Effect of right ventricular anatomy on the cardiopulmonary response to exercise. Implications for the Fontan procedure

Exercise Capacity in Patients with Pulmonary Atresia with Intact Ventricular Septum: Does the Type of Surgical Repair Matter?

Two standard surgical palliative options for neonates born with pulmonary atresia and intact ventricular septum (PA/IVS) include uni-or biventricular repair. Whenever feasible, the biventricular repair is considered to have better exercise capacity (XC) and outcomes. However, there is a paucity of data comparing objective XC between these two surgical techniques. Our aim was to compare XC, including longitudinal changes in patients with PA/IVS following uni-biventricular repair. We performed a single-center retrospective study of survivors with repaired PA/IVS who underwent comprehensive treadmill cardiopulmonary exercise testing. Initial and latest exercise parameters were compared for longitudinal analysis. Demographic and exercise parameters were collated. Peak oxygen uptake (VO₂ in ml/kg/min), an indicator of maximal aerobic capacity, peak heart rate, and other measures of spirometry performed at the same time were collected. Recorded parameters included, (a) Percentage of predicted VO₂ (% VO2) normalized for age, weight, height, and gender, (b) % oxygen (O₂) pulse, (c) anaerobic threshold (AT), (d) Chronotropic index (CI), (e) % Breathing reserve, (f) Forced vital capacity (FVC), (g) % Forced Expiratory volume in 1 s (FEV1), (h) Maximum voluntary ventilation (MVV), and (i) VE/VCO₂. Appropriate statistical tests were performed, and a p value < 0.05 was considered significant. A total of 35 patients (43% male, 57% univentricular repair) were included, with a mean (SD) age of 20.1(7.5) years. Patients with univentricular palliation demonstrated significantly impaired peak heart rate, chronotropic index (0.50 ± 0.2 vs. 0.90 ± 0.1, p = 0.02), VE/VCO₂ (35.4 ± 5.0 vs. 30.2 ± 2.8, p = 0.001), and %FVC (78.3 ± 8.3 vs. 88.6 ± 15.1, p = 0.02). There was a trend towards reduction in % VO₂ in the Fontan patients though it was statistically similar between the groups (68.4 ± 21.4 vs. 81.2 ± 18.9, p = 0.07). Longitudinal data were available for 11 patients in each group, and there was no longitudinal decline in their exercise parameters over similar intermediate follow-up duration [6.8 (UV) vs. 5.3 (BV) years]. We conclude that young survivors with PA/IVS with prior univentricular palliation demonstrated an objective impairment in their chronotropic parameters compared with the biventricular repair. However, this did not translate into a significant difference in their exercise capacity. There was no longitudinal decline in exercise capacity or other parameters over intermediate follow-up.

Three-dimensional regional bi-ventricular shape remodeling is associated with exercise capacity in endurance athletes

AIMS

Endurance athletes develop cardiac remodeling to cope with increased cardiac output during exercise. This remodeling is both anatomical and functional and shows large interindividual variability. In this study, we quantify local geometric ventricular remodeling related to long-standing endurance training and assess its relationship with cardiovascular performance during exercise.

METHODS

We extracted 3D models of the biventricular shape from end-diastolic cine magnetic resonance images acquired from a cohort of 89 triathlon athletes and 77 healthy sedentary subjects. Additionally, the athletes underwent cardio-pulmonary exercise testing, together with an echocardiographic study at baseline and few minutes after maximal exercise. We used statistical shape analysis to identify regional bi-ventricular shape differences between athletes and non-athletes.

RESULTS

The ventricular shape was significantly different between athletes and controls (p < 1e-6). The observed regional remodeling in the right heart was mainly a shift of the right ventricle (RV) volume distribution towards the right ventricular infundibulum, increasing the overall right ventricular volume. In the left heart, there was an increment of left ventricular mass and a dilation of the left ventricle. Within athletes, the amount of such remodeling was independently associated to higher peak oxygen pulse (p < 0.001) and weakly with greater post-exercise RV free wall longitudinal strain (p = 0.03).

CONCLUSIONS

We were able to identify specific bi-ventricular regional remodeling induced by long-lasting endurance training. The amount of remodeling was associated with better cardiopulmonary performance during an exercise test.

Relationship of Aortic Stiffness to Exercise and Ventricular Volumes in Single Ventricles

BACKGROUND

Patients with single ventricle (SV) may often undergo aortic reconstruction that creates a stiff large vessel, increasing afterload and affecting exercise performance. The objective of this study was to determine the relationship of pulse wave velocity (PWV) and distensibility in reconstructed and normal aortic arches after Fontan with exercise variables.

METHODS

PWV and distensibility of the descending aorta at the level of the diaphragm (DAo) were calculated with real-time exercise cardiac magnetic resonance in 48 patients with SV after Fontan (18 after aortic reconstruction; 30 without aortic reconstruction) and compared with metabolic exercise stress test variables.

RESULTS

PWV was greater in the reconstructed group than in the non-reconstructed group (median 4.4 m/s [range: 2.3 to 9.8 m/s] versus 3.6 [range: 2.6 to 6.3 m/s], respectively, p = 0.003). Statistically significant inverse correlations were found between PWV and end-diastolic, end-systolic, and stroke volumes at rest and at exercise in the reconstructed group. In addition, inverse correlations also existed in the reconstructed group between distensibility of the DAo and the exercise variables such as peak oxygen pulse (R = 0.56, p = 0.02), peak oxygen consumption (R = 0.63, p = 0.008), oxygen consumption at ventilatory anaerobic threshold (R = 0.48, p = 0.04), and peak work (R = 0.54, p = 0.02). Similar correlations were not seen in patients with non-reconstructed aortas.

