Fate of right ventricular hypertrophy in tetralogy of Fallot after corrective surgery

Accelerated Growth, Differentiation, and Ploidy with Reduced Proliferation of Right Ventricular Cardiomyocytes in Children with Congenital Heart Defect Tetralogy of Fallot

The myocardium of children with tetralogy of Fallot (TF) undergoes hemodynamic overload and hypoxemia immediately after birth. Comparative analysis of changes in the ploidy and morphology of the right ventricular cardiomyocytes in children with TF in the first years of life demonstrated their significant increase compared with the control group. In children with TF, there was a predominantly diffuse distribution of Connexin43-containing gap junctions over the cardiomyocytes sarcolemma, which redistributed into the intercalated discs as cardiomyocytes differentiation increased. The number of Ki67-positive cardiomyocytes varied greatly and amounted to 7.0–1025.5/10⁶ cardiomyocytes and also were decreased with increased myocytes differentiation. Ultrastructural signs of immaturity and proliferative activity of cardiomyocytes in children with TF were demonstrated. The proportion of interstitial tissue did not differ significantly from the control group. The myocardium of children with TF under six months of age was most sensitive to hypoxemia, it was manifested by a delay in the intercalated discs and myofibril assembly and the appearance of ultrastructural signs of dystrophic changes in the cardiomyocytes. Thus, the acceleration of ontogenetic growth and differentiation of the cardiomyocytes, but not the reactivation of their proliferation, was an adaptation of the immature myocardium of children with TF to hemodynamic overload and hypoxemia.

Impaired right and left ventricular function and relaxation induced by pulmonary regurgitation are not reversed by tardive antifibrosis treatment

Pulmonary regurgitation (PR) after repair of tetralogy of Fallot (rTOF) is associated with progressive right (RV) and left (LV) ventricular dysfunction and fibrosis. However, angiotensin II receptor blockade therapy has shown mixed and often disappointing results. The aim of this study was to serially assess changes in biventricular remodeling, dysfunction, and interactions in a rat model of isolated severe PR and to study the effects of angiotensin II receptor blockade. PR was induced in Sprague-Dawley rats by leaflet laceration. Shams (n = 6) were compared with PR (n = 5) and PR + losartan treatment (n = 6). In the treatment group, oral losartan (50 mg·kg^-1·day^-1) was started 6 wk after PR induction and continued for 6 wk until the terminal experiment. In all groups, serial echocardiography was performed every 2 wk until the terminal experiment where biventricular myocardium was harvested and analyzed for fibrosis. PR and PR + losartan rats experienced early progressive RV dilatation by 2 wk which then stabilized. RV systolic dysfunction occurred from 4 wk after insult and gradually progressed. In PR rats, RV dilatation caused diastolic LV compression and impaired relaxation. PR rats developed increased RV fibrosis compared with shams. Although losartan decreased RV fibrosis, RV dilatation and dysfunction were not improved. This suggests that RV dilatation is an early consequence of PR and affects LV relaxation. RV dysfunction may progress independent of further remodeling. Reduced RV fibrosis was not associated with improved RV function and may not be a viable therapeutic target in rTOF with predominant RV volume loading.NEW & NOTEWORTHY The time-course of RV dilatation and the mechanisms of biventricular dysfunction caused by PR have not been well characterized and the effect of losartan in volume-overloaded RV remains controversial. Our findings suggest that severe PR induces early onset of RV dilatation and dysfunction with little progression after the first 4 wk. The RV dilatation distorts LV geometry with associated impaired LV relaxation. Losartan reduced RV fibrosis but did not reverse RV dilatation and dysfunction.

[Ultrastructural features of cardiomyocytes in infants with tetralogy of Fallot in the first year of life]

OBJECTIVE

To analyze cardiomyocyte (CMC) ultrastructural changes in the right ventricle outflow tract (RVOT) of infants with tetralogy of Fallot (TF) in the first years of life and to compare the findings with clinical parameters in these patients.

