Washington : Spanish researchers have found that heart attacks that occur in the mornings could turn out to be are more fatal compared to at other times of the day.

Heart attacks that occur between 6am and noon are more likely to leave a 20 percent larger area of dead tissue (infarct) caused by the attack, which is more serious for the patient than at any other time of the day.

It is known that a person''s 24 hour body clock influences several cardiovascular physiological processes including the incidence of heart attacks, which tend to happen more around the time when a person is waking up from sleep. However, the lesser-known fact is the extent of damage that this leads to.

Researchers in Madrid, Spain determined the impact of time of the day of a heart attack on the size of the dead tissue (infarct) caused in patients with an ST segment elevation myocardial infarction (STEMI), a type of heart attack caused by a prolonged period of blocked blood supply.

They analysed data on 811 patients with a STEMI heart attack admitted to the coronary care unit of Hospital Clinico San Carlos in Madrid between 2003 and 2009. They calculated the size of infarct by looking at enzyme release in patients.

The time of STEMI onset was divided into four six-hour time periods in phase with 24-hour body clock rhythms.

It has emerged that patients with the largest infarct size were found to be those who had a heart attack in the dark to light transition period of 6am to noon.

These patients were found to have approximately 21 percent higher level of enzymes in this period (which indicated a larger infarct size) than patients who had their heart attack between 6pm and midnight.

The greatest number of patients (269) had their heart attack in the 6am to noon period, followed by 240 patients who had it between noon and 6pm, 161 during the 6pm to midnight period, and 141 between midnight and 6am.

The study also reveals that patients with a STEMI that happened in the anterior wall of the heart were left with a larger size of infarct than patients whose heart attacks happened in other locations.

"If confirmed, these results may have a significant impact on the interpretation of clinical trials of cardio protective strategies in STEMI," the research authors have concluded.

The research is published ahead of print in Heart journal.(ANI)