Mechanism:

Systolic or diastolic overload of the right atrium resulting in hypertrophy

ECG characteristics:

• Pin II, III ≥ 0.3 mV

Mechanism:

Systolic or diastolic overload of the left atrium resulting in hypertrophy

ECG characteristics:

• P in I, II > 0.11 s
  
• Bifid I,II
  
• Distance between peaks > 0.03 s
  
• Deep negative deflection in V1 > –0.15 mV