mortality in patients with heart failure with preserved ejection fraction. Whether AF is the primary offender in these patients or merely a bystander to worse diastolic function requires further investigation.

Oxygen uptake kinetics

Muscular exercise requires transitions to and from metabolic rates often exceeding an order of magnitude above resting and places prodigious demands on the oxidative machinery and O2-transport pathway. The science of kinetics seeks to characterize the dynamic profiles of the respiratory, cardiovascular, and muscular systems and their integration to resolve the essential control mechanisms of muscle energetics and oxidative function: a goal not feasible using the steady-state response. Essential features of the O2 uptake (VO2) kinetics response are highly conserved across the animal kingdom. For a given metabolic demand, fast VO2 kinetics mandates a smaller O2 deficit, less substrate-level phosphorylation and high exercise tolerance. By the same token, slow VO2 kinetics incurs a high O2 deficit, presents a greater challenge to homeostasis and presages poor exercise tolerance. Compelling evidence supports that, in healthy individuals walking, running, or cycling upright, VO2 kinetics control resides within the exercising muscle(s) and is therefore not dependent upon, or limited by, upstream O2-transport systems. However, disease, aging, and other imposed constraints may redistribute VO2 kinetics control more proximally within the O2-transport system. Greater understanding of VO2 kinetics control and, in particular, its relation to the plasticity of the O2-transport/utilization system is considered important for improving the human condition, not just in athletic populations, but crucially for patients suffering from pathologically slowed VO2 kinetics as well as the burgeoning elderly population.

Standards for the use of cardiopulmonary exercise testing for the functional evaluation of cardiac patients: a report from the Exercise Physiology Section of the European Association for Cardiovascular Prevention and Rehabilitation

Cardiopulmonary exercise testing (CPET) is a methodology that has profoundly affected the approach to patients' functional evaluation, linking performance and physiological parameters to the underlying metabolic substratum and providing highly reproducible exercise capacity descriptors. This study provides professionals with an up-to-date review of the rationale sustaining the use of CPET for functional evaluation of cardiac patients in both the clinical and research settings, describing parameters obtainable either from ramp incremental or step constant-power CPET and illustrating the wealth of information obtainable through an experienced use of this powerful tool. The choice of parameters to be measured will depend on the specific goals of functional evaluation in the individual patient, namely, exercise tolerance assessment, training prescription, treatment efficacy evaluation, and/or investigation of exercise-induced adaptations of the oxygen transport/utilization system. The full potentialities of CPET in the clinical and research setting still remain largely underused and strong efforts are recommended to promote a more widespread use of CPET in the functional evaluation of cardiac patients.

Quality of Life, Exercise Capacity and Comorbidity in Old Patients with Permanent Atrial Fibrillation

Background: The impact of atrial fibrillation (AF) on quality of life (QoL) differs with the AF population studied and is influenced by comorbidity. In hospital-based studies younger and highly symptomatic patients may be overrepresented. We performed an observational cross sectional study in two municipalities, comparing 75 year-old patients with and without permanent atrial fibrillation, with respect to health-related QoL and exercise capacity, with adjustment for the effects of confounders. Methods: Maximal treadmill exercise testing provided peak oxygen uptake (VO2 peak). Health-related QoL was assessed by self-completed SF-36 questionnaires. The lowest quartile identified poor outcomes.

RESULTS

27 subjects with permanent AF and 71 subjects in sinus rhythm participated. AF patients had higher prevalence of compensated chronic heart failure (p < 0.001), valvular heart disease (p < 0.001), lower mean VO2 peak (22.7 ± 5.5 vs. 28.6 ± 6.3 ml/kg/min; p < 0.001), and more often poor VO2 peak; crude OR 5.3 (95%CI 1.8, 15.3), adjusted OR 7.5 (2.0, 28.3). Median Physical Component Summary score (with 25th and 75th percentile) was 41 (31, 51) in AF vs. 52 (45, 55) in controls (p < 0.001). Furthermore, the AF group had higher odds for poor physical QoL scores; crude OR 5.0 (1.8, 13.7), adjusted OR 4.3 (1.5, 12.4). Median Mental Component Summary score was 56 (42, 61) in the AF group vs. 57 (51, 60) in controls (p=0.565). The AF group had non-significantly increased odds for poor mental QoL scores; crude OR 2.3 (0.8, 6.2), adjusted OR 2.8 (1.0, 8.4). Conclusion: Also after adjustment for confounders, older patients with permanent AF had higher odds for poor exercise capacity and poor physical QoL compared to subjects in sinus rhythm.

