| Summary: | 博士 === 國立陽明大學 === 臨床醫學研究所 === 87 === Atrial Fibrillation: Atrial Electrophysiological Properties and Radiofrequency Catheter Ablation Therapy
Background
Atrial fibrillation(AF) has been shown to shorten atrial effective refractory period(ERP) and make atrium more vulnerable to AF. Whether the atrial ERP shortening is a specific response to AF or a common response to rapid atrial rate is not clear. Whether there are regional differences in the change of atrial ERP after rapid atrial pacing is unknown. Furthermore, the effects of calcium channel, potassium channel and different classes of antiarrhythmic drugs on this phenomenon have not been extensively investigated.
Previous reports have demonstrated that complete catheter ablation of the atrioventricular junction (AVJ) with permanent pacing and AVJ modification could effectively control the ventricula rate during AF in the patients with medically refractory AF. However, there were no previous studies to compare the long-term effects of complete AVJ ablation with those of AVJ modification in the patients with medically refractory AF.
Purpose
To assess the change and recovery course of atrial electrophysiological properties after rapid atrial pacing, and the possible mechanisms underlying this phenomenon, to define the rate-dependency of atrial ERP change, to evaluate the effects of different antiarrhythmic drugs on tachycardia-induced change of atrial ERP, and to prospectively compare the long-term effects on quality of life (QOL) and cardiac performance after complete AVJ ablation and permanent pacing with those after AVJ modification in patients who had medically refractory AF.
Methods
In opened-chest dogs, the endocardial monophasic action potential duration at 90% repolarization (APD90) from the right atrial appendage and ERP from seven atrial sites were measured before and after rapid atrial pacing at 800 bpm for 30 minutes. The magnitude and time course of pacing-induced change of atrial ERP were assessed in 8 dogs subjected to the rapid pacing protocol described above. Thirty-two dogs were randomly assigned to receive one of the four drugs before rapid atrial pacing: verapamil, ryanodine, nicorandil, or d-sotalol.
Atrial ERP and inducibility of AF were assessed in 5 dogs before and every 4 hours for 48 hours after complete AVJ ablation with 8-week VVI pacing (80 bpm). Atrial ERP and inducibility of AF were assessed in 15 dogs before and after complete AVJ ablation with 8-week rapid atrial pacing (780 bpm) and VVI pacing.
The right atrial ERP was measured with a drive cycle length of 500ms before and after 10 minutes of rapid atrial pacing using five pacing cycle lengths(450, 400, 350, 300 and 250 ms) in 10 patients. Sixty patients were included to study the effects of antiarrhythmic drugs on change of atrial ERP induced by AF. The atrial ERP was measured with a drive cycle of 500ms before and after an episode of pacing-induced AF. After randomized to receive one of the 6 antiarrhythmic drugs (procainamide, propafenone, propranolol, dl-sotalol, amiodarone and verapamil), the atrial ERP was measured before and after another episode of pacing-induced AF.
Sixty patients with medically refractory AF were randomly assigned to receive or complete AVJ ablation with permanent pacing or AVJ modification. Subjective perception of QOL was assessed by a semiquantative questionnaire before, 1 and 6 months after ablation. Cardiac performance was evaluated by echocardiography and radionuclide angiography within 24 hours (baseline), at first month and at sixth month after ablation.
Results
Both the atrial ERP and APD90 significantly shortened after 30-minute rapid atrial pacing. Pretreatment with nicorandil and d-sotalol had no effects on the magnitude or recovery course of atrial ERP shortening after pacing. However, the degree of ERP and APD90 shortening after pacing was significantly attenuated in the verapamil and ryanodine groups.
Atrial electrophysiological properties obtained immediately and during 48-hour measurements after pacing did not show any change after 8-week VVI pacing. Recovery of atrial electrophysiological properties after 8-week rapid atrial pacing included a progressive recovery of atrial ERP shortening, recovery of atrial ERP maladaptation, and decrease of duration and episode of reinduced AF. However, recovery of shortening and maladaptation of atrial ERP, and inducibility of AF was slower at left atrium (LA) than those at right atrium and Bachmann’s bundle.
In humans, atrial ERP shortened significantly after 10 minutes of rapid atrial pacing and the degree of shortening was correlated with the pacing cycle length. The atrial ERP shortening was attenuated after verapamil infusion(-4.61.2% vs. -15.13.4%, P<0.001) but not changed after infusion of other antiarrhythmic drugs.
Complete AVJ ablation with permanent pacing and AVJ modification were associated with significant improvements in the general QOL, frequency of significant symptoms and symptoms during attacks. The frequency of hospital admission and emergency room visits, and antiarrhythmic drug trials significantly decreased after ablation in both groups. However, patients after complete AVJ ablation had a significantly greater improvement in the general QOL, frequency of significant symptoms and symptoms during attacks (including palpitation, dizziness, chest oppression, blurred vision and syncope).
Conclusions
Shortening of atrial ERP could be induced by 30-minute rapid atrial pacing. Both the ATP-dependent potassium current and rapid component of the delayed rectifier did not significantly influence this phenomenon. Intracellular calcium from both the L-type calcium channel and sacroplasmic reticulum contributed significantly to this phenomenon. LA had a slower recovery of tachycardia-induced changes of atrial electrophysiological properties and this might play a critical role in the initiation of AF. The atrial ERP shortening induced by tachycardia was a rate-dependent response. Verapamil, but not other classes of antiarrhythmic drugs, could markedly attenuate this effect.
Atrioventricular junction ablation with permanent pacing, as compared with AVJ modification, had a significantly greater effect to decrease the attack frequency and symptom extent of AF, and the patients who received this procedure were more satisfied with their general well-being.
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