Patients in intensive care units are disconnected from their natural environment. Synchrony between environmental diurnal rhythms and intracellular circadian rhythms is essential for normal organ biology; disruption causes pathology. Whether disturbing rhythms after myocardial infarction (MI) exacerbates long-term myocardial dysfunction is not known.

Short-term diurnal rhythm disruption immediately after MI impairs remodeling and adversely affects long-term cardiac structure and function in a murine model.

Mice were infarcted by left anterior descending coronary artery ligation (MI model) within a 3-hour time window, randomized to either a normal diurnal or disrupted environment for 5 days, and then maintained under normal diurnal conditions. Initial infarct size was identical. Short-term diurnal disruption adversely affected body metabolism and altered early innate immune responses. In the first 5 days, crucial for scar formation, there were significant differences in cardiac myeloperoxidase, cytokines, neutrophil, and macrophage infiltration. Homozygous clock mutant mice exhibited altered infiltration after MI, consistent with circadian mechanisms underlying innate immune responses crucial for scar formation. In the proliferative phase, 1 week after MI, this led to significantly less blood vessel formation in the infarct region of disrupted mice; by day 14, echocardiography showed increased left ventricular dilation and infarct expansion. These differences continued to evolve with worse cardiac structure and function by 8 weeks after MI.

Diurnal rhythm disruption immediately after MI impaired healing and exacerbated maladaptive cardiac remodeling. These preclinical findings suggest that disrupted diurnal rhythms such as found in modern intensive care unit environments may adversely affect long-term patient outcome.