Intra-Aortic Balloon Pump (IABP)

Overview

Principles (Mechanism of Action - Counterpulsation)

• Rapid balloon inflation displaces blood proximally and distally
• Increases diastolic aortic pressure ("diastolic augmentation")
• Increases coronary artery perfusion pressure (since coronary filling occurs in diastole)
• Augments cerebral perfusion

• Rapid deflation creates a sudden drop in aortic end-diastolic pressure
• Reduces left ventricular afterload (the LV ejects against less resistance)
• Lowers myocardial oxygen demand (MVO2)
• Modestly augments cardiac output by ~0.5-1.0 L/min

IABP Waveform

• Unassisted systole - normal peak pressure
• Diastolic augmentation - a prominent spike during the assisted diastole, often exceeding the previous systolic peak
• Assisted aortic end-diastolic pressure - lower than the unassisted end-diastolic pressure (reflects afterload reduction)
• Assisted systole - reduced systolic peak (less work required from LV)

MCS Device Comparison

Hemodynamic Requirements

• Some residual LV function - any increase in cardiac output still depends on the work of the heart itself
• Electrical stability - the device is triggered by ECG (R wave) or arterial pressure tracing (dicrotic notch)

Indications

Contraindications

• Severe aortic regurgitation - balloon inflation in diastole would worsen regurgitant volume back into the LV
• Aortic dissection - balloon inflation could propagate or worsen the dissection

• Aortic aneurysm
• Significant coagulopathy
• Severe peripheral arterial disease (especially at the insertion site)
• Severe aortoiliac occlusive disease
• Uncontrolled sepsis

Advantages

Disadvantages / Limitations

Complication Rates (Benchmark Registry)

• Major complications: 2.6%
• All complications combined: 8.1%

Summary Table: IABP vs. Other MCS Devices

• Fischer's Mastery of Surgery, 8th ed., p. 345
• Braunwald's Heart Disease, 12th ed. (Table 59.2)
• Tintinalli's Emergency Medicine, 9th ed.
• Rosen's Emergency Medicine, 9th ed. (Table 66.2)

INTRA-AORTIC BALLOON PUMP (IABP)

I. INTRODUCTION

• A double-lumen, 7.5- to 8.0-French catheter with a polyethylene balloon (volume 30-50 mL for adults) attached at its distal end
• One lumen connects to the pneumatic pump console and drives balloon inflation/deflation
• One lumen allows continuous aortic pressure monitoring
• The pump console, which controls timing via ECG or arterial pressure triggers

II. PRINCIPLES OF OPERATION

A. Device Position

• Diastolic augmentation benefits coronary and cerebral perfusion (proximal displacement of blood)
• Deflation reduces LV afterload without occluding major branch vessels

B. The Counterpulsation Cycle

• Triggered at: dicrotic notch on the arterial pressure tracing (= aortic valve closure) or mid-T-wave on ECG
• The balloon rapidly inflates, displacing a volume of blood (~40 mL) bidirectionally - proximally toward the coronary ostia and aortic root, distally toward the peripheral circulation
• Effect: Diastolic augmentation - peak diastolic pressure rises, often exceeding the previous systolic pressure
• This markedly increases coronary perfusion pressure (since ~85% of coronary filling occurs in diastole) and augments cerebral blood flow

• Triggered at: peak R wave on ECG (just before LV contraction)
• Sudden deflation creates a partial vacuum in the aorta
• Effect: Aortic end-diastolic pressure falls (assisted aortic end-diastolic pressure lower than unassisted)
• The LV ejects against reduced resistance (afterload reduction)
• LV wall stress, myocardial oxygen demand (MVO2), and LV end-diastolic pressure all decrease
• Cardiac output augmented by approximately 0.5-1.0 L/min

C. Haemodynamic Effects Summary

D. Timing and Trigger Modes

1. ECG trigger - inflation at mid-T-wave; deflation at R-wave peak (most commonly used)
2. Arterial pressure trigger - inflation at dicrotic notch; deflation timed to precede next systolic upstroke

E. Prerequisite for Effectiveness

• Some residual LV function and forward cardiac output
• A reasonably organised electrical rhythm (less effective in rapid tachyarrhythmias or atrial fibrillation with irregular RR intervals)
• Effective triggers for balloon cycling

III. INDICATIONS

A. Primary Indications

• Post-acute MI cardiogenic shock (with or without revascularisation)
• Acute decompensated heart failure with hypotension
• Used as a bridge to definitive therapy (PCI, CABG, LVAD, or transplant)
• In hospitals without direct PCI capability: IABP + thrombolysis followed by transfer to a tertiary centre is the best management option

