Right ventricular free wall strain predicts functional capacity in patients with repaired Tetralogy of Fallot
Arroyo-Rodríguez C, Fritche-Salazar JF, Posada-Martínez EL, Arías-Godínez JA, Ortiz-León XA, Calvillo-Arguelles O, Ruiz-Esparza ME, Sandoval JP, Sierra-Lara D, Araiza-Garaygordobil D, Picano E, Rodríguez-Zanella H.
Int J Cardiovasc Imaging. 2020 Apr;36(4):595-604. doi: 10.1007/s10554-019-01753-z. Epub 2020 Jan 1.
Take home point:
- Right ventricular free wall longitudinal strain may be useful as a surrogate marker for low functional capacity in patients with repaired tetralogy of Fallot with severe pulmonary regurgitation (PR).
Commentary from Dr. Helen Parry (Leeds UK), section editor of ACHD Journal Watch: Functional capacity can be a useful guide to pulmonary valve replacement in patients with repaired tetralogy of Fallot who are on the borderline for intervention according to current guidelines. However, many patients are unable to exercise well due to non-cardiac reasons. This study looked at surrogate markers for impaired functional capacity to help guide management in borderline cases for pulmonary valve replacement.
Thirty-three patients were included in the study. Inclusion criteria were previous tetralogy of Fallot repair, NYHA class 1, no other significant cardiac abnormality such as AVSD and severe pulmonary regurgitation (PR). Severe PR was defined according to the following criteria:
- Jet: pulmonary annulus diameter >=0.7
- Pressure half time <100ms
- Diastolic flow reversal in the pulmonary branches
- PR index <0.77
The level of PR was classed as severe if 3 of the above criteria were fulfilled, or 2 if PR index<0.77.
Exercise echocardiography was performed using a bike with initial workload of 25W, increasing by 25 W every 2 mins. Patients who managed <7 METS were categorised as low functional capacity.
Strain imaging was performed using a GE machine and analysis was performed offline using the EchoPAC software. Inter-observer variability was assessed by repeat analysis by the same operator with a 2 week difference period.
Statistical analysis was performed by dividing the patients into 2 groups: low and normal functional capacity. Comparisons were made using the Students t-test for normally distributed variables and Wilcoxon sum rank test for non-parametric variables.
Twenty- two patients had normal functional capacity relative to 11 in the low functional capacity group.
The following variables were associated with low functional capacity, p value<0.05:
- Female gender
- Short stature
- Previous shunt palliation
- LV contractile reserve
- Right ventricular free wall longitudinal strain <17%
Right ventricular free wall longitudinal strain may be useful as a surrogate marker for low functional capacity in patients with repaired tetralogy of Fallot with severe PR.
Strengths of the study:
- Timings for pulmonary valve replacement are a continued subject of debate- many clinicians believe we should be doing this at an earlier stage.
- Limited literature regarding the uses of newer echo techniques here, this study is an important contribution to the literature.
- Suggests a useful alternative to exercise testing in these borderline patients.
Weaknesses of the study:
- Very small sample size, only 11 patients in the low functional capacity group-can statistically meaningful associations genuinely be found in such a small sample?
- Strain imaging is both machine specific and supplier specific- many departments do not use GE systems, the cut-off for right ventricular wall strain is likely to be different across manufacturers.
- Many patients do not have adequate echo windows for reliable RV strain imaging.
- Inter-observer variability was tested by the same reporter reviewing the scans with 2 weeks difference. Two individuals performing analysis and testing agreement between the 2 would be a better way of looking at inter-observer variability.