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Exercise responses in functional single ventricle before and after Fontan operation
Exercise Responses in Functional Single Ventricle Before and After Fontan Operation DAVID J. DRISCOLL,
M.D.
Department of Pediatrics Mayo School of Graduate Education Mayo Clinic and Mayo Foundation Rochester, Minnesota
In 1971, Fontan et al.’ described a technique for definitive palliation of patients with tricuspid atresia. The procedure included establishing a Glenn anastomosis, connecting the right atrium to the main or left pulmonary artery, closing the atria1 septal defect, and placing prosthetic valves into the inferior vena cava and the right atrium-pulmonary artery anastomosis. The technique has undergone many modifications. Few surgeons continue to implant prosthetic valves as part of the operation, and the previous establishment of a Glenn anastomosis is not essential. Furthermore, the procedure is not restricted to patients with tricuspid atresia and can be useful for patients with several forms of functional single ventricle. However, the concept of ventricular exclusion with diversion of all systemic venous return to the pulmonary artery without the assistance of a ventricle bears Fontan’s name. The Fontan operation creates a unique hemodynamic situation with complex and interesting effects on the cardiorespiratory responses to exercise.
AEROBIC CAPACITY Aerobic capacity remains subnormal after the Fontan operation. Measurements of aerobic capacity Address correspondence to David J. Driscoll, M.D., Pediatric Cardiology, Mayo Clinic, Rochester, MN 55905-0001.
or maximal oxygen consumption (Oo,max) at peak exercise have been reported by several investigators as values of 47%,2 62%,3 5O%,4 5O%,3 and 59%5 of that predicted. 0ttenkamp5 reported that among patients with a connection of the right atrium to a subpulmonary artery outlet chamber, 9 with a valve had significantly better aerobic capacity (50% to 93 % of predicted capacity) than 14 patients with a nonvalved connection (29% to 69% of predicted capacity). In patients with a functionally single ventricle, Driscoll et a1.4 compared the aerobic capacity of 29 patients after Fontan operation with that in 81 patients before operation. In that study, before operation, Oolmax was 48% of that predicted and was 56% of that predicted postoperatively. For 20 patients studied both before and after operation, Zellers et a1.6 reported that Vozmax increased from 54% to 59% of that predicted. There are four likely reasons for subnormal aerobic capacity in these patients: (1) in general, the maximal heart rate response to exercise is decreased (see below); (2) the function of the single systemic ventricle is subnormal. These ventricles remain dilated and, in general, have reduced ejection fraction, ‘se which, no doubt, accounts in part for the reduced cardiac output and stroke volume response to exercise; (3) the absence of a subpulmonary ventricle adversely affects the volume of effective pulProg Pediatr Cardiol 1993; 2(3):44-49 Copyright 0 1993 by Andover Medical
Single Ventricle - Fontan Operation
monary blood flow, which in turn affects the cardiac output of the systemic ventricle;4*9 and (4) these patients probably have persistent deconditioning as a result of their underlying cyanotic congenital heart defect.
HEART RATE Several investigators have reported different values for maximal heart rate (HRmax) during exercise for patients with functional single ventricle and patients who have had the modified Fontan operation. Driscoll et a1.4 reported reduced HRmax for both preoperative patients (77% of predicted capacity) and patients after the Fontan operation (81% of predicted capacity). 0ttenkamp5 reported an increase of heart rate during exercise from 49% to 200% of baseline values for 27 patients after the Fontan operation. Wessel and PauP reported an HRmax of 148 beats per minute in a group of patients after the Fontan operation. Grant et a1.3 studied 13 patients after the Fontan operation who had very good functional results: Twelve were in New York Heart Association functional class 1 and one was in class 2. The HRmax was 163 + 15 beats per minute with no significant difference from the HRmax in control subjects of 174 + 17 beats per minute. Because most exercise studies in children and adolescents with congenital heart disease are symptom limited, it is doubtful that the tests truly represent maximal exercise effort. A truly maximal test, defined by a plateau of Voz despite increasing work load, is difficult to achieve in these patients. The term “peak” exercise study, therefore, has been coined to distinguish tests in these individuals from a truly maximal study. The HRmax during peak exercise may be less than that measured in control subjects during a maximal study. However, there are data suggesting that patients with cardiac disease and patients who have had a cardiac operation truly have a reduced heart rate response to exercise. In cyanotic patients, the reduced heart rate response to exercise may be related to systemic arterial hypoxemia. Indeed, perfusion of the carotid body with hypoxic blood can cause bradycardia. lo Patients with heart disease have abnormal sympathetic and parasympathetic control of the heart rate,“*12 and sinus node dysfunction can occur after cardiac bypass surgery.
