Supernormal response and conduction in depressed isolated canine ventricular muscle exposed to high potassium concentration

Possible role of supernormal atrial conduction in the genesis of atrial fibrillation in patients with idiopathic paroxysmal atrial fibrillation

OBJECTIVE

The occurrence of supernormal excitability and conduction in the atrium has been attributed to the internodal pathways in several animal experiments. However, little is known about the role of supernormal atrial conduction (SNC) in the genesis of arrhythmias. The specific aim of this study was to evaluate prospectively the relationship between SNC, atrial conduction defects and atrial fibrillation in patients with idiopathic paroxysmal atrial fibrillation.

METHODS

Programmed atrial stimulation was performed in 38 control patients (group 1), and 21 patients with idiopathic paroxysmal atrial fibrillation (group 2) to assess some determinants of atrial conduction defects, SNC, and atrial fibrillation inducibility.

RESULTS

The mean P-wave duration was 99 +/- 8 ms in group 1, and 110 +/- 12 ms in group 2; p < 0.001. The maximum interatrial conduction delay was 36 +/- 40 ms in group 1, and 56 +/- 21 ms in group 2; p < 0.005. Supernormal atrial conduction was observed in 27 (71 percent) patients of group 1, and in 5 (24 percent) of group 2; p < 0.0003. The SNC zone was 70 +/- 29 ms in group 1, and 16 +/- 31 ms in group 2; p < 0.0001. The maximum decrease in conduction time during the period of SNC was 12 +/- 4 ms in group 1 and 3 +/- 6 ms in group 2; p < 0.0005. The SNC zone showed a significant inverse correlation with the P-wave duration (r = -0.53; p < 0.0005), and with the maximum conduction delay (r = -0.38; p < 0.005).

CONCLUSIONS

Patients with idiopathic paroxysmal atrial fibrillation have a significantly decreased incidence of SNC than controls. There is an inverse relation between the atrial conduction defects and the SNC. The association of the absence of SNC with defects in atrial conduction may play some role in the development of atrial fibrillation in patients with idiopathic paroxysmal atrial fibrillation.

Supernormal atrial conduction and its relation to atrial vulnerability and atrial fibrillation in patients with sick sinus syndrome and paroxysmal atrial fibrillation

The purpose of this study was to evaluate prospectively the relationship between supernormal atrial conduction (SNC) and the atrial vulnerability to fibrillation in patients with sick sinus syndrome (SSS) and paroxysmal atrial fibrillation (PAF). Programmed atrial stimulation was performed in 32 age-matched control patients (group I), 26 with SSS but without tachyarrhythmias (group II), and 24 with both SSS and PAF (group III) to assess some determinants of atrial vulnerability, SNC, and atrial fibrillation inducibility. Supernormal atrial conduction was observed in 20 (63%) patients of group I, 12 (46%) patients of group II, and 5 (21%) patients of group III (group I vs group III; p < 0.002). The SNC zone was 46 +/- 44 msec in group I, 36 +/- 42 msec in group II, and 12 +/- 24 msec in group III. (group I vs group III; p < 0.001). The absence of SNC showed a specificity of 89% and a positive predictive accuracy of 79% in predicting inducibility of atrial fibrillation. The sensitivity was 33% and the negative predictive accuracy was 52%. The SNC zone showed a significant inverse correlation with P wave duration (r = -0.32; p < 0.003), intraatrial conduction time (r = -0.28; p < 0.02), and maximum conduction delay (r = -0.23; p < 0.05). The maximum decrease in conduction time during supernormal conduction showed a significant inverse correlation with P wave duration (r = -0.27; p < 0.02), intraatrial conduction time (r = -0.26; p < 0.02), and with the maximum conduction delay (r = -0.27; p < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Incidence and electrophysiologic characteristics of supernormal atrial conduction in humans

The incidence and electrophysiologic characteristics of supernormal atrial conduction (SNC) were examined by cardiac stimulation in 53 control subjects. Their ages ranged from 15 to 71 years (mean age, 50 +/- 21 years) (mean +/- SD). There were 27 women and 26 men in the study. Conduction of premature atrial responses from the sinus node to the atrioventricular node (intraatrial conduction time) was supernormal in 27 (51%) subjects and conduction to the left atrium (interatrial conduction time) was supernormal in 35 (66%) subjects (difference not significant). At coupling intervals ranging between 440 and 240 ms, the conduction time of the premature beats was as much as 25 ms shorter than that of the basic driven beats. The maximum decrease in interatrial conduction time during the period of SNC was 13 +/- 5 ms and the maximum decrease in intraatrial conduction time was 9 +/- 3 ms (P < .001). The supernormal interatrial conduction zone was 71 +/- 29 ms and the supernormal intraatrial conduction zone was 57 +/- 25 ms (P < .05). There was a significant positive correlation between the SNC zone and the maximum decrease in conduction time (r = .82; P < .001). Supernormal atrial conduction was stable, reproducible, and remained constant in individual patients. Supernormal atrial conduction was found to be a relatively frequent phenomenon. There was a significantly greater SNC zone and maximum decrease in conduction time in interartrial conduction than in intraatrial conduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Conversion of Mobitz type II AV block to 1:1 AV conduction by premature ventricular beats

Preliminary experiments in a canine model of Mobitz type II atrioventricular (AV) block showed improvement of conduction after premature ventricular beats. In this investigation, the authors studied the mechanism(s) responsible for this response. In vivo studies were performed in 16 anesthetized dogs. Block was induced by ischemia after septal artery occlusion or by mechanical trauma. Two pairs of plunge electrodes were inserted in the proximal and distal His bundle. An electrode catheter was positioned at the level of the aortic root to provide an overall view of His bundle activation. Bipolar pacing was performed from the high right atrium, right ventricular outflow tract, and proximal and distal His bundle. Infra-nodal 2:1 AV block was consistently induced at an atrial rate of 238 +/- 21 beats/min. In 15 dogs a narrow time window (10-60 ms; mean, 32 +/- 6 ms) was found during which premature beats resulted in transient (2-11 beats; n = 9) or persistent (n = 8) restoration of 1:1 AV conduction. Retrograde penetration of the site of block, that is, Hb, was found even when the anterograde impulse was blocked, demonstrating the asymmetric nature of anterograde versus retrograde conduction. In vitro studies were performed in the same hearts. Intracellular recordings were obtained in the damaged His bundle and proximal right bundle. The site of block showed frequent displacements along the bundle. The introduction of a retrograde stimulus during 2:1 block restored 1:1 anterograde conduction.(ABSTRACT TRUNCATED AT 250 WORDS)