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Cardiorespiratory exercise testing after venous switch operation in children with complete transposition of the great arteries
Cardiorespiratory Exercise Testing After Venous Switch Operation in Children with Complete Transposition of the Great Arteries TONY REYBROUCK, DSc, MONIQUE DUMOULIN, MD, and LUCAS G. VAN DER HAUWAERT, MD
In 14 children who underwent a venous switch operation for complete transposition of the great arteries, exercise testing was performed 3 to 15 years (mean 8) after the operation. Exercise performance capacity was assessed by the determination of the ventilatory threshold during exercise and by the oxygen uptake (VOp) reached at a heart rate of 170 beats/min (VO,,170). The ventilatory threshold was defined as the hiihest oxygen uptake (VO*) at which the pulmonary ventilation (VE) stops to increase linearly when related to VOn. During exercise above. this threshold a disproportionate increase in VE relative to VOp is observed. The mean ventilatory threshold was significantly lower (p KO.01) than the normal mean value and averaged 72 f 15%, 67 f 15% and 70 f 13% of the predlcteci normal value for children of comparable age, \?reight and height, respectively. The mean value for VOp,170 also was significantly lower (p <0.05)
than the normal mean value for children of comparable age, weight and height, and averaged 61 f 20%, 61 f 16% and 60 f 16%, respectively. Compared with normal control subjects of the same sex and age, the ventilatory threshold was surpassed sooner (p
A
fter a venous switch operation, most patients with transposition of the great arteries (TGA) function normally and are clinically well. However, because the right ventricle has to cope with systemic pressures and right ventricular dysfunction has been frequently documented,1-5 it may be questioned whether these patients have the same exercise capacity as their healthy peers. In patients operated for TGA, only limited information is available on maximal exercise performance assessed by maximal endurance time on a treadmill,3+6-8maximal workload on a bicycle ergome-
From the Departments of Pediatric Cardiology and Cardiovascular Rehabilitation, Gasthuisberg University Hospital, University of Leuven, Belgium. Manuscript received July 24, 1987; revised manuscript received and accepted November 23,1987. Address for reprints: Lucas G. Van der Hauwaert, MD, Department of Pediatric Cardiology, Gasthuisberg University Hospital, 3000 Leuven, Belgium.
ter2s4or maximal oxygen uptake.7 To our knowledge, no data are available on gas exchange during submaximal exercise. The purpose of our study was to measure respiratory gas exchange during graded submaximal exercise and thus determine the ventilatpry threshold, defined as the highest o;lrygen uptake (VO,) at which pulmonary ventilation (Vs) stops to increase linearly with increasing VO 2,gJoAbove this exercise intensity a disproportionate increase in Vs relative to VO, is observed. Because heart rate response during exercise still is widely used in the assessment of cardiorespiratory performance capacity, it also was evaluated in our study.
Methods Patients: From 1980 to 1986, 14 asymptomatic patients (9 boys and 5 girls] with regular sinus rhythm were selected from a larger group of TGA patients to undergo graded exercise testing on a treadmill, 3 to 15 881
EXERCISE TESTING IN TRANSPOSITION
062
TABLE I Patients
Pt
Anthropometrical
and Clinical
Age at Testing (yrs), Sex
Age at Surgery (mol
Type of Surgery
6, F 13. F
3 38 23 23 19 12 12 18 21 11 18 51 15 41
MO MO MO MO MO so MO so MO so MO MO MO MO
1 2 3 4 5 6 7 8 9 10 11 12 13 14
8. M 11, F
6, M 4, 12, 7, 10, 5,
M M M M M
8, F 16, M
8. F 18. M
MO = Mustard operation;
45
OF THE GREAT ARTERIES
Characteristics
Interval Between Exercise Testing and Surgery Ws)
of the
Weight (kg)
Height (cm)
21 45 21 31 20 15 34 22 26 17 24 46 23 73
118 157 115 114 122 95 147 124 133 110 131 173 126 167
6 10 6 9 5 3 11 6 9 4 6 12 7 15
SO = Senning operation.
r
. . (
,
,
,
8 40
,
,
10
,
12
,
,
14
,
,
,
16 AGE (years1
18
r
=! IP I $1 b ‘6
I
I 0
I
I 10
I
I 12
t
I
I
14 AGE (years1
I lb
FIGURE 1. Individual values for ventilatory threshold in 8 boys (A) and 4 girls (6) operated on for transposition of the great arteries. The 95% confidence limits of the normal value are shown by the shaded area. For patients in whom repeated exercise studies were avallable, the dots are connected wlth a Ilne.
