Highlights
A comprehensive pooled analysis of four major INTERACT trials involving 11,312 patients confirms that intensive systolic blood pressure (SBP) lowering to a target of less than 140 mmHg is safe and significantly improves functional outcomes in acute intracerebral hemorrhage (ICH).
Key findings indicate that the efficacy of intensive BP lowering is highly time-dependent, with the greatest benefits for functional recovery and the prevention of hematoma expansion occurring when treatment is initiated within 3 hours of symptom onset.
Intensive treatment reduced the odds of poor physical function (mRS 3-6) by 15%, neurological deterioration by 24%, and death by 17%, while also demonstrating a significant reduction in serious adverse events compared to standard guideline-based care.
Background: The Challenge of Acute Hypertension in ICH
Spontaneous intracerebral hemorrhage (ICH) remains the most devastating form of stroke, characterized by high rates of mortality and long-term disability. One of the most critical and modifiable predictors of poor outcome in the acute phase is the expansion of the hematoma, which occurs in approximately one-third of patients within the first few hours. Elevated systolic blood pressure (SBP) is nearly universal in the hyperacute phase of ICH and is strongly associated with hematoma growth and subsequent neurological decline.
While clinical guidelines have long recommended BP management, the optimal target and, more importantly, the optimal timing for intervention have been subjects of intense debate. Earlier trials like INTERACT2 and ATACH-II provided conflicting signals regarding the benefit of a <140 mmHg target compared to a <180 mmHg target. However, the recent completion of INTERACT3 and the pre-hospital focused INTERACT4 trial provided a unique opportunity to synthesize data across a broad spectrum of clinical settings—from pre-hospital ambulances to resource-limited hospitals and specialized stroke centers.
Study Design and Methodology: The INTERACT Pooled Analysis
This study represents an individual patient-data pooled analysis of four landmark trials: INTERACT1 (n=404), INTERACT2 (n=2,829), INTERACT3 (n=7,036), and INTERACT4 (n=1,043). The inclusion criteria across the first three trials focused on adults with acute ICH presenting within 6 hours of onset with elevated SBP (>150 mmHg). INTERACT4 specifically targeted patients with suspected stroke and motor deficits within 2 hours of onset, including a subset of 1,029 confirmed ICH cases.
Patients were randomized to either intensive BP lowering (target SBP <140 mmHg within 1 hour) or guideline-recommended treatment (target SBP <180 mmHg within 1 hour). The primary outcome was functional recovery at 90 days, assessed by the distribution of scores on the modified Rankin scale (mRS). A critical component of the analysis was the CT substudy (n=2,921), which evaluated relative (≥33%) and absolute (≥6 mL) changes in hematoma volume from baseline to 24 hours. The researchers utilized logistic regression models to adjust for trial variance and baseline hematoma volume, with a specific focus on the interaction between treatment effect and time from symptom onset.
Key Findings: Efficacy and Safety of Intensive BP Lowering
Functional Outcomes and Mortality
Among the 11,312 patients analyzed (mean age 63 years; 64.1% male), the median time from symptom onset to randomization was 2.9 hours. The intensive treatment group achieved a mean SBP of 149.6 mmHg at 1 hour, compared to 158.8 mmHg in the guideline group, representing a significant mean difference of 9.13 mmHg (p<0.0001).
The results for functional recovery were compelling. Intensive BP lowering significantly reduced the odds of poor physical function (mRS scores 3-6), with an odds ratio (OR) of 0.85 (95% CI 0.78-0.91). Furthermore, the intensive group showed a marked reduction in neurological deterioration within the first 7 days (OR 0.76, 95% CI 0.66-0.88; p=0.0002) and a significantly lower risk of death (OR 0.83, 95% CI 0.75-0.94; p=0.002). Crucially, intensive treatment was associated with fewer serious adverse events (OR 0.84), debunking concerns that rapid BP lowering might induce cerebral ischemia or renal failure in this population.
