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F Halimi

Publications and source records attributed to F Halimi.

17 recordsLinked to original sources
PubMed2004

[Hypertension and age over 70 years are the two most important risk factors for stroke in patients with atrial fibrillation].

In a registry of 250 patients treated for atrial fibrillation (160 recurrent, 90 permanent forms), we prospectively looked for associated risk factors for cerebrovascular complications. After a 4-years follow-up, 19 patients had presented a cerebral accident (13 strokes, 4 transient ischemic attacks, 2 cerebral hemorrhages). Prognostic factors for cerebrovascular complications were hypertension, valvular heart disease, and age > or = 70 years. When restricting the analysis to stroke and transient ischemic attacks, prognostic factors were limited to hypertension and age > or = 70 years. In conclusion, hypertension and age > or = 70 years are the main independent risk factors for cerebral ischemic attacks in out-of-hospital patients treated for atrial fibrillation.

Age Factors↗
PubMed2003

[Atrial vulnerability: a new protocol by bigeminy pacing].

INTRODUCTION: There is little information available on the events that mediate short term remodeling. In a bigeminy atrial-pacing protocol, we sought to evaluate the electrophysiological consequences of an irregular short-long cycle length atrial pacing. METHODS AND RESULTS: This study included 22 consecutive patients with documented arrhythmias and 10 control subjects. After evaluating the effective and functional refractory periods, bigeminy atrial pacing was performed for 5 min. During bigeminy pacing, in 12 AF patients and in none of the control subjects, AF was started lasting longer than 1 minute (Group I). Short salvos of AF occurred in five patients and three controls (Group II) and no arrhythmia occurred in five patients and seven controls (Group III). Sensitivity, specificity, negative and positive predictive values of sustained AF induced by bigeminy pacing were 54%, 100%, 50% and 100%, respectively. Atrial refractory periods measured immediately after termination of 5 minutes of bigeminy pacing were shorter than during baseline. The degree of shortening was similar in AF patients and in controls. The loco-regional conduction did not change after the bigeminy protocol. CONCLUSION: This study demonstrates that atrial bigeminy pacing unmasks latent atrial vulnerability.

Atrial Fibrillation↗
PubMed2000

Ventricular tachycardia catheter ablation in arrhythmogenic right ventricular dysplasia: a 16-year experience.

Arrhythmogenic right ventricular dysplasia (ARVD) is a structural heart disease affecting young adults that leads to cardiac rhythm disorders including supraventricular and mostly ventricular arrhythmias. Sudden death may be the first presentation of the disease. Ablation techniques have been used for the treatment of ventricular tachycardia in cases resistant to drug therapy. Radiofrequency is appropriate as a first approach for ventricular tachycardia ablation in ARVD; however, its effectiveness is less than 40% at the first session. Fulguration is effective for ventricular tachy-cardia ablation and should be used in the same session after ineffective radiofrequency ablation. However, fulguration requires expertise, general anesthesia, and more than one session in half of all patients. Radiofrequency and fulguration plus other common forms of treatment including pacemakers and automatic implantable cardioverter defibrillators provides a clinical success rate of 81% to 93% in a series of 50 consecutive patients studied during 16 years. Earlier poor reputation of fulguration was the result of poorly understood technical problems concerning the physics and biophysics of the procedure under control with presently available methods. This in-depth study of a large population over a long time period demonstrates that fulguration should be rehabilitated.

Adolescent↗
PubMed2000

Electrophysiological determinants of atrial fibrillation in sinus node dysfunction despite atrial pacing.

