BPD is a chronic lung disease that, throughout the influence of multiple factors, generates lung alterations, not only in the airway but also on the pulmonary vessels, leading to a variable worsening on the cardiopulmonary function. Last advances on perinatal medicine have allowed to decrease its incidence, but BPD is still the responsible for significant morbidity on preterm infants (3). PH is a rare complication after suffering from BPD, but it is known that it the appearance PH worsens the clinical course, morbidity and mortality of BPD (13). The gold standard technique for the diagnosis of PH y cardiac catheterization, an invasive procedure requiring general anesthesia in young children. It allows a direct measurement of the pulmonary arterial pressure (PAP). However, transthoracic echocardiography is more commonly used in children for its ability to estimate PAP and its consequences on RV (14). Mourani et al. did a retrospective review of data from 25 infants who underwent echocardiography and subsequent cardiac catheterization for the evaluation of pulmonary hypertension. Compared with cardiac catheterization, echocardiography had 79% sensitivity for the presence of pulmonary hypertension (15).
Several traditional echocardiographic measurements are usually used on PH screening. Tricuspid regurgitation pressure gradient (TRPG) represents the most common and reliable method to evaluate the presence and severity of PH (6). In our study, TRPG was used to exclude patients with PH. Other echocardiographic methods have been studied to analyze RV function in preterm infants. Sehgal et al. assessed RV function using tissue Doppler imaging (TDI), 2D RV-FS, TAPSE, and myocardial performance index (MPI) using echocardiography. They found that higher E/E and lower RV-FS showed strong correlations with the subsequent duration of respiratory support during hospitalization. The rest of parameters had no relevance. Although in normal values (16), our sample showed lower RV-FS in BPD group at T1, with correlate with their results. However, there is lack of evidence in the literature about the echocardiographic management of these patients.
It´s known that RV strain is a feasible technique (8, 17). RV strain predicts mortality in a population of stable patients with chronic heart failure with reduced LV ejection fraction independent (18), predicts the prognosis after acute myocardial infarction in adults (19) or mortality in patients with COVID-19 (20). RV strain has also been exposed as an useful tool in the evaluation of RV in PH patients of several etiologies (21, 22).That´s why authors decided to study GLS, in order to inquire if added value was shown. Xie et al. evaluated strain in children between 3-5 years old. They found some differences in RV strain between preterm BDP patients and term infants and also that duration of invasive ventilation was as an independent determinant of GLS-RV (23). Our cohort compare BDP with NO-BDP patients, but all of them are PTI. Perhaps, GLS impairment is associated not only with BPD, but also with prematurity.
Haque et al. also studied RV function in BPD patients. They didn´t found differences in traditional echocardiographic parameters, but using speckle tracking they discovered that infants with severe BPD had lower peak global systolic strain than did infants with moderate BPD or mild/none BPD (24). However, other authors did not found differences between BPD and NO-BPD group neither traditional echocardiographic parameters or through myocardial deformation analysis (25).
Blanca et al. designed a similar study to ours (26). They included BPD patients, with and without PH. At 6 months of PMA, they found differences in RV fractional shortening and GLS-RV between non-PH and PH patients (all of them suffered from BPD). In our investigation, we excluded PH, hoping that GLS-RV would contribute to detect subclinical changes in RV myocardial damage. However, it´s probable that larger alterations in clinical situation are needed to find significant differences in GLS. Our cohort also shows an improvement along time, which suggest the theory that patients with non-severe clinical situation (non-PH patients) demonstrate a total recovery of myocardial alterations.
As to GLS-LV data in BPD group at T1, authors purpose its correlation with RV function. When echocardiographic measurements were taken, septum took part of LV strain so RV movement may be related with these results. Czernik et al. studied LV strain for the first month of life in BPD patients. They found higher values of LV strain in BPD group during the first two weeks of life, which disappear at month of life. They explain that findings with the hemodynamic changes that appear within the first days of life and the volume overload that generates a patent ductus permeable (27). In our cohort, first analysis was made at 36 PMA and no relationship was found with the presence of PDA. At this timepoint, PDA-associated problems are usually resolved.
This study has several strengths and limitations. The main strengths include the longitudinal follow-up over 1 year of life. We used the same equipment and protocol for all patients and echocardiographic images and measurements were made by the same investigators. The study was limited by offline speckle tracking analysis. The dependence of 2D-STE imaging on the frame-by-frame tracking of the myocardial pattern means it is influenced by image factors, including reverberation artefacts and attenuation. Thus, we lost to many cases at T3, due to the requirement of a very good loop imagen to complete a reliable strain analysis. Our study was also limited by the small sample size which makes difficult to find significant differences and generates large variances. After statistical analysis, we realize we should include PH patients, given that more variability in clinical situation is needed to find differences.
In conclusion, our study demonstrates that, although challenging, measuring RV longitudinal strain and strain rate derived by speckle tracking is feasible in preterm infants. Although it seems to be a good correlation between RV strain and BPD severity, authors cannot conclude it in our study. More studies should be carried out to investigate the optimum echocardiographic screening model of RV dysfunction in BPD patients (whether including strain measurements or not) and to confirm that non-PH patients who suffered from BPD keep a normal RV function over the years.