Accurate Watchman device sizing with MDCT imaging.

Is Your Watchman Device the Right Size? Why Precise Sizing Matters

Q: What is the Watchman device and how does it work?

The Watchman device is a small, implantable device designed to reduce the risk of stroke in individuals with non-valvular atrial fibrillation (AFib). It works by sealing off the left atrial appendage (LAA), which is a pouch in the heart where blood clots are likely to form in AFib patients. By closing off the LAA, the Watchman device prevents these clots from entering the bloodstream and potentially causing a stroke. This offers an alternative to long-term anticoagulant therapy.

Q: Why is it so important to get the sizing right for the Watchman device?

Accurate sizing of the Watchman device is crucial for its success. If the device is too small, leaks can occur around it, leaving the patient vulnerable to stroke. Conversely, if the device is too large, it can increase the risk of complications like perforation or migration. Proper sizing ensures the device fits securely and effectively seals off the left atrial appendage (LAA), minimizing risks and maximizing long-term stroke prevention.

Q: What is multi-detector computed tomography (MDCT) and how is it used in Watchman procedures?

Multi-detector computed tomography (MDCT) is an advanced imaging technique used to measure the left atrial appendage (LAA) before Watchman device implantation. MDCT provides a more precise and reliable assessment of the LAA dimensions compared to traditional methods like transesophageal echocardiography (TEE). This precision allows physicians to select the optimal Watchman device size, reducing the risk of complications and improving the overall success of the procedure. Specifically, the CTmax measurement (maximum diameter of the LAA) has demonstrated a high degree of correlation with the final deployed device size.

Q: What is transesophageal echocardiography (TEE) and how does it compare to MDCT for Watchman device sizing?

Transesophageal echocardiography (TEE) is a traditional method used to measure the left atrial appendage (LAA) before Watchman device implantation. While TEE has been the primary method, research suggests that multi-detector computed tomography (MDCT) may offer a more precise approach. Studies indicate that MDCT provides a more accurate assessment of the LAA dimensions, leading to more precise device sizing and potentially improved patient outcomes. Specifically, TEEmax (maximum LAA diameter measured by TEE) showed only moderate correlation compared to CTmax.

Q: What does the CTmax measurement mean in the context of Watchman device sizing?

The CTmax measurement refers to the maximum diameter of the left atrial appendage (LAA) as measured by multi-detector computed tomography (MDCT). Studies have shown that CTmax is a strong predictor of the final Watchman device size that will be implanted. Because of it's strong correlation, using CTmax helps physicians choose the appropriately sized device, leading to better outcomes and fewer complications for patients. The CTmax measurement is more accurate and reliable than the TEEmax measurement.

Soraya Malik in Health & Wellness December 2025 • 4 min read.

"A deeper look into how multi-detector computed tomography (MDCT) is revolutionizing Watchman device sizing for better outcomes."

For individuals with non-valvular atrial fibrillation (AFib), the Watchman device offers a life-changing alternative to long-term anticoagulant therapy. This small, implantable device effectively reduces the risk of stroke by sealing off the left atrial appendage (LAA), where blood clots commonly form in AFib patients. However, the success of the Watchman device hinges on one critical factor: accurate sizing.

Implanting a Watchman device that is too small can lead to leaks around the device, leaving patients vulnerable to stroke. Conversely, a device that is too large can increase the risk of complications such as perforation or device migration. Therefore, determining the optimal device size is paramount for ensuring both the safety and efficacy of the procedure.

Traditionally, transesophageal echocardiography (TEE) has been the primary method for measuring the LAA before Watchman implantation. However, recent research suggests that multi-detector computed tomography (MDCT) may offer a more precise and reliable approach to device sizing, potentially leading to improved patient outcomes.

MDCT vs. TEE: Why Precision Matters in Watchman Device Sizing

Accurate Watchman device sizing with MDCT imaging.

A study published in the JACC ( Journal of the American College of Cardiology ) compared the effectiveness of MDCT and TEE in predicting the optimal Watchman device size. The study, titled "WATCHMAN DEVICE SIZING: IS MULTI-DETECTOR COMPUTED TOMOGRAPHY SUPERIOR TO TRANSESOPHAGEAL ECHOCARDIOGRAPHY?", involved 80 patients who underwent Watchman implantation between 2010 and 2016. Researchers analyzed pre-procedural MDCT and intra-procedural TEE measurements, correlating them with the final device size implanted.

