Campbell MJ, White BR, Rychik J, Linder J, Faerber JA, Tian Z, Cohen MS.J Am Soc Echocardiogr. 2022 Nov;35(11):1168-1175. doi: 10.1016/j.echo.2022.07.007. Epub 2022 Jul 19.PMID: 35863543
Take home points:
- Fetal PVVI and maximum, mean, and minimum velocities of the vertical vein were associated with postnatal severe pulmonary vein obstruction in TAPVC
- Accurate prediction can aid in developing safer delivery planning for this cohort
Commentary from Dr. Jared Hershenson (Greater Washington DC), section editor of Pediatric and Fetal Cardiology Journal Watch:
There are a few fetal diagnoses that require urgent postnatal care, one of which is obstructed total anomalous pulmonary venous connection (oTAPVC) due to obstructed vertical venous return. Immediate cath or surgical intervention is often necessary. About 1/3 of patients with TAPVC have obstruction and undiagnosed cases often have both worse morbidity and mortality. Knowledge of oTAPVC prenatally can aid delivery planning and possibly improve outcomes. However, there is limited data on whether prenatal echo findings of oTAPVC can predict severe obstruction postnatally given the lack of standardization and no quantifiable assessment of the vertical vein when present. Currently, qualitative assessment of the pulmonary veins is used to determine presence of obstruction.
This group studied a novel quantitative metric of pulmonary venous flow called pulmonary venous variability index (PVVI) that was initially studied postnatally and predicted catheter gradient and clinical pulmonary venous obstruction. PVVI is measured in the vertical vein and was defined as maximum velocity (Vmax) – minimum velocity (Vmin) / mean velocity (Vmean). Normal values differ based on GA and had been previously reported. This was a retrospective review of 29 patients with prenatally diagnosed TAPVC. Most patients were male, with heterotaxy or single ventricle CHD, and with supracardiac TAPVC (confirmed postnatally). 41% were diagnosed with obstruction based on pulmonary venous Doppler. See Table 1. Clinical and echo factors were evaluated for prediction of oTAPVC, which was defined as either pre-operative death or need for surgery or catheter-based intervention on the first day of life. Initial pH and O2 sats were documented. Secondary outcomes including preoperative intubation, acidosis, hypoxemia, and chest x-ray findings were analyzed. All fetal echos (mean GA of 35 weeks for primary analysis) were reviewed by 2 fetal cardiologists who were blinded to any initial diagnosis, and PVVI (Vmax, Vmin, and Vmean) was measured offline.
12 patients had severe oTAPVC. Univariate analysis showed that heterotaxy, single ventricle CHD, TAPVC type and fetal echo read as obstructed were in fact not associated with severe oTAPVC. However, lower PVVI and V min of the vertical vein were significantly associated (P=0.007). Absolute values of V max and Vmean also showed significance (P=0.03). See Figure 2. With regards to secondary outcomes, 41% required preoperative intubation and all absolute velocity metrics were significantly associated with obstruction whereas PVVI was not. No measurements were associated with acidosis or pulmonary edema on initial x-ray. All absolute measurements were associated with hypoxemia, but PVVI was not. See Table 3. When assessing fetal echos over various GAs, late gestation PVVI was more predictive of oTAPVC than absolute values, while at earlier GA, PVVI was less predictive than the absolute values. Additionally, interobserver reliability was high for all measurements.
In the discussion, the authors discuss a possible reason why Vmin was more strongly associated with oTAPVC than Vmax or Vmean, particularly due to lower pulmonary venous flow during fetal life. Additionally, they discuss how this quantified value, which also represents loss of cardiac cycle variability in vertical vein Doppler blood flow, was associated with oTAPVC, as compared to the qualitative assessment of pulmonary venous Doppler (“lack of return to baseline”) which was not statistically significantly associated. Moreover, they reflect on why PVVI was not as predictive of the secondary measures of obstruction. The authors speculate that the commonly known risk factors for obstruction (heterotaxy, type of TAPVC, etc.) were not significantly significant in this study given the small numbers, definition of obstruction (pre-operative vs. post-operative), and possible referral bias to their fetal program. Additionally, and unfortunately, meaningful cut-off values were not provided, but this was likely due to the small sample size. They conclude that Vmin and PVVI in late gestation may be useful with further study. With hopefully larger studies in the future, having a meaningful quantitative measurement and cut-off to predict severe obstruction could lead to safer delivery planning and hopefully significant improvement in patient outcomes.