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Those with a history of heart disease should stay clear of the Queen and Bay Street area.

It's one of the public places in Toronto where most heart attacks occur, yet it's out of reach from life-saving automated external defibrillators (AEDs), according to new research from 91�Թ�.

“If you have a cardiac arrest, every second counts," said Dr. Laurie Morrison, from St. Michael's hospital. "Only five per cent of people who suffer out-of-hospital cardiac arrest survive to be discharged from hospital. The probability of survival decreases up to 10 per cent with each minute of delay between collapse and treatment.”

In a paper published in Circulation, Morrison and 91�Թ� mechanical and industrial engineering professor Tim Chan note that publicly registered AEDs in Toronto are not in the best locations to help victims of cardiac arrest. In fact, less than one in four of all cardiac arrests had an AED close by (within 100 metres is the required distance). The average distance to the nearest AED was closer to 300 metres.

Morrison and Chan developed a new formula to determine where the costly AEDs are best placed to serve their life-saving purpose—and identified key areas in Toronto where AEDs are not currently within reach, hindering the prompt use that can greatly increase survival rates.

Current guidelines suggest areas associated with the highest risk of cardiac arrest should be targeted for AED deployment, after they have been placed in obvious high-traffic areas such as transportation hubs or major sports venues. But it’s not clear how to identify these "cardiac hot spots."

Chan and Morrison looked at the locations of all 1,310 public cardiac arrests in Toronto between December 2005 and July 2010 and the locations of all 1,699 AEDS registered with Toronto Emergency Medical Services.

They found that 304 cardiac arrests occurred within 100 metres of at least one AED (23 per cent).One hundred metres was chosen as the yardstick because it’s the approximate distance a bystander could transport an AED in a 1.5-minute walk—the maximum recommended by the American Heart Association.

There were almost three times as many public cardiac arrests in downtown Toronto as the rest of the city – 3.5 per square kilometer per year vs. 0.4 – said Chan. Almost half of all downtown cardiac arrests were near an existing AED compared to only 17 per cent of those outside of downtown.

Chan then looked at the 1,006 cardiac arrests that did not take place near an AED. He said that by placing AEDs in the top 30 cardiac arrest “hot spots,” they could have covered an additional 112 historical arrests, or 32 per cent. The average distance between a cardiac arrest and an AED would fall to 262 metres from 281 meters.

“Reducing the distance a bystander needs to travel by 20 metres or up to 40 meters in a roundtrip has the potential to save close to half a minute in response time,” said Morrison, an emergency medicine specialist who heads Rescu, the largest research team of its kind in Canada dedicated to improving out-of-hospital resuscitation.

Chan said his mathematical model is more accurate than a population-based model, in which AEDs are placed in areas of densest daytime population.

“Our optimization model should be viewed as a decision-support tool to help prioritize placement of AEDs, make efficient use of public, donor or private funds directed toward public access defibrillator programs, and potentially maximize survival on the basis of geographic patterns of cardiac arrest,” said Chan. “Because AEDs are expensive and cannot be placed everywhere, our model allows a decision-maker to quantify the trade-off between the number of AEDS deployed and coverage.”

While it was not part of the research paper, Chan used his mathematical model to indicate the top 10 cardiac hot spots in Toronto not currently covered by AEDs:

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1.Jarvis and Gerrard
2.Queen and Bay
3.Jarvis and Dundas
4.Brimley and Progress
5.Eglinton and Warden
6.Wellington and Strachan
7.Dundas and Spadina
8.Queen and Shelbourne
9.Danforth and Pape
10.Jarvis and Adelaide