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PubMed2004

Clinical assessment of antiarrhythmic agents for paroxysmal atrial fibrillation guided by modification of electrophysiologic arrhythmogenicity.

INTRODUCTION: Rapid atrial pacing alters atrial electrophysiology, promoting initiation and maintenance of atrial fibrillation (AF). The aim of this study was to assess differences in the electrophysiologic properties of atrial tissue between patients with and without AF episodes and to determine whether electrophysiologic properties can predict the clinical efficacy of antiarrhythmic agents. METHODS AND RESULTS: Sixty patients were studied, 33 with documented episodes of paroxysmal atrial fibrillation (PAF) and 27 control patients. Atrial effective refractory period (AERP), atrial vulnerability, and intra-atrial conduction time were measured at baseline and after rapid constant atrial pacing for 5 minutes at rates of 130, 150, 170, and 190 beats/min. The clinical efficacy of antiarrhythmic agents for PAF prophylaxis was assessed over 14 months with an antiarrhythmic agent identical to that administered intravenously, and the antiarrhythmic agent effects on AERP, atrial vulnerability, and intra-atrial conduction time were assessed. AERP shortening and atrial vulnerability increase were significantly larger in the PAF group. Antiarrhythmic agents that were clinically effective in suppressing PAF significantly attenuated AERP shortening, but antiarrhythmic agents that were clinically ineffective did not. CONCLUSION: Changes in AERP and atrial vulnerability observed after rapid atrial pacing are considered indicative of the electrophysiologic substrate of PAF. Attenuation of AERP and atrial vulnerability by antiarrhythmic agents might be useful in predicting their clinical efficacy.

Anti-Arrhythmia Agents↗
PubMedDate not supplied

[Changes in rhythm and conduction after atrial correction of transposition of great vessels].

Disorders of rhythm or conduction after correction by baffle of transposition of the great arteries (TGA) has been widely reported. In order to avoid them, transformations on Mustard original technique have been carried out. We analize here the incidence of arrhythmias during the follow up of 20 patients operated, following a modification of the Mustard technique, as well as the postoperative changes on the P wave. The 75% of the patients remained in sinus rhythm during the postoperative first year, but only 28% continued on it after 6 years. The rest of the patients presented nodal or low auricular rhythm, alternating with sinus rhythm. Seven patients fulfilled diagnostic criteria of sick sinus syndrome. Ninety five percent of the patients were asymptomatic. The 9 patients that performed a stress testing after operation presented sinus rhythm and heart rate acceleration, in spite of the rhythm was nodal at the beginning in 4 of them. The modifications of the Mustard technique apparently do not avoid the arrhythmias and disorders of conduction. Nevertheless, the exercise tolerance remain acceptable.

Adolescent↗
PubMed2004

An evaluation of postoperative P-wave variables after cardiothoracic surgery.

Postoperative atrial fibrillation is common after cardiac surgery. Prediction of which patients will develop postoperative atrial fibrillation would be clinically useful. Increased P-wave duration, suggesting atrial conduction delay and measured from preoperative electrocardiograms, predicts postoperative atrial fibrillation. However, postoperative P-wave duration has not been evaluated after cardiac surgery. In this study, we evaluated postoperative P-wave variables (maximum P-wave duration and P-wave dispersion) over 5 days in cardiac surgery patients receiving amiodarone, pacing or no atrial fibrillation prophylaxis. P-wave variables gradually shortened as time passed from surgery. Amiodarone did not shorten P-wave measurements throughout therapy, while pacing shortened P-waves in the immediate postoperative period; however, shortening was not sustained. P-waves did not differ between those who did and did not develop atrial fibrillation with amiodarone or pacing. Our findings suggest that atrial conduction delay resulting from cardiothoracic surgery tends to resolve over time and may not play a critical role in the etiology of postoperative atrial fibrillation.

Aged↗
PubMed2006

Recurrence of pulmonary vein conduction and atrial fibrillation after pulmonary vein isolation for atrial fibrillation: a randomized trial of the ostial versus the extraostial ablation strategy.