45
BLOOD PRESSURE Before the Fontan operation, patients with functional single ventricle have normal systolic blood pressure at rest and with exercise’ and diastolic blood pressure is lower than in control subjects. It is speculated that the lower diastolic pressure reflects the presence of systemic-to-pulmonary-artery connections in patients before the Fontan operation. After the Fontan operation, systolic blood pressure at peak exercise is lower than in control subjects. 4,6~*3 The reason for this is unclear but it may result from decreased cardiac output with exercise. It is unlikely, however, that the reduced cardiac output response to exercise is the only determinant of this abnormal systolic blood pressure response.
SYSTEMIC ARTERIAL OXYGEN SATURATION In a study of 81 patients with functional single ventricle before the Fontan operation, resting systemic arterial blood oxygen saturation was 84 f 6 % and at peak exercise it was 61 + 14% .4 Theoretically, the Fontan operation should eliminate right-to-left shunts, but a small shunt persists in most patients. Several investigators have demonstrated that both resting and exercise systemic arterial blood oxygen saturations are slightly, but significantly, below normal after the operation (Figure 1).There are three possible reasons for persistent hypoxemia after the Fontan operation: 1. A persistent intracardiac communication persists between the atria or the systemic venous atrium and the systemic ventricle. In most studies, mild hypoxemia persists even without a demonstrable intracardiac communication, and even a small anatomic communication would be expected to be associated with a relatively large right-to-left shunt and marked, rather than mild, hypoxemia. 2. Diversion of the coronary sinus blood flow to the physiologic left atrium. There is some evidence that elevated coronary sinus blood pressure may be detrimental to myocardial function. Thus, during the Fontan operation, some surgeons reconstruct the interatrial septum to allow the coronary sinus ostia to drain into the physiological left atrium. Although this prevents coronary sinus hypertension, it allows for a small persistent right-to-left shunt.
Progress in Pediatric Cardiology
46
4
4
4 6 13 3 15
4 6 13 3 15
+++I’ +tt
+
t
Rest Exercise
Without Fontan
Rest
Exercise
With Fontan
FIGURE 1. Systemic arterial blood oxygen saturation at rest and during exercise before and after the Fontan operation. The numbers on the top of the graph reference the appropriate source.
ventilation-perfusion re3. Abnormal pulmonary lationships. The most likely important determinant of persistent hypoxemia after the Fontan operation is abnormal pulmonary ventilation and perfusion matching. Matsushita et a1.14 nicely demonstrated that, after the Fontan operation, the ratio of upper to lower lobe pulmonary blood flow was abnormally increased. These investigators thought this abnormality of perfusion was related to elevated pulmonary vascular resistance, which could result from relatively low pulmonary blood flow.
CARDIAC OUTPUT Several investigators have demonstrated that cardiac output during exercise is subnormal after the The cardiac output at a given Fontan operation. 4r6~15 oxygen consumption is abnormally low with exercise, as illustrated in Figure 2. This abnormal cardiac output response exists with right atria1 to subpulmonary ventricular connections as well as with right atria1 to pulmonary artery connections.9,*3 It results from a blunted heart rate and a reduced stroke volume with exercise. Gellwig et a1.13 demonstrated that impairment of ventricular contractility was the major predictor of the abnormal
stroke volume and reduced performance response to exercise. The absence of a subpulmonary ventricle must adversely affect output of the systemic ventricle. Obviously, the output of the systemic ventricle is critically dependent on the pulmonary blood flow. If pulmonary blood flow is deficient, cardiac output will be deficient. Indeed, in the presence of abnormal left ventricular function, Baker et al.16 showed that exercise capacity is more dependent on right ventricular than on left ventricular ejection function. There is little doubt that, after the Fontan operation, a major reason for reduced aerobic capacity is the limitation in increases of cardiac output.
