PHILADELPHIA -- For competitors in endurance events, the most exhilarating place to be is near the finish line. It is also the riskiest.
Last year, a 40-year-old runner in superb condition collapsed and died about a quarter-mile before the end of the Philadelphia Marathon. A 21-year-old student died shortly after completing that year's half-marathon. The pattern plays out across the country, with deaths in long-distance races concentrated in the last few miles or just afterward.
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"We don't really know what kicks the heart off," said William O. Roberts, a professor at the University of Minnesota Medical School and a founder of the American Road Race Medical Society. The cause could be a surge in adrenaline, a decline in blood oxygen, or something yet to be discovered.
Trained athletes tend to be in better cardiovascular shape than the general population. And if you are destined to go into sudden cardiac arrest, the safest place to drop is on a racecourse, where resuscitation rates can exceed 50 percent vs. 5 percent elsewhere. So experts say the focus for now should be on ensuring the best possible medical coverage at events.
Sunday's Philadelphia Marathon and simultaneous half-marathon will be staffed by about 40 paramedics and emergency medical technicians on roving vehicles: six ambulances, six golf-cart-like Gators, five bicycle teams, and two ATVs, all with advanced life support capability. Two more ambulances will be stationed at the Manayunk turnaround and two more at the end on the Benjamin Franklin Parkway. Medical tents with physicians and nurses will be placed near mile marker 16/23 on Kelly Drive and off the finish line.
The Philadelphia Marathon is unique as a city-owned and -operated event, with medical coverage provided by the city. (The finish-line tent will be staffed by Thomas Jefferson University Hospital volunteers.) Counting supervisors and dedicated 911 dispatchers, nearly 100 emergency personnel will staff the route.
"From our perspective, we are very innovative with covering the course with 'moving resources' to get care to anybody that needs it," usually before a 911 call reaches the dispatcher, said Diane Schweizer, the city Fire Department's EMS operations chief.
In both fatalities last year, she said, paramedics - a bike team on the course and personnel from the finish-line tent - witnessed the collapses and arrived within seconds but could not restart the victims' hearts. A review determined that coverage was "adequate because they were right there, initiated care, and got them to the hospital immediately," Schweizer said.
In Schweizer's five years overseeing EMS, 2011 was the first time a runner collapsed a quarter-mile before the end, she said.
The spot would be familiar to Lewis Maharam.
All around the country, said Maharam, chairman of the International Marathon Medical Directors Association, he hears about cardiac arrests at the exact point where runners first see and hear the end. He calls it the X spot.
"At the X spot, you see the finish line and you get so excited that you get a rush of adrenaline, and that takes a susceptible heart and essentially makes it stop beating," Maharam said. He said he stations paramedics at that spot and demands that announcers not urge competitors to sprint to the finish.
Autopsies of race fatalities often find undiagnosed coronary artery disease, particularly in runners over 40. In those cases, an overtaxed heart muscle may not get enough oxygen-rich blood to fuel the faster pumping action required for a sprint, causing damage that is known as a heart attack.
A heart attack does not stop the pump. But it can lead to disturbances in the electrical signals that control the heartbeat, halting it abruptly in sudden cardiac arrest. Unless the heart is restarted, death occurs within minutes.
The abnormal electrical impulses themselves leave no evidence at autopsy. Runners under 40, even those in seemingly perfect health, are more likely to go into cardiac arrest for no identifiable reason - and they, too, die more frequently near the end of the race. Some drop after finishing.
Bruce Adams, medical director of the Marine Corps Marathon, believes the pattern points to something beyond an X spot adrenaline surge. A decrease in oxygen levels from sprinting to the end can cause a buildup of lactic acid in the blood, he said. The acidosis can shift electrolytes, which in turn can disrupt electrical signals.
A heart that stopped as a result of lactic acidosis may not restart when an EMT delivers electric shocks from a defibrillator. Adams recalled a couple of cases at the finish line when there was no response until the runners were given sodium bicarbonate, a harmless antacid that is not normal protocol in the field. When the blood pH changed, defibrillation worked.
Although there is no proof of what's happening, the marathon medical directors group recommends not sprinting to the end; taking a baby aspirin on the morning of a race (to prevent blood clots); and consuming less than 200mg of caffeine, or about one 8-ounce coffee. (Caffeine might affect heart function.)
Deaths are so rare - one in every 150,000 to 175,000 marathon participants, according to two national studies published this year - that researchers have little to go on. Until last year, only one person is reported to have had died in the 19-year history of the Philadelphia Marathon.
"Every race is different," said David Webner, a sports-medicine doctor at Crozer-Keystone Health System and lead author of the most recent study, who found that 47 percent of sudden cardiac arrests occurred after mile marker 25. Heat, the biggest danger, varies from year to year.
A high in the mid-50 degrees is forecast for Sunday, with 16,000 runners - including 1,454 late entrants from the New York City Marathon, which was canceled in the aftermath of Hurricane Sandy - registered for the Philadelphia Marathon and 12,500 for the half marathon. Both are records.