Chapter 18: Temporary Mechanical Circulatory Support

INTRODUCTION

A number of ventricular assist devices (VADs) are available for acute circulatory support. As opposed to long-term VADs, which are designed primarily for bridge to transplantation or long-term support in the nontransplant patient, temporary VADs are designed to reestablish adequate organ perfusion rapidly. Patients in cardiogenic shock require early aggressive therapy. Despite relief of ischemia, inotropic drugs, and control of cardiac rhythm, some patients remain hemodynamically unstable and require some type of mechanical circulatory support in order to restore a normal cardiac output and maintain end-organ perfusion. Cardiogenic shock occurs in 2.4 to 12% of patients with acute myocardial infarction (AMI).¹ The landmark Should We Emergently Revascularize Occluded Coronaries for Cardiogenic Shock (SHOCK) trial demonstrated mortality of greater than 50% despite revascularization.² If instituted promptly, temporary mechanical support leads to improved survival in this group of patients.³ The need for circulatory support in the postcardiotomy period is relatively low and has been estimated to be in the range of 0.2 to 0.6%,⁴ but when it occurs, it needs to be managed effectively if the patient is to be salvaged. Additional indications for acute VADs are in chronic heart failure patients who suffer cardiovascular collapse, and severe cases of myocarditis and postpartum cardiomyopathy.

All practicing cardiac surgeons should have an understanding of current devices, and have at least one of these support systems available. Studies show that even smaller facilities that do not have advanced heart failure programs can have improved patient survival if a device can be implemented rapidly and the patient is transferred to a tertiary care facility with expanded capabilities.⁵

This chapter describes the devices currently available, indications for support, patient management, and the overall morbidity and mortality associated with temporary mechanical support. In addition, it describes some of the more promising devices that have just received approval or are currently undergoing trial. The goal of all temporary assist devices is to alleviate shock and establish an environment in which the native heart and end organs can recover. If recovery is unlikely, then a bridge to a long-term device, typically for bridging to a heart transplant, may be the best strategy. Rarely should individuals be supported directly to heart transplantation from an acute support device, because the newer generations of long-term devices typically provide more reliable support and allow for better rehabilitation in an out-of-hospital setting. It may be possible to bridge a patient who is not a transplant candidate to a long-term device, but given that these patients often are older with comorbities, bridging a patient from an acute VAD to a long-term DT pump must be done with caution.

COUNTERPULSATION

Intra-aortic balloon pumps (IABPs) are often the first line of mechanical assistance utilized for patients in cardiogenic shock. The concept of increasing coronary blood flow by counterpulsation was demonstrated by Kantrowitz and Kantrowitz in 1953 in a canine ...