VENTIIATORY FUNCTION Cyanotic patients with single ventricle have an abnormal ventilatory pattern at rest and with exercise. Respiratory frequency and minute ventilation are abnormally elevated at rest and the ventilatory equivalent for oxygen is increased both at rest and during exercise. End-tidal carbon dioxide tension is decreased. There are several reasons for this seemingly excessive ventilation. Shepard17 attributed excessive ventilation at rest in cyanotic pa-
Single Ventricle - Fontan Operation
47
/
Cardiac
-
output,
5 -
L/min
c’ / 0’
’
’
’
’
’
0.5
Oxygen
’
’
uptake,
’
’
’ 1
’
’
L/min
FIGURE 2. Relationships of cardiac output and oxygen consumption at rest and during exercise after the Fontan operation in 25 patients. The striped area indicates the normal range of values in our laboratory. The two triangles and two circles represent values measured only at rest in 4 patients. The solid lines indicate cardiac output responses in patients in whom the oxygen saturation during exercise was <90%. The dotted lines indicate cardiac output measurements in patients in whom the exercise oxygen saturation was 290%. Reproduced with permission from Driscoll et al4
tients to true or relative hypercapnia. Increased dead-space ventilation and an increased arterialalveolar carbon dioxide tension led Strieder et al.iB to postulate that a decreased ability to eliminate carbon dioxide in patients with cyanotic congenital heart disease leads to excessive ventilation. Simply speaking, if only half of the systemic venous return (QEP) participates in gas exchange in the lung, then to maintain normal systemic arterial carbon dioxide tension, twice as much carbon dioxide will have to be removed from blood participating in the effective pulmonary blood flow and, hence, ventilation must be increased. After the Fontan operation, the ventilatory pattern tends to normalize, but Grant et a1.3 demonstrated persistent ventilatory abnormalities. Before and after exercise, the ventilatory equivalent for oxygen and carbon dioxide and expired and endtidal carbon dioxide tensions were similar to control subjects. At peak exercise, however, minute ventilation, the ventilatory equivalent for oxygen
and carbon dioxide, and the ratio of dead space to tidal volume were greater than normal. Expired and end-tidal carbon dioxide tensions were less than normal. These abnormal ventilatory patterns were similar for patients with and without a Glenn anastomosis as part of the Fontan operation. These postoperative abnormalities have been attributed to abnormal ventilation-perfusion ratios in the lung, as well as to small persistent right-to-left intrapulmonary shunts.
CARDIAC RHYTHM AND ST SEGMENT CHANGE Driscoll et a1.4 reported cardiac arrhythmias at rest in 14% and 21% of patients before and after the Fontan operation, respectively. During exercise, arrhythmias were noted in 28 % and 38 % of preoperative and postoperative patients, respectively; the differences were not statistically significant. Two patients (one before and one after the Fontan
48
Progress in Pediatric Cardiology
operation) had increasing degrees of atrioventricular block with exercise; both had atrioventricular discordance. Gellwig et a1.13 reported frequent atria1 ectopic beats in patients at rest that disappeared in those who were studied with exercise. They found no ventricular arrhythmias. During exercise, an ST segment change 21 mm was reported for 27% of patients before the Fontan operation and in 38% after it, with no significant statistical difference.
EXERCISE TESTING INDICATIONS AND COMPLICATIONS The major goal of exercise testing in patients with single ventricle and those who have had the Fontan operation has been to delineate and understand the effects of the operation on exercise physiology. Once it was apparent that aerobic capacity and several other physiologic exercise responses remained quite abnormal after operation, investigators began to search for mechanisms. In these patients, formal exercise testing remains useful and important to (1) continue studies of the determinants of abnormal exercise responses; (2) assess the relationship of the Fontan operation to exercise cardiorespiratory function over time; 3) understand the implications of exercise-induced arrhythmias and ST segment change; and (4) determine whether modifications in surgical technique can improve postoperative exercise performance. One must distinguish between evaluating abnormal physiologic responses to exercise and complications of exercise testing. For example, induction of an arrhythmia during exercise testing may not be a complication, but a positive result of the study. With this in mind, complications of exercise testing in patients with cyanotic congenital heart disease and patients who have had the Fontan operation are very uncommon.
