JACC March 6, 2002 mean square residual (RMS) from the linear regression analysis; RMS quantities the deviation of the RR interval from a pure linear change over the 30 sec period. PE was defined as the difference in the 30 sec average RR intervals without (day 1) and with (day 2) atropine. Results: RMS dramatically increases after I minute of recovery. P blockade attenuates the increase in RMS. Day 2 RMS was less than day 1 RMS for all time pedods (p<0.03). There was a correlation between day 1 RMS and PE (R2 = 0.63, p< 0.0001) Conclusion: RMS is a new measure of HRV that is related to recovery of PE after Ex. RMS may help differentiate whether the recently demonstrated prognostic sig- nificance of HR recovery after Ex testing is due to P recovery or sympathetic withdrawal, both of which decrease HR. If P recovery is more important, RMS may provide better dsk stratification than HR recovery. 15 o 1' ~ ~ ~ ~ d ~ ~ ~1~ Time post-e)0erciae Gn 30 sec interuele) 1116-118 Effects of Nesiritide and Dobutamine on Heart Rate Variability in Patients With Decompensated Heart Failure Doren Aronson, Dadene P. Horton, Andrew J. Burger, Rambam Medical Center, Haifa, Israel, Beth Israel Deaconess Medical Center, Boston, Massachusetts. INTRODUCTION: Congestive heart failure (CHF) is characterized by sympathetic over- activity and parasympathetic withdrawal. Clinical trials in patients (pts) with decompen- sated CHF have shown that nesiritide (brain natriuretic peptide) is associated with beneficial hemodynamic effects and symptomatic improvement. Recent studies suggest that nesiritide exerts a favorable effect on autonomic dysfunction in CHF. We compared the effect of nesirifide and dobutamine (Dob) on heart rate variability (HRV) in decom- pensated CHF. METHODS: We studied 185 pts admitted for decompensated CHF requiring intravenous vasoactive therapy. Baseline 24-h Holters were obtained prior to initiation of the study drugs (nesiritide or Dob) and continued for an additional 24-h after initiation of therapy. The study population was divided into 2 groups: highly depressed HRV (SDNN < 50 ms) and moderately depressed HRV (SDNN = 50-100 ms). HRV time domain indices were compared from baseline and treatment Holter recordings. RESULTS: In the Dob group, pts with moderately depressed HRV at baseline (n = 20) displayed a reduction in indices of total variability such as SDNN (82 ± 4 to 71 ± 4 ms, p = 0.01) and SDANN5 (69 ± 3 to 60 ± 4 ms, p = 0.01). Indices of parasympathetic modu- lation, pNN50 (7.2 ± 1.5 to 6,6 ± 1.7 %, p = 0.04) and RMSSD (29 ± 4 to 27 ± 4 ms, p = 0.05), also decreased. With severely depressed HRV (n = 38), no significant changes occurred with Dob in indices of overall HRV or parasympathetic modulation. However, in the nesiritide group, pts with severely depressed HRV (n = 75) displayed a significant increase in SDNN (35 ± 1 to 40 ± 2 ms, p = 0.002), SDANN5 (30 ± 1 to 34 ± 1 ms, p = 0.02), and RMSSD (13 ± 1 to 15 ± 3 ms, p = 0.01). No significant changes occurred in HRV indices with moderately depressed HRV at baseline (n = 53). CONCLUSION: In pts with relatively preserved HRV, Dob reduces overall variability and parasympathetic modulation. With severely depressed HRV, the effect of Dob on HRV is minor, presumably clue to ~,-adrenergic receptor down-regulation or saturation. In con- trast, nesiritide improves indices of overall HRV and parasympathetic modulation in pts with severely depressed HRV and has no adverse effect on pts with relatively preserved HRV. 1118-119 Altered Fractal Behavior and Heart Rate Variability in Daily Life in Neurally Mediated Syncope Bonpei Takase, Haruhiko Hosaka. Yoshihiro Matsushima, Takashi Akima, Syuuichi Katsushika, Toshihiko Nishioka, Fumitaka Ohsuzu, Akira Kurita, National Defense Medical College, Tokorczawa, Japan, Serf Defense Forces Central Hospital, Tokyo, Japan. Background: The fractal dimension is an index to the complexity of cardiovascular con- trol system and autonomic function is important in the pathogenesis of neurally mediated syncope (NMS), However, it is still not fully understood if the derangement of the auto- nomic nervous system exists in NMS in daily life. Methods: Thus, we performed 24-hour ECG monitoring (AECG) and measured traditional heart rate variability indices (HRV) along with long fractal scaling exponent (b) in 36 pts (NMS, 24±3 y/o) with NMS diag- nosed by heed-up tilt testing (HUT, 807 tilt) and 11 age-matched normal controls (NL). AECG was performed within 48 hours before HUT procedure. For HRV, SDANN, SD, rMSSD, pNN50, low frequency (0.04-0.15Hz, LF) and high frequency (0.15-0.40 Hz, HF) were measured. All measurements were analyzed in three different periods such as total 24-hour, awake (09:00-15:00) and sleep (00:00-06:00) phases. The ratio of each mea- surements in awake over sleep phase (A/S ratio) was also calculated, Results: Several 24-hour HRV showed significantly higher values in NMS than those in NL (SD, 91±32 vs 65±11 ms; rMSSD, 60±31 vs 38±11 ms; pNN50, 30±17 vs 14±7%; LF, 35±15 vs 26¢5 ms; HF, 27±11 vs 14±7 ms; p<0.05) while 