Percutaneous Treatment of Pulmonary Vein Stenosis

Computed Tomography and Magnetic Resonance Imaging

CT is one of the most commonly used imaging tools for making the diagnosis of PVS because it provides accurate definition of PV anatomy. There are some caveats to the use of CT imaging. A detailed knowledge of PV anatomy is required by the radiologist reading the images. Secondly, occasionally there may be the appearance of stenosis of the LIPV when there is “pseudostenosis.” This was demonstrated in a study by Yamaji et al, in which they performed CT imaging of the PV in 116 patients undergoing PV isolation for AF preablation and postablation. They found that in 11 patients there was more than 50% stenosis in the LIPV when the CT was performed in the supine position. This was not seen when the patients were imaged on the same day in the prone position. Occasionally when CT imaging is used for diagnosis, the PV may be interpreted as being completely occluded, but on subsequent PV angiography a small orifice may be seen. This was identified by Prieto et al in their study of 44 patients with 80 stenosed PVs. Twenty-seven of the 80 stenosed PVs were identified on CT as being 100% occluded; subsequent PV angiography demonstrated a small lumen in 13 of the 27 PVs. At the Mayo Clinic, CT is the modality of choice for imaging the PVs. A study performed at the Mayo Clinic revealed that the mean PV orifice was 17.3 mm (with a range of 12 to 24 mm), the baseline diameter at the point of stenosis was 3 ± 2 mm, and the stenosis began 1 to 2 mm distal to the PV orifice and extended for variable lengths 7 to 35 mm ( Figure 19–2 ) .

MRI is also an acceptable diagnostic modality ( Figure 19–3 ) . An important caveat with MRI of the PVs is that there may be substantial changes in the size and location of the PV orifice during the cardiac cycle. Lickfett and colleagues examined this issue in a study. They found that the largest orifice diameter was in late atrial diastole with a mean decrease of 32.5% during atrial systole. They also noted location changes of the PV orifice of up to 7 mm and that the orifice was larger in the coronal (lateral–medial) than the sagittal (anteroposterior) direction. MR perfusion imaging can also be reliably used to detect anatomic and functional impact of PVS. Kluge et al examined this in a study of 110 patients after AF ablation. MR perfusion imaging was compared with single-photon emission CT perfusion imaging, and 51 patients with PVS were subsequently studied. They found that MRI detected 20 of 21 perfusion defects with a sensitivity of 95.2% and a specificity of 100%. They also showed a cut-off of 6 mm diameter as being significant. A PV with a diameter of less than 6 mm had substantial decrease in perfusion compared with PVs greater than 6 mm in diameter. MRA has also been used to predict the occurrence of PVS after AF ablation. In a study of 104 patients undergoing AF ablation, MRA was performed preablation and postablation. It was shown that a relative reduction in PV diameter on the day after the procedure of 25% or more was predictive of the development of PVS using multivariate analysis, with a hazard ratio of 7.1 (p < 0.0001).

Transesophageal Echocardiography

TEE is another method that may be used to aid the diagnosis of PVS, although it is not as accurate when compared with CT or MRI and is operator dependent. TEE can give accurate assessment of PV ostial anatomy and PV blood flow and is able to detect more severe stenosis of the PV as seen by changes in Doppler flow velocity. The usefulness of TTE for diagnosis of PVS was examined in a study by Jander et al. They showed that TEE can be reliably used to diagnose or exclude PVS if the diagnosis is restricted to a combination of elevated peak velocity (>110 cm/sec) with turbulence and little flow variation. TEE is limited by its inability to image deeply into all four PVs and is less useful in establishing the extent and location of PVS.

Ventilation/Perfusion Scan

V/Q scan is a useful technique for assessing the hemodynamic significance of PVS. It is an ideal screening tool for patients suspected of having PVS because it is widely available and easy to interpret when compared with CT or MRI scans. VQ scans can be used to characterize the physiology of blood flow within the distribution of the PVS. Under normal conditions the apparent blood flow to one third of the lung ranges from 15% to 30%. A perfusion mismatch is seen with PVS in the range of 65% to 75%, and the level of perfusion to the affected lung is seen to have diminished to less than 25% of the expected perfusion; thus with severe stenosis the blood flow within the affected PV can be decreased to as low as 3% to 4%. In a study by Nanthakumar et al, comparison between functional imaging using V/Q scan, anatomic imaging using CT or pulmonary venography, and hemodynamic assessment of PVS was performed. PVS resulted in decreased perfusion of the affected lobe when the resting PV–LA pressure gradient was at least 5 mmHg or when there was 80% luminal stenosis by venography or CT. When there was less than 50% stenosis, no perfusion defects were seen. Figure 19–4 shows decreased perfusion of the entire left lung in a patient with stenosis involving the left upper and lower PVs.

Pulmonary Vein Angiography

PV angiography provides direct visualization of the degree of stenosis but is limited by its invasiveness, streaming, anatomic complexity, and high cost. A good baseline PV angiogram is required in multiple views before PV intervention. Figure 19–5 , A shows a PV angiogram with stenosis involving the LSPV, and Figure 19–5 , B shows the result of PV intervention.