SUMMARY AND CONCLUSIONS Exercise aerobic capacity is significantly reduced in patients with functional single ventricle before and after the Fontan operation, although it is significantly better after the operation. Before the operation, patients with functional single ventricle have markedly abnormal ventilatory responses to exercise caused primarily by the right-to-left shunt. Be-
cause intracardiac right-to-left shunt is eliminated with a successful Fontan operation, exercise ventilatory responses return toward normal. However, even after operation, mild hypoxemia persists.
REFERENCES 1.
Fontan F, Monicot F, Baudet E, Simonneau J, Gordo J, Go&rant J. “Correction” de l’atresia tricuspidienne; rapport de deux cas“corrigigCs par l’utilization d’une technique chirurgicale nouvelle.” Arm
Chir Thorac Cardiovasc. 1971, 10:39-47. 2. Wessel H, Paul M. Impaired exercise performance in tricuspid atresia after the Fontan operation or palliation by shunt. Pediatr Cardiol. 1983;4:76. Abstract. 3. Grant G, Manse11A, Garofano R, Hayes C, Bowman F, Gersony W. Cardiorespiratory response to exercise after the Fontan procedure for tricuspid atresia. Pediatr Res. 1988;24:1-5. 4. Driscoll D, Danielson G, Puga F, Schaff H, Heise C, Staats B. Exercise tolerance and cardiorespiratory response to exercise after the Fontan operation for tricuspid atresia or functional single ventricle. ] Am Co11 Cardiol. 1986;7:1087-1094. 5. Ottenkamp J. Tricuspid atresia: anatomy, therapy, and (long-term) results. Drukkerij JH, Pasmans BV, ‘s-Gravenhage, 1984. 6. Zellers T, Driscoll D, Mottram C, Puga F, Schaff H, Danielson G. Exercise tolerance and cardiorespiratory response to exercise before and after the Fontan operation. Mayo Clin Proc. 1989;64:1489-1497. 7. Del Torso S, Kelly M, Kalff V, Venables A. Radionuelide assessment of ventricular contraction at rest and during exercise following the Fontan procedure for either tricuspid atresia or single ventricle. Am J Cardiol. 1985;55:1127-1132. 8. Peterson R, Franch R, Fajman W, Jennings J, Jones R. Noninvasive determination of exercise cardiac function following Fontan operation. J Thorac Cardiovasc Surg. 1984;88:263-272. 9. Rhodes J, Garofano R, Bowman F, Grant G, Bierman F, Gersony W. Effective right ventricular anatomy on the cardiopulmonary response to exercise: implications for the Fontan procedure. Circulation. 1990; 81:1811-1817. 10. Daly M, Scott M. The effect of hypoxia and the heart rate of the dog with special reference to the contribution of the carotid body and chemoreceptors. JPhysiol (Land). 1959;145:440-446. 11. Eckberg D, Drabinsky M, Braunwald E. Defective cardiac parasympathetic control in patients with heart disease. N Engl I Med. 1971;285:877-883. 12. Goldstein R, Biser G, Stampfer M, Epstein S. Impair-
Single Ventricle - Fontan Operation
ment of anatomically mediated heart rate control in patients with cardiac dysfunction. Circ Res. 1975;
36:57l-578. 13. Gellwig MH, Lundstrom UR, Bull C, Wyse RK, Deanfield JE. Exercise responses in patients with congenital heart disease after Fontan repair: patterns and determinates of performance. J Am Co11 Cardi01. 1990;15:1424-1432. 14. Matsushita T, Matsuda H, Ogawa M, et al. Assessment of the intrapulmonary ventilation-perfusion distribution after the Fontan procedure for complex cardiac anomalies: relation to pulmonary hemodynamics. J Am Co11 Cardiol. 1990;15:842-848.
49
15. Ben Shachar G, Fuhrman B , Wang Y, Lucas R, Lock J. Rest and exercise hemodynamics after the Fontan procedure. Circulation. 1982;65:1043-1048. 16. Baker B, Wilen M, Boyd C, Dinh H, Franciosa J. Relation of right ventricular ejection fraction to exercise capacity and chronic left ventricular failure. Am J Cardiol. 1984;54:596-599. 17. Shepard R. The resting hyperventilation of congenital heart disease. Br Heart J. 1955;17:153-162. 18. Strieder D, Mesko Z, Zaver A, Gold W. Exercise tolerance in chronic hypoxemia due to right to left shunt. J Appl Physiol. 1973;34:853-858.
