13.2 Sheaths, Catheters, Guidewires & Manifold

Sheaths, Catheters, Guidewires & Manifold

ARRT CI Procedures Focus of Questions item 6 is equipment: types, indications, preparation, setup, and operation. The scored items are not brand trivia. They are whether you can pick a long sheath for a tortuous iliac, tell a diagnostic catheter from a guide catheter, keep a hydrophilic wire out of a careless coronary pass, and zero a transducer before you trust a number. This section is the table that sits between the needle in 13.1 and the closure in 13.3.

Quick Answer: Match French size and sheath length to the vessel and the device. Guide catheters have a larger lumen, are shorter, and often have side holes; diagnostic catheters do not carry stents. Never inject against a damped coronary pressure. Zero the transducer at the phlebostatic axis. An air bubble overdamps the waveform; a loose connection underdamps it. Hydrophilic Glidewire-class wires are perforation risks in coronaries if used carelessly.

Needles: 21-gauge micropuncture versus 18-gauge

Prep starts with the needle that makes the hole.

21-gauge micropuncture. Takes an 0.018-inch wire. Indication: small, calcified, or high-stakes vessels (radial, IJ, hostile CFA) and any case in which a miss should leave a tiny hole. Setup: needle, 0.018-inch wire, coaxial dilator/introducer that converts to 0.035-inch. Operation: single-wall under ultrasound, then upsize. Trap: advancing the stiff dilator without confirming the 0.018-inch wire is intravascular on fluoroscopy.

18-gauge. Takes a 0.035-inch wire directly. Indication: straightforward CFA with a clear pulse and ultrasound. Faster. Larger defect if you miss or transfix. Trap: treating 18-gauge as mandatory real access when micropuncture was the safer plan.

Flush every needle, wire, and hub with heparinized saline (or a heparin-free flush if heparin-induced thrombocytopenia (HIT) is documented — section 5.1). Wet-to-wet connections start here: fluid meets fluid so air never enters the column.

Sheaths: French size, length, coating, destination

French (Fr) size describes the outer diameter of the sheath (teaching conversion: Fr / 3 ≈ millimeters). A 6 Fr sheath is about 2 mm across. The catheter that fits inside is smaller than the sheath's labeled Fr. Indication: pick the smallest sheath that still accepts the planned catheter or device. A 6 Fr diagnostic case does not need an 8 Fr hole.

Length. A standard short sheath (about 10–12 cm) is enough for a straight CFA or a wrist. A long sheath (often 25–45 cm or longer, including destination or reinforced sheaths) is indicated for tortuous iliacs, hostile groins, and when you need rail support so coronary guides or large-bore devices do not buckle in the pelvis. Setup: flush the sheath and the sidearm, load the dilator fully, insert over the 0.035-inch wire under fluoro if the path is not pristine, then aspirate and flush the sidearm until the column is blood-then-saline without clot. Operation: never advance a sheath without its dilator; never lose wire position while exchanging.

Hydrophilic sheaths. A hydrophilic coating eases insertion through scar or spasm (especially radial). Indication: difficult wrist or a scarred groin. Trap: they can slip out more easily — suture or a dedicated holder matters — and they must stay wet per instructions for use.

Destination-class / long reinforced sheaths. Indication: deliver support through tortuous iliacs, some peripheral work, and selected structural or support-device rails. Trap: a long sheath sitting in the iliac can still obstruct if you force a mismatch device; confirm the lumen accepts the planned Fr.

Diagnostic catheters versus guide catheters

Diagnostic catheters (Judkins left/right, Amplatz, pigtail, multipurpose, and graft catheters) are built to inject and record, not to deliver stents. They are typically longer, smaller-lumen, and end-hole or limited side-hole. Indication: coronary, graft, and ventricular angiography; pressure sampling. Prep: flush until bubble-free; wipe the hub; keep the factory shape. Operation: advance over a wire into the aorta, then engage; hand-inject coronaries so you can stop if the pressure damps.

Guide catheters are the PCI rail. Teaching differences the exam cares about:

• Larger inner lumen so balloons, stents, intravascular imaging, and aspiration devices will pass.
• Shorter overall length so working catheters have enough shaft outside the hub.
• Often side holes to maintain aortic-root perfusion when the tip is deeply engaged (and to reduce pressure damping).