years (mean 8 f 3 standard deviation) after a venous switch operation. Children <4 years and patients with overt sinoatrial node dysfunction, hemodynamically important associated lesions, gross cardiomegaly or mental retardation were excluded. The pertinent clinical data are listed in Table I. The age at correction varied from 3 to 51 months (mean 22 f 13). The Mustard operation was performed in 11 patients and the Senning procedure in 3. All patients were asymptomatic at the time of investigation None was taking medication. The interval between operation and exercise testing varied from 3 to 15 years [mean 8 f 31. In 4 patients, exercise testing was repeated 5 months to 2.4 years after the initial assessment.The overall result of surgery in this selected group was considered to be “excellent.” Age, at the time of the exercise test, varied from 4 to 19 years (mean 9 f 4, body weight ranged from 15 to 73 kg (mean 30 f 16) and body height from 95 to 173 cm (mean 131 f 23). When the data for height and weight were expressed as percentiles,l* 1 out of 14 patients was below the third percentile for weight and 3 of 14 were below it for height. Testing procedures: The methods used have already been reported in detai1.12-l4Briefly, graded exercise testing was performed on a treadmill. The speed of the treadmill was set at 4.8 km/hr and 5.6 km/hr for children below and above 6 years of age, respectively.15 The inclination was increased stepwise by 2% every minute until a heart rate of 170 beats/min was reached. The electrocardiogram from a biopolar lead was continuously monitored. Oxygen uptake (VO,) and carbon dioxide output (VCO,) were measured by the Douglas bag method. Exercise performance was assessedby determination of the ventilatory threshold, expressed in ml 02/min/ kg and in units of time (min). The ventilatory threshold was determined as the exercise intensity at which a continuous increase was found for the ventilatory equivalent for 02 (V&02] without a concomitant ingrease in the ventilatory equivalent for CO2 (Vs/ VC02].12J6Furthermore, the exercise intensity or VOZ reached at a heart rate of 170 beats/min (vO2,170) was determined and heart rate response assessed during submaximal exercise at various inclinations of the treadmill. Heart rate, expressed as a percentage of the mean normal value, was considered to be subnormal when it fell below the 95% confidence limit.17 The values for ventilatory threshold and v02,170 in these patients were compared with the values obtained in 234 age-matched healthy children.12 Differences between mean values were calculated by analysis of variance. For correlation analysis, the Pearson correlation method was used. The dispersion of the data is given by the standard deviation of the mean and for normal children also by the 95% confidence limits.
Results Exercise performance: The ventilatory threshold could be determined in 12 of 14 patients. Individual
April 1, 1988
TABLE II Characteristics of Aerobic Transposition of the Great Arteries VT Pt (ml Oa/min/kg) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
24 20 18 27 25 16 23 22 18 23 15 19
Pred = predicted;
Function During Exercise
VT Age Pred W)
VT Weight Pred (%)
82 81 56 97 83 54 73 67 53 85 56 75
77 76 55 98 76 54 68 65 53 79 47 60
i/Os,170
THE AMERICAN
VT Height Pred vo*, 170 (ml Oplmin/kg) (%I 04 79 60 91 78 54 72 66 54 -
ai
54 64
OF CARDIOLOGY
Volume 61
663
in 14 Patients Operated for
i/o*, 170 Age Pred (%I
28 24 29 31 26 36 20 23 34 26 23 18 19
Vo*, 170 Weight Pred (%I
91
106 69 108 60 67 109 92 63 65 49
112 69 102 61 67 102 89 71 60 56
a5
co,, 170 Height Pred W)
a5
92 94
= oxygen uptake at a heart rate of 170 beats/min:
results are listed in Table II and Figure 1A and B. In 11 of these patients, the ventilatory threshold was below the 95% confidence limit obtained in normal children of comparable age. The mean value for the ventilatory threshold was significantly lower (p
JOURNAL
91 89 83 106 69 105 61 68 95 90 64 83 54
a7
VT = ventilatory
threshold.
the 95% confidence limits) and 4 a heart rate response above the 95% confidence limit. In these 8 patients the ventilatory threshold was subnormal. Thus, no relation was found between ventilatory threshold and heart rate response. During exercise and during the immediate recovery period, premature atria1 beats were recorded in 4 patients. In another patient, both premature atria1 and ventricular beats and couplets were observed during and immediately after exercise. Exercise performance and clinical data: No relation was found in this small series of patients between the age at surgery and the ventilatory threshold expressed as a percent of the predicted normal value for children of the same age (r = 0.28), weight (r = 0.18) and height (r = 0.14). Neither was there a significant relation between the exercise performance capacity (% of normal) and the time lapse between surgery and the exercise test (r = 0.07 for age, r = -0.18 for weight and r = -0.08 for height-predicted normal value).
