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Heart Failure Drug Pitfalls & Digoxin Toxicity

Name: Heart Failure Drug Pitfalls & Digoxin Toxicity
Creator: Veli Bakalov, MD

Safe GDMT, harmful co-prescriptions, and the many faces of digoxin toxicity

Cardiology·Heart Failure & Cardiomyopathy·5 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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After starting an ACE inhibitor, ARB or ARNI, a creatinine rise up to about 30% is expected; continue the drug.
Stop an ACE inhibitor at least 36 hours before sacubitril-valsartan, and never give an ARNI after ACE inhibitor or ARB angioedema.
Start an MRA only if K is below 5.0 mEq/L and eGFR is above 30; switch spironolactone to eplerenone for gynecomastia.
SGLT2 inhibitors cause genital mycotic infections and euglycemic DKA; hold them about 3 days before surgery.
Only carvedilol, metoprolol succinate and bisoprolol lower mortality in HFrEF; hydralazine-isosorbide dinitrate adds survival in Black patients with NYHA III–IV.
Ivabradine requires sinus rhythm with resting HR ≥70 on a maximally tolerated beta-blocker and reduces hospitalization, not mortality.
Avoid NSAIDs, thiazolidinediones, verapamil, diltiazem, class I antiarrhythmics, dronedarone and cilostazol in HFrEF; amiodarone, dofetilide and amlodipine are safe.
Digoxin toxicity is triggered by hypokalemia, renal failure, amiodarone, verapamil and macrolides; it causes nausea, confusion, yellow vision, atrial tachycardia with block and bidirectional VT.
Treat dangerous digoxin toxicity (life-threatening arrhythmia, K above 5.0 in acute overdose, end-organ damage) with digoxin immune Fab; dialysis does not work.

RAAS blockers and MRAs: using them safely

Expected creatinine rise. ACE inhibitors, ARBs, and ARNIs dilate the efferent arteriole and lower glomerular pressure, so creatinine rises modestly after initiation. A rise of up to about 30%, with potassium ≤5.5 mEq/L, is expected — continue the drug. A larger rise prompts a search for volume depletion, NSAID use, or bilateral renal artery stenosis; hold for K above 5.5 or symptomatic hypotension.

Bradykinin effects. ACE also degrades bradykinin, so ACE inhibitors cause dry cough (switch to an ARB) and angioedema, which is more common in Black patients and requires permanent discontinuation. Neprilysin degrades bradykinin too: stop an ACE inhibitor at least 36 hours before starting sacubitril-valsartan, never co-prescribe them, and avoid an ARNI after prior ACE inhibitor or ARB angioedema. Switching from an ARB to an ARNI needs no washout.

All RAAS blockers are fetotoxic (renal dysgenesis, oligohydramnios) — stop them in pregnancy.

Mineralocorticoid receptor antagonists. Spironolactone and eplerenone lower HFrEF mortality but are started only when K is below 5.0 mEq/L and eGFR is above 30. Recheck potassium and creatinine within about a week, stop potassium supplements, and hold for K above 5.5; risk climbs with concurrent RAAS blockers, NSAIDs, or trimethoprim. Spironolactone's antiandrogen effects — gynecomastia, breast pain, impotence, menstrual irregularity — resolve by switching to eplerenone, a selective receptor blocker.

SGLT2 inhibitors, beta-blockers and add-ons

SGLT2 inhibitors. Dapagliflozin and empagliflozin reduce HF hospitalization and cardiovascular death in HFrEF and HF events in HFpEF, with or without diabetes. Watch for genital mycotic infections (most common), UTIs, volume depletion, and euglycemic DKA — anion-gap ketoacidosis with glucose often below 250 mg/dL, provoked by surgery, fasting, or acute illness. Hold about 3 days before scheduled surgery. A small early eGFR dip is hemodynamic and expected.

Beta-blockers. Only carvedilol, metoprolol succinate (extended-release), and bisoprolol have mortality data in HFrEF; atenolol and metoprolol tartrate do not. Start low once euvolemic and double about every 2 weeks as tolerated, expecting transient fatigue or fluid retention.

Hydralazine-isosorbide dinitrate. Adds a survival benefit in self-identified Black patients with NYHA III–IV HFrEF on optimal GDMT, and replaces ACEi/ARB/ARNI when renal failure, hyperkalemia, or angioedema rules them out. Side effects: headache, dizziness, reflex tachycardia, and hydralazine-induced lupus.