Endothelial dysfunction and exercise performance in lone atrial fibrillation or associated with hypertension or diabetes: different results with cardioversion

Endothelial dysfunction and underperfusion of exercising muscle contribute to exercise intolerance, hyperventilation, and breathlessness in atrial fibrillation (AF). Cardioversion (CV) improves endothelial function and exercise performance. We examined whether CV is equally beneficial in diabetes and hypertension, diseases that cause endothelial dysfunction and are often associated with AF. Cardiopulmonary exercise and pulmonary and endothelial (brachial artery flow-mediated dilation) function were tested before and after CV in patients with AF alone ( n = 18, group 1) or AF with hypertension ( n = 19, group 2) or diabetes ( n = 19, group 3). Compared with group 1, peak exercise workload, O2 consumption (V̇o2), O2 pulse, aerobic efficiency (ΔV̇o2/ΔWR), and ratio of brachial diameter changes to flow changes (Δ D/ΔF) were reduced in group 2 and, to a greater extent, in group 3; exercise ventilation efficiency (V̇e/V̇co2 slope) and dead space-to-tidal volume ratio (Vd/Vt) were similar among groups. CV had less effect on peak workload (+7% vs. +18%), peak V̇o2 (+12% vs. +17%), O2 pulse (+33% vs. +50%), ΔV̇o2/ΔWR (+7% vs. +12%), V̇e/V̇co2 slope (−6% vs. −12%), Δ D/ΔF (+7% vs. +10%), and breathlessness (Borg scale) in group 2 than in group 1 and was ineffective in group 3. The antioxidant vitamin C, tested in eight additional patients in each cohort, improved flow-mediated dilation in groups 1 and 2 before, but not after, CV and was ineffective in group 3, suggesting that the oxidative injury is least in lone AF, greater in hypertension with AF, and greater still in diabetes with AF. Comorbidities that impair endothelial activity worsen endothelial dysfunction and exercise intolerance in AF. The advantages of CV appear to be inversely related to the extent of the underlying oxidative injury.

Functional Status in Rate- Versus Rhythm-Control Strategies for Atrial Fibrillation

OBJECTIVES

The Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) functional status substudy aimed to test the hypothesis that functional status is similar in rate-control and rhythm-control strategies.

BACKGROUND

Randomized studies, including the AFFIRM study, have failed to demonstrate survival benefits between rate-control and rhythm-control strategies for atrial fibrillation (AF). However, AF may cause functional capacity or cognitive impairment that might justify maintenance of sinus rhythm.

METHODS

Investigators of the AFFIRM study enrolled 4,060 patients with AF who required long-term therapy and who were 65 years of age or older or who had another risk factor for stroke or death. New York Heart Association functional class (NYHA-FC) and Canadian Cardiovascular Society Angina Classification were assessed at initial and each follow-up visit. From 22 randomly chosen functional status substudy sites, 245 participants underwent 6-min walk tests and Mini-Mental State Examination (MMSE) at initial, two-month, and yearly visits. Patients were assigned randomly to rate-controlling drugs, allowing AF to persist, or rhythm-controlling antiarrhythmic drugs, to maintain sinus rhythm.

RESULTS

The NYHA-FC worsened with time in both rate-control and rhythm-control groups, with no differences between groups. Presence of AF was associated with worse NYHA-FC (p < 0.0001). No differences were observed in Canadian Cardiovascular Society Angina Classification or MMSE scores. Six-minute walk distance improved over time in both study arms. On average, walk distance was 94 feet greater in the rhythm-control group (adjusted p = 0.049).

CONCLUSIONS

Modest improvement in 6-min walk distance was noted in the rhythm-control arm. Presence of AF was associated with worse NYHA-FC. No difference in cognitive function was detected.

