# Chronic Total Occlusion Crossing Techniques

## Definition and Pathology

A chronic total occlusion (CTO) is a complete arterial obstruction with no antegrade flow that has been present for at least 30 days. Histologically, a CTO consists of organized thrombus, fibrosis, calcification, and neovascularization within the occluded segment. The proximal and distal fibrous caps are typically the hardest portions to cross, while the body of the occlusion is often softer and more amenable to wire passage. CTOs account for a significant proportion of femoropopliteal disease, representing up to 40 percent of symptomatic PAD cases undergoing intervention.

## Preprocedural Planning

Cross-sectional imaging, preferably CTA, should be reviewed to assess occlusion length (the strongest predictor of crossing success), degree of calcification (especially at the caps), the reconstitution point and quality of distal runoff, and collateral pathways. Longer occlusions (greater than 20 cm), heavy calcification, and an absent stump at the occlusion origin predict lower success rates. Dual access capability (antegrade plus retrograde) should be planned for complex CTOs from the outset.

## Intraluminal Wire Escalation

### First-Line Approach

The standard technique is to attempt to traverse the occlusion within the true lumen. The operator begins with a soft-tip hydrophilic guidewire (such as a Glidewire, 0.035 inches) supported by a catheter (CXI, Navicross) and gently probes at the proximal cap. If the wire does not advance, escalation proceeds through a ladder of increasing stiffness: first a stiff hydrophilic wire (Glidewire Advantage or Stiff Glidewire), then CTO-specific wires with higher tip stiffness for cap penetration (Victory, Astato), and as a last resort, the back end of a wire for very resistant caps, though this carries a high perforation risk. The support catheter should always be advanced close to the wire tip to maximize pushability and prevent wire buckling.

### Confirmation of True Lumen Position

The operator can aspirate and inject contrast through the support catheter at intervals to verify position. A wire in the true lumen should advance smoothly without a "rubbery" feel. If the wire enters a branch vessel, it confirms intraluminal position. Intravascular ultrasound (IVUS) can definitively confirm lumen position when there is uncertainty.

## Subintimal Dissection and Re-entry

### Concept

Originally described by Bolia in 1990, this technique involves intentionally entering the subintimal space to bypass the occlusion and then re-entering the true lumen distally. It creates a neochannel between the intima and the media/adventitia and is particularly useful for long (greater than 10 cm) femoropopliteal CTOs.

### Technique

A wire loop is formed at the proximal cap to enter the subintimal plane. This loop is then advanced through the subintimal space, where it should move freely with minimal resistance. At the distal cap, the wire is redirected into the true lumen, and re-entry is confirmed with a contrast injection showing the reconstituted distal vessel.

### Advantages

Subintimal angioplasty achieves high technical success rates for long occlusions (80-90%), enables rapid procedure times compared with prolonged intraluminal attempts, and can be performed with standard equipment.

### Disadvantages

The approach may cover important collateral or branch vessel origins, creates a longer dissection plane that may limit future reintervention options, and some evidence suggests lower long-term patency compared with intraluminal recanalization, though this remains debated.

## Re-entry Devices

| Device | Guidance Method | Mechanism | Best Application |
|--------|----------------|-----------|-----------------|
| Outback | Fluoroscopy | Curved needle puncture into true lumen | Failed spontaneous re-entry, peripheral vessels |
| Offroad | Fluoroscopy | Similar to Outback, different deployment | Peripheral vasculature |
| Pioneer Plus | IVUS | Real-time visualization + re-entry needle | Iliac and proximal SFA, complex anatomy |

### Outback Re-entry Catheter

The Outback is a fluoroscopically guided re-entry device containing a curved needle that punctures from the subintimal space into the true lumen. It is positioned using bony landmarks and fluoroscopic orientation and is useful when spontaneous re-entry fails.

### Offroad Re-entry Catheter

The Offroad operates on a similar concept to the Outback with a different deployment mechanism and is designed for use in the peripheral vasculature.

### Pioneer Plus (IVUS-Guided)

The Pioneer Plus combines IVUS with a re-entry needle, allowing real-time visualization of the true lumen to guide needle puncture. It offers the highest accuracy but is more expensive and requires IVUS experience. It is particularly valuable in the iliac and proximal SFA segments.

## Retrograde Approaches

### Pedal/Tibial Retrograde Access

When antegrade crossing fails, retrograde access via a tibial artery (usually the anterior tibial/dorsalis pedis or posterior tibial) provides an alternative route. Ultrasound-guided micropuncture access of the pedal or tibial vessel is performed, and a wire is advanced retrograde through the CTO. The proximal cap is often easier to cross from the distal side. The "rendezvous" technique uses a snare or catheter to capture the retrograde wire from the antegrade sheath. The SAFARI technique (Subintimal Arterial Flossing with Antegrade-Retrograde Intervention) combines antegrade and retrograde subintimal planes.

