Basics of ECG

Basics of ECG



Heart Rate [ Ventricular rate ]

Rhythm – Regular (same R-R intervals): 1500 / No. of small squares between 2 R- waves.
Rhythm – Irregular (different  R-R intervals): No. of R- waves in 15 large squares × 20

Atrial Rate

In Total Heart Block, It Is Different From The Ventricular Rate
Atrial rate = 1500 / No. of small squares b/w 2 P- waves

Axis deviation

Study I & III
Normal QRS complexes are predominantly upwards in both these leads

Left Axis Deviation 


Left Axis Deviation– LVH, LBBB & inferior Wall infarct

Right Axis Deviation


Right Axis Deviation- RVH, RBBB & anterior Wall infarct

“Left Leaves & Right Reaches”



Contour Of P- Wave
Seen Best In II
P- Wave Represent Depolarisation Of Both Right & Left Atria. The SA Node Starts Depolarisation In Right Atrium So That Initial Part Of P- Wave Is Contributed By Right Atrium & The Later Part Of P- Wave  Is Contributed By Left Atrium.
Left Atrial Enlargement: 2nd Part Is Delayed & Prominent, Wide (> 2.5 Small Squares) & Notched P- wave (since common in mitral valve diseases  P-mitrale )
Right Atrial Enlargement: Initial Component Is Prominent: Tall (> 2.5 Small Squares) & Peaked  P- wave (since common in pulmonary hypertension  P-pulmonale )
BiLateral  Atrial Enlargement : P- wave  taller > 2.5 small squares & wider > 2.5 small squares



Diagnosed From Pattern And Amplitude Of QRS Complexes In The Chest Leads V₁ To V₆

Left Ventricular Hypertrophy

Pattern Normal
Amplitude Increases
Amplitude Of S- Wave In V₁ Or V₂ (Which Ever Is Larger) & Amplitude Of R- Wave In V₅ Or V₆ (Which Ever Is Larger)
SV₁ > 25 Mm
RV₆ > 25mm
SV₁ + RV₆ > 35mm
Usually associated with LAD
May Be associated with P- Mitrale

Right Ventricular Hypertrophy

Pattern Changed
Prominent R- Wave In V₁ & Deep S- Wave In V₆
RV₁ > 7mm
SV₆ > 7mm
RV₁ + SV₆ > 10 Mm
May Or May not associated with RAD
Often associated with P- Pulmonale

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