A patient with paroxysmal atrial fibrillation is given vernakalant IV. Its clinical advantage over flecainide for acute cardioversion of AF relates to its atrial selectivity, which is due to preferential blockade of:
- A Transient outward current Ito which is prominent in ventricular but not atrial tissue
- B L-type calcium channels which are less abundant in ventricular myocytes
- C Ultra-rapid delayed rectifier potassium current IKur (Kv1.5) expressed mainly in atria ✓
- D Inward rectifier current IK1 that shortens atrial but not ventricular action potentials
Explanation
Vernakalant selectively blocks IKur (ultra-rapid delayed rectifier K+ current carried by Kv1.5 channels), which is expressed predominantly in atrial but not ventricular myocardium, along with frequency-dependent INa blockade. This atrial selectivity means vernakalant prolongs atrial refractory period and terminates AF without significant ventricular proarrhythmia. Flecainide blocks INa broadly and can paradoxically organize AF into atrial flutter with 1:1 conduction in certain patients. IKur-based selectivity represents a conceptual advance in atrial-specific antiarrhythmic pharmacology.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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