AIMS: The effectiveness of atrial pacing in reducing the incidence of atrial fibrillation in patients with sinus node dysfunction is incomplete, and the correlation between electrophysiological atrial properties and the effect of permanent atrial pacing has been poorly investigated. Accordingly, the aim of the present study was to correlate electrophysiological data, in terms of atrial refractoriness, conduction parameters, and propensity to atrial fibrillation induction, and the likelihood of atrial fibrillation after DDD device implantation. METHODS AND RESULTS: The authors reviewed electrophysiological data of 41 patients with sinus node dysfunction (mean age 70 +/- 8 years, who were investigated free of anti-arrhythmic treatments before pacemaker implantation. At a drive cycle length of 600 ms, effective and functional refractory periods, S1-A1 and S2-A2 latency, A1 and A2 width, and latent vulnerability index (effective refractory period [ERP] A2), were measured. Atrial fibrillation induction was tested with up to three extrastimuli in 34 patients. Induction of sustained atrial fibrillation (> 1 min) was considered as the end-point. P-wave duration on the surface ECG in lead II/V1 was also measured. Minimal atrial rate was programmed between 60 and 75 bpm (mean: 64 +/- 4 bpm). After implantation, the patients were followed-up for 28 +/- 17 months, and ECG-documented occurrence of atrial fibrillation was determined. Electrophysiological characteristics of patients with (n = 12) or without (n = 29) paroxysmal atrial fibrillation before implantation were similar. When comparing patients with (n = 11) or without (n = 30) post-pacing atrial fibrillation occurrence, no differences were found in age, underlying heart disease, left atrial size, minimal pacing rate, and follow-up duration. Additionally, between the two former groups, there was no significant difference in terms of effective refractory periods (233 +/- 47 ms vs 239 +/- 25 ms), functional refractory periods (280 +/- 48 ms vs 272 +/- 21 ms), S1-A1 (44 +/- 20 ms vs 37 +/- 13 ms) and S2-A2 latency (77 +/- 28 ms vs 66 +/- 22 ms), and A1 duration (60 +/- 23 ms vs 53 +/- 16 ms). In contrast, in patients with post-pacing atrial fibrillation occurrence, the P wave was more prolonged (116 +/- 22 ms vs 98 +/- 13 ms; P < 0.01), A2 was longer (116 +/- 41 ms vs 87 +/- 27 ms; P < 0.01), effective refractory periods/A2 was lower (2.1 +/- 0.4 cm vs 3.1 +/- 1.4 cm; P < 0.05), and rate of atrial fibrillation induction was higher (8/11 patients vs 8/23 patients; P < 0.05). Electrophysiological characteristics of patients free of post-pacing atrial fibrillation with associated (n = 6) or unassociated (n = 24) paroxysmal atrial fibrillation history before implantation were quite similar. In patients with post-pacing atrial fibrillation with associated (n = 6) or unassociated atrial fibrillation history (n = 5) before implantation, effective refractory periods was statistically different (207 +/- 23 ms vs 264 +/- 46 ms; P < 0.05). Values of effective refractory periods < 220 ms were significantly more frequent in patients with post-pacing atrial fibrillation than in patients without (4/11 patients vs 2/30 patients; P < 0.05). When comparing patients with post-pacing atrial fibrillation with effective refractory periods > or = 220 ms (n = 7) and < 220 ms (n = 4), A2 duration was remarkably prolonged (145 +/- 42 ms vs 90 +/- 11 ms; P < 0.05) in those with effective refractory periods > or = 220 ms. By contrast, between the two groups, effective refractory periods/A2 were identical (2.08 +/- 0.6 cm vs 2.15 +/- 0.3 cm; P = n.s.). CONCLUSION: Prolonged atrial refractoriness, lesser degrees of conduction disturbance and a lower rate of atrial fibrillation induction seem to be predictive of stable sinus rhythm. In contrast, patients with persistence of atrial fibrillation despite pacing have a more abnormal and inhomogeneous atrial substrate, as well as a higher rate of atrial fibrillation induction. Prolonged P wave, shortened refractoriness, or remarkably abnormal conduction disturbances in the presence of prolonged refractoriness limit the effectiveness of standard atrial pacing in atrial fibrillation prevention. Identification of predictive criteria of failure of single-site atrial pacing may be used to consider dual-site atrial pacing in such patients with sinus node dysfunction.

Aged↗
PubMed2000

Is dual site better than single site atrial pacing in the prevention of atrial fibrillation?

