Clinical Application of Current Techniques and Treatment in Cardiology Adv. Cardiol., vol. 17, pp. 2-12 (Karger, Basel 1976)
Indications for and Results of Surgery in Congenital Aortic Stenosis WILLIAM F. FRIEDMAN
Department of Pediatrics, University of California, San Diego, School of Medicine, La Jolla, Calif.
Introduction
Aortic stenosis (AS) is a common congenital malformation accounting for 5-6% of all forms of congenital heart disease. The congenitally deformed valve is most often bicuspid with fused commissures and an eccentric stenotic orifice. Less often the valve has three fused cusps - fortunately, the unicommissural aortic valve which has no lateral attachment to the aorta or only a single cusp is encountered rarely. It is necessary when discussing discrete valvar AS to recognize that the majority of patients with this lesion fall into one of three groups [8]: those detected in infancy and presenting in congestive heart failure; those detected in childhood, or before the age of 15 years who are commonly symptom-free, and the third group comprising older, adult patients, usually in the fifth decade and beyond, in whom it now seems likely that a congenital bicuspid aortic valve provides a basis for the development of obstruction to left ventricular outflow late in life. The remarks in this report will not be concerned with this latter group of older adult patients, but will deal mainly with group 2, the largest category seen by pediatric cardiologists - those presenting initially in childhood. At the outset, however, it is appropriate to discuss the valvar lesion as it presents in infancy.
Although isolated valvar AS seldom causes symptoms in infancy, occasionally the lesion may be responsible for profound, intractable congestive
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
Aortic Stenosis in Infancy
3
heart failure [4]. Within this group of critically ill infants with severe stenosis, it is necessary to distinguish those in whom the left ventricle is essentially normal-sized or enlarged from those who fit into, or very close to, the spectrum of anomalies that we recognize as the hypoplastic left heart syndrome. The hypoplastic left heart syndrome will not be discussed here - no effective therapy exists, the mortality is 100%, and in our hospital we can make this diagnosis with certainty by echocardiography and when we do, we do not pursue diagnosis or treatment further. The symptomatic infant with an essentially normal-sized left ventricle is irritable, pale, and hypotensive and presents with tachycardia, cardiomegaly, and pumonary congestion. The systolic murmur is often atypical and located at the lower left sternal border or apex, often resulting in its confusion with that caused by a ventricular septal defect. The ECG often shows left ventricular hypertrophy and strain, although right ventricular hypertrophy also results often from volume loading of the right ventricle due to left-to-right shunting across the foramen ovale and from pulmonary hypertension secondary to elevated left ventricular end diastolic and left atrial pressures. The chest X-ray often shows marked left ventricular and left atrial enlargement with pulmonary venous congestion. There is no question that these newborns should be considered as medical emergencies. Unfortunately, many ofthese babies have associated endocardial fibroelastosis, most likely the result of reduced subendocardial oxygen delivery and mitral regurgitation. Prompt hemodynamic study should be performed, since even with medical therapy prolonged periods of stabilization are uncommon. The type of operation to be performed depends on the experience of the surgical team with either hypothermia and inflow occlusion or bypass in infancy. In our hands six infants in the past 2 years underwent transaortic valvotomy after corecooling, with 2 early deaths. Moreover, moderate-to-severe aortic regurgitation has complicated the late postoperative course in half the survivors, although we, thus far, have withheld aortic valve replacement because of their young age. Recently, a preliminary report [11] from the Boston's Children Hospital described a substantial reduction in their surgical mortality when comparing the past several years to their earlier experience [4]. This is the only report that exists demonstrating a mortality rate less than 10% in infants under age 2 years but, thus far, late postoperative follow-up is unavailable as are postoperative hemodynamic studies. There is little doubt that in time most, if not all, of these patients will need further palliative surgery or prosthetic valve replacement.
