The atria   The ventricles


  ECG recording and coding

The Atria

Normal Atria
  • Atrial depolarization begins at the SA node and travels through the right atrium, across the intra-atrial septum to the left atrium.
  • The electrocardiographic representation of atrial depolarization is the P wave.
  • Right atrial depolarization forms the initial portion of the P wave. The left atrial depolarization forms the terminal portion of the P wave.
  • The normal P wave axis is falls between +45o and +60o.
Atrial Enlargement Left Atrial Enlargement Diagnostic Criteria
  • The terminal portion of the P wave in lead V1 must be one small box wide by one small box deep or larger to qualify as left atrial enlargement.
  • This force can be calculated by multiplying the time in seconds by the depth in millimeters. If this product is more negative than -0.04 LAE is present.
  • A notched P wave in leads I & II with a duration of 0.12 msecs or more. "P mitrale"
  • LAE can shift the P wave axis to +15o or less.
Differential Diagnosis
  • Valvular disease
    • Mitral stenosis
    • Mitral regurgitation
  •  Decreased Left Ventricular Compliance
    • Longstanding hypertension
    • Obstructive cardiomyopathy
    • Aortic stenosis
    • Aortic regurgitation
    • Infiltrative heart disease
  • All of these conditions increase either pressure or volume loading on the atria leading to enlargement and/or hypertrophy.
Right Atrial Enlargement   Diagnostic Criteria
  • The P wave in leads II, II and aVF is peaked with a height greater than 2.5mm. "P pulmonale"
  • The P wave axis is +75o or greater.
  • The positive aspect of the P wave in lead V1 or V2 is >1.5mm in height.
Differential Diagnosis
  • Valvular Disease
    • Tricuspid stenosis
    • Tricuspid regurgitation
  • Pulmonary Hypertension
    • COPD
    • Pulmonary emboli
    • Interstitial lung disease
    • Sleep apnea
    • Mitral valve disease
    • Left ventricular systolic dysfunction
  • Congenital Heart Disease
    • Ebstein's anomaly
Biatrial Enlargement Diagnostic Criteria

Because the P wave is composed of distinct right and left atrial components, the diagnosis of biatrial enlargement is simply made by looking for the criteria for both right and left atrial enlargement.

  • A large biphasic P wave in lead V1 with the initial component greater than 1.5mm in height and  the terminal component at least 1mm in depth and 0.04 sec in duration.
  • A P wave amplitude of >2.5mm and duration of >0.12 seconds in the limb leads. II.

The Ventricles

Normal Ventricles
  • Depolarization of the ventricles is represented by the QRS waveform on the surface ECG.
  • The normal axis of ventricular depolarization is between -30o and +105o.
Ventricular Hypertrophy Conditions that increase the load, pressure or volume, on either the left or right ventricle, cause a compensatory increase in the ventricular muscle mass. This increase in muscle mass is seen on the surface electrocardiogram as an increase in QRS voltage.
  Left Ventricular Hypertrophy Diagnostic Criteria (>40 years of age)
  • Limb Leads (Low sensitivity, high specificity)
    • R wave lead I + S wave lead III > 25 mm
    • R wave aVL > 11mm
    • R wave aVF > 20mm
    • S wave in aVR > 14mm
  • Precordial Leads (High sensitivity, low specificity)
    • R wave V5 or V6 > 26mm
    • R wave V5 or V6 + S wave in V1 > 35mm
    • Largest R wave + largest S wave in precordial leads > 45mm

Differential Diagnosis

  • Aortic stenosis
  • Aortic regurgitation
  • Mitral regurgitation
  • Systemic hypertension
  • Hypertrophic cardiomyopathy

Other criteria

  • Sokolow + Lyon (Am Heart J, 1949;37:161)
    • S V1+ R V5 or V6 > 35 mm
  • Cornell criteria (Circulation, 1987;3: 565-72)
    • SV3 + R avl > 28 mm in men
    • SV3 + R avl > 20 mm in women
  • Framingham criteria (Circulation,1990; 81:815-820)
    • R avl > 11mm, R V4-6 > 25mm
    • S V1-3 > 25 mm, S V1 or V2 +
    • R V5 or V6 > 35 mm, R I + S III > 25 mm
  • Romhilt + Estes (Am Heart J, 1986:75:752-58)
    • Point score system


Right Ventricular Hypertrophy Diagnostic Criteria
  • Right axis deviation of +110o or more
  • R/S ratio > 1 in lead V1
  • R wave lead V1  <7mm
  • S wave lead V1 < 2mm
  • qR in V1
  • rSR' V1 with R' >10mm

Differential Diagnosis

  • Pulmonary stenosis
  • Mitral stenosis
  • Ventricular septal defect
  • Atrial septal defect
  • Pulmonary hypertension
    • COPD
    • Pulmonary emboli
    • Sleep apnoea
    • Interstitial lung disease
Other causes of a large R wave in lead V1 are posterior infarct, muscular dystrophy, type A Wolff-Parkinson-White syndrome and right bundle branch block.
Biventricular Hypertrophy Diagnostic Criteria
  • One or more criteria for both left and right ventricular hypertrophy
  • LVH in the precordial leads with an axis > +90o
Ventricular Strain Patterns ST-T wave changes associated with abnormal repolarisation secondary to increased ventricular tension have classically referred to as "strain" pattern.
  Left Ventricular Strain Left ventricular hypertrophy is often associated with ST depression and deep T wave inversion. These changes occur in the left precordial leads, V5 and V6. In the limb leads the ST-T changes occur opposite the main QRS forces. Therefore, if the axis is vertical, the ST-T changes are seen in II, III and aVF. If the axis is horizontal the ST-T changes are seen in I and aVL.
Right Ventricular Strain Right ventricular hypertrophy can be associated with ST depression and T wave inversion in the right precordial leads, V1 - V3. Leads II, II and aVF may also show similar ST - T wave changes.
Low Voltage Diagnostic Criteria
  • Voltage of entire QRS complex in all limb leads <5mm.
  • Voltage of entire QRS complex in all precordial leads < 10mm.
  • Either criteria may be met to qualify as "low voltage".
Differential Diagnosis

An increase in the distance between the heart and the ECG leads, infiltration of the heart muscle itself and metabolic abnormalities are all associated with low voltage.

  1. Increased Distance
    • Pericardial effusion
    • Obesity
    • COPD with hyperinflation
    • Pleural effusion
    • Constrictive pericarditis
  2. Infiltrative Heart Disease
    • Amyloidosis
    • Scleroderma
    • Hemachromatosis
  3. Metabolic Abnormality
    • Myxoedema