M.D.
Department of Pediatrics Mayo School of Graduate Education Mayo Clinic and Mayo Foundation Rochester, Minnesota
In 1971, Fontan et al.’ described a technique for definitive palliation of patients with tricuspid atresia. The procedure included establishing a Glenn anastomosis, connecting the right atrium to the main or left pulmonary artery, closing the atria1 septal defect, and placing prosthetic valves into the inferior vena cava and the right atrium-pulmonary artery anastomosis. The technique has undergone many modifications. Few surgeons continue to implant prosthetic valves as part of the operation, and the previous establishment of a Glenn anastomosis is not essential. Furthermore, the procedure is not restricted to patients with tricuspid atresia and can be useful for patients with several forms of functional single ventricle. However, the concept of ventricular exclusion with diversion of all systemic venous return to the pulmonary artery without the assistance of a ventricle bears Fontan’s name. The Fontan operation creates a unique hemodynamic situation with complex and interesting effects on the cardiorespiratory responses to exercise.
AEROBIC CAPACITY Aerobic capacity remains subnormal after the Fontan operation. Measurements of aerobic capacity Address correspondence to David J. Driscoll, M.D., Pediatric Cardiology, Mayo Clinic, Rochester, MN 55905-0001.
or maximal oxygen consumption (Oo,max) at peak exercise have been reported by several investigators as values of 47%,2 62%,3 5O%,4 5O%,3 and 59%5 of that predicted. 0ttenkamp5 reported that among patients with a connection of the right atrium to a subpulmonary artery outlet chamber, 9 with a valve had significantly better aerobic capacity (50% to 93 % of predicted capacity) than 14 patients with a nonvalved connection (29% to 69% of predicted capacity). In patients with a functionally single ventricle, Driscoll et a1.4 compared the aerobic capacity of 29 patients after Fontan operation with that in 81 patients before operation. In that study, before operation, Oolmax was 48% of that predicted and was 56% of that predicted postoperatively. For 20 patients studied both before and after operation, Zellers et a1.6 reported that Vozmax increased from 54% to 59% of that predicted. There are four likely reasons for subnormal aerobic capacity in these patients: (1) in general, the maximal heart rate response to exercise is decreased (see below); (2) the function of the single systemic ventricle is subnormal. These ventricles remain dilated and, in general, have reduced ejection fraction, ‘se which, no doubt, accounts in part for the reduced cardiac output and stroke volume response to exercise; (3) the absence of a subpulmonary ventricle adversely affects the volume of effective pulProg Pediatr Cardiol 1993; 2(3):44-49 Copyright 0 1993 by Andover Medical
Single Ventricle - Fontan Operation
monary blood flow, which in turn affects the cardiac output of the systemic ventricle;4*9 and (4) these patients probably have persistent deconditioning as a result of their underlying cyanotic congenital heart defect.
HEART RATE Several investigators have reported different values for maximal heart rate (HRmax) during exercise for patients with functional single ventricle and patients who have had the modified Fontan operation. Driscoll et a1.4 reported reduced HRmax for both preoperative patients (77% of predicted capacity) and patients after the Fontan operation (81% of predicted capacity). 0ttenkamp5 reported an increase of heart rate during exercise from 49% to 200% of baseline values for 27 patients after the Fontan operation. Wessel and PauP reported an HRmax of 148 beats per minute in a group of patients after the Fontan operation. Grant et a1.3 studied 13 patients after the Fontan operation who had very good functional results: Twelve were in New York Heart Association functional class 1 and one was in class 2. The HRmax was 163 + 15 beats per minute with no significant difference from the HRmax in control subjects of 174 + 17 beats per minute. Because most exercise studies in children and adolescents with congenital heart disease are symptom limited, it is doubtful that the tests truly represent maximal exercise effort. A truly maximal test, defined by a plateau of Voz despite increasing work load, is difficult to achieve in these patients. The term “peak” exercise study, therefore, has been coined to distinguish tests in these individuals from a truly maximal study. The HRmax during peak exercise may be less than that measured in control subjects during a maximal study. However, there are data suggesting that patients with cardiac disease and patients who have had a cardiac operation truly have a reduced heart rate response to exercise. In cyanotic patients, the reduced heart rate response to exercise may be related to systemic arterial hypoxemia. Indeed, perfusion of the carotid body with hypoxic blood can cause bradycardia. lo Patients with heart disease have abnormal sympathetic and parasympathetic control of the heart rate,“*12 and sinus node dysfunction can occur after cardiac bypass surgery.