MATERIAL AND METHODS

Intraoperative RVOT myocardial biopsy specimens obtained from 51 patients aged 3-33 months with TF during radical correction of defect were investigated. CMC diameter and length were measured using the semithin myocardial sections stained with periodic acid-Schiff. The ultrathin sections were examined in the electron microscope.

RESULTS

The diameter of CMCs in the RVOT of infants with TF varied significantly (7.3-17.0 µm) and averaged 10.8±2.2 µm; a large number of multinucleated CMCs were observed. There were ultrastructural signs of incomplete differentiation of CMCs: active myofibril assembly in the free sarcoplasmic region; gap junctions on the lateral surfaces of CMCs; and centrioli in their sarcoplasm. Myofibrillogenesis in babies under 6 months increased in response to hemodynamic overload and hypoxemia. In addition, organelles suggestive of the synthetic activity of CMCs, such as cisterns and vesicles of the Golgi complex and granular endoplasmic reticulum, were detected in the sarcoplasm of a number of CMCs. TF infants' myocardium also displayed focal disorders of CMC interposition; the change in the shape of myocytes was accompanied by the appearance of additional lateral insert discs. Some CMCs showed the abnormal localization of the nucleus beneath the sarcolemma, sarcoplasmic bulging areas, and dystrophic changes.

CONCLUSION

There were ultrastructural features characteristic for the myocardium that was at the state of active growth and differentiation (increases in the diameter and length of CMCs and in the number of nuclei; myofibrillogenesis; signs of synthetic and proliferative activity along with insignificant dystrophic changes) in the CMCs of myocardial RVOT in infants with TF in the first years of life.

Cardiomyocyte Hypertrophy in Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (AC) is a hereditary disease leading to sudden cardiac death or heart failure. AC pathology is characterized by cardiomyocyte loss and replacement fibrosis. Our goal was to determine whether cardiomyocytes respond to AC progression by pathological hypertrophy. To this end, we examined tissue samples from AC patients with end-stage heart failure and tissue samples that were collected at different disease stages from desmoglein 2-mutant mice, a well characterized AC model. We find that cardiomyocyte diameters are significantly increased in right ventricles of AC patients. Increased mRNA expression of the cardiac stress marker natriuretic peptide B is also observed in the right ventricle of AC patients. Elevated myosin heavy chain 7 mRNA expression is detected in left ventricles. In desmoglein 2-mutant mice, cardiomyocyte diameters are normal during the concealed disease phase but increase significantly after acute disease onset on cardiomyocyte death and fibrotic myocardial remodeling. Hypertrophy progresses further during the chronic disease stage. In parallel, mRNA expression of myosin heavy chain 7 and natriuretic peptide B is up-regulated in both ventricles with right ventricular preference. Calcineurin/nuclear factor of activated T cells (Nfat) signaling, which is linked to pathological hypertrophy, is observed during AC progression, as evidenced by Nfatc2 and Nfatc3 mRNA in cardiomyocytes and increased mRNA of the Nfat target regulator of calcineurin 1. Taken together, we demonstrate that pathological hypertrophy occurs in AC and is secondary to cardiomyocyte loss and cardiac remodeling.

Adaptive capacity of the right ventricle: why does it fail?

Only in recent years has the right ventricle (RV) function become appreciated to be equally important to the left ventricle (LV) function to maintain cardiac output. Right ventricular failure is, irrespectively of the etiology, associated with impaired exercise tolerance and poor survival. Since the anatomy and physiology of the RV is distinctly different than that of the LV, its adaptive mechanisms and the pathways involved are different as well. RV hypertrophy is an important mechanism of the RV to preserve cardiac output. This review summarizes the current knowledge on the right ventricle and its response to pathologic situations. We will focus on the adaptive capacity of the right ventricle and the molecular pathways involved, and we will discuss potential therapeutic interventions.

