Mechanical Circulatory Support

Wayne E. Richenbacher

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9781000724691
• Edition: 1
• Topic: Médecine
• Subtopic: Hématologie

This book is a concise, portable handbook that focuses on the clinical use of mechanical blood pumps. All aspects of mechanical circulatory support are addressed, including patient selection, preoperative preparation, operative management, anesthetic considerations and conduct of cardiopulmonary bypass, postop management including complications associated with blood pump use and long-term care and rehabilitation.

Overview of Mechanical Circulatory Support

Wayne E. Richenbacher

Introduction

Developmental Hurdles Encountered During Mechanical Blood Pump Development

Management of Heart Failure

Future of Mechanical Circulatory Support

INTRODUCTION

The concept of assisted circulation began with the development of cardiopulmonary bypass (CPB), (Table 1.1). As the techniques for extracorporeal circulation utilizing CPB were perfected during the 1950s, the era of open heart surgery began. When CPB was introduced into the clinical arena in 1953 open intracardiac repairs were performed for the first time. Ultimately, attempts were made to utilize CPB for temporary support or replacement of cardiac function. However, the oxygenator, an integral component in the CPB circuit has a large blood contacting surface area which results in a significant blood:biomaterial interaction. Activation of the systemic inflammatory response and the resultant capillary leak syndrome produce profound systemic side effects. Furthermore, attempts to utilize CPB for long-term cardiac support were limited by bleeding associated with the need for full systemic anticoagulation and damage to formed blood elements.

As open heart surgery became more commonplace patients with postoperative ventricular dysfunction were encountered creating a need for a device capable of supporting the patient’s circulation.¹ The simplest such device, the intraaortic balloon pump (IABP) is a catheter mounted balloon that is positioned in the descending thoracic aorta. When properly timed with the patient’s native cardiac rhythm the IABP is capable of improving coronary perfusion, reducing left ventricular afterload and augmenting cardiac output to a very modest degree. The IABP was first employed clinically in 1968. Milestones in IABP development include the conversion from an open to percutaneous insertion technique in 1980, manufacture of balloons of smaller dimension that can be employed in patients with a small body habitus and in the pediatric patient population and timing schema that permit balloon pump use in patients with rapid and/or irregular cardiac rhythms. The IABP is now a standard form of therapy for patients with a variety of cardiovascular diseases (see Chapter 3: Intraaortic Balloon Counirrpulsation).

Table 1.1. Timeline for the development of mechanical circulatory support devices

1953	First clinical application of cardiopulmonary bypass.
1963	First clinical use of a left heart assist device.
1968	First clinical application of intraaortic balloon counterpulsation.
1969	First insertion of a pneumatic artificial heart as a bridge to transplantation.
1980	First percutaneous intraaortic balloon pump insertion.
1982	First permanent implantation of a pneumatic artificial heart.
1992	First Food and Drug Administration (FDA) approval of a pneumatic ventricular assist device (VAD) for use in a patient with postcardiotomy cardiogenic shock.
1994	First FDA approval of a pneumatic VAD for use in a patient as a bridge to cardiac transplantation.
1998	Initiation of first FDA approved clinical trial in which an electric VAD is implanted as a permanent form of circulatory support.
1998	First FDA approval of an implantable electric VAD for use in a patient as a bridge to cardiac transplantation—including home discharge.

There remained a need for a cardiac replacement device.² During the 1960s and 1970s a variety of intracorporeal and extracorporeal mechanical blood pumps were developed and tested in the laboratory with occasional clinical use. During the 1980s clinical experience increased. Patient selection criteria and management techniques were developed and refined. Although blood pumps were used in a variety of clinical situations by the end of the 1980s, interim support of the circulation with a mechanical blood pump was proven efficacious in two distinct patient populations: those patients requiring temporary mechanical circulatory support pending ventricular recovery (see Chapter 5: Ventricular Assistance for Postcardiotomy Cardiogenic Shock), and patients who required a mechanical bridge to cardiac transplantation (see Chapter 6: Ventricular Assistance as a Bridge to Cardiac Transplantation). During the past 9 years a number of ventricular assist devices (VADs) have received Food and Drug Administration (FDA) approval. Most recently, the first FDA approved clinical trial in which a VAD is implanted as a permanent form of circulatory support was initiated in the United States in 1998.

DEVELOPMENTAL HURDLES ENCOUNTERED DURING MECHANICAL BLOOD PUMP DEVELOPMENT

Developmental at hurdles for cardiac replacement devices are listed in Table 1.2. Blood contacting surfaces have to be nonthrombogenic in order to avoid thromboembolic complications during the period of mechanical circulatory support. Blood contacting surface design varies from ultrasmooth, seam-free surfaces to textured surfaces that actually promote stable neointimal formation. In general, blood pumps are constructed with flow dynamics that minimize areas of blood stasis within the pump itself. Regardless of whether the blood pump is nonpulsatile, as in the case of a centrifugal pump or pulsatile, the pumping action must be gentle enough to avoid blood trauma. Injury to formed blood elements can result in platelet and white blood cell activation as well as hemolysis. Control systems in the more sophisticated pulsatile devices allow these pumps to function without supervision by a trained healthcare provider. In addition, the pumps are physiologically responsive, raising and lowering the patient’s cardiac output in accordance with activity level. In the case of the total artificial heart, the control system must also balance the output of the two prosthetic ventricles. The blood pumps must be capable of generating forward flow comparable to the cardiac output of a native heart. The size of the blood pump and configuration of the cardiac replacement device assumes greater significance in the total artificial heart as it must be located within the patient’s pericardium.

Table 1.2. Developmental hurdles for cardiac replacement devices

1. Nonthrombogenic blood contacting surface. 2. Pumping action that avoids blood trauma. 3. Control schema. 4. Size and configuration. 5. Portability. 6. Reliability.

Although portable pneumatic drive units are currently the subject of clinical trials, commercially available air driven mechanical blood pumps require a bulky external drive unit. The patients are able to move about, but they frequently require assistance and experience a less than satisfactory quality of life. Portability becomes a more pressing issue in patients who require long-term circulatory support. Electrically powered devices are considerably more complex but require a much smaller controller and power source. The electric motor is implanted as part of the blood pump. The external controller and battery pack can be worn on a belt, satchel or shoulder harness eliminating the need for a wheel based drive unit. Reliability is of critical importance as these devices must pump blood for months or even years without malfunction. An in-depth discussion of these developmental issues is beyond the scope of this handbook. Suffice it to say that the mechanical blood pump industry is tightly regulated.³ In the United States, the Medical Device Amendment of 1976 amended the Federal Food, Drug and Cosmetic Act to approve clinical investigation of medical devices and approve new medical devices before commercialization. Rigorous preclinic...