UPDATE 1-Brilinta patients less likely to die after bypass

* Bypass patient less likely to die with Brilinta v Plavix

* Overall death risk cut by 51 pct, 48 pct for CV death

* No difference in major bleeding seen in bypass patients (Adds study details, researcher comment, background)

By Bill Berkrot and Debra Sherman

ATLANTA, March 16 (Reuters) - AstraZeneca's (AZN.L) experimental blood clot preventer Brilinta cut the risk of death by half in heart patients who underwent bypass surgery when compared with widely used Plavix, according to a subanalysis of a large clinical trial.

The analysis looked at 1,261 subjects from the more than 18,000-patient Plato trial who underwent coronary artery bypass surgery within seven days of taking either Brilinta, known chemically as ticagrelor, or Plavix -- the world's second most prescribed medicine with annual sales of about $8 billion.

In this group of high risk patients, researchers found that Brilinta cut the risk of heart-related death compared to Plavix by 48 percent, and death for any reason by 51 percent, both of which were considered statistically significant.

In the Brilinta group, 4.6 percent of patients died compared with 9.2 percent of those who received Plavix, which is sold by Bristol-Myers Sqibb Co (BMY.N) and Sanofi-Aventis (SASY.PA) and is known chemically as clopidogrel.

"I think this drug looks very, very promising," said Claes Held, lead researcher of the subanalysis presented at the American College of Cardiology scientific meeting in Atlanta.

"We saw a strong effect on mortality that we don't often see. This is very good news," said Held, associate professor of cardiology at Uppsala Clinical Research Center in Sweden.

Analysts see Brilinta as a potential multibillion-dollar a year seller for AstraZeneca.

The overall goal of the study was to assess the drugs' ability to reduce the combined risk of heart attack, stroke, or death from cardiovascular causes. The result in bypass patients -- a 16-percent risk reduction compared with Plavix -- mirrored that of the full Plato trial.

There was no significant difference in strokes, heart attacks or major bleeding between the two medicines.

Bleeding is a major source of worry with drugs that prevent blood clots by keeping blood cells called platelets from clumping together.

The data showing no increased risk of serious bleeding compared to the current standard of care has helped alleviate concerns that safety might be compromised by higher efficacy.

The latest analysis did not shed any light on the one cloud hanging over Plato -- the as yet unexplained apparent lack of benefit over Plavix seen in North American patients, who accounted for some 9 percent of total Plato subjects, but who would represent the most important market for the drug's future success.

There has been speculation that higher doses of aspirin being taken by U.S. patients in the study could account for the disparity, or that it was potentially a statistical fluke.

Meanwhile, researchers remain optimistic about the drug.

"Because there is such an obvious risk of severe bleeding and fatal complications during surgery, patients with a potential need for CABG (coronary artery bypass grafts) comprise an especially important group, for which platelet inhibitors with a better safety-efficacy profile are needed," Held said.

"First from the main Plato trial, and in this population, ticagrelor is the more effective alternative to clopidogrel because it prevents both cardiovascular and total death without an increase in major bleeding," Held said.

"For cardiologists this is really good news." (Reporting by Bill Berkrot and Debra Sherman; Editing by Derek Caney, Dave Zimmerman)