Impaired heart rate response to exercise in adult patients with a systemic right ventricle or univentricular circulation: Prevalence, relation to exercise, and potential therapeutic implications

Novel techniques for quantifying oxygen pulse curve characteristics during cardiopulmonary exercise testing in tetralogy of fallot

Background

Cardiopulmonary exercise testing (CPET) is used in evaluation of repaired tetralogy of Fallot (rTOF), particularly for pulmonary valve replacement need. Oxygen pulse (O2P) is the CPET surrogate for stroke volume and peripheral oxygen extraction.

Objectives

This study assessed O2P curve properties against non-invasive cardiac output monitoring (NICOM) and clinical testing.

Methods

This cross-sectional study included 44 rTOF patients and 10 controls. Three new evaluations for O2P curve analysis during CPET were developed. Best fit early and late regression slopes of the O2P curve were used to calculate: 1) the early to late ratio, or "O2 pulse response ratio" (O2PRR); 2) the portion of exercise until slope inflection, or "flattening fraction" (FF); 3) the area under the O2P response curve, or "O2P curve area".

Results

rTOF patients (median age 35.2 (27.6-39.4); 61% female) had a lower VO2 max (23.4 vs 45.6 ml/kg/min; p < 0.001) and O2P max (11.5 vs 19.1 ml/beat; p < 0.001) compared to controls. Those with a FF occurring <50% through exercise had a lower peak cardiac index and stroke volume, but not VO2 max, compared to those >50%. FF and O2P curve area significantly correlated with peak cardiac index, stroke volume, left and right ventricular ejection fraction, and right ventricular systolic pressure.

Conclusion

CPET remains an integral part in the evaluation of rTOF. We introduce three non-invasive methods to assess exercise hemodynamics using the O2P curve data. These evaluations demonstrated significant correlations with stroke volume, cardiac output, and right ventricular pressure.

Long-term myocardial performance of the systemic right ventricle during exercise in patients with transposition of the great arteries and atrial switch operation

The most common clinical scenario in which RV is systemic, is dextroposition transposition of the great arteries (dTGA). This is the second most common cyanotic congenital heart disease [2]. Before the arterial switch operation was introduced in 1975 [3], patients with dTGA were treated with the Mustard or Senning procedure, also referred to as the atrial switch operation, where the systemic veins are routed to the subpulmonary morphological left ventricle and the pulmonary veins are routed to the systemic right ventricle [4].The atrial switch operation leaves the RV in a systemic position, leading to gradual RV dysfunction and RV failure [5-8]. In this context, sRV functional reserve and its ability to augment performance with exercise performance is not well studied.

Cardiopulmonary Exercise Testing in Children and Adolescents with Repaired Tetralogy of Fallot: Mechanisms of Exercise Intolerance and Clinical Implications

By comparison with adults, cardiopulmonary exercise testing in children with Tetralogy of Fallot is limited, and its clinical application less clarified. This study provides a comprehensive CPET profile in a child-adolescent population with repaired TOF, explores mechanisms underpinning exercise intolerance and associations with clinical outcome. Seventy-four CPETs were completed in 58 child-adolescents with rTOF (age 13.8 SD 2.4 years). CPET parameters were corrected for age, sex and body size. At follow-up (4.9 years, IQR 3.5-7.9) clinical status and re-intervention was evaluated and CPET indices predicting these outcomes determined. Cohort peak V̇O2 was within low-normal limits (% pred: 74.1% SD 15.4) with 15 patients (26%) displaying moderately severe reduction in V̇O2peak (< 65% pred). Oxygen uptake efficiency slope highly correlated with V̇O2peak (r = 0.94, p < 0.001) and was insensitive to exercise intensity. No significant change in CPET occurred in patients who underwent interval testing at 24 SD 14.5 months, although there was a variable response in V̇O2peak between individuals. Chronotropic response, lung vital capacity, heart rate-V̇O2 slope (indicator of stroke volume) predicted oxygen consumption: V̇O2peak (R2 = 50.91%, p < 0.001) and workload (R2 = 58.39%, p < 0.001). Adverse clinical status was associated with reduced workload (OR 0.97, p = 0.011). V̇E/V̇CO2 slope was steeper in those that died ((%pred:137.8 SD 60.5 vs. 108.4 SD 17.0, p < 0.019). RVOT reintervention post-CPET (24 patients, 43.8%) was associated with an increased gradient of HR-VO2 slope (OR 1.042, p = 0.004). In child-adolescents with TOF important reductions in cardiopulmonary functioning were apparent in 25% of patients. Exercise intolerance was related to reduced vital capacity, impaired chronotropic response and deficient stroke volume increment.