45
BLOOD PRESSURE Before the Fontan operation, patients with functional single ventricle have normal systolic blood pressure at rest and with exercise’ and diastolic blood pressure is lower than in control subjects. It is speculated that the lower diastolic pressure reflects the presence of systemic-to-pulmonary-artery connections in patients before the Fontan operation. After the Fontan operation, systolic blood pressure at peak exercise is lower than in control subjects. 4,6~*3 The reason for this is unclear but it may result from decreased cardiac output with exercise. It is unlikely, however, that the reduced cardiac output response to exercise is the only determinant of this abnormal systolic blood pressure response.
SYSTEMIC ARTERIAL OXYGEN SATURATION In a study of 81 patients with functional single ventricle before the Fontan operation, resting systemic arterial blood oxygen saturation was 84 f 6 % and at peak exercise it was 61 + 14% .4 Theoretically, the Fontan operation should eliminate right-to-left shunts, but a small shunt persists in most patients. Several investigators have demonstrated that both resting and exercise systemic arterial blood oxygen saturations are slightly, but significantly, below normal after the operation (Figure 1).There are three possible reasons for persistent hypoxemia after the Fontan operation: 1. A persistent intracardiac communication persists between the atria or the systemic venous atrium and the systemic ventricle. In most studies, mild hypoxemia persists even without a demonstrable intracardiac communication, and even a small anatomic communication would be expected to be associated with a relatively large right-to-left shunt and marked, rather than mild, hypoxemia. 2. Diversion of the coronary sinus blood flow to the physiologic left atrium. There is some evidence that elevated coronary sinus blood pressure may be detrimental to myocardial function. Thus, during the Fontan operation, some surgeons reconstruct the interatrial septum to allow the coronary sinus ostia to drain into the physiological left atrium. Although this prevents coronary sinus hypertension, it allows for a small persistent right-to-left shunt.
Progress in Pediatric Cardiology
46
4
4
4 6 13 3 15
4 6 13 3 15
+++I’ +tt
+
t
Rest Exercise
Without Fontan
Rest
Exercise
With Fontan
FIGURE 1. Systemic arterial blood oxygen saturation at rest and during exercise before and after the Fontan operation. The numbers on the top of the graph reference the appropriate source.
ventilation-perfusion re3. Abnormal pulmonary lationships. The most likely important determinant of persistent hypoxemia after the Fontan operation is abnormal pulmonary ventilation and perfusion matching. Matsushita et a1.14 nicely demonstrated that, after the Fontan operation, the ratio of upper to lower lobe pulmonary blood flow was abnormally increased. These investigators thought this abnormality of perfusion was related to elevated pulmonary vascular resistance, which could result from relatively low pulmonary blood flow.
CARDIAC OUTPUT Several investigators have demonstrated that cardiac output during exercise is subnormal after the The cardiac output at a given Fontan operation. 4r6~15 oxygen consumption is abnormally low with exercise, as illustrated in Figure 2. This abnormal cardiac output response exists with right atria1 to subpulmonary ventricular connections as well as with right atria1 to pulmonary artery connections.9,*3 It results from a blunted heart rate and a reduced stroke volume with exercise. Gellwig et a1.13 demonstrated that impairment of ventricular contractility was the major predictor of the abnormal
stroke volume and reduced performance response to exercise. The absence of a subpulmonary ventricle must adversely affect output of the systemic ventricle. Obviously, the output of the systemic ventricle is critically dependent on the pulmonary blood flow. If pulmonary blood flow is deficient, cardiac output will be deficient. Indeed, in the presence of abnormal left ventricular function, Baker et al.16 showed that exercise capacity is more dependent on right ventricular than on left ventricular ejection function. There is little doubt that, after the Fontan operation, a major reason for reduced aerobic capacity is the limitation in increases of cardiac output.
