Unexpected persistence into adulthood of low wall stress in patients with congenital aortic stenosis: is there a fundamental difference in the hypertrophic response to a pressure overload present from birth?

Single nucleus transcriptomics supports a role for CCNA2-induced human adult cardiomyocyte cytokinesis

Cyclin A2 (CCNA2) is a master regulatory gene of the cell cycle that is normally silenced in postnatal mammalian cardiomyocytes. We have previously demonstrated that it can induce significant cardiac repair in both small and large animals when delivered to the heart via a viral vector. To date, whether CCNA2 gene delivery can induce cytokinesis in isolated cardiomyocytes from adult human hearts has not been investigated. Therefore, we designed a human gene therapy vector featuring a replication-deficient, E1/E3-deleted human adenovirus five encoding human CCNA2 driven by the cardiac Troponin T promoter to enable the expression of CCNA2 in freshly isolated human cardiomyocytes. Utilizing time-lapse microscopy live imaging of cultured adult human cardiomyocytes isolated from a 21-year-old male, 41-year-old female, and 55-year-old male, we now report that human adult cardiomyocytes can be induced to undergo complete cytokinesis in response to CCNA2 gene delivery with preservation of sarcomere integrity in the resulting daughter cells. To elucidate the mechanistic underpinnings of CCNA2-dependent gene regulation in governing cardiomyocyte cytokinesis, we conducted single nucleus transcriptomics (snRNA-seq, 10X Genomics) analysis in hearts isolated from adult transgenic mice that constitutively express CCNA2 in cardiomyocytes (CCNA2-Tg) and non-transgenic mice (nTg). Remarkably, we identified a subpopulation of cardiomyocytes enriched with cytokinesis, proliferative, and reprogramming genes in hearts obtained from CCNA2-Tg mice as compared to hearts obtained from nTg mice. We also performed bulk RNA sequencing of human adult and fetal hearts, and we identified key reprogramming genes that are involved in CCNA2-induced cytokinesis. These results provide a compelling path forward for the clinical development of cardiac regenerative therapy based on strategic manipulation of the cardiomyocyte cell cycle.

Trajectory of Left Ventricular Remodeling in Children With Valvar Aortic Stenosis Following Balloon Aortic Valvuloplasty

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Background:

Aortic valve stenosis is the most common type of congenital left ventricular (LV) outflow tract obstruction. Balloon aortic valvuloplasty (BAV) has become the first-line treatment pathway in many centers. Our aim was to assess the trajectory of LV remodeling following BAV in children and its relationship to residual aortic stenosis (AS) and insufficiency (AI).

Methods:

Children <18 years of age who underwent BAV for isolated aortic stenosis from 2004 to 2012 were eligible for inclusion. Those with AI before BAV, other complex congenital heart lesions, or <2 accessible follow-up echocardiograms were excluded. Baseline and serial echocardiographic data pertaining to aortic valve and LV size and function were retrospectively collected through December 2017 or the first reintervention. Longitudinal data was assessed using per-patient time profiles with superimposed trend lines using locally estimated scatterplot smoothing. Associations with reintervention or death were also evaluated.

Results:

Among the 98 enrolled children, the median (interquartile range) age at BAV was 2.8 months (0.2–75). The median (interquartile range) follow-up was 6.8 years (1.9–9.0). Children with predominantly residual AI (n=11) demonstrated progressive increases in their LV end-diastolic dimension Z score within the first 3 years after the BAV, followed by a plateau (P<0.001). Their mean LV circumferential and longitudinal strain values remained within the normal range but lower than in the non-AI group (P<0.001 and P=0.001, respectively). Children with predominantly residual aortic stenosis (n=44) had no changes in LV dimensions but had a rapid early increase in mean LV circumferential and longitudinal strain. The cumulative proportion (95% CI) of reintervention at 5 years following BAV was 33.7% (23.6%–42.4%).

Conclusions:

Our study demonstrates that LV remodeling occurs mainly during the first 3 years in children with predominantly residual AI after BAV, with no subsequent significant functional changes over the medium term. These data improve our understanding of expected patient trajectories and thus may inform decisions on the timing of reintervention.

