3.6 Digoxin in Chronic Heart Failure: Mechanisms of Prognostic Benefit

Cardiac glycosides have been used to treat heart failure for 200 years, but their clinical value remains controversial. The 1997 DIG (Digitalis Investigation Group) trial showed that digoxin failed to reduce all-cause mortality in patients with heart failure with reduced ejection fraction (HFrEF), only reducing hospitalization rates for HF exacerbation, with high serum concentrations potentially leading to adverse outcomes. This conclusion directly led to the gradual decline of this drug class from the core stage of HF treatment. The DIGIT-HF trial published in 2025 is the first to confirm that digitoxin can reduce all-cause mortality and HF-exacerbation hospitalization risk in advanced HFrEF patients. By comparing key design differences (protocol, population selection, dosing) between DIGIT-HF and previous studies, this section explores potential reasons for its positive results, providing reference for clinical practice and future research.

1. Research Background: Therapeutic Dilemma and Breakthrough Opportunity for Cardiac Glycosides

Cardiac glycosides are long-standing positive inotropic agents that enhance myocardial contractility and modulate neuroendocrine function by inhibiting myocardial cell membrane Na⁺-K⁺-ATPase, widely used since the 18th century. However, in the era of evidence-based medicine, their efficacy and safety have always been debated.

The 1997 landmark DIG trial was a key study defining the clinical status of cardiac glycosides in HF treatment. This randomized placebo-controlled trial enrolled over 6,800 chronic HF patients. Results showed digoxin was not superior to placebo for all-cause mortality but reduced HF-exacerbation hospitalization risk. Further analysis revealed efficacy and safety highly depend on serum concentration: benefits at low concentrations (0.5–0.9 ng/mL), increased adverse event risk above 1.0 ng/mL, leaving clinicians facing the “efficacy–risk balance” dilemma. Moreover, the DIG trial was conducted decades ago when HF background therapy only included ACEI plus diuretics, significantly differing from modern multi-drug combination paradigms.

Digitoxin is another commonly used cardiac glycoside. Compared to digoxin, it has similar pharmacodynamics but higher intestinal absorption and serum protein binding rates, primarily cleared via hepatic and enterohepatic circulation with lower renal dependence, theoretically more suitable for chronic HF and renal impairment patients. However, high-quality double-blind RCTs systematically evaluating digitoxin’s value in modern HF treatment were lacking. Against this backdrop, the DIGIT-HF trial was launched to evaluate the clinical efficacy and safety of low-concentration digitoxin in HFrEF patients receiving modern pharmacological and device therapies.

2. Positive Results of the DIGIT-HF Trial: Core Efficacy Data

DIGIT-HF is a randomized, double-blind, placebo-controlled, multicenter study enrolling 1,212 HFrEF patients, randomized 1:1 to digitoxin (n = 613) or placebo (n = 599). The primary endpoint was the composite of all-cause mortality or first HF hospitalization. At median 36-month follow-up, 242 (39.5%) primary events occurred in the digitoxin group vs 264 (44.1%) in placebo, HR = 0.82 (95%CI 0.69–0.98, P = 0.03), showing digitoxin significantly reduced composite endpoint risk. For all-cause mortality, digitoxin was 27.2% vs 29.5% placebo, indicating non-inferiority (HR = 0.86, 95%CI 0.69–1.07, meeting prespecified non-inferiority margin). First HF hospitalization rates were 28.1% vs 30.4%, showing consistent risk reduction. Safety-wise, serious adverse events were 4.7% vs 2.8%, overall controllable, with similar discontinuation rates due to AEs (9.1% vs 10.2%), indicating good tolerability. Prespecified subgroup analyses showed consistent benefits across different demographics (sex, renal function, AF status, ARNI/SGLT2i use, triple/quadruple GDMT), with more significant benefits in patients with HR ≥ 75 bpm or SBP ≤ 120 mmHg.

3. Key Design Factors for DIGIT-HF’s Positive Results

(1) Precise Population Stratification: Focusing on Refractory Symptomatic HF Patients

DIGIT-HF precisely defined inclusion criteria, significantly differing from DIG. Enrolled patients required LVEF ≤ 40% with NYHA II–IV, or LVEF ≤ 30% with NYHA I, and ≥ 6 months of guideline-directed medical therapy (GDMT). 70% were NYHA II–IV, whereas DIG primarily enrolled NYHA II–III. These refractory symptomatic patients have worse myocardial contractility, greater need for positive inotropes, and are more likely to benefit from digitoxin. Furthermore, baseline characteristics closely mirror real-world advanced HF patients requiring intensified therapy, ensuring clinical translational value.

