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A nonlinear predictive forecasting algorithm was developed to search for predictability and sensitive dependence on initial conditions in the ventricular response during atrial fibrillation. A linear oscillator with and without superimposed white noise was used to test the algorithm for simulated R-R intervals. The linear oscillators showed short-term predictability without loss of predictive ability farther into the future. Without sensitive dependence on initial conditions, the ventricular response in atrial fibrillation was weakly predictable.

Ectopy correction is essential for heart rate variability determination. Deletion of ectopy-containing segments of data from the analysis is possible only when long data collection intervals are involved as the method excludes the periods at which important changes in autonomic tone occur. The technique is not applicable during cute interventions.

Beta-blockers are a first line therapy for neurocardiac syncope, but are not always effective. The purpose of this study was to determine whether differential autonomic responses to orthostasis predict the response of patients with neurocardiac syncope to p-adrenergic blockade. We computed the RMS successive difference of the BB intervals (BMSSD: a measure of cardiac parasympathetic tone) during supine and upright phases of the initial tilt test in 28 patients with syncope and positive tilt tests who were treated with atenolol. Follow-up tilt testing was performed to assess the efficacy of the drug in preventing tilt induced neurocardiac syncope. BMSSD did not differ at baseline (supine) between those who did (n = 20) and did not (n = 8) respond to β-blockade. However, withdrawal of parasympathetic tone in response to tilt varied inversely with age (r = -0.69; P < 0.01 ). Reduced age adjusted parasympathetic withdrawal during orthostasis was associated with a 47% versus 8% risk of β-blockade failure (odds ratio = 11; P = 0.01). Patients with diminished age adjusted parasympathetic withdrawal during orthostatic stress are less likely to respond to β-Blocker therapy of neurocardiac syncope than their counterparts. This may reflect a correspondingly greater sympathetic response to orthostasis in these patients, but the mechanism for this interaction is undetermined. [ABSTRACT FROM AUTHOR]

Background: It is unclear whether acute conversion of atrial fibrillation (AF) with anti-arrhythmic drugs following cardiac surgery restores and/or maintains sinus rhythm or reduces hospital length of stay (LOS)., Material/methods: A randomized prospective pilot study was conducted in 2 teaching hospitals from 3/28/98 to 8/2/99 to study the effect of the early use of ibutilide or propafenone on the duration of AF, rhythm at discharge, and LOS. A total of 42 stable patients with new AF after surgery were randomized to oral propafenone (600mg, single dose; n=20), ibutilide (1 mg up to 2 doses if necessary; n=10), or rate control only (n=12). Agents used for rate control were left to the discretion of the primary physician but beta-blockers were encouraged., Results: Pre-randomization distribution of diabetes, CHF, previous AF, and the use of beta-blockers were similar in all groups. At 24 hours 0%, 65% and 34% of patients in the ibutilide (p=0.01), propafenone (p=ns), and rate control groups respectively remained in AF. Although ibutilide decreased AF duration, recurrence rates were 90%, 41%, and 58% in those groups (p=ns compared to rate control). Of the 3 patients who did not convert, all received propafenone. There was no difference in LOS or rhythm at discharge., Conclusions: Ibutilide but not propafenone decreases the duration of AF after cardiac surgery and neither appears to affect LOS or rhythm at discharge. This data suggests that post operative AF is transient and routine anti-arrhythmic therapy is not necessary for the majority of patients.