Percutaneous Cardiac Support Systems

30 Percutaneous Cardiac Support Systems

Percutaneous circulatory support systems play an established role in the peri- and postprocedural therapy of high-risk cardiac patients. Pump-driven systems can be differentiated from the intra-aortic balloon pump: for the intra-aortic balloon pump to be efficacious, the cardiac index generated by the patient must be sufficient, whereas for pump-driven systems the pump itself actively transports blood. The major indications for the systems are

Cardiogenic shock of various origins

High-risk interventions

Systems for complete cardiopulmonary support including oxygenation will not be discussed.

The more complex active pump systems result in more powerful hemodynamic unloading and thus symptomatic improvement in the patient. However, they are also associated with a higher rate of complications.

Personal view

We believe it is important that an intra-aortic balloon pump is available in all hospitals that treat patients with acute cardiac diseases. The pump systems that actively unload the heart should be reserved for centers with appropriate experience in interventional and intensive care.

Intra-aortic Balloon Pump

Basics

The intra-aortic balloon pump (IABP) is a mechanical circulatory support system for hemodynamic stabilization of patients in cardiogenic shock. The system consists of a polyurethane balloon catheter, which is positioned in the descending thoracic aorta, and an extracorporeal pump with control unit. The pump rapidly fills the balloon with helium in diastole and before the beginning of systole completely empties it again (intra-aortic counter-pulsation). As a consequence, the diastolic aortic pressure is augmented by the balloon. In contrast, the rapid run-off of the blood when the balloon is emptied just before systole decreases the effective aortic blood volumes, with reduction in the systolic aortic pressure and thus left ventricular afterload (Fig. 30.1).

Intra-aortic counterpulsation has the following effects:

Augmentation of the diastolic aortic pressure with

– Increase in coronary perfusion pressure

– Increased perfusion of other organs: brain, kidney, etc.

Afterload reduction with

– Decreased cardiac work

– Reduction in myocardial oxygen consumption

– Increased cardiac output

For an IABP to be of benefit, the stroke volume has to be above a certain threshold. The cardiac index should be at least 1.2 to 1.4 L/m², the mean arterial pressure should be > 40 mm Hg.

Tachyarrhythmias can significantly impair augmentation or even completely abolish it.

The intra-aortic pressure can be measured via the catheter tip while the IABP is in action. For that purpose balloons with fiberoptic pressure recording or with conventional pressure measurement are available. The balloons are available in different volumes (30, 34, or 40 mL), the use of which depends on the patient’s sex, body surface area, and putative aortic diameter. Depending on the manufacturer, the diameter of the nonexpanded balloon is 7F, 7.5F, or 8F.

Indications and Contraindications

Indications:

Cardiogenic shock in acute myocardial infarction

Mechanical complications of acute myocardial infarction with shock:

Fig. 30.1 Mechanism of action of intra-aortic counterpulsation.

– Ventricular septal rupture: reduction of the shunt volume by decreasing afterload

– Severe acute mitral regurgitation due to papillary muscle rupture: reduction of the regurgitant fraction by decreasing afterload

Severe, refractory myocardial ischemia with multivessel disease or main stem stenosis (bridging until CABG)

High-risk percutaneous coronary intervention (PCI) during shock

Elective high-risk PCI with prophylactic IABP insertion

Weaning from cardiopulmonary bypass

Bridging to cardiac transplant

IABP should only be used in patients if the severe left ventricular dysfunction is presumed transient (example: stunned myocardium) or if the cause of the shock can be treated in the short term (examples: severe ischemia, ventricular septal rupture, transplantation).

Thus, there is no indication for IABP in patients with end-stage heart failure or terminal, inoperable CAD. Other contraindications are

Significant aortic regurgitation (increase in regurgitant volumes by diastolic augmentation)

Abdominal aortic aneurysm

Aortic dissection

Severe peripheral arterial disease of the pelvis and the lower extremity

Technique

The IABP in cardiology is used exclusively in the critically sick patient, usually under emergency conditions.

In our center, IABPs are used most frequently in patients with cardiogenic shock due to acute myocardial infarction. With persistent shock after PCI of the infarct vessel, the IABP is placed during or immediately after completion of the intervention and while the patient is still in the catheterization laboratory. Thus, vessel access via the femoral artery has already been established and fluoroscopy allows immediate verification of the position of the catheter.

In contrast, placement of the IABP in the intensive care unit/cardiac care unit is usually done at the bedside and without fluoroscopy.