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
FRIEDMAN
FRnIDMAN
4
Aortic Stenosis in Childhood Let us turn now to the much more common question of aortic stenosis in childhood and adolescence. Most of these children are asymptomatic and grow and develop normally. 80% of these patients are boys, and they are almost invariably referred to the cardiologist because of a precordial murmur detected by an examining physician. At issue in this group of patients is the question of sudden death, since this threat constitutes a major indication for hemodynamic study and operation. A recent international study [12] of sudden death has demonstrated that AS is the most common congenital cardiac malformation associated with this phenomenon. The precise cause of sudden death is poorly understood, but ventricular arrhythmias probably initiated by acute myocardial ischemia may be an inciting event. It seems clear that only those patients with truly severe obstruction are at risk. The reported incidence of sudden death in groups of children with congenital AS followed for varying periods has been wide, ranging from about 1 ro 19% [7]. Each of these studies has biases with respect to patient selection, and an incidence of sudden death of 7-8% has been accepted as representative of the average incidence, although it may well be a minimum value. Data from the literature would suggest that if patients with left ventricular 'strain' or symptoms are selected out of the general group of patients with AS, the risk of sudden death over their lifetime approaches 30%. The real problem is posed by patients who clearly have AS, but are entirely asymptomatic, especially since the risk of operation in this group is substantially less than the risk of sudden death. In managing such patients it must be emphasized that the absence of symptoms by no means excludes the possibility of severe obstruction or the threat of sudden death. Thus, it is mandatory that the cardiologist decide which asymptomatic patient may have severe obstruction.
In making the decision as to which asymptomatic patient should undergo cardiac catheterization, the cardiologist seeks clues to the presence of severe stenosis by physical findings and laboratory tests. It is important to evaluate the reliability of each of these indicators [1]. If the A wave in the jugular venous pulse is abnormally prominent, it usually does not suggest the presence of pulmonary hypertension, but rather indicates an abnormally
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
Indications for Hemodynamic Study
5
high resistance to right ventricular filling, probably as the result of that chamber sharing a common wall, the ventricular septum, with a hypertrophied left ventricle. A prominent left ventricular lift and systolic precordial thrill accompany moderate-to-severe obstruction. If they are absent, mild stenosis is the rule. The presence and intensity of an aortic ejection sound appears to depend on aortic valve mobility. In very severe valvar obstructions, an ejection sound may be absent. The disappearance of the sound, if one is present initially, certainly suggests progressive stenosis. The intensity of the aortic component of the second sound is often normal in young patients with mobile valve leaflets. The second heart sound may split normally, and often does, or it may be single, or, quite uncommonly, more widely split during expiration, that is to say, paradoxical splitting. Paradoxical splitting in the absence of left bundle branch block usually indicates severe stenosis. The presence of a fourth heart sound, or its counterpart on palpation, the presystolic expansion, generally signifies that severe stenosis exists. Palpable, or graphically recorded changes in the arterial pulse, can be helpful if one perceives a narrow pulse pressure, a slow rate of rise, and a prolonged upstroke and systolic shudder. However, it must be recognized that attempts to correlate severity of obstruction with analysis of pulses have not been uniformly successful. This is especially true in young children with a healthy vascular tree and none of the associated arterial distensibility problems that one sees in older patients. It has often been said that the ECG or VCG is the most sensitive index of the severity of obstruction. The ECG or the VCG are unquestionably valuable clinical tools, but they are far from infallible, especially in patients beyond age 10 years. We have seen a goodly number of patients with essentially normal EeGs and only moderate LVH by vector, in whom critical stenosis existed hemodynamically. In our judgment, the only truly good ECG indicator of the presence of severe obstruction is the LV 'strain' pattern of ST depression and T wave inversions in the left precordial leads suggesting subendocardial ischemia. While X-ray evidence of left ventricular enlargement or left atrial enlargement may be helpful, the roentgenologic examination is not specific in most cases. It is not at all uncommon to see an essentially normal chest X-ray with just slight dilatation of the ascending aorta in patients with severe obstruction. As re~ ported initially by HALLORAN [10], bicycle or treadmill exercise tests seem to be quite helpful. There are recent suggestions that a good relationship exists between exercise-induced electrocardiographic changes and the degree of gradient across the aortic valve. The development during exercise of ischemic ST segment changes appears to occur in patients with normal resting cardiac
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
Congenital Aortic Stenosis
FRIEDMAN
6
