Cardiac Glycosides in HFrEF

Definition

Cardiac glycosides (digoxin, digitoxin) are Na⁺/K⁺-ATPase inhibitors that increase intracellular calcium in cardiomyocytes, enhancing contractility (positive inotropy), and reduce heart rate via indirect sympathetic tone suppression. In HFrEF, they have been used for >200 years to alleviate symptoms and reduce HF hospitalization, but do not reduce all-cause mortality. Current guidelines position them as fourth-line adjunct agents for symptomatic relief in patients who remain symptomatic despite or cannot tolerate GDMT.

Key Concepts

Mechanism

• Inhibits Na⁺/K⁺-ATPase → intracellular Na⁺ accumulates → Na⁺/Ca²⁺ exchanger reduces Ca²⁺ extrusion → increased intracellular Ca²⁺ → positive inotropy
• Reduces heart rate via indirect vagotonic effect (indirect sympathetic tone suppression)
• Both digoxin and digitoxin share this pharmacodynamic mechanism but differ pharmacokinetically

Pharmacokinetic differences: digoxin vs digitoxin

• Digoxin: hydrophilic; renally cleared (85%); narrow therapeutic index; dose adjustment required in renal impairment; therapeutic window 0.5–0.9 ng/mL (lower concentrations better per DIG post-hoc analyses)
• Digitoxin: lipophilic → higher intestinal absorption; stronger serum protein binding (~97%); predominantly hepatic clearance via enterohepatic circulation → effective even in severe renal impairment; more stable plasma concentrations; therapeutic drug monitoring (TDM) used in DIGIT-HF

Clinical evidence: mortality (no benefit)

• 6 RCTs (n=8,488): cardiac glycosides vs placebo in HFrEF — HR = 0.98 (95% CI 0.92–1.04); NS sources/cardiac-glycosides-hfrEF-fcvm-2026 (medium)
• DIG trial (1997, n=6,800): no mortality benefit; the largest single trial and dominant contributor to pooled estimate
• DIGIT-HF trial (2025, n=1,212): composite of death/HF hospitalization HR=0.82 (P=0.03); individual mortality component NS sources/digitoxin-hfref-digithf-nejm-2025 (high)

Clinical evidence: HF hospitalization (benefit)

• 5 RCTs: HR = 0.79 (95% CI 0.67–0.94) — significant reduction in HF hospitalization sources/cardiac-glycosides-hfrEF-fcvm-2026 (medium)
• Result sensitive to DIG trial exclusion (single-study sensitivity analysis: HR 0.71 [0.44–1.15], crosses null without DIG trial)
• Consistent with DIG trial subgroup: lower serum digoxin concentrations (0.5–0.9 ng/mL) yield greater benefit with less harm

Digitoxin vs digoxin: indirect comparison

• No head-to-head RCT exists comparing the two agents
• Network meta-analysis (indirect via placebo reference node): mortality HR=0.93 (0.77–1.13) NS; HF hospitalization HR=1.35 (0.70–2.60) NS sources/cardiac-glycosides-hfrEF-fcvm-2026 (medium)
• Indirect comparison severely limited by ~30-year GDMT evolution gap: DIG trial (1997) pre-dates ARNi, SGLT2i, CRT, ICD; DIGIT-HF (2025) includes all four pillars
• Pharmacokinetic advantage of digitoxin (renal sparing, stable levels) does not translate to demonstrated clinical superiority; hypothesis-generating only

Current guideline recommendations

• 2022 AHA/ACC/HFSA: digoxin COR IIb, Level B-R — may be considered in symptomatic HFrEF despite GDMT or who cannot tolerate GDMT, to decrease HF hospitalizations (not mortality)
• ESC 2021: similar; digoxin IIb/C in sinus rhythm for symptom control/hospitalization reduction
• DIGIT-HF 2025 findings have not yet led to guideline upgrade of digitoxin; no formal recommendation for digitoxin as preferred agent over digoxin
• DECISION trial (ongoing): low-dose digoxin in HFrEF on contemporary GDMT — will provide higher-quality comparative evidence

Evolving GDMT context

• SGLT2 inhibitors, ARNi, CRT/ICD device therapy have substantially improved HF prognosis between 1997 (DIG) and 2025 (DIGIT-HF)
• Swedish National Patient Register: annual HF mortality fell from 33.4 to 23.8 per 100,000 between 1997 and 2022 — background improvement attenuates absolute glycoside benefit
• TDM-guided therapy (used in DIGIT-HF) may be key to optimizing benefit while minimizing toxicity; not universally adopted in clinical practice

Contradictions / Open Questions

• Digitoxin vs digoxin: DIGIT-HF (2025) showed composite outcome benefit for digitoxin on contemporary GDMT; indirect meta-analysis shows no significant advantage over digoxin sources/cardiac-glycosides-hfrEF-fcvm-2026. These are not directly contradictory (DIGIT-HF had no placebo comparator issue; indirect comparison is underpowered) but the apparent discordance requires head-to-head data
• Mortality signal in observational studies: Vamos 2015 meta-analysis suggested digoxin associated with increased mortality; this was driven by observational studies susceptible to confounding (sicker patients preferentially receive digoxin). RCT-only meta-analyses (Ziff 2015; Wang 2026) show no mortality increase, resolving the apparent contradiction for RCT-eligible populations
• HF hospitalization stability: The pooled HR=0.79 benefit is sensitive to DIG trial exclusion. Without DIG, the result is NS. The entire hospitalization signal may be DIG-dependent; replication in a modern trial (DECISION) is needed
• Optimal serum concentration: DIG post-hoc analyses showed benefit concentrated at lower concentrations (0.5–0.9 ng/mL); higher levels → harm. No modern RCT has formally tested concentration-guided dosing except DIGIT-HF TDM approach for digitoxin

Connections

• Related to concepts/Iron-Deficiency-in-HF — co-treatment in HFrEF symptom management
• Related to concepts/Cardiac-Resynchronization-Therapy — device therapies that have evolved alongside glycoside evidence
• Related to concepts/Pharmacogenomics-in-HF — individualized GDMT framework in which glycosides sit
• Related to concepts/Diuretic-Resistance — glycosides often co-prescribed with diuretics in advanced HF
• Related to concepts/Drug-Induced-Arrhythmia — digoxin toxicity (bradyarrhythmia, AV block, triggered arrhythmias) is a significant clinical concern
• Related to concepts/Antiarrhythmic-Drugs — digoxin used for rate control in AF+HF, not classified as antiarrhythmic per VW system but has class effects
• Related to concepts/CAM-in-Heart-Failure — context of adjunct therapies in HF management

Sources

• sources/cardiac-glycosides-hfrEF-fcvm-2026 — 2026 systematic review + meta-analysis, 6 RCTs, n=8,488; medium quality
• sources/digitoxin-hfref-digithf-nejm-2025 — DIGIT-HF RCT 2025; only contemporary GDMT digitoxin trial; high quality