Medicine: Safer Heart Operations

On the operating table, the heart of the baby boy began fibrillating—quivering ineffectually. His surgeons quickly restored blood circulation by manual massage, but that solved nothing. Nearly an hour later, they tried something entirely new: a small (10-milligram) dose of tetraethylammonium chloride injected directly into the child’s coronary artery system. Almost immediately the heart began beating regularly again.

Last week the child, thereby saved during a recent delicate pulmonary-valve operation at Denver’s National Jewish Hospital, was recovering normally. Unpublished so far, the technique originated this summer with Physiologist Baruch Bromberger, 40, and Dr. Paolo Caldini, 30, an Italian physician working in the U.S. on a Fulbright grant. They went to work on ventricular fibrillation, which is still a grave danger when a patient’s body is cooled for heart surgery (hypothermia). The cooling itself protects the brain from lack of oxygen (anoxia), has greatly advanced modern heart surgery. But hearts cooled to an average 28° C. during hypothermia also become highly irritable; they may fibrillate and cause death.

Using an isolated dog’s heart, connected to the donor dog’s circulatory system, Bromberger and Caldini found that magnesium ions, released from the rest of the body during hypothermia, seemed to concentrate in the cold heart. They were then able to show that this magnesium could trigger fibrillation; a small magne sium increase caused fibrillation even at normal temperature.

To counter the magnesium, they finally tried tetraethylammonium chloride (TEA) on the strength of a report in a Swedish journal that TEA would remove magnesium-caused neuromuscular blocks in other parts of the body. Coupled with an electric shock, TEA promptly defibrillated 44 isolated dog hearts up to eight times each. The technique then saved the baby boy. In four other fibrillating human patients since treated in the same way, it has worked equally well. TEA may be the trick that wall allow considerably longer, cooler, safer heart operations than have been possible.