indices and left ventricular-aortic pressure gradients beyond 50 mm Hg. However, further studies are needed of this noninvasive modality in order to estimate the incidence of false positive and false negative results. After all of these comments, we want to stress that one must recognize that there is an absence of a truly reliable indirect method for determining the severity of obstruction in aortic stenosis. There is no question that clinical data used to assess the lesion may be misleading, so that, if one relies excessively on any of the findings or techniques mentioned above, it is quite clear that there will be occasional errors in individual patient management. We believe every patient with symptoms or LV 'strain' by EeG should undergo cardiac catheterization. It is quite simple to detect the presence of trivial or quite mild obstruction, but much more difficult to distinguish moderate from severe obstruction in the asymptomatic child. If one cannot decide whether moderate or severe obstruction is present, we believe strongly that it is the physician's responsibility to exclude severe obstruction. Thus, once we make the clinical diagnosis, if any suspicion exists that severe obstruction is present, we do not hesitate to proceed with hemodynamic study. Even if only mild or moderate obstruction is detected after cardiac catheterization is performed, a strong argument can now be put forth to incorporate repeated hemodynamic studies at 5- to 8-year intervals into the routine of patient follow-up. We make this statement because of the data that are available about the natural history of valvar AS.
Natural History
Until quite recently the interruption of the course of AS by operation, as well as a lack of prospective information concerning the outlook of patients with this malformation, created major uncertainties about the natural history of the lesion. Evaluation of natural history has been difficult because the development of objective means for the determination of the severity of AS by left heart catheterization, and the initial attempts at operative treatment occurred almost simultaneously. Information now available suggests strongly that a progressive increase in the severity of obstruction may occur commonly even among young children. In two separate studies of ours, serial hemodynamic observations were obtained initially asymptomatic chilwas observed in most of the children over an average time span of approxi-
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
dren [2, 9]. An intensification of left ventricular outflow tract obstruction
Congenital Aortic Stenosis
7
mately 6 years. In 5 of 24 patients so studied, the degree of stenosis observed at second study was considered of sufficient severity to warrant a recommendation for cardiac operation. Implicit in the findings of both serial studies was that a longer follow-up period would have identified even more patients in whom critical obstruction developed and that clinical deterioration, with time, could be anticipated. Of interest was the fact that in none of the patients in either study was SBE encountered and in none did aortic regurgitation become a problem. Quite similar data have been reported by others [5, 13].
From all of our previous remarks it should be clear that the presence of severe obstruction, rather than of symptoms, is the primary indication for operation. We consider a peak transvalvar gradient exceeding 75 mm Hg in association with a normal cardiac output, or an effective aortic orifice less than 0.5 cm2/m2 of body surface area, to represent critical obstruction. Just knowing the magnitude of the systolic pressure gradient is not sufficient, since it is also necessary to measure the cardiac output to evaluate the severity of stenosis. The pressure gradient is not a simple linear function of flow, but rather is proportional to the square of the flow rate across the site of obstruction. Since the gradient is determined by the flow, as well as the size of the orifice, the only way to accurately determine severity is by measuring both the pressure difference and the flow, simultaneously if possible. When aortic regurgitation exists, the flow rate across the valve is the sum of the effective cardiac output and of the regurgitant flow. Since most clinical techniques for measuring flow record only the effective cardiac output, the valvar flow rate may be underestimated and the severity of valve stenosis may, therefore, be falsely exaggerated if allowance is not made for associated regurgitation. Alterations in heart rate also change the velocity of blood flow across the stenotic valve at any given level of cardiac output. At high rates, diastole is shortened relatively more than systole, and the total time available for flow across the obstruction is greater. These facts are important to keep in mind since it is the presence of severe obstruction alone in asymptomatic patients that is a primary indication for operation. In the presence of symptoms or left ventricular 'strain' pattern on the ECG, we will consider operating on patients with gradients in the 50 mm Hg range and valve orifice indices of 0.7 cm2• We are less rigid about the magnitude of the pressure gradient
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
Indications for Operation
FRIEDMAN
8
in this group of patients since the risk of sudden death is so high and there is already ECG evidence of myocardial ischemia, and improvement of aortic valve flow may result in an increase in coronary artery perfusion. Moreover, if the transvalvar gradient is in the 50 mm Hg range and an exercise test demonstrates ST + T wave changes, we will most likely consider operating on the patient even if he is asymptomatic.