Long-term prevention of atrial fibrillation is not constantly realized by single-site right atrial pacing, and the beneficial role of multisite atrial pacing is still being studied. Accordingly, we compared the effectiveness of dual site and single site atrial pacing in 83 patients (50 men, 33 women, aged 69 +/- 10 years), who received a DDD device for primary sinus node dysfunction or bradycardia with documented atrial fibrillation. Inclusion criteria for dual site pacing were a sinus P wave > or = 120 ms and at least two episodes of documented paroxysmal AF in the 6 months preceding implantation. Dual site atrial pacing (high right atrium-coronary sinus ostium) was performed in 30 cases, and was compared to 53 single site paced patients, 21 with a P wave > or = 120 ms and 32 with a P wave < 120 ms. The basic pacing rate was programmed at 68 +/- 4 beats/min (range 60-75 beats/min). Sinus P wave (133 +/- 20 vs 95 +/- 9 ms; P < 0.001), paced P wave (107 +/- 14 vs 99 +/- 15; P < 0.05), number of antiarrhythmic drugs used (2.4 +/- 1.2 vs 1.6 +/- 1.5, P < 0.05), and the duration of symptoms (8.1 +/- 4.5 vs 3.8 +/- 2.4 years; P < 0.001) were significantly higher in dual site patients. The other characteristics were similar. During the follow-up of 18 +/- 15 months (range 3-30 months), paroxysmal AF was documented in 33 patients. Among these patients, 13 developed permanent AF following at least one episode of paroxysmal AF. When comparing dual site patients and single site patients with a P wave duration > or = 120 ms, paroxysmal AF incidence was lower in the dual site group (9/30 patients vs 15/21 patients, P < 0.01), as well as permanent AF (1/30 patients vs 8/21 patients, P < 0.01). By contrast, comparison between dual site patients and the group of single site patients with a P wave duration < 120 ms did not evidence any significant differences in paroxysmal (9/30 patients vs 9/32 patients) and permanent (1/30 patients vs 4/32 patients) AF incidences. Dual site seems better able than single site atrial pacing to improve the natural history of patients with a prolonged P wave, reducing the incidence of paroxysmal and permanent AF. No benefit could be expected in patients with a normal P wave duration.

Aged↗
PubMed2000

Electrophysiological characteristics of the atrium in sinus node dysfunction with and without postpacing atrial fibrillation.

In patients with sinus node dysfunction (SND) with or without associated paroxysmal atrial fibrillation (AF), the effectiveness of atrial pacing in reducing the incidence of AF is not definitive. In addition, despite several studies involving large populations of implanted patients, little attention has been paid to the electrophysiological (EP) atrial substrate and the effect of permanent atrial pacing. The aim of this study is to correlate EP data and the risk of AF after DDD device implantation. We reviewed EP data of 38 consecutive patients with SND, mean age 70 +/- 8 years, who were investigated free of antiarrhythmic treatment, for the evaluation of the atrial substrate. We also considered as control group 25 subjects, mean age 63 +/- 14 years, referred to our EP laboratory for unexplained syncope or various atrioventricular disturbances. Following pharmacological washout and at a drive cycle length of 600 ms, effective and functional refractory periods (ERP, FRP), S1-A1 and S2-A2 latency, A1 and A2 conduction duration, and latent vulnerability index (ERP/A2) were measured. AF induction was tested with up to three extrastimuli at paced cycle lengths of 600 and 400 ms in 20 patients. Induction of sustained AF (> 30 seconds) was considered as the endpoint. P wave duration on the surface ECG in lead II/V1 was also measured. DDD pacing mode was chosen in all patients with the minimal atrial rate programmed between 60 and 75 beats/min (mean 64 +/- 4 beats/min). After implantation, the patients were followed-up for 29 +/- 17 months and clinically documented occurrence of AF was determined. When comparing patients with SND and subjects of the control group, we did not find any significant statistical differences in terms of ERP (237 +/- 33 vs 250 +/- 29 ms), FRP (276 +/- 30 vs 280 +/- 32 ms) and S1-A1 (39 +/- 16 vs 33 +/- 11 ms) and S2-A2 latency (69 +/- 24 vs 63 +/- 25 ms). In contrast, we observed significant differences regarding A1 (55 +/- 19 vs 39 +/- 13 ms; P < 0.001), A2 (95 +/- 34 vs 57 +/- 18 ms; P < 0.001) and P wave duration (104 +/- 18 vs 94 +/- 15 ms; P < 0.05), and ERP/A2 (2.8 +/- 1.2 vs 4.8 +/- 1.6; P < 0.001). When comparing patients with (n = 11) or without (n = 27) postpacing AF occurrence, we did not find any difference with reference to ERP, FRP, S1-A1, S2-A2, A1 duration, or follow-up duration. In patients with postpacing AF occurrence, A2 was longer (116 +/- 41 vs 87 +/- 27 ms; P < 0.01), ERP/A2 lower (2.1 +/- 0.4 vs 3.1 +/- 1.4; P < 0.05), P wave more prolonged (116 +/- 22 vs 99 +/- 14 ms; P < 0.01), and preexisting AF history predominant (6/11 vs 5/27 patients; P < 0.05). No difference was observed between patients with (n = 8) and without (n = 12) AF induction during the EP study. In patients with SND, the atrial refractoriness appears normal and the most important abnormality concerns conduction slowing disturbances. Persistence of AF despite pacing stresses the importance of mechanisms responsible for AF not entirely brady-dependent. In this setting, more prolonged atrial conduction disturbances, responsible for a low vulnerability index, and a preexisting history of AF enable us to identify a high risk patient group for AF in the follow-up.