CONCLUSIONS

Patients with SV with reconstructed aortas have increased aortic stiffness, increasing afterload on the ventricle. Native DAo stiffness distal to the reconstruction is inversely correlated with exercise performance, presumably to decrease impedance mismatch to maintain homogeneity of the aortic wall. This information suggests a possible mechanism for decreased exercise performance in patients with SV with aortic reconstructions.

Should We Recommend Exercise after the Fontan Procedure?

BACKGROUND

The Fontan procedure, the last of a series of operations performed in patients with congenital heart defects, offers improved exercise capacity compared to baseline function but is still reduced compared to healthy peers. Exercise training may improve exercise tolerance but there is no consensus on the safety of this practice or the optimal training regimen. We performed a systematic literature review on the effects of exercise training in patients with a Fontan circulation.

METHODS

Medline and Embase databases were systematically searched for articles regarding Fontan Procedure and cardiac rehabilitation.

RESULTS

A total of 23 articles met all inclusion criteria; in total, 201 Fontan subjects were included. Characteristics of the exercise training programs varied significantly. There were no adverse effects related to training programs reported in the literature. Most studies reported benefit across various exercise parameters related to exercise tolerance.

CONCLUSIONS

Exercise training is safe and beneficial in patients with a Fontan circulation. Exercise training should become a standard of care within this population. Physiological adaptation following exercise training needs to be investigated more extensively.

Cardiopulmonary exercise performance after total cavopulmonary connection with or without prior superior cavopulmonary connection

OBJECTIVE

To compare cardiopulmonary exercise capacity of patients undergoing primary total cavopulmonary connection (TCPC) with those undergoing TCPC after a prior bidirectional Glenn (BDG).

METHODS

Out of 42 patients in this study, 24 had undergone primary TCPC while 18 had undergone staged TCPC. The peak oxygen consumption (O(2) peak), O(2) pulse, chronotropic index, and other exercise parameters were studied.

RESULTS

There were no significant differences in O(2) peak (940 ± 538 vs. 1010 ± 417 mL/min, p=0.42) and O(2) pulse (5.76 ± 3.52 vs. 6.85 ± 2.95) of patients undergoing staged TCPC versus primary TCPC, respectively; however, chronotropic index (0.43 ± 0.23 vs. 0.30 ± 017, p=0.047) was significantly different. Exercise tolerance was the same in fenestrated versus nonfenestrated TCPC groups and age at TCPC less than or more than 7 years. However, O(2) peak and O(2) pulse of patients with extracardiac TCPC was better than patients with lateral tunnel TCPC (p values 0.05, 0.04 and respectively). Some parameters of exercise tolerance of patients with antegrade pulmonary blood flow (APBF) interrupted at the time of BDG were better than those with APBF open.

CONCLUSION

There were no differences in the exercise parameters of patients undergoing a staged versus a primary TCPC, fenestrated versus nonfenestrated TCPC, and age at surgery less than or more than 7 years. Exercise parameters were better in the extracardiac conduit group versus lateral tunnel TCPC groups. Patients who had a TCPC after prior interruption of APBF had better exercise parameters.

Resistance training improves cardiac output, exercise capacity and tolerance to positive airway pressure in Fontan physiology

BACKGROUND

Subjects with Fontan-type circulation have no sub-pulmonary ventricle and thus depend exquisitely on the respiratory bellows and peripheral muscle pump for cardiac filling. We hypothesised that resistance training to augment the peripheral muscle pump might improve cardiac filling, reduce inspiratory-dependence of IVC return to the heart and thus improve exercise capacity and cardiac output on constant positive airway pressure (CPAP).

METHODS

Eleven Fontan subjects (32+/-2 years, mean+/-SEM) had cardiac magnetic resonance imaging (MRI) and exercise testing (CPET); six underwent 20 weeks of high-intensity resistance training; others were non-exercising controls. After training, CPET was repeated. Four trainers had MRI with real-time flow measurement at rest, exercise and on CPAP in the trained state and following a 12-month detrain.

RESULTS

In the trained state, muscle strength increased by 43% (p=0.002), as did total muscle mass (by 1.94 kg, p=0.003) and peak VO2 (by 183 ml/min, p=0.02). After detraining, calf muscle mass and peak workload had fallen significantly (p<0.03 for both) as did peak VO2 (2.72 vs. 2.18 l/min, p<0.001) and oxygen pulse, a surrogate for SV (16% lower, p=0.005). Furthermore after detraining, SV on MRI decreased at rest (by 11 ml, p=0.01) and during moderate-intensity exercise (by 16 ml, p=0.04); inspiratory-dependent IVC blood return during exercise was 40% higher (p=0.02). On CPAP, cardiac output was lower in the detrained state (101 vs. 77 ml/s, p=0.03).

CONCLUSIONS

Resistance muscle training improves muscle mass, strength and is associated with improved cardiac filling, stroke volume, exercise capacity and cardiac output on CPAP, in adults with Fontan-type circulation.

Long-term results of the Fontan operation

Modifications of the Fontan operation can afford excellent palliation for many patients with a variety of forms of single ventricle. In properly selected patients who are good candidates, early and late survival can be as high as 95-97%. However, mortality is considerably higher for patients with risk factors for poor outcome. For high-risk patients, inclusion of a fenestration may reduce morbidity and mortality. Important long-term undesirable events include the ongoing risk of death, arrhythmias, protein-losing enteropathy, and cardiac failure. The key to excellent long-term outcome is proper selection of patients for the operation.

