Morphology of the native ascending aorta after the Norwood procedure for aortic atresia: impact on survival and right ventricular dysfunction.

OBJECTIVES: To evaluate the impact of variable morphology of the native ascending aorta after the Norwood I procedure in patients with hypoplastic left heart syndrome/aortic atresia on long-term survival and systemic right ventricular dysfunction. METHODS: Of 151 survivors of the Norwood procedure for hypoplastic left heart syndrome/aortic atresia at our institution between January 2001 and December 2020, we included patients with available and measurable aortography prior to stage II palliation. Diameter of the native ascending aorta, length of the native ascending aorta, and the angle between the the native ascending aorta and the proximal pulmonary artery were measured. We investigated the impact of these morphologic parameters on the mortality and the right ventricular dysfunction (defined as at least moderate). RESULTS: Angiography was available in 78 patients. Median diameter of native ascending aorta was 3.2 mm (2.6-3.7), median length of native ascending aorta was 15.4 mm (13.3-17.9), and median angle between the native ascending aorta and the proximal pulmonary artery was 44° (35° - 51°). During median follow-up of 6.5 years, eight (10%) patients died and systemic right ventricular dysfunction occurred in 19 patients (24%). No significant association between the aortic morphology and mortality could be detected. Right ventricular function was negatively affected by a larger angle between the native ascending aorta and the proximal pulmonary artery and (odds ratio 1.07 [1.01-1.14], P= 0.02). CONCLUSIONS: In survivors of the Norwood procedure for hypoplastic left heart syndrome/aortic atresia with available angiography, no significant association between the native aortic morphology and mortality could be demonstrated after stage II palliation, within the scope of this limited study. A larger anastomosis angle between the native ascending aorta and the proximal pulmonary artery emerged as a risk factor for right ventricular dysfunction.

Atrioventricular valve surgery in patients with univentricular heart and two separate atrioventricular valves.

OBJECTIVES: Atrioventricular valve regurgitation in patients with univentricular heart is a well-known risk factor for adverse outcomes and atrioventricular valve repair remains a particular surgical challenge. METHODS: We reviewed all surgical atrioventricular valve procedures in patients with univentricular heart and two separate atrioventricular valves who underwent surgical palliation. Endpoints of the study were reoperation-free survival and cumulative incidence of reoperation. RESULTS: Between 1994 and 2021, 202 patients with univentricular heart and two separate atrioventricular valve morphology underwent surgical palliation, with 15.8% (32/202) requiring atrioventricular valve surgery. Primary diagnoses were double inlet left ventricle (n = 14, 43.8%), double outlet right ventricle (n = 7, 21.9%), and congenitally corrected transposition of the great arteries (n = 7, 21.9%). Median weight at valve surgery was 10.6 kg (interquartile range, 7.9-18.9). Isolated left or right atrioventricular valve surgery was required in nine (28.1%) and 22 patients (68.8%), respectively. Concomitant left and right atrioventricular valve surgery was performed in one patient (3.1%). Closure of the left valve was conducted in four patients (12.5%) and closure of the right valve in three (9.4%). Operative and late mortality were 3.1% and 9.7%, respectively. Reoperation-free survival and cumulative incidence of reoperation at 10 years after surgery were 62.3% (standard error of the mean: 6.9) and 30.9% (standard error of the mean: 9.6), respectively. CONCLUSIONS: In patients with univentricular heart and two separate atrioventricular valves, surgical intervention on these valves is required in a minority of patients and is associated with low mortality but high incidence of reoperation.

Longitudinal analysis of systemic ventricular function and atrioventricular valve function after the Norwood procedure.

