An official investigation has been launched into the routine medical procedure that left JOAN RIVERS dead, The ENQUIRER has learned exclusively.

And in a chilling twist, an expert says it’s possible the 81-year-old comedy icon stopped breathing and suffered both respiratory and cardiac arrest after she may hev been was given propofol – the same drug that police said killed pop star Michael Jackson.

“Investigators will look into the anesthetic given to her and also determine whether she was given too high a dosage,” a source told The ENQUIRER.

While it was not immediately known which drug was used to sedate the 5-foot-2, 102-pound star, or what caused her respiratory and cardiac arrest, a physician familiar with the 
procedure said the fashion maven could have received propofol.

Dr. Gabe Mirkin, author of “The Healthy Heart Miracle” who has not treated Joan, told The ENQUIRER: “Propofol is a respiratory depressant and can cause cessation of breathing. If stopped for more than 60 seconds, it can trigger a heart attack.”

Joan checked into Yorkville Endoscopy, a medical clinic on Manhattan’s Upper East Side, for a minor procedure on Aug. 28. After she was sedated, a tube was passed down her throat to examine her vocal cords.

According to a report, “things went wrong” after Joan – whose six-decade showbiz career has earned her an estimated $150 million – was sedated.

A source told The ENQUIRER: “After she stopped breathing, paramedics arrived to find Joan unconscious with no pulse. She was in very bad shape.”

She was rushed by ambulance to nearby Mount Sinai Hospital, where doctors put her in a medically-induced coma. Her daughter Melissa, 46, was at her side.

Joan has famously undergone dozens of plastic surgery procedures over the years. She also battled bulimia after her husband Edgar Rosenberg committed suicide in 1987.

“Her numerous surgeries – and bulimia – increased her risk of having a heart attack,” Dr. Mirkin told The ENQUIRER. I think it was poor judgment to put an 81-year-old woman under anesthesia.”

Ironically, Joan once told The ENQUIRER that she’d planned to have surgery, but the anesthesiologist couldn’t knock her out!

“He went to put the Valium in my arm and missed my vein twice,” Joan said. “I said ‘Over and out’ – and I literally got off the table and left. I walked out of the operating room with my gown flapping around me. Not a pretty picture!”

As The ENQUIRER previously reported she has been placed on life support before succumbing to death, her daughter Melissa Rivers confirmed.