Adult↗
PubMed2000

Low chronic pacing thresholds of steroid-eluting active-fixation ventricular pacemaker leads: a useful alternative to passive-fixation leads.

Active-fixation pacemaker leads enable pacing at various sites, have a low dislodgment rate, and are easier to extract than passive-fixation leads, though are usually not routinely implanted in the ventricle because of their higher pacing threshold. The long-term pacing threshold associated with an active-fixation steroid-eluting lead was prospectively measured in 18 women and 20 men. At a mean follow-up of 14 months (range 3-25 months), pacing threshold increased from 0.71 +/- 0.29 V to 0.96 +/- 0.28 V (P = 0.01) between implant and the first month of follow-up, then remained stable over time, consistently allowing the long-term programming of the ventricular output at 2.5 V, while lead impedance remained stable (from 647 +/- 161 omega at implant to 666 +/- 122 omega at last follow-up). If the long-term performance of this type of lead is confirmed, the routine implantation of ventricular steroid-eluting active-fixation leads should be considered since lead extraction has become a major concern.

Adult↗
PubMed2000

Electrophysiologic characteristics of the atrium in sinus node dysfunction: atrial refractoriness and conduction.

INTRODUCTION: Clinical electrophysiology (EP) has focused attention on the EP properties of atrial muscle in patients with atrial fibrillation (AF). Patients with sinus node dysfunction (SND) sometimes are included in these studies, but the characteristics of these patients with SND alone appear less well investigated. METHODS AND RESULTS: We reviewed EP data of 46 patients (mean age 70 +/- 8 years) with SND, who underwent EP study for evaluation of the atrial substrate. In 16 patients, a history of paroxysmal AF was documented, but not in the remaining 30 patients who had SND alone. We considered as control a group of 25 subjects (mean age 63 +/- 14 years), who were referred to our EP laboratory for unexplained syncope or AV conduction disturbances. Following pharmacologic washout and at a drive cycle of 600 msec, effective (ERP) and functional refractory periods (FRP), S1-A1 and S2-A2 latency, A1 and A2 width, latent vulnerability index (ERP/A2), and P wave duration on the surface ECG were measured. Intra-atrial conduction times were measured from the stimulus artifact by pacing the high right atrium (HRA), to the corresponding atriograms at the AV node (HRA-AVN), low lateral atrium (HRA-LLA), and low interatrial septum close to the coronary sinus ostium (HRA-CSO). Compared with the control group, SND patients did not show differences in ERP (238 +/- 26 msec vs 250 +/- 29 msec), FRP (274 +/- 25 msec vs 280 +/- 32 msec), S1-A1 (38 +/- 15 msec vs 33 +/- 11 msec) and S2-A2 latency (67 +/- 24 msec vs 63 +/- 25 msec), or HRA-AVN (81 +/- 24 msec vs 65 +/- 19 msec), HRA-LLA (36 +/- 30 msec vs 40 +/- 27 msec), and HRA-CSO (77 +/- 17 msec vs 80 +/- 15 msec) conduction times. In contrast, we observed strong differences in atriogram durations A1 (59 +/- 19 msec vs 39 +/- 13 msec; P < 0.001) and A2 (92 +/- 28 msec vs 57 +/- 18 msec; P < 0.001), as well as in the latent vulnerability index ERP/A2 (2.8 +/- 1.2 msec vs 4.8 +/- 1.7; P < 0.001). Also, the P wave was slightly longer (104 +/- 18 msec vs 94 +/- 45 msec; P < 0.05). No significant statistical difference in EP parameters was found between SND patients with or without documented AF. CONCLUSION: In patients with SND, atrial refractoriness appears similar to that of control subjects. The most important EP abnormality appears to be local conduction slowing disturbances, with prolonged basal and postextrastimuli atriograms, responsible for a lower vulnerability index. This could explain, at least in part, the tendency of patients with SND to develop AF during their natural history. Normality of atrial refractoriness, in contrast to atrial conduction disorders, might explain why atrial pacing shows a preventative effect on the development of AF and why antiarrhythmic drugs often are ineffective.

