A heart attack that occurs in the morning, between 6am and midday, tends to leave a much larger area of dead tissue than those that occur at other times of the day, Spanish researchers revealed in the journal Heart.
The authors explain that a human's 24-hour body clock has an impact on various cardiovascular physiological processes, including heart attack incidence. These processes are at their height when we wake up in the morning. However, no studies had examined how much damage a morning heart attack causes, compared to those at other times of the day.
Aida Suárez-Barrientos and team wanted to find out what impact the time of day of a heart attack had on the size of the infarct (dead tissue). They focused on patients with a type of heart attack caused when the blood supply is blocked for a long time - known as STEMI (ST segment elevation myocardial infarction).
They gathered information on 811 individuals who had had a STEMI heart attack and were hospitalized at Hospital San Carlos, Madrid, Spain, between 2003 and 2009.
By examining enzyme release in patients they were able to work out how much dead tissue was caused by the heart attack.
They divided the patients into four groups; four six-hour time periods synchronized to human 24-hour body clock rhythms.
They found that the infarct size of those who had a heart attack between 6am and midday was 21% bigger than those whose heart attacks occurred between 6pm and midnight.
The patients had their heart attacks at:
Between 6am and midday - 269 patients
Between midday and 6pm - 240 patients
Between 6pm and midnight - 161 patients
Between midnight and 6am - 141 patients
The authors added that infarct size was larger among those whose STEMI occurred in the anterior wall of the heart.
The researchers concluded:
"If confirmed, these results may have a significant impact on the interpretation of clinical trials of cardioprotective strategies in STEMI."
"Circadian variations of infarct size in acute myocardial infarction"
Aida Suárez-Barrientos, Pedro López-Romero, David Vivas, Francisco Castro-Ferreira, Ivan Núñez-Gil, Eduardo Franco, Borja Ruiz-Mateos, Juan Carlos García-Rubira, Antonio Fernández-Ortiz, Carlos Macaya, Borja Ibanez
Heart doi:10.1136/hrt.2010.212621