Effect of acute blood pressure reduction on oxygen uptake kinetics at the onset of exercise in hypertensive patients

The aim of the present study was to investigate the adverse effects of hypertension on the cardiovascular system in daily activities and the effect of acute blood pressure reduction on oxygen (O(2)) uptake kinetics. Twenty hypertensive patients were included in the study group. Patients performed treadmill exercise tests (2.5 km/hour and 5 inclines) twice, before and after blood pressure reduction with sublingual captopril. In the control group, ten hypertensive patients underwent two tests one hour apart without blood pressure reduction brought about by drug therapy. The changes in O(2) kinetic values (O(2) deficit and mean response time [MRT]) between the two tests were investigated. In the study group, the O(2) deficit and MRT values measured during the first exercise testing were found to be 547 +/- 183 mL and 40 +/- 9 seconds, while those in the second exercise testing were 401 +/- 127 mL and 34 +/- 7 seconds, respectively. In the control group, the O(2) deficit and MRT values measured during the first exercise test were 491 +/- 217 mL and 42 +/- 16 seconds and 515 +/- 159 mL and 41 +/- 13 seconds in the second exercise test. The differences in O(2) deficit and MRT in the study group were considered to be statistically significant (P = 0.008 and P = 0.004, respectively). Based on our findings, there was a significant improvement in O(2) kinetic values with an acute reduction in blood pressure in hypertensive patients, most likely as a result of an improved response in cardiac output.

Exercise hyperventilation, dyspnea sensation, and ergoreflex activation in lone atrial fibrillation

Lone atrial fibrillation may be associated with daily life disability and exercise limitation. The extracardiac pathophysiology of these effects is poorly explored. In 35 subjects with lone atrial fibrillation (mean age 67 +/- 7 yr), we investigated pulmonary function, symptom-limited cardiopulmonary exercise performance, muscle ergoreflex (handgrip exercise) contribution to ventilation, and brachial artery flow-mediated dilation (as a measure of endothelial function) before and after (average interval 20 +/- 5 days) restoring sinus rhythm with external cardioversion. Respiratory volumes and lung diffusing capacity at rest were within normal limits during both atrial fibrillation and after restoring sinus rhythm. Cardioversion was associated with the following changes: a decrease of the slope of exercise ventilation vs. CO2 production (from 35 +/- 5 to 29 +/- 3; P <0.01) and of dyspnea sensation (Borg score from 4 to 2) and an increase of peak oxygen uptake (Vo2; from 16 +/- 4 to 20 +/- 5 ml.min(-1).kg(-1); P <0.01), Vo2 at anaerobic threshold (from 11 +/- 2 to 13 +/- 2 ml.min(-1).kg(-1); P <0.05), and O2 pulse (from 8 +/- 3 to 11 +/- 3 ml/beat; P <0.01). After cardioversion, the observed improvement in ventilatory efficiency was accompanied by a significant peak end-tidal CO2 increase (from 33 +/- 2 to 37 +/- 2 mmHg; P <0.01) and no changes in dead space-to-tidal volume ratio (from 0.23 +/- 0.03 to 0.23 +/- 0.02; P=not significant). In addition, the ergoreflex contribution to ventilation was remarkably attenuated, and the brachial artery flow-mediated dilatation was significantly augmented (from 0.32 +/- 0.07 to 0.42 +/- 0.08 mm; P <0.01). Ten patients had atrial fibrillation relapse and, compared with values after restoration of regular sinus rhythm, invariably showed worsening of endothelial function, exercise ventilatory efficiency, and muscle ergoreflex contribution to ventilation. In subjects with lone atrial fibrillation, an impairment in ventilatory efficiency appears to be involved in the pathophysiology of exercise limitation, and to be primarily related with a demodulated peripheral control of ventilation.

Impact of informed consent requirements on cardiac arrest research in the United States: exception from consent or from research?

INTRODUCTION

Research in patients with life-threatening illness such as cardiac arrest is challenging since they can not consent. The Food and Drug Administration addressed research under emergency conditions by publishing new criteria for exception from informed consent in 1996. We systematically reviewed randomized trials over a 10-year period to assess the impact of these regulations.