Phenotypic patterns of right ventricular dysfunction: analysis by cardiac magnetic imaging

The aim of this study was to use magnetic resonance imaging (MRI) to classify the morphological changes and remodeling of the right ventricle (RV) that occur in different clinical situations and that have an impact on RV function. Most literature has traditionally focused on the left ventricle (LV) and as a result, few studies analyze RV behavior and remodeling. The study evaluated all cardiac MRI performed at our center from 2008 to 2010. We retrospectively identified 159 patients who had some sign of right ventricular dysfunction (RVD) based on MRI findings. We classified patients according to a combination of criteria for RVD and the presence of left ventricle dysfunction (LVD). We considered RVD as any of the following abnormalities: i) depressed RV function; ii) RV dilatation; iii) RV hypertrophy. LVD was considered when there was atrial dilatation, LV hypertrophy, LV dilatation and/or depressed LV function. We obtained 6 pathophysiological patterns: RV pressure overload (1.9%), RV volume overload (15.7%), RV volume overload + LVD (32.7%), depressed RV function + LVD (42.1%), mixed RV overload + LVD (6.9%) and other (0.6%). The most frequent etiology was congenital heart disease (33.3%), followed by idiopathic dilated cardiomyopathy (18.2%), left valvular disease (17.6%), ischemic heart disease (15%), pulmonary disease (9.8%), and other (6.1%). This study helps to classify the different patterns that RV can adopt in different clinical situations and can, therefore, help us to understand the RV pathophysiology.

Right ventricular failure secondary to chronic overload in congenital heart disease: an experimental model for therapeutic innovation

OBJECTIVE

Mortality and morbidity related to right ventricular failure remain a problem for the long-term outcome of congenital heart diseases. Therapeutic innovation requires establishing an animal model reproducing right ventricular dysfunction secondary to chronic pressure-volume overload.

METHODS

Right ventricular tract enlargement by transvalvular patch and pulmonary artery banding were created in 2-month-old piglets (n = 6) to mimic repaired tetralogy of Fallot. Age-matched piglets were used as controls (n = 5). Right ventricular function was evaluated at baseline and 3 and 4 months of follow-up by hemodynamic parameters and electrocardiography. Right ventricular tissue remodeling was characterized using cellular electrophysiologic and histologic analyses.

RESULTS

Four months after surgery, right ventricular peak pressure increased to 75% of systemic pressure and pulmonary regurgitation significantly progressed, end-systolic and end-diastolic volumes significantly increased, and efficient ejection fraction significantly decreased compared with controls. At 3 months, the slope of the end-systolic pressure-volume relationship was significantly elevated compared with baseline and controls; a significant rightward shift of the slope, returning to the baseline value, was observed at 4 months, whereas stroke work progressed at each step and was significantly higher than in controls. Four months after surgery, QRS duration was significantly prolonged as action potential duration. Significant fibrosis and myocyte hypertrophy without myolysis and inflammation were observed in the operated group at 4 months.

CONCLUSION

Various aspects of early right ventricular remodeling were analyzed in this model. This model reproduced evolving right ventricular alterations secondary to chronic volumetric and barometric overload, as observed in repaired tetralogy of Fallot with usual sequelae, and can be used for therapeutic innovation.

Delayed improvement of right ventricular diastolic function and regression of right ventricular mass after percutaneous pulmonary valve implantation in patients with congenital heart disease

BACKGROUND

Percutaneous pulmonary valve implantation (PPVI) has been introduced as therapy for right ventricular (RV) to pulmonary artery conduit dysfunction in patients with congenital heart disease. It has been shown that RV systolic function improved early after PPVI. The effects of PPVI on RV diastolic function and RV hypertrophy have not yet been studied.

PURPOSE

The objective of this study is to assess early and late changes in systolic and diastolic RV function and RV mass after PPVI.

MATERIALS AND METHODS

Fourteen patients underwent PPVI (7 male, median age 15 years). Cardiac magnetic resonance imaging was performed before and at 2 time points after PPVI (at 1 and 16 months). Right ventricular volume and systolic and diastolic function as well as RV mass were assessed.