OBJECTIVES: To evaluate longitudinal systemic ventricular function and atrioventricular valve regurgitation in patients after the neonatal Norwood procedure. METHODS: Serial postoperative echocardiographic images before Fontan completion were assessed in neonates who underwent the Norwood procedure between 2001 and 2020. Ventricular function and atrioventricular valve regurgitation were compared between patients with modified Blalock-Taussig shunt and right ventricle to pulmonary artery conduit. RESULTS: A total of 335 patients were identified including 273 hypoplastic left heart syndrome and 62 of its variants. Median age at Norwood was 8 (7-12) days. Modified Blalock-Taussig shunt was performed in 171 patients and the right ventricle to pulmonary artery conduit in 164 patients. Longitudinal ventricular function and atrioventricular valve regurgitation were evaluated using a total of 4352 echocardiograms. After the Norwood procedure, ventricular function was initially worse (1-30 days) but thereafter better (30 days to stage II) in the right ventricle to pulmonary artery conduit group (P < 0.001). After stage II, the ventricular function was inferior in the right ventricle to the pulmonary artery conduit group (P < 0.001). Atrioventricular valve regurgitation between the Norwood procedure and stage II was more frequent in the modified Blalock-Taussig shunt group (P < 0.001). After stage II, there was no significant difference in atrioventricular valve regurgitation between the groups (P = 0.171). CONCLUSIONS: The effect of shunt type on haemodynamics after the Norwood procedure seems to vary according to the stage of palliation. After the Norwood, the modified Blalock-Taussig shunt is associated with poorer ventricular function and worse atrioventricular valve regurgitation compared to right ventricle to pulmonary artery conduit. Whereas, after stage II, modified Blalock-Taussig shunt is associated with better ventricular function and comparable atrioventricular valve regurgitation, compared to the right ventricle to pulmonary artery conduit.

Long-Term Survival Is Superior in Patients With Pulsatile Pulmonary Flow After the Björk Procedure.

Background: This study aims to evaluate clinical outcomes and hemodynamic variables late after the Björk procedure, regarding the pulmonary flow pattern. Methods: Patients who survived more than 15 years after the Björk procedure were included and then divided into two groups according to their pulmonary flow pattern by pulsed-wave Doppler assessment of echocardiography: patients with pulsatile systolic pulmonary flow (Group P) and those without (Group N). Results: A total of 43 patients were identified, of whom 13 patients were divided into Group P and 30 in Group N. Median age at the Björk procedure was 5.7 (2.1-7.3) years, and median follow-up was 32 (28-36) years. Survival after 15 years was higher in Group P, compared with Group N (100% vs 76% at 30 years, P = .045). Cardiac catheterization data demonstrated higher cardiac index in Group P patients compared with Group N patients (3.5 vs 2.8 L/m2, P = .014). Cardiac magnetic resonance imaging study revealed that Group P patients had higher right ventricular end-diastolic volume index (96 vs 57 mL/m2, P = .005), higher end-systolic volume index (49 vs 30 mL/m2, P = .013) and higher right ventricular stroke volume index (48 vs 25 mL/m2, P < .001), compared with Group N patients. Exercise capacity tests demonstrated that Group P patients showed a higher percent predicted peak oxygen consumption, compared with Group N patients (73 vs 58%, P < .001). Conclusions: Late after the Björk procedure, patients with a pulsatile systolic pulmonary flow had a larger right ventricle and better exercise capacity compared with those without pulsatile systolic pulmonary flow.

Longitudinal analysis of systemic ventricular function and atrioventricular valve function after the Fontan procedure.

OBJECTIVES: This study aimed to determine the longitudinal change of systemic ventricular function and atrioventricular valve (AVV) regurgitation after total cavopulmonary connection (TCPC). METHODS: In 620 patients who underwent TCPC between 1994 and 2021, 4219 longitudinal echocardiographic examinations of systemic ventricular function and AVV regurgitation were evaluated retrospectively. RESULTS: The most frequent primary diagnosis was hypoplastic left heart syndrome in 172, followed by single ventricle in 131, tricuspid atresia in 95 and double inlet left ventricle (LV) in 91 patients. Dominant right ventricle (RV) was observed in 329 (53%) and dominant LV in 291 (47%). The median age at TCPC was 2.3 (1.8-3.4) years. Transplant-free survival at 5, 10 and 15 years after TCPC was 96.3%, 94.7% and 93.6%, respectively, in patients with dominant RV and 97.3%, 94.6% and 94.6%, respectively, in those with dominant LV (P = 0.987). Longitudinal analysis of systemic ventricular function was similar in both groups during the first 10 years postoperatively. Thereafter, systemic ventricular function worsened significantly in patients with dominant RV, compared with those with dominant LV (15 years: P = 0.007, 20 years: P = 0.03). AVV regurgitation was more frequent after TCPC in patients with dominant RV compared with those with dominant LV (P < 0.001 at 3 months, 3 years, 5 years, 10 years and 15 years, P = 0.023 at 20 years). There was a significant correlation between postoperative systemic ventricular dysfunction and AVV regurgitation (P < 0.001). CONCLUSIONS: There were no transplant-free survival difference and no difference in ventricular function between dominant RV and dominant LV for the first 10 years after TCPC. Thereafter, ventricular function in dominant RV was inferior to that in dominant LV. The degree of AVV regurgitation was significantly higher in dominant RV, compared with dominant LV, and it was positively associated with ventricular dysfunction, especially in dominant RV.