Exercise prescription for patients with a Fontan circulation: current evidence and future directions

It is well documented that children with a Fontan circulation have a reduced exercise capacity. One of the modalities to improve exercise capacity might be exercise training. We performed a systematic literature review on the effects of exercise training in patients with a Fontan circulation. Six published studies were included that reported on the effects of exercise training in 40 patients. All studies had a small sample size and/or did not include a control group.Based on the six published studies we can conclude that children who have undergone a Fontan operation and who are in a stable haemodynamic condition can safely participate in an exercise training programme and that exercise training results in an improved exercise capacity. However, more research is needed to establish the optimal exercise mode, dose-response relation, and the effects of exercise training on cardiac function, peripheral muscle function, physical activity, and health-related quality of life. (Neth Heart J 2007;15:142-7.).

Exercise capacity and impact of exercise training in patients after a Fontan procedure: a review

After a successful Fontan procedure, children and adolescents should improve their exercise capacity. However, several studies have shown that these children have a reduced maximal oxygen consumption compared with healthy children. The lower exercise performance in these patients was mainly explained by a reduced cardiorespiratory functional capacity. However, it has recently been reported that the lower exercise performance may also be related to altered skeletal muscle function. Moreover, exercise training had a beneficial impact on several parameters related to exercise tolerance in these patients. The main studies supporting these observations are reviewed, with a focus on the physiological adaptation and limitation of the exercise performance as well as the benefits of exercise training in patients after a Fontan procedure.

Impact of cardiac rehabilitation on the exercise function of children with serious congenital heart disease

OBJECTIVES

The exercise capacity of children with congenital heart disease (CHD) is often depressed. This depression is thought to be attributable to (1) residual hemodynamic defects and (2) deconditioning secondary to physical inactivity. We hypothesized that this latter component would be ameliorated by a formal cardiac rehabilitation program designed specifically for children. The objective of this study was to characterize the effect of a cardiac rehabilitation program on the exercise performance of children with CHD and to define the physiologic mechanisms that might account for any improvements that are observed.

METHODS

Nineteen patients with CHD who were referred for exercise testing and found to have a peak oxygen consumption (VO2) and/or peak work rate <80% of predicted were enrolled in the study. Sixteen patients (11 Fontan patients, 5 with other CHD) completed the program and had postrehabilitation exercise tests, results of which were compared with the prerehabilitation studies.

RESULTS

Improvements were found in 15 of 16 patients. Peak VO2 rose from 26.4 +/- 9.1 to 30.7 +/- 9.2 mL/kg per min; peak work rate from 93 +/- 32 to 106 +/- 34 W, and the ventilatory anaerobic threshold from 14.2 +/- 4.8 to 17.4 +/- 4.5 mL/kg per min. The peak heart rate and peak respiratory exchange ratio did not change, suggesting that the improvements were not attributable merely to an increased effort. In contrast, the peak oxygen pulse rose significantly, from 7.6 +/- 2.8 to 9.7 +/- 4.1 mL/beat, an improvement that can be attributed only to an increase in stroke volume and/or oxygen extraction at peak exercise. No patient experienced rehabilitation-related complications.

CONCLUSION

Cardiac rehabilitation can improve the exercise performance of children with CHD. This improvement is mediated by an increase in stroke volume and/or oxygen extraction during exercise. Routine use of formal cardiac rehabilitation may greatly reduce the morbidity of complex CHD.

Estimation of Pa co 2 During Exercise in Children and Postoperative Pediatric Patients With Congenital Heart Disease

We evaluated how Paco(2) and respiratory variables relate during and after exercise and derived a new noninvasive estimation of Paco(2) in children and postoperative patients with congenital heart disease. We randomly selected 8 subjects from each of three categorized groups from our previous studies: 15 control subjects (8 to 21 years old), 16 Fontan procedure patients (9 to 22 years old), and 13 patients after right ventricular outflow tract reconstruction (RVOTR) [7 to 21 years old], and used their respiratory variables during exercise testing to estimate Paco(2) (study 1). In a stepwise multiple regression analysis, end-tidal carbon dioxide tension (Petco(2)), age, ventilatory equivalent for carbon dioxide (minute ventilation [Ve]/carbon dioxide production [Vco(2)]), and gas exchange ratio (R) were major determinants of Paco(2) in control subjects: Paco(2) = 12.0 + 0.54 Petco(2) + 0.15 Ve/Vco(2) - 3.6 R + 0.22 age (r = 0.86). In addition to Petco(2) and Ve/Vco(2), arterial oxygen saturation and tidal volume were additional major determinants for Fontan procedure and RVOTR patients, respectively. We derived equations to predict the Paco(2) (r = 0.92 for Fontan procedure and r = 0.74 for RVOTR). These equations were applied to the remaining study subjects to estimate Paco(2) (study 2). Estimated values correlated with the measured Paco(2) (r = 0.71 to 0.86), and the mean differences for the control subjects, Fontan procedure, and RVOTR patients were - 0.1, - 0.1, and - 1.0, with limits of agreement of +/- 3.3, +/- 4.4, and +/- 3.1, respectively. Although estimated Paco(2) based on the Jones equation correlated with the measured Paco(2) in all groups, their slopes were significantly flatter than ours. Paco(2) throughout exercise testing may be estimated in control children and postoperative pediatric patients. The Jones equation should be applied with great care in pediatric subjects.

