Interatrial Conduction Block Research Articles

Variable interatrial conduction illustrated in a hypertrophic cardiomyopathy population.

Patients with hypertrophic cardiomyopathy (HCM) have a high incidence of atrial fibrillation. They also have a longer P-wave duration than healthy controls, indicating conduction alterations. Previous studies have demonstrated orthogonal P-wave morphology alterations in patients with paroxysmal atrial fibrillation. In the present study, the P-wave morphology of patients with HCM was compared with that of matched controls in order to explore the nature of the atrial conduction alterations. A total of 65 patients (45 men, mean age 49 +/- 15) with HCM were included. The control population (n = 65) was age and gender matched (45 men, mean age 49 +/- 15). Five minutes of 12-lead ECG was recorded. The data were subsequently transformed to orthogonal lead data, and unfiltered signal-averaged P-wave analysis was performed. The P-wave duration was longer in the HCM patients compared to the controls (149 +/- 22 vs 130 +/- 16 ms, P < 0.0001). Examination of the P-wave morphology demonstrated changes in conduction patterns compatible with interatrial conduction block of varying severity in both groups, but a higher degree of interatrial block seen in the HCM population. These changes were most prominent in the Leads Y and Z. The present study suggests that the longer P-wave duration observed in HCM patients may be explained by a higher prevalence of block in one or more of the interatrial conduction routes.

Age-related sensitivity to nicotine for inducible atrial tachycardia and atrial fibrillation

The influence of nicotine in modulating vulnerability to atrial tachycardia and fibrillation (AT/AF) remains ill defined. The isolated hearts of six young (2-3 mo) and six old (22-24 mo) male Fischer 344 rats were Langendorff perfused at 5 ml/min with oxygenated Tyrode solution at 37 degrees C, and the whole heart was also super-fused with warmed oxygenated Tyrode solution at 15 ml/min. Nicotine prolonged the interatrial conduction time and effective refractory period that were significantly (P < 0.05) higher in the old than in the young rats in a concentration-dependent manner. Nicotine had a biphasic effect on burst atrial pacing-induced AT in both groups, increasing it at 10-30 ng/ml while decreasing it at 50-100 ng/ml (P < 0.01). Nicotine at 10-100 ng/ml increased burst atrial pacing-induced AF in the young rats but suppressed it in the old rats (P < 0.01). Optical mapping showed the presence of multiple independent wavefronts during AF and a single periodic large wavefront during AT in both groups. Nicotine, at concentrations found in the blood of smokers (30-85 ng/ml), exerts biphasic effects on inducible AT/AF in young rats and suppresses it in the old rats by causing high degrees of interatrial conduction block.

Attenuation of interatrial conduction using right atrial septal catheter ablation

OBJECTIVESWe sought to characterize a method of attenuating interatrial conduction using radiofrequency ablated lesions applied to the right atrial septum.BACKGROUNDInteratrial conduction occurs in specific zones. Recent data suggest that interatrial conduction can be important in triggering and sustaining atrial fibrillation. Therefore, a method for attenuating interatrial conduction may have therapeutic value.METHODSIn 13 healthy pigs, interatrial conduction was evaluated before and after sequential ablation of the right atrial septum, targeting interatrial conduction zones. In six animals, zone 1 (crista terminalis and limbus) was ablated first, followed by ablation of zone 2 (fossa ovalis and coronary sinus ostium). In the other seven animals, the order of ablation was reversed. Electrophysiologic and pathologic findings were correlated.RESULTSAfter ablation of zone 1, interatrial conduction was slowed, but there was no block. After ablation of zone 2, conduction was unchanged. After ablation of both zones, complete block was observed in four animals, and there was left atrial quiescence. In the remaining nine animals, incomplete block was observed, with marked conduction slowing or block during sinus rhythm and pacing. Ablation did not adversely affect atrioventricular node conduction, nor did it facilitate sustenance of an atrial arrhythmia. Pathologic analysis revealed that complete interatrial conduction block was associated with confluent ablation of both targeted zones.CONCLUSIONSCatheter ablation of the right atrial septum attenuated interatrial conduction without disturbing atrioventricular conduction.

