Pulmonary Vein Stenosis after Catheter Ablation for Atrial Fibrillation: An Early Diagnosis Using Unenhanced Computed Tomography

Authors: Soichiro Kojima, Mitsuru Matsuki, Nana Fujii, Naoki Kunitomo, Akihiro Nakamata, Hiroyuki Fujii, Kota Yokoyama, Moto Nakaya, Hiroaki Watanabe, Masashi Kamioka, Tomonori Watanabe, Harushi Mori

Abstract

Pulmonary vein stenosis (PVS) is a serious complication of catheter ablation (CA) for atrial fibrillation (AF). PVS generally occurs several months after CA and presents with non-specific symptoms and imaging findings. There have been reports of delayed diagnoses due to a misdiagnosis as infection, interstitial pneumonia, or organizing pneumonia. We introduced six cases of PVS after CA, all of which showed narrowing of the unilateral pulmonary vessels with or without lobar volume loss in the left lung on unenhanced computed tomography. We report these findings as important results indicating the possibility of PVS after CA for AF and contributing to the early diagnosis and management of PVS.

Introduction

Atrial fibrillation (AF), a type of arrhythmia associated with increased morbidity and mortality, is typically triggered by ectopic foci within the pulmonary veins (1). As AF progresses, significant atrial remodeling occurs, which may lead to permanent atrial myopathy, inconsistent impulse transmission, and irregular ventricular rate (2). The prevalence of AF increases with age. While AF is often asymptomatic, many patients present with palpitations, vague chest discomfort, or symptoms of heart failure. The absence of atrial contractions predisposes patients to thrombus formation, which can lead to stroke and emboli in other organs or limbs (1).

Management strategies for AF include antiarrhythmic therapy, anti*-*thrombotic therapy, and catheter ablation (CA) (1). CA is a procedure in which small burns or freezes are used to induce scarring inside the heart, which helps break up the electrical signals that cause irregular heartbeats and promote a normal heart rhythm (3). Reported complications after CA include cardiac perforation, tamponade, thromboembolism, pulmonary vein stenosis, transverse nerve palsy, esophageal ulcer, left atrial esophageal fistula, and myocardial infarction (3). In particular, high thermal energy emitted into the wall of the pulmonary vein can lead to pulmonary vein stenosis (PVS), the risk of which is related to the amount of energy transmitted (4).

PVS commonly occurs several months after CA and presents with non-specific respiratory symptoms, such as dyspnea, cough, chest pain and hemoptysis (4). Furthermore, chest radiography and computed tomography (CT) show nonspecific parenchymal opacities (5-10). Accordingly, the diagnosis of PVS is often delayed or entirely missed, given the long interval from CA to the onset and the lack of symptomatic specificity and imaging characteristics (5-9). Such delays in diagnoses have been associated with major adverse events related to the progression of stenosis as well as severe parenchymal lung damage (11). Therefore, an early diagnosis and management of PVS are important.

We encountered a case in which PVS was diagnosed based on the narrowing of the unilateral pulmonary vessels in the left lung on unenhanced CT, suggesting that unenhanced CT can contribute to the early diagnosis and management of PVS. In this retrospective study, we analyzed data from six patients with PVS after CA for AF to identify the unenhanced CT characteristics that can aid in the early diagnosis and management of PVS after CA in this population.

Material and Methods

Patients

Our institutional review board waived the requirement to obtain written informed consent for this retrospective case series, which evaluated de-identified data and involved no potential risk to patients. To avoid any potential breach of confidentiality, no link between patients and researchers was made available. From June 22, 2018, to July 6, 2022, a total of 6 patients (4 men, 2 women; mean age, 58.5 years old; range, 54-64 years old) with confirmed PVS after CA for AF were admitted to 3 hospitals. All patients were diagnosed with PVS after CA for AF using contrast-enhanced CT and/or conventional angiography. All six patients underwent unenhanced CT and contrast-enhanced CT, and five underwent angiography. Data on symptoms, management, and clinical outcomes, along with the white blood cell count and C-reactive protein (CRP) levels, were extracted from the medical records (Table). The time from CA to the symptom onset, time from unenhanced CT to the diagnosis, and the initial diagnosis on unenhanced CT were examined.

