In a statement detailing autopsy results, Dr. Michael Newman said his famous patient had passed a stress test on April 29 and had even worked out on a treadmill the morning of his death.
"Russert, age 58, was known to have asymptomatic coronary artery disease (atherosclerosis), which resulted in hardening of his coronary arteries," Newman said. "The autopsy revealed an enlarged heart and significant atherosclerosis of the left anterior descending coronary artery with (a) fresh clot which caused a heart attack resulting in a fatal ventricular arrhythmia."
Russert's stress test on April 29 was "normal," Newman said. "At a high level of exercise he had no symptoms," Newman said, adding that his blood pressure and cholesterol were "well-controlled."
The newsman collapsed while preparing for his show Meet the Press Friday afternoon. Resuscitation attempts began immediately and after the Washington, D.C., paramedics arrived on the scene a full code was initiated, he said. He was taken to Sibley Memorial Hospital in Washington, D.C., where resuscitation efforts continued to no avail. Studies show that survival is only 4 to 5 percent with sudden cardiac arrest, even with immediate medical attention like Russert had, Newman noted.
His Final MorningDr. Cyril Wecht, a nationally renowned forensic pathologist, said Newman's description of why Russert died makes sense. "The left anterior descending artery is well known among pathologists as the widow-maker," he tells PEOPLE. "That tells you a lot, doesn't it? It's a classical situation that one encounters with great frequency in sudden unexpected death where you get a blood clot, or a thrombosis, or bleeding and if he had an enlarged heart, that adds to it."
Clots can be caused by any number of things, he said. "Sometimes it's associated with stress and exertion, physical and/or emotional," he said. "Was he flying a long time? Was he tired? People shoveling snow in the wintertime can get them. People working excessively hard. Or people under great physical and/or emotional stress and that can include flying."
Russert had flown in from Italy late Thursday night, where he'd been celebrating his son Luke's recent graduation from Boston College with his son and his wife, Vanity Fair writer Maureen Orth.
CNBC chief Washington correspondent John Harwood and Gerald Seib, his co-author on the new book, Pennsylvania Avenue: Profiles in Backroom Power, had seen Russert the morning he died. They were with Russert to tape an hour-long discussion of their new book for his CNBC cable show, The Tim Russert Program.
"We walked out of the taping around 10:15 and Gerry said, 'You know, I don't think Tim felt very well,' " Harwood tells PEOPLE. "I knew he was tired because he had flown in from Rome the night before, but I didn't think much of it."
Wecht said only one thing does not make sense to him – Newman's claim that Russert passed the stress test on April 29 and that he could have passed one an hour before his death. "This hardening of the arteries is something that builds up over a period of years," said Wecht. "So he wouldn't be able to continue the stress test. He'd get short of breath."
Newman could not be reached for comment.
Additional reporting by SANDRA SOBIERAJ WESTFALL