Vasodilator Therapy in Heart Failure

Pathophysiological Rationale

Heart failure induces excessive compensatory mechanisms including arteriolar and venous vasoconstriction mediated by catecholamines.
Arteriolar constriction increases systemic vascular resistance (SVR), increasing cardiac work and afterload.
Venoconstriction decreases venous capacitance, increasing venous return and elevating ventricular filling pressures (preload).
Vasodilators counteract inappropriate vasoconstriction, decreasing cardiac work.
Reductions in SVR and venous tone improve tissue oxygenation, reduce fatigue, and provide better work capacity.

Acute mitral or aortic regurgitation.
Ventricular dysfunction secondary to myocarditis.
Anomalous left coronary artery from pulmonary artery (ALCAPA).
Early postoperative cardiac surgery period.
Left-to-right shunts (e.g., large VSDs); afterload reduction selectively lowers systemic resistance over pulmonary resistance, decreasing Qp:Qs ratio.
"Warm-Wet" hemodynamic profile; indicates adequate perfusion with significant congestion.
"Cold-Wet" hemodynamic profile (cardiogenic shock with high SVR); vasodilators combined with inotropes (or utilizing inodilators) improve perfusion.

First-line oral vasodilators for pediatric heart failure.
Suppress renin-angiotensin-aldosterone system (RAAS), reducing vasoconstriction, salt retention, and water retention.
Prevent arrhythmias and adverse myocardial effects by suppressing catecholamine release.
Exert beneficial effects on cardiac remodeling; decrease myocardial fibrosis formation.

Utilized primarily when persistent cough necessitates discontinuation of ACE inhibitors.
Block angiotensin II receptors, achieving similar afterload reduction without bradykinin accumulation.

Sacubitril/Valsartan combination therapy.
Inhibits neprilysin (neutral endopeptidase), preventing degradation of circulating natriuretic peptides (BNP), bradykinin, and adrenomedullin.
Concomitant ARB (valsartan) prevents paradoxical RAAS potentiation.
Approved for pediatric patients >1 year of age with systemic left ventricular systolic dysfunction.

Sodium Nitroprusside: Direct action on venous and arteriolar smooth muscle; acts on both systems. Extreme short half-life allows precise titration for afterload and preload reduction.
Nitrates (Nitroglycerin): Preferential venodilators. Increase cGMP causing smooth muscle relaxation. Reduce preload greater than afterload.

Milrinone: Myocardial selective cAMP phosphodiesterase type-3 inhibitor. Increases intracellular cAMP, resulting in vasodilation (lowers SVR/PVR), inotropy, and lusitropy. Preferred first-line vasoactive medication with adequate blood pressure.
Levosimendan: Calcium sensitizer; opens ATP-sensitive potassium channels without altering intracellular calcium levels. Potent inodilator without increasing arrhythmia risk compared to milrinone.

Medication	Class	Pediatric Dosing
Captopril	ACEi	0.1–0.5 mg/kg/dose PO q6–24 h (Max: 6 mg/kg/day).
Enalapril	ACEi	0.05–0.1 mg/kg/day PO (Max: 0.5 mg/kg/day).
Lisinopril	ACEi	0.07 mg/kg/dose PO daily (Max: 0.6 mg/kg/day or 40 mg/day).
Losartan	ARB	0.7 mg/kg/day PO (Max: 1.4 mg/kg/day or 100 mg/day).
Valsartan/Sacubitril	ARNi	Weight-based titration (e.g., <40 kg: 1.6 to 3.1 mg/kg BID).
Sodium Nitroprusside	Direct Vasodilator	0.3–0.5 mcg/kg/min IV continuous (Max: 10 mcg/kg/min).
Nitroglycerin	Nitrate	0.25–0.5 mcg/kg/min IV continuous (Usual: 1–5 mcg/kg/min).
Milrinone	Inodilator	0.25–1 mcg/kg/min IV continuous infusion.
Levosimendan	Inodilator	12 mcg/kg loading over 1 h; maintenance 0.1–0.2 mcg/kg/min.

First-Dose Hypotension: Initiate at one-quarter calculated dose to prevent acute decompensation.
Renal Toxicity: Avoid in neonates due to risk of acute kidney injury. Withhold in settings of severe dehydration. Monitor creatinine and electrolytes every 1–2 weeks for initial 4–6 weeks.
Hyperkalemia: Risk increased when co-administered with spironolactone or potassium supplements; requires regular serum monitoring.

Cyanide/Thiocyanate Toxicity: Drug metabolism produces cyanide, detoxified by liver to thiocyanate, excreted in urine. Prolonged infusion (> several days) causes toxicity. Symptoms include fatigue, nausea, disorientation, acidosis, and muscular spasm. Monitor blood thiocyanate levels during prolonged use.
Hypotension: Contraindicated in patients with preexisting hypotension. May cause profound hypotension and reflex tachycardia.
Overdose Management: Drug withdrawal, recumbent position with leg elevation, IV fluid resuscitation, norepinephrine/vasopressin infusion (epinephrine contraindicated).

Side Effects: Methemoglobinemia, tolerance, flushing, headache, hypotension, tachycardia.
Contraindications: Increased intracranial pressure, hypovolemia.

Milrinone: Hypotension secondary to peripheral vasodilation often necessitates IV fluid resuscitation. Renal clearance necessitates extreme caution in renal insufficiency. Associated with proarrhythmia, thrombocytopenia, transaminitis, and bronchospasm. Contraindicated in severe right/left ventricular outflow obstruction.
Levosimendan: Symptomatic hypotension, palpitations, dizziness, nausea, vertigo.

Calcium Channel Blockers: Exert adverse negative inotropic effects; strictly avoided in pediatric heart failure unless specifically indicated for concurrent systemic hypertension.
Hydralazine/Isosorbide Dinitrate (Bidil): Combination not recommended for pediatric patients due to high adverse reaction rates (headache, GI complaints) and lack of survival benefit superiority over ACE inhibitors in non-specific cohorts (Class III, LOE C).

Routine preventative ACE inhibition demonstrates no proven clinical benefit in patients lacking systolic dysfunction.
Indicated strictly for afterload reduction in documented symptomatic heart failure to lower end-diastolic and pulmonary artery pressures.
Phosphodiesterase inhibitors (milrinone) act favorably in early postoperative Fontan settings by providing afterload reduction without increasing pulmonary vascular resistance.

Vasodilator therapy (ACEi/ARBs) carries significant risk.
Hypotension frequently ensues without augmentation of cardiac output, due to strict inability to augment stroke volume against fixed diastolic restriction.
Routine use of renin-angiotensin antagonists is not recommended for RCM unless alternative indications (e.g., hypertension) are present.

Decompensated right heart failure requires cautious optimization of RV preload.
Excessive diuretic use or potent systemic vasodilation can drop cardiac output precipitously, compromising therapies aimed at lowering pulmonary vascular resistance.
Inotropes (dobutamine/milrinone) utilized concurrently with IV diuretics improve CO. Systemic hypotension must be vigorously avoided (utilizing norepinephrine/vasopressin) to maintain RV coronary perfusion.