Impact of pulsatile pulmonary blood flow on cardiopulmonary exercise performance after the Fontan procedure.

Objective: To evaluate the exercise capacity in patients following Fontan-Kreutzer, Fontan-Björk, and total cavopulmonary connection (TCPC). Methods: Patients who performed exercise capacity tests at least once after the Fontan procedure between 1979 and 2007 were included. Patients after Fontan-Björk procedure were divided into 2 groups according to the pulmonary blood flow (PBF) pattern: patients with pulsatile PBF and those without. Peak oxygen uptake (VO2) was measured and percent-predicted VO2 was calculated. Results: A total of 227 patients were nominated. The types of Fontan procedure included Fontan-Kreutzer in 48 (21.1%) patients, Fontan-Björk in 38 (16.7%); 11 (4.8%) with pulsatile PBF and 27 (11.9%) without pulsatile PBF; and TCPC in 141 (62.1%). Median age at the Fontan procedure was 4.5 years (interquartile range, 2.1-8.2 years). A total of 978 cardiopulmonary exercise tests were performed at median follow-up of 17.7 years (interquartile range, 11.3-23.4 years) postoperatively. Analysis using linear mixed-effects models demonstrated that percent-predicted VO2 was greater in patients with pulsatile PBF after Fontan-Björk compared with patients after other types of Fontan procedure (P < .001). The same results were obtained when the longitudinal percent predicted VO2 was performed using only patients with tricuspid atresia and double inlet left ventricle (P < .001). Conclusions: Among long-term survivors after various types of Fontan procedures, patients with pulsatile PBF after the Fontan-Björk procedure demonstrated better exercise performance compared to those after TCPC, those after the Fontan-Kreutzer procedure, and those after the Fontan-Björk procedure with non-pulsatile PBF. The results implicate the importance of pulsatile PBF to maintain the Fontan circulation.

Influence of Shunt Type on Survival and Right Heart Function after the Norwood Procedure for Aortic Atresia.

The study objective was to compare the results after Norwood procedure between modified Blalock-Taussig shunt (MBTS) and right ventricle-to-pulmonary artery conduit (RVPAC) according to Sano in patients with hypoplastic left heart syndrome (HLHS) and aortic atresia (AA). A total of 146 neonates with HLHS and AA who underwent the Norwood procedure at our institution between 2001 and 2020 were divided into 2 groups according to shunt type (MBTS or RVPAC). Survival after the Norwood procedure was compared between the groups. Longitudinal right ventricular and tricuspid valve function in each group were evaluated using cubic splines method. RVPAC was performed in 103 patients and MBTS in 43 according to surgeon preference. There were no differences in the 30-day mortality rates (16.5% vs 16.3%, P  = 0.973). Survival at 0.5, 1 and 3 years was 79.6%, 74.6%, and 68.9% in RVPAC and 66.8%, 64.3%, and 58.5% in MBTS (P  =  0.293). Among 23 patients undergoing tricuspid valve procedure, different mechanisms of tricuspid regurgitation were observed between the groups. Longitudinal analysis revealed greater prevalence of late right ventricular dysfunction in RVPAC patients. In 77 patients who completed Fontan procedure, the postoperative N-terminal pro B-type natriuretic peptide value was significantly higher in RVPAC vs MBTS (554 vs 276 ng/L, P  =  0.007). No survival advantage of RVPAC over MBTS was observed in neonates with HLHS and AA undergoing the Norwood procedure. Longitudinal analysis demonstrated a greater prevalence of right ventricular dysfunction and higher N-terminal pro B-type natriuretic peptide values during late follow-up in patients with RVPAC.

Tricuspid valve repair in children with hypoplastic left heart syndrome: impact of timing and mechanism on outcome.

