Artificial Arteries

In 1950, surgeon Michael E. DeBakey made the first Dacron synthetic artery, called a graft, on a home sewing machine in hopes of using it to repair damaged aortas. He knew the dangers of aortic aneurysm, when the wall of the vessel thins, weakens, and swells into a bulge. Such a bulge may burst and cause fatal, rapid blood loss.

Dacron polyester turned out to be an excellent material for grafts. Blood cells and clotting proteins get trapped in its fibers, creating a natural lining that seals the fabric's mesh and strengthens the patch. In 1954, he removed an aortic aneurysm and replaced it with a graft. The patient lived with the graft for 10 years with no complications. Today, Dacron is widely used in grafts as well as in implantable organ replacements.

Pacemakers

Pacemakers were invented in the late 1950s, after cardiologists learned that arrhythmias, or irregular heartbeats, were responsible for many sudden deaths after heart attacks. The scar tissue from a heart attack interferes with the electrical impulses that control the heartbeat.

This early battery-powered pacemaker was designed to implant just beneath the skin of the abdomen. Electrodes attached to the heart conveyed electrical pulses that triggered regular heart beats and maintained a healthy rhythm. Modern pacemakers work the same way but are much more compact than this model. In the first 15 years after their introduction, pacemakers were implanted into 150,000 Americans.

"An amazing new pocket-size ticker sparks hesitant heartbeats and provides added years of near-normal life for many cardiac patients."
Saturday Evening Post, March 4, 1961.

Artificial Valves

Replacing heart valves

Soon after the introduction of the heart-lung machine, surgeons began to experiment with ways to repair damaged heart valves and replace them with artificial ones. There were many failures among the earliest replacement valves, because surgeons and inventors could not anticipate the mechanical and biological problems to come. Many different shapes and materials were tried. Eventual success came from collaboration among surgeons, physiologists, engineers, biochemists, and manufacturers.

The ins and outs of artificial valves

Developers of synthetic valves faced many challenges. Some valves caused turbulence that impeded blood flow, and some leaked when closed. Blood tended to clot on the valves' structures. If such a clot breaks free, it can block an artery, causing stroke or heart attack.

Additionally, valves have to be sturdy—they must open and close about 40 million times per year, with each beat of the recipient's heart. Models in use today have achieved remarkable durability. Hundreds of thousands have been successfully implanted and have endured for years without breakdown.

Hufnagel valve, 1952 This early valve was used in the aorta, not the heart, to relieve problems of inadequate blood flow to the body. Its use proved that human-made materials could be tolerated in the bloodstream.

Braunwald-Morrow mitral valve, 1960 Nina Morrow was the first to successfully implant a mitral valve in a human heart. Earlier the same year, an aortic valve had been replaced for the first time.

Van der Spuy "toilet seat" valve Blood tended to clot at the spring pivot of this valve.

Starr-Edwards aortic valve, model 2400 This model improved upon the first of its type, introduced in 1961. Similar models in use today are proving durable and reliable.

Bjork-Shiley tilting disc valve This type of valve causes less turbulence in blood flow than the larger ball valves. But blood clots and structural failures did occur with this model.

St. Jude Medical bileaflet valve This valve was introduced in 1977 and is still being used today. When open, it causes minimal resistance to blood flow.

Pig tissue valve To avoid the problems of blood clots caused by mechanical valves, researchers experimented with valves made of animal tissue. A valve from a pig's heart would be treated chemically to prevent an immune response by its new human host. This type, mounted on a support frame, was introduced in 1976. A drawback of tissue valves is that they eventually deteriorate.