17.1 IABP & Catheter-Based Ventricular Assist Devices

IABP & Catheter-Based Ventricular Assist Devices

ARRT Cardiac-Interventional Procedures 2.A.8–A.9 are the intra-aortic balloon pump (IABP) and catheter-based ventricular assist devices (VADs). The same interventional Focus of Questions used throughout 2.A applies: anatomy and pathophysiology, indications, contraindications, imaging, access, ultrasound, equipment, complications, and closure. These consoles are not décor. They are how a high-risk PCI stays a PCI instead of a spiral into cardiogenic shock.

Quick Answer: An IABP inflates at the dicrotic notch and deflates just before systole, augmenting diastolic coronary perfusion and reducing afterload. Ratios are 1:1, 1:2, and 1:3. Insert via the femoral artery; the tip sits 1–2 cm below the aortic arch / at the carina — not in the left subclavian, not covering the renals. Helium shuttles the balloon. Blood in the tubing is rupture — stop. Contraindications: significant aortic regurgitation (AR), aortic dissection, severe peripheral vascular disease (PVD). An Impella-class LV pump goes femoral arterial, across the aortic valve (AV) into the LV, runs a heparinized dextrose purge, and is parked on echo/fluoro — never leave it poorly in the LVOT. RV support (Impella RP-class / Protek conceptually) runs vein to pulmonary artery (PA). Indications: cardiogenic shock and high-risk PCI.

Anatomy the balloon and the axial pump occupy

The descending thoracic aorta has three fluoro landmarks: the aortic arch / left subclavian origin (upper fence), the carina (chest-film and fluoro proxy for a correct IABP tip), and the renal arteries near L1 (lower fence). A balloon that rides into the left subclavian steals left-arm flow and can threaten the arch. A balloon that covers the renals turns support into acute kidney injury.

A catheter-based LV VAD does not live in the aorta. It crosses the AV. The inlet sits in the mid-cavity LV; the outlet sits in the ascending aorta. Too ventricular and the inlet eats mitral chordae and sucks against myocardium. Too aortic and the pump sits in the LVOT / AV plane, unloads poorly, and can create or worsen AR. RV catheter pumps must traverse the tricuspid and pulmonary valves and park an outlet in the PA, not coiled in the RV.

Pathophysiology is blunt. In cardiogenic shock and high-risk PCI, the LV cannot generate forward flow without punishing wall stress. IABP counterpulsation raises diastolic coronary driving pressure and drops systolic afterload. An Impella-class device continuously unloads the LV into the aorta and does not need a native QRS to trigger.

IABP timing, ratios, helium, and the waveform

Inflation is timed to the dicrotic notch on the aortic tracing — aortic valve closure, the start of diastole. Deflation is timed just before systole (classically the R wave, immediately before AV opening). Inflate too early and you slam a still-open AV, raise LV afterload, and cut stroke volume. Inflate too late and you miss the coronary-perfusion window. Deflate too early and you lose afterload reduction (and can steal coronary flow). Deflate too late and the LV ejects against an inflated balloon.

Assist ratios:

• 1:1 — every beat. Full support for shock or protected PCI.
• 1:2 — every other beat. Weaning, and the strip that lets you compare assisted versus unassisted beats.
• 1:3 — every third beat. Further wean, not a destination for a crashing patient.

Trigger from ECG when the QRS is clean; trigger from the arterial waveform when the ECG is noisy or the rhythm is chaotic AF. Irregular rhythms make 1:1 ugly — 1:2 may be the timing that actually hits a real dicrotic notch.

Helium is the shuttle gas because it is low-density and can fill and empty in a single diastole. The console autofills and alarms for a gas leak. A leak is not a cue to keep pumping through a ruptured balloon.

Waveform teaching: augmented diastolic pressure should exceed unassisted systolic pressure. Assisted end-diastolic and assisted systolic pressures should fall below the unassisted values — that is afterload reduction, not a broken transducer.

IABP insertion, imaging, and position

Access is typically the common femoral artery, ultrasound-guided, with a documented distal pulse before the sheath. Axillary or subclavian insertion exists when the groins are hostile; it does not change the aortic landing zone. Advance over the device wire under fluoro. The tip belongs 1–2 cm distal to the left subclavian origin, which on a chest film or fluoro overlay is at the carina. Confirm the balloon is in the descending aorta, not coiled in the arch, not in the left subclavian, and not so caudal that it covers the renals.

A left radial line that suddenly dampens is a too-high balloon until proven otherwise. Falling urine output with a caudal balloon is a too-low balloon until proven otherwise.

IABP contraindications and complications

Classic contraindications:

• Significant AR — diastolic inflation throws volume back into the LV.
• Aortic dissection (and a surgically relevant aneurysm) — the balloon can extend the flap.
• Severe PVD — you cannot insert, or you occlude the remaining limb vessel.

