Autonomic modulation and atrial fibrillation in the Wolff-Parkinson-White syndrome.

A association between atrial fibrillation (AF) and Wolff-Parkinson-White (WPW) syndrome has been recognized since the earliest description of the condition.1 AF has been documented in approximately 30% of patients with WPW syndrome,2 and it appears to be associated with faster atrioventricular reciprocating tachycardia (AVRT), shorter accessory pathway effective refractory periods, slower intra-atrial conduction, structural heart disease, and advanced age.2–4 Rates of cure of AF by ablation of the accessory pathway in some series have been .91%.4,5 Autonomic modulation of accessory pathway refractoriness and conduction became evident in experiments involving exercise,6 postural changes,7 and drugs.6,8 Timeand frequency-domain analysis of heart period variability performed in patients with paroxysmal AF suggests that autonomic modulation is important in selected patients.9,10 Assessment of autonomic balance using analysis of heart period variability in patients with WPW syndrome has not been performed. The purpose of this study was to determine if frequency-domain analysis of heart period variability can predict the occurrence of AF in patients with the WPW syndrome and identify characteristics of supraventricular tachycardia in this population. • • • The study included 22 consecutive patients with WPW syndrome who underwent electrophysiologic study and radiofrequency ablation of an accessory pathway. All 22 patients underwent 24-hour ambulatory Holter monitoring immediately before electrophysiologic study. The patients were studied .5 halflives after discontinuation of antiarrhythmic medications, including b blockers. Effective refractory periods and conduction characteristics of the accessory pathway were obtained by atrial and ventricular programmed stimulation before mapping and ablation of the accessory pathway. All patients underwent transthoracic echocardiography. Patients with evidence of structural heart disease, decreased left ventricular function, hypertension, and diabetes mellitus were excluded from this study. Three-channel 24-hour electrocardiographic recordings were analyzed using a Zymed 1600 digital scanner (Camarillo, California) with a sampling frequency of 192/s. The data were transferred to a computer for analysis of heart period variability using custom Zymed HRV software. All RR interval sequences were individually reviewed to ensure correct identification and classification of each QRS complex. Power spectral analysis using Fourier transformation was then performed providing spectral power (square milliseconds) in the low-frequency (LF) bandwidth of 0.04 to 0.15 Hz (believed to reflect both sympathetic and parasympathetic influences modulated by baroreflex activity) and the high-frequency (HF) bandwidth of 0.15 to 0.40 Hz (which primarily reflects vagal modulation).11 The LF/HF ratio (defined as the ratio between LF and HF spectral power) is believed by many investigators to represent a relative composite index of parasympathetic and sympathetic modulation.11 Power spectral values were analyzed before and after transformation to their natural logarithms (Ln) in view of their non-normal distributions. All data are expressed as mean 6 SD. The 2-tailed unpaired t test for independent variables was used in the analysis of continuous variables. Differences in categorical variables between the 2 groups were assessed using the chi-square or Fisher’s exact test. Bivariate analysis (Pearson’s correlation) was used to compare continuous numeric variables. A p value of ,0.05 was considered significant. Of the 22 consecutive patients enrolled in this study, 6 (27%) were male, and ages ranged from 12 to 57 years (mean 37 6 13) (Table I). After a careful medical history and chart review, paroxysmal AF was documented in 8 of 22 patients (36%) (group I) and was associated with continuous pre-excitation in all patients with a mean shortest pre-excited RR interval during AF of 234 6 79 ms. In 14 of 22 patients, no documentation or history of spontaneous AF was found (group II). During electrophysiologic study, AF was induced by programmed electrical stimulation in all patients in group I compared with only 3 of 14 (21%) patients in group II (p 5 0.001). The duration of induced AF was .30 minutes in 4 of 8 patients in group I; these patients required direct-current cardioversion. Of the 3 patients with inducible AF in group II, all of the episodes were self-terminating. The mean of the shortest pre-excited RR interval during AF was shorter in group I (243 6 39 ms) compared with group II (346 6 84 ms, p ,0.05). Orthodromic AVRT was induced in 6 of 8 patients in group I, who exhibited a mean cycle length of 335 6 75 ms compared with 9 of 14 patients in group II with a mean cycle length of 371 6 61 ms (p 5 NS). The average recording time for the entire group was 17:56 6 2:48 hours and did not differ significantly between group I (18:52 6 3:56 hours) and group II (17:23 6 1:46 hours) patients. The percent of complexes excluded from analysis because of noise was 2.0 6 2.4% in group I and 1.9 6 3.2% in group II (p 5 NS). In 8 patients with documented From the Department of Medicine, Montefiore Medical Center, Bronx, New York, and Albert Einstein College of Medicine, New York, New York; and the Department of Pharmacology, Columbia-Presbyterian Medical Center, College of Physicians and Surgeons, New York, New York. Dr. Ferrick’s address is: Division of Cardiology, Montefiore Medical Center, 111 East 210 Street, Bronx, NY 10467. Manuscript received July 22, 1999; revised manuscript received and accepted December 1, 1999.