Three-Dimensional Echocardiographic Method for the Visualization and Assessment of Specific Parameters of the Pulmonary Veins

Summary

The dimensions of the pulmonary veins (PV) are important parameters when planning pulmonary vein isolation. 2D transoesophageal echocardiography can only provide limited data about the PVs; however, 3D echocardiography can evaluate relevant diameters and areas of the PVs, as well as their spatial relationship to surrounding structures.

Abstract

The dimensions of the pulmonary veins are important parameters when planning pulmonary vein isolation (PVI), especially with the cryoballoon ablation technique. Acknowledging the dimensions and anatomical variations of the pulmonary veins (PVs) may improve the outcome of the intervention. Conventional 2D transoesophageal echocardiography can only provide limited data about the dimensions of the PVs; however, 3D echocardiography can further evaluate relevant diameters and areas of the PVs, as well as their spatial relationship to surrounding structures. In previous literature data, parameters influencing the success rate of PVI have already been identified. These are the left lateral ridge, the intervenous ridge, the ostial area of the PVs and the ovality index of the ostium. Proper imaging of the PVs by 3D echocardiography is a technically challenging method. One crucial step is the collection of images. Three individual transducer positions are necessary to visualize the important structures; these are the left lateral ridge, the ostium of the PVs and the intervenous ridge of the left and right PVs. Next, 3D images are acquired and saved as digital loops. These datasets are cropped, which result in the en face views displaying spatial relationships. This step can also be employed to determine the anatomical variations of the PVs. Finally, multiplanar reconstructions are created to measure each individual parameter of the PVs.

Optimal quality and orientation of the acquired images are paramount for the appropriate assessment of PV anatomy. In the present work, we examined the 3D visibility of the PVs and the suitability of the above method in 80 patients. The aim was to provide a detailed outline of the essential steps and potential pitfalls of PV visualization and assessment with 3D echocardiography.

Introduction

The drainage pattern of the pulmonary veins (PV) is highly variable with 56.5% variation in the average population¹. Evaluation of the PV drainage pattern is crucial when planning PV isolation (PVI), which is the most common interventional treatment of atrial fibrillation nowadays^2,3,4. Although radiofrequency catheter ablation has been the standard technology for achieving PVI, the cryoballoon (CB)-based ablation technology (CA) is an alternative method requiring less procedural time. The technique is less complicated compared with radiofrequency ablation^5,6, while the efficacy and safety of CA are similar to those of radiofrequency ablation⁷.

The rate of procedural PV occlusion by the CB and the continuous circumferential extension of tissue injury in the PV ostium determines the permanent success of PVI after CA. One of the main determinants of PV occlusion is the variation of PV anatomy. In recent, computed tomography- (CT) and cardiac MRI-based studies, several PV parameters were identified with predictive values of short and long term success rates following CA. These parameters included variations of both the PV anatomy (left common PV, supernumerary PVs^8,9,10, ostial area, ovality index^8,11,12,13) and its surroundings (intervenous ridge^8,14,15,16, thickness of left lateral ridge^8,9,17).

Although conventional 2D echocardiography is not suitable for displaying and measuring most of the above parameters, three-dimensional transesophageal echocardiography (3D TEE) seems to be an alternative tool to visualize the PVs, as demonstrated in previous literature data^18,19.

Furthermore, 3D TEE prior to PVI brings additional value compared to CT or MRI, as it not only provides data on PV characteristics for procedural design, but also clarifies whether a thrombus in the left atrial appendage (LAA) is present. This investigation is especially important prior to PVI. At the same time, 3D TEE requires less time, its procedural cost is low, and it does not expose the patient and the medical staff to radiation.

In the past, several types of CBs existed with different sizes, which made it difficult to extrapolate how the various parameters of the PVs influence the success rate of CA. Today, the newly introduced second-generation CB is used for CA, which only exists in one size. Thanks to its improved cooling effect, the second-generation CB offers a much higher performance compared to the first-generation CB²⁰, which further highlights the importance of PV anatomy and interventional planning before PVI.

Protocol

All the patients signed informed consent before examination according to approval of the local ethical committee (OGYÉI/12743/2018).

1. Preparation

1. Start the examination with patient preparation: ensuring at least a 4-hour fasting status, questionnaire about problems with swallowing and known upper gastrointestinal diseases.
2. Ensure that written informed consent is read and signed.
3. Prepare an intravenous line before the examination.
4. Position the patient in a left lateral decubitus position.
5. Administer mild sedation using intravenous midazolam (2.5-5 mg).
6. Monitor ECG and oxygen saturation.

