Sheath Sizes, Guide Compatibility, and Fluoro 101: What Every New Cath Lab Rep Should Know

If you're new to cath lab sales, you’ve probably heard terms like “6 French sheath,” “fluoro time,” or “guide catheter compatibility” and nodded along—without really understanding what they meant.

But in the lab, small misunderstandings can lead to big mistakes.

This post breaks down the core technical concepts every new medical device rep needs to grasp before supporting cases.

🧵 What Is a Sheath? And What Does 'French Size' Mean?

A vascular sheath is the short, hollow tube inserted into the artery (usually radial or femoral) that provides access for wires, catheters, and devices.

• French size (Fr) refers to the inner diameter of the sheath, measured in thirds of a millimeter.
  👉 1 Fr = 0.33 mm
  👉 A 6 Fr sheath has a 2.0 mm inner diameter

Why this matters:
Your device must be compatible with the sheath size used during the procedure. If your balloon catheter requires a 6 Fr guide, and the lab is using a 5 Fr sheath, your product won’t fit.

✅ Know your device’s minimum sheath size
✅ Know what sheath sizes your physicians prefer

👉 Suggested link: Understanding the Cath Lab: Devices, Team Roles, and Common Procedures

🔀 Guide Catheter Compatibility: The Overlooked Dealbreaker

A guide catheter is the tool used to direct wires and devices to the target vessel. Not only does your product need to fit through the guide’s inner lumen, it must also be able to make the bends and torques required to navigate anatomy.

Key compatibility concerns:

• Inner diameter: Can your product pass through a 6 Fr guide? What about a 5 Fr?

• Length: Will it reach the lesion or target anatomy?

• Torqueability: Can it navigate tortuous or calcified vessels?

💡 Tip: Carry a compatibility chart or quick-reference sheet that lists which guide sizes, wire types, and sheath sizes your device works with. Know the difference between ID= inner diameter and OD= outer diameter. We cover this and more in Device 101. Enroll here.

💡 Fluoro 101: Understanding Imaging in the Cath Lab

Fluoroscopy is real-time X-ray imaging that allows the team to visualize devices and anatomy during a procedure. It’s the visual backbone of interventional cardiology.

As a rep, here’s what you need to know:

1. Fluoro Time

This is the total duration the X-ray beam is activated. Physicians and staff monitor this to minimize radiation exposure.

• Tip for reps: Know how long it takes to deploy or reposition your product under fluoro. Time = dose.

2. Views and Angles

Terms like RAO, LAO, cranial, and caudal refer to camera positioning to get optimal visualization. You’re not expected to call shots—but you should understand the setup. This is also covered in detail in Device 101- take a look at the course curriculum here.

3. Radiopacity

Can your product be seen clearly under fluoro? If not, physicians may be reluctant to use it.

✅ Know which markers, coils, or wires are visible and where.
✅ Know how to guide staff on device positioning if asked.

📋 Top 5 Things to Know Before a Case

1. What sheath size does this doctor typically use—radial or femoral?

2. Is your device compatible with 5 Fr or 6 Fr guides?

3. What guide shape and curve are most common for this procedure?

4. How visible is your product under fluoro, and where are the markers?

5. Does your product require any special flushing or prep that impacts case flow?

🚫 Common Rookie Mistakes to Avoid

• Bringing a 6 Fr device to a 5 Fr case

• Not knowing which guide shapes work best for your product

• Interrupting or offering unsolicited input during live fluoro

• Guessing about product visibility or prep during the case

Remember: credibility is built on preparation, not presence.

Final Word: Learn the Language of the Lab

You don’t need to be a clinician—but you do need to speak the language of access, compatibility, and imaging. Mastering these core concepts will help you avoid mistakes, build trust with your team, and establish yourself as a reliable rep in the cath lab.

More for New Reps:

• Understanding the Cath Lab: Devices, Team Roles, and Common Procedures

• Enroll in Device 201 to level up your cath lab confidence.