O2 pulse slope correlates with stroke volume during exercise in patients with a Fontan circulation

BACKGROUND

Peak oxygen pulse (O2pulse=oxygen consumption/heart rate) is calculated by the product of stroke volume (SV) and oxygen extraction. It has been shown to be reduced in patients with a Fontan circulation. However, in the Fontan population, it may be a poor marker of SV. We propose that the slope of the O2 pulse curve may be more reflective of SV during exercise.

METHODS

We analysed cardiopulmonary exercise test data in 22 subjects with a Fontan circulation (cohort A) and examined the association between peak SV during exercise (aortic flow measured on exercise cardiac MRI), and O2 pulse parameters (absolute O2 pulse and O2 pulse slopes up to anaerobic threshold (AT) and peak exercise). In a separate Fontan cohort (cohort B, n=131), associations between clinical characteristics and O2 pulse kinetics were examined.

RESULTS

In cohort A, peak aortic flow was moderately and significantly associated with O2pulseslopePEAK (r=0.47, p=0.02). However, neither absolute O2pulseAT nor O2pulsePEAK was significantly associated with peak aortic flow. In cohort B, O2pulseslopePEAK and O2pulseslopeAT were not significantly associated with clinical parameters, apart from a weak association with forced vital capacity.

CONCLUSION

The slope of the O2 pulse curve to peak exercise may be more reflective of peak SV in the Fontan population than a single peak O2 pulse value.

Respiratory Muscle Function and Exercise Performance in Adult Patients with Fontan Circulation

At rest, a good Fontan circulation can provide a normal cardiac output (CO). However, as a consequence of its unique hemodynamic nature, the limitations of the Fontan circuit are exposed during exercise. We aimed to provide a comprehensive assessment of the pathophysiology of exercise in adult Fontan patients (FPs) and identify factors limiting their functional capacity (FC). In a single-center study conducted in 37 FPs aged ≥16 years and 19 healthy-controls (HCs) who underwent CPET on a cycle ergometer in February and March 2022, the mean peakVO₂ was 21 ± 5.4 mL/kg/min, which was 55% of the predicted value. Morphologically, the left single ventricle showed a higher peakVO₂% predicted value (57.4 ± 14.4% vs. 43.4 ± 8.1%, p = 0.045). The factors associated with low peakVO₂ values were an early flattened or descending O₂ pulse at maximal exertion (52 ± 14% vs. 62 ± 12.5, p = 0.04 and 47.6 ± 9% vs. 60 ± 14, p = 0.018, respectively) and chronotropic insufficiency (53 ± 12% vs. 69.8 ± 20%, p = 0.008). The OUES was found to be a useful parameter to assess the FC in FPs in maximal and submaximal exercise testing. A strong positive correlation was observed between the %OUES and peakVO₂%predicted (r = 0.726, p > 0.001). The lung function was impaired in the FPs, mostly with a mild restrictive pattern (56.8%). The FPs showed lower inspiratory muscle strength compared to the HCs but it was not statistically associated with either the peakVO₂ or VE/VCO₂ slope. Regular intense physical activity improves one's FC. Although FPs have inspiratory muscle weakness, its impact on their FC is unclear. The peakVO₂% predicted grew progressively higher as the level of physical activity increased (low level 49.5 ± 14%, moderate level 55 ± 12%, intense level 69 ± 20%).

Adequate exercise response at artificial altitude in Fontan patients

PURPOSE

For Fontan-palliated patients, altitude exposure is still a part of discussion since the extent of hypoxic pulmonary vasoconstriction potentially resulting in decreasing cardiac output (Qc), especially during physical exercise, is still unclear. We investigated the effects of normobaric hypoxia (15.2% O₂) simulating 2,500 m above sea level on cardiopulmonary and metabolic parameters and the benefit of daily physical activity (PA) on hypoxic exercise capacity.