RESULTS

At 1 and 16 months after PPVI, the RV mass decreased from 28.6 +/- 2.1 to 25.6 +/- 2.2 g/m(2) (P = .03) and to 22.3 +/- 2.1 g/m(2) (P = .002). E/A volume ratio increased from 1.91 +/- 0.4 to 2.6 +/- 0.4 (not significant [NS]) and to 3.3 +/- 0.4 (P = .01). E/A peak flow ratio increased from 1.34 +/- 0.14 to 1.48 +/- 0.16 (NS) and to 1.73 +/- 0.14 (P = .04). E-wave deceleration time increased from 142 +/- 25 to 160 +/- 27 milliseconds (NS) and to 211 +/- 26 milliseconds (P = .007). At 1 month, RV end-diastolic volume decreased from 124 +/- 8 to 113 +/- 8 mL (P = .01) and RV ejection fraction increased from 36% +/- 2% to 46% +/- 2% (P = .001) without further improvement at 16 months.

CONCLUSION

After PPVI, in contrast to rapid improvement of RV systolic function, the improvement of RV diastolic function is delayed. The reduction of RV mass appears to be the underlying mechanism for improvement of RV diastolic function. Long follow-up for patients with PPVI is recommended.

Diastolic Function in Repaired Tetralogy of Fallot at Rest and during Stress: Assessment with MR Imaging

PURPOSE

To prospectively assess, with magnetic resonance (MR) imaging, right ventricular (RV) diastolic function after repair of tetralogy of Fallot (TOF) at rest and during pharmacologic stress and to study relationship between main pulmonary artery end-diastolic forward flow (EDFF) (indicative of restrictive RV physiology) and clinical status.

MATERIALS AND METHODS

Institutional medical ethics committee approval and patient or parent informed consent were obtained. Patients with TOF corrected through the transatrial-transpulmonary approach underwent MR imaging at rest and during dobutamine stress and maximal exercise testing. Two-dimensional (2D) cine volumetric data were acquired. Flow measurements were performed with a standard 2D flow-sensitized sequence. MR imaging flow curves for tricuspid and pulmonary valves were combined into RV time-volume change curves, from which indexes of RV filling were derived. Patient results were compared with published data in control subjects. Student t tests, Mann-Whitney U tests, analysis of covariance, and paired and one-sample t tests were used.

RESULTS

Thirty-six patients (mean age at repair, 0.9 year +/- 0.5 [standard deviation]; median age at study inclusion, 17 years [range, 7-23 years]; 26 male and 10 female patients) were included. Abnormalities in RV filling included impaired relaxation (prolonged deceleration time, P = .002; smaller early filling fraction, P = .02) in the entire group compared with published data in healthy control subjects and signs of restriction to RV filling (smaller atrial filling fraction and higher early filling/atrial filling peak ratio, P < .05 for both) in patients with EDFF (n = 24) compared with patients without EDFF (n = 12). Stress response was abnormal in patients with EDFF, who developed impaired RV relaxation not appreciated at rest. Patients with EDFF had more severe pulmonary regurgitation (P < .05) and poorer exercise performance (P < .001).

CONCLUSION

In patients with TOF corrected with currently widely accepted surgical strategies, pulmonary artery EDFF relates to worse clinical state at mid- to long-term follow-up. Dobutamine stress imaging may unmask abnormalities in RV diastolic filling not appreciated with rest imaging alone.

Impairment of mitochondrial respiratory chain enzyme activities in tetralogy of Fallot

BACKGROUND

During the last decade, disorders of the respiratory chain, so-called mitochondrial disorders, have emerged as a major clinical entity. Tetralogy of fallot (TOF) children>2 month of age are at risk for postoperative myocardial contractile failure. Myocardial ischemia is associated with a reduction in mitochondrial enzyme activity and have impaired metabolism resulting in decreased postoperative myocardial adenosine triphosphate (ATP) concentrations and increased lactate levels. With this in view, we measured the mitochondrial energy system (respiration and OXPHOS) and to study morphological changes from the right ventricular outflow tract (RVOT) muscle of patients with TOF.

