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Advanced Heart Failure Drugs & Inotropes

Name: Advanced Heart Failure Drugs & Inotropes
Creator: Veli Bakalov, MD

Add-on HFrEF drugs and IV inotropes: odd mechanisms, narrow niches, classic pitfalls

Cardiovascular·Pharmacology·4 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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Sacubitril inhibits neprilysin, raising ANP, BNP and bradykinin; valsartan is added because neprilysin inhibition also raises angiotensin II.
Never combine sacubitril-valsartan with an ACE inhibitor: stop the ACE inhibitor at least 36 hours before, because dual bradykinin accumulation causes angioedema.
BNP rises on sacubitril-valsartan (it is a neprilysin substrate); follow NT-proBNP instead.
Ivabradine blocks HCN channels (funny current, If) in the SA node → ↓HR without negative inotropy; needs sinus rhythm and HR ≥70 on a maximal β-blocker; causes phosphenes, bradycardia, AF and fetal toxicity.
Hydralazine (↓afterload) plus isosorbide dinitrate (↓preload) reduces mortality in self-identified Black patients with HFrEF and substitutes for RAAS blockers when they are not tolerated.
Vericiguat stimulates soluble guanylate cyclase → ↑cGMP; never with riociguat, avoid PDE-5 inhibitors, contraindicated in pregnancy.
Dobutamine is a β1 agonist; milrinone is a PDE3 inhibitor (↑cAMP, inodilator, renally cleared, effective despite β-blockers).
Dopamine acts on D1 at low doses, β1 at moderate doses and α1 at high doses; renal-dose dopamine does not protect the kidney.
Inotropes improve hemodynamics, not survival: reserve them for cardiogenic shock, bridge to transplant or LVAD, or palliation.

Where these drugs fit

Beyond the foundation. Chronic HFrEF therapy rests on four classes with proven survival benefit: renin-angiotensin blockade (preferably an angiotensin receptor–neprilysin inhibitor), an evidence-based β-blocker (carvedilol, metoprolol succinate, bisoprolol), a mineralocorticoid receptor antagonist and an SGLT2 inhibitor. The drugs in this chapter upgrade that foundation (sacubitril-valsartan), add to it in selected patients (ivabradine, hydralazine–isosorbide dinitrate, vericiguat), or support a failing circulation in hospital (IV inotropes).

Sacubitril-valsartan (ARNI)

Neprilysin inhibition. Sacubitril is a prodrug whose active metabolite (LBQ657) inhibits neprilysin, the endopeptidase that degrades ANP, BNP, bradykinin and substance P. Higher natriuretic peptide levels activate particulate guanylate cyclase → ↑cGMP → natriuresis, diuresis, vasodilation, suppression of renin and aldosterone, and less myocardial fibrosis and remodeling. Sacubitril-valsartan reduced cardiovascular death and HF hospitalization compared with enalapril and is preferred over an ACE inhibitor or ARB in symptomatic HFrEF.

Why an ARB and never an ACE inhibitor. Neprilysin also breaks down angiotensin II, so neprilysin inhibition alone would raise Ang II; valsartan blocks the AT1 receptor to neutralize it. ACE and neprilysin both degrade bradykinin, so inhibiting both at once invites bradykinin-mediated angioedema — the reason the dual inhibitor omapatrilat never reached the market. The ACE inhibitor must be stopped at least 36 hours before the first sacubitril-valsartan dose, and the same gap applies when switching back.

Contraindicated with any history of angioedema, with an ACE inhibitor taken within 36 hours, with aliskiren in diabetes, and in pregnancy (fetal renal toxicity of RAAS blockade).

Adverse effects and monitoring. Hypotension (more than with ACE inhibitors), hyperkalemia, rising creatinine and angioedema; cough is less common. BNP is itself a neprilysin substrate, so it rises on therapy even as the patient improves. NT-proBNP, the inactive fragment cleaved from the same proBNP precursor, is not degraded by neprilysin and remains a valid marker of wall stress.