Ivabradine. Blocks the SA node funny current (If). It is added for EF ≤35%, sinus rhythm, and resting HR ≥70 despite a maximally tolerated beta-blocker, and reduces HF hospitalization but not mortality. It is useless in AF and causes bradycardia, luminous visual phenomena (phosphenes), and fetal toxicity.

GDMT safety at a glance

Drug class	Start when	Monitor	Key adverse effects
ACEi / ARB / ARNI	Adequate BP; 36-h ACEi washout before ARNI	Creatinine (≤30% rise acceptable), K	Hyperkalemia, hypotension, cough (ACEi), angioedema
MRA	K <5.0, eGFR >30	K and creatinine within ~1 week	Hyperkalemia; gynecomastia (spironolactone)
SGLT2 inhibitor	Stable; hold ~3 days before surgery	Volume status; ketones if ill	Genital mycotic infection, euglycemic DKA
Beta-blocker	Euvolemic	HR, BP, congestion	Bradycardia, fatigue, transient fluid retention
Ivabradine	Sinus rhythm, HR ≥70 on maximal beta-blocker	HR	Bradycardia, phosphenes, fetal toxicity

Drugs that worsen HFrEF

Harmful drugs and safer substitutes

Drug	Harm in HFrEF	Safer alternative
NSAIDs	Sodium retention, blunted diuretics, AKI	Acetaminophen
Pioglitazone, rosiglitazone	Fluid retention; contraindicated in NYHA III–IV	SGLT2 inhibitor; metformin in stable HF
Verapamil, diltiazem	Negative inotropy	Amlodipine for BP or angina
Flecainide, propafenone, disopyramide	Proarrhythmia and ↑mortality; disopyramide is negatively inotropic	Amiodarone or dofetilide
Dronedarone	↑Mortality in NYHA IV or recent decompensation	Amiodarone or dofetilide
Cilostazol	PDE-3 inhibitor; contraindicated in HF of any severity	Supervised exercise for claudication

Alpha-blockers such as doxazosin are poor antihypertensive choices in HF: in a large hypertension trial the doxazosin arm developed more heart failure than the diuretic arm.

Digoxin: mechanism and role

Mechanism. Digoxin inhibits the myocyte Na+/K+-ATPase. Intracellular sodium rises, the Na+/Ca2+ exchanger extrudes less calcium, and more calcium is available for contraction. Digoxin also increases vagal tone, slowing AV nodal conduction.

Role. In HFrEF it reduces HF hospitalizations with no mortality benefit (DIG trial); it is used for persistent symptoms despite GDMT or for rate control in AF with HF. Aim for a low level of 0.5–0.9 ng/mL, drawn at least 6 hours after a dose. It is renally cleared, so reduce the dose in CKD and the elderly.

Digoxin toxicity

Precipitants. Hypokalemia (less potassium competing at the Na+/K+-ATPase, usually from diuretics), hypomagnesemia, hypercalcemia, renal failure, hypothyroidism, and older age. Drugs that raise levels, mostly through P-glycoprotein inhibition: amiodarone, verapamil, quinidine, clarithromycin and erythromycin (which also kill gut bacteria that inactivate digoxin), azole antifungals, and cyclosporine. Halve the digoxin dose when amiodarone is started.

Symptoms. GI symptoms come first — anorexia, nausea, vomiting, abdominal pain — then fatigue, confusion, or delirium (especially in the elderly) and visual change: blurring, yellow-green tinting (xanthopsia), and halos. Chronic toxicity is often subtle, appearing after a renal insult or a new interacting drug and coexisting with diuretic-induced hypokalemia; acute overdose causes hyperkalemia.

Arrhythmias. Increased automaticity plus AV nodal block: PVCs and bigeminy (most common), atrial tachycardia with block, accelerated junctional rhythm, regularized AF (complete heart block with a junctional escape), bradycardia and AV block, and bidirectional VT, which is nearly pathognomonic. Scooped ST depression with a short QT and flattened T waves is a therapeutic effect, not toxicity.

Stop digoxin and monitorTelemetry, serum level, potassium, magnesium, creatinine.
Give digoxin immune FabFor VT/VF, symptomatic bradycardia or high-grade block, K >5.0 mEq/L in acute toxicity, end-organ dysfunction, or a large ingestion or very high level.
SupportCorrect hypokalemia and hypomagnesemia; atropine for bradycardia; activated charcoal after a recent ingestion.
After FabTotal digoxin levels become falsely high and uninterpretable; potassium can fall quickly, so recheck it.

Hemodialysis does not remove digoxin (large volume of distribution), and electrical cardioversion can provoke ventricular fibrillation in digoxin toxicity. IV calcium for hyperkalemia was classically avoided; Fab is the definitive treatment.