DDD Pacing and Interatrial Conduction Block: Importance of Optimal AV Interval Setting

The case of a 83-year-old patient undergoing DDD pacemaker implantation for sick sinus syndrome with postimplant detection of advanced interatrial conduction block is described. At nominal AV interval programming values (175 ms), absence of P wave following an atrial spike was observed, and the presence of an interatrial conduction disturbance was demonstrated by a Doppler transmitral flow pattern analysis and transesophageal ECG recording. AV interval lengthening up to 300 ms resulted in proper timing of atrial and ventricular contractions. Awaiting for conclusive data about biatrial pacing, interatrial conduction blocks can be managed in some cases by proper programming of conventional DDD systems.

Simultaneous occurrence of atrial fibrillation and atrial flutter.

Early reports suggested that some patients with "atrial fibrillation/flutter" might have atrial fibrillation in one atrium and atrial flutter in the other. However, more recent conceptions of atrial fibrillation/flutter postulate that the pattern is due to a relatively organized (type I) form of atrial fibrillation. We report the occurrence and ECG manifestations of simultaneous atrial fibrillation and flutter in patients undergoing attempted catheter ablation of atrial flutter. In patients undergoing radiofrequency ablation for atrial flutter, an attempt was made to entrain atrial flutter by pacing in the right atrium. The arrhythmias observed occurred following attempts at entrainment, or spontaneously in one case. Twelve transient episodes of simultaneous atrial fibrillation and flutter were observed in five patients. The atrial fibrillation was localized to all or a portion of one atrium, during which the other atrium maintained atrial flutter. In each case, the surface 12-lead ECG reflected the right atrial activation pattern. No patients had interatrial or intra-atrial conduction block during sinus rhythm, suggesting functional intra-atrial block as a mechanism for simultaneous atrial fibrillation/flutter. In certain patients, the occurrence of transient, simultaneous atrial fibrillation and flutter is possible. In contrast to prior studies in which it was suggested that left atrial or septal activation determines P wave morphology, the results of the present study show that P wave morphology is determined by right atrial activation. Functional interatrial block appears to be a likely mechanism for this phenomenon.

754-1 Biatrial Synchronous Pacing: A New Therapeutic Approach to Prevent Refractory Atrial Tachyarrhythmias

To test the hypothesis that biatrial synchronous pacing (BASP) may prevent atrial tachyarrhythmia (AT) recurrences in selected cases, we prospectively implanted permanent pacemakers providing BASP in 20 consecutive patients. Inclusion criteria were the association of (1) multiple (≥ 3) recurrences of permanent AT without any efficacy of drug therapy (mean = 3.5 drugs/pt). Atrial fibrillation in 12 Pts; atypical Atrial Flutter involving the left atrium in the reentry circuit in 12 pts; common Atrial Flutter in 3 pts; and Atrial Tachycardia in 4 Pts (2) major intra- and interatrial conduction block with a mean interatrial conduction time of 150 ± 40 ms during spontaneous sinus rhythm (SSR). The pacing system consisted of two atrial leads, one placed in the high right atrium and the other one into the coronary sinus to sense and pace the left atrium, both connected via a Y bifurcated connector at the atrial port of a SSI pacemaker programmed in the AAT or AATR mode (bipolar pacing and sensing configuration) in 5 pts with normal AV conduction, or of a DDD pacemaker with a special program of “atrial resynchronization” loaded into the RAM memory in 15 pts. In all pts, BASP provided permanent atrial resynchronization as well during atrial pacing, as during SSR and after atrial extrasystoles. During permanent A pacing the mean P wave duration decreased from 209 ± 38 ms without BASP to 108 ± 13 ms with BAS P (p &lt; 0.001). After a mean follow-up of 18 months (range: 3–66), 12 pts (60%) remained totally free from AT recurrences. 4 pts had short episodes of AT which resolved spontaneously. Only 4 pts (20%) returned to permanent AT. There was no significant difference according to the type of AT. These preliminary results suggest a potential role for BASP to prevent recurrences of drug refractory AT in selected pts with intra- and interatrial conduction block.

Interatrial conduction block with retrograde activation of the left atrium and paroxysmal supraventricular tachyarrhythmias: influence of preventive antiarrhythmic treatment

Patients with advanced interatrial conduction block with retrograde activation to the left atrium present a high incidence of supraventricular tachyarrhythmias. We report the value of preventive antiarrhythmic treatment in these patients.