Timing Matters: The 3-Hour Threshold
Perhaps the most significant contribution of this pooled analysis is the clarification of the “time-to-treatment” effect. The researchers found a significant interaction between the time from symptom onset and the efficacy of the intervention. The benefit of intensive BP lowering for functional recovery was most pronounced when initiated early, with the treatment effect crossing unity (becoming non-significant) at approximately the 3-hour mark (p=0.002 for interaction). This suggests that while BP lowering is safe up to 6 hours, the window for maximizing clinical recovery is much narrower than previously appreciated.
Radiological Substudy: Hematoma Expansion
In the CT substudy, intensive treatment did not show a statistically significant overall effect on relative or absolute hematoma growth across the entire cohort. However, the interaction analysis revealed that the effect on relative hematoma growth also decreased as time from onset increased (p=0.01 for interaction). Patients treated within the earliest windows showed a trend toward reduced expansion, reinforcing the biological plausibility that early BP control stabilizes the hematoma before it reaches its peak volume.
Expert Commentary and Clinical Implications
The INTERACT pooled analysis provides the most robust evidence to date that ‘time is brain’ in the context of ICH blood pressure management, just as it is in ischemic stroke thrombolysis. The 3-hour window identified here provides a clear target for emergency medical services and emergency department protocols.
One of the striking aspects of this analysis is the inclusion of INTERACT3 and INTERACT4. INTERACT3 demonstrated that a low-cost, bundle-of-care approach in diverse hospital settings can be effective, while INTERACT4 showed that even pre-hospital initiation is feasible. The consistent safety profile across all four trials should reassure clinicians who have been hesitant to aggressively lower BP due to fear of ‘watershed’ infarcts. The reduction in serious adverse events in the intensive group suggests that the risks of uncontrolled hypertension far outweigh the risks of rapid reduction in the acute phase.
However, limitations remain. The lack of a major overall effect on hematoma volume in the CT substudy suggests that the benefits of BP lowering may extend beyond simple volume restriction—potentially involving reduced perihematomal edema or improved microvascular stability. Additionally, the analysis is dominated by the large INTERACT3 cohort, which utilized a bundle of care, making it difficult to isolate the effect of BP lowering alone from other supportive measures.
Conclusion: Redefining the Standard of Care
The pooled analysis of the INTERACT trials marks a definitive shift in our understanding of acute ICH management. Intensive BP lowering to a target of <140 mmHg is not only safe but highly effective at improving survival and functional independence, provided it is delivered within the first 3 hours of symptom onset. These findings underscore the necessity of rapid diagnosis and immediate therapeutic intervention in the hyperacute phase of ICH. Future clinical pathways should prioritize minimizing 'door-to-needle' time for antihypertensive therapy, mirroring the urgency applied to revascularization therapies in ischemic stroke.
Funding and ClinicalTrials.gov
This research was supported by the National Health and Medical Research Council of Australia (NHMRC), the Medical Research Council (UK), the Wellcome Trust, and various national and provincial health foundations in China. Individual trial registrations include INTERACT1 (NCT00226096), INTERACT2 (NCT00716079), INTERACT3 (NCT03209258), and INTERACT4 (NCT03790800). The pooled analysis is registered with PROSPERO (CRD420251001539).
References
1. Wang X, Ren X, Li Q, et al. Effects of blood pressure lowering in relation to time in acute intracerebral haemorrhage: a pooled analysis of the four INTERACT trials. Lancet Neurol. 2025;24(7):571-579.
2. Anderson CS, Heeley E, Huang Y, et al. Rapid blood-pressure lowering in patients with acute intracerebral hemorrhage. N Engl J Med. 2013;368(25):2355-2365. (INTERACT2)
3. Qureshi AI, Palesch YY, Barsan WG, et al. Intensive Blood-Pressure Lowering in Patients with Acute Cerebral Hemorrhage. N Engl J Med. 2016;375(11):1033-1043. (ATACH-II)
4. Song L, Wang X, Arima H, et al. Intensive blood pressure lowering in patients with acute intracerebral haemorrhage: a secondary analysis of the INTERACT2 study. Lancet Neurol. 2023.