BACKGROUND: Both segmental ostial and circumferential extraostial pulmonary vein (PV) isolation have been proven effective in the treatment of atrial fibrillation (AF). However, the recurrence of AF and PV conduction after the 2 ablation strategies has never been compared in a randomized study. METHODS: A total of 100 consecutive patients (age 56 +/- 10; 71 men) with symptomatic AF (paroxysmal, 51; persistent, 49) were randomized to segmental ostial (n = 54) or circumferential extraostial (n = 46) PV isolation. A circular catheter positioned at the ostium of each target PV guided the ostial PV isolation. Extraostial PV isolation was performed by encircling the paired left and right PVs, respectively, guided by an electroanatomic mapping system. RESULTS: A total of 84% of the patients had recurrent AF after the first PV isolation procedure, showing 72% with AF and 12% with organized left atrial tachycardia. In patients undergoing reablation, all but 2 patients had recurrence of left atrium PV conduction (>95%). During a mean follow-up of 12 months without antiarrhythmic medication, 57% of patients who underwent extraostial PV isolation were free of arrhythmia symptoms compared with 31% of patients who underwent ostial PV isolation (P < .05). This difference in success rate between the 2 ablation strategies was mainly seen in patients known with persistent AF (52% and 15%, respectively; P = .02) as opposed to patients with paroxysmal AF (65% and 46%, respectively; P = .26). CONCLUSIONS: Overall, the more proximal, extraostial PV isolation was found to be superior to ostial PV isolation, especially in patients known with persistent AF. A high recurrence rate of 84% after a single complete PV isolation procedure was seen. At reablation, more than 95% had recurrence of left atrium PV conduction regardless of the procedure used, supporting the idea that complete PV isolation seems essential to prevent arrhythmia recurrences.

Aged↗
PubMed1993

Regional entrainment of atrial fibrillation studied by high-resolution mapping in open-chest dogs.

BACKGROUND: It recently has been demonstrated that during atrial fibrillation, a short and variable excitable gap exists, allowing regional control of atrial fibrillation by local stimulation. In the present study, we visualized the process of excitation during regional entrainment of atrial fibrillation by rapid pacing. METHODS AND RESULTS: In six open-chest dogs, the excitation of the left atrial free wall was mapped using a spoon-shaped mapping electrode (248 points). Episodes of atrial fibrillation were induced by burst pacing (50 Hz, 2 seconds). During atrial fibrillation, the electrograms showed rapid irregular activity with a median cycle length of 98 +/- 16 ms (mean +/- SD, n = 6). Rapid pacing in the center of the mapping electrode at intervals slightly shorter or longer than the median atrial fibrillation interval resulted in regional capture of atrial fibrillation. The window of entrainment was 16 +/- 5 ms. Mapping of atrial fibrillation showed that the left atrium was activated by fibrillatory wavelets coming from different directions. During entrainment, a relatively large area with a diameter of about 4 cm was activated by uniform wave fronts propagating away from the site of stimulation. The area of entrainment was limited by intra-atrial conduction block and by collision with fibrillation waves. Regional control of atrial fibrillation was lost by pacing either too slowly or too rapidly. In the first case, retrograde invasion of the area of entrainment by fibrillatory waves resulted in depolarization of the pacing site prior to the stimulus. Pacing too rapidly caused acceleration of atrial fibrillation by induction of local intra-atrial reentry circuits with a revolution time shorter than the pacing interval. CONCLUSIONS: During atrial fibrillation, an area with a diameter of about 4 cm can be entrained by local pacing. The resulting reduction in fibrillating tissue mass was not sufficient to terminate atrial fibrillation. Extension of the area of entrainment was limited by intra-atrial conduction block, whereas entrainment at a too high rate resulted in acceleration of atrial fibrillation by induction of local microreentry.

Animals↗
PubMed2001

Electropharmacologic effects of pilsicainide, a pure sodium channel blocker, on the remodeled atrium subjected to chronic rapid pacing.

Clinical experience suggests that sodium channel blockers are effective in converting atrial fibrillation of recent onset but not chronic atrial fibrillation. We investigated changes in the electrophysiologic effects of pilsicainide, a pure sodium channel blocker, on the canine atrium during chronic rapid pacing (400/min). Three pairs of bipolar electrodes were sutured to the right atrial appendage in six dogs. Five days later, rapid atrial pacing was started after baseline measurements of the effective refractory period (ERP), the intra-atrial conduction velocity, the atrial wavelength, and the inducibility of atrial fibrillation. These studies were repeated at 2, 7, and 14 days of pacing, both before and after pilsicainide administration. Before pacing, pilsicainide increased ERP more than it decreased conduction velocity, causing an increase of wavelength, particularly at faster rates. However, this use-dependent prolongation of ERP disappeared after 2 days of pacing. Thus, pilsicainide failed to prolong ERP during chronic pacing, allowing progressive shortening of wavelength in the remodeled atrium. The effect of sodium channel blockers on atrial refractoriness may decline as rapid atrial excitation persists, limiting the usefulness of these agents for the treatment of chronic atrial fibrillation.

