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Notes: Ablation of Atrial Fibrillation. Introduction: Atrial fibrillation (AF) is often refractory to antiarrhythmic drugs, and patients who are intolerant of AF may require the maze operation for cure. As a less Invasive alternative, a catheter-based, right atrial compartmentalization procedure was evaluated. Methods and Results: Twelve patients with AF refractory to Class I and III antiarrhythmic drugs were studied. Four linear right atrial radiofrequency ablations were performed, from superior to inferior vena cava in the posterior wall and interatrial septum, anteriorly from the superior vena cava to the tricuspid annulus through the appendage, and across the tricuspid valve-inferior vena cava isthmus. The radiofrequency catheter was dragged along each line three to four times, until the atrial electrogram amplitude decreased by 75% and there was bidirectional conduction block in the tricuspid valve-inferior vena cava isthmus. One complication occurred: sinus node dysfunction requiring a pacemaker. Eight patients were discharged from the hospital on no antiarrhythmic drugs, and four were discharged on previously ineffective antiarrhythmic drugs. Total duration of follow-up was 21.3 ± 11.2 months. Four patients discharged on previously ineffective antiarrhythmic drugs had no recurrence of AF. One patient discharged off antiarrhythmic drugs had no recurrence of AF. Seven patients discharged off antiarrhythmic drugs had recurrent AF by 12.6 ± 13.0 months (median 6, range 1 to 39); 3 of these 7 responded to previously ineffective antiarrhythmic drugs without further AF and 4 did not. Thus, 8 of 12 patients (67%) had suppression of AF after ablation on previously ineffective medication or no medication. Conclusion: Right atrial compartmentalization may alter the substrate for AF, thus improving the efficacy of previously ineffective antiarrhythmic drugs. Because it is relatively safe, it may be a reasonable adjunctive intervention to maintain sinus rhythm in patients with drugrefractory AF.

Notes: Slower Conduction in the TV-IVC Isthmus. Introduction: In human type I atrial flutter, the electrophysiologic substrate is unclear. In order to determine if slow conduction is mechanistically important, we evaluated conduction velocity in the tricuspid valve-inferior vena cava (TV-IVC) isthmus, right atriai free wall, and interatrial septum in patients with and without a history of atrial flutter undergoing electrophysiologic study. Methods and Results: Nine patients with (group 1) and nine without a history of type I atrial flutter (group 2) were studied. Conduction time (msec) in the right atrial free wall. TV-IVC isthmus (bidirectional), and interatrial septum was measured during pacing in sinus rhythm at cycle lengths of 600, 500, 400, and 300 msec from the low lateral right atrium and coronary sinus ostium. Conduction velocity (cm/sec) was calculated by dividing the distance between pacing electrodes and sensing electrodes (cm) by the conduction time (sec). Conduction velocity was slower in the TV-IVC isthmus in group 1 (range 37 ± 8 to 42 ± 8 cm/sec) versus group 2 (range 50 ± 8 to 55 ± 9 msec) at all pacing cycle lengths (P 〈 0.05). However, conduction velocity was not different in the right atrial free wall or interatrial septum between groups 1 and 2. Conduction velocity was also slower in the TV-IVC isthmus than in the right atrial free wall and interatrial septum in group 1 patients, at all pacing cycle lengths (P 〈 0.05). Atrial flutter cycle length correlated with total atrial conduction time (r ≥ 0.832, P 〈 0.05). Conclusion: Slow conduction in the TV-IVC isthmus may be mechanistically important for the development of human type I atrial flutter.