VENTIIATORY FUNCTION Cyanotic patients with single ventricle have an abnormal ventilatory pattern at rest and with exercise. Respiratory frequency and minute ventilation are abnormally elevated at rest and the ventilatory equivalent for oxygen is increased both at rest and during exercise. End-tidal carbon dioxide tension is decreased. There are several reasons for this seemingly excessive ventilation. Shepard17 attributed excessive ventilation at rest in cyanotic pa-
Single Ventricle - Fontan Operation
47
/
Cardiac
-
output,
5 -
L/min
c’ / 0’
’
’
’
’
’
0.5
Oxygen
’
’
uptake,
’
’
’ 1
’
’
L/min
FIGURE 2. Relationships of cardiac output and oxygen consumption at rest and during exercise after the Fontan operation in 25 patients. The striped area indicates the normal range of values in our laboratory. The two triangles and two circles represent values measured only at rest in 4 patients. The solid lines indicate cardiac output responses in patients in whom the oxygen saturation during exercise was <90%. The dotted lines indicate cardiac output measurements in patients in whom the exercise oxygen saturation was 290%. Reproduced with permission from Driscoll et al4
tients to true or relative hypercapnia. Increased dead-space ventilation and an increased arterialalveolar carbon dioxide tension led Strieder et al.iB to postulate that a decreased ability to eliminate carbon dioxide in patients with cyanotic congenital heart disease leads to excessive ventilation. Simply speaking, if only half of the systemic venous return (QEP) participates in gas exchange in the lung, then to maintain normal systemic arterial carbon dioxide tension, twice as much carbon dioxide will have to be removed from blood participating in the effective pulmonary blood flow and, hence, ventilation must be increased. After the Fontan operation, the ventilatory pattern tends to normalize, but Grant et a1.3 demonstrated persistent ventilatory abnormalities. Before and after exercise, the ventilatory equivalent for oxygen and carbon dioxide and expired and endtidal carbon dioxide tensions were similar to control subjects. At peak exercise, however, minute ventilation, the ventilatory equivalent for oxygen
and carbon dioxide, and the ratio of dead space to tidal volume were greater than normal. Expired and end-tidal carbon dioxide tensions were less than normal. These abnormal ventilatory patterns were similar for patients with and without a Glenn anastomosis as part of the Fontan operation. These postoperative abnormalities have been attributed to abnormal ventilation-perfusion ratios in the lung, as well as to small persistent right-to-left intrapulmonary shunts.
CARDIAC RHYTHM AND ST SEGMENT CHANGE Driscoll et a1.4 reported cardiac arrhythmias at rest in 14% and 21% of patients before and after the Fontan operation, respectively. During exercise, arrhythmias were noted in 28 % and 38 % of preoperative and postoperative patients, respectively; the differences were not statistically significant. Two patients (one before and one after the Fontan
48
Progress in Pediatric Cardiology
operation) had increasing degrees of atrioventricular block with exercise; both had atrioventricular discordance. Gellwig et a1.13 reported frequent atria1 ectopic beats in patients at rest that disappeared in those who were studied with exercise. They found no ventricular arrhythmias. During exercise, an ST segment change 21 mm was reported for 27% of patients before the Fontan operation and in 38% after it, with no significant statistical difference.
EXERCISE TESTING INDICATIONS AND COMPLICATIONS The major goal of exercise testing in patients with single ventricle and those who have had the Fontan operation has been to delineate and understand the effects of the operation on exercise physiology. Once it was apparent that aerobic capacity and several other physiologic exercise responses remained quite abnormal after operation, investigators began to search for mechanisms. In these patients, formal exercise testing remains useful and important to (1) continue studies of the determinants of abnormal exercise responses; (2) assess the relationship of the Fontan operation to exercise cardiorespiratory function over time; 3) understand the implications of exercise-induced arrhythmias and ST segment change; and (4) determine whether modifications in surgical technique can improve postoperative exercise performance. One must distinguish between evaluating abnormal physiologic responses to exercise and complications of exercise testing. For example, induction of an arrhythmia during exercise testing may not be a complication, but a positive result of the study. With this in mind, complications of exercise testing in patients with cyanotic congenital heart disease and patients who have had the Fontan operation are very uncommon.