Animals↗
PubMed1995

Sino-atrial Wenckebach conduction in thyrotoxic periodic paralysis: a case report.

A 28-year-old male presented with thyrotoxic periodic paralysis. On admission to hospital the serum potassium level was 1.4 mmol/l. The ECG showed classical features of hypokalaemia. In addition, sino-atrial block with Wenckebach conduction was also present. With the normalization of the serum potassium, the ECG became completely normal and showed no evidence of any arrhythmia.

Adult↗
PubMed2000

Long-term effects of biatrial synchronous pacing to prevent drug-refractory atrial tachyarrhythmia: a nine-year experience.

INTRODUCTION: Results of previous studies suggest that atrial resynchronization by multisite atrial pacing may contribute to prevention of recurrences in patients with drug-refractory atrial tachyarrhythmias and significant intra-atrial conduction delay. METHODS AND RESULTS: To verify this hypothesis, a prospective noncontrolled study of 86 patients (mean age 66 +/- 10 years) was conducted in a single center between January 1989 and February 1998. Inclusion criteria were P wave duration > or = 120 msec with interatrial conduction time > or = 100 msec, and history of multiple recurrences of atrial tachyarrhythmias (mean 7 +/- 4.8 episodes) evolving in a persistent mode for at least 6 months despite optimized drug treatment (mean 2.7 +/- 1.8 drugs/patient). Patients were chronically implanted with a pacing system that ensured permanent biatrial pacing using two atrial leads, one placed in the high right atrium and the other one into the mid or the distal part of the coronary sinus. P wave duration decreased from a mean value of 187 +/- 29 msec before implant to 106 +/- 14 msec (P < 0.0001) under biatrial pacing. After a 33-month mean follow-up (range 6 to 109), 55 patients (64%) remained in sinus rhythm, including 28 patients (32.6%) without any documented recurrence and 27 patients with one or more recurrences in a paroxysmal or in a persistent form. In these 55 patients, drug treatment was significantly reduced in relation to the preimplantation period (1.4 +/- 0.6 vs 1.7 +/- 0.5 drugs/patient; P = 0.011). The other 31 patients went into chronic atrial arrhythmia after a mean period of 26 months. The only predictive factor of positive response was a spontaneous P wave duration < 160 msec at baseline. CONCLUSION: The results are consistent with a preventive effect of permanent biatrial pacing on recurrent and drug-refractory atrial arrhythmias associated with intra-atrial conduction delay.

Adult↗
PubMed1998

Electrophysiological properties of the fibrillating atrium: implications for therapy.

1. Atrial fibrillation (AF) is the most commonly occurring cardiac dysrhythmia and remains a challenge to medical therapy. Although the disorder has been recognized for over 100 years, surprisingly very little is understood about its pathophysiology. Over the past decade, a variety of experimental and animal models of AF have been developed and these have provided insights into the mechanism of AF. 2. The pathophysiology of AF is complex. Atrial fibrillation can be caused either by a single source of very rapid impulses or, in the majority of cases, by multiple random re-entering wavelets. The notion that AF may be initiated by a single rapid firing focus and the perpetuation of AF may be partly dependent on macro re-entry around the natural atrial orifices provides a new potential curative therapy for AF by radiofrequency ablation. 3. Shortening of atrial wavelength, either by slow atrial conduction velocities, short atrial refractory periods or both, seems to predispose to development of intra-atrial re-entry and, thus, AF. The functional mechanism by which anti-arrhythmic drugs terminate AF appears to be by prolonging the wavelength and decreasing the number of re-entry wavelets. These understandings are important for the future development of effective anti-arrhythmic agents against AF. 4. The presence of a short and variable excitable gap during AF may be potentially important for termination of AF by pacing. 5. New insights are being gained into the potential role and mechanism of electrical remodelling of the atrium due to AF. Repeated induction of AF by rapid atrial pacing leads to a shortening of atrial refractoriness with loss of rate adaptation, which favours the induction and maintenance of AF. These electrophysiological changes were assumed to occur during repeated AF and to facilitate the generation of multiple re-entrant wavelets. These data suggest that prompt restoration of sinus rhythm and new novel therapy that prevents or diminishes electrical remodelling may promote maintenance of sinus rhythm after successful cardioversion.