Notes: WPW Variant. Introduction: The differentiation between a nodoventricular fiber and an accessory atrioventricular (AV) pathway with long conduction times and decremental properties could he very difficult even at detailed electrophysiologic study. Methods and Results: A 20-year-old male with a history of a wide QRS tachycardia underwent electrophysiologic study. Baseline intervals were normal. There was evidence of dual AV pathways, and a sudden increase in AH interval was associated with the emergence of a delta wave. The atrio-delta interval showed a progressive prolongation. The preexcited QRS complex was typical of a posteroseptal pathway, and the earliest ventricular activation site was recorded at the posteroseptal region. Retrograde conduction was exclusively over the normal conduction system. During ventricular extrastimulation, a sudden increase in HA interval was associated with anterograde conduction over the accessory pathway. The intervals between the stimulus artifact and the onset of the delta wave during atrial pacing from two atrial sites (S-Delta) were compared with those between the retrograde atrial electrogram on the His channel and the onset of the delta wave during ventricular pacing (A2HB-Delta). When pacing from the proximal coronary sinus, the shortest S-Delta interval did become shorter than the longest A2HK-Delta interval (155 vs 170 msec). Conclusion: The finding that the S-Delta interval could become shorter than the A2HB-Delta interval provides strong evidence that this accessory pathway was not connected to the AV node hut arose directly from the atrial tissue of the posteroseptal region.

Notes: Endoscopy for Ablation Around the CS Ostium. Introduction: Radiofrequency ablation of the slow pathway can prolong atrioventricular (AV) nodal properties and RR intervals during atrial fibrillation (AF) in many patients with AV nodal reentrant tachycardia. However, it is not well elucidated whether these changes are related to the presence of dual AV nodal pathway physiology. The aim of this study was to evaluate changes of AV nodal properties and RR intervals during AF caused by ablation of two specific areas in dogs. Methods and Results: Assisted by fiberoptic endoscopy, linear lesions were created between the coronary sinus ostium and tricuspid valve annulus (area 1) or posterior to the ostium (area 2) in 15 dogs. Three additional dogs served as controls. The measurements were made under autonomic blockade. Catheter ablation could be assisted in all dogs by means of endoscopy. Linear lesions were confirmed at autopsy. AV nodal parameters and RR intervals showed no overall changes. Individual data showed that ablation of area I resulted in modification of AV nodal properties in 54.5% (facilitation in 363% and inhibition in 18.2%), whereas ablation of area 2 induced changes in 50% (facilitation in 10% and inhibition in 40%). The RR intervals were shortened in 33.3% and 20% and prolonged in 44.5% and 40% after ablation of areas 1 and 2, respectively. The RR intervals during AF correlated well with the Wenckebach cycle length and the AV node functional refractory period before and after ablation (r = 0.78 to 0.94, P 〈 0.01 for each). Conclusions: Ablation of the two specific areas around the coronary sinus ostium was equally effective in modifying AV nodal properties and the ventricular response during AF without dual AV nodal pathway physiology. The ventricular rate to AF after ablation correlated well with the residual AV nodal properties.

Notes: Concealed conduction is demonstrated to occur in an accessory AV pathway (AP). To test the hypothesis that anterograde and retrograde concealed conduction in the AP would have different characteristics, 35 consecutive patients with single APs were studied. The anterograde or retrograde ERP of the AP could be determined in 23 of those patients. Anterograde concealed conduction in the AP was assessed in the first 13 patients with retrograde AP conduction (8 APs with retrograde conduction only and 5 with both directions) (group A). Retrograde concealed conduction in the AP was evaluated in the remaining 10 patients with anterograde AP conduction (6 APs with anterograde conduction only and 4 with both directions) (group B). The concealed conduction in the AP was quantified by determining the ERP of the AP using a “probe” extrastimulus (Sp) introduced in the opposite chamber. The ERP was determined both during conventional extrastimulus (S1S2 method; ERPc) and during that with an Sp (S1SpS2 method; ERPp). The Sp was delivered before or after the last S1 with various S1Sp intervals. The ERPp was determined at each S1Sp interval. Three distinct patterns in concealed conduction in the AP were noted. In the first pattern, the ERPp was always shorter than the ERPc, whereas the reverse relation was noted in the second pattern. The third pattern showed a combination of the two. In group A, only the first pattern was noted. In group B, the first, second, and third patterns were noted in 4, 2, and 4 patients, respectively. The first pattern was noted only in septal APs and the second and third were seen only in left free-wall APs. The second pattern was seen in patients with retrograde AP conduction, whereas the third one was mainly noted in patients without retrograde AP conduction. These observations indicate that anterograde and retrograde concealed conduction in the AP have different characteristics. Shortening of the ERPp might be due to the “peeling back” phenomenon, and its lengthening might be caused by the presence of the inhomogeneous refractory periods of the AP. (PACE 1997; 20[Pt. I]:1342-1353)