### Popliteal Retrograde Access

Direct popliteal artery access, performed with the patient prone or in a lateral position, is useful for SFA CTOs when pedal access is not feasible due to absent pedal pulses or small vessels. This approach carries higher complication risk given the deeper location and proximity to the popliteal vein.

## Advanced and Adjunctive Techniques

### IVUS-Guided CTO Crossing

Real-time IVUS can help navigate through the CTO body by identifying the true lumen versus the subintimal space and guiding re-entry when combined with a re-entry device. It adds cost but may reduce procedural time and complications in complex cases.

### Crossing Catheters

Several specialized crossing catheters exist for when wire escalation fails. The TruePath has a rotating tip that creates a channel through the CTO by cutting through fibrotic tissue. The Frontrunner XP uses blunt microdissection for cap penetration. The Wildcat and Kittycat employ rotating tips for navigating CTOs.

### Atherectomy for CTO

Excimer laser atherectomy can serve as a step-up for crossing resistant CTOs. The "step-by-step" technique delivers laser energy to photoablate fibrotic tissue, facilitating wire advancement. This approach is typically reserved for cases where wire and catheter crossing have failed.

## When to Abandon an Attempt

The procedure should be abandoned if there is a perforation with active extravasation not controllable with balloon tamponade, extensive subintimal dissection compromising critical collateral vessels, inability to cross after exhausting available techniques (typically after 45 to 90 minutes of crossing attempts), excessive contrast volume approaching the nephrotoxicity threshold, or patient tolerance issues such as pain or hemodynamic instability. The option to return for a second attempt or refer for surgical bypass should always be maintained.

<image>Step-by-step illustration of subintimal dissection and re-entry technique for a chronic total occlusion of the superficial femoral artery. Four sequential panels: (1) Wire loop formation at the proximal fibrous cap entering the subintimal plane; (2) Wire loop advancing freely through the subintimal space alongside the occluded true lumen (shown in cross-section); (3) Wire reaching the distal cap and redirecting toward the true lumen with re-entry; (4) Balloon angioplasty of the neochannel with the final result showing a patent subintimal channel. Cross-sectional insets at each stage show the wire position relative to the intima, media, and adventitia.</image>

<image>Illustration of retrograde pedal access for CTO crossing (SAFARI technique). Shows a patient's leg with an antegrade femoral sheath and a retrograde micropuncture needle in the dorsalis pedis artery. A wire from the retrograde access is shown traversing a long SFA CTO while a catheter from the antegrade approach is advanced to meet it. An inset panel shows the rendezvous technique with a snare capturing the retrograde wire through the antegrade sheath. Key anatomical landmarks (inguinal ligament, knee, ankle) are labeled.</image>

<image>Comparison of re-entry devices for CTO crossing. Three panels showing: (1) Outback catheter with its curved needle deployed from the subintimal space into the true lumen under fluoroscopic guidance, with a magnified view of the needle tip puncturing the intimal flap; (2) Pioneer Plus catheter with the IVUS transducer visualizing the true lumen and guiding needle deployment shown on a simulated IVUS screen; (3) Fluoroscopic image showing successful re-entry with contrast confirming flow in the true lumen distally. Labels indicate the subintimal space, true lumen, and reconstitution point.</image>

## Clinical Pearls

CTO length is the single strongest predictor of crossing success and should always be measured on CTA before the procedure. The approach should begin with an intraluminal attempt, escalating to subintimal only after reasonable intraluminal efforts fail. The proximal cap is usually the hardest part; once through, the CTO body is often softer.

Knowing when to stop is critical: prolonged unsuccessful crossing attempts expose patients to contrast, radiation, and complication risk without benefit. Retrograde pedal and tibial access is a powerful tool that should be in every IR trainee's skillset. Subintimal angioplasty works -- long-term patency is reasonable and limb salvage rates are comparable to intraluminal approaches. Dual access capability should always be planned for, even if not ultimately used.

## References

- Bolia A et al. Percutaneous transluminal angioplasty of occlusions of the femoral and popliteal arteries by subintimal dissection. Cardiovasc Intervent Radiol 1990
- Defined by the SAFARI technique: Spinosa DJ et al. J Vasc Interv Radiol 2005
- Defined by the CLEVER trial: Murphy TP et al. Circulation 2012
- Defined by the Global Vascular Guidelines (GVG) on CLTI. J Vasc Surg 2019
- Defined by the Expert consensus on CTO crossing: CIRSE Standards of Practice. Cardiovasc Intervent Radiol 2021