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An overcrowded ER does not seem to delay patients in getting an emergency procedure to stop a heart attack in progress -- at least at one U.S. hospital, a new study finds.

Over the past couple of decades, the number of emergency rooms in the U.S. has dropped by about one-quarter, even as the number of patients visiting them has climbed. That often equals ER overcrowding and research suggests it's taking a toll.

A recent study of California ERs, for instance, found that elderly heart attack patients had a higher death rate when their nearest hospital was on a high level of "diversion" -- meaning the ER was so crowded it was turning ambulances away.

And some research, though not all, has suggested that when heart attack patients arrive at a crowded ER, their care may be slowed down -- whether they require an invasive procedure or blood-clot-dissolving drugs.

For the new study, reported in the Annals of Emergency Medicine, researchers at Advocate Christ Medical Center in Oak Lawn, Illinois, evaluated the treatment given to 210 heart attack patients at their suburban hospital.

All of the patients received emergency angioplasty, wherein a balloon-tipped catheter is threaded into the arteries to clear the blockages causing the heart attack.

Experts say that when a patient needs emergency angioplasty, it should happen within 90 minutes of their arrival at the hospital.

In this study, patients waited an average of 65 minutes. And the level of ER crowding did not appear to affect that wait time.

On average, the ER was filled to 127 percent of its capacity, but across the study period conditions ranged from 28 percent full to 214 percent.

Dr. Ben Harris, who led the study, called the findings "somewhat reassuring." But he added that U.S. ERs are still operating beyond capacity and it remains a general problem.

"I don't think there's any doubt that overcrowding is having an adverse effect overall," agreed Dr. Erik B. Kulstad, who also worked on the study.

However, those critical patients who need an emergency heart procedure are given priority.

According to Kulstad, ER crowding may not have had an effect in this study because the hospital has a plan in place to speed the right patients to angioplasty.

"When an ultra-critical patient arrives requiring treatment and intervention, that is carefully measured...resources to care for the patient are brought in from not just the emergency department alone, but from throughout the hospital," Kulstad explained.

The flip side to that, he noted, is that it may draw staff and resources away from other patients' care.

The main limitation of the study is that it focused on one hospital. It's not clear if the same results would be seen at other centers with different levels of staffing, for example, or those in settings other than the suburbs.

But Kulstad said they suspect the findings could be similar in other U.S. hospitals, since all centers now have to publicly report their heart attack treatment outcomes.

As a result, he said, they're putting high priority on cutting the wait time to treatment.

The one factor that did affect patients' wait time in this study was whether they got to the hospital during "business hours" or off-hours.

Patients who arrived on a weekday between 6 a.m. and 6 p.m. -- when the angioplasty team was on-site -- started treatment in 55 minutes, on average. If they arrived on a weekend or at night, when the angioplasty team was on-call, they waited 76 minutes.

Of course, people can't decide when a heart attack will strike, or whether the ER will be crowded once they arrive.

The main thing they can do, Kulstad said, is to call 911 if they think they are having symptoms of a heart attack -- which can include pain or pressure in the chest; pain in the arms, neck, jaw or stomach; breathing difficulty; light-headedness and nausea.

In the future, though, Kulstad noted, people may be able to get information on crowding in their local ERs.

There are plans to publicly report hospitals' ER-crowding rates on the government's Hospital Compare website starting in 2014.

Public reporting is also considered a good motivator for hospitals to find ways to improve.