METHODS

Case-control study of published trials for cardiac arrest (cases) and atrial fibrillation (controls.) Studies were identified by using structured searches of MEDLINE and EMBASE from 1992 to 2002. Included were studies using random allocation in humans with cardiac arrest or atrial fibrillation prior to enrollment. Excluded were duplicate publications. Number of American trials, foreign trials and proportion of trials of American origin were compared by using regression analysis. Changes in cardiac arrest versus atrial fibrillation trials were calculated as risk differences.

RESULTS

Of 4982 identified cardiac arrest studies, 57 (1.1%) were randomized trials. The number of American cardiac arrest trials decreased by 15% (95% CI: 8, 22%) annually (P = 0.05). The proportion of cardiac arrest trials of American origin decreased by 16% (95% CI: 10, 22%) annually (P = 0.006). Of 5596 identified atrial fibrillation studies, 197 trials (3.5%) were randomized trials. The risk difference between cardiac arrest versus atrial fibrillation trials being of American origin decreased significantly (annual difference -5.8% (95% CI: -10, -0.1%), P = 0.03).

INTERPRETATION

Fewer American cardiac arrest trials were published during the last decade, when federal consent requirements changed. Regulatory requirements for clinical trials may inhibit improvements in care and threaten public health.

Pharmacological rate control of atrial fibrillation

To control ventricular rate in patients with AF, physicians should seek to control heart rate at rest and with exertion. The goal has to be achieved while minimizing costs and adverse effects. For emergency use, i.v. diltiazem or esmolol are drugs useful because of their rapid onset of action. They have to be used with caution in patients with concomitant left ventricular failure symptoms, however. For most patients with AF, chronic control of the ventricular rate can be achieved with one drug. For the chronic control of ventricular rate in patients with AF and normal ventricular function, diltiazem, atenolol, are metoprolol are probably the drugs of choice. For patients with AF and structurally abnormal hearts, atenolol, metoprolol, or carvedilol are appropriate choices. Adequate ventricular rate control by pharmacological agents should be evaluated by either 24-hour Holter monitoring or a submaximal stress test to determine the resting and exercise ventricular rate. If the mean ventricular rate is not close to 80 beats per minute, or the heart rate on moderate exertion is not between 90 to 115 beats per minute, a second agent to control the rate should be added. Excessive reductions in ventricular rates that could limit exercise tolerance should be avoided.

Impaired oxygen on-kinetics in persons with human immunodeficiency virus are not due to highly active antiretroviral therapy

OBJECTIVE

To determine the effects of human immunodeficiency virus (HIV) and highly active antiretroviral therapy (HAART) on oxygen on-kinetics in HIV-positive persons.

DESIGN

Quasi-experimental cross-sectional.

SETTING

Infectious disease clinic and exercise laboratory.

PARTICIPANTS

Referred participants (N=39) included 13 HIV-positive participants taking HAART, 13 HIV-positive participants not taking HAART, and 13 noninfected controls.

INTERVENTIONS

Participants performed 1 submaximal exercise treadmill test below the ventilatory threshold, 1 above the ventilatory threshold, and 1 maximal treadmill exercise test to exhaustion.

MAIN OUTCOME MEASURES

Change in oxygen consumption (Delta.VO2) and oxidative response index (Delta.VO2/mean response time).

RESULTS

Delta.VO2 was significantly lower in both HIV-positive participants taking (946.5+/-68.1mL) and not taking (871.6+/-119.6mL) HAART than in controls (1265.3+/-99.8mL) during submaximal exercise above the ventilatory threshold. The oxidative response index was also significantly lower (P<.05) in HIV-positive participants both taking (15.0+/-1.3mL/s) and not taking (15.1+/-1.7mL/s) HAART than in controls (20.8+/-2.1mL/s) during exercise above the ventilatory threshold.

CONCLUSION

Oxygen on-kinetics during submaximal exercise above the ventilatory threshold was impaired in HIV-positive participants compared with a control group, and it appeared that the attenuated oxygen on-kinetic response was primarily caused by HIV infection rather than HAART.