Hemodynamics in Adults With the Shone Complex

Patients with Shone complex (SC) have multiple left-sided obstructive lesions and thus are at risk for left ventricular (LV) remodeling, LV diastolic dysfunction and pulmonary hypertension. Yet, to date, there has been no description of hemodynamics in adults with SC. Retrospective chart review of 25 patients with SC who underwent cardiac catheterization at Mayo Clinic, MN between 2002 and 2019 was performed. SC was defined as multiple left-sided obstructive lesions in the presence of an anatomically abnormal mitral valve. Median age was 32 years (22.5, 42) and 15 patients (60%) were female. The majority of patients (84%) had history of coarctation of the aorta, 10 (40%) had subaortic stenosis, 11 (44%) had prior aortic valve replacement, and 10 (40%) had prior mitral valve replacement. Structural disease at the time of catheterization which warranted intervention within the next year was present in 13 patients (52%). The mean LV end-diastolic pressure was 21.3 ± 9.0 mm Hg (>15 mm Hg in 71%), pulmonary artery peak systolic pressure was 55.4 ± 13.4 mm Hg, and the pulmonary artery mean pressure was 37.0 ± 9.4 mm Hg (>20 mm Hg in 96%). During a mean follow-up of 8.3 ± 4.4 years, there were 7 deaths (28%) and 3 additional patients (12%) underwent cardiac transplantation. In conclusion, adults with SC who underwent catheterization showed significant left-sided heart and pulmonary vascular remodeling. Elevated LV end-diastolic pressure and pulmonary artery pressures were highly prevalent. There were high mortality and cardiac transplant rates in our cohort.

Effects of early aldosterone antagonism on cardiac remodeling in rats with aortic stenosis-induced pressure overload

Aldosterone plays a pivotal role in the pathophysiology of systolic heart failure. However, whether early aldosterone antagonism improves cardiac remodeling during persistent pressure overload is unsettled. We evaluated the effects of aldosterone antagonist spironolactone on cardiac remodeling in rats with ascending aortic stenosis (AS).

METHODS

Three days after inducing AS, weaning rats were randomized to receive spironolactone (AS-SPR, 20mg/kg/day) or no drug (AS) for 18weeks, and compared with sham-operated rats. Myocardial function was studied in isolated left ventricular (LV) papillary muscles.

STATISTICAL ANALYSES

ANOVA or Kruskal-Wallis tests.

RESULTS

Echocardiogram showed that LV diastolic (Sham 8.73±0.57; AS 8.30±1.10; AS-SPR 9.19±1.15mm) and systolic (Sham 4.57±0.67; AS 3.61±1.49; AS-SPR 4.62±1.48mm) diameters, left atrial diameter (Sham 5.80±0.44; AS 7.15±1.22; AS-SPR 8.02±1.17mm), and LV mass were higher in AS-SPR than AS. Posterior wall shortening velocity (Sham 38.5±3.8; AS 35.6±5.6; AS-SPR 31.1±3.8mm/s) was lower in AS-SPR than Sham and AS; E/A ratio was higher in AS-SPR than Sham. Developed tension was lower in AS and AS-SPR than Sham. Time to peak tension was higher in AS-SPR than Sham and AS after post-rest contraction. Right ventricle weight was higher in AS-SPR than AS, suggesting more severe heart failure in AS-SPR than AS. Interstitial collagen fractional area and myocardial hydroxyproline concentration were higher in AS than Sham. Metalloproteinase-2 and -9 activity, evaluated by zymography, did not differ between groups.

CONCLUSION

Early spironolactone administration causes further hypertrophy in cardiac chambers, and left ventricular dilation and dysfunction in rats with AS-induced chronic pressure overload.

Biventricular systolic function in young lambs subject to chronic systemic right ventricular pressure overload

In various clinical situations of congenital heart disease, the right ventricle (RV) is subject to a chronic systemic pressure overload which affects biventricular function and may progress to the development of RV failure. Young lambs (2-3 wk old) underwent adjustable pulmonary artery banding (PAB) at systemic (aortic) level for 8 wk. Biventricular function was determined by using load-independent indexes of global ventricular contractile performance by the end-systolic pressure-volume relationship (ESPVR) using the conductance catheter at baseline and during dobutamine infusion. PAB resulted in a significant fivefold increase in RV end-systolic pressure (12-64 mmHg) and a doubling of the RV-to-left ventricular (LV) wall thickness ratio (P < 0.01). RV global contractile performance increased significantly, as indicated by an increased slope of the ESPVR. Compared with age-matched control lambs, cardiac output decreased from 2.6 to 1.6 l/min (P < 0.05) whereas heart rates were equal. In contrast with RV volume, LV volume decreased significantly after PAB (P < 0.01), whereas the LV-ESPVR slope was unchanged. In the PAB group, the RV, but not the LV, showed a reduced response to dobutamine. We concluded that chronic RV pressure overload for 8 wk results in diminished pump function despite compensatory increased RV global contractile performance.

