Infarct Size Varies According to Time of Day

Significantly larger ST-segment elevation myocardial infarctions occur in the morning

THURSDAY, April 28 (HealthDay News) -- Significant variations in infarct size are associated with circadian oscillations at the time of ST-segment elevation myocardial infarction (STEMI) onset, with the largest infarcts occurring during the dark-to-light transition period (6:00 am to noon), according to a study published online April 27 in Heart.

Aida Suárez-Barrientos, from the Hospital Clínico San Carlos in Madrid, Spain, and colleagues evaluated the relationship between the time of day of STEMI onset and infarct size in 811 patients admitted with STEMI between 2003 and 2009. The time of STEMI onset was categorized into four six-hour time periods in phase with circadian rhythms. Size of infarct was estimated by peak creatine kinase (CK) and troponin-I (TnI) enzyme concentration, and the association between peak enzyme concentrations and time of day was assessed.

The investigators found that there was a circadian variation in infarct size according to the time of day of STEMI onset. Both CK and TnI concentrations had a global maximum during the 6:00 to noon period and a local minimum during the noon to 18:00 period. The largest infarct size with a corresponding significant increase in peak CK and TnI concentrations of 18.3 and 24.6 percent, respectively, was seen in patients with STEMI onset in the dark-to-light transition period (6:00 to noon) compared to STEMI onset in the 18:00 to midnight period. Anterior-wall STEMI resulted in significantly larger infarcts than STEMI in other locations.

"We found an independent circadian oscillating pattern in infarct size across the time of day. Patients with STEMI onset in the dark-to-light transition period (6:00 to noon) had significantly larger myocardial infarctions than those with symptom onset at any other time of the day," the authors write.

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