METHODS

A total of 21 Fontan patients (14-31 years) and 20 healthy controls performed cardiopulmonary exercise tests on a bicycle ergometer in normoxia and hypoxia until subjective exhaustion, measuring capillary lactate (cLa) every 2 min. In between, participants underwent an activity tracking over 5 days with a triaxial accelerometer.

RESULTS

Hypoxic exercise was well tolerated by Fontan patients, and no adverse clinical events were observed. Fontan patients showed reduced physical capacity under both conditions compared to controls (63% normoxia, 62% hypoxia), but the relative impairment due to hypoxia was similar for both (≈10%). Up to workloads of 2 W/kg oxygen uptake ( V . O₂) and heart rate (HR) developed similarly in patients and controls. cLa increased faster in relation to workload in Fontan patients, but remained significantly lower at peak workload (normoxia 3.88 ± 1.19 mmol/l vs. 7.05 ± 2.1 mmol/l; hypoxia 4.01 ± 1.12 mmol/l vs. 7.56 ± 1.82 mmol/l). Qc was diminished but could be increased similar to controls. Fontan patients with higher PA levels showed a higher V . O_2peak in hypoxia.

CONCLUSION

Exercise during short-time artificial altitude exposure seems to be safe for young Fontan patients. Further studies are needed to validate longer exposure under real conditions. V . O₂, HR, and Qc might not be a limiting factor for exercise until workloads of 2 W/kg. Higher daily PA levels might improve physical capacity under altitude conditions.

Heart Rate Reserve in Fontan Patients: Chronotropic Incompetence or Hemodynamic Limitation?

Background Patients with a Fontan circulation achieve lower peak heart rates ( HR ) during exercise. Whether this impaired chronotropic response reflects pathology of the sinoatrial node or is a consequence of altered cardiac hemodynamics is uncertain. We evaluated the adequacy of HR acceleration throughout exercise relative to metabolic demand and cardiac output in patients with a Fontan circulation relative to healthy controls. Methods and Results Thirty subjects (20 healthy controls and 10 Fontan patients) underwent cardiac magnetic resonance imaging with simultaneous invasive pressure recording via a pulmonary and radial artery catheter during supine bicycle exercise to near maximal exertion. Adequacy of cardiac index, stroke volume, and HR reserve was assessed by determining the exercise-induced increase (∆) in cardiac index, stroke volume, and HR relative to the increase in oxygen consumption ( VO ₂). HR reserve was lower in Fontan patients compared with controls (71±21 versus 92±15 bpm; P=0.001). In contrast, increases in HR relative to workload and VO ₂ were higher than in controls. The change in cardiac index relative to the change in VO ₂ (∆cardiac index/∆ VO ₂) was similar between groups, but Fontan patients had increased ∆ HR /∆ VO ₂ and reduced ∆ stroke volume/∆ VO ₂ compared with controls. There was an early and marked reduction in stroke volume during exercise in Fontan patients corresponding with a plateau in cardiac output at a low peak HR . Conclusions In Fontan patients, the chronotropic response is appropriate relative to exercise intensity, implying normal sinoatrial function. However, premature reductions in ventricular filling and stroke volume cause an early plateau in cardiac output beyond which further increases in HR would be physiologically implausible. Thus, abnormal cardiac filling rather than sinoatrial node dysfunction explains the diminished HR reserve in Fontan patients.

Heart rate response during exercise predicts exercise tolerance in adults with transposition of the great arteries and atrial switch operation

BACKGROUND

To assess the relationship between heart rate response and exercise tolerance in adults with systemic right ventricle (sRV) after atrial switch repair for Transposition of the Great Artery (TGA) in addition to other physiological parameters.

METHODS

All patients with a sRV after atrial switch repair for TGA followed in our institution between June 2015 and April 2018 who underwent cardiopulmonary exercise testing (CPET) were analyzed. Cardiac imaging performed within a six-month time period of the CPET were also collected. Chronotropic incompetence was defined as the inability to achieve 80% of age-predicted maximal heart rate reserve (HRR) and <62% on a beta-blocker regimen. Patient characteristics were assessed according to tertiles of the percentage of predicted pVO2 (%ppVO2).