Discussion Despite the absence of clinical symptoms and the fact that all patients were normally attending school and took part in games, most showed a subnormal exercise tolerance when assessed by the ventilatory threshold method. Poor exercise tolerance has previously been reported in a considerable number of patients who underwent a Mustard or Senning operation for TGA.4,6JJ1aJg The comparison of these studies is difficult because different methods for evaluating exercise performance were used: VOzmax,l* maximal endurance time on the treadmil16s8Jgor maximal workload on the bicycle ergometer.2 Also, different criteria for normality were applied, that is, maximal treadmill time <8 minutes,18 V02max <40 ml/min/kgls and 1 standard deviation below the mean normal value for maximal endurance time on the treadmill.6JJs Our observation that a larger fraction of patients had subnormal values for exercise performance than
a64
EXERCISE TESTING IN TRANSPOSITION
0~ THE GREAT ARTERIES
noted in previous studies may be explained by the sensitivity of the method we elected to use. In previous investigations on cardiorespiratory endurance capacity in children with congenital heart disease and left-toright shunt13 and in children operated on for tetralogy of Fallot14 it has been shown that the ventilatory threshold method is more sensitive to detect subnormal exercise capacity than other indexes of cardiorespiratory performance capacity such as \jO,,l70, irOzmax20 or the maximal endurance time on a treadmi11.21A considerable advantage of the ventilatory threshold measurement is its independence of the child’s motivation to perform a maximal effort as required in the Bruce treadmill protocol. Furthermore, when repeated within a time interval of 1 to 3 years after the initial testing, we found the measurements to be reproducible (Figure 1A and B]. This confirms the results of Lipkin et a1,22who found reproducible results in a group of adults with impaired ventricular function who underwent at least 3 exercise tests over 2 to 14 days. Although the ventilatory [anaerobic] threshold was originally defined as the exercise intensity or VOa2at which a concomitant disproportionate increase in VE and lactate occurred relative to VOZ,~,~~ we have been using this index of exercise performance in a pragmatic way, without implying a causal relationship with the onset of metabolic acidosis during graded exercise. Subnormal exercise performance in patients after venous switch operations for TGA has generally been attributed to dysfunction of the right (systemic] ventri-
z 140 E ki ,’ 130 0
if!
r 2
120 t 110 c
G g 100 90-
Acknowledgment: We gratefully acknowledge the help of M. Weymans, DSc, in the statistical analysis of the data and the assistance of L. Van den Berghe during exercise testing.
80-
70, _ L
I
I
0
2
I
cle,1-5as demonstrated by a depressed right ventricular ejection fraction ,24-26failure to increase the right ventricular ejection fraction or stroke volume during exercise2-5 or an increased right ventricular end-diastolic volume.1p24s25 It has been suggested that the intrinsic geometry and fiber array of the right ventricle make it less suitable to function as a systemic pump.25,27Our findings, which indicate a reduced exercise performance and a lowered ventilatory threshold in the majority of patients, are in accordance with these hemodynamic studies. Another contributing factor to the reduction of exercise performance is the impaired chronotropic reserve. In patients operated for TGA, heart rate response to maximal exercise has been shown to be significantly reduced. 5-7~18~1g Therefore, when these patients undergo a given exercise, their heart rates should be considered to represent a higher percentage of the maximal exercise capacity than is the case in normal subjects. This is confirmed by the fact that TGA-operated patients experience an exercise at a heart rate of 170 beats/min as being close to their maximal capacity, whereas normal children will perceive it as only moderately heavy. In the present study, based on submaximal exercise, a lower than normal heart rate response was found in nearly half of the patients. Theoretically, a low or normal heart rate response during exercise-as observed in endurancetrained individuals-should be associated with a high or normal value for ventilatory threshold or maximal oxygen uptake. However, in our patients there was no relation between heart rate response and ventilatory threshold, which illustrates the fact that the latter, a parameter of aerobic function, is independent of heart rate response. This is also confirmed by the lower mean value for ventilatory threshold (72 f 15%) expressed as a percentage of the age-predicted normal value, compared to the mean value for V02,170 (81 f 20%). In previous studies, a blunted heart rate response during submaximal exercise has been attributed to sinoatrial node dysfunction after intraatrial operation.6,28 At variance with other studies6J8J8in which multifocal ventricular premature beats, sinus node dysfunction and atrioventricular block were recorded during exercise in a large proportion of patients, no serious arrhythmia was observed in our study. The probable reason was our exclusion of patients with overt sinoatria1 node dysfunction or other types of arrhythmia on the rest electrocardiogram.
I
4 6 INCLINATION (%)
FIGURE 2. Individual values for heart rate response during graded treadmill exercise. The 95 % confidence limits of the normal value are shown by the shaded area. The numbers refer to the patient numbers listed in Table 1.
