Summary
Background
Although dysfunction of the systemic right ventricle (RV) in patients with complete transposition of the great arteries (TGA) after atrial redirection by Mustard or Senning procedures is well recognized, there are few data on systemic RV geometry and function. Echocardiography is a widely available imaging technique that is particularly suitable for clinical follow-up because of its non-invasive nature, low cost and lack of ionizing radiation.
Aim
To examine the feasibility and variability of transthoracic echocardiography variables in the assessment of the systemic RV.
Methods
Multivariable transthoracic echocardiographic analysis, including assessment of global function variables (RV ejection fraction [RVEF; Simpson’s method], RV fractional shortening [RVFS] and dP/dt), longitudinal function variables (tricuspid annular plane systolic excursion [TAPSE], peak systolic velocity at the junction of the RV free wall and the tricuspid annulus, assessed with pulsed tissue Doppler imaging [S’ TDI]), tricuspid regurgitation and asynchrony, was performed in 35 consecutive patients with TGA after atrial redirection. Functional variables were compared with magnetic resonance imaging (MRI). Inter- and intraobserver echocardiographic analysis variability was assessed in ten randomly selected cases.
Results
Global and longitudinal function variables were not correlated with RVEF calculated by MRI, except for S’ TDI, which was weakly correlated ( P = 0.02, r = 0.37). Asynchrony assessment was feasible in all patients. Inter- and intraobserver echocardiographic analysis variability was high for RVEF, RVFS and dP/dt (> 10%), and low for TAPSE and S’ TDI (5%).
Conclusion
Owing to geometric changes, presumed contractility pattern shift and retrosternal position, conventional echocardiographic variables are not relevant for RV function assessment. Assessment of asynchrony and tricuspid regurgitation is easily feasible in routine practice and highly reproducible. Echocardiography does not permit complete assessment of the systemic RV after atrial redirection but is fully complementary with MRI and should not be abandoned. Future improvements in transducers and dedicated software should permit major improvements in the near future.
Résumé
Contexte
Bien que la dysfonction du ventricule droit systémique soit connue chez les patients porteurs d’une transposition des gros vaisseaux (TGV) opérés par technique de Senning ou Mustard, il existe peu de données sur sa géométrie et ses paramètres fonctionnels. L’échocardiographie transthoracique (ETT) est la modalité d’imagerie la plus utilisée dans l’exploration cardiaque en raison de son caractère non invasif, non irradiant, accessible et peu couteux.
Objective
Notre étude a pour but d’évaluer la corrélation entre l’imagerie par résonance magnétique et l’échocardiographie cardiaque transthoracique dans l’approche du ventricule droit systémique.
Méthodes
Trente-cinq patients porteurs d’une TGV opérée par Senning/Mustard ont bénéficié d’une IRM et d’une ETT au repos. Une analyse échographique mutiparamètrique de la fonction systolique du VD a été effectuée : fraction d’éjection du ventricule droit par méthode Simpson, fraction de raccourcissement de surface, dP/dt, index de Tei, TAPSE, S’TDI), ainsi qu’une quantification de l’insuffisance tricuspide et une analyse de l’asynchronisme inter et intraventriculaire. Les marqueurs de la fonction systolique ont été comparés avec le fraction d’éjection du ventricule droit à l’IRM, considéré comme le gold standard dans l’évaluation du ventricule droit systémique. Une étude de la variabilité intra- et interobservateur à également été réalisé sur dix patients randomisés.
Résultats
De tous les différents paramètres de la fonction systolique du ventricule droit (FEVD, FR, dP/dt, index de Tei, TAPSE, S’ TDI) seul le S’ TDI est corrélé avec la FEVD à l’IRM ( p = 0,02, r = 0,37). L’étude de l’asynchronisme a été faisable chez tous les patients. Pour l’analyse de la variabilité en inter- ou intraobservateurs, on retrouve une variabilité importante (10 à 20 %) pour la fraction d’éjection du ventricule droit (RVEF), et la dP/dt mais faible pour le TAPSE ou le S’ TDI (< 5 %).
