To stop the heart, surgeons infuse an icy solution into it. But the cold can dampen the heart’s electrical circuitry, said Dr. Jonathan Haft, a heart surgeon at the University of Michigan. So when doctors try to wean patients off the heart-lung machine, the electrical circuits can be slow to recover and the heart may beat feebly, or not at all.
So when surgeons finish the operation, they almost always sew fine wires, not much thicker than a human hair, onto the surface of the heart. They thread the bright blue or orange wires through the chest wall and skin.
The wires are hooked to a box the size of an clunky, old-fashioned cellphone, which generates electrical impulses that control the heart’s rhythm.
Once the heart’s electrical system has recovered, a member of the medical staff gently tugs the wires. They are so fine that they almost always come right out; if they don’t, they are simply clipped at the skin’s surface and left in place.
No harm is done most of the time, as the heart’s own circuitry takes over. (Permanent pacemakers, which are not meant to come out, are placed inside the heart, Dr. Haft noted.)
What went wrong in Mr. Armstrong’s case?
Very occasionally, when a nurse or other staff member tugs on one of the pacemaker wires, it tears the heart surface and causes bleeding. That usually occurs because the wire was stitched on too tightly, or someone pulled too hard, Dr. Mack said.
At first there may be no sign of a problem, Dr. Haft said. But as bleeding continues, blood pressure drops and the heart rate rises. The condition, called tamponade, occurs because blood is pooling around the heart and starting to clot. This inhibits the heart’s ability to relax and fill with blood.
Source : Nytimes