Story highlights A toxicologist says Houston's death could have stemmed from cardiac arrhythmia

Coroner: Death was from accidental drowning; cocaine, heart disease were factors

Investigators found "a small spoon with a white crystal like substance " in her bathroom

Her assistant found Houston 35 minutes after telling her to take a bath

Whitney Houston drowned face down in a tub of "extremely hot water" about 12 inches deep, the final autopsy report on the singer's death said.

The Los Angeles County coroner ruled that Houston's February 11 death was an accidental drowning with the "effects of atherosclerotic heart disease and cocaine use" as contributing factors.

The coroner's report stopped short of detailing what happened to Houston, but HLN's Dr. Drew Pinsky, an addiction medicine specialist, examined the autopsy report for CNN and suggested she might have suffered a seizure brought on by the use of cocaine possibly combined with a withdrawal from alcohol and a prescription sedative.

An empty bottle of the Xanax was found in her room, but the level of the sedative found in her blood was low, he said. Empty beer bottles were also found, but alcohol was not detected in her body, he said.

"To me, a sudden drop off in the Xanax level, a drop off in your alcohol consumption, add cocaine, that's a recipe for a seizure," Pinsky said. "Somebody who's now upside down in a bathtub could easily seize and drown."

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However, Henry Spiller, a toxicologist and director of the Kentucky Regional Poison Control Center, said the level of Xanax found in Houston's blood was not low enough to trigger a seizure. Those who abuse Xanax can take up to 20 pills a day, he said, and the level found in Houston's body would indicate she took four to six pills several hours before she died.

Since the drug was found in her blood, a seizure brought on by withdrawal is unlikely, he said.

The coroner's report notes that Houston suffered several small scald burns on her face at the time of her death.

A 60% narrowing of her arteries found in the autopsy is "very mild heart disease," Pinsky said, which should not have caused a problem.

Spiller said that based on his experience with cocaine abusers, two things may have happened -- either Houston had a seizure and fell into the tub, or had a cardiac arrhythmia. An arrhythmia occurs when the heart stops beating properly and fails to pump for a period of time, depriving the brain of oxygen and causing a loss of consciousness. It can be fatal.

"If you look at cocaine deaths, more deaths are from arrhythmias than seizures," Spiller said. "Based on what is the report, it seems more likely that she had a vasospasm (which shuts off blood flow to the heart) or a fatal arrhythmia."

Toxicology testing measured .58 micrograms of cocaine per milliliter of blood drawn from a vein in her leg during the autopsy, which Pinsky called a moderate level.

Spiller said for that level of cocaine to be in Houston's body, "we're talking about approximately half a gram of cocaine having been possibly ingested within 30 minutes to 90 minutes before her death. For someone who has been abusing cocaine, this may be their routine amount, but (for) someone who doesn't regularly use cocaine and therefore doesn't have a tolerance for the drug, this would be a high level."

Houston's cocaine use appeared to have occurred "in the time period just immediately prior to her collapse in the bathtub at the hotel," Chief Coroner Craig Harvey told reporters when he released the preliminary report last month.

Investigators found "a small spoon with a white crystal like substance in it and a rolled up piece of white paper" in the bathroom where Houston drowned, coroner's investigator Kristy McCracken wrote.

"Remnants of a white powdery substance" were found on a bathroom counter, McCracken wrote.

"I also collected remnants of a white powdery substance from out of a drawer and from the bottom of a mirror in the same drawer in the bathroom counter," she wrote.

Detectives found a "plethora of medications bottles" in the hotel room, although the coroner concluded the prescription drugs "did not contribute to the death."

Along with cocaine, the toxicology tests found other drugs in her body, including marijuana, the anti-anxiety drug Xanax, the muscle relaxant Flexeril and the allergy medicine Benadryl, the report said.

Houston was last seen alive by her personal assistant in her Beverly Hilton hotel room at about 3 p.m. that Saturday, the report said. The assistant left to run errands after telling Houston to take a bath in preparation for a pre-Grammy Awards party at the hotel that night, it said.

When the assistant returned to the locked room at 3:35 p.m., she found Houston "lying face down in the bathtub filled with water, unresponsive."

"The assistant called for her bodyguard, and together they pulled the decedent out of the bathtub," the report said.

When paramedics arrived about 10 minutes later they moved Houston to the living room floor. It was at 3:55 p.m., 20 minutes after she was found by the assistant, that paramedics concluded she was dead, the report said.

Houston won six Grammys and sold 170 million albums, singles and videos over her career.

In recent years, the singer's accomplishments were overtaken by her struggles with drug addiction.