Evidence of mechanoelectric feedback in the atria of patients with atrioventricular nodal reentrant tachycardia.

OBJECTIVE: Patients with atrioventricular nodal reentrant tachycardia (AVNRT) could serve as a clinical model to study the effects of mechanical stretch in the electrical properties of atrial myocardium. MATERIALS AND METHODS: We studied 14 patients with AVNRT. Peak, mean and minimal atrial pressures, atrial refractoriness (ERP) in the right atrial appendage and high right atrial lateral wall and monophasic action potential duration at 90% of repolarisation (MAPd90) in the right atrial appendage were assessed during atrial pacing at 500 and 400 ms and after 2 min of pacing at the tachycardia cycle length. Measurements were repeated from the same positions after ventricular pacing at the same cycle lengths and after 2 min of tachycardia. Susceptibility to atrial fibrillation (AF) was assessed by noting whether AF was induced during ERP evaluation. RESULTS: Atrial pressure showed a statistically significant increase during ventricular pacing compared to baseline. This increase remained substantially unchanged when the tachycardia was induced. A significant reduction in atrial ERP and MAPd90 was also observed during ventricular pacing at all cycle lengths compared to atrial pacing. Two minutes of spontaneous tachycardia were enough to change the atrial ERP and MAPd90 to values significantly lower than those during atrial pacing at the cycle length of tachycardia. During the ERP evaluation AF was induced more often during the tachycardia (28%) than during ventricular (14%) and atrial pacing (0%). CONCLUSION: In AVNRT patients, ventricular pacing and reentrant tachycardia significantly increase right atrial pressures and subsequently shorten ERP and MAPd90, leading to an enhanced propensity for AF.

Efficacy and safety of oral amiodarone in controlling heart rate in patients with persistent atrial fibrillation who have undergone digitalisation.

INTRODUCTION: Oral amiodarone has been suggested by some authors for rate control in patients with persistent atrial fibrillation. In this study we evaluated the efficacy and safety of oral amiodarone versus placebo for rate control during exercise and daily activities in patients with chronic atrial fibrillation who had undergone digitalisation. METHODS: The study group consisted of 53 patients (35 men, mean age 65 +/- 9 years) with persistent atrial fibrillation (mean duration 17 +/- 7 months). All patients had therapeutic levels of digitalis and were under anticoagulation treatment with acenocoumarol. Twenty-eight of them were treated with amiodarone (200 mg per day orally) and 25 received placebo. All patients were assessed with 24-hour ECG monitoring, a maximal symptom-limited cardiopulmonary exercise test and evaluation of adverse events. RESULTS: The mean exercise duration was similar in both groups. Amiodarone produced a lower heart rate than placebo at all exercise levels (p<0.0001 for all). VO2 was similar in both groups whereas O2 pulse was higher in the amiodarone group at all exercise levels. During daily life, heart rate showed a significant circadian pattern in both groups, with higher values during the day than at night (time effect for both p<0.001). The mean value of heart rate under amiodarone was lower than for placebo (75 +/- 10 vs. 86 +/- 12/min, p<0.001) but this difference was due to a significant difference during the day (p<0.001) that was not present during the night (p =0.48). CONCLUSIONS: Oral amiodarone is very effective when combined with digoxin for control of heart rate in patients with chronic atrial fibrillation and it should be considered as an alternative treatment when more traditional drugs, such as Ca(+2) inhibitors or b-blockers have proven ineffective or are contraindicated.