Constraints on cardiac hypertrophy imposed by myocardial viscosity

Laplace's law constrains how thin the ventricular wall may be without experiencing excessive stress. The present study investigated constraints, imposed by myocardial viscosity (resistance to internal rearrangement), on how thick the wall may be. The ventricle was modeled as a contracting, spherical shell. The analysis demonstrated that viscosity generates stress and energy dissipation with inverse fourth- and eighth-power dependence, respectively, on distance from the cavity center. This result derives from the combination of squared dependence of viscous forces on shearing velocity gradients and the greater shear rearrangement required for inner layers of a contracting sphere. These predictions are based solely on geometry and fundamentals of viscosity and are independent of material properties, cytoskeletal structure, and internal structural forces. Calculated values of energy and force required to overcome viscosity were clearly large enough to affect the extent of thickening of the left ventricle. It is concluded that load-independent viscous resistance to contraction is an important factor in cardiac mechanics, especially of the thickened ventricles of concentric hypertrophy.

Effect of myocardial hypertrophy on systolic and diastolic function in children: insights from the force-frequency and relaxation-frequency relationships

OBJECTIVE

The objective of this study was to evaluate the effect of myocardial hypertrophy on systolic and diastolic properties of the left ventricle in children.

BACKGROUND

In children with myocardial hypertrophy, ejection phase indices are invariably increased. However, indices of force-generation, e.g., end-systolic elastance and invasive indices of diastolic properties, have been studied infrequently in children with myocardial hypertrophy.

METHODS

We studied 10 children with congenital aortic stenosis or coarctation of aorta and nine control patients. Systolic properties were assessed from shortening fraction, end-systolic fiber elastance (Ef(es)) measured at resting heart rates, and force-frequency relationship measured at heart rates increasing from 110 to 160 beats per minute. Diastolic properties were assessed from time constant of relaxation (tau) at matched heart rates, chamber stiffness constant, myocardial stiffness constant, and relaxation-frequency relationship measured at gradually increasing heart rates.

RESULTS

Ef(es) remained unchanged by myocardial hypertrophy, however, tau was prolonged (tauL: 27.3+/-2.3 vs. 21.8+/-2.2 ms, p < 0.001; and tauD: 43.2+/-3.1 vs. 34.3+/-3.3 ms, p < 0.001). Both chamber and myocardial stiffness constants remained unchanged. Incremental increases in heart rate produced incremental improvement in both contraction and relaxation. Slopes of force-frequency and relaxation-frequency relationships remained unchanged in the experimental group. However, the relaxation-frequency relationship manifested a parallel shift upward.

CONCLUSIONS

In conscious, sedated children with myocardial hypertrophy, systolic function assessed by an index of force generation remains unchanged. However, relaxation is prolonged but passive diastolic properties remain unaffected. The combined effect of hypertrophy and heart rate does not alter the force-frequency and relaxation-frequency relationships.

Right ventricular function and exercise performance late after primary repair of tetralogy of Fallot with the transannular patch in infancy

To evaluate the late effects of chronic pulmonary regurgitation against the putative benefits from the current surgical trend of primary repair of tetralogy of Fallot with a transannular patch in infancy, 10 patients > 10 years after early primary repair and 7 matched normal controls underwent exercise stress test and cine magnetic resonance imaging assessment of ventricular functions. Right ventricular impaired diastolic function and decreased exercise capacity, both significantly associated with pulmonary regurgitation in patients, indicated that early primary repair of tetralogy may not prevent late ventricular dysfunction and diminished exercise performance if chronic regurgitation results from right ventricular outflow tract reconstruction.

Effect of young age on coronary adaptations to left ventricular pressure overload hypertrophy in sheep

OBJECTIVES

This study attempted to determine the effect of young age on changes in coronary conductance and capillary density with left ventricular pressure overload hypertrophy. Mechanisms responsible for age differences in perfusion capacity were examined.