Complications the exam expects you to name:

• Limb ischemia — lost Doppler signal, mottling, pain. The sheath plus balloon is a large occupancy in a diseased iliac. Treatment is removal, repair, or perfusion, not another hour of hope.
• Thrombocytopenia — mechanical platelet destruction on the balloon. Check a count; do not assume every drop is heparin-induced thrombocytopenia.
• Balloon rupture — blood in the helium tubing. Stop pumping, clamp, and remove the balloon. Continuing to shuttle helium through a hole is a gas-embolus plan.
• Gas leak without frank blood — treat as circuit-integrity failure; do not silence the alarm.
• Infection, dissection, and compartment syndrome after a long ischemic dwell.

Closure after removal is large-bore femoral craft: compression or a closure device when anatomy allows, then a documented distal pulse. Ultrasound that guided the stick also finds the hematoma.

Catheter-based LV VAD (Impella-class)

Cannulation: femoral arterial access (ultrasound), peel-away sheath, catheter across the AV into the LV. Teaching sheath size for the common percutaneous pumps is 12–14 Fr (larger surgical or axillary pumps exist; they are not the everyday table-side 2.5/CP story). Wire the LV, confirm the pigtail is free in the cavity, and pull the inlet to a mid-LV position with the motor across the AV.

Position checks — echo and fluoro, not hope:

• Fluoro: pigtail in the LV, not wrapped in mitral chordae, not sitting in the aorta.
• Echo (transthoracic or TEE): inlet in the LV, below the AV, not in the LVOT, not against the wall, not in the left atrium.
• Console placement signals: ventricular at the inlet, aortic at the outlet.

Never leave the device poorly in the LVOT. A malpositioned inlet there fails to unload, hemolyzes, can worsen AR, and can injure the valve. Suction alarms and new mitral regurgitation are repositioning cues, not “turn it up.”

Purge: heparinized dextrose (typically D5W with heparin) flows through the motor so blood does not stagnate in the pump. A dry or clotted purge is a pump-stop emergency. Know where the purge cassette lives before the case starts.

Hemolysis is the signature complication: tea-colored urine, rising plasma free hemoglobin or LDH, falling haptoglobin. Causes include a malpositioned inlet, a sucking empty ventricle, or a device against the wall. Reposition and volume-fill before you assume the pump is “just like that.”

Contraindications (teaching): a mechanical aortic prosthesis (you cannot cross it), LV thrombus (the inlet emulsifies clot into the brain), significant AR, and severe PVD that forbids large-bore femoral access.

Catheter-based RV support

Impella RP-class teaching: femoral venous access, across the right heart, outlet in the PA. Protek-class dual-lumen cannulae (conceptually) often enter from the internal jugular, with drainage in the RA and return in the PA — same physiology, different hole. Fluoro must show the catheter through the TV and PV, not coiled in the RV. Right-heart thrombus and PA anatomy that will not accept the cannula are stop signs.

Indications the outline actually tests

• Cardiogenic shock (including shock during STEMI PCI) when drugs are not enough, or as the planned first support device.
• High-risk PCI (protected PCI): unprotected left main, last remaining conduit, severe LV dysfunction — the VAD is placed before the longest ischemic inflation.

IABP is lighter, ECG-triggered, and afterload-reducing. Impella-class support unloads the LV even if the native rhythm is ugly. They are not interchangeable on the exam. Large-bore arterial access still needs ultrasound, a documented distal pulse, and a closure plan (manual compression, preclose, or surgical) — 13.1 and 13.3, at bigger French sizes.

Table: device / cannulation / contraindication / tech check

Worked case

A 68-year-old with a 20% EF and an unprotected left main is booked for PCI. The IABP inflates after the dicrotic notch and the assisted systolic pressure rises. That is late timing — afterload is worse, not better. Fix inflation to the dicrotic notch and deflation to just before ejection. If the LV still collapses when the main-body balloon goes up, an Impella-class catheter goes in before the next inflation: femoral artery, across the AV, purge running, echo confirming the inlet is not in the LVOT.

Separately, the IABP tubing that was clear is now pink. That is balloon rupture. Stop. Do not “flush the helium line.” Remove the balloon.

Exam traps

• Inflation on the QRS is not inflation at the dicrotic notch.
• 1:3 is a wean, not shock support.
• A tip in the left subclavian is not extra coronary flow.
• Significant AR is a reason not to balloon, not a reason to turn augmentation up.
• Blood in tubing is rupture, not a helium refill.
• Impella-class support crosses the AV and needs a purge; it is not a second IABP.
• RV support is a venous-to-PA path, not a second femoral artery.