Your heart is the engine inside your body that keeps everything running. Basically, the heart is a muscular pump that maintains oxygen and blood circulation through your lungs and body. In a day, your heart pumps about 2,000 gallons of blood. Like any engine, if the heart is not well taken care of it can break down and pump less efficiently, a condition called heart failure.
Until recently, the only option for many severe heart failure patients has been heart transplants. However, there are only slightly more than 2,000 heart transplants performed in the United States annually, meaning that tens of thousands of people die waiting for a donor heart. On July 2, 2001, heart failure patients were given new hope as surgeons at Jewish Hospital in Louisville, Kentucky, performed the first artificial heart transplant in nearly two decades. The AbioCor Implantable Replacement Heart is the first completely self-contained artificial heart and is expected to at least double the life expectancy of heart patients.
In this article, you will get an in-depth look at how this new artificial heart works, how it's implanted into a patient's chest and who might be a candidate for receiving one of these mechanical hearts. We will also compare the AbioCor heart to the artificial hearts that have failed in the past.
A Hydraulic-driven Heart
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:
- In the first stage, the right and left atria contract at the same time, pumping blood to the right and left ventricles.
- In the second stage, the ventricles contract together to propel blood out of the heart.
The heart muscle then relaxes before the next heartbeat. This allows blood to fill up the heart again.
Patients with an implanted AbioCor heart will 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 will alternately send blood to the lungs and then to the body, instead of both at the same time as a natural heart does. The AbioCor is able to 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:
- Hydraulic pump - The basic idea with this device is similar to the hydraulic pumps used in heavy equipment. Force that is applied at one point is transmitted to another point using an incompressible fluid. A gear inside the pump spins at 10,000 revolutions per minute (rpm) to create pressure.
- Porting valve - This valve opens and closes to let the hydraulic fluid flow from one side of the artificial heart to the other. When the fluid moves to the right, blood gets pumped to the lungs through an artificial ventricle. When the fluid moves to the left, blood gets pumped to the rest of the body.
- Wireless energy-transfer system - Also called the Transcutaneous Energy Transfer (TET), this system consists of two coils, one internal and one external, that transmit power via magnetic force from an external battery across the skin without piercing the surface. The internal coil receives the power and sends it to the internal battery and controller device.
- Internal battery - A rechargeable battery is implanted inside the patient's abdomen. This gives a patient 30 to 40 minutes to perform certain activities, such as showering, while disconnected from the main battery pack.
- External battery - This battery is worn on a Velcro-belt pack around the patient's waist. Each rechargeable battery offers about four to five hours of power.
- Controller - This small electronic device is implanted in the patient's abdominal wall. It monitors and controls the pumping speed of the heart.
The AbioCor heart, which is composed of titanium and plastic, connects to four locations:
- Right atrium
- Left atrium
- Pulmonary artery
The entire system weighs about 2 pounds (0.9 kg). In the next section, you will learn how surgeons implanted the AbioCor heart during a seven-hour operation.
The Seven-hour Surgery
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:
- Surgeons implant the energy-transfer coil in the abdomen.
- The breast bone is opened and the patient is placed on a heart-lung machine.
- Surgeons remove the right and left ventricles of the native heart. They leave in the right and left atria, the aorta and the pulmonary artery. This part of the surgery alone takes two to three hours.
- Atrial cuffs are sewn to the native heart's right and left atria.
- A plastic model is placed in the chest to determine the proper placement and fit of the heart in the patient.
- Grafts are cut to an appropriate length and sewn to the aorta and pulmonary artery.
- The AbioCor is placed in the chest. Surgeons use "quick connects" -- sort of like little snaps -- to connect the heart to the pulmonary artery, aorta and left and right atria.
- All of the air in the device is removed.
- The patient is taken off the heart-lung machine.
- The surgical team ensures that the heart is working properly.
Since this first transplant, another 11 procedures have been done. The most recent one took place on February 20, 2004. As part of a clinical trial, patient number 12 underwent surgery at St. Luke's Episcopal Hospital in Houston at the Texas Heart Institute.
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 only designed to double life expectancy for patients who had only about 30 days to live prior to 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 Sickest of the Sick
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:
- Have end-stage heart failure
- Have a life-expectancy of less than 30 days
- Is not a candidate for a natural heart transplant
- Have no other viable treatment option
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.
Blocks of ice can be sculpted into anything from swans to full-size buildings. Find out how ice sculpting is done from HowStuffWorks.