BACKGROUND

Hypertension in adults causes alterations in the coronary vasculature, resulting in diminished coronary perfusion capacity and myocardial ischemia. These processes are worsened in adults by advanced age. Young age may provide advantages in coronary adaptation to hypertension.

METHODS

Coronary conductance was examined in conscious chronically instrumented 10-week old lambs and adult sheep with progressive ascending aortic stenosis of 6-week's duration and age-matched control sheep by means of the microsphere technique and vasodilators. Capillary density was measured post-mortem.

RESULTS

Adult sheep with aortic stenosis had a decrease in left ventricular subendomyocardial capillary density by 17% and maximal coronary conductance with adenosine by 67%. In the nonhypertrophied right ventricle, maximal coronary conductance was depressed by 47%, whereas capillary density was normal, implying an effect of coronary hypertension on resistance vessels. In contrast, lambs with aortic stenosis maintained normal left ventricular capillary density, maximal coronary conductance and coronary reserve and had relatively little impairment of conductance in the right ventricular coronary bed (-15%, p = NS). Similar responses were found with other vasodilators, isoproterenol and chromonar.

CONCLUSIONS

Young age confers advantages to coronary adaptation to left ventricular pressure overload, including angiogenesis proportionate to hypertrophy, resulting in normal capillary density and coronary conductance. There is also less hypertension-induced impairment of coronary conductance distinct from the effects of hypertrophy.

Effect of chronic supraventricular tachycardia on left ventricular function and structure in newborn pigs

OBJECTIVES

The purpose of this study was to examine the effects of supraventricular pacing tachycardia on left ventricular function and myocardial structure in newborn, immature pigs and to determine whether immature pigs respond to supraventricular tachycardia differently from adults.

BACKGROUND

Previous studies have shown that supraventricular tachycardia causes dilated cardiomyopathy in adult animals; however, in humans, supraventricular tachycardia-induced congestive heart failure occurs most frequently in children and newborns. Because some clinical diseases may cause myocardial failure in adults but rarely do so in children, it was hypothesized that the effects of supraventricular tachycardia in newborns may be different from those in adults.

METHODS

In two groups of newborn swine (3 weeks of age), left ventricular volume, mass and function were assessed with simultaneous echocardiography and cardiac catheterization and myocardial structure was examined with light and electron microscopy. Six piglets underwent 3 weeks of left atrial pacing tachycardia (240 beats/min) and six littermates served as a control group. Both groups were followed up for 3 weeks.

RESULTS

At the end of the protocol, left ventricular dimensions increased in the piglets with supraventricular tachycardia compared with values in the control group, but there were no differences in left ventricular mass. Systolic function, assessed by fractional shortening, peak ejection rate and maximal rate of pressure development, was decreased in the group with supraventricular tachycardia. The fractional shortening-end-systolic stress relation in the piglets with supraventricular tachycardia decreased below normal values. Left ventricular diastolic function assessed by the relaxation time constant was prolonged, the peak filling rate was decreased and left ventricular stiffness was increased in the supraventricular tachycardia group. The morphologic data demonstrated that supraventricular tachycardia did not change total myocyte volume but did decrease total myofibrillar volume.

CONCLUSIONS

Supraventricular tachycardia caused dilated cardiomyopathy in immature pigs. These changes in left ventricular function were associated with a decrease in cellular contractile proteins. Thus, the effects of supraventricular tachycardia on left ventricular function and structure in immature animals were comparable to previous findings in mature animals.

Segmental systolic responses to brief ischemia and reperfusion in the hypertrophied canine left ventricle

OBJECTIVES AND BACKGROUND

Left ventricular hypertrophy is associated with increased mortality, increased myocardial infarct size and an increased incidence of sudden death. Although reperfusion after ischemia has been shown to result in decreased infarct size and recovery of systolic thickening, it is unknown how left ventricular hypertrophy might influence recovery of regional systolic thickening after ischemia and reperfusion. We hypothesized that left ventricular hypertrophy might attenuate or abolish the functional response to reperfusion.

