To improve recovery for heart attack patients, hospitals should maintain patients’ normal day and night cycles during the first few days after the event, say University of Guelph researchers.

The new study shows that interrupting diurnal rhythms impairs healing immediately after a heart attack, says Professor Tami Martino of the Department of Biomedical Sciences.

Researchers already knew that circadian rhythms, or day-night cycles, can affect timing of a heart attack. This is the first study to show the importance of circadian rhythms during the few days after an attack.

The study appears this week online in Circulation Research journal.

“We have devised a simple way to better practise medicine to improve the outcome from heart attacks by considering normal circadian rhythms,” she says in a release.

She and PhD student Faisal Alibhai conducted the study with clinician collaborators, who are already looking at ways to use the results to change practices in intensive care units (ICUs). “It has an immediate life application,” Martino says.

Hospital ICUs are busy places at night, with noise, light, nursing and medical procedures, and other interruptions that disturb acutely ill patients.

The team induced heart attacks in mice, and then compared rodents held under normal light and dark cycles with others whose diurnal cycles were disrupted for 5 days after the attacks.

Early heart repair and remodeling were impaired in the disrupted mice. Diurnal disruptions interfered with their normal inflammatory and immune responses crucial for scar formation and healing.

“These mice were likely to go more quickly to heart failure,” Martino says. “Disrupting circadian rhythms for the first few days after a heart attack worsens the disease outcome.”

The first 5 days after a heart attack are crucial for proper scar formation, removal of dead tissue, proliferation of new cells, and growth of blood vessels in the heart.