Medicine & USMLE

Class 1A Antiarrhythmics

Cardio Drugs - Antiarrhythmics
  1. Diltiazem and Verapamil (Calcium Channel Blockers)
  2. Class 1A Antiarrhythmics
  3. Class 1B Antiarrhythmics
  4. Class 1C Antiarrhythmics
  5. Class 3 Antiarrhythmics
  6. Amiodarone Side Effects
  7. Adenosine


Class 1A Antiarrhythmics include the drugs disopyramide, quinidine, and procainamide.

These medications work by blocking sodium channels, which slows conduction and prolongs repolarization of the heart cells.

These drugs are used to treat arrhythmias, such as SVT, atrial flutter, a-fib, and v-tach.

Side effects of the class 1A antiarrhythmics include gastrointestinal effects such as diarrhea, nausea, and vomiting. Other side effects include dizziness, thrombocytopenia, and hypotension. These medications may affect the heart’s rhythm by causing a prolonged QT interval and/or a widened QRS complex. Both of these conditions can lead to dangerous cardiac arrhythmias so it’s important to closely monitor the cardiac rhythm of patients taking these drugs. Confusion is a sign of drug toxicity and should be reported to the provider.

Quinidine has the potential to cause tinnitus. Procainamide may cause drug-induced lupus.

Key Points

  • Class 1A Antiarrhythmics
    • Drug Names
      • Procainamide (Procanbid, Pronestyl)
      • Quinidine (Quinidex)
      • Disopyramide (Norpace)
    • Mechanism
      • Blocks sodium channels
        • Often referred to as “Sodium Channel Blockers”
        • Slows conduction in heart cells (except for SA and AV nodes)
          • Sodium channel blockade blocks electrical conduction between the cells of the heart, primarily in the atria, ventricles and in the Bundle of His/Purkinje fibers
          • Note: the SA and AV nodes themselves are not dependent on sodium for their conduction and are actually stimulated by weak anticholinergic functions of these drugs
      • Blocks potassium channels
        • Prolongs repolarization
          • This manifests on ECG as a prolonged QT interval, since the QT interval is primarily a measure of ventricular repolarization
    • Clinical Use
      • Ventricular tachycardia
      • Atrial tachycardia
        • Atrial fibrillation
          • Especially for rhythm control after cardioversion
        • Atrial flutter
        • Supraventricular Tachycardia (SVT)
    • Side Effects
      • Drug-induced lupus (procainamide)
        • Lupus-like symptoms may appear, including muscle and joint pain, fever, and fatigue
        • Symptoms usually resolve with discontinuation of the drug
        • Effects can often be controlled with NSAIDs
      • Widening of the QRS complex
        • Indication of toxicity
        • Can lead to other complications such as development of arrhythmias or heart block
        • Monitor cardiac rhythm
      • Prolongs QT Interval
        • Can lead to torsades de pointes, a life-threatening heart rhythm
        • Monitor cardiac rhythm
      • Thrombocytopenia
        • Bone marrow suppression can cause decreased platelets, as well as anemia and neutropenia in rare cases.
      • Tinnitus (quinidine)
        • This presents with ringing in the ears, deafness, and headache
      • Confusion
        • Indication of toxicity
      • GI disturbances
        • Nausea/vomiting
        • Diarrhea
      • Hypotension
        • Monitor blood pressure
      • Dizziness
        • Patient should remain supine when receiving the drug through an IV