Pulmonary regurgitation is a common complication after TFTC surgery, often leading to valve replacement. Factors, such as trans-annular patching, right ventriculotomy, peripheral pulmonary stenosis, pulmonary vascular resistance, residual atrial or ventricular septal defects, underlying lung diseases, and residual pulmonary valve abnormalities, can contribute to postoperative PR [7].

The measurement of pulmonary arteries diameter, as a part of the preparation for total TOF correction, is a crucial parameter. In this regard, a McGoon ratio of 2 is considered normal, indicating no restriction in the right and left pulmonary arteries. A ratio above 1.2 is acceptable for postoperative right ventricle systolic pressure in total correction of TOF, while a ratio below 0.8 is inadequate for complete TOF repair. Another method, the Nakata index, relies on an average value of 330mm2/m2 as normal. A Nakata index > 150 mm2/m2 is acceptable for complete TOF repair, but < 150 mm2/m2 indicates a narrow pulmonary artery [11].

However, our study found that pulmonary arteries diameter, Nakata index, and McGoon ratio were not correlated with the severity of post-TFTC pulmonary regurgitation. Other studies have reported varying results, with some showing correlations between PR and certain measurements, but our findings suggest otherwise. For example, Gao et al. found a positive correlation between PR and left pulmonary artery diameter, Nakata index, and McGoon ratio, but these were not significant in our study. They concluded that a Nakata index > 270.05 mm2/m2, McGoon > 1.63, and LPA diameter > 18.29 mm can predict the risk of postoperative pulmonary regurgitation. They explained that the expanded pulmonary arteries may lead to reduced vascular elasticity and compliance. However, similar to our study, postoperative pulmonary regurgitation had no significant correlation with the diameter of the right pulmonary artery or the main pulmonary artery. Their explanation for this was that most of the blood that returns to the heart from the pulmonary artery due to pulmonary regurgitation is more from the left pulmonary artery than from the right pulmonary artery [8]. Similarly, Kilner et al. reported a correlation between larger pulmonary arteries and higher PR fraction [12]. Apandi et al. also associated a McGoon ratio > 1.8 with severe postoperative PR after tans-annular patch repair [13]. In another study conducted by Hennein et al., it was observed that the McGoon ratio and Nakata index did not exhibit a significant relationship with the freedom from reoperation or death [14]. On the other hand, Yuan et al. also reported that the McGoon ratio < 0.89 and the Nakata index < 0.79 were related to early death [15]. Nevertheless, our study indicates that while Nakata index and McGoon ratio are important criteria for deciding whether to perform one-stage or two-stage surgery in TOF patients, but they do not predict postoperative pulmonary regurgitation. However, due to the lack of similar studies in pediatric TOF patients, further investigations are warranted.

Regarding the history of shunt operation, our study did not find a significant relationship with postoperative PR. However, the Nakata index was lower in patient with shunt history. The complete repair of TOF is recommended between 3 months and 1 year old, and palliative procedures such as systemic to pulmonary shunts are indicated in some patients due to small or hypoplastic pulmonary arteries [16]. Although the overall results of palliation with systemic to pulmonary shunt in TOF patients are favorable, it is possible that the palliation with a modified Blalock–Taussig shunt leads to an increase in the incidence of hypoplasia or distortion of the pulmonary arteries [17] and the hypoplasia or stenosis of the pulmonary arteries can be determinants of the postoperative pulmonary regurgitation [7]. Therefore, theoretically, shunt implantation in TOF patients may be associated with an increased risk of pulmonary regurgitation after surgery. However, this relationship was not found in our study.

In recent years, more studies have investigated the clinical management post-TFTC, particularly on long-term complications and surgical methods. Pulmonary regurgitation is the most common complication after the repair of TOF, and most studies focus on the best time for pulmonary valve replacement. Moving forward, it is crucial to investigate clinical management after TFTC, particularly long-term complications. Understanding parameters that affect the severity of the pulmonary regurgitation after TFTC can aid in determining the timing and type of surgery (one-stage or two-stage). This study suggests that complete repair of TOF can be performed even in patients with small pulmonary artery branches without an elevated risk of severe pulmonary regurgitation.

The statistical significance of data in this study might be affected by the unequal number of participants between the two PR and No PR groups. The inconsistency between the group numbers may also be a reason for the conflicts of the results with existing literature. This study examined the outcomes post-surgery, and there was no available data on long-term follow-up times. Larger sample sizes from different cardiovascular centers and follow-up examinations are recommended for future studies.