METHODS

Three groups of chronically instrumented, conscious dogs (dogs with left ventricular hypertrophy and hypertension; dogs with left ventricular hypertrophy and reduced blood pressure and a control group without hypertrophy and with normal blood pressure) underwent 15 min of ischemia and 24 h of reperfusion. Segmental systolic thickening was measured by sonomicrometers and myocardial segments were grouped by percent of control segmental systolic thickening retained at 15 min of ischemia (class 1 greater than or equal to 67%, class 2 from 0% to 66%, class 3 less than 0% control systolic thickening). The recovery of each class of segment was measured serially during reperfusion. Hemodynamic variables and regional myocardial blood flow were also measured.

RESULTS

There were no differences among groups in recovery of segmental systolic thickening for class 1 segments. Systolic thickening in class 2 (hypokinetic) segments was significantly depressed (p less than 0.05 compared with control value) in the group with left ventricular hypertrophy and reduced blood pressure (but not in the group with hypertrophy and hypertension) during early reperfusion; systolic thickening in class 3 (dyskinetic) segments showed a similar trend in the group with hypertrophy and reduced pressure.

CONCLUSIONS

Although left ventricular hypertrophy with hypertension did not attenuate the contractile response to reperfusion, hypertrophy with reduced blood pressure was associated with significantly greater depression of segmental systolic thickening early during reperfusion.

Pulmonary autograft replacement in children. The ideal solution?

Fifty-one children, aged 1.8 to 21 years (mean, 11.4) with aortic valve replacement using a pulmonary autograft are reviewed. Twenty-nine were intra-aortic implants and 22 were root replacements. There was one operative death, no late deaths, and two have required reoperation. Actuarial freedom from reoperation was 93% +/- 5.5 at 5.6 years. Freedom from progression of aortic insufficiency (AI) was 81% +/- 9 at 5.6 years in the intra-aortic implants and 86% +/- 10 in the root replacement. Enlargement of the pulmonary autograft was seen echocardiographically in both groups. This enlargement was consistent with somatic growth and not associated with progression of AI. Ten of 19 patients with aortic stenosis had an LV mass index suggestive of LV hypertrophy before operation. At 1 year, 18 of 25 had a normal LV mass index. Thirteen of 16 patients with AI had preoperative abnormal LV mass index. All but four returned to normal by 1 year. Low operative risk, excellent function, resolution of abnormal LV hemodynamics, and enlargement consistent with somatic growth suggest that the pulmonary autograft is the ideal replacement for the malfunctioning aortic valve.

Developmental modulation of myocardial mechanics: age- and growth-related alterations in afterload and contractility

Somatic growth is associated with alterations in myocardial mechanics in children with heart disease and in most animal models of congenital heart disease. However, the effect of age and body size on myocardial contractility and loading conditions in normal infants and children is not known. Therefore, 256 normal children aged 7 days to 19 years (34% less than 3 years old) were evaluated with noninvasive indexes of left ventricular contractility and loading conditions. Two-dimensional and M-mode echocardiographic recordings of the left ventricle were obtained with a phonocardiogram, indirect pulse tracing and blood pressure recordings. Left ventricular dimensions, wall thickness and pressure measurements obtained from these data were used to calculate peak and end-systolic circumferential and meridional wall stress and mean and integrated meridional wall stress. Velocity of shortening adjusted for heart rate was compared with end-systolic stress to assess contractility independently of loading status. The subjects were stratified for gender and each of the derived variables was related to age and body surface area. Ventricular shape, assessed as the major/minor axis ratio, and the circumferential/meridional stress ratio were found to be invariant with growth. The ratio of posterior wall thickness to minor axis dimension did not change with age, despite the normal age-related increase in blood pressure. The increase in pressure despite unvarying ventricular shape and wall thickness/dimension ratio resulted in a substantial increase in wall stress that was most dramatic during the first few years of life. In association with the increase in afterload, systolic function decreased with age. However, the age-related decrease in the velocity of shortening was greater than that expected from the increase in afterload alone, indicating a higher level of contractility in infants and children during the first years of life than in older subjects. The process of normal growth and development, similar to that in children with heart disease, is associated with a rapid decrease in the trophic response to hemodynamic loads, resulting in an age-associated increase in wall stress. There is a similar but somewhat more rapid decrease in contractility, with the highest values seen in the youngest patients.

