Routine medical tests could be missing as many as two-thirds of heart attack diagnoses, researchers reported at CMR 2018, an annual conference dedicated to cardiac magnetic resonance imaging in Barcelona.

Unrecognized myocardial infarction (MI)—heart attacks that are missed during routine care but picked up by electrocardiograms (ECGs) or cardiovascular magnetic resonance (CMR) imaging—can actually outnumber recognized cases, which are formally diagnosed. While undiagnosed and diagnosed patients alike see the same long-term risk of mortality, a release from the European Society of Cardiology stated, unrecognized patients suffer from a lack of medication to treat their condition and reduce their future risk of death.

“Unrecognized MI has a poor short-term prognosis but until now the long-term outlook was unknown,” lead author and cardiologist Tushar Acharya, MD, said in the release. “This study investigated long-term outcomes.”

Acharya’s team analyzed the differences between unrecognized and recognized MI in a population of 935 older individuals from the ICELAND MI study. All patients underwent an ECG and CMR at the baseline of the study and were diagnosed with either recognized MI, unrecognized MI or no MI.

There were 91 participants—10 percent of the pool—who had a recognized heart attack, the research stated. In comparison, 156 patients—or 17 percent—were diagnosed with unrecognized MI. Seventy-four percent had no MI.

“That means 63 percent of the myocardial infarctions identified by CMR were missed in routine medical care,” Acharya said. “Unrecognized MI may be more common than recognized MI.”

Acharya said patients with unrecognized MI commonly don’t receive the same medications prescribed to diagnosed heart attack patients, who often receive aspirin, high-intensity statins, angiotensin converting enzyme inhibitors and beta blockers to reduce future risk of cardiovascular complications or another heart attack. These overlooked patients should also be advised to control risk factors like diabetes and hypertension in their daily lives, he said.

According to the study, ten-year mortality rates were similar in patients with both unrecognized and recognized MI. At five years, though, the death rate in patients with diagnosed MI was 6 percent higher than the rate in those with undiagnosed heart attacks.

“This shows that with time, the mortality rate of patients with sub-clinical MI increases and is the same as those with diagnosed MI,” Acharya said. “Knowing that they had a heart attack may also persuade some people to adopt a healthier lifestyle with adequate physical exercise and no smoking.”