OBJECTIVES: Our aim was to evaluate the results of tricuspid valve repair (TVr) in patients with hypoplastic left heart syndrome during staged reconstruction, focussing on the timing of the repair and the mechanisms of tricuspid regurgitation (TR). METHODS: Records of 44 children with hypoplastic left heart syndrome who underwent a total of 62 tricuspid valve (TV) procedures during staged reconstruction were retrospectively analysed. RESULTS: TVr was performed before stage II in 4 (9%) patients, at stage II in 23 (52%) patients, between stages II and III in 3 (7%) patients and at stage III in 14 (32%) patients. The median age at the first TV procedure was 5 months. At surgery, TR emanated commonly from the anteroseptal commissure in 21 (48%) patients. Anterior leaflet prolapse was observed most frequently (n = 23; 52%), followed by septal leaflet restriction (n = 22; 50%), dilated annulus (n = 21; 48%) and cleft anterior leaflet (n = 9; 21%). Surgical techniques included commissuroplasty in 27 (61.4%) patients, leaflet adaptation in 20 (44%) patients, partial annuloplasty in 11 (25%) patients, chordal reconstruction in 10 (23%) patients and cleft closure in 10 (23%) patients. Among all 44 patients, 27 (61%) patients had preoperative grade III TR and 17 (39%) patients had grade IV; postoperatively, there were no patients with grade IV, 25 patients with grade III (57%), 10 patients with grade II (23%) and 6 patients with grade I (14%). Fifteen patients required redo TV surgeries. Reoperation-free survival was 52% at 5 years. Lower weight at initial TVr predicted mortality [hazard ratio (HR) 0.7, P = 0.044] and reoperation (HR 0.8, P = 0.015). TVr before stage II was a risk for both reoperation (HR 5.5, P = 0.042) and TV replacement (HR 36.9, P = 0.013). Among morphological factors, septal leaflet restriction was a risk for reoperation (HR 4.7, P = 0.017) and anterior (HR 4.7, P = 0.037) and posterior (HR 7.3, P = 0.015) leaflet chordal anomaly for TV replacement. CONCLUSIONS: Anterior leaflet prolapse and septal leaflet restriction are the main mechanisms of TR in hypoplastic left heart syndrome. Early-onset TR before stage II predicts worse outcome. Refinements to repair techniques in early infancy, especially for septal leaflet restrictions and chordal anomalies, are mandatory to improve outcomes.

Impact of Characteristics at Stage-2-Palliation on Outcome Following Fontan Completion.

The optimal timing of stage-2-palliation (S2P) in single left ventricle is not clear. The aim of this study was to identify S2P related factors associated with outcomes after total cavopulmonary connection (TCPC), particularly relative to the dominant systemic ventricle. A total of 405 patients who underwent both S2P and TCPC at our institute between 1997 and 2017 was included. Patients were divided into two groups, dominant right ventricle (RV type, n = 235) and dominant left ventricle (LV type, n = 170). S2P related factors associated with mortality, postoperative ventricular function, and late exercise capacity following TCPC, were analyzed. The median age at S2P was 4 [3-7] and 6 [3-11] months in RV and LV type patients, respectively (p = 0.092). Survival after TCPC was similar in RV and LV type patients (p = 0.280). In those with RV type, risk factors for mortality following TCPC were older age (p < 0.001), heavier weight (p = 0.001), higher PAP (p < 0.001), higher TPG (p = 0.010), and lower SO2 (p = 0.008) at S2P. In those with LV type, no risk factor was identified. Risk factors for postoperative impaired ventricular function were older age and higher weight at S2P in both RV and LV type patients. Older age at S2P was also identified as a risk for inferior peak oxygen uptake (VO2) years after TCPC both in RV and LV type patients. Older age at S2P was associated with higher mortality after Fontan completion only in RV type patients. However, it was associated with postoperative ventricular dysfunction and lower exercise capacity after TCPC in both RV and LV type patients.

Long-term outcome of preadolescents, adolescents, and adult patients undergoing total cavopulmonary connection.

