What are the risks and considerations for manually shaping a microcatheter without a mandrel in a patient with a history of vascular disease?

Manual Microcatheter Shaping Without a Mandrel: Safety and Technique

Manual shaping of microcatheters without a mandrel is not recommended and represents a significant deviation from established safe practice, as all contemporary evidence demonstrates that controlled shaping using mandrels—whether through steam shaping or manual bending of the mandrel itself—is the standard approach to achieve predictable, stable catheter configurations while minimizing vessel trauma risk.

Why Mandrels Are Essential

The mandrel serves as the structural support that allows controlled, reproducible shaping of the microcatheter tip. Without this support:

• Unpredictable shape formation: Attempting to manually bend a microcatheter without internal support creates inconsistent, unstable configurations that may collapse or deform during navigation through tortuous vessels 1

• Catheter structural damage: Direct manual manipulation without mandrel support can cause kinking, compression damage, or weakening of the catheter wall, potentially leading to catheter fracture or embolization 2

• Loss of shape stability: Research demonstrates that even properly shaped microcatheters lose 17.4%-30.3% of their angle when passing through guide catheters, and 24.1%-61.2% when inserting microguidewires 1. Without mandrel-based shaping, these losses would be far more severe and unpredictable.

Established Safe Shaping Methods

Steam Shaping with Mandrels (Preferred)

• Mandrels are bent to desired angles (L-shape 90°, U-shape 180°, O-shape 360°), inserted into the microcatheter, and steam is applied to set the shape 1
• This produces mean angles of 42.4°-54.1° for L-shapes, 80.2°-96.7° for U-shapes, and 130.7°-150.8° for O-shapes 1
• Shape recovery after guidewire withdrawal is excellent at 93.2%-101.6% 1

Manual Mandrel Shaping (Acceptable Alternative)

• Mandrels are manually bent to the intended angle, inserted into the microcatheter, and the catheter conforms to the mandrel shape 3, 4
• Manual-shaped microcatheters show only 4.2%-6.3% greater angle reduction compared to steam-shaped catheters when passing through guide catheters, with final tip angles not significantly different 1
• This technique achieved successful positioning in 81% of cases without modification in one series 3

Advanced Planning with 3D Models

• Patient-specific 3D printed vessel models allow pre-procedural mandrel shaping that matches exact anatomy 3, 4
• This approach required catheter shape modification in only 19% of cases and repositioning in only 29% due to kickback 3
• All procedures were completed without complications including aneurysm rupture 3

Risks Specific to Vascular Disease Patients

In patients with vascular disease, the risks of improper catheter shaping are amplified:

• Vessel perforation: Poorly shaped catheters may traumatize diseased vessel walls, leading to perforation, haemothorax, or mediastinal bleeding requiring urgent surgical intervention 2

• Thrombotic complications: Unstable catheter positioning increases manipulation time and vessel wall trauma, promoting thrombus formation—already elevated risk in vascular disease patients 5

• Inability to achieve stable positioning: Atherosclerotic vessels with irregular lumens require precise catheter shaping for stable positioning; inadequate shaping leads to repeated attempts and cumulative trauma 2

Critical Safety Principles

• Never advance guidewires or dilators against resistance, as this is a primary cause of vessel perforation and cardiac tamponade 2

• Maintain guidewire control during all catheter manipulations to prevent guidewire embolization, now classified as an NHS Never Event 2

• Limit guidewire advancement to no more than 20 cm without imaging to prevent myocardial perforation 2

• If catheter positioning is suboptimal, reposition using proper technique rather than proceeding with inadequate access, as poorly positioned catheters increase complication risk 2

What To Do Instead

If you lack a pre-shaped mandrel or steam shaping capability:

1. Use a straight microcatheter with intravascular placement shaping: Insert the SL-10 straight microcatheter into the parent vessel for 5 minutes, allowing it to conform to the vessel anatomy, then withdraw and steam-shape based on the acquired configuration 6

2. Employ steerable microcatheter technology: Remote-controlled flexible tip catheters (e.g., SwiftNINJA) allow real-time tip angle adjustment without pre-shaping 7

3. Defer the procedure until proper shaping equipment is available if the anatomy is complex and stable catheter positioning is critical for safety 3, 4