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Stephan Willems

Publications and source records attributed to Stephan Willems.

25 records · Page 2Linked to original sources
PubMed2003

Electrical disconnection of an arrhythmogenic superior vena cava with discrete radiofrequency current lesions guided by noncontact mapping.

This case describes a 54-year-old patient with paroxysmal atrial fibrillation and atrial flutter. Conventionally recorded local electrogram demonstrated a cycle length of 245 ms in the SVC which was conducted to the right atrium in a 2:1 fashion. The analysis of the virtual unipolar local electrogram from the noncontact mapping system demonstrated slow conduction between SVC and right atrium orthogonal to the atrial breakthrough in the upper part of the crista terminalis. RF ablation at the atrial breakthrough induced the electrical disconnection between the CVC and the right atrium.

Atrial Fibrillation↗
PubMed2002

Functional disconnection of arrhythmogenic pulmonary veins in patients with paroxysmal atrial fibrillation guided by combined electroanatomical (CARTO) and conventional mapping.

BACKGROUND: Isolation of arrhythmogenic pulmonary veins (PVs) by radiofrequency current (RF) application has been introduced as a curative treatment for patients (pts) with paroxysmal atrial fibrillation (AF). The present study sought to investigate the feasibility and efficacy of this approach guided by conventional and electroanatomical mapping (CARTO). METHODS: Twenty pts (13 male; 57 +/- 8 years) with recurrent documented focally triggered idiopathic AF refractory to multiple antiarrhythmic drugs were prospectively included. Atrial premature beats were present at baseline in 9 pts and could be provoked in further 8 pts. Empirical ablation of both superior PVs was performed in 3 pts with no focal activity. After transseptal puncture selective angiography of all PVs was obtained. Thirty-six PVs (left superior: n = 18, right superior: n = 10, left inferior: n = 8) were targeted for RF ablation. A complete left atrial CARTO-map including the left atrial (LA) to pulmonary vein (PV) junction was obtained during sinus rhythm and/or coronary sinus pacing. RF was initially applied at the PV-LA junction at areas with the shortest left atrial- to PV potential interval (target 50 degrees C, max. 30 W, duration 60 sec). Isolation was confirmed by the complete disappearance of specific PV potentials. RF lesions were analyzed with respect to the number of segment-quarters covering the PV ostium. RESULTS: Functional isolation could be achieved in 35 out of 36 PVs following 10 +/- 5 RF applications for each PV. RF applications covered 2 or less quarter segments of the overall PV circumference in 29 (80%) PVs. Total session duration was 6.5 +/- 1.6 h with a mean fluoro-time of 54 +/- 18 minutes. For CARTO mapping and ablation a mean fluoro time of 34 +/- 6 min was required. During a mean follow up period of 8.3 +/- 2.5 months AF relapsed in 9 pts (46%). A second approach was performed in 5 pts. and demonstrated either new foci (n = 2) or recurrence of previously isolated PV (n = 8). The second RF ablation procedure led to stable sinus rhythm in 3 out 5 pts. Thus, the overall success rate including the second procedure was 70%. CONCLUSIONS: CARTO guided functional isolation of presumed arrhythmogenic PVs by RF lesions covering 2 or less segments of the PV ostium in most patients is feasible. However, repeat procedures are often warranted to permanently treat paroxysmal atrial fibrillation.

Adult↗
PubMed2002

Radiofrequency catheter ablation using cooled electrodes: impact of irrigation flow rate and catheter contact pressure on lesion dimensions.

Irrigation of radiofrequency current (RF) ablation reduces the risk of thrombus formation. The aim of this study was to investigate the impact of different irrigation catheter flow rates and contact pressures from the catheter on the development of lesion dimension and thrombus formation. A thigh muscle preparation was achieved in six sheep to create a cradle that was filled and perfused with heparinized blood (250 mL/min, 37 C degrees). RF ablation (30 s, 30 W) was initially performed with three different irrigation flow rates (5 mL/min, 10 mL/min, and 20 mL/min) and a perpendicular position (0.1 N contact pressure) of the irrigated ablation catheter ("Sprinklr," Medtronic, Inc., Minneapolis, MN, USA). The next lesions were induced with constant contact pressure of 0.05 Newton (N); 0.1 N; 0.3 and 0.5 N and a parallel or perpendicular orientation of the catheter, respectively. A constant irrigation flow of 10 mL/min was maintained during these RF applications. Cross sections of the lesions were investigated with regard to maximal depth and maximal diameter at and below the surface. During high flow irrigation (20 mL/min) the surface diameter was significantly smaller (0.63 +/- 0.1 cm) compared to irrigation flowrates of 5 mL/min (0.88 +/- 0.2 cm) and 10 mL/min (1 +/- 0.1 cm). Thrombus formation was not observed during any RF application. Only in perpendicular catheter orientations with a contact pressure of 0.5 N were significantly deeper lesions (0.85 +/- 0.12 cm) induced compared to 0.05 N (0.55 +/- 0.02 cm), 0.1 N (0.7 +/- 0.01 cm) and 0.3 N (0.67 +/- 0.01 cm) contact pressure. There was no significant difference in lesion depth with different flow rates. Irrigated RF ablation even with low flow rates and high catheter contact pressure prevented thrombus formation at the electrode. Smaller lesion diameters have been created with high irrigation flow rates. The deeper lesion created with high catheter contact pressure might be caused by a greater power transmission to the tissue.

Animals↗
PubMed2002

Can radiofrequency current isthmus ablation damage the right coronary artery? Histopathological findings following the use of a long (8 mm) tip electrode.

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.

Aged↗
PubMed2002

Impact of the distribution and structure of myocardium in the pulmonary veins for radiofrequency ablation of atrial fibrillation.

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.

Atrial Fibrillation↗
PubMed2002

Atrial premature beats in patients with focal atrial fibrillation: incidence at baseline and impact of provocative maneuvers.

This study evaluated the incidence of atrial premature beats (APBs) and the impact of various provocative maneuvers in patients with focally initiated AF. Fifty patients (39 men, 57 +/- 0.4 years) with focally initiated, paroxysmal AF underwent Holter recording and a standardized protocol of provocative maneuvers: vagomechanical stimulation, adenosine 12 mg i.v., esmolol 500 ng/kg i.v., orciprenaline i.v. 5 mg/50 mL saline 0.9%, and atropine 0.01 mg/kg i.v. A surface ECG was recorded for 20 minutes at baseline and following each part of the protocol. High focal activity was defined as > or = 1 APB/minute. During Holter ECG, 29 (58%) patients had an amount of < 200 APBs, 12 (24%) patients < 700 > or = 200, and 9 (18%) patients > or = 700 APBs. Less than 1 hour of high focal activity was observed in 34 (68%) of the 50 patients. Before starting provocative maneuvers 15 (30%) patients had high focal activity whereas 35 (70%) presented < 1 APB/minute. In 29 (58%) patients APBs increased by > or = 1/min during provocative maneuvers: by vagomechanical stimulation in 11 patients, after adenosine in 15, esmolol in 12, orciprenaline in 15, and after atropine in 9 patients. In all patients with > or = 1 APB/min at baseline, focal activity decreased or disappeared during some single provocative maneuvers. AF occurred in eight patients under provocative maneuvers. No predictive factors of a successful provocative maneuver were detected with regard to the baseline patients characteristics and Holter results. In conclusion, patients with focally initiated AF have a low incidence of spontaneous APBs. Various provocative maneuvers successfully increase APBs in more than half of the patients; orciprenaline had the highest efficacy. Some provocative maneuvers may suppress APBs in the setting of high focal activity at baseline.

Adenosine↗