Impact of exercise training on muscle function and ergoreflex in Fontan patients: a pilot study

BACKGROUND

Several studies have demonstrated persistent reduced exercise capacity in Fontan patients even after surgical intervention. The purpose of this study was to evaluate if the skeletal muscle function of these patients is abnormal, if it correlates with exercise tolerance and if it can be improved by exercise training.

METHODS

We evaluated the functional capacity of seven patients who underwent Fontan procedure (age:16+/-5 years, mean+/-SD) and seven healthy children (19+/-7 years) paired for age, sex, height and weight. Evaluation included pulmonary evaluation, neuromuscular function and exercise tolerance. Secondly, an 8-week exercise training program was performed by five of these patients.

RESULTS

The ergoreflex contribution to absolute diastolic blood pressure was higher (12.5+/-4.8 vs. 5.6+/-4.2 mmHg; p=0.04) in Fontan patients vs. healthy subjects whereas a trend was encountered regarding the ergoreflex contribution to absolute systolic blood pressure (9.0+/-7.0 vs. 0.4+/-9.0 mmHg; p=0.09). Furthermore, time to fatigue of the non-dominant forearm muscles was shorter in Fontan patients vs. healthy subjects (431+/-290 vs. 847+/-347 s; p=0.03). Following exercise training, there was a significant reduction of the ergoreflex contribution to absolute values of systolic blood pressure (9.8+/-0.9 vs. 0.3+/-2.7 mmHg; p<0.05). There was an association between muscle strength and VO2 peak in Fontan patients (upper limb: r=0.895; p<0.01; lower limb: r=0.838; p<0.05, respectively).

CONCLUSIONS

Skeletal muscle function in Fontan patients is abnormal which may have an impact in the reduced exercise tolerance encountered in these patients. Exercise training may have beneficial impacts on the skeletal muscle function in this population.

Exercise testing in pediatrics

This article discusses exercise physiology and its application in the pediatric population. This article discusses exercise physiology and its application in the pediatric population. The authors briefly review the normal physiologic response to exercise. They then discuss populations in which exercise testing is most useful, the indications and contraindications for graded exercise, and the usual parameters that are measured during testing. Finally, the authors review some of the recent data on exercise performance in specific pediatric populations.

Restrictive ventilatory impairment and arterial oxygenation characterize rest and exercise ventilation in patients after fontan operation

The objective of this study was evaluate the relationships between abnormal pulmonary circulation, lung function, and respiratory response during exercise in Fontan patients. Pulmonary function and cardiopulmonary exercise tests were performed in 101 Fontan patients and 122 controls. A small vital capacity (VC) with a high residual volume-to-total lung capacity ratio and a slight but significant low arterial saturation with hypocapnia were observed in Fontan patients. The number of surgical procedures determined VC. Total cavopulmonary connection, fenestration, higher pulmonary arterial wedge pressure, and smaller VC were independent determinants of low arterial saturation, which was the only determinant of hypocapnia. Arterial saturation decreased during exercise and resting arterial saturation correlated with that at peak exercise. Improvement in dead space ventilation was less in Fontan patients and was independently determined by resting arterial saturation. A steeper minute ventilation-carbon dioxide production slope was determined by resting arterial saturation, arterial carbon dioxide tension, and peak oxygen uptake. In Fontan patients, in addition to dead space ventilation, surgery-related reduced VC, the type of repair, and high pulmonary arterial wedge pressure cause arterial desaturation with subsequent hypocapnia, resulting in accelerated inefficient ventilation at rest and during exercise.

Cardiorespiratory response to exercise in children after modified fontan operation

OBJECTIVE

Examination of exercise function of Fontan patients and comparison with healthy control subjects.

DESIGN

Fourteen patients (6 males, 8 females; age: 5.7-17 years, mean 8.1 years) after Fontan repair in New York Heart Association (NYHA) class I with rest O(2)sat > 85% requiring no cardiovascular medications performed graded exercises on a treadmill 0.5-3.2 years postoperatively (mean 1.8 years). During the tests the heart and respiratory rate, blood pressure, oxygen uptake, carbon dioxide production, minute ventilation, tidal volume and O(2)sat were recorded. Spirometry was performed before and during exercise.

RESULTS

The peak VO(2)max in Fontan patients was significantly reduced compared with controls (p = 0.0002). Other parameters: anaerobic threshold (p = 0.0001); pulsO(2) (p = 0.00005); peak minute ventilation (p = 0.0014); physiological dead space to tidal volume ratio at peak exercise (p = 0.0004); maximal work rate (p = 0.00008); exercise time (p = 0.00003) were significantly reduced in univentricular patients. The heart rate at peak exercise was lower in the patients (p = 0.0003) and O(2)sat dropped significantly (p = 0.003).

CONCLUSION

The aerobic capacity, work and ventilatory parameters in Fontan patients are markedly reduced compared with controls. The anaerobic threshold was significantly lower. The decreased O(2)sat at peak exercise may suggest intrapulmonary shunting.

Lung function and aerobic capacity in adult patients following modified Fontan procedure

OBJECTIVE

To examine cardiopulmonary performance in 52 adult patients with a Fontan circulation.

DESIGN

Retrospective cohort study. Values of maximum oxygen uptake (VO(2)max), maximum heart rate (HRmax), forced vital capacity (FVC), and forced expiratory volume in one second (FEV(1)) were compared with predictive values for different age groups. Patients were further subdivided into those with a pulmonary artery connection (RA-PA) or right atrium to right ventricle conduit (RA-RV).

