The Intra-Aortic Balloon Pump

Summary

We describe the steps for the percutaneous implantation of the intra-aortic balloon pump (IABP), a mechanical circulatory support device. It acts by counterpulsation, inflating at the onset of diastole, augmenting diastolic aortic pressure and improving coronary blood flow and systemic perfusion, and deflating before systole, reducing left ventricular afterload.

Abstract

Cardiogenic shock remains one of the most challenging clinical syndromes in modern medicine. Mechanical support is being increasingly used in the management of cardiogenic shock. Intra-aortic balloon pump (IABP) is one of the earliest and most widely used types of mechanical circulatory support. The device acts by external counterpulsation and uses systolic unloading and diastolic augmentation of aortic pressure to improve hemodynamics. Although IABP provides less hemodynamic support when compared with newer mechanical circulatory support devices, it can still be the mechanical support device of choice in appropriate situations because of its relative simplicity of insertion and removal, need for smaller size vascular access and better safety profile. In this review, we discuss the equipment, procedural and technical aspects, hemodynamic effects, indications, evidence, current status and recent advances in the use of IABP in cardiogenic shock.

Introduction

Cardiogenic shock is a clinical condition characterized by decreased end organ perfusion due to severe cardiac dysfunction. The most widely accepted definition of cardiogenic shock is based on the Should We Emergently Revascularize Occluded Coronaries for Cardiogenic Shock trial (SHOCK)¹ and Intra-aortic Balloon Support for Myocardial Infarction with Cardiogenic Shock (IABP-SHOCK-II) trial² and includes the following parameters:

1. Systolic blood pressure <90 mm Hg for ≥30 min or vasopressor and/or mechanical support to maintain SBP ≥90 mm Hg

2. Evidence of end-organ hypoperfusion (urine output <30 mL/h or cool extremities)

3. Hemodynamic criteria: cardiac index ≤2.2 L/min/m² and pulmonary capillary wedge pressure ≥15 mm Hg

Acute myocardial infarction (AMI) is the most common cause of cardiogenic shock accounting for approximately 30% of cases³. Despite advances in the treatment of patients with AMI with early invasive revascularization, the mortality of cardiogenic shock remains high⁴. The mechanism of diastolic augmentation showing improvement in coronary perfusion and decreased left ventricular work was first demonstrated in 1958⁵. Subsequently, in 1962 the first experimental prototype of IABP was developed⁶. Six years later, Kantrowitz et al.⁷ presented the first clinical experience of IABP use in four patients with AMI and cardiogenic shock unresponsive to medical therapy.

The IABP's mechanism of action involves inflation of the balloon during diastole and deflation during systole. This results in two important hemodynamic consequences: When the balloon inflates in diastole, the blood in the aorta is displaced proximally towards the aortic root thereby increasing coronary blood flow. When the balloon deflates in systole, it causes a vacuum or suction effect decreasing afterload and augmenting cardiac output⁸. The hemodynamic changes caused by IABP are listed below⁹ (Table 1):

1.Increase in aortic diastolic pressure

2.Decrease in systolic blood pressure

3.Increase in mean arterial pressure

4.Decrease in pulmonary capillary wedge pressure

5.Increase in cardiac output by ~20%

6.Increase in coronary blood flow¹⁰

The major indications of IABP are cardiogenic shock (due to AMI and other causes like ischemic and non-ischemic cardiomyopathy, myocarditis), mechanical complications of AMI like ventricular septal defect or severe mitral regurgitation, mechanical support during high risk percutaneous coronary interventions¹¹, as a bridge to coronary artery bypass surgery in patients with critical CAD, inability to wean off cardiopulmonary bypass and as a bridge to decision or advanced therapies like left ventricular assist devices (LVAD) or cardiac transplantation in end stage heart failure^12,13,14,15. Contraindications to use of IABP include moderate or severe aortic regurgitation which can worsen with counterpulsation, severe peripheral vascular disease which would preclude optimal arterial access and placement of the device and aortic pathologies like dissection^12,15.

The IABP device consists of a console to control the unit and a vascular catheter with the balloon.