Indication: any coronary or graft intervention that needs equipment delivery. Trap: using a diagnostic catheter as a guide to force a stent — it will not pass, and the extra force dissects. Trap: deep-seating a side-hole guide and trusting the pressure because side holes still show an aortic waveform while the tip is subintimal. Look at the picture, not only the number.

Prep/setup: flush the guide, load a Y-adapter/hemostasis valve, connect the manifold wet-to-wet, and confirm a crisp aortic waveform before you wire the coronary.

Guidewires: 0.035-inch starters to 0.014-inch coronaries

J-wire (0.035-inch). The atraumatic starter. Indication: sheath insertion, aortic passage, pigtail exchanges. The J keeps the tip from diving into a side branch. Trap: a straightened J is no longer a J.

Wholey-class (0.035-inch). A steerable, floppy-tip wire for tortuous iliacs and difficult aortic paths. Indication: when a standard J will not track. Trap: still not a coronary wire.

Hydrophilic (Glidewire-class). Extremely slippery, excellent through stenoses and loops in peripheral and access anatomy. Perforation risk in coronaries if used carelessly — the tip can leave a small branch or go subintimal with little tactile warning. Indication: hostile iliacs, radial loops outside the coronary. Operation: keep the tip moving under fluoro; never park it in a blind coronary. Trap: grabbing the hydrophilic as a workhorse 0.014-inch because it is on the table.

Workhorse coronary 0.014-inch. Balanced tip and rail for routine PCI. Indication: most lesion crossing. Prep: wipe, wet, load the clip or torque device. Operation: short, controlled movements; watch the tip, not the hub.

Extra-support 0.014-inch. Stiffer rail for calcified lesions, buddy-wire support, and delivering bulky devices. Trap: the stiff body can prolapse a loop and straighten a vessel into perforation if you over-advance.

Extra-floppy 0.014-inch. Soft tip for distal, tortuous, or recently ruptured anatomy when you want less penetration. Trap: it will not support a stent; do not be surprised when the balloon telescopes.

Store wires in heparinized bowls, wipe before re-insertion, and never reuse a wire that has a damaged tip.

Manifold and pressure transducer

The manifold is the three- or four-port plastic block that chooses saline flush, contrast, pressure, and waste. Three-way stopcocks on each port must be fully open or fully closed — a half-turn is a leak or an overdamped tracing.

Prep/setup:

1. Prime the pressure bag and tubing with saline (heparinized per protocol).
2. Connect wet-to-wet — fluid to fluid, no air.
3. Fill the contrast syringe or contrast port; keep that column bubble-free.
4. Zero the transducer at the phlebostatic axis (teaching landmark: mid-axillary line at the fourth intercostal space, right-atrial level) with the stopcock open to air at the transducer. Re-zero if the table height changes relative to the transducer.
5. Fast-flush (square-wave / dynamic-response test) and inspect the waveform.

Saline versus contrast. Pressure is read through a saline column. A manifold left open to viscous contrast overdamps the tracing. After a coronary injection, flush contrast out of the catheter before you call a pressure damped as anatomy.

Damping physics the exam wants:

• Air bubble → overdamped waveform (sluggish, rounded, systolic too low, diastolic too high).
• Loose connection → underdamped waveform (overshoot, ringing, whip).
• Clot, a half-open stopcock, and contrast in the line also overdamp.

Never inject against a damped coronary pressure. Damping or ventricularization means the catheter tip is against plaque, too deep in a conus, or subintimal. Contrast fired into that position is dissection, hydraulic perforation, and ventricular fibrillation. Back the catheter out, confirm a crisp aortic waveform, and only then inject. Side holes do not make a damped tip safe.

Do not let the manifold run dry (air embolism — section 6.3). Do not leave an empty contrast syringe sucking air.

Device / job / trap

Scenario and exam traps

Left coronary engagement. The aortic waveform suddenly flattens, systolic pressure on the monitor is nonsense, and the operator asks for a cine. Do not inject. Back out until the waveform is aortic. Then look for an air bubble (overdamped) versus a loose stopcock (underdamped) if the catheter position is clearly free. A tortuous iliac that kinks every guide is a long sheath case, not a reason to grab a hydrophilic coronary wire and just push.

Traps: diagnostic catheter as a stent rail; Glidewire-class in a careless coronary; zeroing the transducer on the floor; reading pressure through a contrast-filled manifold; injecting into a damped left main.