Notes: Abstract Background: The upper limit of vulnerability (ULV) is the stimulus strength above which ventricular fibrillation cannot be induced, even when the stimulus occurs during the vulnerable period of the cardiac cycle. Determination of ULV using T-wave shocks during ventricular pacing has been shown to closely correlate with the defibrillation threshold (DFT) at ICD implantation. However, there are no data correlating ULV determined in sinus rhythm at ICD implantation, with DFT determined at implantation or during long-term follow-up. This is of clinical importance since ULV may be used to estimate DFT during ICD implantation, both during ventricular pacing or sinus rhythm. Methods and Results: Twenty-one patients receiving a transvenous ICD system were studied prospectively. There were 16 males and 5 females, mean age 68 ± 15 years, with mean ejection fraction 37.4 ± 17.4%. All had structural heart disease. The ULV was defined as the lowest energy that did not induce ventricular fibrillation with shocks at 0, 20 and 40ms before the peak of the T-wave, using a step-down protocol. The initial energy tested was 15J and the lowest energy 2J. DFT was determined following a similar step-down protocol. The DFT was defined as the lowest energy that successfully defibrillated the ventricles. The linear correlation coefficient between ULV and DFT was r = 0.73 (p 〈 0.001). At implant, mean ULV was 9.2 ± 5J, not statistically different from mean DFT 9.4 ± 4J. ULV plus 5J successfully defibrillated 19 of 21 patients. During long-term follow-up of 10.1 ± 1.8 months in eight patients, DFT was 8.8 ± 5.8J, not significantly different than the DFT of 7.5 ± 4.1J or ULV of 8.0 ± 5.3 at implant. Conclusion: 1) When determined during normal sinus rhythm the ULV significantly correlates with DFT. 2) ULV testing might be used in lieu of standard DFT testing to confirm adequate lead placement thus minimizing or eliminating VF inductions, particularly in hemodynamically unstable patients. 3) Since ULV + 5J has a high probability of successful defibrillation in most patients, programming ICD first shock energy for VF at ULV + 5J may result in lower first shock energies compared to the standard methods of programming first shock energy at twice DFT. Condensed Abstract. The purpose of this study was to determine if the upper limit of vulnerability (ULV) determined during normal sinus rhythm correlates with the defibrillation threshold (DFT), as has been previously shown when determined during ventricular pacing. The linear correlation coefficient between the ULV and DFT was r = 0.73 (p 〈 0.001). Mean ULV at implant was 9.2 ± 5J, not statistically different from mean DFT of 0.4 ± 4J. During long-term follow-up of 10.1 ± 1.8 months in 8 patients, DFT was 8.75 ± 8J, not significantly different than the DFT of 7.5 ± 4.1J or ULV of 8.0 ± 5.3 at implant. Shocks energies of ULV + 5J successfully defibrillated 19 of 21 patients at implant and 8 of 8 at follow-up. This study indicates that the ULV determined in normal sinus rhythm closely correlates with the DFT, and that ULV + 5J defibrillated most patients. ULV testing could be used to predict DFT and reduce or eliminate the need for DFT testing and VF induction. Programming ICD first shock energy for VF to ULV + 5J will result in lower energy than that used with standard DFT testing.