METHODS

30 infants with TOF were studied with age-matched control group consisted of 12 normal patients who died due to extracardiac causes. Mitochondrial respiratory chain complexes, OXPHOS, cytochrome content and ATPase activity were measured by documented standard procedure. Morphological changes examined with a transmission electron microscope.

RESULTS

In the presence of glutamate and succinate as substrates, the rate of mitochondrial oxygen consumption was significantly lower in RVOT muscles (p<0.001) by using with and without addition of ADP. The ADP/O ratio indices for glutamate and succinate were not significantly affected. The activities of rotenone-sensitive NADH cytochrome c reductase (complexes I+III), cytochrome c oxidase (complex IV) and the ratio of I and III to II and III complexes (complex I) were significantly lower in TOF (p<0.001). A significant reduction of total cytochrome content and ATPase activity (p<0.001) was noted in study group. Morphological changes were also seen in study group as compared with control.

CONCLUSIONS

OXPHOS, mitochondrial respiratory chain complex I, I+III and IV, cytochrome content and ATPase activity are more impaired in RVOT muscles in patients with TOF.

Exercise MR imaging in the assessment of pulmonary regurgitation and biventricular function in patients after tetralogy of fallot repair

PURPOSE

To assess the responses of pulmonary regurgitation (PR) and biventricular function to submaximal exercise by using a magnetic resonance (MR) imaging exercise protocol with young adult patients who underwent tetralogy of Fallot repair at a young age.

MATERIALS AND METHODS

Fifteen patients with corrected tetralogy of Fallot (mean age, 17.5 years +/- 2.5 [SD]) underwent MR imaging at rest and during exercise for the evaluation of PR and biventricular function. Results were compared with findings from 16 control subjects (mean age, 17.5 years +/- 2.3). Mean age at tetralogy of Fallot repair was 2.1 years +/- 1.6, and mean follow-up time after repair was 15.4 years +/- 2.6. Exercise level at MR imaging was calculated individually and corresponded to 60% of peak oxygen uptake. The parameters of cardiac function obtained at rest and during exercise were compared by using a paired t test. An unpaired t test was used to compare parameters of cardiac function between patients and control subjects.

RESULTS

PR decreased during exercise (from 27 mL/m(2) +/- 17 to 23 mL/m(2) +/- 15; P =.012). At rest, right ventricular (RV) ejection fraction was normal (>47%) in 80% of patients. RV response to exercise in the patient group was abnormal compared with response in the control group, as demonstrated by an increase in RV end-diastolic volume index (132 mL/m(2) +/- 36 to 137 mL/m(2) +/- 38; P =.041) and no significant change in end-systolic volume index or ejection fraction. In only one patient, RV ejection fraction increased by more than 5%. Left ventricular response was not different between patients and control subjects.

CONCLUSION

MR imaging is well suited to assess cardiac response to exercise, and findings revealed a decrease in PR and an abnormal RV response to exercise in patients with corrected tetralogy of Fallot.

Left ventricular function in adults with mild pulmonary insufficiency late after Fallot repair

OBJECTIVE

To assess left ventricular function in adult Fallot patients with residual pulmonary regurgitation.

SETTING

The radiology department of a tertiary referral centre.

PATIENTS

14 patients with chronic pulmonary regurgitation and right ventricular volume overload after repair of tetralogy of Fallot and 10 healthy subjects were studied using magnetic resonance imaging.

MAIN OUTCOME MEASURES

Biventricular volumes, global biventricular function, and regional left ventricular function were assessed in all subjects.