The console includes the following four components:

a) Monitor unit which helps to process and determine a trigger signal for the balloon. The signal can be either electrocardiographic (ECG) triggering or pressure signal triggering;

b) Control unit: Processes the trigger signal and activates the gas valve to help with inflation or deflation;

c) A gas cylinder that contains helium. Carbon dioxide is an alternative but is less preferred than helium. Helium has a lower density and provides better balloon inflation characteristics with more rapid inflation and deflation¹⁶;

d) A valve unit which helps with gas delivery.

The IABP (balloon) catheter is a 7-8.5 F vascular catheter with distance markings. The catheter has a polyethylene balloon mounted at the tip. The balloon size can vary from 20-50 mL. The ideal balloon has a length to cover from the left subclavian artery to the celiac artery take off, the inflated diameter measuring 90 to 95% of that of the descending aorta. The most commonly used balloon size in adult patients (height 5'4″/162 cm to 6'/182 cm) is 40 mL. A 50 mL balloon is used for patients >6'/182 cm and 34 cm balloon for 5'/152 cm to 5'4″/162 cm tall patients^12,17 (Table 2).

Protocol

This protocol follows the guidelines of institutional human research ethics committee.

1. Pre-insertion preparation

NOTE: The IABP is preferably inserted in the cardiac catheterization lab under fluoroscopic guidance. Bedside placement can be considered in very critical clinical situations.

1. Begin by preparing the catheterization laboratory for the procedure. Prepare sterile drapes and chlorhexidine or povidone iodine, IABP control unit, IABP catheter, ultrasound for arterial access, 1% lidocaine for local anesthesia, micropuncture needle and wire, micropuncture sheath, 7-8.5 F arterial access sheath for the IABP depending on the balloon size or IABP manufacturer, sutures and sterile dressing.
2. Prepare and drape the patient in the usual sterile fashion with a plan to access the femoral artery.
   ​NOTE: IABP can also be inserted through the axillary artery but this often requires a surgical cut down.
3. Have the patient lay down flat on his or her back. Administer moderate conscious sedation if the clinical scenario permits, by infiltrating the groin access site liberally with 1% Lidocaine.
4. Prepare the IABP catheter. Use a 50 mL syringe to apply a vacuum and completely deflate the balloon, using the one-way valve at the catheter hub.
5. Remove the stylet in the catheter and manually flush the inner lumen with 3-5 mL of saline.

2. Insertion of the IABP

1. Obtain arterial access using the Seldinger technique¹⁸. Use ultrasound guided vascular access to improve first pass success and minimize vascular complications.
2. Insert a micropuncture needle at a 45˚ angle and insert the introducer wire once blood return is obtained.
3. Insert the micropuncture sheath.
4. Exchange the micropuncture sheath for a larger IABP sheath. The sheath size varies by manufacturers and balloon size but is usually 7-8.5 F.
   NOTE: There are two methods to introduce and advance the IABP catheter. The catheter can either be backloaded with a wire or can be advanced over a wire.
5. Advance the IABP catheter through the sheath using short strokes until correct placement is achieved. The optimal balloon position is where the tip is situated distal to the left subclavian artery take off. This is often not easy to identify, and hence, use the carina of the trachea as a landmark, ensuring that the proximal end is above the renal arteries.
6. Confirm position by fluoroscopy. Secure the catheter in place either by using sutures or manufacturer provided locking plates and apply sterile dressing.
   ​CAUTION: Incorrect balloon position results in reduced diastolic augmentation or vascular complications due to direct endovascular injury.

