To the Editor: Chronic thromboembolic pulmonary hypertension (CTEPH) is a chronic progressive disease in which pulmonary artery pressure (PAP) increases and eventually leads to right heart failure and death. Balloon pulmonary angioplasty (BPA) is a new and effective treatment for CTEPH patients who are unsuitable for surgery or who develop recurrent or persistent pulmonary hypertension after pulmonary endarterectomy (PEA). In recent years, major medical centers at home and abroad have been gradually developing and improving BPA, but overall, a unified treatment process and complication control strategy is lacking.
We enrolled 108 CTEPH patients who received BPA at the Pulmonary Vascular Disease Interventional Center of the Guangzhou Institute of Respiratory Health from January 2019 to June 2021 to assess the learning curve of this procedure and evaluate the efficacy and safety of BPA in the treatment of CTEPH. This study was approved by the Research Project Review Ethics Committee of the First Affiliated Hospital of Guangzhou Medical University (No. 2020135), and all patients were informed and agreed to use the data. Non-qualification for PEA and indications for BPA were based on a multidisciplinary team consensus of all patients with CTEPH. All the BPA procedures in this study were performed by the same operator. SPSS 22.0 software (IBM, Armonk, NY, USA) was used for statistical analysis. Continuous variables with normal distribution were presented as mean ± standard deviation and compared by independent samples t test, and the multiple groups were compared via one-way analysis of variance. Continuous variables with non-normal distribution were shown as median (Q1,Q3), and Mann–Whitney U test or Kruskal–Wallis H test was used for the analysis. Categorical variables were presented as numbers and percentages, and compared using either Chi-squared or Fisher exact test. P < 0.05 was considered statistically significant.
A total of 108 CTEPH patients unsuitable for PEA with 194 times of BPA treatment were included: 39 males (36.1%) and 69 females (63.9%), aged 55.85 ± 15.14 years, including 59 patients with BPA ≥2 times [Supplementary Table 1, https://links.lww.com/CM9/A969].
In order to study the BPA learning curve, we divided the 194 times of BPA treatment into four groups (A-D) in chronological order (50 cases in groups A, B, and C, and the remaining 44 cases in group D) and compared the operation time, number of dilated blood vessels and mean time to dilate one blood vessel in each group. With the accumulation of surgical experience, the number of blood vessels dilated by BPA gradually increased (P < 0.001), and the mean time to dilate one blood vessel gradually decreased (P < 0.001) [Table 1]. BPA is largely dependent on the skill and proficiency of the operator. Japanese scholars Ogo believe that the BPA learning curve must accumulate more than 50 operation cases to achieve stable surgical results. Our study shows that the learning curve of this procedure is steep, and stable procedures can be performed after at least 50 BPA sessions, as the number of vessels dilated per BPA session increased, and the average time required for the dilation of one vessel decreased after the initial execution of 50 cases (Group A). There were significant differences between Group A and the other groups, and the subsequent implementation indicators of BPA such as number of dilated blood vessels per BPA and mean time to dilate one blood vessel tended to be basically stable after 50 BPA sessions.
Table 1 -
Comparison of surgical indexes in four BPA groups.
||Operation time (min)
||Number of dilated blood vessels per BPA
||Mean time to dilate one blood vessel (min)
||230.00 (191.25, 270.00)
||4 (2, 6)
||52.00 (43.93, 80.00)
||210.00 (186.25, 240.00)
||3 (2, 4)
||78.33 (37.77, 75.00)
||252.50 (210.00, 300.00)
||4 (3, 6)
||58.33 (37.77, 75.00)
||234.00 (200.75, 290.00)
||5 (4, 7)
||48.67 (35.48, 70.25)
||230.00 (161.25, 254.25)
||6 (4, 8)
||40.77 (26.88, 51.92)
Data were presented as median (Q1,Q3). BPA: Balloon pulmonary angioplasty.
We analyzed the complication rate and clinical and hemodynamic improvement of CTEPH patients who received BPA. Each patient usually requires two to ten sessions of BPA to achieve the required PAP reduction and treat all amenable lesions. Therefore, we analyzed the changes in various indicators of 59 CTEPH patients who received BPA twice or more. The results showed that the heart rate (beats per minute [bpm]) ([75.51 ± 12.12] bpm vs. [81.94 ± 13.86] bpm), mean pulmonary arterial pressure (mPAP) ([34.27 ± 11.34] mmHg vs. [41.87 ± 15.26] mmHg), pulmonary vascular resistance (PVR) (6.50 [3.40, 9.10] WOOD units [WU] vs. 8.78 [5.30, 15.95] WU), brain natriuretic peptide precursor (proBNP) (140.30 [57.76, 601.20] ng/L vs. 387.90 [101.80, 2004.00] ng/L) and World Health Organization (WHO) functional classification (WHO FC) (2.00 [2.00, 2.00] vs. 2.00 [2.00,3.00]) significantly decreased after the last BPA session (all P < 0.05) [Supplementary Table 2, https://links.lww.com/CM9/A969]. The 59 patients were divided into the previous group (29 cases) and later group (30 cases) in chronological order to analyze the efficacy before and after the BPA learning curve. The hemodynamic data showed that mPAP and PVR significantly decreased after previous BPA, that is, (35.69 ± 11.28) mmHg vs. (44.62 ± 13.78) mmHg, and (8.20 ± 4.75) WU vs. (13.30 ± 8.15) WU (both P < 0.05); PVR significantly decreased after later BPA ([5.54 ± 3.15] WU vs. [8.22 ± 5.67] WU, P < 0.05); and mPAP decreased after later BPA ([32.91 ± 11.43] mmHg vs. [39.20 ± 16.36] mmHg, P= 0.09), but the difference was not significant, it may be that the sample size is not large enough, and there may be significant differences in the later period as the sample size expands. A comparison of the changes in mPAP (7.00 [–1.50, 15.50] mmHg vs. 7.00 [0.00, 15.00] mmHg, P= 0.767) and PVR (5.82 [–0.31, 10.09] WU vs. 1.23 [–0.10, 6.24]) WU, P= 0.168) between previous and later BPA showed no significant difference. When experienced pulmonary vascular intervention centers in Japan performed BPA for CTEPH patients who could not undergo PEA, the mPAP after BPA was less than 25 mmHg, and some could even reach the normal level, while the data reported by some centers in France showed that the mPAP after BPA was between 31 and 37 mmHg.
