Diurnal Variation in Mechanical Circulatory Support Initiation and Associated Outcomes.

Background: Mechanical circulatory support (MCS) is increasingly deployed for cardiogenic shock and refractory hemodynamic instability. Emergent device implantation frequently occurs outside routine daytime hours, yet whether nighttime initiation is associated with delays in care or worse outcomes remains uncertain. Historical "off-hours" effects have been described for other time-sensitive cardiovascular interventions, but contemporary data in MCS populations are limited. We assessed whether nighttime vs daytime MCS initiation impacts mortality, complications, and time to escalation of care. Methods: We performed a retrospective cohort study using the Medical Information Mart for Intensive Care IV database. Adults undergoing first-time MCS placement during ICU admission were included. Device initiations were categorized as daytime (06:00 - 17:59) or nighttime (18:00 - 05:59). The primary outcome was in-hospital mortality. Secondary outcomes included acute kidney injury, bleeding complications, time from ICU admission to device placement, and postimplant survival. Multivariable logistic and Cox regression models adjusted for age, sex, admission type, and ICU location. Results: Among 1120 patients undergoing MCS initiation, 570 (50.9%) occurred at night. Baseline characteristics were similar between groups. In-hospital mortality was 27.9% for nighttime vs 25.5% for daytime initiation. Nighttime placement was not associated with increased mortality after adjustment (adjusted odds ratio, 1.17; 95% CI, 0.89-1.55). Rates of acute kidney injury (48.4% vs 47.1%) and bleeding (8.9% vs 7.5%) were comparable. Median time from ICU admission to device implantation was identical at 1.4 hours for both groups. Postimplant survival curves demonstrated no significant differences. Conclusions: Nighttime initiation of mechanical circulatory support was not associated with higher mortality, complications, or delays in escalation. These findings suggest that contemporary ICU systems deliver time-consistent, around-the-clock readiness for advanced shock therapies, mitigating traditional off-hours disparities.