RESULTS

At late follow up (median 10 years, range 1 to 26 years), patients with Fontan circulation had greatly diminished VO(2)max, HRmax, FVC, and FEV(1) compared with predicted values. Early age at surgery had a positive impact on aerobic capacity. The FEV(1):FVC ratio indicated restrictive lung function. No differences were found with respect to any variable between patients with RA-PA connections and those with RA-RV connections.

CONCLUSIONS

Patients with a Fontan circulation have greatly diminished values of aerobic capacity and a restrictive pattern of lung function. Patients with an early surgical procedure obtained higher values of VO(2)max. The theoretical benefits of including the right ventricle in a Fontan circulation were not apparent.

Similarities and differences in the exercise performance of patients after a modified Fontan procedure compared to patients with complete transposition following a Senning operation

OBJECTIVE

To investigate cardiopulmonary performance in patients after a Fontan procedure, comparing it to patients following a Senning operation.

METHODS

We studied 21 children, with a mean age of 11.1 years, after a total cavopulmonary anastomosis, comparing them to 13 with complete transposition after a Senning procedure, having a mean age of 11.8 years, and 21 control subjects with a mean age of 11.2 years. All were tested on a bicycle ergospirometer.

RESULTS

Peak consumption of oxygen, maximal work rate, peak oxygen pulse and endexpiratory pressure of carbon dioxide at a work rate of 1.5 Watt/kg were lowest in patients with a modified Fontan procedure, and highest in the control group (p < or = 0.0278). Production of carbon dioxide, and minute ventilation at a work rate of 1.5 Watt/kg, was highest in the patients after Fontan procedure, and lowest in the healthy subjects (p < or = 0.0163). Production of carbon dioxide per single breath was lower in those having a Fontan procedure (28.9 ml) than in the two other groups (35.1 ml; p = 0.0243). The tidal volume showed no significant differences between the three groups.

CONCLUSIONS

The reaction to exercise was identical qualitatively in both groups of patients, and comparable to the behaviour of patients with chronic heart failure. Quantitatively, the results of the patients following a Senning procedure lay between those of control subjects and those who had undergone a Fontan operation. The only exception was dead space ventilation, where the patients after a Fontan procedure differed from the two other groups because of their increased ventilation-perfusion mismatch.

Impact of early ventricular unloading on exercise performance in preadolescents with single ventricle Fontan physiology

OBJECTIVES

We sought to determine if early ventricular volume unloading improves aerobic capacity in patients with single ventricle Fontan physiology.

BACKGROUND

Surgical strategies for patients with single ventricle include intermediate staging or early Fontan completion to reduce the adverse affects of prolonged ventricular volume load. The impact of this strategy on exercise performance has not been evaluated.

METHODS

Retrospectively, we reviewed the exercise stress test results of all preadolescents with single ventricle Fontan physiology. "Volume unloading" was considered to have occurred at the time of bidirectional cavopulmonary anastomosis or at the time of Fontan surgery in those patients who did not undergo intermediate staging. Potential predictors of aerobic capacity were analyzed using multivariate regression.

RESULTS

The patients (n = 46) achieved a mean percentage predicted of maximal oxygen consumption (VO2max) of 76.1% +/- 21.1%. The mean age at the time of volume unloading was 2.7 +/- 2.4 years, and the mean age at testing was 8.7 +/- 2 years. Intermediate staging was performed in 16 of 46 patients (35%). In multivariate analysis, younger age at volume unloading was associated with increased aerobic capacity (p = 0.003). Other variables were not predictive. The subgroup of patients who underwent volume unloading before two years of age achieved a mean percentage predicted VO2max of 88.6% +/- 24.1%.

CONCLUSIONS

Preadolescents with single ventricle who undergo volume unloading surgery at an early age demonstrate superior aerobic capacity compared with those whose surgery is delayed until a later age.

The role of the right ventricle during hypobaric hypoxic exercise: insights from patients after the Fontan operation

OBJECTIVES

The principal objective of this study was to examine the importance of the right ventricle for maximal systemic oxygen transport during exercise at high altitude by studying patients after the Fontan operation.

BACKGROUND

High-altitude-induced hypoxia causes a reduction in maximal oxygen uptake. Normal right ventricular pump function may be critical to sustain cardiac output in the face of hypoxic pulmonary vasoconstriction. We hypothesized that patients after the Fontan operation, who lack a functional subpulmonary ventricle, would have a limited exercise capacity at altitude, with an inability to increase cardiac output.

METHODS

We measured oxygen uptake (VO2, Douglas bag), cardiac output (Qc, C2H2 rebreathing), heart rate (HR) (ECG), blood pressure (BP) (cuff), and O2 Sat (pulse oximetry) in 11 patients aged 14.5+/-5.2 yr (mean +/- SD) at 4.7+/-1.6 yr after surgery. Data were obtained at rest, at three submaximal steady state workrates, and at peak exercise on a cycle ergometer. All tests were performed at sea level (SL) and at simulated altitude (ALT) of 3048 m (10,000 ft, 522 torr) in a hypobaric chamber.

