Joan Rivers' death is now the subject of a second investigation by the New York City Medical Examiner's office.  (Photo: Getty)

Joan Rivers’ death is now the subject of a second investigation by the New York City Medical Examiner’s office. (Photo: Getty)

Joan Rivers’ cause of death could not be immediately determine by an autopsy, according to results released today by the New York City medical examiner’s office. But drugs used for her throat surgery may have played a role.

Rivers, 81, went into cardiac and respiratory arrest while undergoing minor surgery on her vocal chords at an outpatient clinic.

Prior to that she exhibited no signs of ill health.

Co-workers and friends described the octogenarian as “athletic” and energetic. She said recently she walked about three miles every day to stay fit. But she also joked that, at 81, she could go anytime.

Rivers died Sept. 4 without ever regaining consciousness after she stopped breathing during the procedure. She was rushed to Mt. Sinai Hospital in critical condition.

In the wake of her death, New York State Health Department officials have launched their own, separate inquiry into the procedures followed by Yorkville Endoscopy during Rivers’ surgical procedure.

Some tabloid reports claim Yorkville was using propofol, a powerful anesthesia, to sedate her. But those reports are unconfirmed.

The drug was responsible for Michael Jackson’s death, at 50, in 2009. In that case it was being administered outside a hospital setting, which is against the drug’s protocol.

Jackson’s doctor, Conrad Murray, was convicted of negligence in his death.

The medical examiner’s office is reportedly planning its own investigation to determine the exact “cause and manner” of the iconic comedian’s death. Toxicology reports typically take weeks to process.

The fact that Rivers was placed in a medically induced coma, usually involving powerful sedatives, may make it impossible to chart exactly what drugs were in her system prior to her hospital admission.

Rivers’ family is reportedly planning to file a malpractice lawsuit against Yorkville Endoscopy, but so far those reports are unconfirmed as well.

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Books by Joan Rivers: Click Titles to Purchase
Diary of a Mad Diva
Joan Rivers at her best… complaining.

I Hate Everyone…Starting with Me
Joan Rivers speaks out on everything she hates. Like people who think giving birth is a unique achievement.

Murder at the Academy Awards (R): A Red Carpet Murder Mystery
It’s Hollywood’s biggest night, and there’s no star better equipped than the tart-tongued Max Taylor to hold court on the glamorous Red Carpet.

Bouncing Back : I’ve Survived Everything…and I Mean Everything…and You Can Too!
With inspirational thoughts with humor, Joan describes how she overcame a series of personal tragedies and setbacks, including her husband’s suicide, financial disaster, and estrangement from her daughter.

Men Are Stupid . . . And They Like Big Boobs
Joan is uniquely qualified to talk about plastic surgery — because she’s one of the few celebrities unafraid to admit to the world what she’s “had done.”

Having a Baby Can Be a Scream
Rare Joan Rivers from early in her career. Expect to pay a premium for this book.

Don’t Count the Candles: Just Keep the Fire Lit!
Joan Rivers tells the whole truth about how women feel when it comes to getting older. Filled with the latest information on anti-aging breakthroughs.

From Mother to Daughter: Thoughts and Advice on Life, Love, and Marriage
Based on a letter to her daughter Melissa, Joan Rivers writes about a series of highly personal but universal truths involving relationships.

The Life and Hard Times of Heidi Abromowitz
An “unauthorized biography” of the comedienne’s free-living childhood friend, this intimate profile discloses Heidi’s deepest, darkest secrets.

Jewelry by Joan Rivers
Joan Rivers’ love and knowledge of jewelry is reflected in the pieces she designs for her own collection, hundreds of which are reproduced here in specially commissioned full-color photos.