The results of operation differ according to the patient's age, the type of obstructing lesion, and the experience of the surgical team. Currently in ours, and in most major centers, immediate operative mortality does not exceed 2%. Essentially no data are available concerning the truly long-term hemodynamic results of aortic valvotomy. When patients undergo cardiac catheterization, an average of 1 year after cardiac operation, the left ventricularaortic pressure gradient is noted to be little changed from that observed on the operating table at the conclusion of the valvotomy, and substantial reductions in the severity of obstruction are noted in almost all patients [6]. Moreover, if symptoms were present preoperatively, survivors are almost uniformly found to be asymptomatic following surgery. Thus, it can be stated with reasonable assurance that in children with congenital valvar stenosis and hemodynamically severe obstruction, the risk of operation is less than that of sudden death. However, it must be remembered that the valve is not rendered normal anatomically by operation, since valve leaflets remain deformed after commissurotomy and further degenerative changes, including calcification, may very well lead to progressive stenosis in later years in a significant number of patients. In addition, both subacute bacterial endocarditis (SBE) and aortic regurgitation may become problems in the years following an operation. One study is available in which the late results of aortic valvotomy have been evaluated. CONKLE et al. [3] have described the follow-up results in a group of 38 patients with congenital AS who underwent aortic valvotomy with the aid of cardiopulmonary bypass at the National Heart and Lung Institute between 1957 and 1967. It was our privilege to participate in the initial evaluation of many of these patients. The study group consisted of 30 males and 8 females whose average age at operation was 12.5 years with a range of 1-21 years. The postoperative follow-up averaged 10 years with a range of 5-14 years.
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
Results of Operation
9
Congenital Aortic Stenosis
Preoperatively, the symptoms described included fatigue in 19, dyspnea in 18, syncope in 10, angina in 9 and presyncope in 6 patients. Eight patients were asymptomatic. Left ventricular hypertrophy was detected by ECG in 33 patients and 15 had a hypertrophy pattern with ST+T wave changes of subendocardial ischemia. Chest roentgenograms revealed left ventricular hypertrophy in 19 patients. Every patient underwent preoperative hemodynamic and angiographic study. The average peak transvalvar pressure difference at rest was 91 mmHg (range of 30-180); left ventricular peak pressure averaged 194 mm Hg (range of 120-300); the left ventricular end-diastolic pressure averaged 12 mm Hg, but 16 patients had end-diastolic pressures in excess of this value. The mean cardiac index was 4.2 l/min/m2 (range of 2.3-7.3); and the
lBO
.!!
:e
~
20
.>:
10
&0 Postoperatively
(27mm Hg)
Fig. 1. Peak transvalvar systolic pressure gradients preoperatively and postoperatively in 32 patients.
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
Preoperatively
(91mm Hg)
10
FRIEDMAN
2.0
1.8
1.6
0.2
1.0
0.8
NE
0.6
U:.------,
u
.:;;
,; 0.4-
..
