Effects of digitalis on atrial vulnerability

Area of Science:

• Cardiology
• Electrophysiology
• Pharmacology

Background:

• Atrial fibrillation and flutter are common arrhythmias.
• Digitalis is a cardiac glycoside used to treat heart failure and arrhythmias.
• The antiarrhythmic effects of digitalis, particularly its impact on atrial vulnerability, require further elucidation.

Purpose of the Study:

• To investigate the effects of digitalis on atrial vulnerability to fibrillation and flutter in humans.
• To determine if digitalis alters the functional refractory period and vulnerable zone in the atria.

Main Methods:

• Nine patients without heart failure were studied before and after ouabain administration.
• Repetitive atrial firing was induced using post-drive atrial extrastimulation.
• Functional refractory period and vulnerable zone were measured.

Main Results:

• Ouabain significantly lengthened the atrial functional refractory period (231 to 246 msec).
• Ouabain significantly reduced the vulnerable zone (32.2 to 9.4 msec).
• No consistent alteration in flutter cycle length was observed.

Conclusions:

• Digitalis demonstrates a protective effect against atrial fibrillation and flutter.
• This antiarrhythmic effect is likely mediated by increased atrial refractoriness and reduced vulnerable zone.
• The protective effect is independent of digitalis' hemodynamic actions.