LOWE, M.D., et al .: Catheter Cryoablation of Supraventricular Arrhythmias: A Painless Alternative to Radiofrequency Energy. Cryothermy has potential advantages over RF energy for catheter ablation, including reversibility of lesion formation, catheter stability, and less procedural discomfort. Cryoablation procedures were performed in 14 patients with atrioventricular reentrant tachycardias (AVNRTs), 13 patients with accessory pathway (AP)‐mediated tachycardias, and 5 patients with atrial fibrillation. The numbers of energy applications, pain scores, procedural times, and outcomes were recorded and compared with age‐ and sex‐matched patients undergoing similar RF procedures. Cryoablation was successful in 26 of 32 patients (11/14 AVNRT, 10/13 AP, 5/5 AF) compared with 30 of 32 undergoing RF procedures, with similar numbers of energy applications and procedural times. Cryothermy was painless in all patients, and the overall procedural discomfort was significantly less than in patients treated with RF (1.3 ± 2.2 vs 6.1 ± 3.5) . In patients with anteroseptal pathways, cryomapping successfully identified safe sites to target the delivery of energy. Cryothermy is a painless and safe alternative to RF. It may be particularly useful for catheter ablation of patients with pathways close to the atrioventricular node. (PACE 2003; 26[Pt. II]:500–503)

SAVELIEVA, I., et al.: Heart Rate Turbulence After Atrial and Ventricular Premature Beats: Relation to Left Ventricular Function and Coupling Intervals. Heart rate turbulence (HRT) represents a biphasic chronotropic response of the sinus node to a single ventricular premature beat (VPB). Objectives: To determine whether HRT is present after an atrial premature beat (APB) and to investigate the effects of paced VPB and APB coupling intervals on HRT quantifiers in patients with and without left ventricular dysfunction. Methods: A total of 37 subjects ( 54 ± 16 years, 32 men) referred for electrophysiologic evaluation for ventricular tachycardia underwent a stimulation protocol consisting of 3 series of single atrial and ventricular extrastimuli with coupling intervals decremented from 750 to 400 ms at a 50 ms‐step. Turbulence onset (TO) and turbulence slope (TS) after an APB and a VPB were calculated separately using a dedicated computer algorithm. Results: After an APB, TS was significantly attenuated ( 3.95 ± 0.99 vs 8.32 ± 1.9 ms/RR, P < 0.008 ) and TO was positive ( 1.37 ± 0.35% vs ‐2.03 ± 0.42%, P < 0.001 ) compared with those after a VPB. There was a strong correlation between TS (r = 0.71, P = 0.0002) but not between TO (r = 0.07, P = 0.074) after an APB and a VPB. In subjects with normal ejection fraction, the prematurity of ventricular coupling intervals was strongly related to TO (r = 0.68) and TS (r =−0.61), P < 0.0001 for both. These effects were less pronounced in patients with left ventricular dysfunction (TO: r = 0.25 , P < 0.01; TS:r =−0.07, P = ns). No correlation was found between the APB coupling interval and TS or TO in both groups. Conclusions: An APB induces HRT but the response is substantially attenuated and is not influenced by the APB coupling interval. In contrast to a VPB, TO is positive after an APB. Lack of correlation between HRT after a VPB and the VBP coupling interval indicates blunted baroreflex response in patients with left ventricular dysfunction. (PACE 2003; 26[Pt. II]:401–405)

WICHTERLE, D., et al.: Paradoxical Autonomic Modulation of Atrioventricular Nodal Conduction During Heart Rate Turbulence. Heart rate turbulence (HRT) represents a biphasic chronotropic response of sinus rhythm to a single ventricular premature beat (VPB). It consists of early acceleration and late deceleration of heart rate and is predominantly mediated by the autonomic nervous system. The aim of this study was to investigate if autonomic perturbations after a VPB exert a significant effect on AV conduction. Both surface ECG and the high right atrial electrogram were recorded at a sampling frequency of 1000 Hz in 26 patients (24 men, mean age 49 ± 12 years) referred for electrophysiological evaluation. The stimulation protocol consisted of series of single ventricular extrastimuli delivered from the right ventricular apex at decreasing coupling intervals. A biphasic profile of AV intervals after a single VPB was observed. The response of AV conduction to a VPB was approximately 25 times and 15 times weaker in the early and late phase, respectively, than that of R‐R intervals. Thus, AV interval dynamics significantly preceded the change in R‐R intervals, which is in conflict with the near to zero phase of transfer function between R‐R and AV intervals described in previous studies. A significant AV turbulence was observed consisting of early shortening and later prolongation of AV intervals after VPB. Its magnitude was much smaller than that of HRT. Dynamics of AV delay has little impact on the accuracy of HRT assessment from surface ECG. The significant temporal dissociation of R‐R and AV interval dynamics after a VPB remains unexplained. (PACE 2003; 26[Pt. II]:440–443)

Heart rate turbulence (HRT) describes a bi-phasic chronotropic response of sinus rhythm to a ventricular premature beat (VPB). The aim of the study was to investigate whether an atrial premature beat (APB) can produce HRT and whether it can be described using ventricular HRT quantifiers (turbulence onset, TO, and turbulence slope, TS). Methods: Thirty-seven subjects (54±16 years) referred for electrophysiologic evaluation for ventricular tachyarrhythmias underwent a stimulation protocol consisting of 3 series of single atrial and ventricular extrastimuli delivered from the high right atrium and right ventricular apex prior to programmed electrical stimulation. Atrial and ventricular TO and TS (ATO, ATS, VTO, VTS) were calculated separately using a dedicated computer algorithm. Results: Expressed as mean±SD, VTO -2.03±0.42%, ATO 1.37±0.35% (p <0.001); VTS 8.32±1.9 ms/RR, ATS 3.95±0.99 ms/RR (p <0.008). There was a strong correlation between VTS and ATS (r=0.71, p=0.0002; Figure, right) but not between VTO and ATO (r=0.83, p=0,074; left). Conclusions: HRT phenomenon is present after an APB, suggesting that similar baroreceptor mechanisms operate following both VPB and APB. After an APB, the late phase response (rhythm deceleration) is significantly attenuated and the early phase response is different than that after a VPB, indicating the presence of alternative mechanisms. Atrial HRT can be measured using existing technique but algorithm adjustments are desirable. ACC 2002 / 51st Annual Scientific Session March 17-20, 2002, Atlanta, Georgia, USA Page 1