Los Angeles (CNN) -- Dr. Conrad Murray's delay in calling 911 for help as soon as he realized Michael Jackson was not breathing may have cost the pop icon his life, according to a cardiologist who testified Wednesday in Murray's involuntary manslaughter trial. Dr. Alon Steinberg, a cardiologist called as an expert witness by the prosecution, listed Murray's failure to immediately call for paramedics as one of six examples of gross negligence that contributed to Jackson's death. "If these deviations would not have happened, Mr. Jackson would be alive," Steinberg testified. Earlier Wednesday, Murray's defense team dropped its theory that Jackson may have orally ingested the surgical anesthetic propofol that the coroner says killed him.
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NEW: Sleep expert says using propofol to treat insomnia is "beyond comprehension"
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Michael Jackson would be alive now if Murray called 911 quicker, doctor says
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Cardiologist cites six examples of Murray's gross negligence in Jackson's death
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Defense still contends Jackson may have injected himself with the fatal dose
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@placeholder's deviations from medical standards of care include the doctor leaving his patient alone with propofol and lorazepam nearby, which could have led to Jackson self-administering the fatal drugs, Steinberg testified.
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That assumption, he said, was made because @placeholder told police he had used such a drip on most previous nights.
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A sleep expert and an anesthesiologist are expected to follow @placeholder on the witness stand Wednesday and Thursday.
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@placeholder, in the interview played for the jury over the past two days of testimony, told detectives he gave Jackson a series of three sedatives -- Valium, lorazepam and midazolam -- over a 10-hour period before finally giving in to Jackson's plea for propofol.
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"I've got to sleep, Dr. @placeholder," Murray said Jackson pleaded to him.