Abstract Body (Do not enter title and authors here):
Background:
The Impella 5.5 (Abiomed; I5.5) is a temporary mechanical circulatory support (tMCS) device currently approved for periods of ≤14 days. Although many centers have reported successful I5.5 utilization beyond this duration, the indications and clinical outcomes associated with this practice are unknown.

Methods:
We retrospectively analyzed patients at our institution receiving I5.5 from April 2021-September 2023. Inclusion criteria were patients which received I5.5 at our institution that reached first event– specified as death/hospice, durable VAD/heart transplant, or recovery – prior to discharge or transfer. The primary outcome was differences in first event between patients receiving I5.5 support for ≤14-days vs >14-days. Secondary outcomes were complication rates, defined by occurrence of bleeding, stroke, significant hemolysis, or device migration/malfunction. Propensity-matching was utilized to help account for potential confounders. Statistical analysis involved Wilcoxon rank-sum testing and Chi-square/Fisher’s exact tests with Benjamini-Hochberg correction.

Results:
Among the 162 patients which met inclusion criteria, 76 (47%) required ≤14-days of support and 86 (53%) required >14-days. Baseline demographics and baseline INTERMACS profile and SCAI class were similar. In the ≤14-days group vs >14-day group, 54% vs 72% progressed to durable VAD/transplant (p = 0.02), 28% vs 21% died/pursued hospice (p = 0.48), and 18% vs 7% recovered (p = 0.04). Sub-group analysis on a propensity-matched cohort with similar INTERMACS profile and SCAI classification did not alter the above results, with similar probability of death/hospice (p = 0.52) and increased probability of durable VAD/transplant (54% ≤14-days, 71% >14-days; p = 0.04). Time-adjusted complication rates between cohorts were similar (IRR = 1.1 ≤14 vs >14-days; 95% CI 0.3 - 1.9), but overall complication frequency was higher in the >14-day group (11% ≤14-days, 41% >14 days, p < 0.01).

Conclusion:
I5.5-based tMCS beyond 14 days was not associated with increased mortality or decreased probability of eventual durable VAD/transplant. We did not observe an increased incidence rate of complications for I5.5 usage beyond 14 days but did note an increased absolute probability of complications with prolonged support. Future randomized-control studies which better control for potential confounds are warranted to better identify appropriate indications for I5.5 tMCS utilization beyond 14 days.