Focal AF is frequently triggered by ectopic beats mostly originating from the pulmonary veins (PVs). So far, the morphological substrate for this entity is not well defined. Therefore, the distribution of myocardial cells within the PV were examined as potential target sites for RF application. The PVs (118) of 30 human autopsied hearts (age of death 63 +/- 13 years, 17 men) were dissected in their complete circumference starting 1 cm from the ostium. Tissue sections of the PV were stained with hematoxylin-eosin and with Masson's trichrome. To characterize the developmental state of the myocardial tissue in the PV, immunohistochemistry was performed with antibodies reacting with antigens which are stage specifically expressed during cardiac development (HNK1/Leu7, alpha-SMA, calponin and desmin). Furthermore, proliferative activity was assessed using antibodies against the Ki-67 antigen (MIB-1). In two hearts a left-sided common PV ostium was found. The other hearts showed four separated PV ostia. The ostium diameter of the right inferior PV (1.2 +/- 0.3 cm) was significantly smaller (P < 0.05) than remaining PV ostia (right superior 1.5 +/- 0.2, left superior, 1.5 +/- 0.3 and left inferior 1.4 +/- 0.3 cm) of the 118 specimen. There was no significant difference in the presence of myocardium in the PV 1-cm distant from the ostium comparing the right superior (78%), the right inferior (81 %), the left superior (81%), and the left inferior (81%) PV. In 54% of cases the myocardial bundles covered the complete PV circumference. In up to 38% of the small extensions of the myocardial bundles myocardial cells, characterized by distinct cross-striations and spindle shape were found. However, since these cells could not be labeled for other markers than desmin, their immature state seems unlikely. The anatomic distribution of myocardium in the PV suggests that RF applied to the entire circumference may be frequently required for its electrical isolation. Whether spindle-shaped myocytes have different electrophysiological behavior has to be further investigated.

This report describes the histopathological findings following successful RF isthmus ablation for common atrial flutter in a 68-years-old man using a long 8-mm tip ablation catheter. No acute complication was observed. The patient died 3 weeks after ablation due to severe heart failure and consecutive pneumonia. Lesion width (1.0 and 2.4 cm) and depth (0.4 and 0.8 cm) was measured. The right coronary artery showed an intramural hemorrhage adjacent to the side of the lesion. However, despite this finding no apparent injury of other layers of the coronary artery was detectable.

OBJECTIVE This randomized prospective study sought to assess the value of slow pathway (SP) mapping and ablation guided by subthreshold stimulation (STS) in comparison with a strategy based on conventional criteria.BACKGROUND Previous studies have demonstrated that STS can be used as a highly specific and sensitive marker for successful SP ablation in the setting of atrioventricular nodal re-entrant tachycardia (AVNRT). Nonetheless, thus far this mapping strategy has not been investigated in contrast with the conventional approach.METHODS One hundred patients with sustained AVNRT were included. Fifty patients (group A) were randomly assigned to endocardial mapping and SP ablation using currently established criteria. In the other 50 patients (group B), SP ablation was guided by STS mapping. Tn group B patients, only radiofrequency current (RFC) was applied if additionally constant current STS (up to 5 mA) during AVNRT interrupted the tachycardia due to selective block within the SP.RESULTS Termination of AVNRT without apparent capture was observed during STS in 47 of 50 group B patients (94%). In all cases, this effect was indicative for successful subsequent SP ablation, The mean number of RFC pulses required for successful SP ablation was significantly lower in patients assigned to the STS-guided strategy (1.6 +/- 1.3 vs. 3.9 +/- 3.4; p = 0.0003). Similarly, the mean procedure duration was shorter in the STS group (156.9 +/- 34.5 vs. 173.2 +/- 49.7 min; p = 0.0221); the fluoroscopy time was comparable between both groups (14.1 +/- 8.7 vs. 16.9 +/- 10.6 min; p = 0.1278).CONCLUSIONS Subthreshold stimulation is an effective method for detection of target sites for selective SP ablation. This technique helps to minimize the number of RFC pulses without prolongation of the overall procedure and fluoroscopy time required for SP ablation. (J Am Coil Cardiol 2001;3731645-50) (C) 2001 by the American College of Cardiology.