Aged↗
PubMed2000

[Burst of idiopathic ventricular tachycardia complicated by arrhythmia-induced cardiomyopathy].

The authors report the case of a young man with idiopathic ventricular tachycardia occurring in bursts and arising from the pulmonary infundibulum. During follow-up, progressive, severe, dilated cardiomyopathy was observed. Radiofrequency ablation of the site of origin of this very active arrhythmia resulted in total regression of the cardiomyopathy. Contrary to generally accepted concepts, paroxystic ventricular tachycardia, usually qualified as benign, may be complicated by cardiomyopathy when the ventricular extrasystole is incessant and repetitive.

Adult↗
PubMed1999

Radiofrequency catheter ablation of common atrial flutter: role of the eustachian valve.

INTRODUCTION: During radiofrequency catheter ablation of a common atrial flutter between the tricuspid annulus and the Eustachian valve "septal isthmus", double potentials were recorded along the Eustachian valve, previously described as an anatomical line of conduction block between the coronary sinus ostium and the inferior vena cava. RESULTS: Just before flutter termination, lengthening and beat to beat delay variations between the 2 components of the double potentials were correlated with simultaneous modifications of the flutter cycle length. CONCLUSION: The "septal isthmus" is a common pathway for the flutter wavefront and the impulse generating the second component of the double potential. It is also a good target for flutter ablation.

Adult↗
PubMed1999

Sick sinus syndrome with and without atrial fibrillation: atrial refractoriness and conduction characteristics.