RESULTS

At SL, resting O2 sat was 92.6+/-4%. At ALT, O2 sat decreased to 88.2+/-4.6% (P < 0.05) at rest and decreased further to 80+/-6.3% (P < 0.05) with peak exercise. At SL, VO2 increased from 5.1+/-0.9 mL x kg(-1) x min(-1) at rest to 23.5+/-5.3 mL x kg(-1) x min(-1) at peak exercise and CI (Qc x m(-2)) increased from 3.3+/-0.7 L x m(-2) to 6.2+/-1.2 L x m(-2). VO2 peak, 17.8+/-4 mL x kg(-1) x min(-1) (P < 0.05), and CI peak, 5.0+/-1.5 L x m(-2) (P < 0.05), were both decreased at ALT. Remarkably, the relationship between Qc and VO2 was normal during submaximal exercise at both SL and ALT. However at ALT, stroke volume index (SVI, SV x m(-2)) decreased from 37.7+/-8.6 mL x min(-1) x m2 at rest, to 31.3+/-8.6 mL x min(-1) x m2 at peak exercise (P < 0.05), whereas it did not fall during sea level exercise.

CONCLUSIONS

During submaximal exercise at altitude, right ventricular contractile function is not necessary to increase cardiac output appropriately for oxygen uptake. However, normal right ventricular pump function may be necessary to achieve maximal cardiac output during exercise with acute high altitude exposure.

Alveolar-arterial gas tension differences during progressive exercise in patients after the Fontan operation

We investigated alveolar-arterial gas tension differences as a measurement of ventilatory impairment during exercise in patients who had undergone the Fontan operation. The ventilatory response to exercise in 13 operated patients was compared with that of 11 control subjects. The difference between end-tidal and arterial oxygen tension (P(ET-a)DO2) and between arterial and end-tidal carbon dioxide tension (P(a-ET)DCO2) as well as the physiologic dead space-tidal volume ratio were calculated during progressive treadmill exercise testing. In the Fontan group, P(ET-a)DO2 and P(a-ET)DCO2 were significantly higher than in control subjects and increased in parallel during the study period. The physiologic dead space-tidal volume ratio was higher in the Fontan group than in the control group, and the difference in these ratios between the values obtained using end-tidal carbon dioxide tension and those using arterial carbon dioxide tension correlated well with P(a-ET)DCO2 (r = -0.79 to -0.98, p < 0.001). The physiologic dead space-tidal volume ratio during exercise was significantly higher in patients with low exercise capacities than in those with high exercise capacities (p < 0.05). The alveolar-arterial gas tension differences during exercise were greater in Fontan patients than in control subjects. We conclude that the size of the physiologic dead space can be evaluated from measurements of arterial carbon dioxide tension and is correlated with impaired exercise capacity after the Fontan operation.

Cardiorespiratory responses to exercise after repair of the univentricular heart

The purpose of this study is to evaluate cardiorespiratory responses to exercise in patients with univentricular heart according to the type of repair used. Forty-three patients with univentricular heart were divided into three groups: 15 preoperative patients (group A), 18 who had Fontan repair (group B) and 10 who had ventricular septation (group C). Group C was further divided into two subgroups, 7 with normal atrioventricular valve function (group C1) and 3 with atrioventricular valve regurgitation (group C2). Cardiorespiratory variables were determined after performance of cardiopulmonary exercise testing. One-hundred-and-twenty-five healthy subjects, age 5-26 years, served as controls. Oxygen uptake in group C1 at both ventilatory threshold and peak exercise was highest in all groups of univentricular heart (P < 0.05), while peak oxygen uptake in group C1 was significantly lower vs controls (P < 0.001), and that in group B was significantly higher than that for group A. Although chronotropic incompetence was noted in all groups of univentricular heart, marked improvements in both the relationship between heart rate and oxygen uptake and in the ventilatory efficiency were observed after definitive repair. While ventilatory efficiency was still impaired in group B, there was no significant difference between that in group C1 and the control group. When patients with univentricular heart of the left ventricular type (Van Praagh's type A single ventricle) were analyzed separately, superior cardiorespiratory response after ventricular septation was also found. In view of these findings, the ventricular septation procedure is preferred to the Fontan method in patients with univentricular heart when morphological conditions are suitable for this procedure so as not to make residual complications, such as significant atrioventricular valve regurgitation.

The adult patient with congenital heart disease

In adults with congenital heart disease who are confronted with noncardiac surgery, perioperative risks can be reduced, often appreciably, when problems inherent to this patient population are anticipated. The first necessity is to clarify the diagnosis and to be certain that appropriate information is obtained from a cardiologist with adequate knowledge of congenital heart disease in adults. Physiology and anatomy can vary significantly among patients who superficially carry identical diagnoses. Elective noncardiac surgery should be preceded by clinical assessment including review of clinical and laboratory data and securing the results of necessary diagnostic studies. Preoperative assessment should be performed far enough in advance of the anticipated date of surgery to allow critical assessment of the data and potential discussions with colleagues. Appropriate cardiovascular laboratory studies to be obtained or reviewed include electrocardiograms, chest radiographs, echocardiograms, and cardiac catheterization data, which may include specialized intracardiac electrophysiologic testing. Congenital heart disease in adults is a new and evolving area of special interest and expertise in cardiovascular medicine. Multidisciplinary centers for the care of these patients are being developed. The 22nd Bethesda Conference recommended that these centers include among their consultants anesthesiologists with special expertise in managing patients with congenital heart disease. These anesthesiologists can have the option of serving either as the attending anesthesiologists when patients require noncardiac surgery or as consultants and resource individuals to other anesthesiologists.

Cardiopulmonary function in adult patients late after Fontan repair

OBJECTIVES

The clinical status and exercise assessment of adult patients late after the Fontan operation were reviewed to determine cardiovascular function.