CT image review

All CT images were reviewed by 2 radiologists with 4 and 29 years of experience using a viewing console. The images were reviewed independently, and final decisions were reached by consensus. No negative control cases were examined, and no blinding was performed. For each of the six patients, unenhanced CT scans were evaluated for the following (a) pulmonary parenchymal opacities, (b) narrowing of unilateral pulmonary vessels in comparison with the contralateral side, and (c) lobar volume loss. On enhanced CT images, the PVS was measured along the stenosed vein by comparing the minimal diameter of the stenotic section with the diameter of the adjacent normal reference vein. PVS grading was defined as ≤50%, grade 1; 51-75%, grade 2; 76-99%, grade 3; and total occlusion, grade 4 (11).

CT technique

The six patients were examined using different CT scan models at different a SOMATOM Definition Flash CT scanner (Siemens AG, Erlangen, Germany), SOMATOM Definition AS+ (Siemens AG), Discovery CT750 HD CT scanner (GE Healthcare, Milwaukee, USA) and SOMATOM Force CT scanner (Siemens AG).

The imaging parameters were as voltage, 120 kV; automatic tube current (average 172-221 mA); 512×512 matrix; pitch, 0.828-0.95; and slice thickness, 0.8-3 mm. All images were evaluated using lung window settings (window level -650 HU, window width, 1,650 HU).

Results (Table)

The time from the ablation date to the symptom onset ranged from 3 to 24 months (median, 4 months). The time from unenhanced CT to the diagnosis ranged from 7 to 305 days (median: 70.5 days) (Table).

Lung parenchymal opacification on unenhanced CT images included reticular opacities (Fig. 1, 2), ground-glass opacities (Fig. 1-4), collapse (Fig. 1, 5), consolidation (Fig. 3), masses (Fig. 5) and centrilobular nodules (Fig. 6). The initial diagnoses based on unenhanced CT were infective pneumonia (n=2), alveolar hemorrhaging (n=2), primary lung cancer or organized pneumonia (n=1) and impaired blood flow in the left lung (n=1). On unenhanced CT, five of the six patients exhibited narrowing of the pulmonary vessels in the left lobe in comparison with the contralateral side with lobar volume loss. In one patient (Fig. 6), narrowing of the pulmonary vessels without lobar volume loss in the left lung was detected on unenhanced CT, and impaired blood flow was diagnosed, which promoted an early diagnosis and management. The PVS was located in the left inferior pulmonary vein (n=4), left superior pulmonary vein (n=1) and both superior and inferior pulmonary veins (n=1). The stenosis grades were grade 3 (n=4) or grade 4 (n=3). The management strategies included stent placement (n=2), plain balloon angioplasty (n=2), lobectomy (n=1) and conservative therapy (n=1). Clinical outcomes included symptom improvement (n=2), no change (n=2), temporary improvement followed by worsening (n=1) and improvement of hemoptysis with persistent shortness of breath (n=1). On follow-up CT (n=5), lung parenchymal opacification demonstrated improvement (n=3), no change (n=1) and deteriorating (n=1); narrowing of the unilateral pulmonary vessels demonstrated no change (n=4) and deteriorating (n=1); and lobar volume loss demonstrated no change (n=4) and a case without any lobar volume loss in the initial images demonstrated no change.

Case Report

Case 1

A 64-year-old man presented with no relevant symptoms. The patient had undergone ablation for paroxysmal atrial fibrillation nine months earlier. He was referred to our Department of Respiratory Medicine because of abnormal chest shadows noted on CT performed during a physical checkup. Unenhanced CT showed reticular opacities superimposed on ground-glass opacities and partial collapse in the subpleural periphery of the left lower lobe (Fig. 1). The initial diagnosis was infectious pneumonia.

Five months after the visit, the patient was suspected of having pulmonary vein stenosis due to his history of ablation, and contrast-enhanced CT was performed, which confirmed stenosis of the left inferior pulmonary vein. Subsequently, a stent was placed. A retrospective analysis of the CT images revealed narrowing of the pulmonary vessels in the left lower lobe compared with the contralateral side and lobar volume loss.