OBJECTIVES: Patients with a single ventricle infrequently undergo total cavopulmonary connection as preadolescents, adolescents, or adults. The purpose of this study was to clarify the characteristics of this cohort and to analyze the factors influencing outcomes. METHODS: Between 1994 and 2015, 50 of 460 patients underwent total cavopulmonary connection as preadolescents, adolescents, or adults (group A). The patients' characteristics and operative results were compared with those of the remaining 410 patients aged less than 9 years who underwent total cavopulmonary connection (group B). Post-total cavopulmonary connection echocardiogram reports (n = 4862) were used to evaluate longitudinal ventricular function, and ejection fraction was characterized using nonlinear mixed-effects models and compared between groups. RESULTS: The median follow-up time was 10.3 (2.8-15.5) years. The differences between groups in 30-day mortality (P = .20), intensive care unit stay (P = .20), and incidence of prolonged effusion (P = .08) were not significant. The estimated survival at 15 years was lower in group A (86.5%) than in group B (94.0%, P = .04) patients. Long-term systemic ventricular ejection fraction, analyzed with linear mixed-effect models, was significantly reduced in group A than in group B patients (P < .001). At a median postoperative period of 8.4 (7.1-10.5) years, the peak oxygen uptake as measured by exercise capacity testing was lower in group A than in group B patients, respectively (22.3 ± 6.5 [n = 25] vs 30.6 ± 8.1 [n = 100] mL/kg/min, P < .001). CONCLUSIONS: The total cavopulmonary connection procedure was performed in preadolescent, adolescent, and adult patients with no significant difference in 30-day or hospital mortality compared with those in young children. However, long-term survival and ventricular performance were reduced in this older cohort.

Outcomes of a total cavopulmonary connection in patients with impaired ventricular function.

OBJECTIVES: Our aim was to evaluate outcomes following a total cavopulmonary connection (TCPC) in patients with preoperatively impaired ventricular function (VF). METHODS: Of 483 consecutive TCPC patients, 44 (9.1%) had impaired VF (ejection fraction <50%, Group A), and 439 patients had normal VF (ejection fraction ≥50%, Group B). We compared the clinical outcomes between the groups. RESULTS: The median age at TCPC was 2.8 (interquartile range 1.9-8.3) years in Group A and 2.3 (1.8-3.5) years in Group B (P = 0.025). An atrioventricular valve (AVV) operation prior to (38.6 vs 27.1%, P < 0.001) and concomitant with (31.8 vs 12.1%, P < 0.001) the TCPC was performed more frequently in Group A. The median intensive care unit stay (7.0 vs 7.0 days, P = 0.737) and 30-day survival (97.7 vs 98.4%, P = 0.737) were not significantly different between groups. Freedom from death, transplantation (P = 0.115) and catheter intervention (P = 0.603) showed no difference between groups. However, freedom from cardiac reoperation was significantly lower in Group A (P < 0.001). VF was resolved in 22 of the 39 (56.4%) survivors in Group A. The recovered patients had a lower incidence of AVV reoperation (0 vs 6, P = 0.002) and pacemaker rhythm (0 vs 5, P = 0.006). CONCLUSIONS: In patients planned for TCPC, impaired VF is often associated with AVV regurgitation. TCPC can be performed with low risk and comparable clinical results except for cardiac reoperation in patients with impaired VF when compared to patients with normal VF. Following TCPC, VF recovers in half of the survivors. A competent AVV and sinus rhythm are prerequisites for recovery.

Non-volumetric echocardiographic indices and qualitative assessment of right ventricular systolic function in Ebstein's anomaly: comparison with CMR-derived ejection fraction in 49 patients.

AIMS: Ebstein's anomaly (EA) is often associated with right ventricular (RV) dysfunction. Data on echocardiographic quantification of RV function are, however, rare. The aim of this study was to determine how non-volumetric echocardiographic indices and qualitative assessment of global systolic RV function correlate with cardiovascular magnetic resonance (CMR)-derived RV ejection fraction (EF). METHODS AND RESULTS: We compared six echocardiographic indices and qualitative assessment of RV function with the gold standard CMR. A total of 49 unoperated patients with EA and a mean age of 32 ± 18 years were examined. Tricuspid annular plane systolic excursion, tissue Doppler myocardial velocities (peak S and IVA) and 2D strain and strain rate measures for the RV were compared with CMR-derived EF. Only 2D global longitudinal strain (2D-GLS), out of the six parameters investigated, showed a weak, although statistically significant correlation with CMR-derived RVEF (R = -0.4, P = 0.01). Using a cut-off value of -20.15, 2D-GLS sensitivity (77%) and specificity (46%) in detecting patients with a CMR-derived EF of <50% were comparable with qualitative assessment (sensitivity 77%, specificity 45%). CONCLUSION: Overall echocardiographic parameters of RV function correlate poorly with CMR-derived EF in patients with EA. Only 2D global longitudinal RV strain correlated weakly with CMR-derived RVEF. However, the sensitivity and specificity for detecting RV dysfunction using 2D strain imaging were comparable with qualitative RV functional assessment.