BACKGROUND

The Fontan operation is the final operation for many patients with tricuspid atresia or a single ventricle. Follow-up reports describe most patients to be in Canadian Cardiovascular Society functional class I or II. Objective measures of cardiac performance in the pediatric age group have shown significant dysfunction.

METHODS

Forty-seven adult patients were seen late after the Fontan operation at the Toronto Congenital Cardiac Centre for Adults. Thirty of these underwent cycle ergometry to determine maximal exercise capacity. Maximal ventilation, maximal oxygen uptake and anaerobic threshold were determined from a ramp exercise protocol. Ejection fraction at rest and during exercise was measured with gated radionuclide angiography. Results were compared with those of eight normal volunteers. Results are given as mean +/- SD.

RESULTS

Thirty patients underwent cardiopulmonary exercise testing 6.7 +/- 3.9 years after a first Fontan operation. Clinically 93% were in functional class I or II. The Fontan group patients had a significantly lower maximal work load (548 +/- 171 vs. 1,094 +/- 190 kilopond-meters, p < 0.00001), anaerobic threshold (11.2 +/- 2.9 vs. 23.6 +/- 4.6 ml/kg per min) and maximal oxygen consumption (14.8 +/- 4.5 vs. 42.1 +/- 10.0 ml/kg per min). Systemic ventricular ejection fraction was lower at rest (38 +/- 12% vs. 58 +/- 7%) and during exercise (40 +/- 15% vs. 70 +/- 8%).

CONCLUSIONS

Despite a clinical impression of good function, by objective measures adult patients continue to have significant cardiovascular limitation late after the Fontan operation.

Inaccuracy of noninvasive estimates of VD/VT in clinical exercise testing

To evaluate the accuracy of noninvasive estimates of VD/VT in clinical exercise testing, we compared measurements of standard VD/VT with estimates based either on end-tidal CO2 (VD/VTET) or a published estimate of arterial PCO2 (VD/VTest) at peak exercise in 68 patients. Using regression analysis, we identified highly significant differences (p < 0.001) between each method and VD/VTstand across a broad range of observed VD/VT. Assuming a normal exercise VD/VT < or = 0.30, estimate methods were specific but were insensitive (50 percent for VD/VTET and 57 percent for VD/VTest) for identifying patients with abnormal gas exchange during exercise. Separate analysis of subgroups based on resting pulmonary function did not identify any group for which either method was acceptable. Our analysis showed that errors in estimating PaCO2, which are amplified by the Bohr equation when calculating VD/VT, are responsible for the inaccuracies of each noninvasive method. We conclude that noninvasive estimates of PaCO2 cannot replace measured arterial PCO2 for calculation of VD/VT during exercise.

Maximal hemodynamic response after the Fontan procedure: Doppler evaluation during the treadmill test

After undergoing the Fontan procedure for congenital heart disease, 16 young patients performed a maximal treadmill test according to the Bruce protocol. The peak velocity of the blood flow in the ascending aorta, stroke index, and cardiac index were measured by continuous-wave Doppler echocardiography at rest and at each stage of the test. The results were compared with those from 18 normal children. The body surface area was similar in the two groups. The endurance time was 37% shorter in the Fontan group than in the control group. From the beginning of exercise until the sixth minute, the increase in stroke index was lower in the Fontan group (NS). After that point, the stroke index was maintained at a high level in the control group but decreased toward its original level in the Fontan group. The response of cardiac index to exercise in the two groups was comparable until the sixth minute, after which the Fontan group failed to maintain an ascending curve. All the hemodynamic values were significantly higher in the control group at maximal exercise; at this point the cardiac index had increased 79% in the Fontan group and 170% in the control group. The subnormal response of the stroke volume at submaximal exercise and the subsequent decrease at maximal exercise following the Fontan procedure are important hemodynamic findings.

Adult congenital heart disease: principles and management guidelines: Part II

The treatment of congenital heart disease may be palliative because many residua and sequelae persist into adulthood. Except for trivial lesions and anomalies such as PDA or secundum ASD where surgical cure is possible, continued supervision is mandatory. These patients deserve expert medical assessment from adult cardiologists and from other specialists when appropriate. The prevalence of postoperative adult congenital heart disease is increasing: by the year 2000 it is estimated that over 2000 in each million of the adult population will have congenital heart disease, one third of these having undergone cardiac surgery. It is important that some adult cardiologists in each major centre develop skills in adult congenital heart disease for this new patient population.

Cardiorespiratory response to exercise after the Fontan operation: a serial study

OBJECTIVES

The purpose of this study was to assess whether there is deterioration of aerobic capacity over time after the Fontan operation in individual patients.

BACKGROUND

We previously observed that maximal aerobic capacity after the Fontan operation was lower in older patients than in younger patients. It was unclear whether this represented a decrease in aerobic capacity with time after operation or was a function of studying patients of different ages at different times postoperatively.

METHODS

All patients who had more than one postoperative exercise study were included. There were 25 patients (19 male, 6 female), aged 3.8 to 39 years at the time of the operation. The first exercise test was performed, on average, 2.2 years after the Fontan operation, and the last exercise test was performed, on average, 5.9 years (range 1.8 to 13) after the operation. In 11 patients, coronary sinus drainage was left on the pulmonary venous side. Five patients had had a previous Glenn operation. Exercise was performed to exhaustion with use of a 3-min incremental cycle protocol.

