Effect of High-Dose Omega-3 Fatty Acids vs Corn Oil on Major Adverse Cardiovascular Events in Patients at High Cardiovascular Risk: The STRENGTH Randomized Clinical Trial
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The STRENGTH trial demonstrated that a high-dose carboxylic acid formulation of EPA and DHA did not reduce major adverse cardiovascular events compared to a corn oil placebo in statin-treated patients at high cardiovascular risk and was associated with an increased risk of atrial fibrillation.
Key Findings
Study Design
Study Limitations
Clinical Significance
The STRENGTH trial provides definitive evidence that this specific high-dose EPA/DHA carboxylic acid formulation does not provide cardiovascular protection in high-risk patients on background statin therapy. Coupled with the increased risk of atrial fibrillation, these findings underscore the need for caution when prescribing omega-3 fatty acid supplements for cardiovascular risk reduction and highlight that not all omega-3 formulations are clinically equivalent.
Historical Context
Following the positive results of the 2007 JELIS trial and the 2018 REDUCE-IT trial (which tested purified icosapent ethyl), there was significant debate regarding whether cardiovascular benefits were a class effect of omega-3 fatty acids or specific to EPA. STRENGTH was designed to test whether a carboxylic acid formulation of combined EPA and DHA would yield similar or superior benefits to previous trials; however, its neutral findings significantly tempered clinical enthusiasm for combined fish oil preparations for secondary cardiovascular prevention.
Guided Discussion
High-yield insights from every perspective
The STRENGTH trial evaluated a carboxylic acid formulation of EPA and DHA. Mechanistically, how do high-dose omega-3 fatty acids primarily lower triglyceride levels, and why was this expected to translate into reduced major adverse cardiovascular events (MACE)?
Key Response
Omega-3 fatty acids lower triglycerides (TG) by inhibiting phosphatidic acid phosphatase and acyl-CoA:1,2-diacylglycerol acyltransferase, reducing hepatic VLDL synthesis and increasing lipoprotein lipase activity. Because hypertriglyceridemia is an independent marker of residual cardiovascular risk in statin-treated patients, it was hypothesized that TG reduction would directly lead to fewer atherosclerotic events.
A patient with high cardiovascular risk and a TG level of 250 mg/dL asks if they should start a high-dose EPA/DHA supplement similar to the one used in STRENGTH. Based on the trial's findings, how would you counsel them regarding the benefit-risk profile compared to pure icosapent ethyl (EPA)?
Key Response
Counseling should highlight that while REDUCE-IT showed benefit with pure EPA, the STRENGTH trial found no MACE benefit for the EPA/DHA combination. Furthermore, STRENGTH demonstrated a significant 67% relative increase in the risk of new-onset atrial fibrillation (2.1% vs 1.3%), making the benefit-risk ratio unfavorable for this specific formulation.
Compare the 'placebo controversy' between the REDUCE-IT trial (which used mineral oil) and the STRENGTH trial (which used corn oil). How does the choice of comparator influence the interpretation of the divergent results between these two high-dose omega-3 trials?
Key Response
REDUCE-IT faced criticism that mineral oil was not inert and increased LDL-C and CRP in the control group, potentially exaggerating the drug's benefit. In contrast, STRENGTH used corn oil, which is considered more neutral. This raises the question of whether the benefit in REDUCE-IT was due to EPA's unique properties, or if the STRENGTH results are a more 'honest' reflection of omega-3 efficacy when compared against a truly neutral placebo.
The STRENGTH trial was stopped early for futility. As a clinician-educator, how do you explain the implications of 'stopping for futility' to your team in the context of cardiovascular outcomes trials, and how does this affect our confidence in the observed increase in atrial fibrillation?
Key Response
Stopping for futility occurs when the interim analysis indicates a low probability of reaching a statistically significant benefit if the trial continued. While it prevents further resource expenditure on a failed therapy, it can leave secondary endpoints (like safety signals) underpowered. However, the AF signal in STRENGTH was so robust (HR 1.69) that it remains a clinically significant warning, even with early termination.
Scholarly Review
Critical appraisal through the lens of expert reviewers and guideline development
In the STRENGTH trial, the carboxylic acid formulation achieved significantly higher plasma EPA levels than seen in previous trials, yet no benefit was observed. What are the methodological implications of using plasma biomarker levels as surrogates for clinical efficacy in lipid-lowering trials, and how might the presence of DHA have modulated the potential benefits of EPA?
Key Response
This suggests that plasma levels of EPA/DHA are not reliable surrogates for MACE reduction. Methodologically, it indicates potential 'antagonism' or lack of synergy; some hypothesize that DHA may counteract some of EPA's membrane-stabilizing effects or that the carboxylic acid form, despite higher bioavailability, does not produce the same tissue-level anti-atherosclerotic effects as ethyl esters.
As a reviewer, evaluate the internal validity of STRENGTH's neutral finding. Could the early termination of the trial have masked a late-emerging benefit, or was the statistical threshold for futility robust enough to dismiss the efficacy of the EPA/DHA carboxylic acid formulation entirely?
Key Response
A tough reviewer would examine the conditional power at the time of termination. In STRENGTH, the hazard ratio for the primary endpoint was 0.99, and the predictive power of reaching significance was near zero. Therefore, the neutral finding is robust. The editor would focus on the fact that despite achieving higher EPA levels than other successful trials, the lack of even a trend toward benefit makes the futility decision highly defensible.
Given the results of STRENGTH vs REDUCE-IT, how should current guidelines (e.g., AHA/ACC or ESC) distinguish between the recommendations for icosapent ethyl and mixed omega-3 formulations for cardiovascular risk reduction?
Key Response
Guidelines should emphasize that the evidence for MACE reduction is specific to high-dose purified icosapent ethyl (Class 2a or 1, depending on the guideline). STRENGTH provides Level 1a evidence that mixed EPA/DHA formulations should not be used for MACE prevention, even if they lower triglycerides, and that the risk of atrial fibrillation is a class-wide concern that must be acknowledged in safety recommendations.
Clinical Landscape
Noteworthy Related Trials
GISSI-Prevenzione Trial
Tested
Omega-3 acid ethyl esters (1g daily)
Population
Patients with recent myocardial infarction
Comparator
Usual care
Endpoint
Composite of death, non-fatal MI, and stroke
ASCEND Trial
Tested
Omega-3 fatty acids (1g daily)
Population
Patients with diabetes mellitus without atherosclerotic cardiovascular disease
Comparator
Placebo
Endpoint
Serious vascular events
REDUCE-IT Trial
Tested
Icosapent ethyl 4g daily
Population
Patients with established CVD or diabetes and other risk factors with elevated triglycerides
Comparator
Mineral oil placebo
Endpoint
5-point MACE
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