Animals↗
PubMed1997

Effects of different atrial pacing modes on atrial electrophysiology: implicating the mechanism of biatrial pacing in prevention of atrial fibrillation.

BACKGROUND: Multiple-site atrial pacing has been shown to prevent recurrence of atrial fibrillation. However, information about the mechanisms of different atrial pacing modes in prevention of atrial fibrillation was not clear. METHODS AND RESULTS: Forty-two patients without structural heart disease were classified into group 1 and group 2 according to absence or presence of clinical atrial fibrillation, respectively. Atrial conduction time and electrogram width of the right posterior interatrial septum (RPS) were measured during drive-train stimulation (S1) and early extrastimulation (S2). The locations of S1 were the high right atrium (HRA), distal coronary sinus (DCS), or both sites simultaneously. Effective refractory periods (ERPs) of the HRA and DCS were also determined during S1 stimulation at each site and during biatrial pacing. The ERPs were not different between single-site atrial pacing and biatrial pacing. In contrast, early S2 stimulation at the HRA caused greater atrial conduction delay and greater increment of electrogram width of the RPS in patients with a history of atrial fibrillation. Biatrial pacing significantly reduced the conduction delay and electrogram width of the RPS caused by HRA extrastimulation. In addition, in 17 group 2 patients, atrial fibrillation was induced by an early HRA S2 coupled to HRA pacing. However, with the same coupling interval of S2 at HRA, only 6 of them had the arrhythmia induced during biatrial pacing. Furthermore, conduction delay and increase of electrogram width caused by early S2 at the HRA were reduced by biatrial pacing only in patients whose arrhythmia induction was successfully prevented by biatrial pacing. CONCLUSIONS: Biatrial pacing reduced both the atrial conduction delay and increase of electrogram width at the RPS caused by early S2 at HRA, and these effects could prevent induction of atrial fibrillation.

Adult↗
PubMed1983

Mechanism and clinical significance of atrial repetitive responses in man.

We have studied the electrophysiological correlates of atrial repetitive responses, induced by single extrastimuli, in a group of 25 patients undergoing electrophysiologic studies for a variety of supraventricular and ventricular arrhythmias. The incidence of repetitive responses was not related to a previous history of atrial tachyarrhythmias. Repetitive responses were observed only when the extrastimulus elicited a significant intra-atrial conduction delay, as measured from the extrastimulus artifact, to two or three points in the atria. This condition was fulfilled only when the basic atrial rhythm was paced, and it was also facilitated by increasing atrial rate, which shortened the atrial effective refractory period. Atrial pacing thus seemed to facilitate the production of atrial repetitive responses by both promoting intra-atrial conduction delays during extrastimulation, and by shortening the atrial refractory period. Atrial repetitive responses are probably a nonspecific phenomenon, unrelated to a tendency towards atrial tachyarrhythmias; their mechanism is probably local re-entry, related to slow conduction of impulses during incomplete repolarization, and under favorable conditions they may precipitate atrial flutter or fibrillation in predisposed patients.

Adult↗
PubMed1978

Alpha and beta adrenergic effects on human atrial specialized conducting fibers.

We determined the effects of epinephrine on automaticity and action potential characteristics of right atrial specialized fibers (RAF) from human atria obtained during cardiac surgery. RAF were studied with standard microelectrode techniques during superfusion with Tyrode's solution at 37 degrees C. A biphasic response to epinephrine was seen, rate slowing at low agonist concentrations and increasing at high concentrations. The epinephrine-induced slowing of spontaneous rate was due to a decrease in the slope of phase 4 depolarization. At the high epinephrine concentrations RAF hyperpolarized. The alpha-adrenergic blocker, phentolamine, shifted the dose-response curve upward and to the left and enhanced the hyperpolarization of RAF. The beta blocker, propranolol, shifted the curve to the right and decreased the degree of hyperpolarization. Our study suggests the presence of alpha and beta receptors in RAF. The alpha response consists of a slowing of rate, the beta response of an acceleration of rate and hyperpolarization of RAF.

Action Potentials↗
PubMed1995

Atrial electromechanical sequence in normal subjects and patients with DDD pacemakers.

