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Notes: The typical fourth criterion for transient entrainment is defined when both a sudden shortening in conduction interval to and a distinct change in electrogram morphology at a bipolar recording site are demonstrated while performing overdrive pacing of a reentrant tachycardia from a single pacing site at two different constant rates. The purpose of this article was to test the hypothesis that if an intracardiac recording site showing both orthodromic and antidromic capture with entrainment pacing is located suitably distant from the circuit, sudden shortening in conduction interval to that site may occur without any significant change in the bipolar electrogram morphology (i.e., atypical form of the fourth criterion). Atrial overdrive pacing of orthodromic tachycardia was performed in 20 patients with either left anterior (12 patients) or left posterior (8 patients) accessory pathways. We investigated the effects of overdrive pacing from the proximal or distal coronary sinus, specifically effects on the electrogram interval and the electrogram morphology at the right atrial appendage. Overdrive pacing of orthodromic tachycardia from the proximal coronary sinus was performed in 10 of the 12 patients with left anterior accessory pathways; those 10 patients demonstrated the first entrainment criterion at the right atrial appendage site. Overdrive pacing of orthodromic tachycardia at still shorter cycle lengths demonstrated a sudden shortening in conduction interval to the right atrial appendage site. Despite shortening in conduction interval the morphology of the right atrial appendage electrogram was completely or almost identical to that during orthodromic tachycardia, indicating an atypical form of the fourth criterion. This criterion was not demonstrated in patients with left posterior accessory pathways. Thus, atypical fourth entrainment criterion was demonstrated during overdrive pacing of orthodromic tachycardia from the proximal coronary sinus only in patients with left anterior accessory path ways. Demonstration of atypical fourth criterion seems largely dependent on the location of the accessory pathway, the pacing, and the recording sites.

Notes: KISHI, R., et al.: Influence of Mobile Magnetic Resonance Imaging on Implanted Pacemakers. Purpose: Mobile magnetic resonance imaging (MRI) systems will be widely used in Japan. When traveling, mobile MRI generate alternating electromagnetic waves which may cause electromagnetic interference (EMI). This study was designed to determine whether this may influence the function of implanted pacemakers (PM). Methods and Results: The influence of the static magnetic fields was tested in the first method using a PM-human model (Phantom). Magnetic force was simultaneously measured. The PM was switched to the magnet mode within 90 cm from the vehicle, where the magnetic force was = 2 mT. In the second method, six phantoms were placed on the side of the road, facing in three different directions in X-Y-Z axis orientations, at 1.3 m and 2.0 m above the ground. The mobile MRI passed by at a distance of 1 m from the phantoms at the speed of 20 or 40 km/h. In these experiments, magnet mode switch of the PM was observed for 2 seconds when the vehicle passed close to the phantoms, though no electrical noise was recorded. Conclusion: Mobile MRI vehicles can switch a PM to magnet mode when the distance between patient and vehicle is 〈90 cm, regardless of whether the vehicle is moving or at a stop. Patients with implanted PM should not approach within 〈1 m of a mobile MRI. No other EMI-induced PM dysfunction was detected. (PACE 2003; 26[Pt. II]:527–529)

Notes: In drug refractory and highly symptomatic atrial fibrillation (AF) patients, hemodynamic effects of AV node ablation and pacing therapy (APT) were evaluated. Thirty-eight patients with drug refractory and symptomatic AF, underwent APT in eight centers in Japan. The outcome of this therapy was assessed in terms of quality-of-life, cardiac performance measured by echocardiogram, and plasma ANP and BNP levels before and after APT. Quality-of-life assessed by self-administered semiquantitative questionnaires: WHO QOL 26 ( 3.0 ± 0.5 vs 3.4 ± 0.6, P 〈 0.01 ) and the Symptom Checklist: Frequency Scale ( 1.6 ± 0.6 vs 0.7 ± 0.7, P 〈 0.01 ) and Severity Scale ( 1.3 ± 0.4 vs 0.6 ± 0.6, P 〈 0.01 ), improved significantly 6 months after APT. Ejection fraction (EF) by echocardiogram improved 1 week after APT ( 59.0%± 13.3% vs 63.3%± 11.6%, P = 0.02 ). Plasma ANP levels in the group of ANP 〉 40 pg/mL at enrollment significantly decreased 1 month later (P = 0.03) , and plasma BNP levels in the group of BNP 〉 20 pg/mL at enrollment significantly decreased 1 month later (P 〈 0.01) . In conclusion, APT has beneficial hemodynamic effects, and plasma BNP levels can predict the most optimal candidates for ablation and pacing therapy. (PACE 2003; 26:1212–1217)