References 1. Alpert BS, Bloom KR, Olley P, Trusler GA, Williams CM, Rowe RD. Echocardiographic evaluation of right ventricular function in complete transposition of the great arteries: angiographic correlates. Am J Cardiof 1979;44:270275. 2. Parrisch MD, Graham TP, Bender HW, Jones JP, Patton J. Partain LC. Radionuclide angiographic evaluation of right and left ventricular function during exercise after repair of transposition of the great arteries. Comparison
April 1, 1988
with normal subjects and patients with congenitally corrected transposition. CircuIotion 1983;67:178-183. 3. Murphy ]H, Barlai-Kovatch MM, Mathews RA, Beerman LB, Park SC, Neches WH, Zuberbuhler JR. Rest and exercise right and left ventricular function late after the Mustard operation: assessment by radionuclide ventriculography. Am J Cardiol 1983;51:1520-1526, 4. Benson LN, Bonet J, McLaughlin P, Olley PM, Feighlin D, Druck M, Trusler G, Rowe RD, March J. Assessment of right ventricular function during supine exercise after Mustard’s operation. Circulation 1982;65:1052-1059. 5. Ramsay JM, Venables AW, Kelly MJ, Kalff V. Right and left ventricular function at rest and with exercise after the Mustard operation for transposition of the great arteries. Br Heart J 1984;51:364-370. 6. Hesslein PS, Gutgesell HP, Gilette PC, McNamarra DG. Exercise assessment of sinoatrial node function following the Mustard operation, Am Heart J 1982;103:351-357, 7. Ruttenberg HD. Adams TD, Orsmond GS, Conlee RK, Fisher AG. Effects of exercise training on aerobic fitness in children after open heart surgery. Pediatr Cardiol 1983;4:19-24. 8. Matthys D, Devloo-Blanquaert A. The evaluation of exercise performance in children after surgical correction of congenital heart disease. In: Fagard R, Bekaert I. eds. Sportscardiology: Exercise in Health and Cardiovascular Disease. Dordrecht: Martinus Nijhoff, 1986214-219. 9. Wasserman K, Whipp BJ, Koyal NS, Beaver W. Anaerobic threshold and respiratory gas exchange during exercise. J Appl Physiol 1973;35:236-243. 10. Reybrouck T, Ghesquiere J, Cattaert A, Fagard R, Amely A. VentiIatory thresholds during short- and long-term exerdse. J Appl Physioll983;55:16941700. 11. Stuart HC, Meredith HV. Use of body measurements in the school health program. Am J Public Health 1946;36:1365-1386. 12. Reybrouck T, Weymans M, Stijns H, Knops J, Van der Hauwaert L. Ventilatory anaerobic threshold in healthy children: age and sex differences. Eur J Appl Physiol 1985;54:278-284. 13. Reybrouck T, Weymans M, Stijns H, Van der Hauwaert LG. VentiIatory anaerobic threshold for evaluating exercise performance in children with congenital left-to-right intracardiac shunt. Pediatr Cardiol 1986;7:19-24. 14. Reybrouck T, Weymans M, Stijns H, Van der Hauwaert L. Exercise testing after correction of tetralogy of FaIIot: the fallacy of a reduced heart rate response. Am Heart J 1988;112:998-1003. 15. Chandramouli B, Ehmke DA, Lauer RM. Exercise-induced electrocardio-
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JOURNAL
OF CARDIOLOGY
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graphic changes in children with congenital aortic stenosis. J Pediatr 1973;87:725-730. 16. Caiozzo V, Davis JA, Ellis JF, Azus JL, Vandagriff R, Prietto CA, McMaster WC. A comparison of gas exchange indices used to detect the anaerobic threshold. J Appl PhysioI1982;53:1184-1189. 17. Snedecor GW, Cochran WG. Statistical Methods. 6th ed. Iowa: Iowa State University Press, 1972. 18. Mathews RA, Fricker FJ, Beerman LB, Stephenson R], Fisher DR, Neches WH, Park SC, Lenox CC, Zuberbuhler JR. Exercise studies after the Mustard operation in transposition of the great arteries. Am J Cordial 1983;51:15261529. 19. Issenberg HJ, Freed MD. Exercise capacity and heart rate response after Mustard operation (abstr]. Pediatr Cardiol 1980;1:322. 20. Mocellin R, Bastanier C, Hofacker W, Biihlmeyer K. Exercise performance in children and adolescents after surgical repair of tetralogy of FaIIot. Eur J Cardiol 1976;4:367-374. 21. Cumming GR. Maximal exercise capcity of children with heart defects. Am J Cardiol 1978;42:613-619. 22. Lipkin DL, Perrins J, Poole-Wilson PA. Respiratory gas exchange in the assessment of patients with impaired ventricular function. Br Heart J 1985;54:321-328. 23. Wasserman K. Physiology of gas exchange and exertional dyspnoea. Clin Sci 1981;61:7-13. 24. Mocellin R. Henglein D, Btihlmeyer K. Ventrikelfunktion vor und nach Senning-operation bei patienten mit transposition der grossen arterien. Hers 1982;7:267-273. 25. Hagler DJ, Ritter DG, Mair DD, Tajik AJ, Seward J, Fulton RE, Ritman EL. Right and left ventricular function after the Mustard procedure in transposition of the great arteries. Am J Cardiol 1979;44:276-283. 26. Graham TP, Atwood GF, Boucek RJ, Boerth RC, Bender HW. Abnormalities of right ventricular function following Mustard’s operation for transposition of the great arteries. Circulation 1975;52:678-684. 27. Borow KM, Keane JF, Castaneda AR, Freed MD. Systemic ventricular function in patients with tetralogy of FaIIot, ventricular septal defect and transposition of the great arteries repaired during infancy. Circulation 1981;64:878-888. 28. Beerman LB, Neches WH, Fricker FJ, Mathews RA, Fischer DR. Park SC, Lenox CC, Zuberbuhler JR. Arrhythmias in transposition of the great arteries after the Mustard operation. Am r Cardial 1983;51:1530-1534.