BACKGROUND: Clinical electrophysiology has focused the attention on the electrophysiological properties of the atrial muscle in patients with atrial fibrillation: shortened and inhomogeneous refractoriness and local and regional conduction slowing, as well as prolonged intra- and interatrial conduction disturbances, are well described as electrophysiological parameters associated with the genesis of atrial fibrillation. Patients with sick sinus syndrome are variously included in these studies, but electrophysiological characteristics of patients with sick sinus syndrome alone appear less investigated, even if atrial fibrillation is part of its natural history. The aim of the present study was to define the electrophysiological characteristics of sick sinus syndrome patients with or without paroxysmal atrial fibrillation, compared to subjects without atrial fibrillation and sick sinus syndrome. METHODS: We reviewed the electrophysiological data of 39 patients with sick sinus syndrome (mean age 70 +/- 8 years), who underwent an electrophysiological study in sinus rhythm for the evaluation of the atrial substrate. In 12 patients an associated history of paroxysmal atrial fibrillation was documented. Twenty-seven patients were included in the study with a diagnosis of sinus node dysfunction alone. We also considered as control group 25 subjects (mean age 63 +/- 14 years), referred to our electrophysiological laboratory for unexplained syncope or atrioventricular disturbances. Following pharmacological wash-out and at a drive cycle of 600 ms, effective and functional refractory periods, S1-A1 and S2-A2 latency, A1 and A2 width, and the latent vulnerability index (effective refractory period/A2), were measured. In addition, the P-wave duration during spontaneous sinus rhythm on the surface ECG in D II/V1 leads was measured. RESULTS: Between sick sinus syndrome patients with or without atrial fibrillation, no significant statistical differences in electrophysiological parameters were found. When compared to the control group, sick sinus syndrome patients did not show any differences in effective refractory period (239 +/- 34 vs 250 +/- 29 ms), functional refractory period (276 +/- 28 vs 280 +/- 32 ms), S1-A1 (38 +/- 16 vs 33 +/- 11 ms), and S2-A2 latency (68 +/- 25 vs 63 +/- 25 ms). In contrast, we observed remarkable differences in terms of atriogram duration A1 (60 +/- 20 vs 39 +/- 13 ms, p < 0.001), A2 (95 +/- 34 vs 57 +/- 18 ms, p < 0.001), and effective refractory period/A2 (2.8 +/- 1.2 vs 4.8 +/- 1.7 cm, p < 0.001). Also the duration of the P wave was longer (103 +/- 17 vs 94 +/- 45 ms, p < 0.05). CONCLUSIONS: In sick sinus syndrome patients with or without atrial fibrillation, electrophysiological characteristics appear homogeneous. When compared to the control group, refractoriness was quite similar. In contrast, the most important abnormalities appear based on conduction slowing disturbances, responsible for a low latent vulnerability index. This could explain, at least in part, the tendency of sick sinus syndrome to develop atrial fibrillation as a part of its natural history. At present, the influence of an altered electrophysiological substrate on pharmacological or pacing therapy in patients with sick sinus syndrome is not yet known.

Aged↗
PubMed1997

Electrophysiological effects of vasoactive intestinal peptide in rabbit atrium: a modulation of acetylcholine activity.

Vasoactive Intestinal Peptide (VIP) is a 28-amino acid peptide partially co-secreted with acetylcholine (Ach) in the atrial tissue. We studied the electrophysiological effects of VIP and Ach in rabbit isolated right atrium by the microelectrode technique. After a 10-min superfusion with VIP, action potential duration at 90% of repolarization (APD90) was lengthened by 23% (P = 0.01) at the concentration of 10(-8) M (n = 10), by 22% (P = 0.004) at 10(-7) M (n = 10) and by 33% (P = 0.03) at 2 x 10(-7) M (n = 5). To explain this APD90 lengthening, we performed 10 other experiments with VIP 10(-7) M, including five preparations pretreated with verapamil (10(-6) M) for 20 min. In the five preparations not pretreated, APD90 was increased by 27% (P = 0.04) after 10 min but remained unchanged in those previously exposed to verapamil, suggesting that VIP is a calcium current activator. Ach (1.4 x 10(-5) M) was superfused in five other experiments and we observed a 31% decrease in APD90 (P= 0.04) at 10 min. After washout, we simultaneously perfused, on the same preparations, Ach (same concentration) and VIP (10(-7) M) for 10 min. The decrease in APD90 (19%) was no longer significant. VIP (2 x 10(-7) M) lengthened cellular effective refractory periods (ERP) by 26% (P = 0.04) after 10 min (n = 5), whereas Ach (1.4 x 10(-5) M) decreased ERP by 33% (P = 0.04) at 10 min (n = 5). In conclusion, VIP lengthens atrial APD90, which may be the result of calcium current activation. In addition, VIP could modulate Ach activity in limiting APD90 shortening in the presence of Ach and because of its opposite effect on atrial ERP. Therefore, VIP could be involved in the control of vagal atrial arrhythmias.

Acetylcholine↗
PubMed1996

[Role of power and temperature monitoring in radiofrequency ablation].