3. Switching on and setting up the IABP

1. Remove the guidewire and aspirate 3 mL of blood from the inner lumen. Flush the inner lumen with 3-5 mL of saline.
2. Attach a standard arterial pressure monitoring tubing to the catheter hub. Remove the one-way valve from the catheter and attach the catheter hub to the console using the provided extension catheter.
3. Turn IABP On, then open the gas tank. Connect the ECG cable to the console. Connect the fiber optic or pressure cable to the console (depending on the manufacturer).
4. Press the Start key on the console. This automatically purges and fills the balloon, calibrates, selects an appropriate ECG lead and trigger, and automatically sets the inflation and deflation timing.
   1. Select an appropriate operation mode - Automatic, Semi-automatic or Manual depending on the clinical scenario.
   2. Select a trigger source. The IABP uses a trigger to identify the beginning of the next cardiac cycle. It deflates the balloon when it recognizes a trigger event. Trigger can be either ECG (R wave) or pressure (systolic upstroke).
   3. Observe the pressure changes on the IABP console by setting a 1:2 frequency. Confirm that the assisted systolic pressure is lower than unassisted one, there is decrease in assisted end-diastolic pressure and that diastolic augmentation is above the systolic pressure - all of which is associated with optimal IABP support (Figure 1).
   4. Set appropriate IABP frequency which can be 1:1, 1:2 or 1:3. This represents the frequency of balloon inflation with each trigger.
   5. Confirm that the IABP timing is appropriate.
      NOTE: An ideal IABP timing consists of the following: a) Inflation occurring at the dicrotic notch which appears as a sharp "V". Ideally, the diastolic augmentation rises above systole, and b) Deflation occurring just prior to the next systole (Figure 1).
5. Use a continuous flush through the inner lumen (usually 3 mL/h).
   NOTE: The patient and the IABP console are now ready to be transported.
6. Use systemic anticoagulation to reduce the risk of arterial thromboembolism.
   ​NOTE: This is institution dependent and some centers do not use systemic anticoagulation for an IABP frequency of 1:1¹⁹.

4. Assessment of the patient after placement of IABP

1. Check distal pulses. If the left radial pulse is weak, verify the position of the balloon to make sure that it is not occluding the left subclavian artery. If no distal pulses are detected in the lower limb, consider removing the IABP and possibly alternate access.
2. Check the insertion site for any bleeding or hematoma.
3. Monitor urine output. If there is a drop in urine output or if there is a concern for hematuria, recheck balloon position to confirm that the balloon lies above the level of the renal arteries.
4. If there is blood in the IABP tubing, suspect balloon rupture. Immediately stop the IABP (this is usually done automatically) and remove the catheter.
5. Obtain a chest X-ray daily to verify optimal device positioning. Also change the sterile dressing daily to reduce the chances of infection.

5. Removal of IABP

1. Stop systemic anticoagulation and set IABP to 1:1.
2. Palpate the femoral pulse and check the baseline distal perfusion by obtaining a Doppler of the pedal pulse.
3. Check the activated clotting time. It should ideally be less than 150-160 seconds.
4. Remove sutures.
5. Once ready to pull, press the Stop button on the IABP console screen.
6. Pull the IABP until resistance is met against the sheath.
7. Pull the sheath and IABP as a unit.
8. Hold manual pressure over the femoral artery for 20-30 minutes or until bleeding stops.
9. Reassess distal pulses with Doppler.
   NOTE: Manual pressure has been mentioned here in the protocol because it is universal. However, there are numerous other methods apart from manual pressure to help achieve femoral arterial hemostasis. These are institution dependent and include but are not limited to: external compression devices like FemoStop, vascular closure devices like Angioseal and Perclose ProGlide Suture-Mediated Closure System. The above-mentioned protocol was partly developed by using official device information guides and manuals across various manufactures of IABP.

Results

Despite being used for many decades now, the evidence on IABP use has been controversial. Routine use of IABP in patients with AMI and cardiogenic shock is not recommended. The previous guidelines of the American Heart Association/American College of Cardiology (AHA/ACC) and the European Society of Cardiology (ESC) strongly recommended the use of the IABP in patients with AMI-associated cardiogenic shock (Class I B and Class I C) on the basis of pathophysiological considerations, non-randomized trials and registry data. ...

Discussion

Mechanical circulatory support is a rapidly evolving field. Even with the arrival of newer support devices, IABP remains the most widely used and simplest to deploy mechanical circulatory support device available currently²⁵. In this article we describe in detail, the procedure for percutaneous insertion of IABP, the indications, evidence, troubleshooting and complications. Despite conflicting evidence regarding the use of IABP in AMI-related cardiogenic shock, it remains the most widely used form...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
IABP catheter and console	Getinge	Sensation Plus
Micropuncture Introducer Set	Cook Medical	G48006
Sterile drapes	Haylard
Ultrasound	GE
Lidocaine	Pfizer