In 14 children who underwent a venous switch operation for complete transposition of the great arteries, exercise testing was performed 3 to 15 years (mean 8) after the operation. Exercise performance capacity was assessed by the determination of the ventilatory threshold during exercise and by the oxygen uptake (VOp) reached at a heart rate of 170 beats/min (VO,,170). The ventilatory threshold was defined as the hiihest oxygen uptake (VO*) at which the pulmonary ventilation (VE) stops to increase linearly when related to VOn. During exercise above. this threshold a disproportionate increase in VE relative to VOp is observed. The mean ventilatory threshold was significantly lower (p KO.01) than the normal mean value and averaged 72 f 15%, 67 f 15% and 70 f 13% of the predlcteci normal value for children of comparable age, \?reight and height, respectively. The mean value for VOp,170 also was significantly lower (p <0.05)
than the normal mean value for children of comparable age, weight and height, and averaged 61 f 20%, 61 f 16% and 60 f 16%, respectively. Compared with normal control subjects of the same sex and age, the ventilatory threshold was surpassed sooner (p
A
fter a venous switch operation, most patients with transposition of the great arteries (TGA) function normally and are clinically well. However, because the right ventricle has to cope with systemic pressures and right ventricular dysfunction has been frequently documented,1-5 it may be questioned whether these patients have the same exercise capacity as their healthy peers. In patients operated for TGA, only limited information is available on maximal exercise performance assessed by maximal endurance time on a treadmill,3+6-8maximal workload on a bicycle ergome-
From the Departments of Pediatric Cardiology and Cardiovascular Rehabilitation, Gasthuisberg University Hospital, University of Leuven, Belgium. Manuscript received July 24, 1987; revised manuscript received and accepted November 23,1987. Address for reprints: Lucas G. Van der Hauwaert, MD, Department of Pediatric Cardiology, Gasthuisberg University Hospital, 3000 Leuven, Belgium.
ter2s4or maximal oxygen uptake.7 To our knowledge, no data are available on gas exchange during submaximal exercise. The purpose of our study was to measure respiratory gas exchange during graded submaximal exercise and thus determine the ventilatpry threshold, defined as the highest o;lrygen uptake (VO,) at which pulmonary ventilation (Vs) stops to increase linearly with increasing VO 2,gJoAbove this exercise intensity a disproportionate increase in Vs relative to VO, is observed. Because heart rate response during exercise still is widely used in the assessment of cardiorespiratory performance capacity, it also was evaluated in our study.
Methods Patients: From 1980 to 1986, 14 asymptomatic patients (9 boys and 5 girls] with regular sinus rhythm were selected from a larger group of TGA patients to undergo graded exercise testing on a treadmill, 3 to 15 881
EXERCISE TESTING IN TRANSPOSITION
062
TABLE I Patients
Pt
Anthropometrical
and Clinical
Age at Testing (yrs), Sex
Age at Surgery (mol
Type of Surgery
6, F 13. F
3 38 23 23 19 12 12 18 21 11 18 51 15 41
MO MO MO MO MO so MO so MO so MO MO MO MO
1 2 3 4 5 6 7 8 9 10 11 12 13 14
8. M 11, F
6, M 4, 12, 7, 10, 5,
M M M M M
8, F 16, M
8. F 18. M
MO = Mustard operation;
45
OF THE GREAT ARTERIES
Characteristics
Interval Between Exercise Testing and Surgery Ws)
of the
Weight (kg)
Height (cm)
21 45 21 31 20 15 34 22 26 17 24 46 23 73
118 157 115 114 122 95 147 124 133 110 131 173 126 167
6 10 6 9 5 3 11 6 9 4 6 12 7 15
SO = Senning operation.
r
. . (
,
,
,
8 40
,
,
10
,
12
,
,
14
,
,
,
16 AGE (years1
18
r
=! IP I $1 b ‘6
I
I 0
I
I 10
I
I 12
t
I
I
14 AGE (years1
I lb
FIGURE 1. Individual values for ventilatory threshold in 8 boys (A) and 4 girls (6) operated on for transposition of the great arteries. The 95% confidence limits of the normal value are shown by the shaded area. For patients in whom repeated exercise studies were avallable, the dots are connected wlth a Ilne.
