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Session Reading

Advanced Achievement in Transplant Management

 

                     Case Studies in Heart Failure

 

 

This segment of our AATMC program is designed as a refresher on heart failure and the role of mechanical assist devices in the management of that condition. It also serves as the introduction of the two case studies that will be used throughout the entire course to provide you with examples of decisions needed to be made along the course of management of the potential heart transplant candidate. A brief review of data on outcomes of both heart transplant and destination therapy mechanical assist devices will give you a feel for the complexities involved.

Mechanical Support Devices – A Primer

Until the arrival of devices that could be connected to the heart to support cardiac output, advanced heart failure management was limited to drugs and attempts at re-synchronizing the sequence of ventricular functions. Now that devices have become available and increasingly sophisticated, teams have become more proficient in detecting and managing these devices and attendant complications. Mechanical circulatory support (MCS) use is skyrocketing.

There are two main types of MCS devices, pulsatile and continuous. Pulsatile ventricular assist devices (VAD) were the early solutions and were built on the principle that the output should be like a normal heart, with rises and falls of intravascular pressure. These pumps, because of their complexity and the formation of eddy currents of blood related to the mechanical design had moderately high incidences of clot formation and hemolysis from shearing forces. They were also fairly large and were placed outside the heart with large air-driven drivelines penetrating the chest wall. Infections were and continue to be a problem with this design.

In the past few years continuous flow devices have begun to replace the pulsatile pumps, although each type still has its own indications. These newer support systems use either a centrifugal pump or an axial design providing continuous flow, thus reducing the chance of clots forming as well as reducing shearing forces. Commonly used centrifugal VADs include Thoratec’s HeartMate III and HeartWare HVAD. The slightly older axial devices include the HeartMate II. This type can also be made small enough to fully implant in the chest cavity, allowing for much more freedom for the patient. Some are used percutaneously to partially support a heart that still has some output capacity (Impella®, TandemHeart® or Centrimag, for right ventricular support®), allowing the heart some rest, and hopefully recovery, as from an acute cardiomyopathy, or as a bridge to transplant if no recovery is seen. The total artificial heart can also be used in these circumstances, but because it completely replaces the greater portion of the native heart, it commits the patient and team to transplant. This article gives a very complete description of types and uses of MCS’s (Shekar, Gregory, and Fraser, Critical Care 2016 20:66)

In an increasing number of critical end-stage heart failure (New York class IV, or what INTERMACS (the Interagency Registry for Mechanically Assisted Circular Support) calls the “crash and burn” scenario, multiple devices may be called upon to deliver adequate circulatory support. The patient may have an intra-aortic balloon pump placed outside a tertiary care setting, then, once arrived where services are available, may be placed on temporary veno-arterial Extracorporeal Membrane Oxygenator (ECMO) while preparations are made for insertion of a VAD. Some of these patients go on to develop right heart failure as well and may require a bi-ventricular support system by adding an additional pump to the pulmonary side of the circulation. If a heart does not become available in the near term, some of these candidates proceed to the removal of all devices and most of the heart for placement of a TAH.

All of this activity described above is highly sophisticated, very technical, and takes very skilled and trained team members to keep these (often young) patients alive and well enough to gain conditioning, preparing them for transplant. All this is also very, very expensive. Some of the stories of salvage and successful outcomes from either recovery or transplant are very gratifying. How our society ultimately rates these activities with respect to the other great needs for health care remains to be seen.

For those patients whose condition or choice leads to a long-term device that allows maximum freedom and activity, the HeartMate II remains the most highly used with about 22,000 inserted as “destination” therapy. Newer devices are continuing to come on the market and fully implantable pumps with no external support and battery charging by electric coils found in charging stations like for electric cars or even embedded in walls in one’s home will open the field to even more opportunities for use in both acute and chronic end-stage heart failure. It will be exciting to watch these developments and payers will need to give close attention to funding mechanisms.

Note: The Case Study Dr. Potts mentions in the video can be found here.  Case Study