Case 2

A 55-year-old woman presented with hemoptysis. Three months after ablation was performed, left chest pain appeared, and approximately 10 days later, a fever and bloody sputum also appeared, which led to a visit to the Department of Respiratory Medicine. Unenhanced CT revealed an infiltrating shadow with frosted density around the transapical distribution in the lower lobe of the left lung (Fig. 2). The initial diagnosis was infectious pneumonia.

The patient was treated with antimicrobial agents for five days, but there was no improvement on imaging. Various tests, including bronchoalveolar lavage and a transbronchial lung biopsy, were performed to investigate the cause of the disease. Three months after the initial visit, contrast-enhanced CT showed occlusion of the left upper and lower pulmonary veins, and a diagnosis of pulmonary vein stenosis was made after catheter ablation. Plain balloon angioplasty was performed.

A retrospective analysis of the CT images revealed narrowing of the pulmonary vessels in the left lower lobe compared to the contralateral side and lobar volume loss.

Case 3

A 61-year-old woman presented with hemoptysis, chest pain and a fever. Three months earlier, ablation had been performed for atrial fibrillation. She visited our hospital with hemoptysis and chest pain. Unenhanced CT showed a crazy-paving appearance, mainly in S3 of the left lung (Fig. 3). The initial diagnosis was alveolar hemorrhaging and pleuritis. Blood tests showed an elevated white blood cell count of 12,400 /μL and CRP level of 6.64 mg/dL, and she was admitted to the hospital for a close examination and treatment. Seven days after admission, contrast-enhanced CT showed stenosis of the left upper pulmonary vein, and a diagnosis of pulmonary vein stenosis was made after catheter ablation. Plain balloon angioplasty was performed. A retrospective analysis of the CT images revealed narrowing of the pulmonary vessels in the left upper lobe compared to the contralateral side and lobar volume loss.

Case 4

A 54-year-old man presented with hemoptysis. Four months earlier, ablation had been performed for atrial fibrillation. Hemoptysis and shortness of breath appeared one week prior to the visit. He visited his previous physician, who found an infiltrative shadow in the left lower lung field on chest radiography and referred him to our Department of Respiratory Medicine for a close examination and treatment. Unenhanced CT showed patchy ground-glass opacities with interlobular septal thickening in the left lower lobe (Fig. 4). The initial diagnosis was alveolar hemorrhaging. Hemostatic agents were used, but the infiltrative shadow worsened, and antibacterial agents were administered. However, there was no improvement, so the patient was hospitalized.

Various tests were performed to rule out bleeding due to anticoagulant medication, tumor, infection and vasculitis, but no diagnosis was made. One month after the initial examination, contrast-enhanced CT showed that the left inferior pulmonary vein was not contrasted, and a diagnosis of pulmonary vein stenosis after catheter ablation was made.

Subsequently, lobectomy of the lower lobe of the left lung was performed. A retrospective analysis of the CT images revealed narrowing of the pulmonary vessels in the left lower lobe compared to the contralateral side and lobar volume loss.

Case 5

A 57-year-old man who presented with no relevant symptoms. He had undergone ablation at another hospital several years previously. CT performed during a physical checkup revealed a mass in the left lower lobe, which led to a visit to the hospital. The initial diagnosis was primary lung cancer or organized pneumonia. Positron emission tomography-CT was performed, which indicated a probable round atelectasis due to the lack of any accumulation in the mass (Fig. 5). It was also noted that there were inflammatory changes in the same area six months earlier (images not shown). Follow-up contrast-enhanced CT showed stenosis of the left inferior pulmonary vein, which was diagnosed as pulmonary vein stenosis after catheter ablation.

As no specific symptoms were noted in this case, the plan was to follow the patient without treatment. A retrospective analysis of the CT images revealed narrowing of the pulmonary vessels in the left lower lobe compared to the contralateral side and lobar volume loss.

Case 6

A 60-year-old man presented with exertional dyspnea. The patient had undergone ablation for long-term persistent atrial fibrillation 16 and 4 months previously. Approximately four months after the second ablation procedure, shortness of breath on exertion appeared and gradually worsened. Two months later, during the follow-up visit, the patient complained of symptoms and underwent chest CT. On unenhanced CT, multiple centrilobular nodules and narrowing of the pulmonary vessels in the left upper lobe in comparison with the contralateral side were initially detected (Fig. 6a). Similar findings were observed in the left lower lobe (data not shown). Based on these findings, we suspected an impaired blood flow in the left lung, confirmed catheter ablation for atrial fibrillation and compared these images with those before ablation (Fig. 6b), which demonstrated that the pulmonary vessels in the left lung had narrowed after ablation. Therefore, pulmonary vein stenosis after catheter ablation was diagnosed.