;; 0.2 >
~
5
Indications for and Results of Surgery in Congenital Aortic Stenosis WILLIAM F. FRIEDMAN
Department of Pediatrics, University of California, San Diego, School of Medicine, La Jolla, Calif.
Introduction
Aortic stenosis (AS) is a common congenital malformation accounting for 5-6% of all forms of congenital heart disease. The congenitally deformed valve is most often bicuspid with fused commissures and an eccentric stenotic orifice. Less often the valve has three fused cusps - fortunately, the unicommissural aortic valve which has no lateral attachment to the aorta or only a single cusp is encountered rarely. It is necessary when discussing discrete valvar AS to recognize that the majority of patients with this lesion fall into one of three groups [8]: those detected in infancy and presenting in congestive heart failure; those detected in childhood, or before the age of 15 years who are commonly symptom-free, and the third group comprising older, adult patients, usually in the fifth decade and beyond, in whom it now seems likely that a congenital bicuspid aortic valve provides a basis for the development of obstruction to left ventricular outflow late in life. The remarks in this report will not be concerned with this latter group of older adult patients, but will deal mainly with group 2, the largest category seen by pediatric cardiologists - those presenting initially in childhood. At the outset, however, it is appropriate to discuss the valvar lesion as it presents in infancy.
Although isolated valvar AS seldom causes symptoms in infancy, occasionally the lesion may be responsible for profound, intractable congestive
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
Aortic Stenosis in Infancy
3
heart failure [4]. Within this group of critically ill infants with severe stenosis, it is necessary to distinguish those in whom the left ventricle is essentially normal-sized or enlarged from those who fit into, or very close to, the spectrum of anomalies that we recognize as the hypoplastic left heart syndrome. The hypoplastic left heart syndrome will not be discussed here - no effective therapy exists, the mortality is 100%, and in our hospital we can make this diagnosis with certainty by echocardiography and when we do, we do not pursue diagnosis or treatment further. The symptomatic infant with an essentially normal-sized left ventricle is irritable, pale, and hypotensive and presents with tachycardia, cardiomegaly, and pumonary congestion. The systolic murmur is often atypical and located at the lower left sternal border or apex, often resulting in its confusion with that caused by a ventricular septal defect. The ECG often shows left ventricular hypertrophy and strain, although right ventricular hypertrophy also results often from volume loading of the right ventricle due to left-to-right shunting across the foramen ovale and from pulmonary hypertension secondary to elevated left ventricular end diastolic and left atrial pressures. The chest X-ray often shows marked left ventricular and left atrial enlargement with pulmonary venous congestion. There is no question that these newborns should be considered as medical emergencies. Unfortunately, many ofthese babies have associated endocardial fibroelastosis, most likely the result of reduced subendocardial oxygen delivery and mitral regurgitation. Prompt hemodynamic study should be performed, since even with medical therapy prolonged periods of stabilization are uncommon. The type of operation to be performed depends on the experience of the surgical team with either hypothermia and inflow occlusion or bypass in infancy. In our hands six infants in the past 2 years underwent transaortic valvotomy after corecooling, with 2 early deaths. Moreover, moderate-to-severe aortic regurgitation has complicated the late postoperative course in half the survivors, although we, thus far, have withheld aortic valve replacement because of their young age. Recently, a preliminary report [11] from the Boston's Children Hospital described a substantial reduction in their surgical mortality when comparing the past several years to their earlier experience [4]. This is the only report that exists demonstrating a mortality rate less than 10% in infants under age 2 years but, thus far, late postoperative follow-up is unavailable as are postoperative hemodynamic studies. There is little doubt that in time most, if not all, of these patients will need further palliative surgery or prosthetic valve replacement.
