Electrocardiography Electrocardiography

An ECG is essential if an arrhythmia is detected on auscultation but may not be particularly helpful in some cases, e.g. chronic valvular endocardiosis.

Left atrial enlargement may cause a prolonged P wave (greater than 0.04s in both the dog and cat) called P mitrale. Prolonged P waves may be biphasic.

Right atrial enlargement (seen with tricuspid insufficiency) may cause an increased P wave voltage (greater than 0.4 mV in the dog, greater than 0.2 mV in the cat) called P pulmonale. Both P pulmonale and P mitrale may be present at the same time.

Left ventricular enlargement may result in tall R waves, and prolonged QRS complexes. Slurring of the ST segment may be seen.

Right ventricular enlargement may result in right axis deviation and deep S waves (greater than 0.35 mV in lead II), and positive T waves in lead V10.

Notching of the QRS complex (R wave) is often seen in geriatric dogs and is thought to be caused by the presence of MIMIs.