Notes: Objective: To identify target sites for radiofrequency ablation of ventricular tachycardia (VT) by entrainment mapping techniques in patients with arrhythmogenic right ventricular dysplasia. Methods: Entrainment mapping and radiofrequency ablation of eight VTs was performed in seven patients. Radiofrequency ablation was applied at 31 reentry circuits sites that were classified based on findings during entrainment. Results: By entrainment criteria the 31 sites were classified as: exit sites (n = 12), proximal sites (n = 6), and outer loop sites (n = 13). Radiofrequency current application terminated VT at 7 of 31 sites: 2 of 12 exit sites (17%), 4 of 6 proximal sites (67%), and 1 of 13 outer loop sites (8%). Conclusion: Radiofrequency ablation terminated VTs most often at sites proximal to the exit as opposed to outer loop sites and exit sites (P = 0.05). The critical isthmus for ablation of VT in right ventricular dysplasia often may be distant to the exit.

Notes: Reentrant VT Post MI. Introduction: For relatively slow monomorphic ventricular tachycardia (VT) after myocardial infarction, entrainment can be used to identify reentry circuit “isthmus sites” (exit sites and sites proximal to the exit) where radioifrequency (RF) catheter ablation has the greatest likelihood of interrupting reentry. Similarities in coronary and ventricular anatomy may cause such sites to form in preferential locations. The objective of this study is to determine if there are preferential locations for reentry circuit isthmus regions in chronic inferior wall infarctions causing VT. Methods and Results: Catheter mapping and RF catheter ablation was performed in 21 patients with an old inferior wall myocardial infarction and VT. The inferior wall was divided into 9 anatomic regions: 3 apical, 3 mid, and 3 basal segments. Of 46 different VTs, an endocardial isthmus site was identified in one or more zones in 28 (61%), with 10 VTs having isthmus sites in two or more adjacent regions. Isthmus zones were found in a basal region of the left ventricle in 24 (86%) of 28 VTs, in a mid segment in 9 (32%) VTs, and in an apical segment in 1 (4%) (P = 0.002). Of 30 RF current applications that terminated VT, 21 (70%) were at basal isthmus sites. Conclusion: The high prevalence of endocardial isthmus zones near the base of the left ventricle suggests that the mitral annulus often plays a role in defining the margins of reentry circuits that cau.se relatively slow VTs after inferior wall myocardial infarction.

Notes: Postpacing Interval and VTCL. Introduction: During entrainment of reentrant ventricular tachycardia (VT), the difference between the postpacing interval (PPI) and the VT cycle length (VTCL) measured at the pacing site is an indication of the conduction time from the pacing site to the reentry circuit. The difference is usually ≤ 30 msec at successful ablation sites. However, electrical noise during pacing sometimes obscures the electrograms recorded directly from the pacing site. The objective of this study is to determine if the PPI-VTCL difference measured at the mapping catheter electrodes proximal to the stimulating electrode accurately predicts the PPI-VTCL difference at the stimulating electrode. Methods and Results: Endocardial catheter mapping was performed in 26 patients with in-farct-related VT. At 191 sites during 56 VTs, unipolar pacing from the distal electrode entrained VT and electrograms recorded from the mapping catheter were discernable following pacing in both the bipolar recordings from the distal electrode pair (BI 1–2) and the electrode pair 6 mm proximal to the distal electrode (BI 3–4). The PPI-VTCL difference at BI 1–2 correlated well with that measured at BI 3–4 (r = 0.88, P = 0.001). A PPI-VTCL difference at BI 3–4 ≤ 30 msec predicted a PPI-VTCL difference at BI 1–2 ≤ 30 msec with a sensitivity of 95%, specificity of 87%, and predictive accuracy of 91 %. Conclusions: Measurement of the PPI from electrodes proximal to the stimulating electrode is a reasonable alternative when the PPI cannot be assessed from the pacing electrode.