years (mean 8 f 3 standard deviation) after a venous switch operation. Children <4 years and patients with overt sinoatrial node dysfunction, hemodynamically important associated lesions, gross cardiomegaly or mental retardation were excluded. The pertinent clinical data are listed in Table I. The age at correction varied from 3 to 51 months (mean 22 f 13). The Mustard operation was performed in 11 patients and the Senning procedure in 3. All patients were asymptomatic at the time of investigation None was taking medication. The interval between operation and exercise testing varied from 3 to 15 years [mean 8 f 31. In 4 patients, exercise testing was repeated 5 months to 2.4 years after the initial assessment.The overall result of surgery in this selected group was considered to be “excellent.” Age, at the time of the exercise test, varied from 4 to 19 years (mean 9 f 4, body weight ranged from 15 to 73 kg (mean 30 f 16) and body height from 95 to 173 cm (mean 131 f 23). When the data for height and weight were expressed as percentiles,l* 1 out of 14 patients was below the third percentile for weight and 3 of 14 were below it for height. Testing procedures: The methods used have already been reported in detai1.12-l4Briefly, graded exercise testing was performed on a treadmill. The speed of the treadmill was set at 4.8 km/hr and 5.6 km/hr for children below and above 6 years of age, respectively.15 The inclination was increased stepwise by 2% every minute until a heart rate of 170 beats/min was reached. The electrocardiogram from a biopolar lead was continuously monitored. Oxygen uptake (VO,) and carbon dioxide output (VCO,) were measured by the Douglas bag method. Exercise performance was assessedby determination of the ventilatory threshold, expressed in ml 02/min/ kg and in units of time (min). The ventilatory threshold was determined as the exercise intensity at which a continuous increase was found for the ventilatory equivalent for 02 (V&02] without a concomitant ingrease in the ventilatory equivalent for CO2 (Vs/ VC02].12J6Furthermore, the exercise intensity or VOZ reached at a heart rate of 170 beats/min (vO2,170) was determined and heart rate response assessed during submaximal exercise at various inclinations of the treadmill. Heart rate, expressed as a percentage of the mean normal value, was considered to be subnormal when it fell below the 95% confidence limit.17 The values for ventilatory threshold and v02,170 in these patients were compared with the values obtained in 234 age-matched healthy children.12 Differences between mean values were calculated by analysis of variance. For correlation analysis, the Pearson correlation method was used. The dispersion of the data is given by the standard deviation of the mean and for normal children also by the 95% confidence limits.
Results Exercise performance: The ventilatory threshold could be determined in 12 of 14 patients. Individual
April 1, 1988
TABLE II Characteristics of Aerobic Transposition of the Great Arteries VT Pt (ml Oa/min/kg) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
24 20 18 27 25 16 23 22 18 23 15 19
Pred = predicted;
Function During Exercise
VT Age Pred W)
VT Weight Pred (%)
82 81 56 97 83 54 73 67 53 85 56 75
77 76 55 98 76 54 68 65 53 79 47 60
i/Os,170
THE AMERICAN
VT Height Pred vo*, 170 (ml Oplmin/kg) (%I 04 79 60 91 78 54 72 66 54 -
ai
54 64
OF CARDIOLOGY
Volume 61
663
in 14 Patients Operated for
i/o*, 170 Age Pred (%I
28 24 29 31 26 36 20 23 34 26 23 18 19
Vo*, 170 Weight Pred (%I
91
106 69 108 60 67 109 92 63 65 49
112 69 102 61 67 102 89 71 60 56
a5
co,, 170 Height Pred W)
a5
92 94
= oxygen uptake at a heart rate of 170 beats/min:
results are listed in Table II and Figure 1A and B. In 11 of these patients, the ventilatory threshold was below the 95% confidence limit obtained in normal children of comparable age. The mean value for the ventilatory threshold was significantly lower (p
JOURNAL
91 89 83 106 69 105 61 68 95 90 64 83 54
a7
VT = ventilatory
threshold.
the 95% confidence limits) and 4 a heart rate response above the 95% confidence limit. In these 8 patients the ventilatory threshold was subnormal. Thus, no relation was found between ventilatory threshold and heart rate response. During exercise and during the immediate recovery period, premature atria1 beats were recorded in 4 patients. In another patient, both premature atria1 and ventricular beats and couplets were observed during and immediately after exercise. Exercise performance and clinical data: No relation was found in this small series of patients between the age at surgery and the ventilatory threshold expressed as a percent of the predicted normal value for children of the same age (r = 0.28), weight (r = 0.18) and height (r = 0.14). Neither was there a significant relation between the exercise performance capacity (% of normal) and the time lapse between surgery and the exercise test (r = 0.07 for age, r = -0.18 for weight and r = -0.08 for height-predicted normal value).