Angiographic assessment of left ventricular volume, afterload and contractile state in normal children

Left ventricular (LV) volume, mass and end-systolic stress were determined angiographically in 20 normal children aged 3 months to 16 years. LV contractile state was assessed by the analysis of the relation between end-systolic stress and ejection phase index or end-systolic volume. The LV volume and mass closely correlated with the body surface area. The LV mass/end-diastolic volume ratio (0.94 +/- 0.13 g/ml), ejection fraction (0.67 +/- 0.03) and circumferential end-systolic stress (163 +/- 21 kdynes/cm2, 165 +/- 21 g/cm2) remained constant despite the extensive increase in LV volume with physical growth. In all subjects significant inverse correlations were observed between end-systolic stress and ejection fraction or mean normalized systolic ejection rate. The ratio of the circumferential end-systolic stress to end-systolic volume index ranged from 5.00 to 12.57 (7.49 +/- 1.88). The ratio inversely correlated with age (r = -0.74, p less than 0.001), indicating that this ratio for estimating LV contractility is associated with ventricular size. These results suggested that the LV mass increased adequately in response to the extensive increase in LV cavity volume to maintain the end-systolic stress during growth in childhood and that physiologic cardiac growth was associated with appropriate hypertrophy with no significant change in LV contractile state.

Preoperative left ventricular wall stress, ejection fraction, and aortic valve gradient as prognostic indicators in aortic valve stenosis

Patients with aortic valve stenosis (AS) and left ventricular (LV) dysfunction may dramatically improve after aortic valve replacement, but operative risk is high. In an earlier study, all patients with low preoperative wall stress and low ejection fraction, or with low aortic valve gradient, died or had persistent heart failure after operation. Because wall stress is difficult to calculate, we reassessed its effect and the effect of other preoperative characteristics on outcome in 66 consecutive catheterization patients with predominant aortic stenosis referred for valve replacement. Despite ejection fraction that was inordinately low compared with afterloading wall stress in nine patients, seven patients improved with surgery. All three patients with ejection fraction less than 20% improved after surgery. Two of three patients with mean aortic valve gradients of less than 30 mm Hg improved. Mortality was 33% in patients with mean gradient less than 30 mm Hg and 19% with mean gradient less than 50 mm Hg. In the 54 patients with calculated aortic valve areas of less than or equal to 0.8 cm2, 1 (2%) had continuing heart failure, while 6 of 12 (50%, P less than .01) patients with aortic valve areas of 0.9-1.2 cm2 had continued symptoms of or died of heart failure. Patients who died or failed to improve after operation were older (71 +/- 9 years) than those who improved (65 +/- 9 years, P = .02). We conclude that wall stress calculations do not predict which patients with aortic stenosis will benefit from aortic valve replacement and that poor left ventricular function and low mean aortic valve gradient do not absolutely preclude operation. On the other hand, low gradient, non-critical valve area, and advanced age are all relative contraindications to aortic valve replacement in aortic stenosis.

Supernormal ejection performance is isolated to the ipsilateral congenitally pressure-overloaded ventricle

Congenital left ventricular pressure overload is associated with "excessive" hypertrophy that leads to subnormal afterload (wall stress), permitting enhanced ventricular ejection performance. Whether congenital right ventricular pressure overload is associated with a similar phenomenon is uncertain. It is also unknown whether supranormal ejection performance affects only the overloaded ventricle or is a general process affecting both ventricles. Conflicting data exist about whether the hypertrophic process associated with pressure overload is induced primarily by local loading conditions or by neuroendocrine influences. If the former postulate is true, the hypertrophic response should be confined to the overloaded ventricle; if the latter is true, one might predict that both ventricles would be affected by a less specific response to circulating catecholamines. To help resolve these issues, both right and left ventricular performance was examined in seven patients with isolated congenital pulmonary stenosis (average pulmonary pressure gradient 78 +/- 13 mm Hg), six patients with isolated congenital aortic stenosis (average gradient 80 +/- 10 mm Hg) and six normal subjects. Right ventricular ejection fraction was increased in patients with pulmonary stenosis (61 +/- 2%) compared with the value in normal subjects (53 +/- 2%, p less than 0.01) and in patients with aortic stenosis (50 +/- 3%, p = 0.007). Left ventricular ejection fraction was increased in patients with congenital aortic stenosis (84 +/- 4%) compared with the value in normal subjects (70 +/- 4%, p less than 0.01) and in patients with congenital pulmonary stenosis (65 +/- 2%, p less than 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)