The American journal of cardiology
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Propafenone was administered to 58 patients with a mean age of 3.2 years (range 0.1 to 16). Mean intravenous dose was 1.2 mg/kg body weight (range 0.3 to 1.5 mg). The final mean oral maintenance dose was 308 mg/m2 body surface area (range 200 to 600 mg/m2, 16.8 mg/kg body weight). ⋯ Chaotic atrial tachycardia (n = 3) and junctional ectopic tachycardia (n = 2) were controlled after successful intravenous therapy. Systemic side effects were rare. Two patients developed a proarrhythmic effect, and 1 patient with ventricular ectopy after repair of tetralogy of Fallot died suddenly during propafenone maintenance therapy.
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Withdrawal of beta-blocker therapy has been associated with the development of adrenergic hypersensitivity and adverse clinical effects in patients with coronary artery disease and hypertension. The aim of this study was to establish the occurrence and clinical significance of adrenergic hypersensitivity after abrupt withdrawal of long-term beta blockade in hypertrophic cardiomyopathy. Beta-adrenergic sensitivity was measured using the isoprenaline chronotropic dose25. ⋯ Of 3 patients with inducible outflow tract gradients, 2 developed resting gradients greater than 30 mm Hg during the acute withdrawal period. There was an increase in peak late filling velocity of mitral inflow after beta-blocker withdrawal. In conclusion, transient beta-adrenergic hypersensitivity occurs after beta-blocker withdrawal in hypertrophic cardiomyopathy and is associated with significant physiologic changes and adverse clinical consequences.