Joan Rivers
Joan Rivers and her daughter Melissa, at the 55th annual Emmy Awards in Los Angeles in 2003. Rivers passed away at the age of 81 in New York Sep. 4. Reuters

Joan Rivers was laid to rest in New York City Sunday, but questions still remain regarding the outpatient procedure which led to her death. In a new exposé of Rivers’ procedure, her clinic, Yorkville Endoscopy, is reported as having called 911 the morning of Aug. 28, telling dispatchers that an unnamed patient was in cardiac arrest, a “Segment 1,” high-priority coded call. That patient was Rivers.

Rivers, who is believed to have undergone a vocal procedure at the Upper East Side Manhattan clinic, reportedly stopped breathing while under its care at around 9:40 a.m. Within five minutes, medical responders and firefighters were at the scene treating Rivers, the New York Times reports. New York City officials, who spoke under the guise of anonymity, said clinic staff were seen trying to revive Rivers, who had been medicated, given CPR, hooked up a defibrillator and a had a breathing tube placed in her windpipe. Firefighters took over to perform CPR. By 9:50 a.m., 10 emergency workers were on the scene, including paramedics from Mount Sinai Hospital. “The resuscitation efforts appear to be as good as one could hope for,” one of the officials said.

Rivers was later transported to Mount Sinai Hospital where she remained on life support for several days. She passed away surrounded by family and friends Sep. 4. So what happened to Rivers?

Yorkville Endoscopy has declined to speak about the comedienne’s case due to federal privacy laws. The clinic received death threats after allowing Rivers, an 81-year-old suffering from heart arrhythmia, to participate in the outpatient procedure.

“We would love to set the record straight from all the misinformation that’s out there,” Dr. Daniel J. Adler, a gastroenterologist and colleague of Rivers’ physician, Dr. Lawrence B. Cohen at Yorkville Endoscopy, said. “Unfortunately, our lips are sealed.”

Yorkville Endoscopy doctors may not be talking, but others are now claiming that the decision to perform endotracheal intubation on Rivers, a procedure which includes planting a breathing tube in between the vocal cords and windpipe, was risky. “Experts said most doctors lacked the skill to intubate a person in distress,” reads the report. Dr. Eric Manheimer, a former medical director at Bellevue Hospital Center in New York, said of the procedure, “It is something you need to practice and do or you lose it.”

The New York State Health Department is investigating into the cause of Rivers’ death, New York Health officials confirmed last week. Sources tells ABC News the clinic is not suspected of any "wrongdoing." Following an inconclusive autopsy, the New York City Medical Examiner’s Office said additional tests will be needed in order to determine Rivers' “cause and manner of death.”