Centerline Tracking for Quantification of Reverse Structural Remodeling of the Pulmonary Veins Following Cardiac Ablation Therapy

Rationale and Objectives

Patients with atrial fibrillation undergo structural remodeling resulting in increased pulmonary vein sizes. Studies have demonstrated that these changes are reversible following successful ablation therapy. To date, analyses of pulmonary vein structure have focused on measurements at the pulmonary vein ostia, and the full extent of reverse remodeling along the length of the pulmonary veins has not yet been fully characterized.

Materials and Methods

An automated, three-dimensional method is proposed that quantifies pulmonary vein geometry starting at the ostia and extending several centimeters into the veins. A centerline is tracked along the length of the pulmonary vein, and orthogonal planes are computed along the curve. The method was validated against manual measurements on each of the four pulmonary veins for 10 subjects. The proposed methodology was used to analyze the pulmonary veins in 21 patients undergoing cardiac ablation therapy with preoperative and postoperative computed tomographic scans.

Results

Validation results demonstrated that the automated measurements closely followed the manual measurements, with an overall mean difference of 11.50 mm 2 . Significant differences in cross-sectional area at the two time points were observed at all pulmonary vein ostia and extending for 2.0 cm (excluding the 0.5-cm interval) into the left inferior pulmonary vein, 3.5 cm into the left superior pulmonary vein, and 2.0 cm into the right superior pulmonary vein.

Conclusions

Quantitative analysis along the length of the pulmonary veins can be accomplished using centerline tracking and measurements from orthogonal planes along the curve. The patient study demonstrated that reverse structural remodeling following ablation therapy occurs not only at the ostia but for several centimeters extending into the pulmonary veins.

Atrial fibrillation is a condition of the heart in which the atria beat rapidly and irregularly, resulting in a lack of synchrony in the beating of the heart. Although the exact etiology of the disease is not yet fully understood, it has been shown that the origin of ectopic beats is frequently located in the pulmonary veins . In catheter ablation therapy, a standard treatment strategy, catheters are guided into the left atrium, and radiofrequency energy is delivered circumferentially to each of the pulmonary veins to create an electrical block to the left atrium. Structural remodeling occurs in conjunction with this disease, with patients with atrial fibrillation having larger left atria and pulmonary veins than normal controls. Following ablation therapy, these structural changes are reversible, a process termed reverse remodeling, with left atrial size and pulmonary vein diameters significantly decreasing in patients who have returned to normal sinus rhythm.

Left atrial size has been quantified using either two-dimensional diameter measurements or three-dimensional (3D) volume measurements from high-resolution computed tomographic and magnetic resonance data sets. Efforts have also been made to quantify pulmonary vein structure , but these techniques primarily include manual line measurements on either volume renderings or within image cross-sections. The number and location of measurements are typically limited to the junction between the pulmonary vein and left atrium and a collection of specified distances within the pulmonary veins. Accurately defining a distance into the pulmonary vein, however, can be difficult because the pulmonary veins traverse a 3D path through the volume. The current lack of 3D quantification tools for pulmonary vein structure limits the ability to assess complex changes that may occur in response to ablation therapy.

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Figure 1

Back view of left atrium illustrating measurements made along pulmonary vein using successive planes orthogonal to a centerline curve. LIPV, left inferior pulmonary vein; LSPV, left superior pulmonary vein; RIPV, right inferior pulmonary vein; RSPV, right superior pulmonary vein.

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Materials and methods

Data Preprocessing

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Overall Method

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Centerline Calculation

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Cross-sectional Area Computation

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v3=α1v1+α2v2, v

where α 1 + α 2 = 1 and α 1 = 1/ c__n . c is a constant, and n is the point number along the curve. c was empirically set using a single data set and held constant for all subsequent data sets. v 3 is the unit vector used to compute the oblique image plane, v 1 is the normal of the segmentation cut plane, and v 2 is defined in equation 2 :

v2=xn−xc|xn+xc|, v

−

where x c is the current point and x n is the next point on the centerline. The effect of equations 1 and 2 is that near the pulmonary vein ostia, v 3 is approximately equal to the segmentation plane normal, and further into the vein, v 3 is approximately equal to the vector along the centerline. At each point along the centerline curve, the oblique image plane defined by v 3 is extracted from the volume, and the cross-sectional area for the specified pulmonary vein is computed as

A=(∑iυi)×d2s.t.υi∈PVjwherej={1,…4}, A

(

∑

)

.υ

∈

where

{

…

}

where A is cross-sectional area, υ i are the voxels within the specified pulmonary vein PV j , and d is the voxel resolution.

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Validation Experiments

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Patient Study

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Results

Validation Results

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Table 1

Mean Absolute Differences between Manual and Automatic Measurements for Each of the Four Pulmonary Veins across 10 Subjects

Subject LIPV (mm 2 ) LSPV (mm 2 ) RIPV (mm 2 ) RSPV (mm 2 ) Mean (mm 2 ) 1 5.75 8.35 3.71 9.59 6.85 2 7.84 9.80 6.93 14.40 9.74 3 7.15 21.33 7.70 8.89 11.27 4 10.86 26.67 7.17 12.87 14.39 5 18.75 18.35 17.19 11.68 16.49 6 8.42 9.83 12.38 10.88 10.38 7 16.28 10.62 18.82 8.24 13.49 8 4.11 8.35 5.94 14.87 8.32 9 8.82 18.41 18.06 15.30 15.15 10 13.95 9.17 7.25 5.17 8.89 Mean 10.19 14.09 10.52 11.19 11.50

LIPV, left inferior pulmonary vein; LSPV, left superior pulmonary vein; RIPV, right inferior pulmonary vein; RSPV, right superior pulmonary vein.

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Patient Study

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Discussion

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Acknowledgments

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Appendix

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References

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Centerline Tracking for Quantification of Reverse Structural Remodeling of the Pulmonary Veins Following Cardiac Ablation Therapy

Rationale and Objectives

Materials and Methods

Results

Conclusions

Materials and methods

Data Preprocessing

Overall Method

Centerline Calculation

Cross-sectional Area Computation

Validation Experiments

Patient Study

Results

Validation Results

Patient Study

Discussion

Acknowledgments

Appendix

References

Further Reading

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Coronary Artery Atherosclerosis and Risk Stratification in Young Adults with an Intermediate Pretest Likelihood Detected by Multidetector Computed Tomography