13.1 IABP & Impella

Mechanical Support in the Cath Lab

Mechanical circulatory support (MCS) devices bridge patients through cardiogenic shock, high-risk PCI, and mechanical complications of acute myocardial infarction. For the RCIS technologist, Domain C Task 7 requires understanding how these devices work, how to recognize correct versus malpositioned waveforms, when placement is appropriate, and how to troubleshoot common problems at the bedside. The cath lab most frequently encounters intra-aortic balloon pumps (IABP) and Impella microaxial pumps; both unload the failing left ventricle but through fundamentally different mechanisms. Knowing the difference is a recurring RCIS exam theme.

Intra-Aortic Balloon Pump: Mechanism and Hemodynamics

The IABP is a counterpulsation device. A polyurethane balloon sits in the descending aorta, typically positioned so the tip lies 1–2 cm below the left subclavian artery (confirmed by fluoroscopy or chest X-ray). Helium fills the balloon because it is low-density and rapidly compressible. During diastole, the balloon inflates, displacing blood volume and augmenting diastolic aortic pressure. This increases coronary perfusion pressure — the gradient driving blood through the coronary arteries during diastole when the aortic valve is closed. During systole, the balloon deflates rapidly, creating a low-pressure zone in the aorta that reduces left ventricular afterload and decreases myocardial oxygen demand.

The hemodynamic goals are therefore twofold: more coronary blood flow during diastole and easier ejection during systole. IABP support typically increases cardiac output by 0.5–1.0 L/min in cardiogenic shock — modest compared with active pumps, but valuable as a bridge when less invasive support is sufficient.

Timing: The Heart of IABP Management

Proper timing is the single most tested IABP concept on the RCIS exam. The pump must synchronize with the patient's ECG or arterial pressure waveform:

Inflation is triggered at the dicrotic notch — the brief downward deflection on the arterial waveform marking aortic valve closure and the start of diastole. Deflation must complete before the next systolic upstroke so the balloon does not impede ventricular ejection.

Most modern consoles offer 1:1 (every beat), 1:2, and 1:3 assist ratios. A 1:2 ratio assists every other beat and is used when augmentation is adequate but helium conservation or weaning is desired. During weaning trials, the team gradually reduces the assist ratio while monitoring hemodynamics.

Waveform Analysis and Timing Errors

The arterial waveform displayed on the IABP console is the primary tool for timing verification. Learn to recognize four maltiming patterns:

Correct timing produces a sharp diastolic augmentation immediately after the dicrotic notch, a lower end-diastolic pressure compared with unassisted beats, and an unchanged or slightly reduced systolic peak because afterload is lowered.

The RCIS role includes calling attention to maltiming, verifying the trigger source (ECG versus arterial pressure), and ensuring the arterial line used for timing is not damped. A damped waveform can cause the pump to miss the dicrotic notch and inflate at the wrong phase.

IABP Indications and Contraindications

Recognized indications include cardiogenic shock complicating acute MI (as a bridge to recovery, revascularization, or advanced MCS), mechanical complications such as acute mitral regurgitation from papillary muscle rupture or ventricular septal defect, refractory unstable angina, hemodynamic support during high-risk PCI, and pre-operative stabilization in selected cases.

Absolute or relative contraindications — high-yield for the exam — include:

Acute mitral regurgitation from papillary muscle rupture is an indication, not a contraindication — the IABP reduces afterload and supports the patient until surgical repair.

IABP Access and Cath Lab Considerations

IABP insertion typically uses femoral arterial access through a 7–8 Fr sheath. The balloon catheter is advanced over a guidewire into the descending thoracic aorta. Large-bore femoral access (8–10 Fr or greater) may be required when IABP and Impella share the same side or when concomitant PCI is planned. The RCIS assists with sheath management, hemostasis planning, and ensuring the console trigger cable connects to the patient's ECG or arterial pressure transducer.

Post-insertion, confirm balloon position on imaging, verify timing on the console waveform, and monitor the access site for bleeding, hematoma, and limb ischemia (pallor, coolness, diminished pulses distal to insertion).

Impella: Microaxial Left Ventricular Support

The Impella family (2.5, CP, 5.0, 5.5) provides active continuous-flow support rather than counterpulsation. A catheter-mounted microaxial pump sits across the aortic valve, drawing blood from the left ventricle through an inlet area in the LV cavity and ejecting it into the ascending aorta through an outlet. This directly unloads the LV, reducing wall stress and myocardial oxygen consumption while maintaining forward flow.

The Impella console displays P-level (motor performance), flow estimate, and alarm states. Correct positioning is critical: the inlet must sit ~3.5 cm below the aortic valve (device-specific; verify manufacturer markings). Too deep and the inlet pulls on papillary muscles or mitral apparatus; too shallow and the inlet is above the valve, reducing flow and causing hemolysis.

Impella Versus IABP: Exam Comparison

When IABP support is insufficient in refractory cardiogenic shock, escalation to Impella, ECMO, or surgical MCS is the next step.

Impella Troubleshooting in the Cath Lab

Common Impella alarms and responses:

• Low flow / P-level low: Check catheter position (pull back or advance per protocol), assess volume status (hypovolemia reduces preload), rule out kinking at the sheath hub.
• High motor current: Suggests contact with endocardium or valve — reposition under fluoroscopy.
• Hemolysis (elevated LDH, dark plasma, anemia): Often from malposition or excessive speed relative to preload; notify the operator.
• Bleeding at access site: Large-bore sheath requires aggressive hemostasis planning; consider closure devices per protocol.

The RCIS maintains sterile technique during repositioning, monitors hemodynamics continuously, and documents flow parameters at defined intervals.

RCIS Exam Focus

Expect questions on dicrotic notch inflation timing, waveform maltiming patterns, IABP contraindications (especially severe AR and aortic dissection), Impella mechanism (transvalvular axial pump unloading the LV), and device escalation when balloon pump support is inadequate. Always connect the device to the hemodynamic problem: counterpulsation for diastolic augmentation versus active pumping for direct ventricular unloading.