Effects of procainamide on the excitable gap composition in common human atrial flutter

Area of Science:

• Electrophysiology
• Cardiac Arrhythmias
• Pharmacology

Background:

• Common atrial flutter (AF1) is a significant arrhythmia.
• Understanding the electrophysiological properties of AF1 is crucial for developing effective treatments.
• The role of the excitable gap (EG) in AF1 maintenance and termination is an area of ongoing research.

Purpose of the Study:

• To determine the composition of the excitable gap (EG) in common atrial flutter (AF1) before and during procainamide (PA) infusion.
• To investigate the electrophysiological effects of procainamide on AF1 maintenance.
• To elucidate the mechanisms underlying procainamide's efficacy or inefficacy in terminating AF1.

Main Methods:

• Utilized a quadripolar electrode catheter to assess EG in 9 AF1 patients.
• Introduced premature stimuli to determine the atrial effective refractory period (ERP) and reset-response curves (RRC).
• Administered procainamide (15 mg/kg) and repeated electrophysiological measurements to evaluate its effects.

Main Results:

• Procainamide significantly prolonged AF1 cycle length (CL) and ERP.
• The absolute duration of the excitable gap (EG) increased with procainamide, but its proportion of the AF1 CL remained unchanged.
• Procainamide did not alter the duration of the fully excitable tissue within the EG.

Conclusions:

• Procainamide prolongs AF1 cycle length and refractoriness but does not terminate the arrhythmia.
• The persistence of fully excitable tissue at the wavefront's leading edge, despite procainamide, likely explains its limited efficacy in acute AF1 termination.
• These findings highlight the importance of the excitable gap's composition in guiding antiarrhythmic drug therapy for atrial flutter.