Ivabradine, hydralazine–nitrate and vericiguat

Oral add-on drugs for HFrEF

Drug	Mechanism	Who benefits	Watch for
Ivabradine	Blocks HCN channels (funny current, If) in the SA node → slower phase 4	EF ≤35%, sinus rhythm, resting HR ≥70 on a maximally tolerated β-blocker; ↓HF hospitalization	Phosphenes, bradycardia, atrial fibrillation, fetal toxicity, strong CYP3A4 inhibitors
Hydralazine + isosorbide dinitrate	Arteriolar dilation (↓afterload) + NO-mediated venodilation (↓preload)	Self-identified Black patients with NYHA III–IV on GDMT (mortality benefit); patients who cannot take ACEi/ARB/ARNI	Reflex tachycardia, fluid retention, drug-induced lupus; headache, hypotension, nitrate tolerance
Vericiguat	Stimulates soluble guanylate cyclase and sensitizes it to NO → ↑cGMP	EF <45% after a recent HF hospitalization or outpatient IV diuretics	Hypotension, anemia; contraindicated with riociguat and in pregnancy; avoid PDE-5 inhibitors

Ivabradine. The funny current is an inward Na+/K+ current through hyperpolarization-activated cyclic nucleotide-gated (HCN) channels that drives phase 4 depolarization in SA nodal cells. Blocking it lowers heart rate without negative inotropy, slowed AV conduction or much change in blood pressure. It has no role in rate control of atrial fibrillation and actually raises AF incidence. Retinal photoreceptors carry a related current (Ih), so blockade causes transient luminous phenomena. It is avoided in pregnancy, sick sinus syndrome and high-grade AV block.

Hydralazine–isosorbide dinitrate. Hydralazine relaxes arteriolar smooth muscle (↑cGMP in classic teaching) and lowers afterload; isosorbide dinitrate is converted to NO, raising cGMP in venous smooth muscle and lowering preload. Alone, hydralazine provokes reflex tachycardia and salt retention and can cause a lupus-like syndrome with anti-histone antibodies, especially in slow acetylators. Nitrates are contraindicated with PDE-5 inhibitors (sildenafil, tadalafil) because of profound hypotension.

Vericiguat. HF impairs NO availability and cGMP signaling. Vericiguat binds soluble guanylate cyclase, stimulating it directly and making it more responsive to endogenous NO. It must not be combined with another sGC stimulator (riociguat, used for pulmonary hypertension) and carries a boxed warning for embryo-fetal toxicity.

IV inotropes

Dobutamine, milrinone and dopamine

Drug	Mechanism	Hemodynamic effect	Pitfalls
Dobutamine	β1 > β2 (and α1) agonist → Gs → ↑cAMP	↑Contractility and CO, modest ↑HR, slight ↓SVR	Tachyarrhythmias, ischemia, tolerance; blunted by β-blockers
Milrinone	PDE3 inhibitor → ↑cAMP in heart and vessels	↑Contractility plus arterial and venous dilation (↓SVR, ↓PVR): an inodilator	Hypotension, ventricular arrhythmias; renally cleared; works despite β-blockade
Dopamine	Dose-dependent D1 → β1 → α1, plus norepinephrine release	Low: renal/mesenteric vasodilation; moderate: inotropy; high: vasoconstriction	More arrhythmias than norepinephrine; renal-dose dopamine does not protect the kidney

cAMP is the common currency. β1 stimulation and PDE3 inhibition both raise cAMP in cardiomyocytes. Protein kinase A then phosphorylates L-type Ca2+ channels (more trigger calcium) and phospholamban (faster SERCA reuptake), giving stronger contraction and quicker relaxation. In vascular smooth muscle cAMP causes relaxation, which is why milrinone lowers systemic and pulmonary vascular resistance.

Choosing an agent. Dobutamine acts and wears off within minutes but loses effect on high-dose β-blockers; it is also the stressor in dobutamine stress echocardiography. Milrinone bypasses the β-receptor, but renal elimination lets hypotension and arrhythmias persist in kidney failure. Dopamine stimulates D1 receptors at about 1–3 μg/kg/min, β1 at about 3–10 and α1 above 10.

Inotropes improve numbers, not survival. Chronic oral milrinone increased mortality, so IV inotropes are reserved for cardiogenic shock or low output with end-organ hypoperfusion, as a bridge to transplant or LVAD, or for palliation in stage D HF. Digoxin, the oral inotrope, reduces hospitalizations but not mortality.