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
FRIEDMAN
FRnIDMAN
4
Aortic Stenosis in Childhood Let us turn now to the much more common question of aortic stenosis in childhood and adolescence. Most of these children are asymptomatic and grow and develop normally. 80% of these patients are boys, and they are almost invariably referred to the cardiologist because of a precordial murmur detected by an examining physician. At issue in this group of patients is the question of sudden death, since this threat constitutes a major indication for hemodynamic study and operation. A recent international study [12] of sudden death has demonstrated that AS is the most common congenital cardiac malformation associated with this phenomenon. The precise cause of sudden death is poorly understood, but ventricular arrhythmias probably initiated by acute myocardial ischemia may be an inciting event. It seems clear that only those patients with truly severe obstruction are at risk. The reported incidence of sudden death in groups of children with congenital AS followed for varying periods has been wide, ranging from about 1 ro 19% [7]. Each of these studies has biases with respect to patient selection, and an incidence of sudden death of 7-8% has been accepted as representative of the average incidence, although it may well be a minimum value. Data from the literature would suggest that if patients with left ventricular 'strain' or symptoms are selected out of the general group of patients with AS, the risk of sudden death over their lifetime approaches 30%. The real problem is posed by patients who clearly have AS, but are entirely asymptomatic, especially since the risk of operation in this group is substantially less than the risk of sudden death. In managing such patients it must be emphasized that the absence of symptoms by no means excludes the possibility of severe obstruction or the threat of sudden death. Thus, it is mandatory that the cardiologist decide which asymptomatic patient may have severe obstruction.
In making the decision as to which asymptomatic patient should undergo cardiac catheterization, the cardiologist seeks clues to the presence of severe stenosis by physical findings and laboratory tests. It is important to evaluate the reliability of each of these indicators [1]. If the A wave in the jugular venous pulse is abnormally prominent, it usually does not suggest the presence of pulmonary hypertension, but rather indicates an abnormally
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
Indications for Hemodynamic Study
5
high resistance to right ventricular filling, probably as the result of that chamber sharing a common wall, the ventricular septum, with a hypertrophied left ventricle. A prominent left ventricular lift and systolic precordial thrill accompany moderate-to-severe obstruction. If they are absent, mild stenosis is the rule. The presence and intensity of an aortic ejection sound appears to depend on aortic valve mobility. In very severe valvar obstructions, an ejection sound may be absent. The disappearance of the sound, if one is present initially, certainly suggests progressive stenosis. The intensity of the aortic component of the second sound is often normal in young patients with mobile valve leaflets. The second heart sound may split normally, and often does, or it may be single, or, quite uncommonly, more widely split during expiration, that is to say, paradoxical splitting. Paradoxical splitting in the absence of left bundle branch block usually indicates severe stenosis. The presence of a fourth heart sound, or its counterpart on palpation, the presystolic expansion, generally signifies that severe stenosis exists. Palpable, or graphically recorded changes in the arterial pulse, can be helpful if one perceives a narrow pulse pressure, a slow rate of rise, and a prolonged upstroke and systolic shudder. However, it must be recognized that attempts to correlate severity of obstruction with analysis of pulses have not been uniformly successful. This is especially true in young children with a healthy vascular tree and none of the associated arterial distensibility problems that one sees in older patients. It has often been said that the ECG or VCG is the most sensitive index of the severity of obstruction. The ECG or the VCG are unquestionably valuable clinical tools, but they are far from infallible, especially in patients beyond age 10 years. We have seen a goodly number of patients with essentially normal EeGs and only moderate LVH by vector, in whom critical stenosis existed hemodynamically. In our judgment, the only truly good ECG indicator of the presence of severe obstruction is the LV 'strain' pattern of ST depression and T wave inversions in the left precordial leads suggesting subendocardial ischemia. While X-ray evidence of left ventricular enlargement or left atrial enlargement may be helpful, the roentgenologic examination is not specific in most cases. It is not at all uncommon to see an essentially normal chest X-ray with just slight dilatation of the ascending aorta in patients with severe obstruction. As re~ ported initially by HALLORAN [10], bicycle or treadmill exercise tests seem to be quite helpful. There are recent suggestions that a good relationship exists between exercise-induced electrocardiographic changes and the degree of gradient across the aortic valve. The development during exercise of ischemic ST segment changes appears to occur in patients with normal resting cardiac
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
Congenital Aortic Stenosis
FRIEDMAN
6