The results revealed that MDCT, specifically the CTmax measurement (maximum diameter of the LAA), was a stronger predictor of the final deployed device size compared to TEEmax (maximum LAA diameter measured by TEE). Specifically, CTmax demonstrated a Spearman's rho of 0.81 (p<0.001), indicating a high degree of correlation, while TEEmax showed only moderate correlation (Spearman's rho: 0.61, p<0.001). This suggests that MDCT provides a more accurate assessment of the LAA dimensions, leading to more precise device sizing.

Reduced Risk of Complications: Accurate sizing minimizes the risk of leaks, embolization, and device migration.
Improved Device Stability: Proper fit ensures the Watchman device remains securely in place.
Enhanced Long-Term Outcomes: Precise sizing contributes to the long-term effectiveness of the Watchman device in stroke prevention.

The study also reported a 100% implantation success rate and a mean follow-up of 197 days with no device-related complications like embolization, cardiac perforation, or pericardial tamponade. Furthermore, the majority of patients (95%) had either no or trivial (≤3 mm) residual peri-device leak on TEE at follow-up. This highlights the importance of accurate pre-procedural planning using MDCT in achieving excellent procedural outcomes.

The Future of Watchman Device Implantation: A Focus on Precision

The findings of this study underscore the importance of utilizing advanced imaging techniques like MDCT in Watchman device implantation. By providing a more accurate assessment of the LAA dimensions, MDCT can help physicians select the optimal device size, minimizing the risk of complications and maximizing the long-term benefits for patients with atrial fibrillation. As technology continues to evolve, a focus on precision and individualized treatment strategies will undoubtedly lead to even better outcomes in the field of stroke prevention.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/s0735-1097(18)32121-1, Alternate LINK

Title: Watchman Device Sizing: Is Multi-Detector Computed Tomography Superior To Transesophageal Echocardiography?

Subject: Cardiology and Cardiovascular Medicine

Journal: Journal of the American College of Cardiology

Publisher: Elsevier BV

Authors: Bo Xu, Jorge Betancor, Kimi Sato, Serge Harb, Karim Abdur Rehman, Kunal Patel, Arnav Kumar, Paul Cremer, Wael Jaber, L. Leonardo Rodriguez, Paul Schoenhagen, Oussama Wazni

Published: 2018-03-01

Everything You Need To Know

What is the Watchman device and how does it work?

The Watchman device is a small, implantable device designed to reduce the risk of stroke in individuals with non-valvular atrial fibrillation (AFib). It works by sealing off the left atrial appendage (LAA), which is a pouch in the heart where blood clots are likely to form in AFib patients. By closing off the LAA, the Watchman device prevents these clots from entering the bloodstream and potentially causing a stroke. This offers an alternative to long-term anticoagulant therapy.

Why is it so important to get the sizing right for the Watchman device?

Accurate sizing of the Watchman device is crucial for its success. If the device is too small, leaks can occur around it, leaving the patient vulnerable to stroke. Conversely, if the device is too large, it can increase the risk of complications like perforation or migration. Proper sizing ensures the device fits securely and effectively seals off the left atrial appendage (LAA), minimizing risks and maximizing long-term stroke prevention.

What is multi-detector computed tomography (MDCT) and how is it used in Watchman procedures?

Multi-detector computed tomography (MDCT) is an advanced imaging technique used to measure the left atrial appendage (LAA) before Watchman device implantation. MDCT provides a more precise and reliable assessment of the LAA dimensions compared to traditional methods like transesophageal echocardiography (TEE). This precision allows physicians to select the optimal Watchman device size, reducing the risk of complications and improving the overall success of the procedure. Specifically, the CTmax measurement (maximum diameter of the LAA) has demonstrated a high degree of correlation with the final deployed device size.

What is transesophageal echocardiography (TEE) and how does it compare to MDCT for Watchman device sizing?

Transesophageal echocardiography (TEE) is a traditional method used to measure the left atrial appendage (LAA) before Watchman device implantation. While TEE has been the primary method, research suggests that multi-detector computed tomography (MDCT) may offer a more precise approach. Studies indicate that MDCT provides a more accurate assessment of the LAA dimensions, leading to more precise device sizing and potentially improved patient outcomes. Specifically, TEEmax (maximum LAA diameter measured by TEE) showed only moderate correlation compared to CTmax.

What does the CTmax measurement mean in the context of Watchman device sizing?

The CTmax measurement refers to the maximum diameter of the left atrial appendage (LAA) as measured by multi-detector computed tomography (MDCT). Studies have shown that CTmax is a strong predictor of the final Watchman device size that will be implanted. Because of it's strong correlation, using CTmax helps physicians choose the appropriately sized device, leading to better outcomes and fewer complications for patients. The CTmax measurement is more accurate and reliable than the TEEmax measurement.