RESULTS

We studied 70 patients (mean of age 32.4 ± 7.6 years old, 51 males). Mean peak oxygen uptake was 21.5 ± 5.8 mL/kg/min, corresponding to a %ppVO2 of 57 ± 14.1% while mean VE/VCO2 slope was 37.1 ± 8.2. There was a trend toward more exaggerated hyperventilation in patient with lower pVO2. Mean age-adjusted HRR was 68.5 ± 19%. Chronotropic incompetence was observed in 65.7% and was correlated with %ppVO2 (r = 0.482; p < 0.001) as physical training evaluated with Ventilatory Anaerobic threshold (r = 0.571; p < 0.001), while no difference was found based on respiratory parameters. No echocardiographic or Magnetic Resonance Imaging parameters assessing sRV systolic function at rest were correlated with %ppVO2.

CONCLUSIONS

Exercise limitation is related to the inability to increase cardiac output during exercise and is notably due to the degree of chronotropic incompetence.

Advanced Imaging to Phenotype Patients With a Systemic Right Ventricle

Background

Reduced ventricular function and decreased exercise capacity are widespread in adults with complete transposition of the great arteries after atrial switch (TGA‐Mustard/Senning) and congenitally corrected TGA (ccTGA). Advanced imaging techniques may help to better phenotype these patients and evaluate exercise cardiac response.

Methods and Results

Thirty‐three adults with a systemic right ventricle (70% TGA‐Mustard/Senning, 37±9 years of age, 24% female, 94% New York Heart Association class I‐II) underwent echocardiogram, cardiopulmonary exercise testing, and cardiovascular magnetic resonance imaging at rest and during a 4‐stage free‐breathing bicycle test. They were compared with 12 healthy controls (39±10 years of age, 25% female, all New York Heart Association class I). TGA‐Mustard/Senning patients had a higher global circumferential strain (−15.8±3.6 versus −11.2±5.2%, P=0.008) when compared with ccTGA, whereas global longitudinal strain and systemic right ventricle contractility during exercise were similar in both groups. Septal extracellular volume (ECV) in ccTGA was significantly higher than in TGA‐Mustard/Senning (30.2±2.0 versus 27.1±2.7%, P=0.005). During exercise, TGA‐Mustard/Senning had a fall in end‐diastolic volume and stroke volume (11% and 8%, respectively; both P≤0.002), whereas ccTGA could increase their stroke volume in the same way as healthy controls. Because of a greater heart rate reserve in TGA‐Mustard/Senning (P for interaction=0.010), cardiac index and peak oxygen uptake were similar between both patient groups.

Conclusions

Caution should be exercised when evaluating pooled analyses of systemic right ventricle patients, given the differences in myocardial contraction pattern, septal extracellular volume, and the exercise response of TGA‐Mustard/Senning versus ccTGA patients. Longitudinal follow‐up will determine whether abnormal exercise cardiac response is a marker of earlier failure.

Right Heart-Pulmonary Circulation Unit in Congenital Heart Diseases

The right ventricle plays a major role in congenital heart disease. This article describes the right ventricular mechanics in some selected congenital heart diseases affecting the right ventricle in different ways: tetralogy of Fallot, Ebstein anomaly, and the systemic right ventricle.

Management of Heart Failure in Adult Congenital Heart Disease

There are more than 1 million adults with congenital heart disease (ACHD) in the United States. Heart failure (HF) is the most common late cardiovascular complication. These patients are challenging to manage given their diverse presentation, anatomy, and complex hemodynamics. Examination of underlying anatomy is crucial because many require late transcatheter and surgical interventions after developing HF. Management of arrhythmia is equally important because this can modify HF symptoms. A multidisciplinary team with expertise in the care of ACHD-HF is critical.