Variations of temperature, impedance and power and the relationship between these three factors were studied in 20 patients during 351 applications of radiofrequency energy delivered by a generator with a regulated output power. The applications were divided into 3 groups according to the maximal temperature attained: group I (< 50 degrees C; n = 112), group II (50-60 degrees C; n = 100), and group III (60-70 degrees C; n = 139). Analysis of the total duration of time of applications (average +/- standard deviation) showed: the duration (seconds) was 23.9 +/- 11.9 seconds for group I, 36.1 +/- 18.7 seconds for group II and 45 +/- 23.6 seconds for group III. The time to attain maximal temperature was 6.8 +/- 9.6 seconds in group I, 11.7 +/- 12.7 in group II and 10 +/- 10.4 seconds in group III. The impedance remained under 200 omega in all applications, the target temperature being set at 70 degrees C. Analysis of the first three seconds of application: correlations coefficients between temperature and impedance were -0.08 (p < 0.001) in group I and -0.23 (p < 0.0001) in groups II and III. These coefficients were recalculated with respect to the average power delivered during the applications: < 40 watts (n = 79), r = -0.33; < 30 watts (n = 55), r = -0.41; < 20 watts (n = 33), r = 0.49 and < 10 watts (n = 15), r = -0.7 (p < 0.0001). The authors conclude that radiofrequency generators with thermal regulation allow early interruption of ineffective applications of radiofrequency and avoid increases in impedance. The poor correlations observed between increase in temperature (measured at the tip of the catheter) and the fall in impedance (related to tissue heating) for the first 3 groups, show that temperature alone is not a good indicator of contact. The improvement of the correlations for decreasing output power applications indicates better thermal transfer between the electrode and endocardium. Therefore a low power delivered in the first seconds at > 50 degrees C is to be interpreted as a marker of the quality of contact and a predictive factor of efficacy.

Adolescent↗
PubMed1994

[Limitations of ventricular late potentials in atrial fibrillation].

It is generally admitted that the chaotic atrial activation in atrial fibrillation makes analysis of ventricular late potentials uninterpretable. However, some workers have contradicted this affirmation. The authors performed signal averaged electrocardiogram in 17 patients with atrial fibrillation before cardioversion for external D.C. shock. The recording was repeated 15 minutes after restoration of sinus rhythm. None of the patients had complete bundle branch block in atrial fibrillation or sinus rhythm. Analysis was made with a band pass filter of 40 Hz and to a final noise level of 0.3 microV. The positivity of late ventricular potentials was confirmed by the presence of at least 2 of the usual 3 criteria: an averaged QRS duration > 120 ms, a RMS 40 < 20 microV and a LAS > 40 ms. The mean duration of the averaged filtered QRS complex was 122 ms in atrial fibrillation and 112 ms in sinus rhythm, a non significant decrease of 9%. The mean value of the RMS 40 was 24 microV before cardioversion versus 29 microV after restoration of sinus rhythm, a significant increase of 19% (p < 0.05). Finally, the mean duration of the LAS in atrial fibrillation was 45 ms, decreasing to 35 ms in sinus rhythm, a significant reduction of 22% (p < 0.05). In atrial fibrillation, 10 patients had ventricular late potentials (2 positive criteria) and 7 had no ventricular late potentials. In sinus rhythm, on the other hand, 6 patients were positive and 11 negative.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1994

[Mechanisms of atrial fibrillation: recent advances].

Atrial fibrillation (AF) is due to the presence of multiple reentry pathways. Although this mechanism has been known for some time, new information has recently been acquired about the factors of atrial vulnerability and the conditions of myocardial alteration. There are two main factors of atrial vulnerability: intra-atrial conduction defects and abnormalities of the refractory periods. In addition, the concept of critical mass and the influence of the autonomic nervous system have to be taken into consideration. The abnormalities of the refractory periods liable to increase atrial vulnerability are their shortening, spatial dispersion and poor adaptation to the heart rate. All these changes may be demonstrated at cellular level. The product of the intra-atrial conduction velocity and the duration of the refractory period defines the wave length. The risk of developing reentry pathways increases as the wave length shortens. Moreover, the more the atrium fibrillates, the greater will be the decrease of the refractory periods, atrial fibrillation giving rise to atrial fibrillation. Histological lesions of the atrial tissue may be demonstrated, even in the absence of underlying cardiac disease. They mainly consist of fibrosis, fatty degeneration and myocytic hypertrophy. In the long-term, atrial fibrillation leads to a number of structural abnormalities of the atrial, and sometimes ventricular tissues, progressing to cardiomyopathy in some cases.

Action Potentials↗