Spatial extension of local pacing capture in the lateral free wall of the right atrium during clinical chronic atrial fibrillation.

OBJECTIVES: The aims of our study were to define the spatial extension of local atrial pacing capture (LAPC) in the right lateral atrial wall and to verify the effects of antiarrhythmic drugs on capture extension. BACKGROUND: Recently, LAPC during spontaneous chronic atrial fibrillation (AF) has been demonstrated directly in humans, but no systematic attempt has been made to evaluate its spatial extension. METHODS: The study was conducted in 14 consecutive patients with chronic AF, nine of whom were taking antiarrhythmic drugs. A Franz catheter for pacing and monophasic action potential recording was positioned in the lateral right atrial wall. An octopolar recording lead was positioned about 10 mm apart. The presence of atrial capture and its extension (number of captured bipolar pairs) were evaluated during decremental pacing. RESULTS: Forty-eight atrial capture attempts were made. LAPC was achieved in all the performed attempts. The AF types immediately before capture were type 1 in 35 (73%) and type 2 in 13 (27%) episodes. In 32 episodes, the capture was lost within 15 seconds and in the remaining 16 pacing was stopped after 15 seconds of stable capture. In 26 episodes, capture extended radially up to 4 cm from the pacing site, in 18 up to 3 cm, in 3 up 1 cm and in 1 up 1 cm. The mean extension in patients being treated with antiarrhythmic drugs was significantly greater than what was seen in untreated patients (3.8 +/- 0.4 vs 2.9 +/- 0.7 cm, p < 0.00001). Capture loss was less frequently observed when all four of the bipolar recording sites had been captured (13/25, 52% vs 19/23, 82%, respectively, p = 0.05). CONCLUSIONS: LAPC in the lateral right atrial wall extends over a radius of 30-40 mm in the majority of capture episodes and is greater in patients treated with antiarrhythmic drugs. Our results suggest that, at least theoretically, simultaneous multisite pacing could be used to terminate AF. Moreover, a reduction in the atrial defibrillation threshold could be expected performing low-energy internal cardioversion during LPC.

Electrophysiological characteristics of the human atria after cardioversion of persistent atrial fibrillation.

BACKGROUND: In animal models, induced atrial fibrillation shortens the atrial effective refractory period (ERP) and reverses its physiological adaptation to rate. It is not clear whether this process, known as "electrical remodeling," occurs in humans. METHODS AND RESULTS: We determined the ERPs, at 5 pacing cycle lengths (300 to 700 ms) and in 5 right atrial sites, after internal cardioversion of chronic atrial fibrillation in 25 patients (14 in pharmacological washout and 11 on amiodarone). The ERPs were 195.5+/-18.8 ms in the washout and 206.3+/-17.9 ms in the amiodarone patients (P<0.0001). ERPs were closely correlated with the stimulation rates (r=0.95 in the washout and r=0.94 in the amiodarone group), and slope values indicating a normal (>/=0.07) or nearly normal (0.05 to 0.06) adaptation of ERP to rate were found in 77% of the 84 paced sites. The mean ERP was shorter in the lateral wall (198.1+/-17.9 ms) than in the atrial roof (203.3+/-21.5 ms) and in the septum (210.5+/-20.0 ms) (P<0.03). After 4 weeks of sinus rhythm, the mean ERP, determined again in 8 patients (4 in wash-out and 4 on amiodarone), was significantly increased compared with the basal study (221. 4+/-21.4 versus 197.8+/-18.3 ms, P<0.0001). CONCLUSIONS: After cardioversion of chronic atrial fibrillation, (1) atrial ERP adaptation to rate was normal or nearly normal in the majority of the cases, (2) a significant dispersion of refractoriness between different right atrial sites was present, and (3) ERPs were significantly increased after 4 weeks of sinus rhythm in both washout and amiodarone patients.

Low energy intracardiac cardioversion of persistent atrial fibrillation.

The aims of the study were to verify the efficacy and safety of low energy internal cardioversion (LEIC) in patients with persistent atrial fibrillation (AF) and to identify the factors affecting the atrial defibrillation threshold (ADT). Forty-nine patients with persistent (lasting > or = 10 days) AF underwent LEIC. In each patient, two 6 Fr custom-made catheters with large active surface areas were positioned in the coronary sinus (cathode) and the lateral right wall (anode), respectively, for shock delivery, and a tetrapolar lead was placed in the right ventricular apex for R wave synchronization. Truncated, biphasic (3 ms + 3 ms), exponential shocks were used, beginning at 50 V and increasing in steps of 50 V until sinus rhythm had been restored. Mild sedation (diazepam 5 mg i.v.) was administered to 12 patients. Sinus rhythm was restored in all the subjects with mean voltage and energy levels of 352.0 +/- 80.3 V and 8.2 +/- 3.4 J, respectively. The ADT in patients pretreated with amiodarone (6.4 +/- 1.8 J) was lower than that of patients who had not received any antiarrhythmic drugs (9.2 +/- 3.7) (P = 0.04). No ventricular arrhythmias were induced by any of the atrial shocks, and no other complications were observed. During a mean follow-up of 162.9 +/- 58.7 days, AF recurred in 21 (43%) patients; 71% of these occurred in the first week after cardioversion. LEIC is effective in restoring sinus rhythm in patients with persistent AF. The technique seems to be safe and does not require general anesthesia or, in most cases, sedation. Patients pretreated with amiodarone have lower ADTs.

Local capture by atrial pacing in spontaneous chronic atrial fibrillation.