Continuous infusion of clonidine in ventilated newborns and infants: a randomized controlled trial.

OBJECTIVES: To assess the influence of an infusion of clonidine 1 µg/kg/hr on fentanyl and midazolam requirement in ventilated newborns and infants. DESIGN: Prospective, double-blind, randomized controlled multicenter trial. Controlled trials.com/ISRCTN77772144. SETTING: Twenty-eight level 3 German PICUs/neonatal ICUs. PATIENTS: Ventilated newborns and infants: stratum I (1-28 d), stratum II, (29-120 d), and stratum III (121 d to 2 yr). INTERVENTIONS: Patients received clonidine 1 µg/kg/hr or placebo on day 4 after intubation. Fentanyl and midazolam were adjusted to achieve a defined level of analgesia and sedation according to Hartwig score. MEASUREMENTS AND MAIN RESULTS: Two hundred nineteen infants were randomized; 212 received study medication, 69.7% were ventilated in the postoperative care and 30.3% for other reasons. Primary endpoint: consumption of fentanyl and midazolam in the 72 hours following the onset of study medication (main observation period) in the overall study population. The confirmatory analysis of the overall population showed no difference in the consumption of fentanyl and midazolam. Explorative age-stratified analysis demonstrated that in stratum I (n = 112) the clonidine group had a significantly lower consumption of fentanyl (clonidine: 2.1 ± 1.8 µg/kg/hr, placebo: 3.2 ± 3.1 µg/kg/hr; p = 0.032) and midazolam (clonidine: 113.0 ± 100.1 µg/kg/hr, placebo: 180.2 ± 204.0 µg/kg/hr; p = 0.030). Strata II (n = 43) and III (n = 46) showed no statistical difference. Sedation and withdrawal-scores were significantly lower in the clonidine group of stratum I (p < 0.001). Frequency of severe adverse events did not differ between groups. CONCLUSIONS: Clonidine 1 µg/kg/hr in ventilated newborns reduced fentanyl and midazolam demand with deeper levels of analgesia and sedation without substantial side effects. This was not demonstrated in older infants, possibly due to lower clonidine serum levels.

Tricuspid valve surgery improves cardiac output and exercise performance in patients with Ebstein's anomaly.

BACKGROUND: Clinical, hemodynamic and functional effects of tricuspid valve surgery in patients with Ebstein's anomaly are not well understood. METHODS: Sixteen patients (median age of 27.7 years) were examined before and eight months after surgery by means of echocardiography, cardiovascular magnetic resonance (CMR) and cardiopulmonary exercise testing. RESULTS: Peak work load (1.87 to 2.0W/kg; p=0.026), maximum oxygen uptake (21 to 22 ml/kg/min; p=0.034) as well as cardiac output (2.7 to 2.9l/min/m(2); p=0.035) increased postoperatively. The reduction of tricuspid regurgitation led to a higher pulmonary stroke volume (29 to 42ml/m(2), p=0.005) and augmented the left ventricular (LV) volume (55 to 63ml/min/m(2); p=0.001) with a trend to better ejection fraction (61 to 64%; p=0.083). Right ventricular (RV) volume index (124 to 108ml/m2; p=0.034) and ejection fraction (50 to 42%; p=0.036) decreased on CMR. Echocardiographic measurements of RV function also decreased (tricuspid annular plane systolic excursion 2.3 to 1.7; p=0.002; isovolumic acceleration 0.98 to 0.65; p=0.004; and 2-d longitudinal global strain -19.3 to -16.25; p=0.006). CONCLUSION: Tricuspid valve surgery improves exercise capacity in patients with Ebstein's anomaly. The reduction of tricuspid regurgitation decreases the volume of the right ventricle and increases pulmonary antegrade flow. As a result LV volume and cardiac output increase. This hemodynamic benefit occurs despite the preload dependent reduction in RV volume and ejection fraction.