Abstract
The Impella 5.5 is an axillary mechanical circulatory support device used in patients with cardiogenic shock, but those with small left ventricular (LV) cavities may be at risk for suction events, hemolysis, malpositioning, hypoperfusion, and LV injury. Informally accepted guidelines, extrapolated from durable LVAD studies, suggest a minimum left ventricular internal dimension in diastole (LVIDd) of 58 mm, with some clinical practices using a more stringent ≤52 mm cutoff. We retrospectively analyzed 154 consecutive patients supported with Impella 5.5 between January 2020 and December 2024. Overall, 38 patients had an LVIDd ≤58 mm, and 116 had an LVIDd >58 mm; a key subgroup of 21 patients presented with a very small LVIDd of ≤52 mm]. Baseline demographics, comorbidities, body mass index, and renal function were similar [across groups], although those with larger LVIDd had lower ejection fractions (16% vs. 24%,
p
= 0.001). Median support duration was 24 days in all groups, and pre- and post-implant hemodynamic and laboratory improvements were comparable. Rates of transplantation (79% vs. 90%,
p
= 0.088) and LVAD implantation (2% vs. 6%,
p
= 0.159) did not differ significantly in the ≤58 mm cohort. Notably, within the ≤52 mm subgroup, 90-day survival remained high at 90.5% (
p
= 0.336), with significant improvements in right atrial pressure (17 to 10 mmHg,
p
= 0.041), mean pulmonary artery pressure (36 to 26 mmHg,
p
= 0.008), and eGFR (45 to 57 mL/min/1.73m
2
,
p
= 0.003). Remarkably, native cardiac recovery was observed exclusively in the smaller LV cohorts, occurring in 11% of the ≤58 mm group (
p
= 0.003 vs. 0%,
p
= 0.003) and reaching 19% in the ≤52 mm group (vs. 0% in larger cavities,
p
< 0.001), while durable LVAD escalation was entirely avoided in the ≤52 mm cohort (0% vs. 6%). Ninety-day event-free survival was excellent across all cohorts 92% vs. 96% in the primary analysis, with no major device-related complications, suction events, clinically significant hemolysis, bleeding, stroke, or escalation to Bi-VAD support. These findings strongly support the safety and feasibility of Impella 5.5 in extremely constrained, small LV cavities.