The Role of Cardiopulmonary Exercise Testing for Decision Making in Patients with Repaired Tetralogy of Fallot

Tetralogy of Fallot is the most common form of cyanotic congenital heart disease. As a result of the surgical strategies employed at the time of initial repair, chronic pulmonary regurgitation (PR) is prevalent in this population. Despite sustained research efforts, patient selection and timing of pulmonary valve replacement (PVR) to address PR in young asymptomatic patients with repaired tetralogy of Fallot (rToF) remain a fundamental but as yet unanswered question in the field of congenital heart disease. The ability of the heart to compensate for the chronic volume overload imposed by PR is critical in the evaluation of the risks and benefits of PVR. The difficulty in clarifying the functional impact of PR on the cardiovascular capacity may be in part responsible for the uncertainty surrounding the timing of PVR. Cardiopulmonary exercise testing (CPET) may be used to assess abnormal cardiovascular response to increased physiologic demands. However, its use as a tool for risk stratification in asymptomatic adolescents and young adults with rToF is still ill-defined. In this paper, we review the role of CPET as a potentially valuable adjunct to current risk stratification strategies with a focus on asymptomatic rToF adolescents and young adults being considered for PVR. The role of maximal and submaximal exercise measurements to identify young patients with a decreased or borderline low peak VO₂ resulting from impaired ventricular function is explored. Current knowledge gaps and research perspectives are highlighted.

[Assessment of exercise capacity in congenital heart disease]

For many years, the treatment of congenital heart diseases has been a field in which, based on the seriousness of these conditions, treatment options were viewed with the greatest deference. This has conditioned, in many cases, the interventions to be undertaken in each. In this sense, exercise was thought to have a negative impact and thus the practise of almost any physical activity was limited. Although there has recently been a change in the paradigm with respect to exercise, this idea continues to hold sway. For many cardiopathies, the information obtained through a stress test is essential in order to implement and supervise an exercise program. The aim of this study is to analyze the parameters within the stress test which allow for an adequate stratification of the risk to subjects with congenital heart diseases who undertake exercise, as well as their values in accordance with the type of pathology, the gravity of such, and the age of the patients. Furthermore, these parameters will be analyzed for both their survival markers and the protocols that can best be adjusted for patients with these characteristic.

Oxygen pulse kinetics in Fontan patients during treadmill ramp protocol cardiopulmonary exercise testing

After single-ventricle palliation, patients have variable long-term functional outcomes. Cardiopulmonary exercise testing (CPET) is an assessment tool used to quantify functional outcome. Oxygen pulse kinetics during CPET, which can be an important indicator of dynamic changes in stroke volume reserve, has not been systematically studied in this population. This study aimed to analyze oxygen pulse kinetics during a treadmill ramp protocol among patients with Fontan physiology compared with that of normal subjects and to explore the ability of oxygen pulse kinetics to define functional status further. Peak oxygen pulse and change in oxygen pulse during ramp treadmill CPET were retrospectively collected and compared between 44 Fontan patients and 85 age- and sex-matched control subjects. The peak oxygen pulse was significantly lower in the Fontan group (9.80 ± 4.11 ml/beat) than in the control group (13.62 ± 4.7 ml/beat) (p ≤ 0.001). The resting oxygen pulse did not differ between the two groups (3.13 ± 1.23 vs. 3.09 ± 1.33 ml/beat; p = 0.88). The oxygen pulse was higher in the patients with chronotropic insufficiency, but the difference was not statistically significant (11.11 ± 4.97 vs. 9.25 ± 3.63 ml/beat; p = 0.17). Regression analysis showed a significant difference in the slope of the oxygen pulse-to-workload relationship. The Fontan group showed no relation between degree of reduction in the oxygen pulse from peak to end of exercise and the underlying defect, peak heart rate, peak oxygen consumption, ventilatory anaerobic threshold (VAT), expired volume (VE)/carbon dioxide output (VCO(2)) at the VAT, maximum heart rate, or minimum oxygen saturation. Analysis of oxygen pulse kinetics in Fontan patients suggests that there is an early and progressive limitation in stroke volume compared with control subjects. This limitation may be partially masked by increased oxygen extraction. In patients with chronotropic insufficiency, absolute or body surface area-indexed oxygen pulse may be higher than in those with a normal heart rate response. A composite assessment of the oxygen pulse and oxygen pulse kinetics, including the oxygen pulse slope and the percentage of reduction in oxygen pulse from peak to end of exercise, may allow a more comprehensive assessment of the degree of cardiac limitation in this group of patients.