Another report from China showed that the mPAP after BPA was 40 mmHg, while the average mPAP after BPA in our center was 34 mmHg, which is similar to the European data. Compared with Japan, whether the different postoperative mPAP is due to operator experience problems, different baseline conditions of CTEPH patients in each country or other causes requires further analysis. As for heart function, the plasma proBNP level decreased significantly after previous BPA (240.80 [75.56, 936.56]) ng/L vs. 922.20 [193.10, 3136.00] ng/L, P= 0.009). The plasma proBNP decreased after later BPA but the difference was not significant (115.55 [49.17, 384.75] ng/L vs. 342.60 [56.75, 1676.00] ng/L, P= 0.198). The decrease in the plasma proBNP level in previous BPA was more obvious than that in later BPA (P= 0.015). The preoperative WHO FC of previous BPA was as follows: two cases of Grade I (6.9%), 14 cases of Grade II (48.3%), 13 cases of Grade III (44.8%), and 0 cases of Grade IV. The postoperative WHO FC of previous BPA was as follows: five cases of Grade I (17.2%), 17 cases of Grade II (58.6%), seven cases of Grade III (24.1%), and 0 cases of Grade IV. The difference between postoperative and preoperative WHO FC of previous BPA was not significant ([2.38 ± 0.62] vs. [2.07 ± 0.65], P= 0.234). The preoperative WHO FC of later BPA was as follows: 0 cases of Grade I (0.0%), 16 cases of Grade II (53.3%), 12 cases of Grade III (40.0%), and two cases of Grade IV (6.7%). The postoperative WHO FC of later BPA was as follows: five cases of Grade I (16.7%), 19 cases of Grade II (63.3%), six cases of Grade III (20.0%), and 0 cases of Grade IV. The difference between postoperative and preoperative WHO FC of later BPA was significant ([2.53 ± 0.63] vs. [2.03 ± 0.62], P= 0.035). The preoper-ative WHO FC was mostly concentrated in Grades II and III, and the proportions of Grades II and III were similar in the two groups. There were no WHO FC IV patients enrolled in the previous group and two WHO FC IV patients in the later group. The proportion of WHO FC I and II patients increased after BPA, indicating that WHO FC was improved after BPA.
The learning curve and case load are usually factors in evaluating the complication rate of percutaneous interven-tional surgery. Among the 194 cases of BPA completed in our center, 27 cases (13.9%) had complications [Supplementary Table 3, https://links.lww.com/CM9/A969], including 19 (Group A: 5; Group B: 7; Group C: 5; and Group D: 2; P = 0.278) cases (9.8%) of hemoptysis; 5 (Group A: 0; Group B: 1; Group C: 3; and Group D: 1; P = 0.214) cases (2.6%) of cough; 2 (Group A: 0; Group B: 0; Group C: 1; and Group D: 1; P = 0.592) cases (1.0%) of reperfusion pulmonary edema; and 1 (Group A: 0; Group B: 0; Group C: 1; and Group D: 0; P = 0.323) case (0.5%) of air embolism. There was no renal dysfunction during the study. We can see that complications over time among the four groups showed no significant difference after BPA and were all at lower levels. A meta-analysis showed that in recent years, reperfusion pulmonary edema/injury and pulmonary vascular injury occurred in 25% and 16% of cases. The incidence of BPA complications in our center was lower than that reported in the literature. Measures to reduce the risk of BPA complications include the following: improvement of operator skills; use of intravascular imaging modalities such as intravascular ultrasound and optical coherence tomography; selection of appropriately sized balloon catheters; use of non-invasive imaging methods; and preoperative use of drugs to reduce PAP as much as possible, such as the intravenous use of prostaglandin drugs.
Overall, the learning curve of BPA is steep, and stable procedures can be performed after at least 50 BPA sessions. There is no significant difference in the complication rates of CTEPH patients who received BPA before and after the learning curve. Regardless of previous or later stage, the effective dilation of blood vessels through BPA in CTEPH patients who are unsuitable for PEA can improve the patients’ activity endurance and hemodynamic parameters, and there is no significant difference. With the accumulation of experience, intraoperative complications will be gradually reduced and the efficiency of BPA will gradually improve.
This work was supported by a grant from Natural Science Foundation of Guangdong Province (No. 2021A1515011373).
Conflicts of interest
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