Clinical Question: Does mechanical LV unloading (Impella) + intentional delay to PCI (30 min) reduce infarct size in anterior STEMI without cardiogenic shock?
Why it Matters:
Strong preclinical signal in CMR studies: unloading before reperfusion ↓ infarct size
A very physiologically attractive idea: ↓ wall stress =↓ oxygen demand = ↓ reperfusion injury
But:
- Conflicts with the ‘time is myocardium” paradigm
- System-level logistical implications (delays, device access/troubleshooting)
Study Design
Multicentre RCT (55 sites, US + Europe)
N = 527 anterior STEMI (no shock)
Randomised:
Intervention: Impella CP → 30 min delay → PCI
Control: Immediate PCI
Key inclusion characteristics: 1–6 hours from symptom onset, no cardiogenic shock present
Primary Outcome:
Infarct size (% LV mass) on CMR at 3–5 days
Key Results
Primary Outcome
No difference: 30.8% vs 31.9%; Δ −1.1% (p=0.50)
Ischaemic Time
+47 minutes longer in the unloading group
Secondary Outcomes
Elevated LVEDP mean 25 +/- 9 with good matching between arms
No difference in: Mortality, heart failure, composite endpoints via Win ratio (Cardiovascular death; Cardiogenic shock ≥24 hours after enrolment; LVAD implantation or heart transplantation; Heart failure; ICD or CRT implantation; Infarct size (% LV mass on CMR at 3–5 days)
Safety outcomes
Major bleeding: ~30% (treatment arm) – Significantly higher vs control (34% vs 6%)
Strengths
- Large, contemporary RCT
- Hard imaging endpoint (CMR)
- Mechanistically driven
- Well-executed protocol
Limitations
- Open-label
- High CMR attrition ( only 443 / 527 – 84% got useable CMR data)
- Protocol complexity (real-world applicability?)
- Not powered for clinical outcomes
- Industry involvement significant
Interpretation
This does NOT support the “unload then reperfuse” approach in this cohort
There is no reason to delay PCI for Impella in STEMI without shock
Timing to reperfusion is still the most important factor in STEMI
Bottom Line
Mechanical LV unloading + delayed PCI in STEMI without shock does not reduce infarct size and increases harm (increased bleeding).
Clinical Takeaway
DANGER-Shock showed an impressive mortality benefit (NNT of 8) in STEMI-related CS. The mode of survival benefit (management of shock versus unloading/infarct size) was not clearly elucidated, but the question of whether unloading contributed is perhaps at least partly answered by this study.
It is interesting to note that despite a longer ischaemic time, infarct size was not worse…
Further Questions…
- Are we targeting the wrong population with this strategy (no shock) – perhaps the patients were “too well”, and the potential benefits of unloading will be realised in a patient with systemically compromised perfusion rather than locally compromised perfusion
- Will potentially lead to PCI-then-unload studies…
Review author: Lewis McLean
Peer reviewer: Jeram Hyde