Discussion Despite the absence of clinical symptoms and the fact that all patients were normally attending school and took part in games, most showed a subnormal exercise tolerance when assessed by the ventilatory threshold method. Poor exercise tolerance has previously been reported in a considerable number of patients who underwent a Mustard or Senning operation for TGA.4,6JJ1aJg The comparison of these studies is difficult because different methods for evaluating exercise performance were used: VOzmax,l* maximal endurance time on the treadmil16s8Jgor maximal workload on the bicycle ergometer.2 Also, different criteria for normality were applied, that is, maximal treadmill time <8 minutes,18 V02max <40 ml/min/kgls and 1 standard deviation below the mean normal value for maximal endurance time on the treadmill.6JJs Our observation that a larger fraction of patients had subnormal values for exercise performance than
a64
EXERCISE TESTING IN TRANSPOSITION
0~ THE GREAT ARTERIES
noted in previous studies may be explained by the sensitivity of the method we elected to use. In previous investigations on cardiorespiratory endurance capacity in children with congenital heart disease and left-toright shunt13 and in children operated on for tetralogy of Fallot14 it has been shown that the ventilatory threshold method is more sensitive to detect subnormal exercise capacity than other indexes of cardiorespiratory performance capacity such as \jO,,l70, irOzmax20 or the maximal endurance time on a treadmi11.21A considerable advantage of the ventilatory threshold measurement is its independence of the child’s motivation to perform a maximal effort as required in the Bruce treadmill protocol. Furthermore, when repeated within a time interval of 1 to 3 years after the initial testing, we found the measurements to be reproducible (Figure 1A and B]. This confirms the results of Lipkin et a1,22who found reproducible results in a group of adults with impaired ventricular function who underwent at least 3 exercise tests over 2 to 14 days. Although the ventilatory [anaerobic] threshold was originally defined as the exercise intensity or VOa2at which a concomitant disproportionate increase in VE and lactate occurred relative to VOZ,~,~~ we have been using this index of exercise performance in a pragmatic way, without implying a causal relationship with the onset of metabolic acidosis during graded exercise. Subnormal exercise performance in patients after venous switch operations for TGA has generally been attributed to dysfunction of the right (systemic] ventri-
z 140 E ki ,’ 130 0
if!
r 2
120 t 110 c
G g 100 90-
Acknowledgment: We gratefully acknowledge the help of M. Weymans, DSc, in the statistical analysis of the data and the assistance of L. Van den Berghe during exercise testing.
80-
70, _ L
I
I
0
2
I
cle,1-5as demonstrated by a depressed right ventricular ejection fraction ,24-26failure to increase the right ventricular ejection fraction or stroke volume during exercise2-5 or an increased right ventricular end-diastolic volume.1p24s25 It has been suggested that the intrinsic geometry and fiber array of the right ventricle make it less suitable to function as a systemic pump.25,27Our findings, which indicate a reduced exercise performance and a lowered ventilatory threshold in the majority of patients, are in accordance with these hemodynamic studies. Another contributing factor to the reduction of exercise performance is the impaired chronotropic reserve. In patients operated for TGA, heart rate response to maximal exercise has been shown to be significantly reduced. 5-7~18~1g Therefore, when these patients undergo a given exercise, their heart rates should be considered to represent a higher percentage of the maximal exercise capacity than is the case in normal subjects. This is confirmed by the fact that TGA-operated patients experience an exercise at a heart rate of 170 beats/min as being close to their maximal capacity, whereas normal children will perceive it as only moderately heavy. In the present study, based on submaximal exercise, a lower than normal heart rate response was found in nearly half of the patients. Theoretically, a low or normal heart rate response during exercise-as observed in endurancetrained individuals-should be associated with a high or normal value for ventilatory threshold or maximal oxygen uptake. However, in our patients there was no relation between heart rate response and ventilatory threshold, which illustrates the fact that the latter, a parameter of aerobic function, is independent of heart rate response. This is also confirmed by the lower mean value for ventilatory threshold (72 f 15%) expressed as a percentage of the age-predicted normal value, compared to the mean value for V02,170 (81 f 20%). In previous studies, a blunted heart rate response during submaximal exercise has been attributed to sinoatrial node dysfunction after intraatrial operation.6,28 At variance with other studies6J8J8in which multifocal ventricular premature beats, sinus node dysfunction and atrioventricular block were recorded during exercise in a large proportion of patients, no serious arrhythmia was observed in our study. The probable reason was our exclusion of patients with overt sinoatria1 node dysfunction or other types of arrhythmia on the rest electrocardiogram.
I
4 6 INCLINATION (%)
FIGURE 2. Individual values for heart rate response during graded treadmill exercise. The 95 % confidence limits of the normal value are shown by the shaded area. The numbers refer to the patient numbers listed in Table 1.