2. Image acquisition

1. Visualization of the left PVs
   1. Insert the probe into the oesophagus at approximately 30-40 cm from the front teeth.
   2. In the upper (or mid) transoesophageal probe position visualize the LAA using 2D image acquisition at 20-45°.
   3. Turn the probe slightly clockwise and change the crystal angulation to 60-80° in order to centralize the LAA on the image.
   4. Click the full volume button in order to applying full volume 3D acquisition.
   5. Adjust the image’s lateral and elevational width to display the LAA and the left upper PV. This enhances visualization of the left lateral ridge.
   6. Optimize the image quality (adjusting the depth and gain, applying harmonic imaging).
   7. Record a one-beat (if feasible, multibeat) loop with 2 cardiac cycles.
   8. Change the angulation to approximately 120° on the 2D image to centralize the LAA.
   9. Turn the probe slightly counterclockwise and apply anteflexion to visualize the ostia of the left PVs.
   10. Apply color Doppler-coded imaging to confirm that both the upper and lower PVs are visible.
   11. Click the full volume button in order to applying full volume 3D acquisition.
   12. Adjust the image’s lateral and elevational width to display the left PVs. This enhances visualization of the ostia of the left upper and lower PVs and the intervenous ridge.
   13. Control dataset quality. Check the recorded dataset. If the dataset does not contain both the upper and lower PVs, change the patient position by further tilting to the lateral position, and repeat the procedure from step 2.1.8.
   14. Acquire 3D full volume datasets from the left PVs: one-beat (if feasible, multibeat) loop with 2 cardiac cycles.
   15. Confirm the visibility of PV ostia by cropping the image to the upper or lower PV ostium, respectively. The lower PV ostium requires a specifically careful confirmation. It is not unsual, that some parts of the ostium are outside the 3D dataset due to anatomical reasons, e.g. angulation or close proximity to the transducer.
   16. In case the image is not suitable for visualizing the complete PV structure, repeat the procedure from step 2.1.10. Change the lateral or elevational width of the 3D dataset, if necessary.
2. Visualization of the right PVs
   1. Switch back to 2D mode and focus the image to the LAA at 45° upper (or mid) oesophageal probe position.
   2. Turn the probe clockwise and move the probe head to anteflexion position in order to visualize the right PVs.
   3. Apply color Doppler-coded imaging to confirm that both the upper and lower PVs are visible.
   4. Click the full volume button in order to applying full volume 3D acquisition.
   5. Adjust the image’s lateral and elevational width to display the right PVs. This enhances visualization of the ostia of the right upper and lower PVs and the intervenous ridge. This image can be used to identify the presence of supernumerary PVs.
   6. Acquire 3D full volume datasets from the right PVs: one-beat (if feasible, multibeat) loop with 2 cardiac cycles.
   7. Confirm the visibility of PV ostia by cropping the image to the upper or lower PV ostium, respectively. The lower PV ostium requires a specifically careful confirmation. It is not unusual that some parts of the ostium are outside the 3D dataset due to anatomical reasons (e.g., angulation or close proximity to the transducer).
   8. If the dataset does not contain both the upper and lower PVs, patient position should be changed by further tilting to the right position, and the procedure should be repeated from step 2.2.1. Change the lateral or elevational width of the 3D dataset, if necessary.

3. 3D image reconstruction and measurements

1. Offline 3D multiplanar reconstruction
   1. Activate the 3D analysis software on your scanner or workstation (Philips: activate the 3DQ software in QApps panel; Tomtec: activate the 4D Cardio-view 3 application; GE: activate the FlexiSlice software).
   2. Select a frame in diastolic phase for the measurements. For standardization, it is recommended to select a frame timed to the T wave.
   3. Set the two perpendicular planes to the requested structure (left lateral ridge or each PVs ostium) and adjust plane direction while the 3^rd plane represents the en face view of the examined structure.
   4. On the left panel, select the measurement option. The en face view is suitable for measurements (diameter, area, distance).

Results

Using the above-described image acquisition protocol, the first step is to visualize the left atrial appendage (LAA) using 2D acquisition (Figure 1). The probe is in the upper (or mid) transoesophageal position at 20-45°. The image shows the LAA. The left lateral ridge and the left upper PV is displayed at 60-80° (Figure 2), and then the 3D dataset is acquired and confirmed by cropping the dataset in order to visualize the LAA and the left lateral ridge with the...

Discussion

Here, we demonstrate a step-by-step methodology to study the PVs, their surrounding structures and anatomical characteristics with 3D echocardiography. The above described method for 3D imaging of the PVs is an easily standardizable method, which provides high quality 3D images in most patients suitable for precise measurements. Optimal quality and orientation of the acquired images are paramount for the appropriate assessment of PV anatomy. The 3D reconstructed images enhance the visualization of the PV drainage pattern...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
4D Cardio-view 3 software	Tomtec Imaging Systems GmbH
Epiq 7G scanner	Philips
Q-Lab Software	Philips
X5-1 transducer	Philips
Vivid E95 Scanner	GE
4Vc-D transducer	GE