Introduction: Three-dimensional electroanatomic (CARTO) activation mapping of the cavotricuspid isthmus can be helpful to guide atrial flutter ablation, but to date has not been investigated in comparison to conventional strategies. The aim of the present study was to assess the efficacy of the CARTO navigation system, especially with respect to the fluoroscopy time required for successful atrial flutter ablation.Methods and Results: Eighty patients with recurrent common-type atrial flutter were randomly assigned to temperature-controlled radiofrequency (RF) catheter ablation, either guided by conventional criteria (group 1) or additionally oriented on electroanatomic mapping (group 2). In all patients, similar multipolar catheters were inserted into the coronary sinus and placed at the tricuspid annulus, respectively. In group 2, positioning of the mapping electrode and delivery of RF pulses within the cavotricuspid isthmus was mainly oriented on the CARTO map to achieve the most linear and continuous RF lesions. Abolition of intra-atrial conduction verified by conventional criteria (group 1) and electroanatomic mapping (group 2) could be verified in all patients. The overall number of RF pulses (group 1: 16.7 +/- 6.5; group 2: 13.2 +/- 5.3) and mean procedure duration (group 1: 172.5 +/- 47.4 min; group 2: 169.3 +/- 47.3 min) were not different between the two groups, but mean fluoroscopy time was significantly shorter when the CARTO technology was used (group 1: 29.2 +/- 9.4 min; group 2: 7.7 +/- 2.8 min; P = 0.0001). Recurrence of atrial flutter was observed in 3 (9%) patients in each group after a mean follow-up of 8.5 +/- 2.8 months.Conclusion: Atrial flutter can be abolished effectively using the conventional technique as well as oriented on electroanatomic mapping. However, overall X-ray exposure can be significantly reduced by the CARTO-guided approach without prolongation of procedure duration.

Induction of complete bidirectional conduction block via the posterior isthmus of the right atrium is introduced as a standard endpoint for catheter ablation of atrial flutter. The present study sought to investigate the impact of changes in P wave duration and morphology detected by the surface ECG during coronary sinus and posterolateral right atrial stimulation as a marker for conduction block. Morphology and duration changes of the paced P wave before and after radiofrequency catheter (RFC) ablation were estimated in 22 patients referred for ablation of atrial flutter. We looked for a morphology change of the terminal portion in the 12‐lead ECG and an increment of P wave duration. In 16 of 22 patients in whom atrial flutter ablation resulted in a complete bidirectional block, the conduction block was unidirectional in 4 patients and conduction times remained unchanged in 2 patients. After induction of complete bidirectional block a change of the terminal portion of the P wave towards a more positive morphology in one or more inferior leads was detected in 14 (88%) of 16 patients during coronary sinus stimulation and in 15 (94%) of 16 patients during posterolateral right atrial stimulation. These changes were predominantly observed in the inferior leads. Positive morphology changes of the terminal P wave portion in the inferior leads indicating conduction block with a sensitivity of 86% and a specificity of 100% were observed. An increment of 10 ms or more in P wave duration indicates conduction block with a specificity of 100% and a sensitivity of 67%. There was a significantly larger increment of P wave duration during coronary sinus (CS) stimulation compared to posterolateral right atrial stimulation (38 ± 21 vs 16 ± 21 ms). The analysis of P wave duration and morphology in the inferior leads of the surface ECG is a reliable tool to assess the intraatrial conduction after atrial flutter ablation. Different conduction during coronary sinus and pos‐terolateral right atrial pacing may cause a different P wave duration after ablation.

Catheter ablation orientated on the induction of a functional intraatrial block within the posterior isthmus of the tricuspid annulus has been shown to effectively abolish atrial flutter. In order to improve and simplify the current technique, a strategy based on an electrode catheter for combined right atrial and coronary sinus mapping and stimulation was explored prospectively. Twenty‐four consecutive patients referred for catheter ablation of recurrent type I atrial flutter were included. A steerable 7 Fr catheter (Medtronic/Cardiorhythm) composed of two segments with 20 electrodes was used for right atrial and coronary sinus activation mapping and stimulation. Multiple steering mechanisms allowing intubation and positioning of the distal part within the coronary sinus were incorporated into the device. Adequate positioning of the mapping catheter was achieved solely via a transfemoral approach in all patients after 7.7 ± 4.6 minutes, providing stable electrogram recordings during the entire ablation procedure. Radiofrequency current ablation (16.3 ± 9.6 pulses) caused a significant bidirectional increase of the mean intraatrial conduction times via the posterior isthmus irrespective to the stimulation interval. Significant changes of intraatrial conduction properties were induced during ablation in 22 of 24 patients (bidirectional block: n = 18, unidirectional block: n = 3, conduction delay: n = 1, unchanged conduction: n = 2). Following ablation atrial flutter was noninducible in all patients. Twenty‐two of 24 patients (92%) remained free of atrial flutter episodes during a follow‐up of 12.5 ± 5.7 months. Two of six patients without a bidirectional conduction block had a recurrence of atrial flutter. Atrial flutter ablation guided by the induction of an intraatrial conduction block can be effectively performed with this novel strategy for combined mapping of the posterior tricuspid isthmus, including coronary sinus and right atrial free wall. This transfemoral approach has a high accuracy with respect to the detection of radiofrequency current‐induced changes of intraatrial conduction patterns.