• Acute papillary muscle rupture causing severe mitral regurgitation
• Post-infarction ventricular septal rupture
• Reduces afterload, decreasing the regurgitant fraction and supporting haemodynamics while awaiting surgical correction

• Prophylactic pre-procedural placement in patients with severely reduced LV function, left main disease, or last remaining vessel
• A meta-analysis of 9 RCTs (n = 1,171) in high-risk CABG patients showed significantly lower mortality and major adverse cardiac and cerebrovascular events (MACCEs) with preemptive IABP vs. controls

• Pre-operative: high-risk patients before CABG to reduce operative mortality
• Post-operative: failure to wean from cardiopulmonary bypass; post-CABG low cardiac output syndrome
• Bridge while the heart recovers ("rested" on CPB with IABP running)

• Reduces ischaemic burden while awaiting revascularisation

• Temporary support maintaining end-organ perfusion in terminal heart failure

IV. CONTRAINDICATIONS

Absolute Contraindications

Relative Contraindications

V. ADVANTAGES

• Percutaneous insertion via femoral artery; can be placed within minutes at the bedside, in the catheterisation lab, or in the operating theatre
• Available at most cardiac centres without need for specialist surgical support

• Simultaneously increases coronary perfusion AND decreases myocardial O2 demand - a uniquely favourable combination not achieved by pharmacological agents alone
• Inotropes increase O2 demand while improving output; vasodilators reduce afterload but may drop coronary perfusion pressure

• Unlike ECMO or TandemHeart, no oxygenator, venous cannula, or priming circuit needed
• Simpler setup and management

• The arterial lumen provides continuous aortic pressure monitoring
• The waveform pattern is a real-time quality check on timing accuracy

• Support frequency reduced gradually (1:1 → 1:2 → 1:3)
• Device removed percutaneously with manual compression; no surgical closure required

• In papillary muscle rupture or VSD, afterload reduction substantially reduces the regurgitant/shunt fraction, stabilising the patient for surgery

• Compared to Impella or TandemHeart, IABP causes less haemolysis and thrombocytopenia due to its non-contact, non-rotary mechanism

VI. DISADVANTAGES AND LIMITATIONS

• Increases CO by only ~0.5-1.0 L/min - inadequate for severe biventricular failure
• Compare: Impella provides 2.5-4.0 L/min; ECMO provides 2-6 L/min (full biventricular support)

• Requires a consistent cardiac rhythm for accurate ECG triggering
• In rapid tachyarrhythmias (HR >130 bpm) or irregular rhythms (atrial fibrillation), timing is inaccurate and haemodynamic benefit is substantially reduced

• Cannot sustain circulation in complete cardiac standstill or severe biventricular failure
• Profound shock or cardiac arrest represents a relative contraindication

• Does not correct hypoxaemia; patients with combined cardiorespiratory failure require ECMO

• Limb ischaemia (most serious): femoral artery occlusion; incidence ~3-7%
• Haematoma and bleeding at the insertion site
• Pseudoaneurysm, arteriovenous fistula
• Retroperitoneal haematoma (rare)

• Too high: may occlude the left subclavian artery
• Too low: may occlude renal arteries or compromise mesenteric flow

• Stroke (thromboembolic, from aortic plaque disruption)
• Infection (bacteraemia, local insertion-site infection with prolonged use)
• Thrombocytopenia (mechanical platelet destruction)
• Balloon rupture with gas embolism (rare; helium absorbs rapidly)

• The landmark IABP-SHOCK II trial (2012, n=600) - a prospective, randomised, open-label, multicentre trial - showed no significant reduction in 30-day mortality with IABP vs. medical therapy alone in AMI complicated by cardiogenic shock in patients undergoing early revascularisation
  • 30-day mortality: 39.7% (IABP) vs. 41.3% (control); RR 0.96; 95% CI 0.79-1.17; P=0.69
  • No significant differences in secondary endpoints, time to haemodynamic stabilisation, or ICU length of stay
  • 6-year follow-up confirmed no long-term survival benefit
• This has led current ESC and AHA/ACC guidelines to downgrade the routine use of IABP in cardiogenic shock complicating AMI (Class III / no benefit recommendation)

VII. COMPLICATIONS (Benchmark Registry Data)

VIII. WEANING AND REMOVAL

1. Decreasing counterpulsation frequency: 1:1 → 1:2 → 1:3
2. Reducing augmentation volume (partial inflation)

IX. COMPARISON WITH OTHER MCS DEVICES

X. SUMMARY