Right ventricular end-diastolic volume (RVEDV) greater than 150 mL/m 2 is a risk factor for sudden death in patients with tetralogy of Fallot (TOF) after repair. Because of its anterior placement and abnormal geometry, two-dimensional echocardiography is limited to a qualitative assessment of RVEDV. Cardiac magnetic resonance imaging (CMRI) and computed tomography angiography (CTA) are the accepted standards for quantifying RVEDV. This study evaluated the ability of a novel echocardiographic measure, the right ventricular annular tilt (RVAT), to identify patients with increased RVEDV.
All patients with repaired TOF with an echocardiogram and CMRI or CTA were included in this retrospective study. The RVAT was determined by measuring the angle of the tricuspid valve plane relative to the mitral valve plane at end-diastole in the apical 4-chamber view in study ( n = 38) and age-matched control ( n = 74) patients. The RVEDV measurements were obtained by CMRI ( n = 32) or CTA ( n = 6). The study and control patients’ ages were no different (11.3 and 11.8 years, P = .73).
The study group RVAT was significantly higher than the control group RVAT (17.4 vs. 0.1 degrees; P < .0001). RVAT values greater than 20 degrees had a mean RVEDV of 166 ± 60 mL/m 2 , whereas RVAT less than 20 degrees had a mean RVEDV of 122 ± 25 mL/m 2 ( P = .0370). Receiver operating characteristic analysis demonstrated an RVAT of 17.9 degrees as the cutoff for predicting a RVEDV of greater than 150 mL/m 2 with a sensitivity of 75% and specificity of 73% (area under the curve = 0.76; confidence interval, 0.56-0.96; P = .0063). Intraclass correlation analysis demonstrated minimal interobserver and intraobserver variability when measuring RVAT (0.99 and 0.92).
An RVAT less than 20 degrees is associated with an RVEDV less than 150 mL/m 2 . RVAT is a useful echocardiographic technique for detecting increased RVEDV in patients with TOF and may help discern which patients should undergo RVEDV quantification by CMRI or CTA.
Right ventricular enlargement is an important risk factor for ventricular arrhythmias, right ventricular failure, and sudden death in patients with repaired tetralogy of Fallot (TOF). These patients typically have pulmonary regurgitation as a result of a transannular patch repair or an incompetent right ventricular to pulmonary artery conduit that leads to right ventricular enlargement. Pulmonary valve replacement can minimize right ventricular enlargement progression and potentially reverse the right ventricular size through remodeling, which is still possible when the right ventricular end-diastolic volume (RVEDV) is 150 mL/m 2 . Because of its anterior placement and abnormal geometry, two-dimensional echocardiography is limited to a qualitative assessment of RVEDV. Cardiac magnetic resonance imaging (CMRI) and computed tomography angiography (CTA) are the accepted standards for quantifying RVEDV. This study evaluated the ability of a novel echocardiographic measure, the right ventricular annular tilt (RVAT), to identify patients with increased RVEDV.
Materials and Methods
All patients with repaired TOF who had both an echocardiogram and a CMRI/CTA study at the Lucile Packard Children’s Hospital Heart Center between January 1, 2001, and November 30, 2009, were initially selected for this retrospective study. Patients who had a time interval of more than 6 months between echocardiogram and CMRI/CTA were excluded from further evaluation. In addition, any patient with an associated atrioventricular canal repair was also excluded because both atrioventricular valves were at the same level, and this may affect the RVAT. Age and body surface area-matched controls were selected by querying the database for patients without structural heart disease or cardiac dysfunction. Approximately double the number of study patients were selected as controls. Each patient’s body surface area using the Mosteller formula; gender, date of birth, date of death, and type of prior surgical intervention were obtained from patients’ electronic medical records. This study was approved by the Stanford University Institutional Review Board.
The ultrasound equipment used for the echocardiographic studies was the Siemens Sequoia C512, rev 12.0 (Siemens Medical Solutions USA, Inc., Mountain View, CA) or the Phillips IE33 (Philips Medical Systems, Bothell, WA). All offline measurements were made using syngo Dynamics workstation (Siemens Medical Solutions USA, Inc, syngo Dynamics Solutions, Ann Arbor, MI). The data were collected from the apical four-chamber view. The RVAT was measured at end-diastole, when the tricuspid valve leaflets coapt, by drawing two lines: 1) The baseline is drawn from the mitral valve annular insertion at the interventricular septum to the mitral valve annular insertion at the posterolateral wall; and 2) the line of the angle is drawn from the tricuspid valve annular insertion at the anterolateral wall to the interventricular septum, to connect with the baseline at the interventricular septum ( Figure 1 ). The RVAT was obtained from the four-chamber view. Because this measurement only depends on the angle between the tricuspid and mitral valve from the apical window, this view was considered acceptable if both atrioventricular valves were well seen in their entirety, and the image was obtained from an apical window.