(2) Optimized Dosing Strategy: Individualized Titration Targeting Minimum Effective Concentration

The narrow therapeutic window of cardiac glycosides, with efficacy and safety closely tied to serum concentration, was likely a core reason for DIG’s negative results. DIG used fixed dosing (digoxin 0.125–0.250 mg/d) without serum concentration adjustment, causing wide fluctuations (0.5–2.0 ng/mL). The study proved adverse event risk significantly increases above 1.0 ng/mL, offsetting benefits and leading to a negative primary endpoint. DIGIT-HF innovatively adopted serum concentration-guided individualized titration. Target digitoxin serum concentration was set at 8–18 ng/mL, starting dose 0.07 mg/d, with concentration testing at 6 weeks and adjustment to 0.05 or 0.1 mg/d based on results. This precise minimum-effective-concentration strategy aligns with previous findings that “low-concentration cardiac glycosides are more beneficial,” maximally reducing high-concentration adverse risks, serving as a key technical factor for positive results.

(3) Alignment with Modern Therapeutic Background: Combination with GDMT

Era-specific design differences are another important factor. DIG was conducted in the 1990s with background therapy of only ACEI + diuretics, lacking β-blockers, ARNI, etc., unable to effectively suppress neuroendocrine overactivation. In DIGIT-HF, >93% used β-blockers and RAS inhibitors (40% ARNI), 76% used MRAs, ~20% used SGLT2i, >60% had ICDs, and ~25% received CRT. Digitoxin’s mechanism complements modern GDMT: by stimulating the vagus nerve and reducing heart rate, it synergizes with β-blockers and SGLT2i to improve HF prognosis, achieving additional benefits on top of full-spectrum GDMT.

(4) Innovative Statistical Design: Stratified Analysis with Non-inferiority + Superiority Testing

DIGIT-HF’s rigorous statistical design further enhanced result reliability. Stratified randomization based on sex, NYHA class, and AF status ensured baseline balance. Efficacy analysis first used non-inferiority testing to exclude adverse mortality impact, then superiority testing to confirm significant composite endpoint benefit. Rich prespecified subgroup analyses (age, LVEF, HF etiology, renal function) showed consistent benefits across subgroups, especially in renal impairment patients who achieved comparable benefits without frequent dose adjustments. This design complies with clinical research standards and provides evidence-based guidance for diverse HF patient treatment.

4. Limitations of the DIGIT-HF Trial

Limitations mainly include three points: (1) sample size fell short of expectations (1,212 vs planned 2,190); although extended follow-up partially compensated for statistical power, subgroup analysis power remains insufficient, requiring cautious interpretation; (2) population limitation—only HFrEF patients enrolled; results cannot be extrapolated to HFpEF or HFmrEF; and (3) insufficient long-term safety data—median treatment duration was 18 months, with some early discontinuations; long-term safety requires further real-world validation.

5. Conclusion and Outlook

As a major breakthrough in HF in 2025, the DIGIT-HF trial lays a solid foundation for the rational use of digitoxin in modern HF management under precise dosing and modern therapeutic backgrounds. Future real-world studies are needed to validate digitoxin’s efficacy and safety in broader populations, and explore combination regimens with novel drugs like SGLT2i and ARNI, along with long-term prognostic impacts.

(Luo Pin, Zhang Lina; Xiangya Hospital, Central South University)

References

  1. Digitalis Investigation Group. The effect of digoxin on mortality and morbidity in patients with heart failure. N Engl J Med. 1997;336(8):525-533.

  2. Ahmed A, Rich MW, Love TE, et al. Digoxin and reduction in mortality and hospitalization in heart failure: a comprehensive post hoc analysis of the DIG trial. Eur Heart J. 2006;27(2):178-186.

  3. Bavendiek U, Grobhenig A, DIGIT-HF Study Group, et al. Digitoxin in patients with heart failure and reduced ejection fraction. N Engl J Med. 2025;393(12):1155-1165.

  4. Bavendiek U, Grobhenig A, Schwab J, et al. Simple and safe digitoxin dosing in heart failure based on data from the DIGIT-HF trial. Clin Res Cardiol. 2023;112(8):1096-1107.