BACKGROUND: Atrial fibrillation (AF) is considered to be maintained by multiple reentrant circuits without or with a very short excitable gap. However, the possibility of local atrial capture has been shown recently in experimental AF or induced AF in humans. METHODS AND RESULTS: This study was undertaken to evaluate the feasibility of atrial capture-suggestive of an excitable gap-in spontaneous chronic AF. Decremental pacing was performed in 47 right atrial sites in 14 patients with chronic AF, not taking antiarrhythmic drugs. A Franz catheter (for pacing and monophasic action potential recording) and a recording quadripolar catheter positioned about 10 mm apart were used. Local capture was achieved in 41 (87.2%) sites for a total of 100 captures. In 71 episodes the capture was lost within 15 seconds, while in the remaining 29, pacing was stopped after 15 seconds of stable capture. AF types immediately before capture were type 1 in 83 and type 2 in 17 episodes. Type 3 AF was never captured. Pacing cycle at capture was 175.7 +/- 20.9 ms. The baseline atrial interval (FF) was 185.4 +/- 24.5, significantly longer than the FF recorded during pacing immediately before capture (176.0 +/- 19.8 ms) (P < .02). CONCLUSIONS: During spontaneous chronic AF in humans, (1) local capture by atrial pacing is possible up to at least 15 mm from the pacing site, (2) regional entrainment is possible during type 1 and type 2 AF but not type 3 AF, and (3) pacing before capture accelerates AF, probably by transient or local capture. These findings suggest that an excitable gap is present in chronic AF, therefore supporting the hypothesis that leading circle reentry is not the unique electrophysiological mechanism maintaining the arrhythmia.

[Electrophysiologic characteristics of the atrium during chronic atrial fibrillation in man]. / Caratteristiche elettrofisiologiche dell'atrio durante fibrillazione atriale cronica nell'uomo.

AIM OF THE STUDY: To evaluate the electrophysiologic characteristics of human atria during chronic atrial fibrillation. METHODS: The study was performed in 24 patients who underwent low energy intracardiac atrial cardioversion for chronic atrial fibrillation before the procedure itself. No patients have been assuming antiarrhythmic drugs for a period of at least 5 half-lives of the drug. In 10 patients the possibility of local capture in several atrial sites (7 tested) by means of high-rate atrial pacing was evaluated. A Franz catheter for recording of monophasic action potential (MAP) and for atrial stimulation was positioned in the right atrium at a distance of 1 cm from a quadripolar catheter which was also positioned for the recording of the bipolar electrogram by the distal and proximal pairs and of the unipolar electrogram by the distal electrode. A decapolar catheter for shock delivery was positioned in the coronary sinus as well. In the remaining 14 patients an additional quadripolar catheter for His recording was positioned but atrial stimulation was not performed. Furthermore, recordings of the bipolar and unipolar electrograms were obtained in several sites and the correlation between MAP and bipolar electrogram morphology was evaluated. The existence of a difference in fibrillation cycle-length in different sites suggestive of a dispersion of refractory periods was also screened. Wells' and Waldo's classification was used for bipolar electrograms whereas MAP was classified into type 1 (regular), type 2 (partially irregular), and type 3 (totally irregular). RESULTS: In 10 patients submitted to atrial stimulation, local capture was obtained in 37 out of 43 stimulation sites (86%). Local capture was more frequently obtained in the lateral wall than in other sites (p < 0.05). The capture was obtained only in type 1 and type 2 atrial fibrillation. In the remaining 14 patients a perfect correlation (100%) between type 1 and 3 atrial fibrillation and type 1 and 3 MAP respectively was observed. In type 2 atrial fibrillation the correspondence was lower (67%). Fibrillation cycle-length contemporary recorded in the 6 different atrial sites were significantly different in 8 patients out of 12 (67%) in whom a stable recording could be obtained in basal conditions. CONCLUSIONS: 1) In chronic atrial fibrillation an excitable gap allowing local capture is present in the majority of patients and in most atrial sites, at least in the right atrium. 2) The morphology of bipolar and MAP recordings are fairly correlated and they reflect the complexity and the degree of synchronization of the arrhythmia. 3) A dispersion of refractoriness seems to contribute to the maintainance of the arrhythmia.

Transcutaneous cardiac pacing for termination of tachyarrhythmias.

Transcutaneous cardiac pacing (TCP) was used for interruption of tachyarrhythmias in 31 patients: 20 with ventricular tachycardia (VT); eight with atrioventricular reentrant tachycardia (AVRT) and three had atrioventricular nodal tachycardia (AVNT). The stimulators used (Pace Aid 50/52) allow pacing at programmable rates (50-160 ppm) and output (10-200 mA at 20-msec pulse duration), when possible overdrive pacing was used. Short bursts of stimuli were delivered with increasing current intensity until interruption of the arrhythmia or to the maximum energy tolerated by the patient. VTs were interrupted in eight of the 20 patients: four of the six (67%) treated by overdrive pacing and four of the 14 (29%) were treated by underdrive pacing. Supraventricular tachycardias (SVT) were terminated in eight of the 11 patients: seven out of eight (88%) AVT, and one out of three AVNT (33%). We observed two cases of arrhythmia worsening: a VT acceleration and induction of ventricular fibrillation in a patient with AVNT. TCP was well tolerated by the majority of the patients. We conclude that TCP is an effective method for interruption of ventricular and supraventricular reentrant tachycardias, but the risk of arrhythmia worsening must be considered.