How Artificial Hearts Work

The average adult human heart pumps blood at a rate of 60 to 100 beats per minute. If you've read How Your Heart Works, then you know that the heart contracts in two stages:

The heart muscle then relaxes before the next heartbeat. This allows blood to fill up the heart again.

Patients with an implanted AbioCor heart still have atria that beat at the same time, but the artificial heart, which replaces both ventricles, can only force blood out one ventricle at a time. So, it alternately sends blood to the lungs and then to the body, instead of both at the same time as a natural heart does. The AbioCor can pump more than 10 liters per minute, which is enough for everyday activities.

The AbioCor, developed by Abiomed, is a very sophisticated medical device, but the core mechanism of the device is the hydraulic pump that shuttles hydraulic fluid from side to side. To understand how it works, let's look at the various components of the system:

The AbioCor heart, which is composed of titanium and plastic, connects to four locations:

The entire system weighs about 2 pounds (0.9 kilograms). In the next section, you will learn how surgeons implanted the AbioCor heart during a seven-hour operation.

The surgery to implant a AbioCor artificial heart is extremely delicate. Not only are the surgeons cutting off and extracting the natural heart's right and left ventricles, but they are also placing a foreign object into the patient's chest. The patient must be placed on, and later removed from, a heart-lung machine. The surgery requires hundreds of stitches, to properly secure the heart to artificial ventricles. Grafts connect the AbioCor to remaining parts of the natural heart. Grafts are a kind of synthetic tissue used to connect the artificial device to the patient's natural tissue.

Due to the complexity of the surgery, there are lots of medical personnel on hand during the operation. The surgery on July 2, 2001, which was the first of its kind in the world, included a team of the two lead surgeons, 14 nurses, perfusionists, anesthesiologists and other support staff.

Here is the procedure, as described by University of Louisville surgeon Robert Dowling:

Since this first transplant, more procedures have been done.

Originally, Abiomed officials cautioned against overly optimistic results; the most optimistic predictions were that a patient could live up to six months with the AbioCor heart. The device is designed to double life expectancy for patients who had only about 30 days to live before the operation.

Robert Tools, the patient who received the heart transplant on July 2, 2001, at Jewish Hospital in Louisville, has passed away. Ten other patients have also died, but the recipients of the AbioCor heart have lived an average of five months after their transplants.

The U.S. Food and Drug Administration (FDA) has allowed Abiomed to perform 15 implants as part of a clinical trial. Twelve of the proposed 15 surgeries have been done. These surgeries have taken place at medical centers in Houston, Los Angeles, Boston and Philadelphia. The FDA has been reviewing the results of these transplants on a case-by-case basis to determine the future of the AbioCor device. If the $70,000 to $100,000 device is successful, meaning it can prolong the life of a patient without complications, it could be approved for use in more heart centers around the United States. In fact, several news agencies report that Abiomed will seek approval from the U.S. Food and Drug Administration this year to sell the AbioCor heart. The device will be used to treat patients with end-stage heart failure under what is known as a "Humanitarian Device Exemption."

Laman Gray said that initial candidates for the heart will be the "sickest of the sick." FDA and Abiomed officials have laid a few parameters for who can become one of the initial recipients of the artificial heart. The patient must fit the following profile:

Another requirement is that the grapefruit-sized device must fit inside the patient's chest. To determine the fit of the device, the patient must undergo a CAT scan and chest X-ray. Then, using a computer-aided design (CAD) program, the natural heart is virtually removed and the AbioCor heart is virtually placed in the patient's chest. If the computer program shows that the device will fit, doctors can proceed with the operation to implant the artificial heart.

For nearly two months following the surgery, hospital and AbioMed officials kept the name of the first recipient a secret. However, on August 21, 2001, it was revealed that Robert Tools, a Kentucky resident and former telephone company employee, was the history-making patient. Although Tools has battled an infection and needed a ventilator following his surgery, his doctors report that the mechanical heart continues to function without problems.

Here is what was known about Tools prior to his surgery:

Currently, there are between 2 million and 3 million Americans living with heart failure, and 400,000 new cases are diagnosed annually. Heart failure causes 39,000 deaths per year, according to the National Heart, Lung, and Blood Institute (NHLBI). Most people diagnosed with heart failure can expect to live about five years, and will usually need to have a heart transplant to extend their life.

In the United States alone, 2,143 heart transplants were performed in 2003. However, thousands of potential recipients die annually while waiting for a heart transplant. Doctors still encourage the public to become organ donors, but the AbioCor may save many of those who don't have the option of a natural transplant or of waiting for an available heart.

For more information on the AbioCor and related topics, check out the links on the next page.