Total isovolumic time relates to exercise capacity in patients with transposition of the great arteries late after atrial switch procedures

BACKGROUND

Systemic right ventricular systolic dysfunction is common late after atrial switch surgery for transposition of the great arteries. Total isovolumic time is the time that the ventricle is neither ejecting nor filling and is calculated without relying on geometric assumptions. We assessed resting total isovolumic time in this population and its relationship to exercise capacity.

METHODS

A total of 40 adult patients with transposition of the great arteries after atrial switch - and 10 healthy controls - underwent transthoracic echocardiography and cardiopulmonary exercise testing from January, 2006 to January, 2009. Resting total isovolumic time was measured in seconds per minute: 60 minus total ejection time plus total filling time.

RESULTS

The mean age was 31.6 plus or minus 7.6 years, and 38.0% were men. There were 16 patients (40%) who had more than or equal to moderate systolic dysfunction of the right ventricle. Intra- and inter-observer agreement was good for total isovolumic time, which was significantly prolonged in patients compared with controls (12.0 plus or minus 3.9 seconds per minute versus 6.0 plus or minus 1.8 seconds per minute, p-value less than 0.001) and correlated significantly with peak oxygen consumption (r equals minus 0.63, p-value less than 0.001). The correlation strengthened (r equals minus 0.73, p-value less than 0.001) after excluding seven patients with exercise-induced cyanosis. No relationship was found between exercise capacity and right ventricular ejection fraction or long-axis amplitude.

CONCLUSION

Resting isovolumic time is prolonged after atrial switch for patients with transposition of the great arteries. It is highly reproducible and relates well to exercise capacity.

Does left ventricular size impact on intrinsic right ventricular function in hypoplastic left heart syndrome?

BACKGROUND

The size of the remnant left ventricle (LV) may influence right ventricular function and thus long-term outcome in palliated hypoplastic left heart syndrome (HLHS). We therefore sought to assess the impact of the size of the hypoplastic LV on intrinsic RV function in HLHS patients after Fontan surgery.

METHODS

Fifty-seven HLHS patients were studied 2.5 (range: 0.8-12.6) years after Fontan-type palliation with the pressure-volume conductance system. The patient cohort was divided into two groups according to the median LV area index (group 1: LV area index ≤ 1.33 cm(2)/m(2), n=29; group 2: LV area index>1.33 cm(2)/m(2), n=28).

RESULTS

The slopes of the end systolic elastance (Ees) and the preload recruitable stroke work relation (Mw) were not different between group 1 and 2 (Ees: 2.70 ± 1.92 vs. 3.68 ± 2.68 mmHg/ml; Mw: 52.75 ± 14.98 vs. 51.09 ± 16.63 mmHg x ml; P=NS for all). Furthermore, the systolic responses to dobutamine were not statistically different between groups. However, the slope of the end diastolic stiffness (Eed) was higher in group 2 and catecholaminergic stimulation resulted in a decrease in Eed in group 2 (group 1: 0.40 ± 0.26 vs. 0.52 ± 0.45; group 2: 0.68 ± 0.44 vs. 0.47 ± 0.38 mmHg/ml, P<0.01). Furthermore Eed was lowest in patients with mitral atresia/aortic atresia, the anatomic subgroup with the smallest LV remnant.

CONCLUSIONS

Intrinsic systolic RV function is not affected by the size of the hypoplastic LV in survivors of surgical palliation of HLHS. Diastolic stiffness, however, was higher in patients with a larger LV remnant.

Permanent transvenous left ventricular endocardial pacing in a patient with univentricular atrioventricular connection

Chronotropic incompetence is associated with poorer effort tolerance and worse mortality outcomes, not only in the general cardiac population but also in patients with congenital heart disease. When present in complex patients, pacing options may be limited by difficult pacing access, and an open surgical approach for epicardial lead placement may not always be desirable. We describe a case of symptomatic chronotropic incompetence in a patient with tricuspid atresia, valvar and subpulmonary stenosis, normally related great vessels, and a modified Blalock-Taussig shunt, awaiting cardiac transplantation, whom we palliated with a transvenous endocardial pacing strategy. This technique may provide an alternative pacing strategy for highly selected patients, where few other treatment options are available.