A new study out of researchers from the Imperial College London and published in the journal The Lancet Public Health has found that heart attack symptoms may have been missed by hospitals in many patients. And it’s not a trivial amount: in as many as one in six heart attack deaths in England, patients were exhibiting early signs that they were about to have a heart attack.

The authors note that more research will be needed to establish if it’s even possible to predict fatal heart attacks when patients are admitted for another reason, but it’s a significant finding that could lead to changes in how patients are evaluated.

The study is based on records from 446,744 NHS hospital stay sin England between 2006 and 2010 that recorded heart attacks, and the hospitalization history of 135,950 deaths from heart attacks. Researchers looked for signs that patients had been admitted in the last four weeks or so, or whether heart attack was the main cause of admission.

Lead author Dr Perviz Asaria, from the School of Public Health at Imperial, said: “Doctors are very good at treating heart attacks when they are the main cause of admission, but we don’t do very well treating secondary heart attacks or at picking up subtle signs which might point to a heart attack death in the near future.”

“Unfortunately in the four weeks following a hospital stay, nearly as many heart attack deaths occur in people for whom heart attack is not recorded as a primary cause, as occur after an admission for heart attack.”