Half of heart attack patients fail to immediately call an ambulance for help, delaying diagnosis and potentially worsening their survival odds, a Swedish study suggests.

Researchers studied treatment timelines from symptom onset to diagnosis for about 450 people hospitalized for the deadliest type of heart attacks, known as ST-elevation myocardial infarction (STEMI), which are caused by prolonged blockage of blood supply to the heart.

Patients who called an ambulance right away were typically diagnosed about 81 minutes after symptoms started a timeline that stretched to 119 minutes for people who found another way to the hospital or made other calls first.

"I think many patients simply may not realize how critical immediate interventions are in treating ST-elevation myocardial infarction, and denial of the potential severity of their symptoms may also contribute to a delay in seeking medical help," Dr. Christopher Lee, an emergency medicine researcher at Yale University School of Medicine in New Haven, Connecticut, said by email.

In any heart attack, a coronary artery is at least partially blocked by a blood clot or arterial plaque. With STEMI, the artery is completely blocked, causing the heart muscle supplied by that vessel to start dying. Symptoms can include chest pain, heart palpitations, sweating, dizziness and nausea, and diagnosis is confirmed with an electrocardiogram (ECG).

For some patients, treatment can start in an ambulance with clot-busting drugs. At the hospital, doctors typically insert a catheter in the groin and snake it through the damaged artery, then deploy a tiny balloon to open the passage. Surgeons may also place a wire mesh cage known as a stent in the vessel to prevent future blockage.

The study by Ingela Thylen of Linkoping University in Sweden and colleagues found that 83 percent of patients eventually took an ambulance to the hospital. But one in five called a healthcare hotline first, and another 14 percent either called their primary care provider before the emergency services or went directly to the emergency room themselves.

Among patients who didn't immediately call emergency medical services, 40 percent said they thought they could get to the hospital faster on their own, 30 percent didn't think they were sick enough to go to the hospital and 25 percent thought it was easier to be driven or take a taxi.

"Often, when people aren't sure they're having a heart attack they want to speak to their doctor first," Dr. Christopher Labos, a cardiologist at McGill University in Montreal who wasn't involved in the study, said by email. "Sometimes people have preferences about what hospital they want to go to so they opt to drive there directly."

Women were less likely to call an ambulance than men, and people with more education or a history of diabetes were also less inclined to contact emergency medical services. When pain was not very intense, or involved the neck, that was also associated with a lower likelihood of calling an ambulance first.

People were more likely to call an ambulance immediately if they had a history of heart attacks, abnormal heart rhythms, abdominal pain or a belief that their symptoms originated in their heart.

Some reluctance to call an ambulance comes from uncertainty about whether symptoms are really a heart attack, Labos said.

"Many times heart attacks can present with atypical symptoms," Labos said. "Sometimes it's a dull ache, sometimes it's burning pain, sometimes it's a sharp stabbing pain, and it can be really tough for patients to know if this is actually their heart or not."

The Swedish study is small, and it can't prove that delaying the call for an ambulance stalls diagnosis and treatment, it can only show that the two are connected, the researchers note in BMJ Open.

"The generalizability of a small observational study conducted in Sweden is fairly limited but, interestingly, these results do seem to be similar to what we see here in the United States," said Lee.

"The observations found in this study highlight areas of public awareness and education that we must continue to improve. The longer the heart goes without oxygen, the more irreversible damage occurs."