Cardiology Logo
VETERINARY CLINICAL CARDIOLOGY
CARDIOLOGY CONCEPTS
Electrocardiology
ECG Interpretation of Chamber Enlargement
1. What is the significance of a P wave that is too tall or too wide?

Measurements at 50 mm/sec:


Normal                Too Tall                  Too Wide

  1. An electrocardiographic criterion of left atrial enlargement is a P wave that is too wide in lead II.
    • Dog: P > 0.04 sec
    • Cat: P > 0.04 sec
  2. An electrocardiographic criterion of right atrial enlargement is a P wave that is too tall in lead II.
    • Dog: P > 0.4 mv
    • Cat: P > 0.2 mv
  3. An electrocardiographic criterion of biatrial enlargement is a P wave that is too tall and too wide in lead II.

Comment: The sensitivity and specificity of the ECG criteria for atrial enlargement are low.

2. What electrocardiographic criteria provide evidence of left ventricular enlargement?
  1. Dog: R amplitude in Lead II
    • <20kg: R amplitude > 2.5 mv
    • >20kg: R amplitude > 3.0 mv
  2. Cat: R amplitude in Lead II > 0.9 mv

Example of Left Ventricular Enlargement in a Dog

3. What are the electrocardiographic criteria of left ventricular concentric hypertrophy?
  • The ECG is often normal in cases of left ventricular concentric hypertrophy.
  • Some suggest a shift in the MEA to the left may occur, though this has not been substantiated.
  • The R wave amplitude in lead II may be increased, as may the QRS duration in lead II.
4. What electrocardiographic criteria provide evidence for right ventricular enlargement?

Dog:

  • Presence of an S wave in leads I, II, and III.
  • MEA in the frontal plane shifted to the right (pointing to the right ventricle): 100o to - 75o
  • Deep S wave in lead V3; S >= 0.7 mV
  • S>R in lead V3

If all 4 criteria are present, there is strong evidence of right ventricular enlargement. The presence of 1 or 2 criteria is still strongly suggestive of right ventricular enlargement

Cat: MEA in the frontal plane shifted to the right (points to the right ventricle): 160° to -75°

Example of Right Ventricular Enlargement in the Dog

Criteria for Chamber Enlargement: Summary
Chambers: ECG Parameter: Body Wt Canine Feline
Left Atrium PII duration > 0.04 s > 0.04 s
Right Atrium PII amplitude >0.4 mv >0.2 mv
Left Ventricle RII amplitude <20 kg >2.5 mv >0.9 mv
>20 kg >3.0 mv
Right Ventricle Pattern of SI, SII, & SIII Present
MEA points to Rt Vent Present Present
S in V3 >0.7 mv
S in V3 > R in V3 Present

production