Contrast-enhanced CT showed grade 4 left superior pulmonary vein stenosis in the left atrium (Fig. 6c). The left inferior pulmonary vein also exhibited grade 3 stenosis (data not shown). Stenting of stenotic vessels was performed. Contrast-enhanced CT after stent placement showed no change in the narrowing of the pulmonary vessels in the left upper and lower lobes, but dilatation of the stenotic left superior (Fig. 6d) and inferior (figure not shown) pulmonary veins after stent implantation was noted. The symptoms of dyspnea on exertion also disappeared.

Discussion

The incidence of severe PVS after CA for AF ranges from 0.32% to 3.4% (4). PVS can lead to pulmonary edema, hypertension, oligemia, and infarction (12). However, unlike other acute complications, PVS develops gradually three to five months after CA, with some reports suggesting that it can develop more than one year after the procedure (13). Previous studies have suggested that left-sided veins are more frequently affected than are right-sided veins (4). Although the mechanism underlying this phenomenon remains unclear, it may be attributable to the small diameter of the left inferior PV, the relative cranial orientation of the left superior PV or the position of the coumadin ridge near the left atrial appendage, forcing ablation closer to the venous ostium (4). As all cases of PVS in our study were left-sided, our findings are in accordance with previous observations.

In patients with PVS after CA for AF, unenhanced CT findings include non-specific parenchymal opacities, including nodules, consolidation, ground-glass opacities, interstitial wall thickening, crazy-paving appearance, bronchial wall thickening and pleural effusion (5-11). Based on these findings, PVS is often mistaken for infectious pneumonia, organized pneumonia and interstitial pneumonia at the initial diagnosis, delaying the correct diagnosis (5-9). In the present study, five of the six patients (Cases 1-5) were misdiagnosed with infective pneumonia, alveolar hemorrhaging, primary lung cancer or organizing pneumonia. In the retrospective analysis, narrowing of the unilateral pulmonary vessels with or without lobar volume loss in the left lung was identified in 100% of the patients. Narrowing of unilateral pulmonary vessels with volume loss can generally be caused by chronic reductions in pulmonary arterial inflow due to congenital disorders or tumor embolism (14-16). Recently, Goitein et al. reported that contrast-enhanced CT showed narrowing of the pulmonary arteries (oligemia), volume loss and mediastinal collaterals in patients with severe PVS after CA for AF (11).

Based on the available evidence, the following mechanism may explain narrowing of the unilateral pulmonary vessels and volume loss in patients with PVS after CA for AF: at first, PVS causes congestion of pulmonary veins and capillaries, with subsequent progression leading to venous hemorrhaging, infarction of the pulmonary interstitium and destruction of capillary vessels. Destruction of the pulmonary interstitium and capillary vessels leads to decreased pulmonary arterial and venous outflow. In one patient (Case 6), we detected narrowing of the unilateral pulmonary vessels without volume loss in the left lung, leading to a diagnosis of an impaired blood flow in the left lung. Given the patient's history of CA for AF, we recommended contrast-enhanced CT, which enabled the early diagnosis and management of PVS and contributed to a good clinical outcome. The current case series emphasizes the importance of unenhanced CT for detecting narrowing of unilateral pulmonary vessels and lobar volume loss (especially on the left side) in patients with post-ablation PVS, as this can promote the early diagnosis and management.

Several limitations associated with the present study warrant mention. First, this was a retrospective study with a small sample size. Second, images were not obtained in the same manner or under the same conditions. Third, the evaluation of narrowing pulmonary vessels and the presence of lobar volume loss in this study was not a quantitative evaluation but a qualitative one.

In conclusion, the current series demonstrates that narrowing of the unilateral pulmonary vessels, with or without lobar volume loss, especially in the left lung, on unenhanced CT indicates the probability of PVS. Therefore, further evaluations using contrast-enhanced CT are recommended when these findings are observed.

The authors state that they have no Conflict of Interest (COI).