indices and left ventricular-aortic pressure gradients beyond 50 mm Hg. However, further studies are needed of this noninvasive modality in order to estimate the incidence of false positive and false negative results. After all of these comments, we want to stress that one must recognize that there is an absence of a truly reliable indirect method for determining the severity of obstruction in aortic stenosis. There is no question that clinical data used to assess the lesion may be misleading, so that, if one relies excessively on any of the findings or techniques mentioned above, it is quite clear that there will be occasional errors in individual patient management. We believe every patient with symptoms or LV 'strain' by EeG should undergo cardiac catheterization. It is quite simple to detect the presence of trivial or quite mild obstruction, but much more difficult to distinguish moderate from severe obstruction in the asymptomatic child. If one cannot decide whether moderate or severe obstruction is present, we believe strongly that it is the physician's responsibility to exclude severe obstruction. Thus, once we make the clinical diagnosis, if any suspicion exists that severe obstruction is present, we do not hesitate to proceed with hemodynamic study. Even if only mild or moderate obstruction is detected after cardiac catheterization is performed, a strong argument can now be put forth to incorporate repeated hemodynamic studies at 5- to 8-year intervals into the routine of patient follow-up. We make this statement because of the data that are available about the natural history of valvar AS.
Natural History
Until quite recently the interruption of the course of AS by operation, as well as a lack of prospective information concerning the outlook of patients with this malformation, created major uncertainties about the natural history of the lesion. Evaluation of natural history has been difficult because the development of objective means for the determination of the severity of AS by left heart catheterization, and the initial attempts at operative treatment occurred almost simultaneously. Information now available suggests strongly that a progressive increase in the severity of obstruction may occur commonly even among young children. In two separate studies of ours, serial hemodynamic observations were obtained initially asymptomatic chilwas observed in most of the children over an average time span of approxi-
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
dren [2, 9]. An intensification of left ventricular outflow tract obstruction
Congenital Aortic Stenosis
7
mately 6 years. In 5 of 24 patients so studied, the degree of stenosis observed at second study was considered of sufficient severity to warrant a recommendation for cardiac operation. Implicit in the findings of both serial studies was that a longer follow-up period would have identified even more patients in whom critical obstruction developed and that clinical deterioration, with time, could be anticipated. Of interest was the fact that in none of the patients in either study was SBE encountered and in none did aortic regurgitation become a problem. Quite similar data have been reported by others [5, 13].
From all of our previous remarks it should be clear that the presence of severe obstruction, rather than of symptoms, is the primary indication for operation. We consider a peak transvalvar gradient exceeding 75 mm Hg in association with a normal cardiac output, or an effective aortic orifice less than 0.5 cm2/m2 of body surface area, to represent critical obstruction. Just knowing the magnitude of the systolic pressure gradient is not sufficient, since it is also necessary to measure the cardiac output to evaluate the severity of stenosis. The pressure gradient is not a simple linear function of flow, but rather is proportional to the square of the flow rate across the site of obstruction. Since the gradient is determined by the flow, as well as the size of the orifice, the only way to accurately determine severity is by measuring both the pressure difference and the flow, simultaneously if possible. When aortic regurgitation exists, the flow rate across the valve is the sum of the effective cardiac output and of the regurgitant flow. Since most clinical techniques for measuring flow record only the effective cardiac output, the valvar flow rate may be underestimated and the severity of valve stenosis may, therefore, be falsely exaggerated if allowance is not made for associated regurgitation. Alterations in heart rate also change the velocity of blood flow across the stenotic valve at any given level of cardiac output. At high rates, diastole is shortened relatively more than systole, and the total time available for flow across the obstruction is greater. These facts are important to keep in mind since it is the presence of severe obstruction alone in asymptomatic patients that is a primary indication for operation. In the presence of symptoms or left ventricular 'strain' pattern on the ECG, we will consider operating on patients with gradients in the 50 mm Hg range and valve orifice indices of 0.7 cm2• We are less rigid about the magnitude of the pressure gradient
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
Indications for Operation
FRIEDMAN
8
in this group of patients since the risk of sudden death is so high and there is already ECG evidence of myocardial ischemia, and improvement of aortic valve flow may result in an increase in coronary artery perfusion. Moreover, if the transvalvar gradient is in the 50 mm Hg range and an exercise test demonstrates ST + T wave changes, we will most likely consider operating on the patient even if he is asymptomatic.
