The vulnerability of the right atrium. III. Electrophysiologic correlates of atrial vulnerability

Effects of verapamil on electrophysiological properties in paroxysmal atrial fibrillation

Verapamil is used to control ventricular response during atrial fibrillation (AF). Limited data is available on the effects of verapamil on atrial vulnerability in human AF. The effects of intravenous verapamil (0.15 mg/kg) on electrophysiological properties of the atrium were investigated in 12 patients with documented paroxysmal AF by electrophysiological studies. Sinus cycle length, sinus node recovery time, and the effective refractory period of the right atrium were not significantly affected by verapamil. The intraatrial conduction delay zone was significantly increased (33 +/- 20 msec before verapamil versus 50 +/- 22 msec after verapamil, P < 0.01), and the maximal intraatrial conduction delay was also significantly prolonged by verapamil, both to the His bundle region (30 +/- 12 msec before verapamil versus 42 +/- 15 msec after verapamil, P < 0.01) and to the coronary sinus (40 +/- 15 msec before verapamil versus 53 +/- 17 msec after verapamil, P < 0.01). The fragmented atrial activity zone was significantly increased (15 +/- 14 msec before verapamil versus 25 +/- 22 msec after verapamil, P < 0.02), and the percentile fragmented atrial activity was also significantly increased by verapamil (149 +/- 18 msec before verapamil versus 174 +/- 44 msec after verapamil, P < 0.05). The repetitive atrial firing zone remained unchanged. Sustained AF spontaneously occurred in only one patient after the administration of verapamil. Thus, verapamil may modulate the abnormal atrial electrophysiology in paroxysmal AF, and would favor production of atrial reentry.

Atrial Vulnerability and Electrophysiology Determined in Patients With and Without Paroxysmal Atrial Fibrillation

For elucidation of atrial electrophysiology and vulnerability an electrophysiological study was performed in 45 patients with documented paroxysmal atrial fibrillation and a control group (n = 46). Atrial vulnerability was assessed by programmed atrial stimulation with up to two extrastimuli during sinus rhythm and paced cycle lengths of 600 msec, 430 msec and 330 msec. Sustained atrial fibrillation or flutter was induced in 37/45 patients with paroxysmal atrial fibrillation in contrast to 9/46 patients in the control group (P less than 0.001). Left atrial diameter (M-mode echocardiogram), P wave duration, sinus cycle length, sinus node recovery time, and the effective refractory period of the right atrium were not significantly different between the two study groups. Intraatrial conduction time from the high right atrium (HRA) to the basal right atrium (A) and the functional refractory period of the right atrium were significantly longer in patients with paroxysmal atrial fibrillation.

Electrophysiologic effects and efficacy of cibenzoline on stimulation-induced atrial fibrillation and flutter and implications for treatment of paroxysmal atrial fibrillation

The effects of intravenous cibenzoline (1.5 mg/kg) on atrial vulnerability and electrophysiology were assessed in 25 patients with documented paroxysmal atrial fibrillation (AF), in whom sustained (greater than 30 seconds) AF was induced by atrial stimulation with up to 2 extrastimuli and paced rates between 100 and 180 beats/min. In 7 patients AF persisted despite the application of cibenzoline, and in 8 patients the induction of sustained AF was prevented by cibenzoline. Intraatrial conduction time, flutter cycle length and shortest ventricular cycle length during AF were increased by cibenzoline (p less than or equal to 0.01). Sinus cycle length was decreased (p less than or equal to 0.05), whereas sinus node recovery time remained unchanged. The effective refractory period of the right atrium was not significantly affected. Eight patients with frequent episodes of paroxysmal AF received oral cibenzoline for control of paroxysmal AF irrespective of the efficacy of intravenous cibenzoline. Prevention of stimulation-induced AF predicted successful treatment of paroxysmal AF (p = 0.018). Cibenzoline could be effective in the treatment of atrial arrhythmias, and selection of an antiarrhythmic therapy for recurrent AF seems to be useful.

Effect of intravenous flecainide on atrial vulnerability in man

Sixteen patients were investigated by means of programmed atrial stimulation at two different driving rates: 100 and 120/min. All patients had an increased atrial vulnerability at both driving rates. After intravenous flecainide application (1 mg/kg body weight as a bolus followed by the same amount given by infusion over a period of 20 min) the increased vulnerability was abolished in 11 and 9 patients respectively. In the remaining patients the rate of induced atrial tachyarrhythmia decreased. These findings correlate with a significant prolongation of the effective refractory period of the right atrium and a significant shortening of the relative refractory period of the right atrium. It is concluded that flecainide may be effective in the treatment of atrial arrhythmias in man.