ABSTRACT
BACKGROUND: Defibrillation threshold (DFT) is the minimum energy required to successfully terminate ventricular fibrillation. Epinephrine has been shown to increase the DFT in the beta-blocker naïve, but using cardioselective beta-blockers leads to a reduction in the DFT on infusion of epinephrine and norepinephrine. We sought to determine the impact of carvedilol therapy on the DFT after infusion of epinephrine and norepinephrine. METHODS: DFT was determined in patients receiving carvedilol by the step-down method (baseline DFT), and then patients (n = 27, 67.3 years, 70.0% were male, average left ventricular ejection fraction = 19%) were randomized to a 7-minute infusion of norepinephrine, epinephrine, or placebo in a double-blind manner. After the study drug infusion, DFT testing was repeated (experimental DFT) and results were compared between groups. RESULTS: No differences in intragroup DFTs were observed among carvedilol-treated patients receiving norepinephrine (9.4 +/- 4.6 J vs 11.1 +/- 7.8 J; P = .589), epinephrine (10.6 +/- 5.3 J vs 9.8 +/- 6.3 J; P = .779), or placebo (11.1 +/- 7.0 vs 8.5 +/- 4.2; P = .349). CONCLUSIONS: Carvedilol prevents alterations in DFT produced by stress levels of catecholamines.
Subject(s)
Adrenergic beta-Antagonists/pharmacology , Carbazoles/pharmacology , Defibrillators, Implantable , Epinephrine/pharmacology , Norepinephrine/pharmacology , Propanolamines/pharmacology , Ventricular Fibrillation , Aged , Carvedilol , Female , Humans , Male , Middle Aged , Stroke VolumeSubject(s)
Death, Sudden, Cardiac/etiology , Electrocardiography/drug effects , Epinephrine/pharmacology , Heart Diseases/physiopathology , Norepinephrine/pharmacology , Risk , Adrenergic beta-Antagonists/therapeutic use , Adult , Aged , Defibrillators, Implantable , Double-Blind Method , Female , Heart Diseases/therapy , Humans , Long QT Syndrome/complications , Male , Middle AgedABSTRACT
Fluid shifts in vasovagal syncope may be reflected in electrocardiographic P-wave duration. We examined the effect of head-upright tilt-table testing (HUT) on P-wave duration among patients with positive or negative HUT. P-wave duration was measured at baseline and several post-HUT time points. In patients with a positive HUT, the test was immediately discontinued. P-wave duration measurements obtained at the completion of the test or when symptoms occurred were compared to baseline measurements. The P-wave duration among patients with a positive HUT was significantly reduced at the onset of symptoms as compared to baseline (-14.0 ms, P = .0054) and 2-minute tilt measurements (-11.3 ms, P = .0246). P-wave duration measurements were not reduced in patients experiencing a negative HUT at any follow-up time. We showed a significant reduction in P-wave duration among patients experiencing positive HUT that suggests a dynamic relationship between atrial volume and P-wave duration.
