Advances in Ventricular Assist Devices for Bridge Treatments of Congestive Heart Failure

Points to Remember

• VADs are indicated for CHF patients who need bridge support while awaiting transplant. Use of VADs for chronic circulatory support in nontransplant candidates is under active study.
• A newer generation of VADs, being evaluated for safety and efficacy at advanced cardiac centers, offers smaller size, increased ease of transplant, and improved durability.
• Early referral of CHF patients to an advanced CHF specialty center is critically important, especially patients who have been hospitalized more than once in the preceding year. Late referral reduces the probability of a good outcome with VADs.

The Challenge

Congestive heart failure (CHF) affects nearly 5 million people in the United States, with an estimated 550,000 new cases diagnosed annually. It is the most common diagnosis in hospitalized patients aged 65 years or older, and hospitalizations continue to increase, rising from 402,000 in 1979 to 1.1 million in 2004, according to the US Centers for Disease Control and Prevention. Although CHF is a serious problem, it can frequently be managed to improve patient quality and length of life through a therapy continuum ranging from medications to placement of ventricular assist devices (VADs) to heart transplant.

The use of VADs as bridge-to-transplant therapy has increased because of several factors. These include recognition that patients with highly advanced CHF who are at risk for worsening cachexia or death on the transplant waiting list can gain strength and become better transplant candidates via VAD implant. In addition, the recent US Food and Drug Administration (FDA) approval of the HeartMate II axial flow pump provides a robust, much smaller pump than previously available outside investigational trials.

Too often, patients with medically refractory CHF are not evaluated at advanced CHF centers early enough to optimize their disease management. This delay may compromise their ability to be suitable candidates for VAD implants. The primary care professional's challenge with CHF patients is therefore 2-fold:

1. To make patients with refractory CHF aware of the options available, particularly the multiple indications for VADs (see sidebar). An assist device may improve quality and length of life in patients who are not suitable candidates for heart transplant, or it may maintain circulation while the patient waits for a donor organ.
2. To provide these patients, in a timely manner, with a comprehensive evaluation at an advanced CHF center with experience in deploying the full medical-surgical continuum of cardiac care. For example, Mayo Clinic performs this service through its multidisciplinary Heart Failure Clinic. The Heart Failure Clinic brings together cardiologists who are experts in CHF assessment and management, surgeons with expertise in conventional cardiac surgery, assist device implantation, and heart transplant, specially trained cardiac rehabilitation nurses, nurse practitioners, pulmonologists, interventionists, physical therapists, and occupational therapists. With this combined expertise, the Mayo Clinic team optimizes and individualizes patient care through a variety of strategies.

VAD Advances

X-ray of older model of implanted VAD

Enlarge

The original VAD pusher-plate model approved by the FDA for bridge-to-transplant use has design disadvantages that have inspired recent technological improvements to VADs. Mayo Clinic specialists are playing a key role in evaluating new devices and assessing outcomes to assure they are safe and effective.

Among the disadvantages of the older pusher-plate model are its larger size, more challenging implant procedure, and lack of durability. By comparison, newer models are smaller and more durable because they have fewer moving parts.

View of newer model of implanted VAD

Although only one of the newer-generation devices (Heartmate II) is FDA approved, and only as a bridge to transplant, this and other investigational devices are being studied, for either bridge-to-transplant or chronic use, at advanced CHF centers, including all 3 Mayo Clinic campuses. In general, preliminary outcome data favor the newer models, especially in terms of durability. The newer models have the potential to last several years compared with approximately 18 months for the older model, an improvement that especially suits extended support of patients who are not candidates for transplants.

Concerns Regarding New VADs

The design of the new VADs introduces new safety concerns, however. Two main issues are now under scrutiny:

1. The primary concerns are VAD-associated clotting and risk of embolic stroke and the need for warfarin anticoagulation with its attendant risk of bleeding. Mayo Clinic experience with the newer VADs indicates varied risk of VAD thrombosis among the devices, resulting in preferential use of those devices that have performed best in the view of Mayo Clinic experts.
2. A second concern is VAD-associated hemolysis, which appears to be related to several factors, including potential for turbulent flow through the VAD. Certain pumps seem more likely to result in this problem than others, which has affected device selection recommendations at Mayo Clinic.

Progress, Not Perfection

The new VADs are not yet perfected, but they offer potential advantages over first-generation pumps. Continued refinements are expected to resolve the current set of problems. While the technology evolves, all can agree that absent perfection, there is real progress compared with the state of the art 25 years ago when bridge-to-transplant interventions were achieved by the mechanical heart. Mayo experts continue to investigate a number of the newer pumps, some of which seem promising.

When to Refer a Patient to the Heart Failure Clinic

Heart failure patients whose condition continues to decline while they are receiving optimal medical therapy should be referred to a comprehensive heart failure clinic as early as possible. The goal of early referral is to provide the best treatment before multiple organ failure (impaired heart, kidney, and liver function) limits the therapeutic options available to the patient.

Clinicians seeing a heart failure patient who has been hospitalized more than once in the preceding year should refer that patient to an advanced CHF specialty center because data show that type of patient is at high risk of dying within 2 years.

Indications for Ventricular Assist Devices

Cardiac ventricular assist devices (VADs) are mechanical pumps connected to the heart to support patients with severe, medically refractory CHF. Devices may support the left ventricle alone; both the right and left ventricles ("bi-VADs"); or the right ventricle alone. VADs are used to address 3 categories of medical conditions:

1. Bridge to transplant for patients awaiting cardiac transplant, who need support for the failing heart during the waiting period.
2. Bridge to recovery for patients with reversible forms of cardiac failure. A VAD can be implanted with the hope that its support will allow the heart to recover, and the device can then be removed.
3. Destination therapy for patients for whom cardiac transplant is not an option because of comorbid conditions. Patients who are likely to die of their heart condition within 2 years are potential candidates for destination therapy. The VAD can be implanted to support circulation as a means of improving quality of life and extending life.