SUMMARY AND CONCLUSIONS Exercise aerobic capacity is significantly reduced in patients with functional single ventricle before and after the Fontan operation, although it is significantly better after the operation. Before the operation, patients with functional single ventricle have markedly abnormal ventilatory responses to exercise caused primarily by the right-to-left shunt. Be-
cause intracardiac right-to-left shunt is eliminated with a successful Fontan operation, exercise ventilatory responses return toward normal. However, even after operation, mild hypoxemia persists.
REFERENCES 1.
Fontan F, Monicot F, Baudet E, Simonneau J, Gordo J, Go&rant J. “Correction” de l’atresia tricuspidienne; rapport de deux cas“corrigigCs par l’utilization d’une technique chirurgicale nouvelle.” Arm
Chir Thorac Cardiovasc. 1971, 10:39-47. 2. Wessel H, Paul M. Impaired exercise performance in tricuspid atresia after the Fontan operation or palliation by shunt. Pediatr Cardiol. 1983;4:76. Abstract. 3. Grant G, Manse11A, Garofano R, Hayes C, Bowman F, Gersony W. Cardiorespiratory response to exercise after the Fontan procedure for tricuspid atresia. Pediatr Res. 1988;24:1-5. 4. Driscoll D, Danielson G, Puga F, Schaff H, Heise C, Staats B. Exercise tolerance and cardiorespiratory response to exercise after the Fontan operation for tricuspid atresia or functional single ventricle. ] Am Co11 Cardiol. 1986;7:1087-1094. 5. Ottenkamp J. Tricuspid atresia: anatomy, therapy, and (long-term) results. Drukkerij JH, Pasmans BV, ‘s-Gravenhage, 1984. 6. Zellers T, Driscoll D, Mottram C, Puga F, Schaff H, Danielson G. Exercise tolerance and cardiorespiratory response to exercise before and after the Fontan operation. Mayo Clin Proc. 1989;64:1489-1497. 7. Del Torso S, Kelly M, Kalff V, Venables A. Radionuelide assessment of ventricular contraction at rest and during exercise following the Fontan procedure for either tricuspid atresia or single ventricle. Am J Cardiol. 1985;55:1127-1132. 8. Peterson R, Franch R, Fajman W, Jennings J, Jones R. Noninvasive determination of exercise cardiac function following Fontan operation. J Thorac Cardiovasc Surg. 1984;88:263-272. 9. Rhodes J, Garofano R, Bowman F, Grant G, Bierman F, Gersony W. Effective right ventricular anatomy on the cardiopulmonary response to exercise: implications for the Fontan procedure. Circulation. 1990; 81:1811-1817. 10. Daly M, Scott M. The effect of hypoxia and the heart rate of the dog with special reference to the contribution of the carotid body and chemoreceptors. JPhysiol (Land). 1959;145:440-446. 11. Eckberg D, Drabinsky M, Braunwald E. Defective cardiac parasympathetic control in patients with heart disease. N Engl I Med. 1971;285:877-883. 12. Goldstein R, Biser G, Stampfer M, Epstein S. Impair-
Single Ventricle - Fontan Operation
ment of anatomically mediated heart rate control in patients with cardiac dysfunction. Circ Res. 1975;
36:57l-578. 13. Gellwig MH, Lundstrom UR, Bull C, Wyse RK, Deanfield JE. Exercise responses in patients with congenital heart disease after Fontan repair: patterns and determinates of performance. J Am Co11 Cardi01. 1990;15:1424-1432. 14. Matsushita T, Matsuda H, Ogawa M, et al. Assessment of the intrapulmonary ventilation-perfusion distribution after the Fontan procedure for complex cardiac anomalies: relation to pulmonary hemodynamics. J Am Co11 Cardiol. 1990;15:842-848.
49
15. Ben Shachar G, Fuhrman B , Wang Y, Lucas R, Lock J. Rest and exercise hemodynamics after the Fontan procedure. Circulation. 1982;65:1043-1048. 16. Baker B, Wilen M, Boyd C, Dinh H, Franciosa J. Relation of right ventricular ejection fraction to exercise capacity and chronic left ventricular failure. Am J Cardiol. 1984;54:596-599. 17. Shepard R. The resting hyperventilation of congenital heart disease. Br Heart J. 1955;17:153-162. 18. Strieder D, Mesko Z, Zaver A, Gold W. Exercise tolerance in chronic hypoxemia due to right to left shunt. J Appl Physiol. 1973;34:853-858.