OBJECTIVE: To assess the effect of right atrial appendage pacing on atrial electromechanical interrelations in patients with DDD pacemakers. DESIGN: Prospective study by M mode echocardiogram, Doppler echocardiogram, and apexcardiogram, along with electrocardiogram and phonocardiogram. SETTING: Tertiary cardiac referral centre. PATIENTS: 20 patients with DDD pacemakers and 20 age matched normal controls. RESULTS: Age, RR interval, atrial size, left ventricular size, and fractional shortening were similar in the two groups. Atrial electromechanical delay (the time from the onset of P wave or atrial pacing spike on ECG to the onset of atrial contraction on M mode echogram) was 68 (SD 7) ms at the lateral site of right atrium, 82 (9) ms at the central fibrous body, 93 (11) ms at the lateral site of left atrium in normals. In patients with DDD pacing, however, this delay increased to 85 (22) ms, 117 (23) ms, and 138 (25) ms respectively (all P < 0.01). Interatrial mechanical delay (the time from the onset of right atrial motion to the onset of the left) increased from 25 (6) ms in normal controls to 53 (18) ms in patients (P < 0.01). Intra-atrial mechanical dispersion (the time from the earliest to the latest onset of regional atrial motion around the atrioventricular ring) in the right atrium increased from 6 (2) ms in normals to 19 (2) ms in patients (P < 0.01), but it remained unchanged in the left atrium (6 (2) ms in normal controls v 7 (2) ms in patients, P > 0.05). Peak atrial shortening rate was not different between the two groups. Differences of atrial electromechanical activity between the two groups were also reflected on Doppler echocardiogram and apexcardiogram. CONCLUSIONS: Right atrial appendage pacing disturbs the normal coordinate sequence of right atrial mechanical activity and leads to a striking and variable increase in intra-atrial conduction time as well as in interatrial conduction time. Left atrial contraction remains synchronous although the timing of the start of its contraction was delayed. These values can be determined in individual patients to allow optimal setting of DDD pacemakers.

Aged↗
PubMed2006

Intraoperative mapping of the right atrial free wall during sinus rhythm: variety of activation patterns and incidence of postoperative atrial fibrillation.

OBJECTIVE: The atrial conduction properties associated with cardiac disease are speculated as the background of postoperative atrial fibrillation (POAF). We examined the atrial conduction patterns and conduction properties during sinus rhythm (SR) in patients that had undergone cardiac operations and evaluated the incidence of POAF in all patients. METHODS: Fifty-two patients with stable SR who underwent cardiac surgery, with a diagnosis of valvular disease in 25, ischemic heart disease in 24, and others in 3, were enrolled in this study. The epicardial recordings were made using a mapping system with 60 unipolar electrodes placed on the right atrium (RA) intraoperatively. The activation patterns of the RA were assessed, and the longitudinal, transverse and oblique conduction velocity and max anisotropic ratio were also examined. RESULTS: Sinus activation was initiated from various sites (single origin at the high-lateral RA in 40, mid-lateral RA in 4, low-lateral RA in 2, and multiple origins in 6 patients) and it demonstrated anisotropic conduction (1.8+/-0.6) with the longitudinal conduction being more rapid than transverse and oblique conduction. Fifteen patients demonstrated non-uniform activation patterns such as, a localized conduction delay in seven, functional conduction block in two and mosaic-activation pattern associated with multiple origins in six. A total of 21 patients (44%) developed POAF. A conduction delay and mosaic activation pattern was found significantly more often in patients with POAF than in patients who remained in sinus rhythm. Multivariate analysis revealed that non-uniform activation pattern (odds ratio=8.71; 95% confidence interval [CI]=1.74-43.67; p=0.008) and TR (odds ratio=4.95; 95% CI=1.14-21.37; p=0.032) were independently associated with the development of POAF. Although all patients had converted to SR at the time of discharge, the administration of antiarrhythmic drugs caused sinus bradycardia in two patients who demonstrated a mosaic activation pattern in RA. CONCLUSIONS: Cardiac surgery patients exhibited a variety of sinus activation patterns, which also provided an arrhythmogenic substrate for POAF. A better understanding of the sinus activation using an intraoperative mapping system may provide benefit in the clinical management of POAF.

Adult↗
PubMed1987

Dopamine-induced increase in atrioventricular conduction in atrial fibrillation-flutter.

We report a patient with controlled atrial fibrillation-flutter (AFF) and mitral stenosis who developed a marked increase in atrioventricular conduction during an infusion of low dose dopamine with development of hemodynamic compromise. This side effect has not been previously described in humans. Dopamine infusion should be used with caution in patients with AFF.

Atrial Fibrillation↗