Doctors at an American College of Cardiology conference — where the results were announced on Wednesday — say the approach is the first big advance in heart attack care in more than a decade, since modern clot-busters became available.
"We now have a therapy that helps open arteries and improves outcomes," said Dr. Christopher Cannon, a cardiologist at Harvard Medical School and Boston's Brigham and Women's Hospital who helped conduct one of the studies.
"It really is a great day for heart attack patients," he said.
About a third of the 865,000 heart attacks in the United States each year and 10 million worldwide are of the type involved in these studies — caused by a large clot fully or almost completely blocking a major artery.
They can be treated with emergency procedures to open the artery, but most of the time they're treated with medications to dissolve the clot until patients can be scheduled for an angiogram to see whether they need surgery or angioplasty.
However, arteries reclose about a fourth of the time in those given medications, doubling their risk of dying before a procedure can be done.
Plavix already is used to prevent clotting, but its safety and effectiveness for treating major heart attacks while they're occurring has not been determined. Two studies funded by the companies that sell Plavix — Sanofi-Aventis and Bristol-Myers Squibb — tested this.
One, involving more than 45,851 heart attack patients in China, found that the risk of death, stroke or another heart attack was 9 percent lower in patients given Plavix along with standard anti-clotting drugs — aspirin, heparin and the clot-busters TPA or streptokinase — than in those who got standard drugs alone.
Risks of bleeding and other serious side effects were no different.
"The treatment was very effective and very safe," said Dr. Zhengming Chen of the University of Oxford in England, who led the study.
The other was led by Dr. Marc Sabatine of Brigham and Harvard, and it involved 3,491 heart attack patients in Europe given standard drugs with or without Plavix. The risk of death, another heart attack or artery reclogging was 21.7 percent in those on standard drugs alone but only 15 percent among those given Plavix. This computed to a 36 percent lower risk for taking Plavix.
Doctors also found that Plavix appeared to be safe even for patients about to have heart bypass surgery. This is good news because surgeons now are reluctant to operate on people who recently received the drug, fearing it will cause excessive bleeding, said Dr. John Hirshfeld, a University of Pennsylvania cardiologist with no role in the studies.
Indeed, former President Bill Clinton's doctors cited his Plavix treatment as a reason they delayed a couple days last summer.
Two weeks of Plavix pills cost $50 to $100 per patient. For every million heart attack patients treated this way, 5,000 deaths and another 5,000 major heart problems or strokes would be prevented, Chen said.
This cheap and simple treatment will have a big impact in such countries as China, where surgery or procedures to open blocked arteries are uncommon and people are mostly treated with medicines.
It also will affect community hospitals in the United States, where most Americans get care, specialists say.
Sabatine's study also was published online by the New England Journal of Medicine and will be in its March 24 print edition.
In an editorial in the New England journal, doctors from Johns Hopkins University in Baltimore and the University of Texas Southwestern Medical Center in Dallas write that results may have been particularly rosy in the European study because patients were generally lower risk than most heart attack sufferers.
The study also didn't include elderly and thin people who have higher risk of bleeding from some anti-clotting and blood-thinning treatments.
But because aspirin doesn't work in many people, finding that a different anti-clotting drug like Plavix works is good news, they write.
In other news at the conference, a separate analysis involving the same patients in the Chinese study found that the common practice of giving heart attack patients drugs called beta blockers should be delayed. People on the drug had fewer repeat heart attacks but more risk of heart shock, so the risks and benefits canceled each other out.
"It may be better to start beta blocker therapy after a patient's condition has stabilized," Canon said.
A third study on 255 people in Italy tested higher doses of Plavix before balloon angioplasty to open blocked arteries. The risk of heart attack, death or the need for repeat procedures was 10 percent among those given the standard dose and only 4 percent among others who got a double dose.