The RVAT was obtained on all study and control patients. Given that the tricuspid valve is lower than the mitral valve in normal patients, some angles less than 0 degrees were anticipated in the control group. When available, each subject had three RVAT measurements from separate echocardiogram clips in the control and study group by one observer; these values were then averaged. The echocardiogram clip and frame number were recorded for each RVAT for reference. An independent reader also measured a subset of 10 studies within each patient group, blinded to the primary readers’ results using the same recorded clip and frame number. An additional 20 patients without structural heart disease or cardiac dysfunction were prospectively analyzed to ensure there was no respiratory variability when deriving an RVAT. The measurement was obtained at end-inspiration and end-expiration.
In addition to RVAT, other echocardiographic measurements in the study patients included the degree of tricuspid/pulmonary regurgitation, right ventricular outflow tract obstruction, and right atrial enlargement. A qualitative grade of pulmonary regurgitation was assigned by determining the width of the regurgitant jet compared with the right ventricular outflow tract diameter, the presence of flow reversal in the branch pulmonary arteries, and the pulmonary regurgitation deceleration time. The pulmonary regurgitation index by M-mode echocardiography was not assessed because M-mode through the right pulmonary artery was not performed. The degree of tricuspid valve regurgitation was determined by examining the vena contracta, and right atrial enlargement was assessed subjectively. Study patients were grouped into two groups according to right atrial size, moderate or greater right atrial enlargement, and mild or no right atrial enlargement. The RVAT was compared between these groups. The images were reviewed by two of the authors (TT/RP), and a consensus grade was obtained for all the study patients. Continuous-wave Doppler was used to assess the degree of right ventricular outflow tract obstruction; velocities were anticipated to be higher in all patients given the expected pulmonary regurgitant volume.
Parametric testing was used to compare data with normal distributions, such as age, RVAT, and RVEDV. All comparisons of RVAT and ages were performed with the Student t test, and the paired t test was used to compare the RVAT at end-inspiration and end-expiration. Intraclass correlation coefficients were establish for interobserver and intraobserver variability analysis for the patients with three RVAT measurements. Nominal data were compared using the chi-square test. Receiver operating characteristic (ROC) curve analysis was used to determine the cutoff for predicting a right ventricular volume of 150 mL/m 2 . A P value of less than .05 was considered statistically significant. All statistical calculations were performed using the SAS Enterprise Guide version 4.2 (SAS Institute Inc, Cary, NC) and Microsoft Excel (Redmond, WA).
Thirty-eight patients were included in the study, of whom 32 had CMRI studies. The remaining six patients had CTA studies ( Table 1 ). All of these patients had echocardiograms performed within an average of 67 ± 121 days of the CMRI or CTA study. Seventy-four age-matched controls were included. There was no difference in mean age (study mean age 11.3 ± 11.0 years, control mean age 11.8 ± 4.8 years; P = .73) or patient size (study mean size 1.3 ± 0.7 m 2 , control mean size 1.3 ± 0.5 m 2 ; P = .98) between study and control groups ( Table 2 ). Fifty-seven percent of the control patients were male, and 37% of the study group were male ( P = .0725). The RVAT among male and female patients in the study group was 17.9 ± 11.9 degrees and 16.5 ± 8.0 degrees, respectively ( P = .6818). The control group RVAT had a small difference of 2.9 degrees that did not quite achieve statistical significance (female = −0.8 ± 7.5 degrees vs males 2.1 ± 5.23 degrees, P = .07).
|Demographic data||MRI/CT-derived data||Echocardiogram-derived data|
|Pt||Diagnosis||Age y||Prior intervention||Mode||RV EDV mL/m 2||RV ESV mL/m 2||RV EF %||PR %||Avg RVAT||TR||PR||RAE||ECG QRSD ms|
|30||TOF ∗||9||RV-PA conduit||MRI||183.0||123.4||32.6||35.0||57.9||mod||severe||mild||NA|