Conclusion
L’ETT présente donc des avantages et des inconvénients dans l’exploration des TGV opérées par switch atrial. En effet, les phénomènes adaptatifs du ventricule droit en position systémique, telles que l’hypertrophie ou les modifications supposées de la mécanique contractile au profit de la composante radiale, ainsi que la position rétrosternale, rendent son approche plus difficile. Néanmoins, elle présente des avantages indéniables comme l’étude de la fuite tricuspide et de l’asynchronisme. L’ETT apparaît donc comme complémentaire de l’IRM et ne doit pas être abandonnée. De nouvelles techniques échocardiographiques à l’étude devraient améliorer des améliorations dans un futur proche.
Introduction
Despite excellent surgical results, atrial switch operations (Mustard or Senning procedures ) in patients with complete transposition of the great arteries (TGA) are associated with increased late mortality, mainly because of heart failure and sustained ventricular tachycardia secondary to failure of the morphologic right ventricle (RV) in the systemic (subaortic) position. Evidence is accumulating that deterioration of right ventricular (RV) function and clinical status is progressive . Hence, accurate assessment of RV function is mandatory to anticipate the need for heart failure treatment in these patients.
Various imaging modalities have been used to evaluate the systemic RV, including angiography, radionuclide imaging and magnetic resonance imaging (MRI) . Nevertheless, in clinical practice, echocardiography is still used predominantly for the assessment of RV function, as it is non-invasive, widely available, relatively inexpensive and has no adverse side effects. However, because of complex geometry, the assessment of systemic RV function by echocardiography has remained mostly qualitative.
Advances in digital echocardiography allow for a more refined assessment of the RV, as demonstrated in patients with pulmonary arterial hypertension or other clinical conditions. These novel echocardiography variables may also be valuable in the functional assessment of the systemic RV .
To redefine the role of echocardiography in the functional assessment of the systemic RV, we investigated the feasibility and variability of standard and novel echocardiographic variables in the assessment of the systolic function of the systemic RV, compared with MRI. Additional variables involved in heart failure physiopathology, such as inter- and intraventricular asynchrony and tricuspid regurgitation, were also studied.
Methods
Patients
We enrolled 35 clinically stable patients with TGA who had undergone atrial redirection by the Senning or Mustard procedures in childhood, attended the Adult Congenital Heart Disease Clinic at the University Hospital of Bordeaux and were in sinus or regular junctional rhythm. The institutional review board approved the study and all subjects gave informed consent. Transthoracic echocardiography and MRI at rest were performed on the same or on the subsequent day, according to the following protocols.
Echocardiography
Standard echocardiography
Transthoracic echocardiography was performed using Vivid 7 ® (GE Vingmed Ultrasound A.S., Horten, Norway) by two experienced cardiologists (A.H., I.X.). All echocardiographic recordings were stored on digital versatile discs for offline analyses. Measurements were made in three cardiac cycles and average values were used for statistical analyses. Intra- and interobserver variability was analysed on the basis of two consecutive results from ten randomly selected patients.
Fig. 1 gives an overview of common echocardiographic variables for RV function, which were also used in the current study. In the apical four-chamber view, RV end-diastolic and end-systolic diameters and areas were assessed. From these measurements, we calculated RV fractional shortening (RVFS) and we estimated RV ejection fraction (RVEF) by Simpson’s one-plane method . Tricuspid annular plane systolic excursion (TAPSE) was assessed in M-mode. Using colour Doppler, tricuspid valve regurgitation was semiquantitatively graded as mild, moderate or severe. Peak systolic velocity (S’) at the junction of the RV free wall and the tricuspid annulus was assessed with pulsed tissue Doppler imaging (TDI) (S’ TDI). RV dP/dt max was estimated from regurgitation along the tricuspid valve using echo Doppler. RV myocardial performance index, also known as the Tei index and defined as the sum of the isovolumic contraction and the isovolumic relaxation time divided by the ejection time, was also assessed by Doppler echocardiography .