References 1. Alpert BS, Bloom KR, Olley P, Trusler GA, Williams CM, Rowe RD. Echocardiographic evaluation of right ventricular function in complete transposition of the great arteries: angiographic correlates. Am J Cardiof 1979;44:270275. 2. Parrisch MD, Graham TP, Bender HW, Jones JP, Patton J. Partain LC. Radionuclide angiographic evaluation of right and left ventricular function during exercise after repair of transposition of the great arteries. Comparison
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with normal subjects and patients with congenitally corrected transposition. CircuIotion 1983;67:178-183. 3. Murphy ]H, Barlai-Kovatch MM, Mathews RA, Beerman LB, Park SC, Neches WH, Zuberbuhler JR. Rest and exercise right and left ventricular function late after the Mustard operation: assessment by radionuclide ventriculography. Am J Cardiol 1983;51:1520-1526, 4. Benson LN, Bonet J, McLaughlin P, Olley PM, Feighlin D, Druck M, Trusler G, Rowe RD, March J. Assessment of right ventricular function during supine exercise after Mustard’s operation. Circulation 1982;65:1052-1059. 5. Ramsay JM, Venables AW, Kelly MJ, Kalff V. Right and left ventricular function at rest and with exercise after the Mustard operation for transposition of the great arteries. Br Heart J 1984;51:364-370. 6. Hesslein PS, Gutgesell HP, Gilette PC, McNamarra DG. Exercise assessment of sinoatrial node function following the Mustard operation, Am Heart J 1982;103:351-357, 7. Ruttenberg HD. Adams TD, Orsmond GS, Conlee RK, Fisher AG. Effects of exercise training on aerobic fitness in children after open heart surgery. Pediatr Cardiol 1983;4:19-24. 8. Matthys D, Devloo-Blanquaert A. The evaluation of exercise performance in children after surgical correction of congenital heart disease. In: Fagard R, Bekaert I. eds. Sportscardiology: Exercise in Health and Cardiovascular Disease. Dordrecht: Martinus Nijhoff, 1986214-219. 9. Wasserman K, Whipp BJ, Koyal NS, Beaver W. Anaerobic threshold and respiratory gas exchange during exercise. J Appl Physiol 1973;35:236-243. 10. Reybrouck T, Ghesquiere J, Cattaert A, Fagard R, Amely A. VentiIatory thresholds during short- and long-term exerdse. J Appl Physioll983;55:16941700. 11. Stuart HC, Meredith HV. Use of body measurements in the school health program. Am J Public Health 1946;36:1365-1386. 12. Reybrouck T, Weymans M, Stijns H, Knops J, Van der Hauwaert L. Ventilatory anaerobic threshold in healthy children: age and sex differences. Eur J Appl Physiol 1985;54:278-284. 13. Reybrouck T, Weymans M, Stijns H, Van der Hauwaert LG. VentiIatory anaerobic threshold for evaluating exercise performance in children with congenital left-to-right intracardiac shunt. Pediatr Cardiol 1986;7:19-24. 14. Reybrouck T, Weymans M, Stijns H, Van der Hauwaert L. Exercise testing after correction of tetralogy of FaIIot: the fallacy of a reduced heart rate response. Am Heart J 1988;112:998-1003. 15. Chandramouli B, Ehmke DA, Lauer RM. Exercise-induced electrocardio-
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graphic changes in children with congenital aortic stenosis. J Pediatr 1973;87:725-730. 16. Caiozzo V, Davis JA, Ellis JF, Azus JL, Vandagriff R, Prietto CA, McMaster WC. A comparison of gas exchange indices used to detect the anaerobic threshold. J Appl PhysioI1982;53:1184-1189. 17. Snedecor GW, Cochran WG. Statistical Methods. 6th ed. Iowa: Iowa State University Press, 1972. 18. Mathews RA, Fricker FJ, Beerman LB, Stephenson R], Fisher DR, Neches WH, Park SC, Lenox CC, Zuberbuhler JR. Exercise studies after the Mustard operation in transposition of the great arteries. Am J Cordial 1983;51:15261529. 19. Issenberg HJ, Freed MD. Exercise capacity and heart rate response after Mustard operation (abstr]. Pediatr Cardiol 1980;1:322. 20. Mocellin R, Bastanier C, Hofacker W, Biihlmeyer K. Exercise performance in children and adolescents after surgical repair of tetralogy of FaIIot. Eur J Cardiol 1976;4:367-374. 21. Cumming GR. Maximal exercise capcity of children with heart defects. Am J Cardiol 1978;42:613-619. 22. Lipkin DL, Perrins J, Poole-Wilson PA. Respiratory gas exchange in the assessment of patients with impaired ventricular function. Br Heart J 1985;54:321-328. 23. Wasserman K. Physiology of gas exchange and exertional dyspnoea. Clin Sci 1981;61:7-13. 24. Mocellin R. Henglein D, Btihlmeyer K. Ventrikelfunktion vor und nach Senning-operation bei patienten mit transposition der grossen arterien. Hers 1982;7:267-273. 25. Hagler DJ, Ritter DG, Mair DD, Tajik AJ, Seward J, Fulton RE, Ritman EL. Right and left ventricular function after the Mustard procedure in transposition of the great arteries. Am J Cardiol 1979;44:276-283. 26. Graham TP, Atwood GF, Boucek RJ, Boerth RC, Bender HW. Abnormalities of right ventricular function following Mustard’s operation for transposition of the great arteries. Circulation 1975;52:678-684. 27. Borow KM, Keane JF, Castaneda AR, Freed MD. Systemic ventricular function in patients with tetralogy of FaIIot, ventricular septal defect and transposition of the great arteries repaired during infancy. Circulation 1981;64:878-888. 28. Beerman LB, Neches WH, Fricker FJ, Mathews RA, Fischer DR. Park SC, Lenox CC, Zuberbuhler JR. Arrhythmias in transposition of the great arteries after the Mustard operation. Am r Cardial 1983;51:1530-1534.