RESULTS

The amount of pulmonary regurgitation in patients (mean (SD)) was 25 (18)% of forward flow and correlated significantly with right ventricular enlargement (p < 0.05). Left ventricular end diastolic volume was decreased in patients (78 (11) v 88 (10) ml/m(2); p < 0.05), ejection fraction was not significantly altered (59 (5)% v 55 (7)%; NS). No significant correlation was found between pulmonary regurgitation and left ventricular function. Overall left ventricular end diastolic wall thickness was significantly lower in patients (5.06 (0.72) v 6.06 (1.06) mm; p < 0. 05), predominantly in the free wall. At the apical level, left ventricular systolic wall thickening was 20% higher in Fallot patients (p < 0.05). Left ventricular shape was normal.

CONCLUSIONS

Adult Fallot patients with mild chronic pulmonary regurgitation and subsequent right ventricular enlargement showed a normal left ventricular shape and global function. Although the left ventricular free wall had reduced wall thickness, compensatory hypercontractility of the apex may contribute to preserved global function.

Quantitative analysis of collagens and fibronectin expression in human right ventricular hypertrophy

One of the main features in human tetralogy of Fallot (TF) is right ventricular hypertrophy (RVH) due to pressure (sub-pulmonary stenosis) and volume overload (ventricular septal defect). Currently, primary correction at a young age is the treatment of choice. To unravel the role of extracellular matrix in RVH, we examined myocardial expression of collagens and fibronectin in TF patients with primary correction (TF1, age 0.7 +/- 0.2 yr.), secondary surgery (TF2, age 36.9 +/- 4.6 yr), and in age-matched control patients. Sirius red staining quantified by video imaging showed significantly increased interstitial staining for collagens in both TF1 and TF2 groups as compared to respective controls. Fibronectin was expressed in extracellular spaces, perivascular regions, and in some cardiomyocytes. Quantitative analysis of fibronectin revealed increased expression in only TF1 group as compared to respective control. Our results indicate an increased amount of myocardial extracellular matrix deposition as a sign of fibrosis during RVH in patients with TF.

Right ventricular diastolic function in children with pulmonary regurgitation after repair of tetralogy of Fallot: volumetric evaluation by magnetic resonance velocity mapping

OBJECTIVES

We sought to assess right ventricular diastolic function in young patients with corrected tetralogy of Fallot and pulmonary regurgitation.

BACKGROUND

Pulmonary regurgitation is an important problem in repair of tetralogy of Fallot. Its effects on right ventricular diastolic function in children are unknown.

METHODS

Nineteen children with repair of tetralogy of Fallot (mean age [+/- SD] 12 +/- 3 years, mean age at operation 1.5 +/- 1) and 12 healthy children were studied. Summation of magnetic resonance velocity mapping pulmonary and tricuspid volume flow curves provided right ventricular time-volume curves. Ventricular size was assessed with tomographic magnetic resonance imaging (MRI). Graded exercise testing was performed.

RESULTS

Systematic and random differences (mean +/- SD) of velocity mapping and Doppler tricuspid time to peak velocities (peak E: 1 +/- 26 ms, r = 0.43; peak A: 2 +/- 11 ms, r = 0.76), E/A ratio (0.04 +/- 0.5, r = 0.63) and duration of pulmonary regurgitation (20 +/- 35 ms, r = 0.74) were satisfactory. In 6 patients (group I), late diastolic forward pulmonary artery flow was absent; in 13 patients (group II), this flow contributed 1% to 14% to right ventricular stroke volume. Significant differences were increased deceleration time (315 +/- 91 vs. 168 +/- 28 ms, p < 0.001), decreased filling fraction (44 +/- 11 vs. 55 +/- 16%, p = 0.02) and increased peak early filling rate (378 +/- 124 vs. 286 +/- 112 ml/s, p = 0.018) between control subjects and group I, and increased deceleration time (230 +/- 40, p = 0.03) between control subjects and group II. Pulmonary regurgitation, ventricular size and ejection fraction did not differ significantly between patient groups. Exercise function was diminished with restrictive right ventricular physiology (p < 0.001, group II vs. control subjects).

CONCLUSIONS

Impaired relaxation and restriction to filling affect right ventricular function in children with repair of tetralogy of Fallot and pulmonary regurgitation. Restrictive right ventricular physiology is associated with decreased exercise function.