Two-dimensional longitudinal strain assessment of the RV
Myocardial deformation imaging by two-dimensional (2D) strain, as an index of contractile function, is based on frame-by-frame tracking of acoustic markers within the myocardial region of interest on greyscale echocardiographic images . In the apical four-chamber view, the myocardium was automatically tracked and divided into six segments ( Fig. 3 ). Global systolic strain was assessed in the longitudinal direction.
Asynchrony
To measure inter- and intraventricular dyssynchrony, regional longitudinal strain was assessed in the basal and mid segments of the RV free wall, the interventricular septum (IVS) and the left ventricular (LV) free wall. The average time from the onset of QRS to peak strain of the basal and mid segments (Tε) was calculated for the RV free wall, the IVS and the LV free wall. Right intraventricular mechanical delay was defined as the difference in Tε between the RV free wall and the IVS (ΔTεRV–IVS); the interventricular mechanical delay was defined as the difference in Tε between the RV and LV free walls (ΔTεRV–LV).
We also used the TDI technique for the assessment of intraventricular asynchrony with different delays in apical four-chamber view, in Doppler pulsed on the free wall and on the interventricular septum. We studied electromechanical and electrosystolic delays.
MRI acquisition and data postprocessing
MRI was performed in 35 patients on a 1.5T system (Sonata; Siemens, Erlangen, Germany) with a phased-array radiofrequency receiver coil placed on the chest. All images were gated to the electrocardiogram. Double oblique long-axis and four-chamber scouts were acquired to obtain true short-axis reference. Steady-state free-precession prospective electrocardiogram-gated breath-hold images, encompassing the whole RV, were then acquired in short-axis orientation with no gap between slices (TrueFISP sequence; slice thickness 7 mm; TE 1.53 ms; TR 33.6 ms, depending on the R–R interval; matrix 256 × 256 mm; field of view 38 cm). RV end-systolic and end-diastolic volumes (RVESV and RVEDV, respectively) and RVEF were measured on a postprocessing workstation (Leonardo, Siemens) using commercially available software (Syngo Argus; Siemens) by a radiologist with 15 years’ experience in cardiac MRI and blinded to the results of echocardiographic evaluation.
Statistical analysis
Data are presented as mean ± standard deviation. Agreement between RVEF assessed by echocardiography and by MRI (“gold standard”; MRI-RVEF) was evaluated using the Bland-Altman analysis. Relationships between other echocardiographic variables and MRI-RVEF were evaluated by Pearson’s correlation coefficient. A P value < 0.05 was considered statistically significant. Statistical analyses were performed using Stata 8.0 (StataCorp, College Station, TX, USA).
Results
Study population
Thirty-five patients were included, all of whom had had atrial redirection for TGA; of these, 31 had undergone the Senning procedure and four had undergone the Mustard procedure. Nine patients had associated ventricular septal defect and are therefore referred to as ‘complex TGA’; in these patients, the ventricular septal defect was closed at the time of the atrial redirection surgeries, without residual leaks. Patient characteristics at study inclusion are presented in Table 1 . Mean age at examination was 23 ± 8 years. Most patients were in New York Heart Association (NYHA) function class I (88%).
| Age (years) | 23 ± 8 |
| Men/women | 26/9 (74/26) |
| Body mass index (kg/m 2 ) | 21.4 ± 3.5 |
| Simple/complex TGA | 26/9 (74/26) |
| Senning/Mustard | 31/4 (89/11) |
| NYHA classification | |
| I | 31 (88) |
| II | 2 (6) |
| III | 2 (6) |
| IV | – |
| Pharmacological treatment | |
| Beta-blockers | 5 (14.2) |
| ACE inhibitors | 5 (14.2) |
| Platelet-suppressive agents | 4 (11.4) |
| Vitamin K antagonists | 4 (11.4) |
| Diuretics | 2 (5.7) |
| Antiarrhythmic agents | 6 (17.1) |
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