The results of operation differ according to the patient's age, the type of obstructing lesion, and the experience of the surgical team. Currently in ours, and in most major centers, immediate operative mortality does not exceed 2%. Essentially no data are available concerning the truly long-term hemodynamic results of aortic valvotomy. When patients undergo cardiac catheterization, an average of 1 year after cardiac operation, the left ventricularaortic pressure gradient is noted to be little changed from that observed on the operating table at the conclusion of the valvotomy, and substantial reductions in the severity of obstruction are noted in almost all patients [6]. Moreover, if symptoms were present preoperatively, survivors are almost uniformly found to be asymptomatic following surgery. Thus, it can be stated with reasonable assurance that in children with congenital valvar stenosis and hemodynamically severe obstruction, the risk of operation is less than that of sudden death. However, it must be remembered that the valve is not rendered normal anatomically by operation, since valve leaflets remain deformed after commissurotomy and further degenerative changes, including calcification, may very well lead to progressive stenosis in later years in a significant number of patients. In addition, both subacute bacterial endocarditis (SBE) and aortic regurgitation may become problems in the years following an operation. One study is available in which the late results of aortic valvotomy have been evaluated. CONKLE et al. [3] have described the follow-up results in a group of 38 patients with congenital AS who underwent aortic valvotomy with the aid of cardiopulmonary bypass at the National Heart and Lung Institute between 1957 and 1967. It was our privilege to participate in the initial evaluation of many of these patients. The study group consisted of 30 males and 8 females whose average age at operation was 12.5 years with a range of 1-21 years. The postoperative follow-up averaged 10 years with a range of 5-14 years.
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
Results of Operation
9
Congenital Aortic Stenosis
Preoperatively, the symptoms described included fatigue in 19, dyspnea in 18, syncope in 10, angina in 9 and presyncope in 6 patients. Eight patients were asymptomatic. Left ventricular hypertrophy was detected by ECG in 33 patients and 15 had a hypertrophy pattern with ST+T wave changes of subendocardial ischemia. Chest roentgenograms revealed left ventricular hypertrophy in 19 patients. Every patient underwent preoperative hemodynamic and angiographic study. The average peak transvalvar pressure difference at rest was 91 mmHg (range of 30-180); left ventricular peak pressure averaged 194 mm Hg (range of 120-300); the left ventricular end-diastolic pressure averaged 12 mm Hg, but 16 patients had end-diastolic pressures in excess of this value. The mean cardiac index was 4.2 l/min/m2 (range of 2.3-7.3); and the
lBO
.!!
:e
~
20
.>:
10
&0 Postoperatively
(27mm Hg)
Fig. 1. Peak transvalvar systolic pressure gradients preoperatively and postoperatively in 32 patients.
Downloaded by: Weizmann Inst. of Science 132.77.150.148 - 2/13/2018 5:01:33 AM
Preoperatively
(91mm Hg)
10
FRIEDMAN
2.0
1.8
1.6
0.2
1.0
0.8
NE
0.6
U:.------,
u
.:;;
,; 0.4-
..
;; 0.2 >
~
5