24-hour b was not different (0.95±0.13 vs 0.95±0.14). In contrast, although NS ratio of any HRV showed no differences,/US ratio of b revealed significantly higher value in NMS than in NL (1,7±0.49 vs 1.2i-0.t5, p<0.05). The awake and sleep values of b in NMS were also significantly different from those in NL, Conclusion; Overall autonomic activity in daily life is exaggerated in NMS. Since in most of the time pts are upright during awake and are supine during sleep ABSTRACTS - Cardiac Arrhythmias 101A phase, the significant differences between awake and sleep values of b, and abnormal A/ S ratio of b suggest that deteriorated fractat behavior exits in NMS. These findings may be associated with the mechanisms of orthostatic intolerance in NMS. 1116-120 Right Atrial Size May Be a Primary Determinant of Atrial Conduction Time of the Sinus Node Impulse Susette K. Therkelsen. Bjoem A. Groenning, Uldk Dixen, Gorm B. Jensen, Department of Cardiology, Copenhagen University Hospital Hvidovre, Copenhagen, Denmark, Danish Research Center of Magnetic Resonance, Copenhagen University Hospital Hvidovre, Denmark. Background: Prolonged signal-averaged p-wave duration (SAPD) measured by a sig- nal-averaged ECG is thought to represent a delay in the intra-atrial conduction of the electrical impulse. Prolonged SAPD is a prognostic manker of development of atrial fibril- lation (AF). In addition, atrial dilatation in patients with previous AF has been associated with dsk of relapse of AF. However, the relation between duration of atrial conduction of the electrical impulse and atrial dimensions is not clear. Our aim was to evaluate the cor- relation between atdal dimensions measured by magnetic resonance imaging (MRI) and the intra-atdal conduction time measured by SAPD. Methods: In 7 subjects with no history of cardiac disease, we measured the total filtered SAPD. Atrial dimensions were evaluated by cinematographic braathhold MRI scans. Results: Right atrial (RA) diastolic volume index (mean+SD=77:P21ml/m2; r=0.83, p=0.02), systolic volume index (49~17ml/m2; r=0.76, p=0.05) and stroke volume index (29-Z6.7ml/m2; r=0.77, p=0.04) were positively associated with SAPD (135±10.6ms). Left atrial (LA) diastolic (64:t:7.1 ml/m 2) and systolic (39~7.3ml/m 2) volume indices and stroke volume index (24+1.0ml/m 2) were completely unrelated to SAPD. The combined RA and LA diastolic (141.+.21.6ml/m2; r=O.80, p=0.03) and systolic (87.8+17.0ml/m2; r=0.70, p=0.08) volume indices correlated positively with SAPD, Conclusion: Our results suggest that RA size may be a primary determinant of atdal conduction time measured by SAPD. A ufiD~ ORAL CONTRIBUTIONS 826 External and Implantable Defibrillators: Clinical Studies Monday, March 18, 2002, 2:00 p.m.-3:30 p.m. Georgia World Congress Center, Room 254W 2:00 p.m. 826-1 New Therapeutic Option for Patients With Time- Dependent Risk of Sudden Cardiac Arrest: Application of Novel Wearable Cardloverter-Defibrillator Arthur M. Feldman, Helmut Klein, Patrick Tchou, The WEARIT & BIROAD Investigators, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, Otto Von Guericke Universi~ Magdeburg, Germany. Background: Outpatient populations with temporary risk for sudden cardiac arrest (SCA), such as patients awaiting cardiac transplant, post-myocardial infarction patients (p-MI) or post-CABG patients (p-CABG), often rely on emergency medical services (EMS) for defibdllation therapy. Success rates for EMS resuscitation are poor. A new therapeutic option, the completely automatic (no bystander intervention) wearable cardioverter- defibdllator (WD), may provide better protection for these populations. Methods: A mulficenter trial studied the use of WD (WCD~ system, LIFECOR Inc., Pitts- burgh). WD provides automatic detection and treatment of ventricular techycardia and fibrillation (VTNF) using unique non-stick ECG electrodes and self-gelling therapy elec- trodes. WEARIT sub-population: patients on the cardiac transplant list or equivalent in cardiac status. WEARIT subjects used WD until transplanted, hospitalized for transplant or circulatory assist device, or receiving an active ICD. BIROAD sub-population: patients not receivingan ICD who were p-MI or p-CABG and had either VTNF within 48 hours, an ejection fraction < .30 or Killip class > II after 72 hours, or syncopal VTNF after 48 hours. BIROAD used WD for -4 months. The effectiveness objective was >25% resuscitation success with 90% confidence, The safety objective was <2.3% false shocks per patient- month with 90% confidence (500 patient-months minimum). Results: There were 8 VTNF SCA events in 6 patients (4 BIROAD, 2 WEARIT). 6 were successfully treated, 2 were unsuccessful with V'rNF detected but treatment prevented by incorrect patient assembly of WD (therapy electrode in pocket backward, gel released away from body). A redesign occurred to prevent this from reoccurring. 6 false shock epi- sodes occurred in 873 patlent-months. The most frequently repoded adverse event (20) was temporary skin rash under electrodes. 285 patients were enrolled over 3 years. Daily