Differential diagnosis:

• Typical atrial flutter
  
• Atrial ectopic tachycardia
  
• AV nodal reentry tachycardia
  
• Orthodromic WPW tachycardia
  
• Sinus tachycardia
  
• Atrial fibrillation

Mechanism:

• Macro-reentry into the right atrium with involvement of the isthmus; direction of excitation counter-clockwise

ECG characteristics:

• P wave morphology: typical “saw-tooth pattern” in leads II and III
  
• Tachycardia with narrow ventricular complex
  
• Atrial frequency: mostly between 250 and 350 per minute

Etiology:

• Cardiac: hypertensive/coronary heart disease, heart defects, carditis
  
• Rarely noncardiac: hyperthyroidosis

Treatment:

• Cardioversion/curative catheter ablation at the isthmus, or
  
• Rate control with embolic prophylaxis
  
• Treatment of the underlying disease