RESULTS

Exercise duration, oxygen uptake, blood pressure, respiratory rate, minute ventilation, pulmonary blood flow index, exercise factor, ST-T wave changes and the prevalence of arrhythmias were similar during the first and last tests. Exercise systemic arterial blood oxygen saturation decreased from the first to the last postoperative test (p < 0.006) regardless of age. The percent of predicted heart rate, at rest and during maximal exercise, decreased more in older patients from the first to the last test (p < 0.05 for rest and exercise).

CONCLUSIONS

In this select group of patients, exercise tolerance remained relatively unchanged over the range of 13 years after the Fontan operation. Heart rate at rest and during maximal exercise decreased more than predicted for age in older patients. A small but significant progressive decrease in systemic arterial blood oxygen saturation was found. The former might represent abnormal sinus node function in patients with functional single ventricle, and the latter might represent a tendency toward development of abnormal ventilation/perfusion patterns resulting from the development of small pulmonary arteriovenous fistulas or an effect of position of the coronary sinus postoperatively.

Ventricular performance before and after Fontan repair for univentricular atrioventricular connection: angiographic and radionuclide assessment

OBJECTIVES

This study was designed to evaluate changes in ventricular volume, mass and cardiac function before and after creation of an atrial to pulmonary connection in patients with a univentricular atrioventricular connection.

BACKGROUND

Intact systolic and diastolic performance is critical for successful establishment of an atrial dependent circulation, and few studies are available comparing cardiac performance before and after creation.

METHODS

With the use of radionuclide blood pool imaging and ventricular cineangiography, 54 patients (mean age 6.4 +/- 3.4 years) were studied. Twenty-eight patients were investigated preoperatively and 36 greater than 1 year after repair and compared with a control population.

RESULTS

Before operation, end-diastolic volume and wall mass were significantly increased compared with those of control subjects; however, the mass/volume ratio was normal (1.08 +/- 0.31 g/ml for the preoperative group; 0.97 +/- 0.19 for control subjects). Although end-diastolic volume returned to normal after the procedure, wall mass remained elevated and contributed to an elevated mass/volume ratio (1.20 +/- 0.38 g/ml). After the procedure, systemic vascular resistance index was significantly elevated compared with that before surgery or with that of control subjects (1,199 +/- 373, 2,120 +/- 645, 1,556 +/- 275 dynes.s.cm-5.m2: pre- and postrepair and control subjects, respectively). Radionuclide studies demonstrated that preoperative ejection fraction (52 +/- 9, 50 +/- 9, 60 +/- 8%), peak ejection (2.58 +/- 0.66, 2.95 +/- 0.81, 3.73 +/- 0.70 EDV/s) and peak filling rates (2.84 +/- 0.75, 2.75 +/- 0.79, 3.84 +/- 0.51 end-diastolic volumes [EDV/s]) were significantly reduced compared with those of control subjects and remained so after surgery.

CONCLUSIONS

These data suggest that systolic and diastolic function is depressed preoperatively in these patients, remains unchanged after the creation of an atrial-dependent circulation and is associated with an increased systemic vascular resistance. Long-term issues addressing preservation of cardiac function need to be prospectively studied.

Corrective surgery for tricuspid atresia: which modification of Fontan-Kreutzer procedure should be used? A review

Various modifications of Fontan-Kreutzer procedure have evolved over the years. The available literature was reviewed in an attempt to evaluate whether one of these operations is preferable to others. Although there is no complete agreement, direct atriopulmonary anastomosis in the absence of a subpulmonary ventricular chamber, and atrioventricular connection via a homograft conduit in patients with a good-sized (greater than 30% of normal), well-formed (with both trabecular and outlet portions) right ventricle appear to be reasonable choices. In patients with more than the usual risk or at low risk for the Fontan-Kreutzer procedure, other alternatives (namely, total cavopulmonary connection for patients with asplenia/polysplenia syndrome and systemic venous anomalies and bidirectional cavopulmonary anastomosis or Fontan-Kreutzer with a small temporary atrial septal defect) could be considered. The role of experimental skeletal muscle augmentation or replacement of right heart chambers and cardiac transplantation in the corrective treatment of tricuspid atresia needs to be defined as more data become available.

Ventricular function during supine bicycle exercise in univentricular connection with absent right atrioventricular connection

Fourteen patients with univentricular connection, absent right connection (tricuspid valve atresia) and normally related great arteries underwent rest and supine bicycle exercise equilibrium radionuclide blood pool studies. Ejection fraction, heart rate, systemic blood pressure and oxygen saturation (ear oximetry) were measured. There were 6 male and 8 female patients. Mean age +/- standard error of the mean was 14.5 +/- 1.1 years (range 6.3 to 21.1). Eight patients (group 1) had systemic to pulmonary shunts placed as palliation 8.2 +/- 2.2 years before study and 6 patients (group II) had caval to pulmonary shunts placed 11.8 +/- 1.6 years previously. Ejection fraction at rest was 54 +/- 2% and an abnormal response to exercise (failure of ejection fraction to increase greater than or equal to 5% from rest to peak exercise) was found in 9 of 14 patients. When analyzed separately, ejection fraction at rest in group I was higher than in group II; however, this difference disappeared at peak exercise. There was a significant negative correlation between ejection fraction at peak exercise and the interval since palliative surgery, although it was not apparent at rest. These data suggest that ventricular function is compromised during exercise and that abnormal performance is influenced by long-standing volume overload. Importantly, this abnormal state is concealed at rest and the choice of palliative shunting procedure appears to have little effect on normalizing pump performance.